94 results on '"Nicholas F. Chilton"'
Search Results
2. Organometallic lanthanide bismuth cluster single-molecule magnets
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Selvan Demir, Florian Benner, Peng Zhang, and Nicholas F. Chilton
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Lanthanide ,Materials science ,General Chemical Engineering ,Biochemistry (medical) ,chemistry.chemical_element ,General Chemistry ,Magnetic hysteresis ,Biochemistry ,Bismuth ,Magnetization ,Crystallography ,chemistry ,Ferromagnetism ,Main group element ,Superexchange ,Materials Chemistry ,Environmental Chemistry ,Diamagnetism - Abstract
Summary Single-molecule magnets (SMMs) are molecules that can retain magnetic polarization in the absence of an external magnetic field and embody the ultimate size limit for spin-based information storage and processing. Multimetallic lanthanide complexes lacking magnetic exchange coupling enable fast relaxation pathways that attenuate the full potential of these species. Employment of diamagnetic heavy main group elements with diffuse orbitals may lead to unprecedented strong coupling. Herein, two bismuth-cluster-bridged lanthanide complexes, [K(THF)4]2[Cp∗2Ln2Bi6] (Cp∗ = pentamethylcyclopentadienyl; 1-Ln, Ln = Tb, Dy), were synthesized via a solution organometallic approach. The neutral [Ln2Bi6] heterometallocubane core features lanthanide centers that are bridged by a rare Bi66− Zintl ion, which supports strong ferromagnetic interactions between lanthanides. This affords the rare observation of magnetic blocking and open hysteresis loops for superexchange-coupled SMMs comprising solely lanthanide ions. Both compounds constitute the first SMMs containing bismuth donors paving the way for promising synthetic targets for quantum computation.
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- 2022
3. Anomalous magnetism of uranium(IV)-oxo and -imido complexes reveals unusual doubly degenerate electronic ground states
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John A. Seed, Stephen T. Liddle, Nicholas F. Chilton, Letitia Birnoschi, Erli Lu, Ashley J. Wooles, and Floriana Tuna
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Magnetism ,General Chemical Engineering ,chemistry.chemical_element ,Electronic structure ,010402 general chemistry ,01 natural sciences ,Biochemistry ,imido ,Physics::Geophysics ,uranium ,Crystal ,Metal ,Materials Chemistry ,oxo ,Environmental Chemistry ,Dalton Nuclear Institute ,multi-reference ,Physics ,Magnetic moment ,010405 organic chemistry ,Biochemistry (medical) ,Degenerate energy levels ,General Chemistry ,Uranium ,0104 chemical sciences ,Crystallography ,ResearchInstitutes_Networks_Beacons/dalton_nuclear_institute ,chemistry ,magnetism ,visual_art ,Affordable and clean energy [SDG7] ,visual_art.visual_art_medium ,Ground state - Abstract
Summary A fundamental part of characterizing any metal complex is understanding its electronic ground state, for which magnetometry provides key insight. Most uranium(IV) complexes exhibit low-temperature magnetic moments tending to zero, consistent with a non-degenerate spin-orbit ground state. However, there is a growing number of uranium(IV) complexes with low-temperature magnetic moments ≥1 μB, suggesting a degenerate ground state, but the electronic structure implications and origins have been unclear. We report uranium(IV)-oxo and -imido complexes with low-temperature magnetic moments (ca. 1.5–1.6 μB) and show that they exhibit near-doubly degenerate spin-orbit ground states. We determine that this results from the strong point-charge-like donor properties of oxo and imido anions generating pseudosymmetric electronic structures and that traditional crystal field arguments are useful for understanding electronic structure and magnetic properties of uranium(IV). This suggests that a significant number of uranium(IV) complexes might benefit from a close re-evaluation of the nature of their spin-orbit ground states.
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- 2021
4. Insights into D4h@metal-symmetry single-molecule magnetism: the case of a dysprosium-bis(boryloxide) complex
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Michal Kern, Ashley J. Wooles, Lewis R. Thomas-Hargreaves, Joris van Slageren, Nicholas F. Chilton, Stephen T. Liddle, and David Hunger
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Physics ,010405 organic chemistry ,Magnetism ,Metals and Alloys ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,Symmetry (physics) ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Metal ,Crystallography ,chemistry ,visual_art ,Materials Chemistry ,Ceramics and Composites ,visual_art.visual_art_medium ,Dysprosium ,Molecule ,Electrostatic model - Abstract
We report the synthesis of the lanthanide-(bis)boryloxide complex [Dy{OB(NArCH)2}2(THF)4][BPh4] (2Dy, Ar = 2,6-Pri2C6H3), with idealised D4h@Dy(III) point-group symmetry. Complex 2Dy exhibits single-molecule magnetism (SMM), with one of the highest energy barriers (Ueff = 1565(298) K) of any six-coordinate lanthanide-SMM. Complex 2Dy validates electrostatic model predictions, informing the future design of lanthanide-SMMs.
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- 2021
5. Enhancing Magnetic Hysteresis in Single-Molecule Magnets by Ligand Functionalization
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Daniel Reta, Yuan-Qi Zhai, Ke-Xin Yu, Yan-Zhen Zheng, You-Song Ding, Jon G. C. Kragskow, and Nicholas F. Chilton
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Materials science ,General Chemical Engineering ,Biochemistry (medical) ,Relaxation (NMR) ,Ab initio ,chemistry.chemical_element ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Magnetic hysteresis ,7. Clean energy ,01 natural sciences ,Biochemistry ,0104 chemical sciences ,Geomagnetic reversal ,Crystallography ,Vibronic coupling ,chemistry ,Magnet ,Materials Chemistry ,Dysprosium ,Environmental Chemistry ,0210 nano-technology ,Quantum tunnelling - Abstract
Summary Design criteria for dysprosium(III) single-molecule magnets (SMMs) with large thermal energy barriers to magnetic reversal have been established and proven, and the challenge to enhance performance is in understanding and controlling electron-vibration coupling that is the origin of magnetic reversal. We have prepared an SMM, [Dy(L)2(py)5][BPh4] 1 (HL = (S)-(-)-1-phenylethanol), based on the archetype [Dy(OtBu)2(py)5][BPh4] 2. Compounds 1 and 2 have similarly large energy barriers of Ueff = 1,130(20) cm−1 and Ueff = 1,250(10) cm−1, and yet 1 shows magnetic hysteresis at a far higher temperature of 22 K cf. TH = 4 K for 2. Ab initio calculation of the electron-vibration coupling and spin dynamics shows that substitution of the alkoxide ligand in fact enhances relaxation over the energy barrier for 1 compared with 2, in agreement with experiment, and that the higher temperature of magnetic hysteresis likely owes to reduced quantum tunneling at low temperatures.
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- 2020
6. Exchange‐Biasing in a Dinuclear Dysprosium(III) Single‐Molecule Magnet with a Large Energy Barrier for Magnetisation Reversal
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Richard E. P. Winpenny, Nicholas F. Chilton, Marcus J. Giansiracusa, Zi-Han Li, You-Song Ding, Tian Han, and Yan-Zhen Zheng
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010405 organic chemistry ,Ligand ,Organic Chemistry ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,Magnetic hysteresis ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Dipole ,Crystallography ,Magnetization ,chemistry ,Ab initio quantum chemistry methods ,Magnet ,Dysprosium ,Single-molecule magnet - Abstract
A dichlorido-bridged dinuclear dysprosium(III) single-molecule magnet [Dy2 L2 (μ-Cl)2 (thf)2 ] has been made by using a diamine-bis(phenolate) ligand, H2 L. Magnetic studies show an energy barrier for magnetisation reversal (Ueff ) around 1000 K. An exchange-biasing effect is clearly seen in magnetic hysteresis with steps up to 3 K. Ab initio calculations exclude the possibility of a pure dipolar origin of this effect leading to the conclusion that super-exchange through the chloride bridging ligands is important.
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- 2020
7. A Study of Magnetic Relaxation in Dysprosium(III) Single‐Molecule Magnets
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Yan-Zhen Zheng, Tian Han, You-Song Ding, Daniel Reta, Nicholas F. Chilton, Richard E. P. Winpenny, and Yuan-Qi Zhai
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Lanthanide ,010405 organic chemistry ,Magnetism ,Organic Chemistry ,Relaxation (NMR) ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,Magnetic hysteresis ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Bond length ,Crystallography ,symbols.namesake ,chemistry ,Cyclopentadienyl complex ,Dysprosium ,symbols ,Raman spectroscopy - Abstract
Although the development of single-molecule magnets (SMMs) is rapid, there are only two families of high energy barrier (Ueff ) dysprosium(III) SMMs known so far: the cyclopentadienyl (Cp) family with a sandwich structure and the pentagonal-bipyramidal (PB) family with D5h symmetry. These high-barrier SMMs, which usually possess Ueff >500 cm-1 allow the separate study of the four magnetic relaxation paths, namely, direct, quantum tunnelling, Raman and Orbach processes, in detail. Whereas the first family is chemically more challenging to modify the Cp rings, it is shown herein that the latter family, with the common formulae [DyX1 X2 (Leq )5 ]+ , such as X1 /X2 =- OCMe3 , - OSiMe3 , - OPh, Cl- or Br- ; Leq =THF/pyridine/4-methylpyridine, can be readily fine-tuned with a range of axial and equatorial ligands by simple substitution reactions. This allows unambiguous confirmation that the Ueff mainly depends on the identity of X1 and X2 , rather than on Leq . More importantly, the fitted parameters are barrier dependent. If X1 is an O donor and X2 is a halide, 500
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- 2020
8. Unravelling the Complexities of Pseudocontact Shift Analysis in Lanthanide Coordination Complexes of Differing Symmetry
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Michele Vonci, Alice C. Harnden, Andrei S. Batsanov, Nicholas F. Chilton, David Parker, Kevin Mason, Eric J. L. McInnes, Mark A. Fox, Elizaveta A. Suturina, and P. Kanthi Senanayake
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Ligand field theory ,Lanthanide ,coordination compounds ,lanthanide ,Chemistry(all) ,ResearchInstitutes_Networks_Beacons/photon_science_institute ,Photon Science Institute ,010402 general chemistry ,01 natural sciences ,Catalysis ,law.invention ,Coordination complex ,Paramagnetism ,NMR spectroscopy ,law ,emission ,Phosphorus-31 NMR spectroscopy ,Electron paramagnetic resonance ,chemistry.chemical_classification ,Physics ,010405 organic chemistry ,General Chemistry ,General Medicine ,Magnetic susceptibility ,0104 chemical sciences ,NMR spectra database ,Crystallography ,chemistry ,EPR spectroscopy - Abstract
In two closely related series of eight-coordinate lanthanide complexes, a switch in the sign of the dominant ligand field parameter and striking variations in the sign, amplitude and orientation of the main component of the magnetic susceptibility tensor as the Ln3+ ion is permuted conspire to mask modest changes in NMR paramagnetic shifts, but are evident in Yb EPR and Eu emission spectra.
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- 2019
9. Electronic structures of bent lanthanide(III) complexes with two N-donor ligands
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Conrad A. P. Goodwin, Daniel Cassim, Song Wei Loo, Michele Vonci, Eric J. L. McInnes, Hannah M. Nicholas, Siobhan Murphy, Nicholas F. Chilton, David P. Mills, and Richard E. P. Winpenny
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Lanthanide ,Denticity ,010405 organic chemistry ,Bent molecular geometry ,Ionic bonding ,General Chemistry ,Electronic structure ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Ion ,chemistry.chemical_compound ,Crystallography ,chemistry ,Oxidation state ,Amide - Abstract
Low coordinate metal complexes can exhibit superlative physicochemical properties, but this chemistry is challenging for the lanthanides (Ln) due to their tendency to maximize electrostatic contacts in predominantly ionic bonding regimes. Although a handful of Ln2+ complexes with only two monodentate ligands have been isolated, examples in the most common +3 oxidation state have remained elusive due to the greater electrostatic forces of Ln3+ ions. Here, we report bent Ln3+ complexes with two bis(silyl)amide ligands; in the solid state the Yb3+ analogue exhibits a crystal field similar to its three coordinate precursor rather than that expected for an axial system. This unanticipated finding is in opposition to the predicted electronic structure for two-coordinate systems, indicating that geometries can be more important than the Ln ion identity for dictating the magnetic ground states of low coordinate complexes; this is crucial transferable information for the construction of systems with enhanced magnetic properties.
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- 2019
10. Studies of hysteresis and quantum tunnelling of the magnetisation in dysprosium(<scp>iii</scp>) single molecule magnets
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Eric J. L. McInnes, Stephen T. Liddle, Daniel Reta, Yan-Zhen Zheng, You-Song Ding, Conrad A. P. Goodwin, Nicholas F. Chilton, David P. Mills, Matthew Gregson, Richard E. P. Winpenny, and Fabrizio Ortu
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Materials science ,Coordination sphere ,Condensed matter physics ,010405 organic chemistry ,chemistry.chemical_element ,010402 general chemistry ,Magnetic hysteresis ,01 natural sciences ,0104 chemical sciences ,Inorganic Chemistry ,Dipole ,Magnetization ,Hysteresis ,chemistry ,Molecular vibration ,Dysprosium ,Quantum tunnelling - Abstract
We report magnetic hysteresis studies of three Dy(III) single-molecule magnets (SMMs). The three compounds are [Dy(tBuO)Cl(THF)5][BPh4] (1), [K(18-crown-6-ether)(THF)2][Dy(BIPM)2] (2, BIPM = C{PPh2NSiMe3}2), and [Dy(Cpttt)2][B(C6F5)4] (3), chosen as they have large energy barriers to magnetisation reversal of 665, 565, and 1223 cm-1, respectively. There are zero-field steps in the hysteresis loops of all three compounds, that remain in magnetically dilute samples and in samples that are isotopically enriched with 164Dy, which has no nuclear spin. These results demonstrate that neither dipolar fields nor nuclear hyperfine coupling are solely responsible for the quantum tunnelling of magnetisation at zero field. Analysing their vibrational modes, we find that the modes that most impact the first coordination sphere occur at the lowest energies for 1, at intermediate energies for 2 and at higher energies for 3, in correlation with the hysteresis coercive fields. Therefore, we suggest that the efficiency of quantum tunnelling of magnetisation is related to molecular flexibility.
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- 2019
11. Isolation and electronic structures of derivatized manganocene, ferrocene and cobaltocene anions
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Marcus J. Giansiracusa, Michele Vonci, Samuel M. Greer, Conrad A. P. Goodwin, David P. Mills, Hannah M. Nicholas, Nicholas F. Chilton, Stephen Hill, and Peter Evans
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010405 organic chemistry ,General Chemical Engineering ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Article ,0104 chemical sciences ,Dication ,chemistry.chemical_compound ,chemistry ,Ferrocene ,Cyclopentadienyl complex ,Ab initio quantum chemistry methods ,Polymer chemistry ,Cobaltocene ,Isostructural ,Cobalt ,Metallocene - Abstract
The discovery of ferrocene nearly 70 years ago marked the genesis of metallocene chemistry. Although the ferrocenium cation was discovered soon afterwards, a derivatized ferrocenium dication was only isolated in 2016 and the monoanion of ferrocene has only been observed in low-temperature electrochemical studies. Here we report the isolation of a derivatized ferrocene anion in the solid state as part of an isostructural family of 3d metallocenates, which consist of anionic complexes of a metal centre (manganese, iron or cobalt) sandwiched between two bulky Cpttt ligands (where Cpttt is {1,2,4-C5H2 tBu3}). These thermally and air-sensitive complexes decompose rapidly above −30 °C; however, we were able to characterize all metallocenates by a wide range of physical techniques and ab initio calculations. These data have allowed us to map the electronic structures of this metallocenate family, including an unexpected high-spin S = 3/2 ground state for the 19e− derivatized ferrocene anion. Unlike ferrocene and its cationic counterpart ferrocenium, the ferrocene monoanion is an unusual species that has been observed through low-temperature electrochemical studies. Now, a family of isostructural 3d metallocenates has been isolated that consists of a manganocene, a cobaltocene and a high-spin ferrocene anion stabilized by cyclopentadienyl ligands bearing bulky aliphatic groups.
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- 2021
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12. Correlating axial and equatorial ligand field effects to the single-molecule magnet performances of a family of dysprosium bis-methanediide complexes
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Lewis R. Thomas-Hargreaves, Matthew Gregson, Marcus J. Giansiracusa, Ashley J. Wooles, Stephen T. Liddle, Felix O'Donnell, Emanuele Zanda, and Nicholas F. Chilton
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Ligand field theory ,Materials science ,010405 organic chemistry ,Relaxation (NMR) ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,Magnetic hysteresis ,01 natural sciences ,Magnetic susceptibility ,3. Good health ,0104 chemical sciences ,Chemistry ,Magnetization ,Hysteresis ,Crystallography ,chemistry ,Dysprosium ,Single-molecule magnet - Abstract
Treatment of the new methanediide–methanide complex [Dy(SCS)(SCSH)(THF)] (1Dy, SCS = {C(PPh2S)2}2−) with alkali metal alkyls and auxillary ethers produces the bis-methanediide complexes [Dy(SCS)2][Dy(SCS)2(K(DME)2)2] (2Dy), [Dy(SCS)2][Na(DME)3] (3Dy) and [Dy(SCS)2][K(2,2,2-cryptand)] (4Dy). For further comparisons, the bis-methanediide complex [Dy(NCN)2][K(DB18C6)(THF)(toluene)] (5Dy, NCN = {C(PPh2NSiMe3)2}2−, DB18C6 = dibenzo-18-crown-6 ether) was prepared. Magnetic susceptibility experiments reveal slow relaxation of the magnetisation for 2Dy–5Dy, with open magnetic hysteresis up to 14, 12, 15, and 12 K, respectively (∼14 Oe s−1). Fitting the alternating current magnetic susceptibility data for 2Dy–5Dy gives energy barriers to magnetic relaxation (Ueff) of 1069(129)/1160(21), 1015(32), 1109(70), and 757(39) K, respectively, thus 2Dy–4Dy join a privileged group of SMMs with Ueff values of ∼1000 K and greater with magnetic hysteresis at temperatures >10 K. These structurally similar Dy-components permit systematic correlation of the effects of axial and equatorial ligand fields on single-molecule magnet performance. For 2Dy–4Dy, the Dy-components can be grouped into 2Dy–cation/4Dy and 2Dy–anion/3Dy, where the former have almost linear C Created by potrace 1.16, written by Peter Selinger 2001-2019 DyC units with short average DyC distances, and the latter have more bent CDyC units with longer average DyC bonds. Both Ueff and hysteresis temperature are superior for the former pair compared to the latter pair as predicted, supporting the hypothesis that a more linear axial ligand field with shorter M–L distances produces enhanced SMM properties. Comparison with 5Dy demonstrates unusually clear-cut examples of: (i) weakening the equatorial ligand field results in enhancement of the SMM performance of a monometallic system; (ii) a positive correlation between Ueff barrier and axial linearity in structurally comparable systems., Studies on equatorial donor and CDyC angle variation effects on energy barriers to the slow relaxation of magnetisation are reported.
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- 2021
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13. Probing Relaxation Dynamics in Five‐Coordinate Dysprosium Single‐Molecule Magnets
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Rodolphe Clérac, Richard E. P. Winpenny, Nicholas F. Chilton, David P. Mills, Vijay S. Parmar, Xiaozhou Ma, Fabrizio Ortu, department of Chemistry, The University of Manchester, School of Chemistry [Manchester], University of Manchester [Manchester], Centre de Recherche Paul Pascal (CRPP), and Université de Bordeaux (UB)-Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)
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Lanthanide ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Catalysis ,Lanthanides ,Molecule ,Magnetic anisotropy ,010405 organic chemistry ,Communication ,Magnetic Properties | Hot Paper ,Organic Chemistry ,Relaxation (NMR) ,Aryloxydes ,Paramagnetic relaxation ,General Chemistry ,Yttrium ,[CHIM.MATE]Chemical Sciences/Material chemistry ,Communications ,Square pyramidal molecular geometry ,0104 chemical sciences ,3. Good health ,aryloxides ,Crystallography ,chemistry ,Dysprosium ,Single-molecule magnets ,Diamagnetism - Abstract
A new family of five‐coordinate lanthanide single‐molecule magnets (Ln SMMs) [Dy(Mes*O)2(THF)2X] (Mes*=2,4,6‐tri‐tert‐butylphenyl; X=Cl, 1; Br, 2; I, 3) is reported with energy barriers to magnetic reversal >1200 K. The five‐coordinate DyIII ions have distorted square pyramidal geometries, with halide anions on the apex, and two Mes*O ligands mutually trans‐ to each other, and the two THF molecules forming the second trans‐ pair. These geometrical features lead to a large magnetic anisotropy in these complexes along the trans‐Mes*O direction. QTM and Raman relaxation times are enhanced by varying the apex halide from Cl to Br to I, or by dilution in a diamagnetic yttrium analogue., Halide influence: A new family of five‐coordinate lanthanide‐based single‐molecule magnets, [Dy(Mes*O)2(THF)2X] (Mes*=2,4,6‐tri‐tert‐butylphenyl), (X=Cl, Br, I) is reported. While the influence of the different halides on the quantum tunnelling of magnetization and Raman processes is clearly established, the Orbach relaxation is independent of the halide substitution.
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- 2020
14. Iron Precatalysts with Bulky Tri( tert ‐butyl)cyclopentadienyl Ligands for the Dehydrocoupling of Dimethylamine‐Borane
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Joshua Turner, Amit Kumar, Ian Manners, Hazel A. Sparkes, Nicholas F. Chilton, Annie L. Colebatch, Andrew S. Weller, and George R. Whittell
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catalysis ,iron catalysts ,010405 organic chemistry ,Chemistry ,boranes ,amines ,Organic Chemistry ,Ab initio ,Boranes ,General Chemistry ,Borane ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,Catalysis ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,Cyclopentadienyl complex ,law ,Yield (chemistry) ,dehydrocoupling ,Electron paramagnetic resonance ,Dimethylamine - Abstract
In an attempt to prepare new Fe catalysts for the dehydrocoupling of amine-boranes and to provide mechanistic insight, the paramagnetic FeII dimeric complex [Cp′FeI]2 (1) (Cp′=η5-((1,2,4-tBu)3C5H2)) was used as a precursor to a series of cyclopentadienyl FeII and FeIII mononuclear species. The complexes prepared were [Cp′Fe(η6-Tol)][Cp′FeI2] (2) (Tol=C6H5Me), [Cp′Fe(η6-Tol)][BArF 4] (3) (BArF 4=[B(C6H3(m-CF3)2)4]−), [N(nBu)4][Cp′FeI2] (4), Cp′FeI2 (5), and [Cp′Fe(MeCN)3][BArF 4] (6). The electronic structure of the [Cp′FeI2]− anion in 2 and 4 was investigated by SQUID magnetometry, EPR spectroscopy and ab initio Complete Active Space Self Consistent Field-Spin Orbit (CASSCF-SO) calculations, and the studies revealed a strongly anisotropic S=2 ground state. Complexes 1–6 were investigated as catalysts for the dehydrocoupling of Me2NH⋅BH3 (I) in THF at 20 °C to yield the cyclodiborazane product [Me2N-BH2]2 (IV). Complexes 1–4 and 6 were active dehydrocoupling catalysts towards I (5 mol % loading), however 5 was inactive, and ultra-violet (UV) irradiation was required for the reaction mediated by 3. Complex 6 was found to be the most active precatalyst, reaching 80 % conversion to IV after 19 h at 22 °C. Dehydrocoupling of I by 1–4 proceeded via formation of the aminoborane Me2N=BH2 (II) as the major intermediate, whereas for 6 the linear diborazane Me2NH-BH2-NMe2-BH3 (III) could be detected, together with trace amounts of II. Reactions of 1 and 6 with Me3N⋅BH3 were investigated in an attempt to identify Fe-based intermediates in the catalytic reactions. The σ-complex [Cp′Fe(MeCN)(κ2-H2BH⋅NMe2H][BArF 4] was proposed to initially form in dehydrocoupling reactions involving 6 based on ESI-MS (ESI=Electrospray Ionisation Mass Spectroscopy) and NMR spectroscopic evidence. The latter also suggests that these complexes function as precursors to iron hydrides which may be the true catalytic species.
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- 2018
15. Biradical Formation by Deprotonation in Thiazole-Derivatives: The Hidden Nature of Dasatinib
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Josep Maria Bofill, I. P. R. de Moreira, Rosendo Valero, C. Heras, G. Albareda Piquer, F. L. Calahorra, Daniel Reta, Nicholas F. Chilton, and Alistair J. Fielding
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chemistry.chemical_compound ,Deprotonation ,chemistry ,law ,Stereochemistry ,Bioorganic chemistry ,Molecule ,Aromaticity ,Conjugated system ,Thiazole ,Electron paramagnetic resonance ,Structural motif ,law.invention - Abstract
The formation of stable organic biradicals by a deprotonation process is reported for a series of conjugated heterocycles that share a Ph-N(H)-2-thiazole structural motif. We characterise the paramagnetic electronic ground state by means of continuous-wave and pulse EPR. We propose a simple valence bond mechanism for a deprotonation-induced formation of paramagnetic organic molecules, based on the interplay between the electronegativity of heteroatomic groups and the recovery of aromaticity to stabilise the biradical species. The Ph-N(H)-2-thiazole motif is found in a variety of biologically active molecules, exemplified here with the anticancer drug Dasatinib, and our results suggest a radical-based mechanism for the protein kinase inhibition activity of the drug. The existence of this structure-property relationship for an elementary chemical motif suggests that biradical species may be more prevalent than previously thought and have an important role in bioorganic chemistry.
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- 2019
16. Modular [FeIII8MII6]n+ (MII = Pd, Co, Ni, Cu) Coordination Cages
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Stergios Piligkos, Priyanka Comar, Amgalanbaatar Baldansuren, Sergio Sanz, Nicholas F. Chilton, Helen M. O'Connor, Høgni Weihe, Paul J. Lusby, Eric J. L. McInnes, Mateusz B. Pitak, Simon J. Coles, and Euan K. Brechin
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010405 organic chemistry ,Chemistry ,Metal ions in aqueous solution ,010402 general chemistry ,01 natural sciences ,Magnetic susceptibility ,0104 chemical sciences ,Ion ,law.invention ,Inorganic Chemistry ,Metal ,Magnetization ,Crystallography ,law ,visual_art ,visual_art.visual_art_medium ,Antiferromagnetism ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance ,Spectroscopy - Abstract
The reaction of the simple metalloligand [FeIIIL3] [HL = 1-(4-pyridyl)butane-1,3-dione] with a variety of different MII salts results in the formation of a family of heterometallic cages of formulae [FeIII8PdII6L24]Cl12 (1), [FeIII8CuII6L24(H2O)4Br4]Br8 (2), [FeIII8CuII6L24(H2O)10](NO3)12 (3), [FeIII8NiII6L24(SCN)11Cl] (4), and [FeIII8CoII6L24(SCN)10(H2O)2]Cl2 (5). The metallic skeleton of each cage describes a cube in which the FeIII ions occupy the eight vertices and the MII ions lie at the center of the six faces. Direct-current magnetic susceptibility and magnetization measurements on 3–5 reveal the presence of weak antiferromagnetic exchange between the metal ions in all three cases. Computational techniques known in theoretical nuclear physics as statistical spectroscopy, which exploit the moments of the Hamiltonian to calculate relevant thermodynamic properties, determine JFe–Cu = 0.10 cm–1 for 3 and JFe–Ni = 0.025 cm–1 for 4. Q-band electron paramagnetic resonance spectra of 1 reveal a significant...
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- 2018
17. Exploring the Coordination Capabilities of a Family of Flexible Benzotriazole-Based Ligands Using Cobalt(II) Sources
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Alaa Abdul-Sada, Nicholas F. Chilton, Edward Loukopoulos, and George E. Kostakis
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Thermogravimetric analysis ,Electrospray ionization ,Inorganic chemistry ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Coordination complex ,Metal ,chemistry.chemical_compound ,General Materials Science ,Spectroscopy ,chemistry.chemical_classification ,Benzotriazole ,010405 organic chemistry ,Chemistry ,Ligand ,Magnetism ,Cobalt ,General Chemistry ,Condensed Matter Physics ,0104 chemical sciences ,Crystallography ,visual_art ,coordination chemistry ,visual_art.visual_art_medium ,QD0146 - Abstract
In this study we focus on the coordination chemistry of a family of three flexible benzotriazole-based ligands (L1-L3) using Cobalt(II) salts. Our efforts have resulted to the formation of ten novel compounds, formulated as [Co2(L1)2Cl4]·2MeCN (1·2MeCN), Co2(L1)2Br4 (2), [Co(L2)Cl2]·MeCN (3·MeCN), Co(L2)Cl2 (4), [Co2(L2)2Br4]·2MeCN (5·2MeCN), [Co(L2)2(NO3)2]·2MeCN (6·2MeCN), [Co2(L3)2Cl4]·2MeCN (7·2MeCN), Co2(L3)2Cl4 (8), Co2(L3)2Br4 (9), and Co(L3)2(NO3)2 (10). The structures have been well characterised through X-Ray crystallography, FT-IR, ESI-MS, PXRD, Elemental Analysis and TGA studies. The compounds show a large structural variety depending on synthetic parameters (ratio, temperature and metal salt) and the ligand selection (various conformations in each ligand). When tuned appropriately, these factors drastically affect dimensionality, metal geometry and the nuclearity of the final product, resulting in a range of 0D dimers (1, 3, 5, 8, 9), 1D (2, 7, 10) and 2D (4, 6) coordination polymers (CPs). A temperature-induced single-crystal to single-crystal transformation of compound 3 to 4 is additionally reported. The magnetic properties of representative compounds (4, 7, 9) are subject to large changes with only minor structural variations, suggesting that tetrahedral Co(II) nodes in CPs or MOFs could function as sensitive reporters of small changes in the local environment.
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- 2017
18. Cu(II) Coordination Polymers as Vehicles in the A3 Coupling
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George E. Kostakis, Edward Loukopoulos, Michael G. Kallitsakis, Nikolaos Tsoureas, Ioannis N. Lykakis, Nicholas F. Chilton, and Alaa Abdul-Sada
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chemistry.chemical_classification ,Benzotriazole ,010405 organic chemistry ,Stereochemistry ,Coordination polymer ,Alkyne ,Polymer ,010402 general chemistry ,01 natural sciences ,Aldehyde ,Medicinal chemistry ,0104 chemical sciences ,Catalysis ,Coordination complex ,Inorganic Chemistry ,chemistry.chemical_compound ,chemistry ,Amine gas treating ,Physical and Theoretical Chemistry - Abstract
A family of benzotriazole based coordination compounds, obtained in two steps and good yields from commercially available materials, formulated [CuII(L1)2(MeCN)2]·2(ClO4)·MeCN (1), [CuII(L1)(NO3)2]·MeCN (2), [ZnII(L1)2(H2O)2]·2(ClO4)·2MeCN (3), [CuII(L1)2Cl2]2 (4), [CuII5(L1)2Cl10] (5), [CuII2(L1)4Br2]·4MeCN·(CuII2Br6) (6), [CuII(L1)2(MeCN)2]·2(BF4) (7), [CuII(L1)2(CF3SO3)2] (8), [ZnII(L1)2(MeCN)2]·2(CF3SO3) (9), [CuII2(L2)4(H2O)2]·4(CF3SO3)·4Me2CO (10) and [CuII2(L3)4(CF3SO3)2]·2(CF3SO3)·Me2CO (11) are reported. These air stable compounds were tested as homogeneous catalysts for the A3 coupling synthesis of propargyl amine derivatives from aldehyde, amine and alkyne under a non-inert atmosphere. Fine-tuning of the catalyst resulted in a one dimensional (1D) coordination polymer (CP) (8) with excellent catalytic activity in a wide range of substrates, avoiding any issues that would inhibit its performance.
- Published
- 2017
19. Analysis of Lanthanide-Radical Magnetic Interactions in Ce(III) 2,2′-Bipyridyl Complexes
- Author
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Fabrizio Ortu, Nicholas F. Chilton, David P. Mills, Jingjing Liu, Matthew Burton, Marie-Emmanuelle Boulon, Jonathan M. Fowler, and Alasdair Formanuik
- Subjects
Lanthanide ,010405 organic chemistry ,Magnetism ,Reducing agent ,Inorganic chemistry ,010402 general chemistry ,Coupling (probability) ,01 natural sciences ,0104 chemical sciences ,Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,chemistry ,Intramolecular force ,Benzophenone ,Physical and Theoretical Chemistry ,Cyclic voltammetry ,Tetrahydrofuran - Abstract
A series of lanthanide complexes bearing organic radical ligands, [Ln(CpR)2(bipy·–)] [Ln = La, CpR = Cptt (1); Ln = Ce, CpR = Cptt (2); Ln = Ce, CpR = Cp″ (3); Ln = Ce, CpR = Cp‴ (4)] [Cptt = {C5H3tBu2-1,3}−; Cp″ = {C5H3(SiMe3)2-1,3}−; Cp‴ = {C5H2(SiMe3)3-1,2,4}−; bipy = 2,2′-bipyridyl], were prepared by reduction of [Ln(CpR)2(μ-I)]2 or [Ce(Cp‴)2(I) (THF)] with KC8 in the presence of bipy (THF = tetrahydrofuran). Complexes 1–4 were thoroughly characterized by structural, spectroscopic, and computational methods, together with magnetism and cyclic voltammetry, to define an unambiguous Ln(III)/bipy·– radical formulation. These complexes can act as selective reducing agents; for example, the reaction of 3 with benzophenone gives [{Ce(Cp”)2(bipy)}2{κ2-O,O′-OPhC(C6H5)CPh2O}] (7), a rare example of a “head-to-tail” coupling product. We estimate the intramolecular exchange coupling for 2–4 using multiconfigurational and spin Hamiltonian methods and find that the commonly used Lines-type isotropic exchange is not appropriate, even for single 4f e–/organic radical pairs.
- Published
- 2017
20. Antimony-ligated dysprosium single-molecule magnets as catalysts for stibine dehydrocoupling
- Author
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Thomas Pugh, Richard A. Layfield, and Nicholas F. Chilton
- Subjects
chemistry.chemical_classification ,010405 organic chemistry ,Chemistry ,Ligand ,Stibine ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Coordination complex ,Crystallography ,chemistry.chemical_compound ,Antimony ,Catalytic cycle ,Dysprosium ,Molecule - Abstract
The synthesis of antimony-ligated dysprosium SMMs is described in addition to the unexpected reactivity of the SMMs in stibine dehydrocoupling catalysis., Single-molecule magnets (SMMs) are coordination compounds that exhibit magnetic bistability below a characteristic blocking temperature. Research in this field continues to evolve from its fundamental foundations towards applications of SMMs in information storage and spintronic devices. Synthetic chemistry plays a crucial role in targeting the properties that could ultimately produce SMMs with technological potential. The ligands in SMMs are invariably based on non-metals; we now report a series of dysprosium SMMs (in addition to their magnetically dilute analogues embedded in yttrium matrices) that contain ligands with the metalloid element antimony as the donor atom, i.e. [(η5-Cp′2Dy){μ-Sb(H)Mes}]3 (1-Dy) and [(η5-Cp′2Dy)3{μ-(SbMes)3Sb}] (2-Dy), which contain the stibinide ligand [Mes(H)Sb]– and the unusual Zintl-like ligand [Sb4Mes3]3–, respectively (Cp′ = methylcyclopentadienyl; Mes = mesityl). The zero-field anisotropy barriers in 1-Dy and 2-Dy are U eff = 345 cm–1 and 270 cm–1, respectively. Stabilization of the antimony-ligated SMMs is contingent upon careful control of reaction time and temperature. With longer reaction times and higher temperatures, the stibine pro-ligands are catalytically dehydrocoupled by the rare-earth precursor complexes. NMR spectroscopic studies of the yttrium-catalysed dehydrocoupling reactions reveal that 1-Y and 2-Y are formed during the catalytic cycle. By implication, 1-Dy and 2-Dy should also be catalytic intermediates, hence the nature of these complexes as SMMs in the solid-state and as catalysts in solution introduces a strategy whereby new molecular magnets can be identified by intercepting species formed during catalytic reactions.
- Published
- 2017
21. Assessing crystal field and magnetic interactions in diuranium-μ-chalcogenide triamidoamine complexes with UIV–E–UIV cores (E = S, Se, Te): implications for determining the presence or absence of actinide–actinide magnetic exchange
- Author
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Benedict M. Gardner, Stephen T. Liddle, Nicholas F. Chilton, Ashley J. Wooles, David M. King, and Floriana Tuna
- Subjects
010405 organic chemistry ,Magnetism ,chemistry.chemical_element ,General Chemistry ,Electronic structure ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Crystal ,Magnetization ,Crystallography ,chemistry.chemical_compound ,chemistry ,Telluride ,Selenide ,Tellurium ,Single crystal - Abstract
We report the synthesis and characterisation of a family of diuranium(IV)-‐μ-‐chalcogenide complexes including a detailed examination of their electronic structures and magnetic behaviours. Treatment of [U(TrenTIPS)] [1, TrenTIPS = N(CH2CH2NSiPri 3)3] with Ph3PS, selenium or tellurium affords the diuranium(IV)-‐sulfide, selenide, and telluride complexes [{U(TrenTIPS)}2(μ-‐E)] (E = S, 2; Se, 5; Te, 6). Complex 2 is also formed by treatment of [U(TrenTIPS){OP(NMe2)3}] (3) with Ph3PS, whereas treatment of 3 with elemental sulfur gives the diuranium(IV)-‐persulfido complex [{U(TrenTIPS)}2(μ-‐η2:η2-‐S2)] (4). Complexes 2-‐6 have been variously characterised by single crystal X-‐ray diffraction, NMR, IR, and optical spectroscopies, room temperature Evans and variable temperature SQUID magnetometry, elemental analyses, and complete active space self consistent field spin orbit calculations. The combined characterisation data present a self-‐consistent picture of the electronic structure and magnetism of 2, 5, and 6, leading to the conclusion that single-‐ion crystal field effects, and not diuranium magnetic coupling, are responsible for features in their variable-‐temperature magnetisation data. The presence of magnetic coupling is often implied and sometimes quantified by such data, and so this study highlights the importance of evaluating other factors, such as crystal field effects, that can produce similar magnetic observables, and to thus avoid misassignments of such phenomena.
- Published
- 2017
22. A Bis-Monophospholyl Dysprosium Cation Showing Magnetic Hysteresis at 48 Kelvin
- Author
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George F. S. Whitehead, Nicholas F. Chilton, David P. Mills, Daniel Reta, and Peter Evans
- Subjects
Lanthanide ,Materials science ,Magnetism ,Ab initio ,chemistry.chemical_element ,010402 general chemistry ,Biochemistry ,01 natural sciences ,Catalysis ,Article ,Magnetization ,Colloid and Surface Chemistry ,Magnetic relaxation ,Condensed matter physics ,business.industry ,010405 organic chemistry ,Relaxation (NMR) ,General Chemistry ,Magnetic hysteresis ,0104 chemical sciences ,chemistry ,Magnet ,Computer data storage ,Dysprosium ,Physical chemistry ,business ,Ground state - Abstract
Single-molecule magnets (SMMs) have potential applications in high-density data storage, but magnetic relaxation times at elevated temperatures must be increased to make them practically useful. Bis-cyclopentadienyl lanthanide sandwich complexes have emerged as the leading candidates for SMMs that show magnetic memory at liquid nitrogen temperatures, but the relaxation mechanisms mediated by aromatic C5 rings have not been fully established. Here we synthesise a bis-monophospholyl dysprosium SMM [Dy(Dtp)2][Al{OC(CF3)3}4] (1, Dtp = {P(CtBuCMe)2}) by the treatment of in situ-prepared “[Dy(Dtp)2(C3H5)]” with [HNEt3][Al{OC(CF3)3}4]. SQUID magnetometry reveals that 1 has an effective barrier to magnetisation reversal of 1,760 K (1,223 cm–1) and magnetic hysteresis up to 48 K. Ab initio calculation of the spin dynamics reveal that transitions out of the ground state are slower in 1 than in the first reported dysprosocenium SMM, [Dy(Cpttt)2][B(C6F5)4] (Cpttt = C5H2tBu3-1,2,4), however relaxation is faster in 1 overall due to the compression of electronic energies and to vibrational modes being brought on-resonance by the chemical and structural changes introduced by the bis-Dtp framework. With the preparation and analysis of 1 we are thus able to further refine our understanding of relaxation processes operating in bis-C5/C4P sandwich lanthanide SMMs, which is the necessary first step towards rationally achieving higher magnetic blocking temperatures in these systems in future.
- Published
- 2019
23. A dichlorido-bridged dinuclear Dy(iii) single-molecule magnet with an effective energy barrier larger than 600 K
- Author
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Ke-Xin Yu, Yan-Zhen Zheng, Zi-Han Li, You-Song Ding, Yuan-Qi Zhai, Nicholas F. Chilton, and Tian Han
- Subjects
Lanthanide ,Materials science ,Condensed matter physics ,010405 organic chemistry ,Magnetization reversal ,Metals and Alloys ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Effective energy ,chemistry ,Magnetic dilution ,Magnet ,Materials Chemistry ,Ceramics and Composites ,Dysprosium ,Relaxation (physics) ,Single-molecule magnet - Abstract
We report a dichlorido-bridged dinuclear dysprosium(III) single-molecule magnet [Dy(Cy2N)2(μ-Cl)(THF)]2 which shows an effective energy barrier for magnetization reversal (Ueff) of ca. 623 K. This is by far the largest Ueff barrier for any chlorido-bridged lanthanide single-molecule magnet. We observe two relaxation processes with near-identical temperature dependencies, one of which disappears upon magnetic dilution. We suspect that these two processes are the isolated and coupled relaxation processes.
- Published
- 2019
24. Light Lanthanide Metallocenium Cations Exhibiting Weak Equatorial Anion Interactions
- Author
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David P. Mills, Conrad A. P. Goodwin, Yu Xuan Yeoh, Daniel Reta, Jake A. Cleghorn, Fabrizio Ortu, Nicholas F. Chilton, and Jingjing Liu
- Subjects
Lanthanide ,sandwich complexes ,Solid-state ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Catalysis ,Ion ,Dalton Nuclear Institute ,lanthanides ,Full Paper ,010405 organic chemistry ,Lanthanides | Hot Paper ,Organic Chemistry ,General Chemistry ,Ion pairs ,Full Papers ,metallocenes ,cyclopentadienyl ligands ,0104 chemical sciences ,Crystallography ,ResearchInstitutes_Networks_Beacons/dalton_nuclear_institute ,chemistry ,Fluorine ,magnetic properties - Abstract
As the dysprosocenium complex [Dy(Cpttt)2][B(C6F5)4] (Cpttt = C5H2tBu3‐1,2,4, 1‐Dy) exhibits magnetic hysteresis at 60 K, similar lanthanide (Ln) complexes have been targeted in order to provide insights into this remarkable property. We recently reported homologous [Ln(Cpttt)2][B(C6F5)4] (1‐Ln) for all the heavier Ln from Gd‐Lu; herein, we extend this motif to the early Ln. We find, for the largest LnIII cations, that contact ion pairs [Ln(Cpttt)2{(C6F5‐κ1‐F)B(C6F5)3}] (1‐Ln; La‐Nd) are isolated from reactions of parent [Ln(Cpttt)2(Cl)] (2‐Ln) with [H(SiEt3)2][B(C6F5)4], where the anion binds weakly to the equatorial sites of [Ln(Cpttt)2]+ through a single fluorine atom in the solid state. For smaller SmIII, [Sm(Cpttt)2][B(C6F5)4] (1‐Sm) is isolated, which like heavier 1‐Ln does not exhibit equatorial anion interactions, but the EuIII analogue 1‐Eu could not be synthesised due to the facile reduction of EuIII precursors to EuII products. Thus with the exception of Eu and radioactive Pm this work constitutes a structurally similar family of Ln metallocenium complexes, over 50 years after the [M(Cp)2]+ series was isolated for the 3d metals.
- Published
- 2019
25. The Sensitivity of Magnetic Anisotropy in the Solid State for Lanthanide Complexes with Small Crystal Field Splitting
- Author
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Michele Vonci, Eric J. L. McInnes, Dmitry S. Yufit, Nicholas F. Chilton, David Parker, Emily R. Neil, and Kevin Mason
- Subjects
Lanthanide ,010405 organic chemistry ,Chemistry ,Crystal structure ,Electronic structure ,010402 general chemistry ,01 natural sciences ,Spectral line ,0104 chemical sciences ,law.invention ,Inorganic Chemistry ,Magnetic anisotropy ,Crystal field theory ,Chemical physics ,law ,Molecule ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance - Abstract
Knowledge of the crystal structure of a monometallic inorganic molecule is often sufficient to calculate its electronic structure and interpret its magnetic properties. Here we show that for a series of nine-coordinate lanthanide complexes based on the 1,4,7-tris[(6-carboxypyridin-2-yl)methyl]-1,4,7-triazacyclononane ligand, the electronic structure is hypersensitive to geometric structure and to the presence of non-coordinated lattice solvent, which renders the magnetic and spectroscopic properties very difficult to interpret. We explore possible explanations for the peculiar electron paramagnetic resonance (EPR) spectra and conclude that a number of entangled factors are at play across the samples, and hence that great care should be taken in the interpretation of EPR spectra for systems with small magnetic anisotropy, even when the molecular structure is known.
- Published
- 2019
26. Slow magnetic relaxation in a {EuCu5} metallacrown
- Author
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Yan-Cong Chen, Guo-Zhang Huang, Ze-Yu Ruan, Nicholas F. Chilton, Quan-Wen Li, Jin Wang, Ming-Liang Tong, Daniel Reta, Jun-Liang Liu, and Zhenxing Wang
- Subjects
Materials science ,010405 organic chemistry ,Relaxation (NMR) ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Ion ,Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,Salicylaldehyde ,chemistry ,Diamagnetism ,Magnetic relaxation ,Isostructural ,Ground state ,Metallacrown - Abstract
A 3d-4f heterometallic metallacrown with formula of [EuCu5(quinha)5(sal)2(py)5]CF3SO3·py·3H2O (1) (H2quinha = quinaldichydroxamic acid; Hsal = salicylaldehyde) has been synthesized. This complex shows field-induced slow magnetic relaxation via a Raman-like process, where studies of the isostructural {LuCu5} (2) and {YCu5} (3) complexes show that the slow dynamics mainly arise from the {Cu5} S = 1/2 ground state rather than the EuIII ion. However, the EuIII ion enhances the relaxation rates of the {Cu5} unit which likely arises from second-order effects in the formally diamagnetic 7F0 ground state of EuIII.
- Published
- 2019
27. Periodic trends and hidden dynamics of magnetic properties in three series of triazacyclononane lanthanide complexes
- Author
-
Elizaveta A. Suturina, Mauro Botta, Kevin Mason, Fabio Carniato, Eric J. L. McInnes, Ilya Kuprov, Nicholas F. Chilton, Michele Vonci, and David Parker
- Subjects
Lanthanide ,Materials science ,Coordination sphere ,010405 organic chemistry ,Gadolinium ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Magnetic susceptibility ,0104 chemical sciences ,law.invention ,Inorganic Chemistry ,Magnetic anisotropy ,Crystallography ,chemistry ,law ,Molecular vibration ,Electron paramagnetic resonance ,Anisotropy - Abstract
In three structurally related series of nine-coordinate lanthanide(iii) complexes (Ln = Tb, Dy, Ho, Er, Tm and Yb) based on triazacyclononane, solution NMR studies and DFT/CASSCF calculations have provided key information on the magnetic susceptibility anisotropy. Both experimental and computational approaches have revealed a poor correlation to Bleaney's theory of magnetic anisotropy. CASSCF calculations suggested that the magnetic susceptibility is very sensitive to small geometric variations within the first coordination sphere, whereas DFT analyses indicate that it is the thermal accessibility of low energy vibrational modes that may lead to distortion. Parallel NMRD and EPR studies on the three Gd(iii) complexes revealed good correspondence in estimating the electronic relaxation time. The Gd(iii) tris-pyridinecarboxylate complex possesses a very long electronic relaxation time making it a promising starting point for responsive gadolinium EPR probe design.
- Published
- 2019
28. Enhancing Magnetic Hysteresis in Single-Molecule Magnets by Ligand Functionalisation
- Author
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Ke-Xin Yu, Daniel Reta, Yuan-Qi Zhai, You-Song Ding, Yan-Zhen Zheng, Nicholas F. Chilton, and Jon G. C. Kragskow
- Subjects
Vibronic coupling ,Materials science ,chemistry ,Molecular vibration ,Magnet ,Relaxation (NMR) ,Dysprosium ,Ab initio ,Physical chemistry ,chemistry.chemical_element ,Magnetic hysteresis ,Quantum tunnelling - Abstract
The design criteria for single-molecule magnets (SMMs) of dysprosium(III) to show large thermal energy barriers to magnetic reversal have been established and proven, and the challenge to enhance their performance is understanding and control of vibrational modes that govern slow relaxation. We have prepared a new SMM, [Dy(L)2(py)5][BPh4] 1 (where HL = (S)-(-)-1-phenylethanol), which is based on the archetype [Dy(OtBu)2(py)5][BPh4] 2. Compounds 1 and 2 have similarly large energy barriers of Ueff = 1130(20) cm-1 and Ueff = 1250(10) cm-1, and yet 1 shows magnetic hysteresis at a far higher temperature of 22 K (cf. TH = 4 K for 2). Ab initio calculation of the spin dynamics show that substitution of the alkoxide ligand in fact enhances relaxation over the energy barrier for 1 over 2, in agreement with experiment, and that the higher temperature of magnetic hysteresis owes to reduced quantum tunnelling at low temperatures.
- Published
- 2019
29. A Low-Symmetry Dysprosium Metallocene Single-Molecule Magnet with a High Anisotropy Barrier
- Author
-
Thomas Pugh, Nicholas F. Chilton, and Richard A. Layfield
- Subjects
Ligand field theory ,Field (physics) ,Chemistry ,010405 organic chemistry ,Inorganic chemistry ,chemistry.chemical_element ,General Chemistry ,General Medicine ,010402 general chemistry ,Molecular physics ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Core (optical fiber) ,chemistry.chemical_compound ,Magnet ,Dysprosium ,Single-molecule magnet ,Anisotropy ,Metallocene - Abstract
The single-molecule magnet (SMM) properties of the isocarbonyl-ligated dysprosium metallocene [Cp*2 Dy{μ-(OC)2 FeCp}]2 (1Dy ), which contains a rhombus-shaped Dy2 Fe2 core, are described. Combining a strong axial [Cp*](-) ligand field with a weak equatorial field consisting of the isocarbonyl ligands leads to an anisotropy barrier of 662 cm(-1) in zero applied field. The dominant thermal relaxation pathways in 1Dy involves at least the fourth-excited Kramers doublet, thus demonstrating that prominent SMM behavior can be observed for dysprosium in low-symmetry environments.
- Published
- 2016
30. Physicochemical Properties of Near-Linear Lanthanide(II) Bis(silylamide) Complexes (Ln = Sm, Eu, Tm, Yb)
- Author
-
Gianni F. Vettese, Eufemio Moreno Pineda, Richard E. P. Winpenny, Conrad A. P. Goodwin, Joseph W. Ziller, David P. Mills, Iain F. Crowe, William J. Evans, and Nicholas F. Chilton
- Subjects
Lanthanide ,Diffraction ,010405 organic chemistry ,010402 general chemistry ,Electrochemistry ,01 natural sciences ,Electron spectroscopy ,London dispersion force ,0104 chemical sciences ,Ion ,law.invention ,Inorganic Chemistry ,Crystallography ,chemistry.chemical_compound ,Monomer ,chemistry ,law ,Physical and Theoretical Chemistry ,Electron paramagnetic resonance - Abstract
Following our report of the first near-linear lanthanide (Ln) complex, [Sm(N††)2] (1), herein we present the synthesis of [Ln(N††)2] [N†† = {N(SiiPr3)2}–; Ln = Eu (2), Tm (3) and Yb (4)], thus achieving approximate uniaxial geometries for a series of “traditional” Ln(II) ions. Experimental evidence, together with calculations performed on a model of 4, indicate that dispersion forces are important for the stabilization of the near-linear geometries of 1-4. The isolation of 3 under a dinitrogen atmosphere is noteworthy, given that “[Tm(N′′)(μ-N′′)]2” (N′′ = {N(SiMe3)2}–) has not previously been structurally authenticated and reacts rapidly with N2(g) to give [{Tm(N′′)¬2}2(μ-η2:η2-N2)]. Complexes 1-4 have been characterized as appropriate by single crystal XRD, magnetic measurements, electrochemistry, and multinuclear NMR, EPR, and electronic spectroscopy, along with computational methods for 3 and 4. The remarkable geometries of monomeric 1-4 lead to interesting physical properties, which complement and contrast with comparatively well understood dimeric [Ln(N′′)(μ-N′′)]2 complexes. EPR spectroscopy of 3 shows that the near-linear geometry stabilizes mJ states with oblate spheroid electron density distributions, validating our previous suggestions. Cyclic voltammetry experiments carried out on 1-4 did not yield Ln(II) reduction potentials, so a reactivity study of 1 was performed with selected substrates in order to benchmark the Sm(III)→Sm(II) couple. The separate reactions of 1 with TEMPO (2,2,6,6-tetramethyl-piperidinyl-1-oxy), azobenzene and benzophenone gave crystals of [Sm(N††)2(TEMPO)] (5), [Sm(N††)2(N2Ph2)] (6) and [Sm(N††){μ-OPhC(C6H5)CPh2O-κ-O,O′}]2 (7), respectively. The isolation of 5-7 shows that the Sm(II) center in 1 is still accessible despite having two bulky N†† moieties, and that the N-donor atoms are able to deviate further from linearity or ligand scrambling occurs in order to accommodate another ligand in the Sm(III) coordination spheres of the products.
- Published
- 2016
31. Correlating Blocking Temperatures in Single Molecule Magnets with Raman Relaxation
- Author
-
George F. S. Whitehead, Andreas K. Kostopoulos, David Collison, Richard E. P. Winpenny, Nicholas F. Chilton, MarcusJ. Giansiracusa, and Floriana Tuna
- Subjects
symbols.namesake ,Materials science ,chemistry ,Blocking (radio) ,Magnet ,Relaxation (NMR) ,symbols ,Dysprosium ,chemistry.chemical_element ,Molecule ,Thermal relaxation ,Raman spectroscopy ,Molecular physics - Abstract
We report a six coordinate DyIII single-molecule magnet(SMM) with an energy barrier of 1110 K for thermal relaxation ofmagnetization. The sample shows no retention of magnetizationeven at 2 K and this led us to find a good correlation between theblocking temperature and the Raman relaxation regime for SMMs.The key parameter is the relaxation time (𝜏switch) at the point wherethe Raman relaxation mechanism becomes more important thanOrbach.
- Published
- 2018
32. Terbocenium: completing a heavy lanthanide metallocenium cation family with an alternative anion abstraction strategy
- Author
-
Conrad A. P. Goodwin, Jingjing Liu, Fabrizio Ortu, Daniel Reta, David P. Mills, and Nicholas F. Chilton
- Subjects
Lanthanide ,010405 organic chemistry ,Chemistry ,Metals and Alloys ,Halide ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Medicinal chemistry ,Catalysis ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Ion ,TheoryofComputation_ANALYSISOFALGORITHMSANDPROBLEMCOMPLEXITY ,Materials Chemistry ,Ceramics and Composites ,Abstraction - Abstract
A series of lanthanide metallocenium cations [Ln(Cp ttt ) 2 ] + (Ln = Y, Gd, Dy, Ho, Er, Tm, Yb, Lu; Cp ttt = C 5 H 2 t Bu 3 -1,2,4) were recently prepared, but curiously the Tb analogue was elusive. Here we access [Tb(Cp ttt ) 2 ] + via an alternative strategy, completing the heavy [Ln(Cp ttt ) 2 ] + family. A series of heavy lanthanide metallocenium cations [Ln(Cp ttt ) 2 ] + (Ln = Y, Gd, Dy, Ho, Er, Tm, Yb, Lu; Cp ttt = C 5 H 2 t Bu 3 -1,2,4) were recently prepared by halide abstraction of [Ln(Cp ttt ) 2 (Cl)], but curiously the Tb analogues remained elusive. Here we report an alternative anion abstraction strategy to access [Tb(Cp ttt ) 2 ] + , completing the heavy [Ln(Cp ttt ) 2 ] + family.
- Published
- 2018
33. Exquisite sensitivity of the ligand field to solvation and donor polarisability in coordinatively saturated lanthanide complexes
- Author
-
Andrei S. Batsanov, Michele Vonci, Nicholas F. Chilton, Eric J. L. McInnes, Connor W Patrick, Alice C. Harnden, Adeline W. J. Poh, David Parker, Kevin Mason, and Elizaveta A. Suturina
- Subjects
Ligand field theory ,Lanthanide ,Quantitative Biology::Biomolecules ,010405 organic chemistry ,Chemistry ,Ligand ,Spectrochemical series ,Metals and Alloys ,Solvation ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Dipole ,Crystallography ,Materials Chemistry ,Ceramics and Composites ,Condensed Matter::Strongly Correlated Electrons ,Sensitivity (control systems) - Abstract
Crystallographic, emission and NMR studies of a series of C3-symmetric, nine-coordinate substituted pyridyl triazacyclononane Yb(iii) and Eu(iii) complexes reveal the impact of local solvation and ligand dipolar polarisability on ligand field strength, leading to dramatic variations in pseudocontact NMR shifts and emission spectral profiles, giving new guidance for responsive NMR and spectral probe design.
- Published
- 2018
34. Zero-Field Quantum Tunneling of the Magnetization in a Series of High Energy-Barrier Dysprosium (III) Single-Molecule Magnets
- Author
-
Stephen T. Liddle, Daniel Reta, David P. Mills, Fabrizio Ortu, Nicholas F. Chilton, Richard E. P. Winpenny, EricJ. L. McInnes, Yan-Zhen Zheng, Matthew Gregson, You-Song Ding, and Conrad A. P. Goodwin
- Subjects
Hysteresis ,Magnetization ,Dipole ,Materials science ,chemistry ,Condensed matter physics ,Molecular vibration ,Dysprosium ,chemistry.chemical_element ,Magnetic hysteresis ,Quantum tunnelling ,Magnetic field - Abstract
Energy barriers to magnetisation reversal (Ueff) in single-molecule magnets (SMMs) have vastly increased recently, but only for the dysprosocenium SMM [Dy(Cpttt)2][B(C6F5)4] (Cpttt = C5H2tBu3-1,2,4) has this translated into a considerable increase in magnetic hysteresis temperatures. The lack of concomitant increases in hysteresis temperatures with Ueff values is due to efficient magnetic relaxation at zero-field, referred to as quantum tunnelling of the magnetisation (QTM); however, the exact nature of this phenomenon is unknown. Recent hypotheses suggest that both transverse dipolar magnetic fields and hyperfine coupling play a significant role in this process for Dy(III) SMMs. Here, by studying the compounds [Dy(tBuO)Cl(THF)5][BPh4] (1), [K(18-crown-6-ether)(THF)2][Dy(BIPM)2] (2, BIPM = C{PPh2NSiMe3}2), and [Dy(Cpttt)2][B(C6F5)4] (3), we show conclusively that neither of these processes are the main contributor to zero-field QTM for Dy(III) SMMs, and suggest that its origin instead owes to molecular flexibility. By analysing the vibrational modes of the three molecules, we show that the modes that most impact the magnetic ion occur at the lowest energies for 1, at intermediate energies for 2 and at higher energies for 3, in correlation with their ability to retain magnetisation. Therefore, we conclude that SMM performance could be improved by employing more rigid ligands with higher-energy metal-ligand vibrational modes.
- Published
- 2018
35. The performance of density functional theory for the description of ground and excited state properties of inorganic and organometallic uranium compounds
- Author
-
Bryan Edwards, Daniel Reta, Louise S. Natrajan, Simon Randall, David P. Mills, Nicholas F. Chilton, Nikolas Kaltsoyannis, Fabrizio Ortu, and Richard E. P. Winpenny
- Subjects
Actinide chemistry ,Valence (chemistry) ,010405 organic chemistry ,Organic Chemistry ,010402 general chemistry ,Uranyl ,01 natural sciences ,Biochemistry ,0104 chemical sciences ,Inorganic Chemistry ,Pseudopotential ,chemistry.chemical_compound ,chemistry ,Computational chemistry ,Chemical physics ,Excited state ,Materials Chemistry ,Density functional theory ,Physical and Theoretical Chemistry ,Relativistic quantum chemistry ,Basis set - Abstract
Molecular uranium complexes are the most widely studied in actinide chemistry, and make a significant and growing contribution to inorganic and organometallic chemistry. However, reliable computational procedures to accurately describe the properties of such systems are not yet available. In this contribution, 18 experimentally characterized molecular uranium compounds, in oxidation states ranging from III to VI and with a variety of ligand environments, are studied computationally using density functional theory. The computed geometries and vibrational frequencies are compared with X-ray crystallographic, and infra-red and Raman spectroscopic data to establish which computational approach yields the closest agreement with experiment. NMR parameters and UV–vis spectra are studied for three and five closed-shell U(VI) compounds respectively. Overall, the most robust methodology for obtaining accurate geometries is the PBE functional with Grimme's D3 dispersion corrections. For IR spectra, different approaches yield almost identical results, which makes the PBE functional with Grimme's D3 dispersion corrections the best choice. However, for Raman spectra the dependence on functional is more pronounced and no clear recommendation can be made. Similarly, for 1 H and 13 C NMR chemical shifts, no unequivocal recommendation emerges as to the best choice of density functional, although for spin-spin couplings, the LC- ω PBE functional with solvent corrections is the best approach. No form of time-dependent density functional theory can be recommended for the simulation of the electronic absorption spectra of uranyl (VI) compounds; the orbitals involved in the transitions are not calculated correctly, and the energies are also typically unreliable. Two main approaches are adopted for the description of relativistic effects on the uranium centres: either a relativistic pseudopotential and associated valence basis set, or an all-electron basis set with the ZORA Hamiltonian. The former provides equal, if not better, agreement with experiment vs all-electron basis set calculations, for all properties investigated.
- Published
- 2018
36. A Family of {CrIII2LnIII2} Butterfly Complexes: Effect of the Lanthanide Ion on the Single-Molecule Magnet Properties
- Author
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Keith S. Murray, Boujemaa Moubaraki, Stuart K. Langley, Nicholas F. Chilton, and Daniel Patrick Wielechowski
- Subjects
Inorganic Chemistry ,Lanthanide ,Crystallography ,Hysteresis ,Magnetization ,Nuclear magnetic resonance ,Chemistry ,Relaxation (NMR) ,Single-molecule magnet ,Physical and Theoretical Chemistry ,Coercivity ,Anisotropy ,Magnetic hysteresis - Abstract
We report the synthesis of several heterometallic 3d-4f complexes which result from the replacement of the Dy(III) ions in the [Cr(III)2Dy(III)2(OMe)2(mdea)2(O2CPh)4(NO3)2] single-molecule magnet (SMM) by the trivalent Pr, Nd, Gd, Tb, Ho, and Er lanthanide ions. The parent {Cr2Dy(III)2} compound displayed an anisotropy barrier to magnetization reversal of 53 cm(-1), with magnetic hysteresis observed up to 3.5 K and with large coercive fields at low temperatures (2.7 T at 1.8 K). Magnetic studies for the new complexes revealed significantly different static and dynamic magnetic behavior in comparison to the parent {Cr(III)2Dy(III)2} complex. When Ln(III) = Pr, a complete loss of SMM behavior is found, but when Ln(III) = Nd or Er, frequency-dependent tails in the out-of-phase susceptibility at low temperatures are observed, indicative of slow magnetic relaxation, but with very small anisotropy barriers and fast relaxation times. When Ln(III) = Tb and Ho, SMM behavior is clearly revealed with anisotropy barriers of 44 and 36 cm(-1), respectively. Magnetic hysteresis is also observed up to 2.5 and 1.8 K (0.003 T/s) for the Tb and Ho complexes, respectively. A large loss of the magnetization is, however, observed at zero-field, and as a result, the large coercivity which is present in the {Cr2Dy2} example is lost. The {Cr2Tb2} and {Cr2Ho2} complexes are rare examples of Tb- and Ho-based SMMs which reveal both slow relaxation in the absence of a static dc field (ac susceptibility) and open hysteresis loops above 1.8 K.
- Published
- 2015
37. Systematic Study of a Family of Butterfly-Like {M2Ln2} Molecular Magnets (M = MgII, MnIII, CoII, NiII, and CuII; Ln = YIII, GdIII, TbIII, DyIII, HoIII, and ErIII)
- Author
-
Floriana Tuna, Eric J. L. McInnes, Eufemio Moreno Pineda, Nicholas F. Chilton, and Richard E. P. Winpenny
- Subjects
Molecular magnets ,Chemistry ,Exchange interaction ,Relaxation (NMR) ,chemistry.chemical_element ,Inorganic Chemistry ,Metal ,Magnetization ,Crystallography ,Nuclear magnetic resonance ,Ab initio quantum chemistry methods ,visual_art ,visual_art.visual_art_medium ,Dysprosium ,Molecule ,Physical and Theoretical Chemistry - Abstract
A family of 3d–4f [MII2LnIII2(μ3-OH)2(O2CtBu)10]2– “butterflies” (where MII = Mg, Co, Ni, and Cu; LnIII = Y, Gd, Tb, Dy, Ho, and Er) and [MnIII2LnIII2(μ3-O)2(O2CtBu)10]2– molecules (where LnIII = Y, Gd, Tb, Dy, Ho, and Er) has been synthesized and characterized through single-crystal X-ray diffraction, SQUID magnetometry, and ab initio calculations. All dysprosium- and some erbium-containing tetramers showed frequency-dependent maxima in the out-of-phase component of the susceptibility associated with slow relaxation of magnetization, and hence, they are single-molecule magnets (SMMs). AC susceptibility measurements have shown that the SMM behavior is entirely intrinsic to the Dy and Er sites and the magnitude of the energy barrier is influenced by the interactions between the 4f and the 3d metal. A trend is observed between the strength of the 3d-4f exchange interaction between and the maximum observed in the χ″M(T).
- Published
- 2015
38. Molecular and electronic structures of donor-functionalized dysprosium pentadienyl complexes
- Author
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Nicholas F. Chilton, Benjamin M. Day, and Richard A. Layfield
- Subjects
Inorganic Chemistry ,Magnetic axis ,Crystallography ,chemistry ,Stereochemistry ,Ligand ,Hapticity ,Dysprosium ,chemistry.chemical_element ,Electronic structure - Abstract
Two dysprosium complexes, [(C5H4Me)2Dy(L(1))] (3) and [(L(1))Dy(μ-Cl)3{Li(tmeda)}]2 (4), with amino-functionalized pentadienyl ligands L(1) are described. Crystallographic studies of 3 and 4 show that the pendant amino group influences the pentadienyl conformation and the ligand hapticity. Electronic structure calculations reveal that L(1) has a strong influence on the orientation of the main magnetic axis of the ground Kramers doublets in 3 and 4.
- Published
- 2015
39. Ligand field influence on the electronic and magnetic properties of quasi-linear two-coordinate iron(<scp>ii</scp>) complexes
- Author
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Aimee M. Bryan, Hao Lei, Philip P. Power, Gary J. Long, Nicholas F. Chilton, and Fernande Grandjean
- Subjects
Inorganic Chemistry ,Ligand field theory ,Crystallography ,chemistry.chemical_compound ,Condensed matter physics ,Magnetic moment ,Chemistry ,Magnetism ,Ab initio quantum chemistry methods ,Dimer ,Antiferromagnetism ,Electron configuration ,Magnetic susceptibility - Abstract
The 2 to 300 K magnetic susceptibilities of Fe{N(SiMe2Ph)2}2, 1, Fe{N(SiMePh2)2}2, 2, and the diaryl complex Fe(Ar(Pr(i)4))2, 3, where Ar(Pr(i)4) is C6H3-2,6(C6H3-2,6-Pr(i)2)2 have been measured. Initial fits of these properties in the absence of an independent knowledge of their ligand field splitting have proven problematic. Ab initio calculations of the CASSCF/RASSI/SINGLE-ANISO type have indicated that the orbital energies of the complexes, as well as those of Fe(Ar(Me6))2, 4, where Ar(Me6) is C6H3-2,6(C6H2-2,4,6-Me3)2), are in the order d(xy)≈ d(x(2)-y(2))d(xz) ≈ d(yz)d(z(2)), and the iron(II) complexes in this ligand field have the (d(xy), d(x(2)-y(2)))(3)(d(xz), d(yz))(2)(d(z(2)))(1) ground electronic configuration with a substantial orbital contribution to their effective magnetic moments. An ab initio-derived ligand field and spin-orbit model is found to yield an excellent simulation of the observed magnetic properties of 1-3. The calculated ligand field strengths of these ligands are placed in the broader context of common coordination ligands in hypothetical two-coordinate linear iron(ii) complexes. This yields the ordering I(-)H(-)Br(-)≈ PMe3CH3(-)Cl(-)≈ C(SiMe3)3(-)CN(-)≈ SAr(Pr(i)6-)Ar(Pr(i)4-)Ar(Me6-)≈ N3(-)NCS(-)≈ NCSe(-)≈ NCBH3(-)≈ MeCN ≈ H2O ≈ NH3NO3(-)≈ THF ≈ CO ≈ N(SiMe2Ph)2(-)≈ N(SiMePh2)2(-)F(-)≈ N(H)Ar(Pr(i)6-)≈ N(SiMe3)Dipp(-)OAr(Pr(i)4-). The magnetic susceptibility of the bridged dimer, [Fe{N(SiMe3)2}2]2, 5, has also been measured between 2 and 300 K and a fit of χMT with the isotropic Heisenberg Hamiltonian, Ĥ = -2JŜ1·Ŝ2 yields an antiferromagnetic exchange coupling constant, J, of -131(2) cm(-1).
- Published
- 2015
40. Salts of the two-coordinate homoleptic manganese(<scp>i</scp>) dialkyl anion [Mn{C(SiMe3)3}2]− with quenched orbital magnetism
- Author
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Fernande Grandjean, Philip P. Power, Chun Yi Lin, Gary J. Long, Alasdair Formanuik, James C. Fettinger, and Nicholas F. Chilton
- Subjects
chemistry.chemical_classification ,Magnetism ,Inorganic chemistry ,Metals and Alloys ,chemistry.chemical_element ,General Chemistry ,Manganese ,Crystal structure ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Crystallography ,chemistry.chemical_compound ,chemistry ,law ,X-ray crystallography ,Materials Chemistry ,Ceramics and Composites ,Homoleptic ,Ground state ,Electron paramagnetic resonance ,Crown ether - Abstract
The structural and magnetic data for the Mn(i) dialkyl anionic salts [K2(18-crown-6)3][Mn{C(SiMe3)3}2]2 and [K(15-crown-5)2][Mn{C(SiMe3)3}2] are presented, indicating that these complexes possess a non-degenerate S = 2 ground state owing to 4s–3dz2 mixing upon reduction from the Mn(ii) parent complexes.
- Published
- 2015
41. The first 4d/4f single-molecule magnet containing a {RuIII2DyIII2} core
- Author
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Veacheslav Vieru, Keith S. Murray, Liviu F. Chibotaru, Daniel Patrick Wielechowski, Nicholas F. Chilton, Stuart K. Langley, and Boujemaa Moubaraki
- Subjects
Chemistry ,Metals and Alloys ,Ab initio ,General Chemistry ,Catalysis ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Core (optical fiber) ,Crystallography ,Computational chemistry ,Magnet ,Materials Chemistry ,Ceramics and Composites ,Single-molecule magnet ,Anisotropy - Abstract
We report the synthesis, structure and magnetic properties of the first 4d-4f single-molecule magnet. The complex [Ru(III)2Dy(III)2(OMe)2(O2CPh)4(mdea)2(NO3)2] displays a butterfly type core, with an anisotropy barrier of 10.7 cm(-1). Ab initio and DFT calculations provide insight into the observed magnetic behaviour.
- Published
- 2015
42. Single-molecule magnetism in {CoIII2DyIII2}-amine-polyalcohol-acetylacetonate complexes: effects of ligand replacement at the DyIII sites on the dynamics of magnetic relaxation
- Author
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Stuart K. Langley, Boujemaa Moubaraki, Keith S. Murray, and Nicholas F. Chilton
- Subjects
Magnetism ,Ligand ,Acetylacetone ,Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,chemistry ,Ab initio quantum chemistry methods ,Computational chemistry ,Triethanolamine ,medicine ,Molecule ,Magnetic relaxation ,Amine gas treating ,medicine.drug - Abstract
The synthesis of three new tetranuclear heterometallic CoIII–DyIII planar butterfly coordination complexes is reported of molecular formulae [DyIII2CoIII2(OH)2(teaH)2(acac)6]·MeCN (3), [DyIII2CoIII2(OH)2(bdea)2(acac)6]·2H2O (4) and [DyIII2CoIII2(OH)2(edea)2(acac)6]·2H2O·4MeCN (5) (teaH3 = triethanolamine, bdeaH2 = N-n-butyldiethanolamine, edeaH2 = N-ethyldiethanolamine and acacH = acetylacetone) each of which display single-molecule magnet (SMM) behaviour. Importantly these new compounds are related to several {CoIII2DyIII2} SMM compounds allowing for the study of the effect that the subtle changes in structure have on the SMM properties. Ab initio calculations are performed on 3–5, as well as on the related structural derivatives in order to gain insight on the effect the structural changes have on the dynamic magnetic behaviour.
- Published
- 2015
43. Molecular magnetic hysteresis at 60 kelvin in dysprosocenium
- Author
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Daniel Reta, Fabrizio Ortu, David P. Mills, Conrad A. P. Goodwin, and Nicholas F. Chilton
- Subjects
Multidisciplinary ,Condensed matter physics ,010405 organic chemistry ,Chemistry ,Oersted ,Relaxation (NMR) ,010402 general chemistry ,Magnetic hysteresis ,01 natural sciences ,0104 chemical sciences ,Magnetic field ,Hysteresis ,Molecular vibration ,Magnet ,Single-molecule magnet - Abstract
Magnetic hysteresis is observed in a dysprosocenium complex at temperatures of up to 60 kelvin, the origin of which is the localized metal–ligand vibrational modes unique to dysprosocenium. The discovery of molecules that exhibit magnetic bistability raised hopes for the use of such molecular systems as tiny building blocks for magnetic data storage. Despite a quarter of a century of research, however, the temperatures at which these molecules display their desirable magnetic properties remain frustratingly low. Conrad Goodwin et al. report the synthesis and characterization of a molecular dysprosocenium complex that shows magnetic bistability up to 60 kelvin—tantalizingly close to liquid nitrogen temperatures, the point at which applications would start to become a realistic possibility. Lanthanides have been investigated extensively for potential applications in quantum information processing and high-density data storage at the molecular and atomic scale. Experimental achievements include reading and manipulating single nuclear spins1,2, exploiting atomic clock transitions for robust qubits3 and, most recently, magnetic data storage in single atoms4,5. Single-molecule magnets exhibit magnetic hysteresis of molecular origin6—a magnetic memory effect and a prerequisite of data storage—and so far lanthanide examples have exhibited this phenomenon at the highest temperatures. However, in the nearly 25 years since the discovery of single-molecule magnets7, hysteresis temperatures have increased from 4 kelvin to only about 14 kelvin8,9,10 using a consistent magnetic field sweep rate of about 20 oersted per second, although higher temperatures have been achieved by using very fast sweep rates11,12 (for example, 30 kelvin with 200 oersted per second)12. Here we report a hexa-tert-butyldysprosocenium complex—[Dy(Cpttt)2][B(C6F5)4], with Cpttt = {C5H2tBu3-1,2,4} and tBu = C(CH3)3—which exhibits magnetic hysteresis at temperatures of up to 60 kelvin at a sweep rate of 22 oersted per second. We observe a clear change in the relaxation dynamics at this temperature, which persists in magnetically diluted samples, suggesting that the origin of the hysteresis is the localized metal–ligand vibrational modes that are unique to dysprosocenium. Ab initio calculations of spin dynamics demonstrate that magnetic relaxation at high temperatures is due to local molecular vibrations. These results indicate that, with judicious molecular design, magnetic data storage in single molecules at temperatures above liquid nitrogen should be possible.
- Published
- 2017
44. Molecules Designed to Contain Two Weakly Coupled Spins with a Photo-switchable Spacer
- Author
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Olivier Roubeau, Marta Estrader, Jorge Salinas Uber, Joris van Slageren, Nicholas F. Chilton, Simon J. Teat, Jordi Garcia, Jordi Ribas-Arino, Guillem Aromí, Anna Sadurní, Dominik Dengler, Paul Lloyd-Williams, Universitat de Barcelona, Generalitat de Catalunya, European Research Council, European Commission, Institución Catalana de Investigación y Estudios Avanzados, Ministerio de Economía y Competitividad (España), Department of Energy (US), and Ministerio de Ciencia e Innovación (España)
- Subjects
Propietats magnètiques ,010405 organic chemistry ,Chemistry ,Stereochemistry ,Organic Chemistry ,Library science ,Organic photochemistry) ,General Chemistry ,Organic photochemistry ,010402 general chemistry ,7. Clean energy ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Light source ,Functional importance ,Fotoquímica orgànica ,Magnetic properties ,Coordination compounds ,Christian ministry ,Compostos de coordinació - Abstract
Controlling the charges and spins of molecules lies at the heart of spintronics. A photoswitchable molecule consisting of two independent spins separated by a photoswitchable moiety was designed in the form of new ligand H4L, which features a dithienylethene photochromic unit and two lateral coordinating moieties, and yields molecules with [MM⋅⋅⋅MM] topology. Compounds [M4L2(py)6] (M=Cu, 1; Co, 2; Ni, 3; Zn, 4) were prepared and studied by single‐crystal X‐ray diffraction (SCXRD). Different metal centers can be selectively distributed among the two chemically distinct sites of the ligand, and this enables the preparation of many double‐spin systems. Heterometallic [MM′⋅⋅⋅M′M] analogues with formulas [Cu2Ni2L2(py)6] (5), [Co2Ni2L2(py)6] (6), [Co2Cu2L2(py)6] (7), [Cu2Zn2L2(py)6] (8), and [Ni2Zn2L2(py)6] (9) were prepared and analyzed by SCXRD. Their composition was established unambiguously. All complexes exhibit two weakly interacting [MM′] moieties, some of which embody two‐level quantum systems. Compounds 5 and 8 each exhibit a pair of weakly coupled S=urn:x-wiley:09476539:media:chem201702171:chem201702171-math-0001 spins that show quantum coherence in pulsed Q‐band EPR spectroscopy, as required for quantum computing, with good phase memory times (TM=3.59 and 6.03 μs at 7 K). Reversible photoswitching of all the molecules was confirmed in solution. DFT calculations on 5 indicate that the interaction between the two spins of the molecule can be switched on and off on photocyclization., G.A. thanks the Generalitat de Catalunya for the prize ICREA Academia 2008 and 2013 and the ERC for a Starting Grant (258060 FuncMolQIP). The authors thank the Spanish MINECO for funding through MAT2014‐53961‐R (OR) and CTQ2015‐68370‐P (GA) and the ERC for a Predoctoral Fellowship (JSU) under Grant 258060 FuncMolQIP. M.E. acknowledges the Spanish Ministry of Science and Innovation through the Juan de la Cierva Program. The Advanced Light Source (SJT) is supported by the Director, Office of Science, Office of Basic Energy Sciences of the U.S. Department of Energy under Contract DE‐AC02‐05CH11231.
- Published
- 2017
45. Metallacrowns as templates for diabolo-like {LnCu8} complexes with nearly perfect square antiprismatic geometry
- Author
-
Guo-Jun Zhou, Nicholas F. Chilton, You-Song Ding, Yan-Zhen Zheng, and Tian Han
- Subjects
Lanthanide ,Square antiprismatic molecular geometry ,Crystallographic point group ,010405 organic chemistry ,Ligand ,Chemistry ,Organic Chemistry ,Geometry ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,Square antiprism ,Lone pair ,Metallacrown ,Coordination geometry - Abstract
A series of diabolo-like nonanuclear {LnIIICuII8} (Ln = Tb, Dy, Ho, Er, Tm, Yb and Y) clusters in which the LnIII ion is capped by two 8-MC-4 metallacrown ligands to form a nearly ideal square antiprismatic (SAP) coordination geometry with D4d-symmetry have been prepared. Despite the lack of crystallographic symmetry these molecules engender the lanthanide ions with highly axial mJ states. We observe that the axial/equatorial nature of the crystal field in environments close to ideal SAP geometry is very subtle and influenced by the nature of the ligand lone pairs. We find slow magnetic relaxation behaviour for the DyIII, ErIII, TmIII and YbIII analogues, and show that the obtained effective energy barriers are not consistent with excitations on the LnIII ion, suggesting a more nuanced situation.
- Published
- 2017
46. Single-Molecule Magnetism in a Family of {CoIII2DyIII2} Butterfly Complexes: Effects of Ligand Replacement on the Dynamics of Magnetic Relaxation
- Author
-
Nicholas F. Chilton, Liviu F. Chibotaru, Liviu Ungur, Boujemaa Moubaraki, Stuart K. Langley, and Keith S. Murray
- Subjects
Diethanolamine ,Stereochemistry ,Magnetism ,Ligand ,Magnetic susceptibility ,Ion ,Inorganic Chemistry ,Crystallography ,chemistry.chemical_compound ,chemistry ,Triethanolamine ,medicine ,Diamagnetism ,Molecule ,Physical and Theoretical Chemistry ,medicine.drug - Abstract
The synthesis and structural characterization of four related heterometallic complexes of formulas [Dy(III)2Co(III)2(OMe)2(teaH)2(O2CPh)4(MeOH)4](NO3)2·MeOH·H2O (1a) and [Dy(III)2Co(III)2(OMe)2(teaH)2(O2CPh)4(MeOH)2(NO3)2]·MeOH·H2O (1b), [Dy(III)2Co(III)2(OMe)2(dea)2(O2CPh)4(MeOH)4](NO3)2 (2), [Dy(III)2Co(III)2(OMe)2(mdea)2(O2CPh)4(NO3)2] (3), and [Dy(III)2Co(III)2(OMe)2(bdea)2(O2CPh)4(MeOH)4](NO3)2·0.5MeOH·H2O (4a) and [Dy(III)2Co(III)2(OMe)2(bdea)2(O2CPh)4(MeOH)2(NO3)2]·MeOH·1.5H2O (4b) are reported (teaH3 = triethanolamine, deaH2 = diethanolamine, mdeaH2 = N-methyldiethanolamine, and bdeaH2 = N-n-butyldiethanolamine). Compounds 1 (≡ 1a and 1b) and 4 (≡ 4a and 4b) both display two unique molecules within the same crystal and all compounds display a butterfly type core, with the Dy(III) ions occupying the central body positions and the diamagnetic Co(III) ions the outer wing-tip sites. Compounds 1-4 were investigated via direct current and alternating current magnetic susceptibility measurements, and it was found that each complex displayed single-molecule magnet (SMM) behavior. All four compounds display unique coordination and geometric environments around the Dy(III) ions and it was found that each displays a different anisotropy barrier. Ab initio calculations were performed on 1-4 and these determined the low lying electronic structure of each Dy(III) ion and the magnetic interactions for each cluster. It was found that there was a strong correlation between the calculated energy gap between the ground and first excited states of the single-ion ligand-field split Dy(III) levels and the experimentally observed anisotropy barrier. Furthermore, the transverse g factors found for the Dy(III) ions, defining the tunnelling rates within the ground Kramers doublets, are largest for 1, which agrees with the experimental observation of the shortest relaxation time in the high-temperature domain for this complex. The magnetic exchange between the Dy(III) ions revealed overall antiferromagnetic interactions for each compound, derived from the dominant dipolar exchange resulting in nonmagnetic ground states for 1-4. The diamagnetic ground states coupled with small tunneling gaps resulted in quantum tunneling time scales at zero field of between 0.1 and1.5 s.
- Published
- 2014
47. Large Zero-Field Splittings of the Ground Spin State Arising from Antisymmetric Exchange Effects in Heterometallic Triangles
- Author
-
Nicholas F. Chilton, Eric J. L. McInnes, Samantha A. Magee, David Collison, Richard E. P. Winpenny, Stephen Sproules, Grigore A. Timco, Anne-Laure Barra, Laboratoire national des champs magnétiques intenses - Grenoble (LNCMI-G), Université Joseph Fourier - Grenoble 1 (UJF)-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS), School of Chemistry [Manchester], University of Manchester [Manchester], Photon Science Institute, Centre National de la Recherche Scientifique (CNRS)-Université Joseph Fourier - Grenoble 1 (UJF)-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), and Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées
- Subjects
Spin states ,Molecular Conformation ,Electrons ,Electronic structure ,Zero field splitting ,010402 general chemistry ,01 natural sciences ,Ruthenium ,Catalysis ,law.invention ,Ion ,Nuclear magnetic resonance ,Zero field ,Coordination Complexes ,law ,Electron paramagnetic resonance ,ComputingMilieux_MISCELLANEOUS ,Antisymmetric exchange ,010405 organic chemistry ,Chemistry ,[PHYS.PHYS.PHYS-ATM-PH]Physics [physics]/Physics [physics]/Atomic and Molecular Clusters [physics.atm-clus] ,Electron Spin Resonance Spectroscopy ,General Medicine ,General Chemistry ,0104 chemical sciences ,Quantum Theory ,[PHYS.PHYS.PHYS-CHEM-PH]Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph] ,Atomic physics ,Ground state - Abstract
[Ru2Mn(O)(O(2)CtBu)(6)(py)(3)] has an S=(5)/(2) ground state with a very large zero-field splitting (ZFS) of D=2.9cm(-1), as characterized by EPR spectroscopy at 4-330GHz. This is far too large to be due to the Mn-II ion (D
- Published
- 2014
48. Modulation of slow magnetic relaxation by tuning magnetic exchange in {Cr2Dy2} single molecule magnets
- Author
-
Liviu F. Chibotaru, Daniel Patrick Wielechowski, Veacheslav Vieru, Keith S. Murray, Boujemaa Moubaraki, Nicholas F. Chilton, and Stuart K. Langley
- Subjects
Magnetization ,Paramagnetism ,Hysteresis ,Crystallography ,Condensed matter physics ,Chemistry ,Relaxation (NMR) ,Molecule ,Diamagnetism ,General Chemistry ,Magnetic hysteresis ,Magnetic susceptibility - Abstract
A new series of heterometallic 3d–4f single molecule magnets (SMMs) of general formula [CrIII2DyIII2(OMe)2(RN{(CH2)2OH}2)2(acac)4(NO3)2] (R = Me, Et, nBu) is reported, displaying slow relaxation of the magnetization and magnetic hysteresis with non-zero coercive fields. Dynamic magnetic susceptibility experiments show that the three complexes possess anisotropy barriers of 34, 37 and 41 K (24, 29 and 26 cm−1); of similar magnitude to their {CoIII2DyIII2} counterparts. The replacement of the diamagnetic CoIII for paramagnetic CrIII ions results in significantly longer relaxation times, as observed via M(H) hysteresis at low temperatures, absent for the CoIII complexes. The present complexes are also compared to those of a similar CrIII–DyIII complex of formula [CrIII2DyIII2(OMe)2(O2CPh)4(mdea)2(NO3)2] (mdeaH2 = N-methyldiethanolamine), which displays SMM behaviour with a larger anisotropy barrier of 77 K (∼54 cm−1) and even longer relaxation times. We show that the long relaxation times compared to the CoIII analogues are due to the significant magnetic exchange interactions between the CrIII and DyIII ions, resulting in the suppression of quantum tunnelling of the magnetization (QTM) and leading to a multilevel relaxation barrier. The height of the relaxation barrier in these CrIII systems is then shown to be directly related to the strength of the exchange interactions between the CrIII and DyIII ions, showing a clear route towards enhancing the slow magnetic relaxation of coupled CrIII–DyIII systems.
- Published
- 2014
49. Fast magnetic relaxation in an octahedral dysprosium tetramethyl-aluminate complex
- Author
-
Eufemio Moreno Pineda, Reiner Anwander, Cäcilia Maichle-Mössmer, Thomas Pugh, Sonja N. König, Nicholas F. Chilton, and Richard A. Layfield
- Subjects
Condensed matter physics ,Aluminate ,Relaxation (NMR) ,chemistry.chemical_element ,Magnetic susceptibility ,Inorganic Chemistry ,Magnetization ,chemistry.chemical_compound ,chemistry ,Octahedron ,Ab initio quantum chemistry methods ,Physics::Atomic and Molecular Clusters ,Dysprosium ,Physical chemistry ,Physics::Atomic Physics ,Quantum tunnelling - Abstract
Ab initio calculations on the octahedral dysprosium aluminate complex [Dy(AlMe4)3] (1) predict weak SMM properties. Dynamic magnetic susceptibility measurements on 1 confirm the theoretical predictions, revealing fast relaxation of the magnetization via quantum tunnelling.
- Published
- 2014
50. Magnetic properties of octa- and heptadeca-nuclear heterometallic CoII–LnIII complexes derived from the ligand 6-chloro-2-hydroxypyridine
- Author
-
Keith S. Murray, Boujemaa Moubaraki, Stuart K. Langley, and Nicholas F. Chilton
- Subjects
Lanthanide ,Pivalic acid ,Chemistry ,Stereochemistry ,Ligand ,Magnetic susceptibility ,Inorganic Chemistry ,chemistry.chemical_compound ,Crystallography ,Ferrimagnetism ,Materials Chemistry ,Antiferromagnetism ,Diamagnetism ,Physical and Theoretical Chemistry ,Isostructural - Abstract
Four isostructural heterometallic octanuclear complexes have been synthesized of general formulae [{CoII}4LnIII4({OH})4(chp)10(acac)6]??solv (Ln = Y (1), Gd (2), Tb (3) and Dy (4); solv = 0.5MeCN for 1, 2 and 4 and Et2O for 3), where Hchp = 6-chloro-2-hydroxypyridine and acac- = acetylacetonate. A fifth complex of formula [{CoII}11DyIII6({OH})14(chp)14(piv)8({NO}3)4({MeCN})4]??2H2O (5) was also isolated using the Hchp ligand with pivalic acid as a co-ligand. X-ray crystallographic studies reveal that complexes 1 - 4 all display a central planar butterfly motif consisting of the four {LnIII} ions, with the {CoII} ions ???capping??? around the periphery of the butterfly. Compound 5 displays a complex metallic core with an unusual disc-like motif capped by two non-planar butterfly motifs. {DC} magnetic susceptibility measurements for the \{{CoII}4LnIII4\} family of compounds (1 ??? 4) reveals that the diamagnetic Y analogue \{{CoII}4YIII4\} (1) displays antiferromagnetic exchange interactions between the Co-Co ions. An overall decrease in the susceptibility (??{MT}) is then observed upon lowering the temperature for \{{CoII}4GdIII4\} (2) and \{{CoII}4TbIII4\} (3), while the \{{CoII}4DyIII4\} (4) complex displays a decrease before a small increase at the lowest temperatures measured, indicating a ferrimagnetic ground state. {AC} susceptibility measurements reveal an absence of any {SMM} behaviour for 1 ??? 3 but show the onset of slow magnetic relaxation below 4 K in the case of 4. The {DC} and {AC} behaviour of complex 5 \{{CoII}11DyIII6\} follows a similar profile to compound 4 revealing a small increase in ??{MT} at low temperatures, with the observation of possible {SMM} behaviour as observed via low temperature ???tails??? of peaks in the out-of-phase susceptibilities.
- Published
- 2013
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