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The hydration behaviour of coordination complexes is important for understanding their roles as bio-imaging agents. Determination of hydration is difficult, and various optical and NMR-based techniques have been used. Here we use EPR spectroscopy to unambiguously demonstrate that a t-butyl-pyridyl-functionalised ErIII DOTA derivative coordinates water, while its methylphosphinate analogue does not.

Interpreting electronic spectra of uranium-containing compounds is an important component of fundamental chemistry as well as in the assessment of waste streams in the nuclear fuel cycle. Here we employ multiconfigurational calculations with CASSCF or DMRGSCF methods on exemplar uranium molecules [U

We report the synthesis and structural characterization of a series of heterometallic rings templated via alkylammonium or imidazolium cations. The template and preference of each metal’s coordination geometry can control the structure of heterometallic compounds, leading to octa-, nona-, deca-, dodeca-, and tetradeca-metallic rings. The compounds were characterized by single-crystal X-ray diffraction, elemental analysis, magnetometry, and EPR measurements. Magnetic measurements show that the exchange coupling between metal centres is antiferromagnetic. EPR spectroscopy shows that the spectra of {Cr7Zn} and {Cr9Zn} have S = 3/2 ground states, while the spectra of {Cr12Zn2} and {Cr8Zn} are consistent with S = 1 and 2 excited states. The EPR spectra of {(ImidH)-Cr6Zn2}, {(1-MeImH)-Cr8Zn2}, and {(1,2-diMeImH)-Cr8Zn2} include a combination of linkage isomers. The results on these related compounds allow us to examine the transferability of magnetic parameters between compounds.

The recent discovery of metal-metal bonding and valence delocalization in the dilanthanide complexes (CpiPr5)2Ln2I3 (CpiPr5 = pentaisopropylcyclopentadienyl; Ln = Y, Gd, Tb, Dy) opened up the prospect of harnessing the 4fn5dz21 electron configurations of non-traditional divalent lanthanide ions to access molecules with novel bonding motifs and magnetism. Here, we report the trinuclear mixed-valence clusters (CpiPr5)3Ln3H3I2 (1-Ln, Ln = Y, Gd), which were synthesized via potassium graphite reduction of the trivalent clusters (CpiPr5)3Ln3H3I3. Structural, computational, and spectroscopic analyses support valence delocalization in 1-Ln resulting from a three-center, one-electron σ bond formed from the 4dz2 and 5dz2 orbitals on Y and Gd, respectively. Dc magnetic susceptibility data obtained for 1-Gd reveal that valence delocalization engenders strong parallel alignment of the σ-bonding electron and the 4f electrons of each gadolinium center to afford a high-spin ground state of S = 11. Notably, this represents the first clear instance of metal-metal bonding in a molecular trilanthanide complex, and the large spin-spin exchange constant of J = 168(1) cm-1 determined for 1-Gd is only the second largest coupling constant characterized to date for a molecular lanthanide compound.

We report two dichloride-bridged dinuclear dysprosium(III) complexes based on salen ligands, namely, [Dy(L1)(μ-Cl)(thf)]2 (1; H2L1 = N,Nʹ-bis(3,5-di-tert-butylsalicylidene)phenylenediamine) and [Dy2(L2)2(μ-Cl)2(thf)2]2 (2; H2L2 = N,Nʹ-bis(3,5-di-tert-butylsalicylidene)ethylenediamine). These two complexes have two short Dy−O(PhO) bonds that have angles of ~90° for 1 and ~143° for 2, leading to clear slow relaxation of the magnetization for 2 and not for 1. Compound 2 has a near-identical core to the recently reported compound [Dy2(L3)2(μ-Cl)2(thf)2] (3; H2L3 = N-(2-pyridylmethyl)-N,N-bis(2ʹ-hydroxy-3ʹ,5ʹ-di-tert-butylbenzyl)amine), the only substantial difference being the relative angle of the two O(PhO)−Dy−O(PhO) vectors, which are collinear in 2 owing to inversion symmetry and make an angle of ~68° in 3 owing to a molecular C2 axis. We show that this subtle structural difference leads to large differences in the dipolar ground states, giving rise to open magnetic hysteresis for 3 and not for 2.

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.

Substituted dysprosocenium complexes of the type [Dy(CpR)2]+ exhibit slow magnetic relaxation at cryogenic temperatures and have emerged as top-performing single-molecule magnets. The remarkable properties of these compounds derive in part from the strong axial ligand field afforded by the cyclopentadiene anions, and the design of analogous compounds with even stronger ligand fields is one promising route toward identifying new single-molecule magnets that retain a magnetic memory at even higher temperatures. Here, we report the synthesis and characterization of a dysprosium bis(borolide) compound, [K(18-crown-6)][Dy(BC4Ph5)2] (1), featuring the dysprosocenate anion [Dy(BC4Ph5)2]− with a pseudoaxial coordination environment afforded by two dianionic pentaphenyl borolide ligands. Variable-field magnetization data reveal open magnetic hysteresis up to 66 K, establishing 1 as a top-performing single-molecule magnet among its dysprosocenium analogues. Ac magnetic susceptibility data indicate that 1 relaxes via an Orbach mechanism above ∼80 K with Ueff = 1500(100) cm–1 and τ0 = 10–12.0(9) s, whereas Raman relaxation and quantum tunneling of the magnetization dominate at lower temperatures. Compound 1 exhibits a 100 s blocking temperature of 65 K, among the highest reported for dysprosium-based single-molecule magnets. Ab initio spin dynamics calculations support the experimental Ueff and τ0 values and enable a quantitative comparison of the relaxation dynamics of 1 and two representative dysprosocenium cations, yielding additional insights into the impact of the crystal field splitting and vibronic coupling on the observed relaxation behavior. Importantly, compound 1 represents a step toward the development of alternatives to substituted dysprosocenium single-molecule magnets with increased axiality.

Accurate modeling of vibronically driven magnetic relaxation from ab initio calculations is of paramount importance to the design of next-generation single-molecule magnets (SMMs). Previous theoretical studies have been relying on numerical differentiation to obtain spin-phonon couplings in the form of derivatives of spin Hamiltonian parameters. In this work, we introduce a novel approach to obtain these derivatives fully analytically by combining the linear vibronic coupling (LVC) approach with analytic complete active space self-consistent field derivatives and nonadiabatic couplings computed at the equilibrium geometry with a single electronic structure calculation. We apply our analytic approach to the computation of Orbach and Raman relaxation rates for a bis-cyclobutadienyl Dy(III) sandwich complex in the frozen-solution phase, where the solution environment is modeled by electrostatic multipole expansions, and benchmark our findings against results obtained using conventional numerical derivatives and a fully electronic description of the whole system. We demonstrate that our LVC approach exhibits high accuracy over a wide range of coupling strengths and enables significant computational savings due to its analytic, "single-shot" nature. Evidently, this offers great potential for advancing the simulation of a wide range of vibronic coupling phenomena in magnetism and spectroscopy, ultimately aiding the design of high-performance SMMs. Considering different environmental representations, we find that a point charge model shows the best agreement with the reference calculation, including the full electronic environment, but note that the main source of discrepancies observed in the magnetic relaxation rates originates from the approximate equilibrium electronic structure computed using the electrostatic environment models rather than from the couplings.

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.

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.

ConspectusComplexes of lanthanide(III) ions are being actively studied because of their unique ground and excited state properties and the associated optical and magnetic behavior. In particular, they are used as emissive probes in optical spectroscopy and microscopy and as contrast agents in magnetic resonance imaging (MRI). However, the design of new complexes with specific optical and magnetic properties requires a thorough understanding of the correlation between molecular structure and electric and magnetic susceptibilities, as well as their anisotropies. The traditional Judd-Ofelt-Mason theory has failed to offer useful guidelines for systematic design of emissive lanthanide optical probes. Similarly, Bleaney's theory of magnetic anisotropy and its modifications fail to provide accurate detail that permits new paramagnetic shift reagents to be designed rather than discovered.A key determinant of optical and magnetic behavior in f-element compounds is the ligand field, often considered as an electrostatic field at the lanthanide created by the ligands. The resulting energy level splitting is a sensitive function of several factors: The nature and polarizability of the whole ligand and its donor atoms; the geometric details of the coordination polyhedron; the presence and extent of solvent interactions; specific hydrogen bonding effects on donor atoms and the degree of supramolecular order in the system. The relative importance of these factors can vary widely for different lanthanide ions and ligands. For nuclear magnetic properties, it is both the ligand field splitting and the magnetic susceptibility tensor, notably its anisotropy, that determine paramagnetic shifts and nuclear relaxation enhancement.We review the factors that control the ligand field in lanthanide complexes and link these to aspects of their utility in magnetic resonance and optical emission spectroscopy and imaging. We examine recent progress in this area particularly in the theory of paramagnetic chemical shift and relaxation enhancement, where some long-neglected effects of zero-field splitting, magnetic susceptibility anisotropy, and spatial distribution of lanthanide tags have been accommodated in an elegant way.

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.

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.

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

We report the synthesis and characterization of two symmetric homo-dimetallic lanthanide complexes based on methyl-substituted 8-hydroxyquinoline (HMeQ). The aryloxo-bridged core gives rise to weak magnetic coupling between pairs of ErIII and YbIII ions, as revealed by magnetic and EPR spectroscopy studies. EPR measurements of magnetically dilute species, coupled with CASSCF-SO calculations, allows modelling of the EPR spectra of the exchange coupled species and the magnetic data simultaneously. This work adds to the database of exchange coupled {Ln}2 molecules which have been thoroughly characterised by EPR spectroscopy and modelled using an Seff = 1/2 approach to describe the interaction of ground Kramers states, and highlights the differences between centro-symmetric and asymmetric dimetallics.

A dinuclear dysprosocenium dication has been synthesised that is bound together by weak interactions between {Dy(Cp*)2}+ fragments and neutral NEt3AlMe3 molecules. The axiality of the Dy3+ crystal fields are perturbed by these equatorial interactions but a relatively large effective barrier to magnetisation reversal of 860(60) cm–1 and magnetic hysteresis up to 12 K are observed.

Vibronic coupling, the interaction between molecular vibrations and electronic states, is a pervasive effect that profoundly affects chemical processes. In the case of molecular magnetic materials, vibronic, or spin-phonon, coupling leads to magnetic relaxation, which equates to loss of magnetic memory and loss of phase coherence in molecular magnets and qubits, respectively. The study of vibronic coupling is challenging, and most experimental evidence is indirect. Here we employ far-infrared magnetospectroscopy to probe vibronic transitions in in [Yb(trensal)] (where H3trensal = 2,2,2-tris(salicylideneimino)trimethylamine). We find intense signals near electronic states, which we show arise due to an “envelope effect” in the vibronic coupling Hamiltonian, and we calculate the vibronic coupling fully ab initio to simulate the spectra. We subsequently show that vibronic coupling is strongest for vibrational modes that simultaneously distort the first coordination sphere and break the C3 symmetry of the molecule. With this knowledge, vibrational modes could be identified and engineered to shift their energy towards or away from particular electronic states to alter their impact. Hence, these findings provide new insights towards developing general guidelines for the control of vibronic coupling in molecules.

A family of heterometallic rings [Me

We discuss a cost-effective approach to understand magnetic relaxation in thenew generation of rare-earth single-molecule magnets. It combines ab initio calculations of thecrystal field parameters, of the magneto-elastic coupling with local modes, and of the phonondensity of states with fitting of only three microscopic parameters. Although much lessdemanding than a fully ab initio approach, the method gives important physical insights intothe origin of the observed relaxation. By applying it to high-anisotropy compounds with verydifferent relaxation, we demonstrate the power of the approach and pinpoint ingredients forimproving theperformance of single-molecule magnets.

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.

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.

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.

Vibronic coupling, the interaction between molecular vibrations and electronic states, is a pervasive effect that profoundly affects chemical processes. In the case of molecular magnetic materials, vibronic, or spin-phonon, coupling leads to magnetic relaxation, which equates to loss of magnetic memory and loss of phase coherence in molecular magnets and qubits, respectively. The study of vibronic coupling is challenging, and most experimental evidence is indirect. Here we employ far-infrared magnetospectroscopy to probe vibronic transitions in a YbIII molecular qubit directly. We find intense signals near electronic states, which we show arise due to an “envelope effect” in the vibronic coupling Hamiltonian, and we calculate the vibronic coupling fully ab initio to simulate the spectra. We subsequently show that vibronic coupling is strongest for vibrational modes that simultaneously distort the first coordination sphere and break the C3 symmetry of the molecule. With this knowledge, vibrational modes could be identified and engineered to shift their energy towards or away from particular electronic states to alter their impact. Hence, these findings provide new insights towards developing general guidelines for the control of vibronic coupling in molecules.

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.

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.

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.

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.

The recent discovery of single-ion magnets with magnetic hysteresis above liquid-nitrogen temperatures placed these compounds among the best candidates to realize high-density storage devices. Starting from a prototypical dysprosocenium molecule, showing hysteresis up to 60 K, we derive here a general recipe to design high-blocking-temperature rare-earth single-ion magnets. The complex magnetic relaxation is unraveled by combining magnetization and nuclear magnetic resonance measurements with inelastic neutron scattering experiments and ab initio calculations, thus disentangling the different mechanisms and identifying the key ingredients behind slow relaxation.

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.

A dichlorido-bridged dinuclear dysprosium(III) single-molecule magnet [Dy2L2(µ-Cl)2(THF)2] has been made using a diamine-bis(phenolate) ligand, H2L. Magnetic studies show an energy barrier for magnetization reversal (Ueff) around 1000 K. Exchange-biasing effect is clearly seen in magnetic hysteresis with steps up to 4 K. Ab initio calculations exclude the possibility of pure dipolar origin of this effect leading to the conclusion that super-exchange via the chloride bridging ligands is important.

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.

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...

Neutral mesoionic carbenes (MICs) have emerged as an important class of carbene, however they are found only in the free form or ligated to a few d-block ions. Here, we report unprecedented f-block MIC complexes [M(N'')3{CN(Me)C(Me)N(Me)CH}] (M = U, Y, La, Nd; N'' = N(SiMe3)2). These complexes were prepared by a formal 1,4-proton migration reaction when the metal-triamides [M(N'')3] were treated with the N-heterocyclic olefin H2C=C(NMeCH)2, which constitutes a new, general way to prepare MIC complexes. Quantum chemical calculations on the 5f3 uranium(III) complex suggest the presence of a U=C donor-acceptor bond, composed of a MIC→U σ-component and a U(5f)→MIC(2p) π-back-bond, but for the d0f0 Y and La and 4f3 Nd congeners only MIC→M σ-bonding is found. Considering the generally negligible π-acidity of MICs, this is surprising and highlights that greater consideration should possibly be given to recognising MICs as potential π-acid ligands when coordinated to reducing metals.

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.

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.

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.

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.

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.