Search

S.P. thanks the Novo Nordisk Foundation for research grant NNF20OC0065610. EPR Equipment funding by BBSRC to B. E. B. (17 Alert grant BB/R013780/1) is also gratefully acknowledged. We demonstrate by use of continuous wave- and pulse-electron paramagnetic resonance spectroscopy on oriented single crystals of magnetically dilute YbIII ions in Yb0.01Lu0.99(trensal) that molecular entangled two-qubit systems can be constructed by exploiting dipolar interactions between neighboring YbIII centers. Furthermore, we show that the phase memory time and Rabi frequencies of these dipolar-interaction-coupled entangled two-qubit systems are comparable to the ones of the corresponding single qubits. Publisher PDF

High-resolution inelastic neutron scattering has been used to study low-energy magnetic transitions in a Ho

Record-breaking magnetic exchange interactions have previously been reported for 3d-metal dimers of the form [M(Pt(SAc)(4))(pyNO(2))](2) (M = Ni or Co) that are linked in the solid state via metallophilic PtMIDLINE HORIZONTAL ELLIPSISPt bridges. This contrasts the terminally capped monomers [M(Pt(SAc)(4))(py)(2)], for which neither metallophilic bridges nor magnetic exchange interactions are found. Computational modeling has shown that the magnetic exchange interaction is facilitated by the pseudo-closed shell d(8)MIDLINE HORIZONTAL ELLIPSISd(8) metallophilic interaction between the filled Pt2+ 5d(z)(2) orbitals. We present here inelastic neutron scattering experiments on these complexes, wherein the dimers present an oscillatory momentum-transfer-dependence of the magnetic transitions. This allows for the unequivocal experimental assignment of the distance between the coupled ions, which matches exactly the coupling pathway via the metallophilic bridges. Furthermore, we have synthesized and magnetically characterized the isostructural palladium-analogues. The magnetic coupling across the PdMIDLINE HORIZONTAL ELLIPSISPd bridge is found through SQUID-magnetometry and FD-FT THz-EPR spectroscopy to be much weaker than via the PtMIDLINE HORIZONTAL ELLIPSISPt bridge. The weaker coupling is traced to the larger radial extent of the 5d(z)(2) orbitals compared to that of the 4d(z)(2) orbitals. The existence of a palladium metallophilic interaction is evaluated computationally from potential surface cuts along the metal stretching direction. Similar behavior is found for the PdMIDLINE HORIZONTAL ELLIPSISPd and PtMIDLINE HORIZONTAL ELLIPSISPt-systems with clear minima along this coordinate and provide estimates for the force constant for this distortion. The estimated MMIDLINE HORIZONTAL ELLIPSISM stretching frequencies are found to match experimental observed, polarized bands in single-crystal Raman spectra close to 45 cm(-1). This substantiates the existence of energetically relevant PdMIDLINE HORIZONTAL ELLIPSISPd metallophilic interactions. The unique properties of both Pt2+ and Pd2+ constitutes an orthogonal reactivity, which can be utilized for steering both the direction and strength of magnetic interactions.

Lytic polysaccharide monooxygenases (LPMOs) are copper-containing enzymes capable of oxidizing crystalline cellulose and the enzyme has large practical application in the process of refining biomass. The LPMO catalytic mechanism still remains debated despite several proposed reaction mechanisms. Here, we report a long-lived intermediate (t½= 6 – 8 minutes) observed in an LPMO fromThermoascus aurantiacus(TaLPMO9A). The intermediate with a strong absorption around 420 nm is formed when reduced LPMO-Cu(I) reacts with H2O2. UV-vis absorption spectroscopy, electron paramagnetic resonance (EPR), and stopped-flow spectroscopy indicate that the observed long-lived intermediate involves the copper center and a nearby tyrosine (Tyr175). We propose that the reaction with H2O2first forms a highly reactive short-lived Cu(III)-intermediate which is subsequently transformed into the observed long-lived copper-dependent intermediate. Since sub-equimolar amount of H2O2to LPMO boosts oxidation of phosphoric acid swollen cellulose (PASC) suggests that the long-lived copper-dependent intermediate is part of the catalytic mechanism for LPMOs. The proposed mechanism offers new perspectives in the oxidative reaction mechanism of copper enzymes and hence for the biomass oxidation and the reactivity of copper in biological systems.

In this paper, we experimentally study and model the electron donating character of an axial diamagnetic Pd2+ ion in four metalloligated lanthanide complexes of formula [PPh4][Ln{Pd(SAc)4}2] (SAc- = thioacetate, Ln = Tb, Dy, Ho, and Er). A global model encompassing inelastic neutron scattering, torque magnetometry, and dc magnetometry allows to precisely determine the energy level structure of the complexes. Solid state nuclear magnetic resonance reveals a less donating character of Pd2+ compared to the previously reported isostructural Pt2+-based complexes. Consequently, all complexes invariably show a lower crystal field strength compared to their Pt2+-analogues. The dynamic properties show an enhanced single molecule magnet behavior due to the suppression of quantum tunneling, in agreement with our model.

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...

Exploitation of HSAB preferences allows for high-yield, one-pot syntheses of lanthanide complexes chelated by two Pd or Pt metalloligands, [MII(SAc)4]2− (SAc− = thioacetate, M = Pd, Pt). The resulting complexes with 8 oxygen donors surrounding the lanthanides can be isolated in crystallographically tetragonal environments as either [NEt4]+ (space group: P4/mcc) or [PPh4]+ (space group: P4/n) salts. In the case of M = Pt, the complete series of lanthanide complexes has been structurally characterized as the [NEt4]+ salts (except for Ln = Pm), while the [PPh4]+ salts have been structurally characterized for Ln = Gd–Er, Y. For M = Pd, selected lanthanide complexes have been structurally characterized as both salts. The only significant structural difference between salts of the two counter ions is the resulting twist angle connecting tetragonal prismatic and tetragonal anti-prismatic configurations, with the [PPh4]+ salts approaching ideal D4d symmetry very closely (φ = 44.52–44.61°) while the [NEt4]+ salts exhibit intermediate twist angles in the interval φ = 17.28–27.41°, the twist increasing as the complete 4f series is traversed. Static magnetic properties for the latter half of the lanthanide series are found to agree well in the high temperature limit with the expected Curie behavior. Perpendicular and parallel mode EPR spectroscopy on randomly oriented powder samples and single crystals of the Gd complexes with respectively Pd- and Pt-based metalloligands demonstrate the nature of the platinum metal to strongly affect the spectra. Consistent parametrization of all of the EPR spectra reveals the main difference to stem from a large difference in the magnitude of the leading axial term, B02, this being almost four times larger for the Pt-based complexes as compared to the Pd analogues, indicating a direct Pt(5dz2)–Ln interaction and an arguable coordination number of 10 rather than 8. The parametrization of the EPR spectra also confirms that off-diagonal operators are associated with non-zero parameters for the [NEt4]+ salts, while only contributing minimally for the [PPh4]+ salts in which lanthanide coordination approximates D4d point group symmetry closely.

Using a new polydentate Schiff-base ligand (H3L) we isolated three new tetranuclear isostructural lanthanide complexes with the general formula [LnNa2(L)4(DMF)4(H2O)2(AcO)2]·4DMF·2H2O [Ln = Dy (1), Ho (2), or Er (3)]. The structural characterization of the complexes reveals that the Na+ ions are coordinated in the structure which gives them a structure-directing role in the molecule. The magnetic behavior of the systems was investigated by means of SQUID magnetometry which revealed that complex 1 exhibits single molecule magnet behavior at low temperatures which is enhanced by the application of a 2000 Oe static magnetic field. We were able to extract an effective barrier of Ueff = 43(1) K, however, we show that the consideration of an Orbach relaxation mechanism being the dominant is not always correct for lanthanides. On the contrary, we elaborate how in this system the relaxation is caused by a combination of a direct and a Raman process.

Three new heterometallic [CrIII8NiII6] coordination cubes of formulae [CrIII8NiII6L24(H2O)12](NO3)12 (1), [CrIII8NiII6L24(MeCN)7(H2O)5](ClO4)12 (2), and [CrIII8NiII6L24Cl12] (3) (where HL = 1-(4-pyridyl)butane-1,3-dione), were synthesised using the paramagnetic metalloligand [CrIIIL3] and the corresponding NiII salt. The magnetic skeleton of each capsule describes a face-centred cube in which the eight CrIII and six NiII ions occupy the eight vertices and six faces of the structure, respectively. Direct current magnetic susceptibility measurements on (1) reveal weak ferromagnetic interactions between the CrIII and NiII ions, with JCr-Ni = + 0.045 cm−1. EPR spectra are consistent with weak exchange, being dominated by the zero-field splitting of the CrIII ions. Excluding wheel-like structures, examples of large heterometallic clusters containing both CrIII and NiII ions are rather rare, and we demonstrate that the use of metalloligands with predictable bonding modes allows for a modular approach to building families of related polymetallic complexes. Compounds (1)–(3) join the previously published, structurally related family of [MIII8MII6] cubes, where MIII = Cr, Fe and MII = Cu, Co, Mn, Pd.

New exotic phenomena have recently been discovered in oxides of paramagnetic Ir4+ ions, widely known as ‘iridates'. Their remarkable properties originate from concerted effects of the crystal field, magnetic interactions and strong spin-orbit coupling, characteristic of 5d metal ions. Despite numerous experimental reports, the electronic structure of these materials is still challenging to elucidate, and not attainable in the isolated, but chemically inaccessible, [IrO6]8– species (the simplest molecular analogue of the elementary {IrO6}8− fragment present in all iridates). Here, we introduce an alternative approach to circumvent this problem by substituting the oxide ions in [IrO6]8− by isoelectronic fluorides to form the fluorido-iridate: [IrF6]2−. This molecular species has the same electronic ground state as the {IrO6}8− fragment, and thus emerges as an ideal model for iridates. These results may open perspectives for using fluorido-iridates as building-blocks for electronic and magnetic quantum materials synthesized by soft chemistry routes., Iridates are known to exhibit a range of exotic electronic and magnetic behaviours but it is difficult to prepare isolated [IrO6]8− species via soft chemical routes. Here, the authors isolate the isoelectronic [IrF6]2− complex, and assess it as a model and for iridate analogues.

The reaction of the simple metalloligand [Fe

The rational design of the magnetic anisotropy of molecular materials constitutes a goal of primary importance in molecular magnetism. Indeed, the applications of molecular nanomagnets, such as single-molecule magnets and molecular magnetic refrigerants, depend on the full control over this property. Axially anisotropic magnetic systems are frequently classified as easy axis or easy plane, depending on whether the lowest energy is obtained by application of a magnetic field parallelly or perpendicularly to the unique axis. Here, the magnetic aniso-tropy of three lanthanide complexes is studied as a function of magnetic field and temperature. It is found that for two of these the type of magnetic aniso-tropy switches as a function of these parameters. Thus, this paper experimen-tally demonstrates that the magnetic anisotropy is not uniquely defined by the intrinsic electronic structure of the systems in question but can also be reversibly switched using external stimuli: temperature and magnetic field., This work is based on experiments performed at the Swiss spallation neutron source SINQ, Paul Scherrer Institute, Villigen, Switzerland. The project was funded by the Independent Research Fund Denmark through the project “Spin Architecture” and the Danish Agency for Science, Technology and Innovation through DANSCATT. M.P., H.B., P.H., S.L., and J.v.S. thank DFG foundation (Project SL 104/5-1). M.A.S. thanks the Oticon Foundation (16-2669) and the Augustinus Foundation (16-2917) for financial support in relation to a research stay at Institut für Physikalische Chemie, Universität Stuttgart, Germany. E.B., A.A., and J. Bartolomé acknowledge the financial support of Spanish MINECO project MAT2017-83468-R. For the experiments conducted at FRM II, this project has received funding from the European Union’s 7th Framework Programme for research, technological development and demonstration under the NMI3-II Grant No. 283883.

Total control over the electronic spin relaxation in molecular nanomagnets is the ultimate goal in the design of new molecules with evermore realizable applications in spin-based devices. For single-ion lanthanide systems, with strong spin-orbit coupling, the potential applications are linked to the energetic structure of the crystal field levels and quantum tunneling within the ground state. Structural engineering of the timescale of these tunneling events via appropriate design of crystal fields represents a fundamental challenge for the synthetic chemist, since tunnel splittings are expected to be suppressed by crystal field environments with sufficiently high-order symmetry. Here, we report the long missing study of the effect of a non-linear (C4) to pseudo-linear (D4d) change in crystal field symmetry in an otherwise chemically unaltered dysprosium complex. From a purely experimental study of crystal field levels and electronic spin dynamics at milliKelvin temperatures, we demonstrate the ensuing threefold reduction of the tunnel splitting., M.A.S., U.B.H., K.L., and J.Be. acknowledge financial support from the Danish Research Councils for Independent Research (12-125226). M.A.S., U.B.H., M.R, and K.L. acknowledge DANSCATT for financial support for the neutron scattering experiments. For the experiments conducted at FRM II, this project has received funding from the European Union’s 7th Framework Programme for research, technological development and demonstration under the NMI3-II Grant number 283883. M.A.S. thanks the Oticon Foundation (16-2669), and the Augustinus Foundation (16-2917) for financial support in relation to a research stay at Institut für Physikalische Chemie, Universität Stuttgart, Germany. M.P. and J.v.S. thank the DFG for funding (SL104/5-1). K.S.P. thanks the Danish Research Council for Independent Research for a DFF-Sapere Aude Research Talent grant (4090-00201). E.B., A.A, and, J.Ba. acknowledge the financial support of Spanish MINECO project MAT2017-83468-R. M.J. acknowledges the Swiss National Science Foundation.

We study the ligand-field splittings and magnetic properties of three ErIII single-ion magnets which differ in the peripheral ligand sphere but exhibit similar first coordination spheres by inelastic neutron scattering (INS) and SQUID magnetometry. The INS spectra of the three compounds are profoundly different pointing at a strong response of the magnetic behavior to minor structural changes, as they are e.g. encountered when depositing molecules on surfaces. The observation of several magnetic excitations within the J = 15/2 ground multiplet together with single-crystal magnetic measurements allows for the extraction of the sign and magnitude of all symmetry-allowed Stevens parameters. The parameter values and the energy spectrum derived from INS are compared to the results of state-of-the-art ab initio CASSCF calculations. Temperature-dependent alternating current (ac) susceptibility measurements suggest that the magnetisation relaxation in the investigated temperature range of 1.9 K < T < 5 K is dominated by quantum tunnelling of magnetisation and two-phonon Raman processes. The possibility of observing electron paramagnetic resonance transitions between the ground-state doublet states, which can be suppressed in perfectly axial single-ion magnets, renders the studied systems interesting as representations of quantum bits., Chemical Science, 5 (4), ISSN:2041-6520, ISSN:2041-6539

The magnetic susceptibility of the dinuclear chromium(III) complex[(CH 3 CN) 5 CrOCr(NCCH 3 ) 5 ](BF 4 ) 4 ·2 CH 3 CN has been measured and analyzed. With a fitted value of the triplet energy J = 650 cm −1 , the antiferromagnetic coupling is the strongest hitherto determined for an unsupported linear oxide-bridged dinuclear Cr(III) system. The applicability of DFT for computational prediction of exchange in strongly coupled chromium(III) dimers was examined and an optimal and accurate modeling approach was devised. By such modeling it was shown possible to reproduce experimental exchange coupling constants with small relative errors typically of less than 10% ranging from the strongest coupled systems to systems with moderately strong couplings. A significant influence (>20%) of the chemical nature of the peripheral, non-bridging ligands on the exchange coupling was found and rationalized.

A tetranuclear [2 × 2] grid-like manganese(III) Schiff base complex, Mn4, has been synthesized and characterized by single-crystal X-ray crystallography. Direct-current magnetization measurements were performed on the system and proved to be insufficient for an accurate magnetic model to be deduced. Combined inelastic neutron scattering (INS) and electron paramagnetic resonance (EPR) experiments provided the necessary information in order to successfully model the magnetic properties of Mn4. The resulting model takes into account both the magnitude and the relative orientations of the single-ion anisotropy tensors.

International audience; Quantum coherence is detected in the 4f single-ion magnet (SIM) Yb(trensal), by isotope selective pulsed EPR spectroscopy on an oriented single crystal. At X-band, the spin-lattice relaxation (T1) and phase memory (Tm) times are found to be independent of the nuclei bearing, or not, a nuclear spin. The observation of Rabi oscillations of the spin echo demonstrates the possibility to coherently manipulate the system for more than 70 rotations. This renders Yb(trensal), a sublimable and chemically modifiable SIM, an excellent candidate for quantum information processing.

The use of a simple two-center model to describe exchange-coupled systems of various complexities is common in the field of coordination chemistry and molecular magnetism. In this work we investigate the applicability of this model experimentally, employing multifrequency, single-crystal EPR on axial dinuclear chromium(III) systems amenable to accurate parametrizations. The very high confidence with which zero-field splitting parameters can be determined by this technique, applied to the systems in question, allows for an in-depth analysis of the modeling. We experimentally demonstrate and qualitatively account for the energy-dependent modification of the spin-multiplet anisotropies, which is introduced by the exchange interaction. Even for the simple systems under consideration, we find that the standard modeling provides an inadequate parametrization of experimental data, and we present a convenient model extension, which improves the description.

The reaction of [MnIII(5-Brsalen)(MeOH)](ClO4) (5-Brsalen2 − = N,N′-ethylenebis(5-bromosalicylidene-iminate)) with [IrIII(CN)6]3 − yields a trinuclear, cyanide-bridged MnIII–IrIII–MnIII cluster which is a member of an isostructural series of MnIII–MIII–MnIII clusters. The presence of the large, diamagnetic [IrIII(CN)6]3 − bridging unit facilitates a precise determination of the MnIII zero-field splitting (zfs) parameters by the combined use of inelastic neutron scattering, high-field, high-frequency EPR spectroscopy and magnetic measurements. The single-ion axial (D) and rhombic (E) zfs parameters are found to be D = − 3.72(5) cm− 1 and |E| = 0.21(1) cm− 1. The experimental data are consistent with a small, antiferromagnetic exchange interaction between the two MnIII ions.

The reaction of diamagnetic trans-[ReV(O)2(py)4]NO3 with [Ln(hfac)3(H2O)2] (Ln = Dy, Y, Tb; hfac− = 1,1,1,5,5,5-hexafluoroacetylacetonate(1–)) in chloroform yields oxide-bridged, trinuclear [Ln(hfac)3(H2O)–Re(O)2(py)4–Ln(hfac)3(NO3)] (DyReDy, YReY, TbReTb). The series is isostructural to a fluoride-bridged {Dy–Cr–Dy} complex previously reported (Dreiser et al., Chem. Sci. 3 (2012) 1024) but, notably, DyReDy exhibits frequency-dependent out-of-phase ac susceptibility (χ″) signals at higher temperatures than the chromium analogue. Magnetic investigations of a solid solution of Dy3+ in YReY reveal the presence of a small Dy–Dy exchange interaction in DyReDy.

We report on the synthesis, crystal structure and magnetic characterisation of the trinuclear, fluoride-bridged, molecular nanomagnet [Dy(hfac)(3)(H2O)-CrF2(py)(4)-Dy(hfac)(3)(NO3)] (1) (hfacH = 1,1,1,5,5,5-hexafluoroacetylacetone, py = pyridine) and a closely related dinuclear species [Dy(hfac)(4)-CrF2( py)(4)]center dot 1/2 CHCl3 (2). Element-specific magnetisation curves obtained on 1 by X-ray magnetic circular dichroism (XMCD) allow us to directly observe the field-induced transition from a ferrimagnetic to a ferromagnetic arrangement of the Dy and Cr magnetic moments. By fitting a spin-Hamiltonian model to the XMCD data we extract a weak antiferromagnetic exchange coupling of j -0.18 cm(-1) between the Dy-III and Cr-III ions. The value found from XMCD is consistent with SQUID magnetometry and inelastic neutron scattering measurements. Furthermore, alternating current susceptibility and muon-spin relaxation measurements reveal that 1 shows thermally activated relaxation of magnetisation with a small effective barrier for magnetisation reversal of Delta(eff) 3 cm(-1). Density-functional theory calculations show that the Dy-Cr couplings originate from superexchange via the fluoride bridges.

The title compound, [Co2(L)2]3+·3NO3−[whereL= CH3C(CH2NHCH2CH2OH1/2)3], has been synthesized from the ligand 1,1,1-tris(2-hydroxyethylaminomethyl)ethane. The cobalt(III) dimer has an interesting and uncommon O—H...O hydrogen-bonding motif with the three bridging hydroxy H atoms each being equally disordered over two positions. In the dimeric trication, the octahedrally coordinated CoIIIatoms and the capping C atoms lie on a threefold rotation axis. The N atoms of two crystallographically independent nitrate anions also lie on threefold rotation axes. N—H...O hydrogen bonding between the complex cations and nitrate anions leads to the formation of a three-dimensional network structure. The compound is a racemic conglomerate of crystals containing either D or L molecules. The crystal used for this study is a D crystal.

We have investigated the novel single-molecule magnet (NEt(4))[Mn(2)(5-Brsalen)(2)(MeOH)(2)Cr(CN)(6)] (1; 5-Brsalen = N,N'-ethylenebis(5-bromosalicylidene)iminato anion) using spectroscopic as well as magnetization and susceptibility measurements. Frequency-domain Fourier-transform terahertz electron paramagnetic resonance (FDFT THz-EPR) based on the generation of THz radiation from a synchrotron in combination with inelastic neutron scattering (INS) allows for the discrimination between intermultiplet and intramultiplet transitions. Together with ac/dc magnetic susceptibility measurements the obtained set of data provides a complete characterization of the lowest energetic magnetic excitations. We find that the new compound 1 exhibits much weaker intermolecular interactions than found in the closely related compound: K[Mn(2)(5-Brsalen)(2)(H(2)O)(2)Cr(CN)(6)] (2). Furthermore, two phonon lines in the vicinity of the magnetic excitations are detected.

We report the first single-molecule magnet (SMM) to incorporate the [Os(CN)(6)](3-) moiety. The compound (1) has a trimeric, cyanide-bridged Mn(III)-Os(III)-Mn(III) skeleton in which Mn(III) designates a [Mn(5-Brsalen)(MeOH)](+) unit (5-Brsalen=N,N'-ethylenebis(5-bromosalicylideneiminato)). X-ray crystallographic experiments reveal that 1 is isostructural with the Mn(III)-Fe(III)-Mn(III) analogue (2). Both compounds exhibit a frequency-dependent out-of-phase χ''(T) alternating current (ac) susceptibility signal that is suggestive of SMM behaviour. From the Arrhenius expression, the effective barrier for 1 is found to be Δ(eff)/k(B)=19 K (τ(0)=5.0×10(-7) s; k(B)=Boltzmann constant), whereas only the onset (1.5 kHz, 1.8 K) of χ''(T) is observed for 2, thus indicating a higher blocking temperature for 1. The strong spin-orbit coupling present in Os(III) isolates the E'(1g(1/2))(O(h)*) Kramers doublet that exhibits orbital contributions to the single-ion anisotropy. Magnetic susceptibility and inelastic neutron-scattering measurements reveal that substitution of [Fe(CN)(6)](3-) by the [Os(CN)(6)](3-) anion results in larger ferromagnetic, anisotropic exchange interactions going from quasi-Ising exchange interactions in 2 to pure Ising exchange for 1 with J(parallel)(MnOs)=-30.6 cm(-1). The combination of diffuse magnetic orbitals and the Ising-type exchange interaction effectively contributes to a higher blocking temperature. This result is in accordance with theoretical predictions and paves the way for the design of a new generation of SMMs with enhanced SMM properties.

Interaction of robust chromium(III) fluoride complexes with sodium or lithium cations in solution lead to hypsochromic spectral shifts of increasing magnitude along the series: trans-[CrF2(py)4]+, mer-[CrF3(terpy)], and fac-[CrF3(Me3tacn)]. Crystalline products isolated from solution exhibit μ2-bridging by the fluoride ligands in a linear fashion between Na+-ions and chromium centres in catena-[Na(H2O)4(μ-F)-trans-{CrF(py)4}](HCO3)2 and in the dimers [Li(H2O)n(μ-F)-trans-{CrF(py)4}]2+ (n = 3, 4). The uncharged chromium complexes fac-[CrF3(Me3tacn)] and mer-[CrF3(terpy)] have been synthesized from mer-[CrF3(py)3] and shown to precipitate sodium salts from solution, of which 3[CrF3(Me3tacn)]·2Na(Bph4)·solv and 6[CrF3(terpy)]·4Na(Bph4)·solv have been crystallographically characterized. In these clusters, the neutral fluoride complexes bring the Na+ cation separation down to 3.610 A and 3.369 A, respectively, which is much closer than the inter-cation distance in NaCl and comparable to that of NaF. DFT calculations support the notion of a strong interaction between Na+ ions and neutral chromium(III) fluoride complexes. The calculations reproduce the magnitude and the counter-intuitive sign of the spectral shifts induced by second sphere complexation in solution, which originates in a breakdown of the assumption of parameter transferability in ligand-field descriptions.

The title compound, aquabis(5-methylisoazole-3-carboxylato-O,N)copper(II) monohydrate, [Cu(L2)(H2O)] · H2O is synthesized and characterized by X-ray diffraction, elementary analysis, and IR. The ligand coordinates to the copper center in a bidentate O,N fashion through the carboxylic acid moiety and the heteroaromatic nitrogen atom. The complex crystallizes in the triclinic space group $${\bar{P}} 1$$ with unit cell parameters a = 8.4080(12)A, b = 8.810(3), c = 10.318(2)A, α = 110.08(3)°, β = 104.81(2)°, γ = 103.149(16)°, V = 650.9(3)A3, Z = 2. In addition, the synthesis of the free acid 5-methylisoazole-3-carboxylic acid and pyridine containing complex bis(5-methylisoazole-3-carboxylato)bispyridinecopper(II) monohydrate is described. Synthesis and crystal structure of aquabis(5-methylisoazole-3-carboxylato-O,N)copper(II)monohydrate. The first coordination compound of 5-methylisoxazole-3-carboxylic acid.

We demonstrate that the electron paramagnetic resonance spectrum of Mn2+ impurities in calcite, and therefore also in marble, may be accurately reproduced by a traditional spin Hamiltonian formalism. The success of such a treatment, however, very much depends on the spin Hamiltonian parameters having the correct signs as well as magnitudes. We present data that determine the sign of the axial anisotropy parameter and thereby facilitate future quantum mechanical characterizations of marble electron paramagnetic resonance spectra that supplement provenance determination.

The electronic structures of the compounds K[(5-Brsalen)2(H2O)2-Mn2MIII(CN)6]·2H2O (MIII = CoIII, CrIII, FeIII) have been determined by inelastic neutron scattering (INS) and magnetic susceptibility studies, revealing the manganese(III) single-ion anisotropy and exchange interactions that define the low-lying states of the Mn−MIII−Mn trimeric units. Despite the presence of an antiferromagnetic intertrimer interaction, the experimental evidence supports the classification of both the Cr(III) and Fe(III) compounds as single-molecule magnets. The value of 17(2) cm−1 established from AC susceptibility measurements for a spin-reversal barrier of K[(5-Brsalen)2(H2O)2-Mn2Cr(CN)6]·2H2O may be readily rationalized in terms of the energy level diagram determined directly by INS. AC susceptibility measurements on samples of K[(5-Brsalen)2(H2O)2-Mn2Fe(CN)6]·2H2O are contrary to those previously reported, exhibiting but the onset of peaks below temperatures of 1.8 K at oscillating frequencies in the range of 100−800 H...

L-, S-, and X-band powder EPR spectra and an L-band single-crystal spectrum of Mn2+ impurities in calcite were analysed by the fitting of full spectral traces to a theoretical model. This analysis gives as parameters the traditional spin Hamiltonian parameters reflecting the three-fold symmetry of the cation lattice site as well as parameters determining the band shape and width of the resonances. The three frequencies give a consistent description of the system. For this spin system it is shown that the relative sign of the axial zero-field splitting parameter Dand the hyperfine coupling constant A may be safely determined at the L-band.

Determination of the electronic energy spectrum of a trigonalsymtnetry mononuclear Yb3+ single-molecule magnet (SMM) by highresolution absorption and luniinescente spectroscopies reveals that the first excited electronic doublet is placed nearly 500 cm(-1) above the ground one. Fitting of the paramagnetic relaxation times of this- SMM to a thermally activated (Orbach) model {tau = tau(0) X exp [Delta(Orbach)/(k(B)T)]} affords an activation barrier, Delta(Orbach), of only 38 cm(-1). This result is incompatible with the spectroscopic observations. Thus, we unambiguously demonstrate, solely on the basis Of experimental data, that Orbach relaxation cannot ci priori be considered as the main mechanism determining the spin dynamics of SM.Ms. This study highlights the fact that the general:synthetic approach of optimizing SMM behavior by maximization of the anisotropy barrier, intimately linked to the ligand field, 'as the sole paratneter to be tuned, is insufficient because of the complete neglect of the interaction of the magnetic moment of the molecule with its environment. The Orbach mechanism is expected dominant only in the cases in which the energy of the excited ligand field state is below the Debye temperature, which is typically low for molecular crystals and, thus, prevents the use of the anisotropy barrier as a design criterion, for the realization of high-temperature SM.Ms. Therefcire, consideration of additional design criteria that address the presence of alternative relaxation processes beyond the traditional double-well picture is required.

The central Mn(II) ions in a series of calix[4]arene-stabilised butterflies can be sequentially replaced with Ln(III) ions, maintaining the structural integrity of the molecule but transforming its magnetic properties. The replacement of Mn(II) for Gd(III) allows for the examination of the transferability of spin-Hamiltonian parameters within the family as well as permitting their reliable determination. The introduction of the 4f ions results in weaker intramolecular magnetic exchange, an increase in the number of low-lying excited states, and an increase in magnetisation relaxation, highlighting the importance of exchange over single-ion anisotropy for the observation of SMM behaviour in this family of complexes. The presence of the [TM(II/III) (TBC[4])(OH)(solvent)] metalloligand (TM=transition metal, TBC=p-tBu-calix[4]arene) suggests that magnetic calix[n]arene building blocks can be employed to encapsulate a range of different "guests" within structurally robust "hosts".

A dinuclear manganese complex {[(Mn2L)-L-II,IIII(mu-OAc)(2)]-ClO4} has been synthesised, where L is the dianion of 2-{[bis-(pyrid-2-ylmethyl)amino]methyl}-6-{[(3,5-di-tert-butyl-2- hydroxybenzyl)(p ...

Caught in the act: Until now, the spatial property of the hyperfine interaction between the S=2 electronic spin and the I=5/2 nuclear spin in any chemically relevant MnIII compound has escaped observation. By taking multifrequency electron paramagnetic resonance measurements (see graph) on the [Mn(OH2)6]3+ ion doped into Cs[Ga(OH2)6](SO4)6 H2O, ground-state spin Hamiltonian parameters have been determined at an unprecedented level of precision.

The syntheses, structures and magnetic properties of five new manganese (III) cyclam complexes, trans-[Mn(cyclam)(OH2)2](CF3SO3)3 AE H2O, trans-[Mn(cyclam)I2]I, trans-[Mn(cyclam)(ONO)2]ClO4, trans-[Mn(cyclam)(OClO3)2]ClO4 and trans-[Mn(cyclam) (CH3COO)(CH3COOH)](ClO4)2, are reported. Cyclam is the tetradentate amine ligand 1,4,8,11-tetraazacyclotetradecane. The complexes all exhibit pronounced tetragonal elongation of the coordination octahedron with the four cyclam nitrogens occupying the four equatorial positions. The magnetic properties are consistent with the formulation of the complexes as high-spin d 4 systems. trans-[Mn(cyclam)(OH2)2](CF3SO3)3 AE H2O is shown to be a convenient starting material for the syntheses of trans cyclam complexes. [Mn(cyclam)(CH3COO)(CH3COOH)](ClO4)2 exhibits extremely short intermolecular hydrogen bonds resulting in a pseudo-chain structure. The tilt of the axial ligands with respect to the equatorial plane containing the manganese and the cyclam nitrogen atoms is discussed. � 2004 Elsevier B.V. All rights reserved.

High-field, multifrequency EPR data are presented for the alum CsMn(SO4)2·12D2O, containing the [Mn(OD2)6]3+ cation. The data are interpreted using the conventional S = 2 spin Hamiltonian, and the following parameters determined for the data obtained below 30 K: D = −4.491(7) cm-1, E = 0.248(5) cm-1, gx = 1.981(5), gy = 1.993(5), gz = 1.988(5). Although the deviation of the MnO6 framework from idealized D4h symmetry is small, the magnitude of E/D is significant. The E parameter is related to ligand field parameters derived from the optical absorption spectrum. The rhombic anisotropy is shown to arise as a consequence of the π-anisotropic nature of the manganese(III)−water interaction.

Inelastic neutron scattering (INS) data are presented for the salt (ND 4 ) 2 Cr(OD 2 ) 6 (SO 4 ) 2 , which enable the zero-field-splitting of the 5 A g ( C i ) ground term of the [Cr(OD 2 ) 6 ] 2+ cation to be defined in the temperature range 1.5–297 K. Above ∼100 K, the energies of the INS transitions are strongly temperature-dependent, as are the documented Cr–O bond lengths. The experimental data are interpreted using a 5 E⊗e Jahn–Teller Hamiltonian perturbed by low symmetry strain. Good agreement is obtained using a parameter set analogous to that employed to describe the electronic and molecular structure of the [Cu(OD 2 ) 6 ] 2+ cation in the isostructural copper(II) salt.

The properties of the spin state manifold of the tetranuclear cluster Ni[(OH)(2)Cr(bispictn)](3)]I(5).5H(2)O (bispictn = N,N'-bis(2-pyridylmethyl)-1,3-propanediamine) are investigated by combining magnetic susceptibility and magnetization measurements with an inelastic neutron scattering (INS) study on an undeuterated sample of Ni[(OH)(2)Cr(bispictn)](3)]I(5).5H(2)O. The temperature dependence of the magnetic susceptibility indicates an S = (1)/(2) ground state, which requires antiferromagnetic interactions both between Cr(3+) and Ni(2+) ions and among the Cr(3+) ions. INS reveals potential single-ion anisotropies to be negligibly small and enables an accurate determination of the exchange parameters. The best fit to the experimental energy level diagram is obtained by an isotropic spin Hamiltonian H = J(CrNi)(S(1)().S(4)() + S(2)().S(4)() + S(3)().S(4)()) + J(CrCr)(S(1)().S(2)() + S(1)().S(3)() + S(2)().S(3)()) with J(CrNi) = 1.47 cm(-)(1) and J(CrCr) = 1.25 cm(-)(1). With this model, the experimental intensities of the observed INS transitions as well as the temperature dependence of the magnetic data are reproduced. The resulting overall antiferromagnetic exchange is rationalized in terms of orbital exchange pathways and compared to the situation in oxalato-bridged clusters.

The synthesis and X-ray structure of a new member of the series of oxo-bridged, dinuclear chromium(III) complexes, the methyl isocyanide complex [(CH3NC)5CrOCr(CNCH3)5](PF6)4·2CH3CN, is reported. This constitutes only the third oxo-bridged, dinuclear chromium(III) complex with a homoleptic auxillay ligand sphere. Experimentally, the system shows unshifted narrow nuclear magnetic resonance (NMR) spectra that are consistent with calculations using broken symmetry density functional theory (DFT), which suggests it to be the strongest coupled, dinuclear chromium(III) complex known. Furthermore, we report the crystal structure and computed magnetic properties for [(bpy)2(SCN)CrOCr(NCS)(bpy)2](ClO4)2·2H2O (bpy = 2,2'-bipyridine), which differs from other reported oxo-bridged species by featuring a bent CrOCr(4+) core. We also interpret the spectacular 10-orders-of-magnitude variation in acid dissociation constant of the bridging hydroxo ligand in mono hydroxo-bridged dinuclear chromium(III) complexes, in terms of a valence bond model parametrized by metal-to-metal charge transfer (MMCT) and ligand-to-metal charge transfer (LMCT) energies.

The nature of the magnetic interaction through fluoride in a simple, dinuclear manganese(III) complex (1), bridged by a single fluoride ion in a perfectly linear fashion, is established by experiment and density functional theory. The magnitude of the antiferromagnetic exchange interaction and the manganese(III) zero-field-splitting parameters are unambiguously determined by inelastic neutron scattering to yield J = 33.0(2) cm(-1) ((H) over cap = J (S-1) over cap.(S-2) over cap Hamiltonian definition) and single-ion D = -4.0(1) cm(-1). Additionally, high-field, high-frequency electron paramagnetic resonance and magnetic measurements support the parameter values and resolve vertical bar E vertical bar approximate to 0.04 cm(-1). The exchange coupling constant (J) is 1 order of magnitude smaller than that found in comparable systems with linear oxide bridging but comparable to typical magnitudes through cyanide, thus underlining the potential of fluoride complexes as promising building blocks for novel magnetic systems.

A facile synthesis of the [ReF6 ](2-) ion and its use as a building block to synthesize magnetic systems are reported. Using dc and ac magnetic susceptibility measurements, INS and EPR spectroscopies, the magnetic properties of the isolated [ReF6 ](2-) unit in (PPh4 )2 [ReF6 ]⋅2 H2 O (1) have been fully studied including the slow relaxation of the magnetization observed below ca. 4 K. This slow dynamic is preserved for the one-dimensional coordination polymer [Zn(viz)4 (ReF6 )]∞ (2, viz=1-vinylimidazole), demonstrating the irrelevance of low symmetry for such magnetization dynamics in systems with easy-plane-type anisotropy. The ability of fluoride to mediate significant exchange interactions is exemplified by the isostructural [Ni(viz)4 (ReF6 )]∞ (3) analogue in which the ferromagnetic Ni(II) -Re(IV) interaction (+10.8 cm(-1) ) dwarfs the coupling present in related cyanide-bridged systems. These results reveal [ReF6 ](2-) to be an unique new module for the design of molecule-based magnetic materials.

Single-crystal W-band (95 GHz) electron paramagnetic resonance (EPR) studies have been performed at 20 K and at room temperature on a tetragonal Mn(III) compound with potential application as a building block for high-spin clusters. The observed EPR spectra correspond to an anisotropic high-spinS = 2 ground state and have been attributed to equivalent centers related by four-fold symmetry. Accurate values for the spin Hamiltonian parameters were obtained from the analysis of the data at both temperatures. At 20 K the contribution of fourth-order zero-field splitting terms was shown to be significant, with parameter values B 4 0 = 0.0009(3) cm−1, B 4 2 = 0.0006(2) cm−1 and B 4 4 = 0.0017(3) cm−1, to be considered together with the second-order parametersD = −1.1677(7) cm−1 andE= −0.0135(6) cm−1.

The synthesis, crystal growth, magnetic susceptibility, and polarized optical absorption spectra in the visible and near UV of (Et(4)N)(3)Fe(2)F(9) are reported. From single-crystal magnetic susceptibility data and high-resolution absorption spectra in the region of the (6)A(1) --(4)A(1) spin-flip transition, exchange splittings in the ground and excited states are derived. Ferromagnetic ground and excited state exchange parameters J(GS) = -1.55 cm(-1) and J(ES) = -0.53 cm(-1) are determined, respectively, and the relevant orbital contributions to the net exchange are derived from the spectra. The results are compared with those reported earlier for the structurally and electronically analogous [Mn(2)X(9)](5-) pairs in CsMgX(3):Mn(2+) (X = Cl(-), Br(-)), in which the splittings are antiferromagnetic. This major difference is found to be due to the increased metal charge of Fe(3+) compared to Mn(2+), leading to orbital contraction and thus to a strong decrease of the orbital overlaps and hence the antiferromagnetic interactions.