The role of dynamical polarization of the ligand to metal charge transfer excitations in {\em ab initio} determination of effective exchange parameters

The role of the bridging ligand on the effective Heisenberg coupling parameters is analyzed in detail. This analysis strongly suggests that the ligand-to-metal charge transfer excitations are responsible for a large part of the final value of the magnetic coupling constant. This permits to suggest a new variant of the Difference Dedicated Configuration Interaction (DDCI) method, presently one of the most accurate and reliable for the evaluation of magnetic effective interactions. This new method treats the bridging ligand orbitals mediating the interaction at the same level than the magnetic orbitals and preserves the high quality of the DDCI results while being much less computationally demanding. The numerical accuracy of the new approach is illustrated on various systems with one or two magnetic electrons per magnetic center. The fact that accurate results can be obtained using a rather reduced configuration interaction space opens the possibility to study more complex systems with many magnetic centers and/or many electrons per center.Comment: 7 pages, 4 figure

Reversible Photoinduced Magnetic properties in the heptanuclear complex [MoIV(CN)8(CN-CuL6)]8 : a photomagnetic high-spin molecule.

International audienc

Electron transfer through norbornadiene and quadricyclane moieties as a model for molecular switching

The bis(pentaammineruthenium(II)) complex of dicyanonorbornadiene has been prepared and characterized. Its photochemical conversion into a dicyanoquadricyclane complex by irradiation in methanol has been followed by UV-visible spectroscopy, IR spectroscopy, H-1 NMR spectroscopy, and cyclic voltammetry. The dicyanonorbornadiene complex exhibits an intervalence transition in the 1000-1600 nm range when oxidized to the ruthenium-(II)-ruthenium(III) state. This allows the determination of the effective coupling V-ab through the dicyanonor-bornadiene ligand, which is found as 0.023 eV. No such band is observed in the case of the dicyanoquadricyclane complex. These results show the possibility to modulate an intramolecular electron transfer process by using a photoisomerizable bridging ligand

New Cyclosiloxanolate Cluster Complexes of Transition Metals

New cyclosiloxanolate transition metal cluster complex derivs. were prepd. PhSiO2K reacted with NiX2 (X2 = Cl2 or acac) to give K2{[η6-(PhSiO2)6]2[μ3-(OH)]2Ni4K4}, a mixed Group 1-group 10 metal complex. PhSiO2Na reacted with Ni(NH3)6I2 to give Na{[η6-(PhSiO2)6]2Ni6(μ6-I)} as the 1st example of encapsulated I- ion in siloxanolate complexes. The macrocyclic Na4{[η12-(PhSiO2)12]Cu4} complex reacted with η6-(1,3,5-C7H8)Cr(CO)3 to give the heterobimetallic adduct Na4{[η12-(PhSiO2)12]Cu4}[Cr(CO)3]3 as one of the rare examples of heterobimetallic complexes with different oxidn. nos. of the metals. The Cu deriv. {[η6-(PhSiO2)6]2Cu6(BuOH)5} reacted in MeOH/CHCl3 (1:6) with Et4NCN to give hexanuclear {[η6-(PhSiO2)6]2Cu6(η2-C3H5N2O2)2}, contg. 2-amino-2-oxoethanimidic acid Me ester monoanion ligands, product of an unexpected C-C coupling reaction. This latter complex was characterized also by x-ray diffraction crystal and mol. structure detn

Hexacyanidometalate molecular chemistry, part III: di-, tri-, tetra-, hexa- and hepta-nuclear chromium-nickel complexes: Control of spin, structural anisotropy, intra- and inter-molecular exchange couplings

Nine mu-cyanido bridged polynuclear complexes, [Cr(CN)(n)(CNNiL)(6) (n)](m+), (with n = 0-5 and L = pentadentate ligand), were synthesised: CrNi, five CrNi2, CrNi3, CrNi5 and CrNi6. The compounds have been fully characterised by IR spectroscopy, mass spectrometry and X-ray crystallography. Their magnetic properties have been studied and the spin and the anisotropy values as well as the intra- and inter-molecular exchange couplings evaluated. The spin state varies from 5/2 to 15/2 (ferromagnetic interaction) and the effective anisotropic factor varies from 0 to 0.5 cm (1). Experimentally, the exchange coupling between the mu-cyanido bridged spin carriers Cr(III) and Ni(II) varies from +4.5 to +18.3 cm (1) increasing with the C-N-Ni angle. A computational study allows to propose a magneto structural correlation and to rationalise the most relevant features of the exchange interaction between Cr(III) (t(2g)(3)) and Ni(II) (e(g)(2)) through a cyanido bridge. In order to decrease the intermolecular interactions, a dilution of the chromium(III)-nickel(II) compounds with the equivalent cobalt(III)-nickel(II) has been successfully performed by co-crystallisation

La molécule, précurseur du solide magnétique

L’obtention et l’étude de nouveaux objets magnétiques pour répondre à de nouvelles applications ou à de nouvelles questions théoriques est un des domaines de coopération fructueuse entre chimistes et physiciens. Nous donnons ici quelques exemples de nouveaux systèmes magnétiques moléculaires synthétisés de manière rationnelle afin de développer certaines de leurs propriétés physiques