Structural and magnetic properties of MnIII and CuII tetranuclear azido polyoxometalate complexes: multifrequency high-field EPR spectroscopy of Cu4 clusters with S = 1 and S = 2 ground states - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue Chemistry - A European Journal Année : 2006

Structural and magnetic properties of MnIII and CuII tetranuclear azido polyoxometalate complexes: multifrequency high-field EPR spectroscopy of Cu4 clusters with S = 1 and S = 2 ground states

Résumé

Two new azido-bridged polyoxometalate compds. were synthesized in acetonitrile/methanol media and their mol. structures have been detd. by X-ray crystallog. The [{(g-SiW10O36)Mn2(OH)2(N3)0.5 (H2O)0.5}2(m-1,3-N3)]10-(1a) tetranuclear MnIII complex, in which an end-to-end N3- ligand acts as a linker between two [(g-SiW10O36)Mn2(OH)2]4- units, represents the first manganese-azido polyoxometalate. The magnetic properties have been studied considering the spin Hamiltonian H = -J1(S1S2+S1*S2*)-J2(S1S1*), showing that antiferromagnetic interactions between the paramagnetic centers (g = 1.98) occur both through the di-(m-OH) bridge (J1 = -25.5 cm-1) and the m-1,3-azido bridge (J2 = -19.6 cm-1). The [(g-SiW10O36)2Cu4(m-1,1,1-N3)2(m-1,1-N3)2]12- (2a) tetranuclear CuII complex consists of two [g-SiW10O36Cu2(N3)2]6- subunits connected through the two m-1,1,1-azido ligands, the four paramagnetic centers forming a lozenge. The magnetic susceptibility data have been fitted. This reveals ferromagnetic interactions between the four CuII centers, leading to an S = 2 ground state (H = -J1(S1S2+S1*S2*)-J2 (S2S2*), J1 = +294.5 cm-1, J2 = +1.6 cm-1, g = 2.085). The ferromagnetic coupling between the CuII centers in each subunit is the strongest ever obsd. either in a polyoxometalate compd. or in a diazido-bridged CuII complex. Considering complex 2a and the previously reported basal-basal di-(m-1,1-N3)-bridged CuII complexes in which the metallic centers are not connected by other magnetically coupling ligands, the linear correlation J1 = 2639.5-24.95*qav between the qav bridging angle and the J1 coupling parameter has been proposed. The electronic structure of complex 2a has also been investigated by using multifrequency high-field ESR (HFEPR) spectroscopy between 95 and 285 GHz. The spin Hamiltonian parameters of the S = 2 ground state (D = -0.135(2) cm-1, E = -0.003(2) cm-1, gx = 2.290(5), gy = 2.135(10), gz = 2.158(5)) as well as of the first excited spin state S = 1 (D = -0.960(4) cm-1, E = -0.080(5) cm-1, gx = 2.042(5), gy = 2.335(5), gz = 2.095(5)) have been detd., since the energy gap between these two spin states is very small (1.6 cm-1). [on SciFinder (R)]
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Dates et versions

hal-00022802 , version 1 (13-04-2006)

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  • HAL Id : hal-00022802 , version 1

Citer

Pierre Mialane, Carole Duboc, Jerome Marrot, Eric Riviere, Anne Dolbecq, et al.. Structural and magnetic properties of MnIII and CuII tetranuclear azido polyoxometalate complexes: multifrequency high-field EPR spectroscopy of Cu4 clusters with S = 1 and S = 2 ground states. Chemistry - A European Journal, 2006, 12, pp.1950-1959. ⟨hal-00022802⟩

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