Département de chimie moléculaire

{Two new azido-bridged polyoxometalate compds. were synthesized in acetonitrile/methanol media and their mol. structures were detd. by x-ray crystallog. The [{\{}($\gamma$-SiW10O36)Mn2(OH)2(N3)0.5 (H2O)0.5{\}}2($μ$-1,3-N3)]10-(1a) tetranuclear MnIII complex, in which an end-to-end N3- ligand acts as a linker between two [($\gamma$-SiW10O36)Mn2(OH)2]4- units, represents the 1st manganese-azido polyoxometalate. The magnetic properties were 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-($μ$-OH) bridge (J1 = -25.5 cm-1) and the $μ$-1,3-azido bridge (J2 = -19.6 cm-1). The [($\gamma$-SiW10O36)2Cu4($μ$-1,1,1-N3)2($μ$-1,1-N3)2]12- (2a) tetranuclear CuII complex consists of two [$\gamma$-SiW10O36Cu2(N3)2]6- subunits connected through the two $μ$-1,1,1-azido ligands, the four paramagnetic centers forming a lozenge. The magnetic susceptibility data were fitted. This reveals ferromagnetic interactions between the four CuII centers, leading to an S = 2 ground state (H = -J1(S1S2+S1*S2*)-J2 (S2S2*)