Inorganic-metalorganic hybrids based on copper(II)-monosubstituted Keggin polyanions and dinuclear copper(II)-oxalate complexes.: Synthesis, X-ray structural characterization, and magnetic properties

Reaction of in situ generated copper(II)-monosubstituted Keggin polyoxometalates and copper(II)-bipyridine-oxalate complexes in the corresponding alkaline acetate buffer led to the formation of hybrid metal organic-inorganic compounds K-2[{SiW11O39Cu(H2O)}{Cu-2(bpy)(2)(H2O)2(mu-ox)}(2)]center dot 14H(2)O (1), K-14[{SiW11O39Cu(H2O)}{Cu-2(bpy)(2)(mu-ox)}](2)-[SiW11O39Cu(H2O)]center dot 55H(2)O (2), (NH4)(4)[{SiW11O39Cu(H2O)}{Cu-2(bpy)(2)(mu-ox)10H(2)O (3), and Rb-4[{SiW11O39Cu-(H2O)}{Cu-2(bpy)(2)(mu-ox)}]center dot 10H(2)O (4). Their structures have been established by single-crystal X-ray diffraction. The main structural feature of these compounds is the presence of copper(II)-monosubstituted alpha-Keggin polyoxoanions as inorganic building blocks, on which the mu-oxalatodicopper metalorganic blocks are supported. Compound 1 contains the discrete hybrid polyanion [{SiW11O39Cu(H2O)}{Cu-2(bpy)(2)(H2O)(2)(mu-ox)}(2)](2-), whereas the polymeric hybrid polyanion [{SiW11O39Cu(H2O)}{Cu-2(bpy)(2)(mu-ox)}(2)](n)(4n-), gives a monodimensional character to compounds 2-4. Magnetic and EPR results are discussed with respect to the crystal structure of the compounds. DFT calculations on both the [Cu-2(bpy)(2)(H2O)(4)(mu-ox)](2+) cationic complex and the metalorganic blocks have been performed in order to determine the optimized geometry and the magnetic coupling constants, respectively.