Metal-oxo cluster-supported transition metal complexes: hydrothermal synthesis and characterization of [{Cu(phen)2}2SiW12O40].

A new neutral α-Keggin polyoxometalate, [{Cu(phen)2}2SiW12O40] (1) (phen = 1,10-phenanthroline) was hydrothermally synthesized and characterized by IR, TG and single-crystal X-ray diffraction. The compound is monoclinic, space group P21/c with a = 26.065(5), b = 11.867(2), c = 23.385(5) Å, β = 113.78(3)°, V = 6619 Å3, Z = 4. X-ray analysis showed that both [Cu(phen)2]2+ units are supported on the α-Keggin polyoxoanion [SiW12O40]4- via the surface bridging and terminal oxygen atoms of two non-adjacent WO6 octahedra; these show unusual coordination environments. One Cu ion displays distorted trigonal bipyramidal geometry and the other square pyramidal. The unusual coexistence of complexes with different geometries is most likely caused by steric effects involving surface oxygen atoms of the heteropolytungstate and phen, which prevent the presence of a sixth coordinating atom. Weak π-π stacking interactions between phen groups give a 1D chain-like structure and hydrogen bonds are responsible for extended 2D and 3D motifs in the crystal. [ABSTRACT FROM AUTHOR]