Dinuclear Manganese and Cobalt Complexes with Cyclic Polyoxovanadate Ligands: Synthesis and Characterization of [Mn2V10O30]6- and [Co2(H2O)2V10O30]6-

An all-inorganic complex, [Mn-2{(VO3)(5)}(2)](6-) (1), was synthesized, and the structure determination reveals a dinuclear manganese complex coordinated by two cyclic pentavanadate ligands. The cyclic pentavanadate units sandwich the edge-sharing octahedral dimanganese core through coordination of the oxido group of the pentavanadate. A dinuclear cobalt complex with a cyclic decavanadate, [Co-2(OH2)(2)(VO3)(10)](6-) (2), was also synthesized. The structure analysis reveals a dinuclear cobalt complex with a macrocyclic decavanadate, which is composed of 10 VO4 units joined by the vertex sharings. The CoO6 octahedrons are edge-shared, with each cobalt octahedron coordinated to five oxido groups from the decavanadate. The remaining site is occupied by water. The coordinated water molecules are supported with hydrogen bonds in two directions. Complex 2 in acetonitrile shows no reactivity with dioxygen even at low temperature, and the cyclic voltammogram of 2 shows no redox chemistry in acetonitrile. Complex 2 exhibits chromism by water exposure both in the solid state and in acetonitrile. Complex 2 is green-yellow in color, and the addition of water causes the complex to turn brown. After heating the sample, it returns to its original color in a reversible manner. The EXAFS data in acetonitrile is also reported and is consistent with the solid-state structure. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)