An all-inorganic complex, [Mn2{(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, [Co2(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. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
Oxidation reactions of the reduced decavanadate [VIV2VV8O26]4– (1) with halide guest anions were investigated for the synthesis of VV host molecules. The reaction with Cl– afforded a new dodecavanadate, [HVV12O32(Cl)]4– (3), which incorporated the guest chloride anion. The polyoxovanadate framework of 3 is different from the bowl-shaped dodecavanadate [VV12O32(CH3CN)]4– (2). The structure of 3 is regarded as a trilacunary counterpart of the pentadecavanadate [VV9VIV6O36Cl]4–. Employment of an F– template yielded the layered polyoxovanadate [HVV11O29F2]4– (4). The framework of 4 is a monolacunary structure of the fluoride-incorporated dodecavanadate [H6VV2VIV10O30F2]6–, in which one of the VO groups at the belt position is removed. The three vanadium atoms in the capping units are connected by μ3-F bridges. Reaction with Br– provided [HVV12O32(Br)]4– (5) with minor formation of [H3VV10O28]3–. Interconversion reactions between 2, 3, and 4 proceeded as follows: the reaction of 2 with Cl– prompted an isomerization reaction of the bowl-type framework, affording 3; the reaction of 3 with F– gave 4; the reaction of 4 with CH3CN reproduced acetonitrile-incorporated 2. Complexes 3 and 4 were characterized by X-ray analysis. Polyoxovanadates 3 and 4, with the highest oxidation cores, exhibited distinct signals in the 51V NMR spectra, corresponding to lacunary polyoxovanadate geometries. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
