Formation of V V Lacunary Polyoxovanadates and Interconversion Reactions of Dodecavanadate Species

Oxidation reactions of the reduced decavanadate [V IV 2 V V 8 O 26 ] 4– ( 1 ) with halide guest anions were investigated for the synthesis of V V host molecules. The reaction with Cl – afforded a new dodecavanadate, [HV V 12 O 32 (Cl)] 4– ( 3 ), which incorporated the guest chloride anion. The polyoxovanadate framework of 3 is different from the bowl‐shaped dodecavanadate [V V 12 O 32 (CH 3 CN)] 4– ( 2 ). The structure of 3 is regarded as a trilacunary counterpart of the pentadecavanadate [V V 9 V IV 6 O 36 Cl] 4– . Employment of an F – template yielded the layered polyoxovanadate [HV V 11 O 29 F 2 ] 4– ( 4 ). The framework of 4 is a monolacunary structure of the fluoride‐incorporated dodecavanadate [H 6 V V 2 V IV 10 O 30 F 2 ] 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 μ 3 ‐F bridges. Reaction with Br – provided [HV V 12 O 32 (Br)] 4– ( 5 ) with minor formation of [H 3 V V 10 O 28 ] 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 CH 3 CN 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 51 V NMR spectra, corresponding to lacunary polyoxovanadate geometries. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)