Tubular polyoxoanion [(SeMo6O21)2(C2O4)3]10− and its transformations†
Abstract
Self-assembly reactions in the Na2MoO4/SeO2/H2C2O4 system lead to the formation of a tubular [(SeMo6O21)2(C2O4)3]10− hybrid polyanion, isolated and characterized by single crystal X-ray diffraction (SCXRD) as Na9H[(SeMo6O21)2(C2O4)3]·NaNO3·20.6H2O (SeMo6-1). Dehydration of this compound leads to the formation of Na10[(SeMo6O21)2(C2O4)3]·0.5NaNO3·8H2O (SeMo6-2). The electrochemical behavior of SeMo6-2 as a component of the paste electrode was studied by CV in CH3CN solution. A concentrated aqueous solution of SeMo6-2 was studied using 77Se and 95Mo NMR techniques, which show extensive degradation of the complex. Addition of TBABr to the concentrated solution leads to a precipitate consisting of TBA salts of [Mo6O19]2− and [β-Mo8O26Na2(NO3)2]2− anions. The latter was characterized by SCXRD as (TBA)3[β-Mo8O26Na2(NO3)]·CH3CN (Mo8-Na). This transformation shows the presence of [β-Mo8O26]4− and [Mo6O19]2− in the aqueous solution of SeMo6-2. The study of (NBu4)4[β-Mo8O26] and (NBu4)2[Mo6O19] solutions in CH3CN by HPLC shows equilibration between [β-Mo8O26]4− and [Mo6O19]2−.