RELATIONSHIP BETWEEN OXO-BRIDGED DIMER FORMATION AND STRUCTURE OF VANADIUM(III) AMINO POLYCARBOXYLATES

The structures of vanadium(III) complexes with several amino polycarboxylates in the solid state as well as in aqueous solution have been investigated using electronic and Raman spectrophotometry and H-1 NMR relaxation time. The amino polycarboxylates employed were dtpa (diethylenetriamine-N,N,N',N'',N''-pentaacetate), edta (ethylenediamine-N,N,N',N'-tetraacetate) cydta (1,2-cyclohexanediamine-N,N,N',N'-tetraacetate), 1,3-pdta (1,3-propanediamine-N,N,N',N'-tetraacetate), S,S'-edds (S,S'-ethylenediamine-N,N-disuccinate), eddda (ethylenediamine-N,N'-diacetate-N,N'-di-3-propionate), tcta (1,4,7-triazacyclononane-1,4,7-triacetate), eed3a (N-ethylethylenediamine-N,N',N',-triacetate), nta (nitrilotriacetate), and ida (iminodiacetate). The dtpa, tcta, and ida complexes, in addition to the edta, cydta, and nta complexes, the structures of which have been determined earlier, adopt heptacoordination in the solid state. The S,S'-edds and eddda complexes adopt hexacoordination as found for the 1,3-pdta complex. In aqueous solution, the hexacoordinate complexes yield the ore-bridged dinuclear vanadium(III) complexes by hydrolysis, but the heptacoordinate ones do not. The vanadium(III) complex with eed3a, Na-2[V(eed3a)(SO4)], is also found to adopt heptacoordination in the solid state, but it changes to the hexacoordinate complex in aqueous solution by releasing the sulfate ion.