Cr(III)-substituted heteropoly-16-tungstates [Cr(III)2(B-β-X(IV)W8O31)2](14-) (X = Si, Ge)

Abstract

The dichromium(III)-containing heteropoly-16-tungstates [CrIII2(B-β-SiIVW8O31)2]14– (1) and [CrIII2(B-β-GeIVW8O31)2]14– (2) were prepared via a one-pot reaction of the composing elements in aqueous, basic medium. Polyanions 1 and 2 represent the first examples of CrIII-containing heteropolytungstates comprising the octatungstate unit {XW8O31} (X = Si, Ge). Magnetic studies demonstrated that, in the solid state, the two polyanions exhibit a weak antiferromagnetic interaction between the two CrIII centers with J = −3.5 ± 0.5 cm−1, with no long-range ordering down to 1.8 K. The ground-state spin of polyanions 1 and 2 was thus deduced to be 0, but the detection of a complex set of EPR signals implies that there are thermally accessible excited states containing unpaired spins resulting from the two S = 3/2 CrIII ions. A comprehensive electrochemistry study on 1 and 2 in solution was performed, and biological tests showed that both polyanions display significant antidiabetic and anticancer activities.