Aggregation of Nb/W mixed addenda Dawson-type polyoxometalates units and lanthanide ions: Synthesis, characterization and electrocatalysis

Abstract

Four isostructural polyoxometalates consisting of Nb/W mixed addenda Dawson-type subunits and lanthanide ions, K4Na8H4{[Nb4O6(H2O)4Na4(H2O)8][LaP2W12Nb6O61(H2O)7]4}·60H2O (1-La), K4Na8H4{[Nb4O6(H2O)4Na4(H2O)8][CeP2W12Nb6O61(H2O)7]4}·58H2O (1-Ce), K4Na8H4{[Nb4O6(H2O)4Na4(H2O)8][PrP2W12Nb6O61(H2O)7]4}·78H2O (1-Pr), K4Na8H4{[Nb4O6(H2O)4Na4(H2O)8][NdP2W12Nb6O61(H2O)7]4}·66H2O (1-Nd), have been synthesized using dimeric Dawson-type POMs, [H6P2W12Nb4O59(NbO2)2]28− and lanthanide salts as starting materials in acidic solution. The single crystal X-ray diffraction analysis indicates that the Dawson-type subunit {P2W12Nb6} is connected by terminal oxygen atoms of Nb at equatorial sites to form the dimeric unit. Two dimeric units are further linked by {Nb4O6} clusters to form tetrameric polyanions. The lanthanide ions are coordinated by the terminal oxygen atoms of Nb at polar sites in Dawson-type subunits. These compounds were further characterized by Fourier transform IR (FT-IR), thermogravimetry (TG), and cyclic voltammetry (CV) and exhibited electrochemical catalytic activity towards reduction of bromate ions.