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

Four isostructural polyoxometalates consisting of Nb/W mixed addenda Dawson-type subunits and lanthanide ions, K4Na8H4 {[Nb4O6(H2O)(4)Na4H2O)(8)][LaP2W12Nb6O61(H2O)(7)](4)}center dot 60H(2)O (1-La), K4Na8H4 {[Nb4O6(H2O)(4) Na-4(H2O)(8)][CeP2W12Nb6O61(H2O)(7)](4)}center dot 58H(2)O (1-Ce), K4Na8H4{[Nb4O6(H2O)(4)Na-4(H2O)(8)][PrP2W12Nb6O61(H2O)(7)](4)}center dot 78 H2O (1-Pr), K4Na8H4{[Nb4O6(H2O)(4)Na-4(H2O)(8)][NdP2W12Nb6O61(H2O)(7)](4)}center dot 66H(2)O (1-Nd), have been synthesized using dimeric Dawson-type POMs, [H6P2W12Nb4O59(NbO2)(2)](2)(8) 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. (C) 2020 Elsevier Ltd. All rights reserved.