Abstract: Polyoxometallates Co(en)₃PMo₁₂O₄₀·8H₂O(+,-)[abbreviated as PMo₁₂-Co(+,-)], nanoparticles were synthesized by the chemical precipitation reaction at room temperature for the first time.They were characterized by means of elemental analyses, IR spectrometry and X-ray diffraction.The images of scanning electron microscopy(SEM) and the results of calculation by using the Scherrer equation for the line widths of the XRD patterns were used to estimate the average particle size of the powder products, which was 40 nm.The results show that the nanoparticle size was affected by starting materials′ concentrations.The particles had a small size and a narrow distribution, when the concentrations of H₃PMo₁₂O₄₀·24H₂O and Co(en)₃I₃·H₂O were around 1.7×10^-4 and 1.0×10^-3 mol/L, respectively.When the concentration was increased, there was no significant increase in the particle size, but more polydisperse Co(en)₃(PMo₁₂O₄₀)(+, -) were obtained.In poly(ethylene glycol)(PEG) with an average molecular weight(M_W) of 600 g/mol and containing LiClO₄[n(O)/n(Li)=100∶1] as the supporting electrolyte, the conductivity of the composite system increases upon the addition of PMo₁₂-Co(+ or -) nanoparticles, which was measured by the a.c.impedance technique.The interactions among PEG, LiClO₄, PMo₁₂, and Co can be used to explain that the PMo₁₂-Co(+ or -) nanoparticles could promote the conductivity of the PEG-LiClO₄-PMo₁₂-Co system.

Key words: Polyoxometallates, Nanoparticles, α-Keggin structure, Optical activity