Measurement Of The Stability Constants Of[Ag/Co（H₂O）(H₃PW₁₁O₃₉)]^3/2-

ItisreportedthatthecomplexesofAg⁺/Co²⁺andlacunaryKeggin polyoxotungstophosphates have exhibited excellent activity in homogeneous catalytic water oxidation into O₂.However,their stability was concerned by people.Based on this,firstly,potassium 11-tungstophosphate was prepared according to the reference,then the pure sample of K₄[H₃PW₁₁O₃₉]·14H₂O was obtained by recryllization.By employing elemental analysis,³¹P NMR,pH value measurement and conductivity measurement,the protonated state of lacunary heteropolyoxotungstophosphates in aqueous solution is determined to be[H₃PW₁₁O₃₉]^4-.Usingitasligand,astabilityconstantoftwocomplexes([Ag（H₂O）(H₃PW₁₁O₃₉)]^3-and[Co（H₂O）(H₃PW₁₁O₃₉)]^2-)is determined.An electrochemical cell is designed as follows:（-）Hg,Hg₂Cl₂∥[Ag（H₂O）(H₃PW₁₁O₃₉)]^3-（aq）│Ag（s）（+）(salt bridge is saturated KNO₃ solution).By measuring the electromotive force（e.m.f.）of the cell,the stability constant of[Ag（H₂O）(H₃PW₁₁O₃₉)]^3-in aqueous solution is determined to be3.43×10³（25 ^oC）.And it is determined that the stability constant of Na₂H₃PW₁₁O₃₉Co（H₂O）in aqueous solution is 5.13×10⁴（25 ^oC）by equimolar coefficients of spectrophotometry.This is the first example of the stability constant of metal ion complexes based polyoxomelate ligands so far.Explore the determination stability constant of[Co₄（H₂O）₂(PW₉O₃₄)₂]^10-by using spectrophotometry,the experiment shows that this method is not feasible.