15-Copper(II)-containing 36-tungsto-4-silicates(IV) [Cu15 O2 (OH)10 X(A-α-SiW9 O34 )4 ]25−(X = Cl, Br): synthesis, structure, magnetic properties, and electrocatalytic CO2 reduction

The 15-copper(II)-containing 36-tungsto-4-silicates [Cu15O2(OH)10X(A-α-SiW9O34)4]25−(X = Cl,1; Br,2)have been prepared in 70% yield by reaction of the trilacunary 9-tungstosilicate precursor[A-α-SiW9O34]10−with Cu2+ions in aqueous pH 8 medium. Both polyanions1and2were isolated ashydrated mixed potassium/sodium salts and characterized in the solid state by FT-IR, TGA, single-crystalXRD, and elemental analysis. DC magnetic susceptibility measurements from 1.8–300 K established theground state to be paramagnetic with a magnetic moment corresponding to 15 uncoupled Cu2+(S= 1/2)ions. EPR measurements and simulations were consistent with this analysis. Electrochemical studies wereperformed for polyanions1and2dissolved in solution to elucidate the electroactivity of both copper andtungstate sites. Using2as a representative example, the electrocatalytic activity towards CO2reductionupon deposition on a glassy carbon electrode surface, while retaining selectivity relative to hydrogenevolution, was demonstrated.