Diversity of Polyoxometalate‐Based Copper Compounds Obtained from the Same Reaction System

Abstract

Two simple pathways using metallic copper or copper salts are proposed for the synthesis of hybrid compounds under mild conditions. A variety of Strandberg‐ and mixed‐metal Keggin‐based products, namely, (NH4)5n{[Cu(en)2][PMo8V4O40]}n·9nH2O (1), (NH4)4n{[Cu(en)(H2O)][P2Mo5O23]}n·3.5nH2O (2), (NH4)7[PMo8V4O40]·17H2O (3) and (NH4)2n{[Cu(en)2][Cu(en)(H2O)][P2Mo5O23]}n·3nH2O (4), were isolated upon the variation of the composition of the reaction system. A rare four‐substituted [PMo8V4O40]7– Keggin anion was obtained. The influence of the vanadium source [V2O5, NH4VO3 or (NH4)2V6O16] and the copper precursor (copper powder vs. copper salts) on the nature of the resulting products was studied. An ex situ electron paramagnetic resonance (EPR) spectroscopy study revealed the formation of VIV and CuII centres in the reaction mixture during Cu0 dissolution. The obtained compounds possess electrocatalytic activity in the reduction of iodate and nitrite anions, and a carbon‐paste electrode modified with 4 exhibited a linear current response to l‐cysteine. Furthermore, 4 demonstrated rapid and almost complete adsorption of a cationic dye.