Synthesis, Characterization, and Catalytic Performance of Modified Keggin‐type Calix[6]arene‐like Polyoxometalates

Abstract

AbstractTwo modified Calix[6]arene‐like polyoxometalates of the Keggin type with similar structures were synthesized under hydrothermal conditions by H3PMo12O40. H3PW12O40, 4H‐1,2,4‐triazol‐3‐amine (3‐atrz) and copper ions were used as precursors, respectively, bridging organic ligand and transition metals. The result of single‐crystal X‐ray diffraction and elemental analysis showed that the structural formulas of the two crystalline compounds were: [2(C6H12N12Cu3PW12O40)] (3‐atrz‐Cu‐PW12), and [2(C6H12N12Cu3PMo12O40)] ⋅ 0.5H2O (3‐atrz‐Cu‐PMo12). They were composed of two classic Keggin‐type polyoxometalate anions and six [Cu(C2H4N4)]+ coordination polymers similar to Calix[6]arene. The catalytic studies represented that the two heterogeneous catalysts catalyzed the oxidation of iodide ions in hydrogen peroxide. The catalytic reaction of 3‐atrz‐Cu‐PW12 only took 30 min and 15 s to complete the reaction. The rate of iodine generation was 6.86×10−7 mol L−1 s−1. The 3‐atrz‐Cu‐PMo12 catalytic reaction needed only 1 min and 51 s, in which the rate of iodine generation was 1.126×10−5 mol L−1 s−1. The catalytic reaction rate of 3‐atrz‐Cu‐PMo12 was 16.35 times higher than 3‐atrz‐Cu‐PW12. Both catalysts were reused nine times, and the conversion rate was still 99.96 %, showing excellent catalytic activity and repeatability.