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

Abstract

Two modified Calix[6]arene-like polyoxometalates of the Keggin type with similar structures were synthesized under hydrothermal conditions by H 3 PMo 12 O 40 . H 3 PW 12 O 40 , 4H-1,2,4triazol-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(C 6 H 12 N 12 Cu 3 PW 12 O 40 )] (3-atrz-Cu-PW 12 ), and [2(C 6 H 12 N 12 Cu 3 PMo 12 O 40 )] ⋅ 0.5H 2 O (3-atrz-Cu-PMo 12 ). They were composed of two classic Keggin-type polyoxometalate anions and six [Cu(C 2 H 4 N 4 )] + coordination polymers similar to Calix[6]arene. The catalytic studies repre-sented that the two heterogeneous catalysts catalyzed the oxidation of iodide ions in hydrogen peroxide. The catalytic reaction of 3-atrz-Cu-PW 12 only took 30 min and 15 s to complete the reaction. The rate of iodine generation was 6.86 × 10 À 7 mol L À 1 s À 1 . The 3-atrz-Cu-PMo 12 catalytic reaction needed only 1 min and 51 s, in which the rate of iodine generation was 1.126 × 10 À 5 mol L À 1 s À 1 . The catalytic reaction rate of 3-atrz-Cu-PMo 12 was 16.35 times higher than 3-atrz-Cu-PW 12 . Both catalysts were reused nine times, and the conversion rate was still 99.96 %, showing excellent catalytic activity and repeatability.