A new hexamolybdate-based copper-2,2'-biimidazole coordination polymer serving as an acid catalyst and support for enzyme immobilization.

Abstract

The hydrothermal reaction of (NH4)3[CoMo6O24H6]·7H2O (CoMo6), CuCl2·2H2O and 2,2'-biimidazole (H2biim) led to the formation of a new coordination polymer, namely poly[diaquabis(2,2'-biimidazole)hexa-μ3-oxo-octa-μ2-oxo-hexaoxodicopper(II)hexamolybdate(VI)], [Cu2Mo6O20(C6H6N4)2(H2O)2]n (Cu-Mo6O20), at pH 2-3. It is obvious that in the formation of crystalline Cu-Mo6O20, the original Anderson-type skeleton of heteropolymolybdate CoMo6 was broken and the new isopolyhexamolybdate Mo6O20 unit was assembled. In Cu-Mo6O20, one Mo6O20 unit connects four [Cu(H2biim)(H2O)]2+ ions in a pentacoordinate mode via four terminal O atoms, resulting in a tetra-supported structure, and each CuII ion is shared by two adjacent Mo6O20 units. Infinite one-dimensional chains are established by linkage between two adjacent Mo6O20 units and two CuII ions, and these chains are further packed into a three-dimensional framework by hydrogen bonds, π-π interactions and electrostatic attractions. The catalytic performance of this crystalline material used as an efficient and reusable heterogeneous acid catalyst for carbonyl-group protection is discussed. In addition, Cu-Mo6O20 was applied as a new support for enzyme (horseradish peroxidase, HRP) immobilization, forming immobilized enzyme HRP/Cu-Mo6O20. HRP/Cu-Mo6O20 showed good catalytic activity and could be reused.