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

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 Cu^II ion is shared by two adjacent Mo₆O₂₀ units. Infinite one-dimensional chains are established by linkage between two adjacent Mo₆O₂₀ units and two Cu^II 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.