PH-dependent assembly of metal–organic hybrid compounds based on octamolybdates and a new flexible multidentate ligand

Abstract

Six novel molybdenum hybrid materials based on a flexible multidentate ligand, namely (H3tib)4(β-Mo8O26)3·5H2O (1), (H3tib)2[Cu(H2O)2(γ-Mo8O26)2]·2H2O (2), [Cu(Htib)2(δ-Mo8O26)]·4H2O (3), [Cu2(tib)2(H2O)2(γ-Mo8O26)]·H2O (4), (H3tib)2[Co(H2O)2(γ-Mo8O26)2]·2H2O (5), and Zn(tib)(MoO4)·3H2O (6) (where tib = 1,3,5-tris(imidazol-1-ylmethyl)benzene), have been synthesized at different pH values under hydrothermal conditions. Their structures have been determined by single-crystal X-ray diffraction analysis and further characterized by PXRD, TGA, IR spectra, and electrochemistry. Compound 1 is a supramolecule with classical β-Mo8O26 cages. Compounds 2 and 5 exhibit a rare one-dimensional (1D) molybdenum oxide duplex chain. We have not yet found any other examples of the two adjacent 1D molybdenum oxide chains linked together through the centers of the Cu/Co cations. In 3, the CuII cations are bridged by Htib+ ligands and (δ-Mo8O26)4− anions to form an interesting two-dimensional (2D) layer. In 4, the CuIIcations, tib ligands and (γ-Mo8O26)4− anions are connected to form a 2D layer, which is further reinforced by the tib ligands through an Mo–N bond. Compound 6 is a 2D coordination polymer possessing a high thermal stability. The structural diversities of 2–4 reveal that the pH value of the reaction system, the metal coordination preference and the ligand configuration play a crucial role in the assembly of POM-based complexes.