Four hybrid compounds based on a new type of molybdates and a flexible tripodal ligand: synthesis, structures, photochemical and electrochemical properties

Abstract

The hydrothermal reaction of a mixture of (NH₄)₆Mo₇O₂₄·4H₂O, a flexible tripodal ligand 1,3,5-tris-(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (TITMB) and metal salts at different temperatures resulted in four novel compounds, namely [H₂TITMB]₂[Mo₁₂O₃₈]·4H₂O (1), [Zn(Mo₂O₇)(TITMB)] (2), [H₃TITMB]₂[Cd(β-Mo₈O₂₆)(H₂O)₂(α-Mo₈O₂₆)]·4H₂O (3) and [H₃TITMB]₂[Co(β-Mo₈O₂₆)(H₂O)₂(α-Mo₈O₂₆)]·4.5H₂O (4). The structures of compounds 1, 2, 3 and 4 were explored with IR spectroscopy, thermal gravimetric analysis (TGA), PXRD, UV-vis diffuse reflectance spectra and single-crystal X-ray diffraction in the solid state. In 1 the new type of isopolymolybdate unit [Mo₁₂O₃₈]⁴⁻ shared ten distorted {MoO₆} octahedra and two distorted {MoO₅} tetragonal pyramid with four kinds of O atoms. And the unprecedented bimetallic oxide chain [Zn(Mo₂O₇)]_n in compound 2 consisted of trigonal bipyramids and octahedra through sharing edges. Both compounds 3 and 4 are 3-D octamolybdate-based inorganic–organic hybrids consisting of the polyacid [α-Mo₈O₂₆]⁴⁻ anions and novel infinite chains of [β-Mo₈O₂₆]⁴⁻ anions covalently linked through [Cd(H₂O)₂]²⁺ groups or [Co(H₂O)₂]²⁺ groups. In addition, the electrochemical behavior and photocatalytic activities of the title compounds were also investigated.