Tuning the dimension of POM-based inorganic–organic hybrids from 3D self-penetrating framework to 1D poly-pendant chain via changing POM clusters and introducing secondary spacers

Abstract

Through tuning the different polyoxometalate (POM) clusters and the secondary spacers, four new various dimensionality inorganic–organic hybrid compounds Cu₅(pzta)₆(H₂O)₂[Mo₈O₂₆] (1), Cu₅(pzta)₆(H₂O)₆[PW₁₂O₄₀]·(OH) (2), Cu₄(pzta)₂(bipy)(H₂O)₄(OH)₂[Mo₈O₂₆]·2H₂O (3) and [Cu₂(pzta)₂(bipy)₂(H₂O)₂][HPW₁₂O₄₀]·8H₂O (4) (pzta = 5-(2-pyrazinyl)tetrazole, bipy = 4,4′-bipyridine) have been synthesized under identical hydrothermal conditions. The four compounds were assembled from copper cations, N-donor ligands and POM clusters. Compound 1 displays a novel self-penetrating 3D framework. When the POM clusters were changed from β-[Mo₈O₂₆]⁴⁻ (β-Mo₈) to [PW₁₂O₄₀]³⁻ (PW₁₂), compound 2 was obtained, which is a 2D layer with square channels into which the tetradentate PW₁₂ anions as templates are incorporated. Furthermore, by introducing second spacer bipy into the reaction system of 1 and 2, respectively, compounds 3 and 4 were obtained. 3 shows a 2D layer that consists of adjacent metal–organic chains fused together by six-connected β-Mo₈ anions, and 4 exhibits a 1D poly-pendant chain constructed by dinuclear copper complexes and PW₁₂ clusters. The distinct structural features of the four compounds suggest that different POM clusters and secondary spacers should have great effect on the structures of POM-based inorganic–organic hybrids. Additionally, the luminescent and electrochemical properties for 1–4 have been investigated.