Assembly of organic–inorganic hybrid materials constructed from polyoxometalate and metal–1,2,4-triazole units: synthesis, structures, magnetic, electrochemical and photocatalytic properties

Abstract

A series of organic–inorganic hybrid compounds built from Keggin and Wells–Dawson polyoxometalates and TM-trz complexes (Htrz = 1,2,4-triazole) were obtained at different pH values under hydrothermal conditions, namely, [Co₂(H₂O)₂(Htrz)₅][SiW₁₂O₄₀]·2.5H₂O (1), [Zn₅(Htrz)₈(trz)₂(H₂O)₈][SiW₁₂O₄₀]₂·10H₂O (2), [Cu^I₂Cu^II₄(Htrz)₄(trz)₄Cl₂][GeW₁₂O₄₀]·15H₂O (3), [Cu^I₂Cu^II₄(Htrz)₄(trz)₄Cl₂][SiW₁₂O₄₀]·15H₂O (4), K₂Na₂(H₂O)₂[Co₁₁(trz)₁₄(H₂O)₁₄][P₂W₁₈O₆₂]₂·29H₂O (5) and [Cu₁₂(trz)₁₀(Htrz)₂(OH)₄(SO₄)₂(H₂O)₆][P₂W₁₈O₆₂]·28H₂O (6). All of the compounds were characterized using single-crystal X-ray diffraction, TG analysis and powder X-ray diffraction. Compound 1 contains a kind of bimetallic–organic segment [Co₂(Htrz)₅]⁴⁺, which could be regarded as a quasi-sinusoid-like chain. 2 is a dimer constructed from two [SiW₁₂O₄₀]⁴⁻ units linked by a [Zn₅(trz)₂(Htrz)₈]⁸⁺ motif. In 3 and 4, the 2D wall-like layers constructed by the Cu(II) ions and Htrz ligands are extended into 3D frameworks by polyanions. 5 shows a complicated three-dimensional (3D) framework with a {4¹²·6¹²·8⁴}{4⁶}₂ topology. Compound 6 is also a complicated 3D structure based on a triangular trinuclear Cu-trz unit and [P₂W₁₈O₆₂] polyanions. To the best of our knowledge, 6 represents the largest copper cluster linked by amines in a POM system. Structural diversities reveal that the pH value of the reaction system plays a crucial role in the assembly of POM-based hybrids. Moreover, the optical band gaps, electrochemical properties, magnetic properties and the photocatalytic properties of the compounds have been investigated.