Using a flexible bis(pyrazol) ligand to construct four new Keggin-based compounds: syntheses, structures and properties

Abstract

Using a flexible bis(pyrazol) ligand, four new compounds based on Keggin anions, namely [Cu(H₂bdpm)₂(H₂O)₂(HPW₁₂O₄₀)] (1), [Cu(H₂bdpm)₂(H₂PW₁₂O₄₀)]₂·2H₂O (2), [Cu₂(H₂bdpm)₃(H₂O)₂(SiW₁₂O₄₀)]·2H₂O (3), and [Cu₂(H₂bdpm)₄(H₂O) (SiW₁₂O₄₀)]·16H₂O (4) (H₂bdpm = bis(3,5-dimethyl-1H-pyrazol-4-yl)methane), have been synthesized under hydrothermal conditions. Compound 1 is a zero dimension (0D) structure, showing a [Cu(H₂bdpm)₂]²⁺ mono-supporting [PW₁₂O₄₀]³⁻ anion. Compound 2 shows a 1D supramolecular chain, with bi-supporting anions lined by discrete [PW₁₂O₄₀]³⁻ anions. Compound 3 contains bi-nuclear Cu²⁺ cycles, which are linked by O4W to form a cycle-connecting-cycle chain. The [SiW₁₂O₄₀]⁴⁻ anions connect adjacent chains to construct a 2D structure. Compound 4 contains a nested cycle subunit [Cu₄(H₂bdpm)₆]⁸⁺, with two bi-nuclear cycles [Cu₂(H₂bdpm)₂]⁴⁺ linked by two H₂bdpm ligands. The nested cycle subunits are connected by H₂bdpm molecules to construct a 2D metal–organic layer. The Keggin anions link adjacent layers to form a 3D framework. The electrochemical and photocatalytic properties of compounds 1–4 are studied.