Assembly of six [HxAs2Mo6O26](6−x)− cluster-based hybrid materials from 1D chains to 3D framework with multiple Cu–N complexes

Abstract

A series of organic–inorganic hybrid compounds, [{Cu(4,4′-bipy)_1.5(H₂O)₂}₂{H₂As₂Mo₆O₂₆}] (1), [{Cu (biim)₂}₂{HAs₂Mo₆O₂₆}{Cu(biim)Cl}]·H₂O (2), (H₂bib)[{Cu(H₂O)₂(bib)}{H₂As₂Mo₆O₂₆}]·2H₂O (3), [{(Hbix)Cu(bix)_0.5}₂{As₂Mo₆O₂₆}]·2H₂O (4), [{Cu(bmb)_1.5(H₂O)}₂{H₂As₂Mo₆O₂₆}]·2H₂O (5), 0 and [{Cu₂(bth)₄}{H₂As₂Mo₆O₂₆}]·H₂O (6) (4,4′-bipy = 4,4′-bipyridine; biim = biimidazole; bib = 1,4-bis(1-imidazolyl)benzene; bix = 1,4-bis(imidazol-1-ylmethyl)benzene; bmb = 1,4-bis(benzimidazol-1-yl)benzene; bth = 1,6-bis(1,2,4-triazol-lyl)hexane), were hydro-thermally synthesized and structurally characterized via elemental analysis, TG, IR, XPS, XRD, and single-crystal X-ray diffraction. The crystal structures 1–6 are formed by metal–organic complexes and the [H_xAs₂Mo₆O₂₆]^(6−x)− cluster. Compounds 1–2 feature infinite 1D-chain structures. Compounds 3–5 form 2D-layer structures in which Cu cations are five-, six-coordinated with polyoxoanions and organic ligands. Notably, compound 6 introduces the POM system into a metal–organic framework (MOF) to form a unique POMOF {4²·6¹¹·8²}{4²·6⁴}{4⁴·6⁹·7·8} topological structure. The coordination modes of the [H_xAs₂Mo₆O₂₆]^(6−x)− cluster in compounds 2, 5 and 6 are reported for the first time. The photocatalytic properties of 1–6 are studied for the decomposition of methylene blue (MB) under UV light. In addition, all the compounds exhibit good electrocatalytic performances for the reduction of nitrite.