Influence of pH and organic ligands on the supramolecular network based on molybdenum phosphate/strontium chemistry

Abstract

Three supramolecular materials based on different poly(oxomolybdophosphate) clusters, (H₂imi)₆(Himi)₄[{Sr(H₂O)₄}₂{Sr ⊂ P₆Mo₄^VMo₁₄^VIO₇₃}₂]·17H₂O (1), (H₂(4,4′-bpy))₂[Cu₂Sr₂Mo₁₂O₂₄·(OH)₆(H₂O)₆(H₂PO₄)₂(HPO₄)₂(PO₄)₄]·5H₂O (2), and (H₂bim)(H₂bim)[SrP₂Mo₅O₂₃(H₂O)₃]·2H₂O (3) (imi = imidazole, 4,4′-bpy = 4,4′-bipyridine, and bim = 2,2′-biimidazole), have been hydrothermally synthesized and structurally characterized by the elemental analysis, TG, IR, UV-vis, XPS and the single-crystal X-ray diffraction. Compound 1 is made up of unusual basket-shape [Sr ⊂ P₆Mo₁₈O₇₃]¹⁰⁻ cages linked by [Sr(H₂O)₄]²⁺ fragments to yield unprecedented dimeric chains, which represent the first 1-D assemblies of basket-type POMs. Compound 2 exhibits a novel string constructed from sandwich-like [Cu(P₄Mo₆O₃₁)₂] units and {Sr₂Cu} trinuclear linkers. Compound 3 is the first chain of Strandberg-type polyoxoanions connected by Sr²⁺ cations. All the 1-D chains are further packed into various 3-D supramolecular assemblies via strong hydrogen-bonding interactions. The electrochemical and electrocatalysis behavior of 1, 2, and 3-CPE have been investigated in detail.