Polyoxometalate-directed assembly and various structures of inorganic–organic hybrid compounds based on a semi-rigid bis-pyridyl-bis-amide

Abstract

Through tuning different kinds of polyoxometalates (POMs), four POM-based inorganic–organic hybrid compounds with different dimensionalities, namely [(H2L)2(Mo8O26)] (1), [CuII2L6(P2W24O79)·4H2O]·7H2O (2), {CuII2L2(μ2-OH)[CrMo6(OH)6O18]·4H2O}·4H2O (3), and {CuI2CuII2L2(μ3-OH)2[CrMo6(OH)5O19]·6H2O}·4H2O (4) [L = 1,4-bis(3-pyridinecarboxamido)benzene], have been synthesized under hydrothermal conditions and characterized by IR spectroscopy, TG analysis, powder XRD and single-crystal X-ray diffraction. Single-crystal X-ray analyses reveal that compound 1 exhibits a two-dimensional (2D) supramolecular network, which is constructed from protonated L ligands and [Mo8O26]4− anions through hydrogen bonding interactions. Compound 2 is a 1D hybrid chain based on an uncommon inorganic [P2W24O79]4− chain and “Y”-shaped (CuL3)2+ subunits. Compound 3 shows a 2D network constructed from 1D inorganic Cu2–CrMo6 chains and bidentate L ligands, which is obtained at pH = 4.1. When the pH was adjusted to 4.8, compound 4 is obtained which exhibits a 4-connected {66} 3D framework. The CrMo6 anions are connected by adjacent [CuI2CuII2(μ3-OH)2(H2O)6]4+ subunits to form 1D Cu4–CrMo6 inorganic chains, which are further extended by L ligands to construct a 3D network. The effect of different types of polyanions and pH values on the assembly and various structures of the title compounds has been discussed. Furthermore, the electrochemical properties of 1 and 2, and the photocatalytic properties of 2 and 3 under different conditions have been investigated.