New organic–inorganic hybrid assemblies based on metal–bis(betaine) coordination complexes and Keggin-type polyoxometalates

The slow diffusion reactions of a double-betaine-containing ligand with YbH[SiMo12O40]·nH2O and Ca2[SiMo12O40]·nH2O led to the isolation of two new organic–inorganic hybrid assemblies, [Yb(O)(HL)2(H2L)0.5(H2O)3][SiMo12O40]·2.5CH3CN·1.5H2O (1) and [Ca(HL)2(L)0.5(H2O)4] [SiMo12O40]·5CH3CN·H2O (2) (L = 1,4-bis(pyridinil-4-carboxylato)-l,4-dimethylbenzene). Compounds 1–2 were characterized by elemental analyses, TG, IR, XPS and single-crystal X-ray diffraction. Compound 1 contains the dinuclear [(YbO)(HL)2(H2O)3]2 coordination moieties and discrete protonated L ligands, which are connected together by H-bonds and π–π interactions to form a 3D supramolecular framework with the Keggin-type [SiMo12O40]4 − polyoxoanions and solvent molecules encapsulated. Compound 2 possesses discrete [Ca(HL)2(L)0.5(H2O)4]2 coordination units that are linked by the extensive intermolecular H-bonds and π–π interactions to form a 3D supramolecular framework with the [SiMo12O40]4 − polyoxoanions and solvent molecules are encapsulated in the interbedded cavities. The structural motifs of the metal–organic coordination units can be obviously modulated by the use of chemically different cationic nodes. The degradation of Rhodamine-B (RhB) under UV irradiation with compounds 1 and 2 as heterogeneous photocatalysts were investigated, both exhibiting good photocatalytic properties. Furthermore, these hybrid compounds display luminescent properties induced by organic ligands.