Two multi-dimensional frameworks constructed from zinc coordination polymers with pyridine carboxylic acids

Two novel zinc coordination polymers [Zn2(H2O)L(MoO4)]n (1) and [Zn4(PO4)2L′(H2O)]n (2) (H2L=2,2′-bipyridine-6.6′-dicarboxylic acid, H2L′=2,2′-bipyridine-4,4′-dicarboxylic acid) have been hydrothermally synthesized and characterized by elemental analyses, IR spectra, UV spectra, single-crystal X-ray diffraction and thermogravimetric analyses. Structural analyses indicate that 1 represents a 2-D sheet structure built by dimeric [Zn2L(H2O)]2+ units and MoO42– groups whereas 2 displays an interesting 3-D framework constructed by tetranuclear zinc clusters, L′2− ligands and PO43– groups. Examination of UV spectra suggests that both 1 and 2 can stably exist in the pH range of 2.45–5.45 and 3.01–8.55 in aqueous solution, respectively. The room-temperature solid-state photoluminescence of 1 and 2 are derived from the intra-ligands π–π⁎ transitions of H2L and H2L′ ligands and the ligand-to-metal-charge-transfer transitions.