Zn( ii ) coordination architectures with mixed ligands of dipyrido[3,2-d ∶ 2′,3′-f]quinoxaline/2,3-di-2-pyridylquinoxaline and benzenedicarboxylate: syntheses, crystal structures, and photoluminescence properties

Five new Zn(II) metal–organic coordination polymers, [Zn2(L1)2(Dpq)2]·H2O (1), [Zn(L2)(Dpq)(H2O)] (2), [Zn(L3)(Dpq)(H2O)]2 (3), [Zn(Dpdq)(L3)] (4) and [Zn(Dpdq)(L4)]·H2O (5) (Dpq = dipyrido[3,2-d∶2′,3′-f]quinoxaline, Dpdq = 2,3-di-2-pyridylquinoxaline, H2L1 = benzene-1,2-dicarboxylic acid, H2L2 = benzene-1,3-dicarboxylic acid, H2L3 = benzene-1,4-dicarboxylic acid, H2L4 = biphenyl-4,4′-dicarboxylic acid), have been hydrothermally synthesized and structurally characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction analyses. Single-crystal X-ray analyses show that complexes 1–4 possess chain structures which are further assembled to form four three-dimensional (3-D) frameworks by π–π stacking and/or hydrogen-bonding interactions, while a similar chain of 5 has a two-dimensional (2-D) network packed by π–π stacking and hydrogen-bonding interactions. In 1–3, the Dpq ligand takes a chelating coordination mode while the other two nitrogen atoms did not coordinate to the Zn(II) ions. In 4 and 5, the Dpdq ligands have two coordination modes. The structural differences of the benzenedicarboxylate ligands and N-containing rigid/flexible chelating ligands have a great influence on the geometries of the corresponding complexes. This result also shows that intramolecular/intermolecular weak interactions play an important role in the formation of supramolecular networks, especially in linking low-dimensional entities into high-dimensional supramolecular frameworks. In addition, complexes 1 and 3–5 exhibit blue emission in the solid state at room temperature.