Cd(ii) coordination polymers constructed with a flexible carboxylate linker and pyridyl co-linkers: variation in the network topologies and photoluminescence properties

Abstract

Six new coordination polymers (CPs) of Cd(II), {[Cd₃(L)₂(H₂O)₅(μ-H₂O)]·6H₂O}_n (1), {[Cd₃(L)₂(4,4′-bpy)₃(H₂O)₂]·4(H₂O)·(DEF)}_n (2), {[Cd(HL)(dpe)_0.5(H₂O)]₂·(H₂O)}_n (3), {[Cd(HL)(dpd)_0.5(H₂O)]}_n (4), {[Cd(HL)(1,2-dpe)_0.5]}_n (5), and {[Cd₃(L)₂(1,3-dpp)₂]·3H₂O}_n (6) (where H₃L = 5-(2-carboxybenzyloxy)isophthalic acid, 1,3-dpp = 1,3-di(4-pyridyl)propane, 1,2-dpe = 1,2-di(4-pyridyl)ethane, dpd = 1,2-di(pyridin-4-yl)diazene, dpe = 1,2-di(4 pyridyl)ethylene, and 4,4′-bpy = 4,4′-bipyridyl), were synthesized under solvothermal/hydrothermal conditions and structurally characterized via elemental analysis, IR spectroscopy, and single-crystal and powder X-ray diffraction. Compound 1 displays infinite 2D sheets, which stack upon each other to form a supramolecular 3D network. Topologically, the network can be viewed as a 3,3,3,5-connected four nodal net, which was assigned to a novel topological type, pkb9. Compound 2 shows a 3D assembly with the 3,4,6-connected topology sqc130. Compound 3 and 4 form interdigitated 3D supramolecular networks with a 4-connected sql/Shubnikov topology. Compound 5 shows an unusual 2D → 3D framework with a 3,8-connected tfz-d; UO₃ topology. In compound 6, 2D → 3D packing was observed due to weak C–H⋯O interactions that aided in the formation of a 3D network with a 4-connected sql/Shubnikov topology. The luminescence properties of all the compounds in their solid state and as emulsions in various solvents were investigated using nitroaromatic compounds.