Three coordination polymers constructed from various polynuclear clusters spaced by 2,2′-azodibenzoic acid: syntheses and fluorescent properties

Abstract

Solvothermal reactions of M(OAc)2·2H2O (M = Zn, Cd, Pb) with 2,2'-azodibenzoic acid (H2L) in MeOH-H2O (MeOH = methanol) at 120 °C gave rise to three coordination polymers, [Zn12(μ4-O)3L9]n (1), [CdL(H2O)]n (2) and [Pb3(μ4-O)L2]n (3). Compounds 1-3 are characterized by elemental analysis, IR, powder X-ray diffraction and single-crystal X-ray diffraction. Compound 1 has two similar tetranuclear [Zn4(μ4-O)(μ2-CO2)6] units as nodes and displays an intriguing three-dimensional (3D) 6-connected network with a 4(12)6(3) topology. Compound 2 exhibits a 3D framework constructed by linking infinite helical Cd-carboxylate chains through L ligands. Compound 3 holds a 3D structure in which each hexanuclear [Pb6(μ4-O)2(CO2)4] unit works as a six-connecting node to connect its equivalent ones via sharing L ligands. In addition, the fluorescent properties and thermal stabilities of 1-3 were also investigated.