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 4¹²6³ 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.