Syntheses, structures and luminescent properties of six divalent metal terephthalate coordination polymers based on three new flexible bis(imidazole) ligands

Abstract

Six coordination polymers based on terephthalate and one of three new symmetry-related ligands which contain two flexible –O–CH₂–CH₂– chains connecting two imidazole-derived groups to a rigid naphthalene ring (2,7-bis(ethoxyimidazole)-naphthalene (L1), 2,7-bis(ethoxybenzimidazole)-naphthalene (L2), 1,5-bis(ethoxybenzimidazole)-naphthalene (L3)), formulated as [Cd(L1)(p-bdc)]·DMF·H₂O (1), [Co(L1)(p-bdc)(H₂O)₂]·H₂O (2), [Zn₂(L1)₂(p-bdc)₂]·3H₂O (3), [Zn(L2)(p-bdc)]·DMF (4), [Co(L2)(p-bdc)]·H₂O (5), [Co(L3)(p-bdc)(H₂O)]·2DMF (6), have been prepared under hydrothermal conditions. Compound 1 shows a two-dimensional (2D) (4⁴)-network with a 2-fold interpenetration structure. Compound 2 possesses a three-dimensional (3D) framework and can be simplified as a qzd (quartz-dual) “dense” net with point (Schläfli) symbol {7⁵·9}. Compound 3 displays an infinite one-dimensional (1D) structure containing three different rings, exhibiting a “cryptand ring” structure. Compound 4 presents a 2D framework and exhibits slightly undulating (4⁴) topology. Compound 5 exhibits a 2D network with point (Schläfli) symbol {12}{4·12⁵}{4}. Compound 6 demonstrates a 2D network with point (Schläfli) symbol {8⁴·12²}{8}₂. A comparison of the six complexes shows that the coordination mode of the terephthalate plays a key role in the construction of the coordination polymers and the three N-containing ligands beautify and enrich the structures. In addition, the powder X-ray diffraction (PXRD), elemental analysis, IR, thermal stability and optical properties of all compounds were investigated.