Three cadmium(II) coordination polymers constructed from polycarboxylate and tri(imidazole) ligands: Syntheses, crystal structures and luminescent properties

Abstract

Three cadmium (II) coordination polymers, namely, Cd(TIPA)(BIPA)·2H2O (1), Cd(TIPA)(HBTB)·H2O (2) and Cd3(TIPA)2(ODA)3(H2O)2·2H2O (3), where H2BIPA = 5-bromoisophthalic acid, H3BTB = 1,3,5-tri(4-carboxyphenyl)benzene, H2ODA = 9-oxofluorene-2,7-dicarboxylic acid and TIPA = tri(4-imidazolylphenyl)amine, have been synthesized using a solvothermal method and characterized by IR, elemental analysis and single crystal X-ray diffraction. In 1, adjacent Cd(II) ions are linked by BIPA anions to generate Cd–BIPA chains, which are further extended by TIPA ligands to form a puckered double sheet. The most peculiar feature of 1 is the entangled fashion between the [Cd2(TIPA)2] loop and the BIPA anion rod. Every [Cd2(TIPA)2] loop of each layer is threaded by one BIPA anion rod of an adjacent layer. In this entangled mode, the 2D → 3D polyrotaxane framework was obtained, which represents an unusual 2D → 3D metal–organic polyrotaxane framework entangled in a highly rare parallel fashion. Complex 2 has a three-dimensional (3D) (3,5)-connected network with (63)(69·8) topology, whereas complex 3 features an unprecedented 4-fold interpenetrating 3D framework with (3,4,4)-connected (4·62·83)2(4·62)2(64·102) topology. The results indicate the importance of the different carboxylate anions in the construction of the final frameworks. Three complexes indicate high thermal stabilities and different photoluminescent behavior in the solid state.