One-pot concomitant preparation of two copper(II) coordination polymers with different configurations of bridging bithiophene ligands.

By employing the conjugated bithiophene ligand 5,5'-bis(1H-imidazol-1-yl)-2,2'-bithiophene (bibp), which can exhibit trans and cis conformations, two different Cu coordination polymers, namely, poly[[μ-5,5'-bis(1H-imidazol-1-yl)-2,2'-bithiophene-κN:N'](μ-4,4'-oxydibenzoato-κO:O')copper(II)], [Cu(CHO)(CHNS)] or [Cu(bibp)(oba)], (I), and catena-poly[μ-aqua-bis[μ-5,5'-bis(1H-imidazol-1-yl)-2,2'-bithiophene-κN:N']bis(μ-4,4'-oxydibenzoato)-κO:O':O'';κO:O',O'':O'-dicopper(II)], [Cu(CHO)(CHNS)(HO)] or [Cu(bibp)(oba)(HO)], (II), have been prepared through one-pot concomitant crystallization and characterized by single-crystal X-ray diffraction, IR spectroscopy, elemental analysis, powder X-ray diffraction (PXRD) and thermogravimetric (TG) analysis. Single-crystal X-ray diffraction indicates that the most interesting aspect of the structure is the existence of sole trans and cis conformations of the bibp ligand in a single net of (I) and (II), respectively. Compound (I) displays a threefold interpenetrating three-dimensional framework with a 4-connected {6.8} cds topology, whereas (II) features a one-dimensional chain structure. In the crystal of (II), the polymeric chains are further extended through C-H...O hydrogen bonds and C-H...π interactions into a three-dimensional supramolecular architecture. In addition, strong intramolecular O-H...O hydrogen bonds formed between the bridging water molecules and the carboxylate O atoms improve the stability of the framework of (II). Furthermore, solid-state UV-Vis spectroscopy experiments show that compounds (I) and (II) exhibit optical band gaps which are characteristic for optical semiconductors, with values of 2.70 and 2.26 eV, respectively.