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

Abstract

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 CuII coordination polymers, namely, poly[[μ-5,5′-bis(1H-imidazol-1-yl)-2,2′-bithiophene-κ2 N:N′](μ2-4,4′-oxydibenzoato-κ2 O:O′)copper(II)], [Cu(C14H8O5)(C14H10N4S2)] n or [Cu(bibp)(oba)] n , (I), and catena-poly[μ-aqua-bis[μ-5,5′-bis(1H-imidazol-1-yl)-2,2′-bithiophene-κ2 N:N′]bis(μ3-4,4′-oxydibenzoato)-κ3 O:O′:O′′;κ4 O:O′,O′′:O′-dicopper(II)], [Cu2(C14H8O5)2(C14H10N4S2)(H2O)] n or [Cu2(bibp)(oba)2(H2O)] n , (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 {65.8} 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.