Syntheses, structures and properties of copper(II) complexes with thiophene-2,5-dicarboxylic acid (H2Tda) and nitrogen-containing ligands

Abstract

Five copper(II) complexes with thiophene-2,5-dicarboxylic acid (H2Tda): Cu(Tda)(H2O)·(H2O)2 (1), Cu(Tda)(im)2·(H2O) (2), Cu(Tda)(im)4 (3), [Cu(Tda)(py)2]n (4) and [Cu(Tda)(bipy)(H2O)]n·n[Cu(Tda)(bipy)(H 2O)2]·2nH2O (5) (im=imidazole, py=pyridine and bipy=2,2′-bipyridine) have been synthesised and their spectroscopic and thermal properties investigated. Three of them (3, 4 and 5) are structurally characterised and the Cu atom is in five coordinate, distorted square pyramidal environments. The thiophene-2,5-dicarboxylate molecule is monodentate in 3 in which the molecular structure is stabilised by intermolecular hydrogen bonding involving two of the four non-coordinated nitrogen atoms of the imidazole ligands and carboxylate groups from adjacent Tda2-. In 4 the thiophene-2,5-dicarboxylate ion is bridging tridentate and bonded to three copper atoms to form a chain polymer with alternating 16-membered ring bridged by two Tda2- and an 8-membered ring bridged by two carboxylates. Complex 5 comprises discrete [Cu(Tda)(bipy)(H2O)2] (5a), one dimensional zig-zag chain of [Cu(Tda)(bipy)(H2O)]n (5b) and water molecules of crystallization. The thiophene-2,5-dicarboxylate molecule is monodentate in 5a and involved in intermolecular stacking interactions with 2,2'-bipyridine rings, and bidentate in 5b to bridge [Cu(bipy)(H2O)] to form a one dimensional zig-zag chain.