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

Abstract

Five copper(II) complexes with thiophene-2,5-dicarboxylic acid (H 2Tda): Cu(Tda)(H 2O)⋅(H 2O) 2 ( 1), Cu(Tda)(im) 2⋅(H 2O) ( 2), Cu(Tda)(im) 4 ( 3), [Cu(Tda)(py) 2] n ( 4) and [Cu(Tda)(bipy)(H 2O)] n ⋅ n[Cu(Tda)(bipy)(H 2O) 2]⋅2 nH 2O ( 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 Tda 2−. 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 Tda 2− and an 8-membered ring bridged by two carboxylates. Complex 5 comprises discrete [Cu(Tda)(bipy)(H 2O) 2] ( 5a), one dimensional zig–zag chain of [Cu(Tda)(bipy)(H 2O)] 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)(H 2O)] to form a one dimensional zig–zag chain.