Preparation and characterization of two new Cu^II supramolecular coordination polymers incorporating sulfobenzoate and flexible heterocyclic ligands

Abstract

The assembly of Cu with the multifunctional ligand 2-amino-4-sulfobenzoic acid (Hasba) in the presence of the auxiliary flexible ligands 1,4-bis(triazol-1-ylmethyl)benzene (bbtz) and 1,4-bis(imidazol-1-ylmethyl)benzene (bix) under ambient conditions resulted in two new supramolecular coordination polymers, namely poly[[(3-amino-4-carboxybenzenesulfonato-κO)aquabis[μ-1,4-bis(triazol-1-ylmethyl)benzene-κN:N]copper(II)] 3-amino-4-carboxybenzenesulfonate tetrahydrate], {[Cu(CHNOS)(CHN)(HO)](CHNOS)·4HO}, (1), and poly[[bis(μ-2-amino-4-sulfonatobenzoato-κO:N,O)tetraaqua[μ-1,4-bis(triazol-1-ylmethyl)benzene-κN:N]dicopper(II)] tetrahydrate], {[Cu(CHNOS)(CHN)(HO)]·4HO}, (2). Single-crystal X-ray structure diffraction analysis of (1) reveals that the bbtz ligand acts as a bridge, linking adjacent Cu ions into a two-dimensional cationic (4,4) topological network, in which the coordinated 3-amino-4-carboxybenzenesulfonate (Hasba) anion uses its sulfonate group to bind with the Cu ion in a monodentate fashion and the carboxylate group remains protonated. The lattice Hasba anion resides in the two-dimensional layer and balances the charge. The carboxylate group of the 2-amino-4-sulfonatobenzoate (asba) ligand in (2) is involved in bidentate coordination, connecting adjacent Cu ions into carboxylate-bridged chains which are further bridged by the auxiliary flexible bix ligand in a trans-gauche (TG) mode, resulting in the formation of a two-dimensional network architecture. The amino group of the asba ligand in (2) also takes part in the coordination with the central Cu ion. The six-coordinated Cu centres in (1) and (2) exhibit distorted octahedral coordination geometries. Extensive hydrogen bonding exists in both (1) and (2). The interlayer hydrogen bonds in both compounds further extend adjacent two-dimensional layers into three-dimensional supramolecular network architectures. Furthermore, a detailed analysis of the solid-state UV-Vis-NIR (NIR is near IR) diffuse reflectance data indicates that (1) and (2) may have potential as wide band gap indirect semiconductor materials. Compounds (1) and (2) show reversible and irreversible dehydration-rehydration behaviours, respectively.