Controlling metal coordination geometry in dinuclear zinc and cadmium hydroxy aryl carboxylates incorporating five-membered aromatic cyclic amine co-ligands

Abstract

Five dinuclear Zn and Cd carboxylate complexes, [Zn(L)(µ-L)(im)·2H2O]2 (1), [Zn(L)(µ-L)(meim).MeOH]2 (2), [Zn(L)(µ-L)(dmp)]2 (3), [Cd(L)(µ-L)(im)·2H2O]2 (4) and [Zn(L)(µ-L)(dmp)]2 (5) (HL = 3,5-diisopropyl-4-hydroxybenzoic acid, im = imidazole, meim = N- methylimidazole, dmp = 3,5-dimethylpyrazole) have been synthesized by reacting M(OAc)2·2H2O (M = Zn and Cd) with a disubstituted aromatic carboxylic acid and various five-membered aromatic cyclic amines in methanol at ambient temperature. All complexes have been characterized by elemental analysis and FT-IR, Mass, UV–Vis, fluorescence, 1H and 13C NMR spectroscopic methods. The molecular structures and bulk purity of the compounds have been established by single-crystal and powder X-ray diffraction studies. In these complexes, the carboxylate groups exhibit terminal, chelating, chelate-bridging modes of coordination. The H-atom of dmp forms an intramolecular hydrogen bond with the carboxylate-O of the nearest ligand. The structures of the binuclear products obtained in the present study have been dictated by coordination mode of the carboxylate (chelate vs brdging) and size of the metal ion (Zn vs Cd). Presence of peripheral free hydroxyl functional groups facilitate intra- and inter-hydrogen bonding in the solid state structure. The luminescent properties of 1–5 have also been studied, exhibiting ligand-centred emission around 315 nm.