Reaction of the biheteroaromatic ligand 2-(2′-pyridyl)quinoxaline (L) were zinc(II) and cadmium(II) halides: Preparation and characterization of the 1 : 1 complexes

Abstract

The reactions of ZnX 2 and CdX 2 (X = Cl, Br, I) with the biheteroaromatic ligand 2-(2′-pyridyl)quinoxaline (L) were studied in ethanolic solutions. The new complexes [ZnX 2L] (X = Cl, Br, I), [CdI 2L] and [Cd 2X 4L 2] were isolated and characterized by elemental analyses, conductivity measurements, X-ray powder patterns, thermal methods (TG/DTG, DTA) and spectroscopic (IR, far-IR, Raman, 1H NMR) studies. The X-ray crystal structure of [ZnCl 2L]·0.5MeOH shows a distorted tetrahedral geometry around the zinc(II) atom. The ligand L acts as a bidentate chelate with ligand atoms being the pyridine nitrogen and one of the quinoxaline nitrogens. A monomeric pseudo-tetrahedral structure is also assigned for [ZnBr 2] and [MI 2L] (M = Zn, Cd). Dimeric structures are proposed for the chloro and bromo cadmium(II) compounds, in which the two metal centres are bridged by two halo ligands, with a terminal halide and a chelating molecule of L completing five-coordination at each metal. All data are discussed in terms of the nature of bonding and known and assigned structures. A complex with the empirical formula Cd 2Cl 4L was isolated during the thermal decomposition of [Cd 2Cl 4L 2]; the vibrational study of this thermally stable intermediate shows that L acts as a tridentate bridging ligand. The crystal structure of [Hg 2Br 4L 2], which was not available when the results of the HgX 2/L chemistry had been published, is also described.