Reactivity between late first-row transition metal halides and the ligand bis(2-pyridylmethyl)disulfide: Vibrantly-colored compounds with variable molecular geometries influenced by metal-sulfur interactions

Abstract

The reactivity between late first-row transition metal halides and the disulfide-containing ligand bis(2-pyridylmethyl)disulfide was examined. From this survey, a series of mononuclear, four- and five-coordinate metal compounds were prepared and characterized. Single-crystal X-ray diffraction was employed to analyze the molecular structures in the solid state. The four-coordinate, tetrahedral compounds adopt either the form MLX2 (M = Zn; L = bis(2-pyridylmethyl)disulfide; X = Cl, Br) where the disulfide ligand is coordinated in a bidentate fashion by two nitrogen donors, or MLX (M = Cu; L = bis(2-pyridylmethyl)disulfide; X = Cl, Br) where the ligand is tridentate, coordinating via one sulfur and two nitrogen donors. The five-coordinate metal compounds, though varying significantly with regard to molecular geometry due to metal-sulfur interaction strength, adopt the form MLX2 (M = Zn, Cu, Co; L = bis(2-pyridylmethyl)disulfide; X = Cl, Br) with the ligand serving as a tridentate scaffold employing one sulfur and two nitrogen donors. The crystal structures ZnLCl2•CHCl3 and ZnLBr2•CHCl3 are isomorphous as are the structures ZnLCl2•CH2Cl2, ZnLBr2•CH2Cl2, and CoLBr2•CH2Cl2. The crystal structure of CoLCl2 is a kryptoracemate, having an enantiomeric pair within the asymmetric unit. Although chemically-identical, both hands of CoLCl2 have strikingly different Co–S distances: 2.599(2) versus 2.755(2) Å. Based on the X-ray crystal structures, the choice of halide does not appear to significantly influence the molecular geometry. For the solvated crystal structures, the identity of the solvent molecule has a drastic effect on the metal-sulfur distances. Compounds that contain metal-sulfur coordination do not appreciably affect the disulfide bond, as determined by X-ray crystallography and Raman spectroscopy. In addition to the standard analytical methods, variable-temperature NMR and UV–vis–NIR spectroscopy was utilized to gain insight into the solution behavior of the vibrantly-colored compounds.