Molecular Structures of Zinc Complexes with Bisbenzimidazole Ligands in Crystals and the Kinetics of Ligand-Exchange Reactions in Their Solutions

Abstract

Abstract Zinc complexes with bisbenzimidazole, [ZnL(PhCOO)2] 1, [ZnLCl2] 2, and [ZnL2]2+ 3, have been synthesized, where L = 2,2′-thiodimethylenebis(benzimidazole). Their molecular structures were determined based on X-ray crystal structure and extended X-ray absorption fine structure (EXAFS) analyses. The molecular structure of 1·1.5DMF shows a distorted tetrahedral geometry around Zn(II) coordinated by each nitrogen atom of two benzimidazolyl groups and each oxygen atom of two benzoate ions. In solutions of 2 or 3·(ClO4)2 the same chemical species, [ZnLCl2] or [ZnL2]2+, exist as in the coordination structure around zinc in each crystal. The combination of 13C NMR data with the most probable molecular structures of zinc complexes in 1, 2, and 3, determined by X-ray crystal structure and EXAFS analyses, allowed us to assign the two different chemical species, [ZnL(PhCOO)2] and [ZnL2]2+, as the major and minor components, respectively, in a solution of 1. A kinetic study of the ligand-exchange reaction between PhCOO− and L was provided us with the lifetimes of the chemical species of [ZnL(PhCOO)2] and [ZnL2]2+: 66 ms and 10 ms at −10 °C, respectively. The major species produced by a zinc-assisted supramolecular process in solution is the same type of chemical species [ZnL(PhCOO)2] as in the coordination structure around zinc in the crystal of 1·1.5DMF. The ESI mass spectra of a solution of 1, 2, and 3·(ClO4)2 supported the chemical species of [ZnL(PhCOO)2], [ZnL2]2+, and [ZnLCl2] in solution.