Synthesis and crystal structures of some bis-benzimidazoles, -benzothiazoles and -benzoxazoles by an alternative route: Their complexation with copper(II) salts

A novel and convenient synthetic route towards new bis-benzimidazoles, -benzothiazoles and -benzoxazoles from readily available starting materials has been established. These compounds have thioethers at the 2 position of the heterocycle and the resultant carbon-thioether linkage is stable under the conditions of synthesis. The crystal structures of bis(benzoxazol-2-ylsulfanyl)methane, bis(benzothiazol-2-ylsulfanyl)methane and 1,8-bis(benzothiazol-2-ylsulfanyl)-3,6-dioxaoctane have been determined. Differences in the packings of the first two are attributed to the greater number of S ... S interactions of the second. Two of the new series have been complexed with copper(II) salts. The bis(benzoxazole) series showed no tendency to complex copper(II). The unusual crystal structure of the copper(II) complex with 1,8-bis(benzimidazol-2-ylsulfanyl)-3,6-dioxaoctane has been determined, indicating a four-co-ordinate copper(rr) atom in a distorted square-planar environment. The two bis(benzimidazole) moieties act as bidentate ligands with nitrogen donors. The thioether donors of the chain, although apparently ordered around the copper, are too distant to be regarded as donors but probably influence the spectroscopic properties of the copper site and are described as quasi-co-ordinated. Relevant spectroscopic and analytical details of the new compounds and their complexes are given.