Spectroscopic and structural properties of complexes of 3,3′-bis(2-benzimidazolyl)-2,2′-bipyridine with copper(I) and silver(I)

The pseudo-tetrahedral complexes [CuL₂]PF₆·7H₂O·CH₃OH (1) and [AgL₂]CF₃SO₃·H₂O (2) (L = 3,3′-bis(2-benzimidazolyl)-2,2′-bipyridine) have been synthesized and characterized through crystal structure analyses, electrochemistry, and spectroscopic methods. X-ray structural analyses of 1 and 2 indicate that sterically constrained N₄ ligands L are cis and behave as bidentate chelates to a single metal ion in a pseudo-tetrahedral fashion through the benzimidazole. As two benzimidazolyl rings exhibit considerable steric hindrance, the bipyridine unit of L remains uncoordinated. The pseudo-tetrahedral cation [CuL₂]⁺ shows a quasi-reversible Cu^I/Cu^II oxidation–reduction wave in the CV in DMF (counter-ion PF₆⁻). The fluorescence titration of L with copper(I), silver(I), and also with pH have been conducted to examine the selectivity. The ligand shows remarkably high selectivity and sensitivity for Ag(I).