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

<div><p>The pseudo-tetrahedral complexes [Cu<b>L</b><sub>2</sub>]PF<sub>6</sub>·7H<sub>2</sub>O·CH<sub>3</sub>OH (<b>1</b>) and [Ag<b>L</b><sub>2</sub>]CF<sub>3</sub>SO<sub>3</sub>·H<sub>2</sub>O (<b>2</b>) (<b>L </b>= 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 <b>1</b> and <b>2</b> indicate that sterically constrained N<sub>4</sub> ligands <b>L</b> are <i>cis</i> 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 <b>L</b> remains uncoordinated. The pseudo-tetrahedral cation [Cu<b>L</b><sub>2</sub>]<sup>+</sup> shows a quasi-reversible Cu<sup>I</sup>/Cu<sup>II</sup> oxidation–reduction wave in the CV in DMF (counter-ion PF<sub>6</sub><sup>−</sup>). The fluorescence titration of <b>L</b> 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).</p></div>