Interaction of an Iridium(III)–Bibenzimidazole Complex with Anions – Implications for Luminescent Sensing

Abstract

AbstractIridium(III) complex [Ir(ppy)2(tmBBI‐H2)](PF6) (IrBBI‐H2) has been exploited as an anion receptor. In this complex, the cis‐diamine function of the bibenzimidazole is coupled in such a way to the photophysics of the iridium metal core that the photophysics is influenced by hydrogen bonds in the ligand periphery. Systematic studies on the complex reveal that IrBBI‐H2 is a convenient sensor for various anions under aerobic conditions and interacts with Cl–, Br–, I–, and HSO4– by forming hydrogen bonds. Whereas H2PO4– is only capable of mono‐deprotonating IrBBI‐H2, a stepwise process is operative when F– and OAc– are added: formation of the mono‐deprotonated complex IrBBI‐H with a low anion concentration, followed by the appearance of double‐deprotonated complex IrBBI– in the presence of higher anion concentration. The interaction of various anions with IrBBI‐H2 has been investigated by emission spectroscopy or NMR titration. According to the conditions chosen, strong binding interactions in the form of a 2:1 complex/anion ratio between the less basic anions and the complex, and a virtually stoichiometric reaction to their respective ion pairs, were observed.