ReI–IrI bimetallic complexes based on a bis(chelating) ligand composed of 1,10-phenanthroline and N-heterocyclic carbene: Coordination chemistry and their application for optical indicator of CO gas

Mono complex [Cl(CO)3ReI(IL-2)](PF6) and bimetallic complexes Cl(CO)3ReI(IL-2)–IrI(Ligand)nCl, where IL-2 = 1,3-dimethyl-2,3-dihydro-1H-imidazo[4,5-f][1,10]phenanthroline-2-yl and Ligand = 1,5-cyclooctadiene (n = 1) or carbon monoxide (n = 2), were synthesized, characterized, and applied to react with carbon monoxide. Bis(chelating) ligand, IL-2, has two coordinating sites, 1,10-phenanthroline and imidazolium moieties. These complexes display typical intraligand transition (π–π∗) and metal-to-ligand charge-transfer (MLCT) bands in the ultraviolet and visible regions, respectively. It was demonstrated that complex Cl(CO)3ReI(IL-2)–IrI(COD)Cl can be used as a carbon monoxide (CO) indicator because Cl(CO)3ReI(IL-2)–IrI(CO)2Cl, a CO-substituted bimetallic complex, displays distinct optical behaviors compared to those of Cl(CO)3ReI(IL-2)–IrI(COD)Cl.