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

•Bis(chelating) ligand based on 1,10-phenanthroline and N-heterocyclic carbene (NHC) has been synthesized.•Mono-ReI and ReI–IrI have been prepared using bis(chelating) ligand.•Optical properties can be tuned by replacing the COD ligand with CO at iridium metal.•Bimetallic complexes have been used as an optical carbon monoxide indicator.

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.

Graphical abstractA bis(chelating) ligand, 1,3-dimethyl-2,3-dihydro-1H-imidazo[4,5-f][1,10]phenanthroline-2-yl (IL-2) has been synthesized and its mono/bimetallic complexes, [mono-ReI, ReI-(IL-2)–IrI(COD)Cl and ReI-(IL-2)–IrI(CO)2Cl] have been prepared. Bimetallic complexes have shown optical properties depending upon the ligand attached to iridium metal. Thus, these complexes have been studied as an optical CO gas indicator.Figure optionsDownload full-size imageDownload as PowerPoint slide