Photochemical and Photophysical Reactions of <i>f</i><i>ac</i>-Rhenium(I) Tricarbonyl Complexes. Effects from Binucleating Spectator Ligands on Excited and Ground State Processes

Abstract

Ground and excited state properties of the newly prepared complexes Re(CO) 3 (2,2‘-biquinoline)L S +, L S = pyrazine or 4,4‘-bipyridine, and Re(CO) 3 (2,2‘-bipy)(2-pyrazinecarboxylate) were investigated by steady state and time-resolved spectroscopy. The X-ray structure of the latter compound showed that the spectator ligand 2-pyrazinecarboxylate is coordinated through the carboxylate group to Re(I). A component of the complexes' luminescence was associated with long-lived Re to ligand, 2,2‘-biquinoline or 2,2‘-bipy, charge transfer, while a fast component of the emission was associated with intraligand excited states. Quenching of the luminescence by CuCl 2 involved energy transfer via dynamic and static mechanisms. The complexes in their excited states were reduced by 2,2‘,2‘ ‘-nitrilotriethanol with the formation of Re(I) ligand-radical species. Similar products were generated by the pulse radiolytic reduction of the complexes. The photochemical properties of the 2,2‘-biquinoline complexes and Re(CO) 3 (1,10-phen)4-nitrobenzoate are compared, and the mechanisms of their photochemical reactions are discussed.