Photophysical and electrochemical studies of heteroleptic cyclometallated complexes of rhodium(III) containing 2-benzoylpyridine

Two heteroleptic cyclometallated complexes, cis-[Rh(bzpy)(bipy)Cl2] (1) and cis-[Rh(bzpy)(phen)Cl2] (2) (where bzpy = 2-(2-pyridylcarbonyl)phenyl, bipy = 2,2′-bipyridine and phen = 1,10-phenanthroline) have been synthesized and characterized. Based on IR and NMR data, it is evident that the coordinated bzpy ligand is N,C coordinated with Rh(III). Each complex shows high intensity bands in the UV region, assigned as spin-allowed π–π∗ transitions. The medium-intensity absorption band profile in the lower energy region can be explained by convolution of carbonyl n–π∗ and d–d∗ transitions. At low temperature (77 K), each complex shows a broad, symmetric and structureless red emission with a microsecond lifetime and, hence, is assigned as dd∗ phosphorescence. Voltammetric data have also been obtained for both complexes. There were two reduction peaks observed for each complex. The first reduction peak involves the transfer of two electrons and the elimination of two chlorides. The redox orbital involved in the second reduction is assigned to be the π∗ orbital localized on the carbonyl fragment of bzpy by examination of the influence on the reduction potentials in the presence of phenol.

Graphical abstractTwo heteroleptic cyclometallated complexes, cis-[Rh(bzpy)(bipy)Cl2] (1) and cis-[Rh(bzpy)(phen)Cl2] (2) have been synthesized (bzpy = 2-(2-pyridylcarbonyl)phenyl, bipy = 2,2′-bipyridine and phen = 1,10-phenanthroline). The coordinated bzpy ligand is N,C coordinated with Rh(III) based on IR and NMR data. At 77 K, 1 and 2 in EtOH/MeOH (9:1, v/v), each show a broad, symmetric and structureless red emission assigned as dd∗ phosphorescence. Analysis of voltammetric data also provides evidence in support of this assignment.Figure optionsDownload full-size imageDownload as PowerPoint slide