Spectral and electrochemical properties of 2-pyridyl N-methyl-2-imidazolyl ketone complex of rhodium(III)

A new complex of [Rh(pik)2Cl2]Cl (where pik is 2-pyridyl N-methyl-2-imidazolyl ketone) has been synthesized and characterized. Both the free pik and the complex show high intensity bands in the UV region, and are assigned to spin-allowed π–π* transitions. Only the complex, however, exhibits medium-intensity absorption band profile in the lower energy region. This low-energy absorption might be explained by spin-allowed CT and, perhaps, convoluted with the weak d–d* transitions. Emission spectra at low temperature (77 K) of both the free pik and the complex in EtOH/MeOH (4:1 v/v) have also been investigated. The less structure spectrum observed for free pik is confirmed as n–π* transition. On the other hand, the complex shows a broad, symmetric, and structureless red emission with microsecond lifetime and hence is assigned as d–d* phosphorescence. Voltammetric data have also been obtained for free pik and the complex. The one-electron transfer occurred at the pi-system of the CO fragment of the free pik. There were three reduction peaks observed for the complex. The first peak, including two reduction steps with elimination of two chlorides, is consistent with ECEC reaction. Through examination of influence on reduction potential in the presence of phenol, the redox orbital involved in the last reduction is assigned to be the π* orbital localized at the carbonyl fragment of pik.