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

A new complex of [Rh(pik)(2)Cl-2]Cl (where pik is 2-pyridyl N-methyl-2-imid azolyl ketone) has been synthesized and characterized. Both the free pik an d the complex show high intensity bands in the UV region, and are assigned to spin-allowed pi-pi* transitions. Only the complex, however, exhibits med ium-intensity absorption band profile in the lower energy region. This low- energy absorption might be explained by spin-allowed CT and, perhaps, convo luted 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 co nfirmed as n-pi* transition. On the other hand, the complex shows a broad, symmetric, and structureless red emission with microsecond lifetime and hen ce is assigned as d-d* phosphorescence. Voltammetric data have also been ob tained 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 reductio n peaks observed for the complex. The first peak, including two reduction s teps with elimination of two chlorides, is consistent with ECEC reaction. T hrough examination of influence on reduction potential in the presence of p henol, the redox orbital involved in the last reduction is assigned to be t he pi* orbital localized at the carbonyl fragment of pik. (C) 2001 Elsevier Science B.V. All rights reserved.