Spectroscopic evaluation of the degree of inequivalence of the carbonyl groups in dicarbonyl complexes of rhodium(I) with singly charged bidentate ligands

The IR spectra of a series of complexes of the type RhL(CO)2 have been studied with the use of the variable isotopic replacement of 12CO by 13CO in dilute solutions and the crystalline state. It has been demonstrated that the splitting of the stretching vibrations of the carbonyl groups in the mixed isotopomers is caused by the inequivalence of the CO groups. A method for the quantitative evaluation of the inequivalence of the carbonyl groups with the aid of IR-spectroscopic parameters, whose sensitivity is comparable to 13C NMR in solutions and surpasses the sensitivity of x-ray structural analysis in crystals, has been proposed. The possibility of its use for natural samples has been demonstrated