A new method for assigning the CO stretching bands in cis-disubstituted octahedral metal carbonyl complexes

The paper describes a method for assigning the CO stretching bands in cis-disubstituted metal carbonyls of the types L2M(CO)4, (LL)M(CO)4, LL′M(CO)4 and (LL′)M(CO)4. The method was based on the parameter δ, defined as δ=(λ1−λ2)/(λ1+λ2−2λ4) where λ1, λ2 and λ4 are the λ parameters of the a1(1), a1(2) and b2 modes, respectively. For a large number of complexes with the above general formulas, the average value of δ was found to be 0.62, with a standard deviation of 0.02. It was shown that this range of δ can be used as a criterion of the correct band assignment for the complexes understudy.