- The integrated infrared intensities of the vco stretching vibrations have been determined for a series of iron complexes of the types (C6H5)Fe(CO)2X (where X = Cl, I, CN, SnCl3, or C(O)CH3) and (C6H6CH2C5H5)Fe(CO)2P(C6H5)3 in chloroform solution. Dipole moment derivatives for the carbonyl stretching modes have been calculated assuming that the A and A vibrational modes each exhibit a characteristic MCO group moment derivative. Variations in these derivatives as a function of the angle () between MCO groupings in the series of complexes have also been considered in detail. In all cases the dipole moment derivatives for the symmetric stretching motion were found to be substantially smaller than that of the corresponding derivatives for the asymmetric stretching motion. It is concluded on the basis of these results that the cyclopentadienyl ligand is primarily acting as a donor grouping in the complexes studied. 1972, American Chemical Society. All rights reserved.