VIBRATIONAL OVERTONE SPECTROSCOPY OF CYCLOHEPTATRIENE CHROMIUM TRICARBONYL, BENZENE CHROMIUM TRICARBONYL, AND CORRESPONDING HYDROCARBON LIGANDS

The vibrational overtone spectra of gaseous cycloheptatriene chromium tricarbonyl (CHTCT) and benzene chromium tricarbonyl (BCT) were record ed at the third overtone region using photoacoustic spectroscopy and c ompared to the spectra of the nonbonded ligands, cycloheptatriene (CHT ) and benzene. Analysis of the spectra leads to the conclusion that th e metal-ligand bonding lengthens the CH bond by 0.007 Angstrom in the cycloheptatriene complex and by 0.003 Angstrom in the benzene complex. The spectrum of BCT exhibits an additional transition which is absent in the spectrum of free benzene. The experimental peaks are assigned to the pure CH overtones and combination bands. The structural informa tion obtained from the spectra is discussed and compared to the result s of gas-phase electron diffraction and microwave spectroscopic studie s. Analysis of experimental data indicates that mu 6-bonding is more f avorable for cycloheptatriene chromium tricarbonyl.