SPECTROSCOPIC STUDIES ON COORDINATED ACETYLENE

The structure and bonding of acetylene in CH≡CHCo2(CO)6 was studied by means of spectroscopic methods. The assignments of the infrared absorption bands were established unequivocally by the use of some isotope-substituted molecules: CH≡CDCo2(CO)6, CD≡CDCo2(CO)6, and 13CH≡CHCo2(CO)6. The frequency of the C≡C stretching vibration of coordinated acetylene was found to be lower than that of free acetylene by about 570 cm-1, and such a marked change in the vibrational frequency implies a large distortion of the coordinated acetylene from its free state. A structure with the C2v symmetry of coordinated acetylene can well explain the observed infrared and nmr spectra. The similarity of the vibrational spectrum of coordinated acetylene to the electronically excited molecule is suggested, and the nature of the bond between acetylene and cobalt is discussed. © 1969, American Chemical Society. All rights reserved.