On internal rotation in gaseous benzenechromium tricarbonyl

Abstract

The vapor phase molecular structure of benzenechromium tricarbonyl, C 6H 6Cr(CO) 3, has been studied by electron diffraction. On the basis of the diffraction data and of auxiliary vibrational calculations, it is concluded that in the vapor phase the molecule is a nearly unhindered internal rotor. Its vapors consist of a mixture of several conformations which differ by the rotational arrangement of the six-ring with respect to the carbonyl groups, whereas solid state studies showed the molecule to be in the pure staggered form. The CC bond distance of the six-ring ( r a ) was found to be 1.417 ± 0.003 Å and slightly longer than in free benzene (1.397 Å). The OCCrCO bond angle was found to be 88.6 ± 1.1° indicating a semi-octahedral arrangement; r a(CrC(CO)) = 1.863 ± 0.005 Å and r a(CrC(C 6H 6)) = 2.208 ± 0.006 Å.