Vibrational spectra and potential constants of the (.eta.6-benzene)chromium(0) chalcocarbonyl complexes, (.eta.6-C6H6)Cr(CO)2(CX) (X = oxygen, sulfur, selenium)

Harmonic Force Fields and Vibrational Frequencies of Benzene, Dibenzene-Chromium, Benzene-Chromium Tricarbonyl, and Chromium-Hexacarbonyl. A Density Functional Study

“…In our frequency assignments we use the frequencies reported by English An important outcome of our frequency assignment is the confirmation of all frequency identifications made by English et al in the CO region. 23 In our assignments, the parallel and perpendicular CrCO bendings are systematically interchanged compared to those of English et al, which might be attributed to differences in notation. In our assignments, a CrCO bending is considered parallel if it is in the symmetry plane of the molecule.…”

“…Since the study by English et al provides the most thorough normal-coordinate analysis, using accurate frequency assignments, this study is our reference for the comparison of empirical and calculated potential constants. 23 Prior to this study, the reported CO and CrC stretching force constants for BzCr(CO)3 by different authors had ranged from 13.55 to 14.64 mdyn/A, and from 1.6 to 3.88 mdyn/A, respectively. This wide range of values is the consequence of the different approximations used in the normalcoordinate analysis.…”

“…The Is2 configuration on carbon and oxygen as well as the ls22s22p6 configuration of chromium were assigned to the core and treated by the frozen-core approximation. 23 A set of auxiliary5 s, p, d, f, and g STO functions, centered on all nuclei, was used in order to fit the molecular density and represent the Coulomb and exchange potentials accurately in each SCF cycle.…”

“…In the empirical studies, it was impossible to determine the complete force fields due to lack of information and it was necessary to introduce approximations that reduced the number of force constants. The problem of the physical meaning of the force constants was recognized in the studies by English et al 23,29 These studies have expressed the potential energy constants in terms of compliance constants Cy, which depend only on the definition of internal coordinates qt and qy. This approach was also favored for the transfer of potential energy constants between similar molecules.…”

A Study of the Adsorption and Thermal Behavior of (η6-C6H6)Cr(CO)3 in Zeolite Y by Vibrational Spectroscopy

“…The frequencies of the other three bands at 1963, 1879, and 1860 cm -1 are similar to those observed by other groups upon adsorption of (η 6 -C 6 H 6 )Cr(CO) 3 in NaY and NaX. , The authors of these studies interpreted these bands to be representative of isolated (η 6 -C 6 H 6 )Cr(CO) 3 molecules located inside the supercages of faujasite zeolite. The IR spectrum of pure (η 6 -C 6 H 6 )Cr(CO) 3 in solution exhibits two ν(CO) bands at 1974 and 1895 cm -1 (Figure B) which are assigned to the a 1 and e modes, respectively, assuming C 3 v local symmetry for the Cr(CO) 3 moiety. It has been reported that the M(CO) 3 moieties of several (arene)M(CO) 3 molecules (M = Cr, Mo) located inside the supercages of faujasite zeolites can undergo a reduction of local symmetry from C 3 v to C s or C 1 . ,, This symmetry distortion can be detected by the splitting of the ν(CO) e mode resulting from interactions between (η 6 -C 6 H 6 )Cr(CO) 3 and the zeolite.…”