DENSITY-FUNCTIONAL STUDY OF THE HARMONIC FORCE-FIELDS OF CP(-) LICP, AND FERROCENE

The complete harmonic force field of the cyclopentadienyl (Cp) anion, LiCp, and ferrocene has been calculated by local (LDA) and nonlocal (L DA/NL) density functional methods at the geometry optimized at LDA/NL level. The calculated LDA force field reproduced the harmonic vibratio nal frequencies of ferrocene with an average deviation of 35 cm(-1) af ter revising the empirical assignments of six observed frequencies. Co nsideration has been given to the proper representation of the skeleta l internal coordinates that facilitate the comparison of the internal force constants between the complexed and the free cyclopentadienyl ri ng. The valence force constants of the three compounds are compared, a nd the differences are interpreted. The complete force field of ferroc ene is expressed in both valence and symmetry coordinate representatio n. A comparison of the force fields of the free Cp(-) and that of ferr ocene shows that the out-of-plane force constants are remarkably diffe rent for the two compounds. Furthermore, the differences in the freque ncies are mainly due to the different force fields and not to the kine matic coupling effect as previously thought.