Ferrocene molecular mechanics calculations

Although vibrational frequencies have been calculated and compared with experimental data since the early days of molecular mechanics refinements using full-matrix second-derivative procedures [13 73], there are few reports on the application of this method in the field of transition metal chemistry. One of the examples is a study on linear metallocenes[108]. Here, the molecular mechanics force constants were obtained by adjusting starting values by fitting the calculated vibrations to thoroughly analyzed experimental spectra. The average difference (rms) between experimental and calculated vibrations was of the order of ca. 30 cm-1. Table 10.1 shows the observed and calculated frequencies associated with the skeletal modes of ferrocene (see Fig. 10.1 for the representation of these modes). 

The interest in the rotation of cyclopentadienyl rings (or aromatic organic rings in general) attached to metals (15) originated with the discovery of ferrocene itself (3b). Many methods have been employed to study the phenomenon, among them solid-state and solution NMR (187), dipole moment measurements (188), electron and X-ray diffraction techniques (189,190), mechanical spectroscopy (117), and last but not least molecular orbital calculations (191). 

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