Interactionless dummy atom

The principle aim of the reported studies was to model structures, conformational equilibria, and fluxionality. Parameters for the model involving interactionless dummy atoms were fitted to infrared spectra and allowed for the structures of metallocenes (M = Fe(H), Ru(II), Os(II), V(U), Cr(II), Cofll), Co(ni), Fe(III), Ni(II)) and analogues with substituted cyclopentadienyl rings (Fig. 13.3) to be accurately reproduced 981. The preferred conformation and the calculated barrier for cyclopentadienyl ring rotation in ferrocene were also found to agree well with the experimentally determined data (Table 13.1). This is not surprising since the relevant experimental data were used in the parameterization procedure. However, the parameters were shown to be self-consistent and transferable (except for the torsional parameters which are dependent on the metal center). An important conclusion was that the preference for an eclipsed conformation of metallocenes is the result of electronic effects. Van der Waals and electrostatic terms were similar for the eclipsed and staggered conformation and the van der Waals interactions were attractive 981. It is important to note, however, that these conclusions are to some extent dependent on the parameterization scheme, and particularly on the parameters used for the nonbonded interactions. 

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