A simple new structural force field for the computation of linear metallocenes

A new structural force field for metallocenes is presented, which involves harmonic bonding potentials from the metal center to each of the carbon ato ms, no angular potentials around the metal ion, inter-ligand 1,3-non-bonded interactions, and transferable parameters for the ligand backbones. The mo del has been parameterized for ferrocene, ruthenocene, and osmocene derivat ives and the force field has been validated with relevant structures from t he CSD files (Fe: 34, Ru: 10, Os: 2). The conformational space [rotation of the Cp (cyclopentadienyl) rings] has been searched with a cartesian stocha stic search routine and energy barriers have been computed by scanning the pseudo-torsional angles involving the centroids of the two Cp rings. The co mputed energy barriers are, smaller than those determined experimentally, b ut the predicted increase in transition energy upon substitution of the Cp rings is in agreement with experiment and the torsional angles for the mini mum structures are computed accurately. It is suggested that the underestim ated barrier height is due to the neglect of solvation.