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Intermolecular Self-Interactions of the Titanium Tetrahalides TiX4 (X = F, Cl, Br)

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journal contribution
posted on 04.03.1999, 00:00 by Simon P. Webb, Mark S. Gordon
Ab initio calculations have been performed on the closed-shell molecules TiX4 and Ti2X8 (X = F, Cl, Br) in order to determine the magnitude and the nature of the intermolecular self-interactions of the titanium tetrahalides. Geometry optimizations have been carried out using an effective core potential basis set with polarization, including the effects of dynamic electron correlation through second-order perturbation theory (MP2). The importance of higher order correlation effects is examined through coupled cluster single-point energy calculations. Basis set effects are investigated using MP2 single-point energy calculations with large all-electron basis sets. Ti2F8 is predicted to be a bound C2h dimer with bridging bonds, lower in energy than the separated monomers by 10.5 kcal/mol. Ti2Cl8 and Ti2Br8 are predicted to be weakly bound dimers whose structures are that of associated monomers with overall D3d point group symmetry. Ti2Cl8 is lower in energy than separated monomers by 4.9 kcal/mol. Transition states have been found that represent paths to halide exchange between monomers supporting experimental evidence for rapid halide exchange in liquid TiCl4 and in mixed systems such as TiCl4/TiBr4.