a Humboldt Universität zu Berlin, Institut für Chemie, Hessische Str. 1-2, D-10115 Berlin, Germany
b Chemical Division/Materials Science Division, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439-4837, USA
Abstract:
Ab initio molecular orbital theory was used to determine the equilibrium structure and vibrational frequencies of Fe2Cl6 and FeAlCl6. The equilibrium structure the Fe2Cl6 dimer has D2h symmetry with a planar arrangement of the four membered {FeClbrFeClbr} ring, similar to the Al2Cl6 dimer. The calculated bond distances and vibrational frequencies are in good agreement with experiment. The potential energy surface for the puckering of the {FeClbrFeClbr} ring is extremely flat. This prevents an unambiguous assignment of either D2h or C2v symmetry to the Fe2Cl6 structure in electron diffraction measurements. The FeAlCl6 molecule is found to have a C2v structure similar to Fe2Cl6 with vibrational frequencies in good agreement with experiment.