The gas phase structures of tungsten chlorides: density functional theory calculations on WCl6, WCl5, WCl4, WCl3 and W2Cl6

The molecular structures of WCl6, WCl5, WCl4, WCl3 and the dimer W2Cl6 have been optimised by density functional theory calculations at the B3LYP leve l using the quasi-relativistic electron core potential in combination with basis sets of DZ+P quality. The experimental, octahedral structure and the vibrational frequencies of the hexachloride are well reproduced by the calc ulations. Calculations on the pentachloride under D-3h symmetry indicated a n orbitally degenerate (E-2") ground state with bond distances in good agre ement with experiment. The Jahn-Teller (J-T) energy of distortion to C-2v s ymmetry was calculated to 1.8 kJ mol(-1), an order of magnitude smaller tha n the estimated spin-orbit (L-S) coupling energy. This is in agreement with an earlier suggestion that J-T distortion is this molecule is quenched by L-S coupling. The ground state of WCl4 is found to be a tetrahedral (T-d) t riplet, that of WCl3 a trigonal planar (D-3h) quartet and that of W2Cl6 to be a metal-metal bonded, ethane-shaped singlet. The structures indicated fo r these molecules are very different from those previously derived from gas electron diffraction data. Investigation by mass spectrometry indicates, h owever, that the composition of the vapours is much more complex and quite different from what was assumed during the structure analysis. The experime ntal structures are therefore open to question.