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

Abstract

The molecular structures of WCl₆, WCl₅, WCl₄, WCl₃ and the dimer W₂Cl₆ have been optimised by density functional theory calculations at the B3LYP level 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 calculations. Calculations on the pentachloride under D_3h symmetry indicated an orbitally degenerate (²E″) ground state with bond distances in good agreement with experiment. The Jahn–Teller (J–T) energy of distortion to C_2v symmetry was calculated to 1.8 kJ mol⁻¹, an order of magnitude smaller than 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) triplet, 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 for these molecules are very different from those previously derived from gas electron diffraction data. Investigation by mass spectrometry indicates, however, that the composition of the vapours is much more complex and quite different from what was assumed during the structure analysis. The experimental structures are therefore open to question.