Geometrical and electronic structure of the molybdenum and tungsten halides MX3 and MX4 (M = Mo, W; X = F, Cl): Jahn-Teller effect and spin-orbit coupling

The ground and lower-lying excited electronic states of MX3 and MX4 (M = Mo, W; X = F, Cl) molecules were systematically studied by the complete active space self-consistent field (CASSCF) and multi configurational quasi-degenerate second-order perturbation (XMCQDPT2) methods. Scalar-relativistic effects and spin-orbit coupling were taken into account employing the third-order Douglas-Kroll-Hess (DKH) Hamiltonian and full Breit-Pauli operator. The ground orbital state of MoF3 and MoCl3 complexes is quadruplet (4)A(2)' state in the equilibrium configuration with D-3h symmetry. If the spin-orbit interaction is taken into account the calculations result in two E-4(1/2) and E-4(3/2) spin-orbit states with 11-14 cm(-1) energy differences instead of one (4)A(2)' state. Spin-orbit interaction quenches the Jahn-Teller effect in E-2 '' ground orbital state of WF3 complex in D-3h configuration, and C-2v configuration with (E-4(1/2) + E-4(3/2)) spin mixed state corresponds to the minimum on the PES. The WCI3 complex reveals strong interaction of the spin-orbit states of different multiplicity. For WCI3 complex the configuration with D3h symmetry corresponds to the minimum on the PES for four lowest spin-mixed electronic states. The MoF4, MoCl4 and WCl4 complexes possess the tetrahedral equilibrium configuration with (3)A(2) orbital electronic state. If the spin-orbit interaction is taken into account the ground state changes to the threefold degenerated T-3(2) spin-orbit state with weak Jahn Tellereffect. In the case of WF4 complex the strong Jahn-Teller effect has been discovered in the first excited E-1 singlet electronic state of the tetrahedral structure, and D-2d configuration with (1)A(1) electronic state possesses the lowest energy. The comparison with available experimental data has been performed. The tendencies in molecular parameters of complexes studied were analyzed. (C) 2016 Elsevier B.V. All rights reserved.