GAS-PHASE ELECTRON-DIFFRACTION STUDIES OF THE MOLECULAR-STRUCTURES OF TETRABROMO(SULFIDO)TUNGSTEN(VI), WSBR4, AND TETRABROMO(SELENO)TUNGSTEN(VI), WSEBR4

The molecular structures of WSBr4 and WSeBr4 at 220 and 250-degrees-C, respectively, have been determined by gas-phase electron diffraction. The experimental data for both compounds are fitted by square-pyramidal models of C4-upsilon symmetry in which the tungsten atom is above the plane of the bromine atoms. The bond lengths (r(a)/angstrom) and bond angles (angle/deg) with estimated 2-sigma uncertainties are as follows. WSBr4: r(W = S) = 2.109 (11), r(W-Br) = 2.433 (3), angle(S = W-Br) = 103.5 (7), angle(Br-W-Br)cis = 86.9 (3), and angle(Br-W-Br)trans = 153.0 (14). WSeBr4: r(W = Se) = 2.220 (22), r(W-Br) = 2.427 (9), angle(Se = W-Br) = 102.5 (9), angle(Br-W-Br)cis = 87.3 (4), and angle(Br-W-Br)trans = 154.9 (19). The structures of the series of nine WYX4 molecules (Y = O, S, Se; X = F, Cl, Br) are discussed.