| Popis: |
Gas-phase electron diffraction structures have been determined for phosphoryl bromide (OPBr3 thiophosphoryl bromide (SPBr3Normal coordinate analyses were carried out for the two molecules using a valence force field, and the resulting amplitude terms used for transformations between ra and rga. An unconstrained refinement of the OPBr3 intensities gives the parameters rg(PO) = 1.455(7) A and rg(PBr) = 2.175(3) A. The weighted average, geometrically-consistent valence angles derived from the four internuclear distances, rα, are θα(OPBr) = 114.4(2)° and θα(BrPBr) = 104.1(2)°. For SPBr3 a constrained fit to a self-consistent rα structure gives the parameters rg(PS) = 1.895(4) A, rg(PBr) = 2.193(3) A, θα(SPBr) = 116.2(2)°, and θα(BrPBr) = 101.9(2)°. Electron diffraction and spectroscopic vibrational amplitudes are reported for both molecules. The electron diffraction structures are compared with those predicted by simple models previously developed to describe main group V trihalides and trihalogen oxides and sulfides. Treatment of valence angles in four-coordinate molecules is found to be the least satisfactory feature of these models. |
