An electron diffraction determination of the molecular structures of phosphoryl bromide and thiophosphoryl bromide |
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Authors: | EJean Jacob Donald D Danielson Svein Samdal |
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Institution: | The Bowman-Oddy Laboratories, Department of Chemistry, The University of Toledo, Toledo, Ohio 43606 U.S.A.;Department of Chemistry, Oregon State University, Corvallis, Oregon 97331 U.S.A. |
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Abstract: | 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) Å and rg(PBr) = 2.175(3) Å. 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) Å, rg(PBr) = 2.193(3) Å, 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. |
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