The experimental gas-phase structures of 1,3,5-trisilylbenzene and hexasilylbenzene and the theoretical structures of all benzenes with three or more silyl substituents

The structures of 1,3,5-trisilylbenzene and hexasilylbenzene in the gas phase have been determined by electron diffraction, and that of 1,3,5-trisilylbenzene by X-ray crystallography. The structures of three trisilylbenzene isomers, three tetrasilylbenzenes, pentasilylbenzene and hexasilylbenzene have been computed, ab initio and using Density Functional Theory, at levels up to MP2/6-31G*. The primary effect of silyl substituents is to narrow the ring angle at the substituted carbon atoms. Steric interactions between silyl groups on neighbouring carbon atoms lead first to displacement of these groups away from one another, and then to displacement out of the ring plane, with alternate groups moving to opposite sides of the ring. In the extreme example, hexasilylbenzene, the SiCCSi dihedral angle is 17.8(8)°

More user-friendly phosphines? Molecular structure of methylphosphine and its adduct with borane, studied by gas-phase electron diffraction and quantum chemical calculations

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Equilibrium gas-phase structures of sodium fluoride, bromide, and iodide monomers and dimers

The alkali halides sodium fluoride, sodium bromide, and sodium iodide exist in the gas phase as both monomer and dimer species. A reanalysis of gas electron diffraction (GED) data collected earlier has been undertaken for each of these molecules using the EXPRESS method to yield experimental equilibrium structures. EXPRESS allows amplitudes of vibration to be estimated and correction terms to be applied to each pair of atoms in the refinement model. These quantities are calculated from the ab initio potential-energy surfaces corresponding to the vibrational modes of the monomer and dimer. Because they include many of the effects associated with large-amplitude modes of vibration and anharmonicity, we have been able to determine highly accurate experimental structures. These results are found to be in good agreement with those from high-level core-valence ab initio calculations and are substantially more precise than those obtained in previous structural studies

Planar 1,3λ⁴δ²,2,4-benzodithiadiazine and its nonplanar 5,6,7,8-tetrafluoro derivative:Gas-phase structures studied by electron diffraction and ab initio calculations

The gas-phase molecular structures of 1,3λ4δ2,2,4-benzodithiadiazine and 5,6,7,8-tetrafluoro-1,3λ4δ 2,2,4-benzodithiadiazine have been investigated by ab initio calculations and electron diffraction using the SARACEN method of structural analysis. Important structural parameters (rh1 structure) for the parent compound were found to be: &lt; r(S=N) &gt; 1.546(3), r(S-N) 1.697(5), r(C-S) 1.784(5), and r(C-N) 1.393(6) Å. For the tetrafluoro derivative, these are (rh1 structure): &lt; r(S=N) &gt; 1.552(3), r(S-N) 1.723(8), r(C-S) 1.812(9), and r(C-N) 1.396(7) Å. Furthermore, the GED experiment (Gas Electron Diffraction) quite convincingly demonstrates the nonplanarity of the former and the planarity of the latter in agreement with DFT calculations; but the results contradict calculations at the MP2 level. The effect of the fluorine atoms on the conformations of the molecules is discussed.</p

An experimental and theoretical study of the molecular structure and vibrational spectra of iodotrimethylsilane (SiIMe3)

The gas-phase molecular structure of iodotrimethylsilane (ITMS) has been determined from electron diffraction data. Infrared and Raman spectra have been completely assigned. The experimental work is supported by ab initio HF and MP2 calculations for the gas-phase structure determination and DFT(B3LYP) calculations, combined with Pulay's SQM method, for the vibrational spectra data. © the Owner Societies 2006.Fil: Montejo, Manuel. Universidad de Jaén; EspañaFil: Hinchley, Sarah L.. University of Edinburgh; Reino UnidoFil: Ben Altabef, Aida. Universidad Nacional de Tucumán; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Robertson, Heather E.. University of Edinburgh; Reino UnidoFil: Ureña, Francisco Partal. Universidad de Jaén; EspañaFil: Rankin, David W. H.. University of Edinburgh; Reino UnidoFil: López González, Juan J.. Universidad de Jaén; Españ