| Abstract
| - The gas-phase structures of the conformers of 1,4-disilabutane and1,5-disilapentane have been analyzedfrom electron-diffraction data augmented by flexible restraints derivedfrom ab initio calculations. This allowedthe simultaneous refinement of 22 and 29 parameters for1,4-disilabutane and 1,5-disilapentane, respectively.1,4-Disilabutane has been found to be present in the vapourpredominantly in the anti (A) form (76(2)% fromthe experiment, 83% predicted by theory). Consistency in thegeometries is found between theoreticalpredictions and experimental findings, except for the torsion angle∠(SiCCSi) of the gauche (G) conformer[exptl 78.5(21)°, theor 68.0°]. The AA conformer of1,5-disilapentane was always found to be the lowestenergy structure, while some doubt still remains about the ordering ofthe AG and G(+)G(−) conformers.The AA conformer is found to be the sole form present in thecrystal [C2/c, a = 15.585(8),b = 4.704(3), c= 9.895(6) Å, β = 95.77(4)°, Z = 4].Good agreement is found for geometrical parametersdeterminedexperimentally in the gas phase and solid state and calculated byab initio methods. The following valuesrepresent the most important distances (rg/Å)and angles (∠g/deg) found for the gas phase and crystalstructures.1,4-Disilabutane GED (A/G, esd's correspond to 1σ): r(CSi) 1.882(1)/1.885(1), r(CC)1.563(5)/1.563(5),r(SiH) both 1.499(3), ∠(CCSi)110.7(2)/114.4(5), ∠(SiCCSi) 180.0/78.5(21).1,5-Disilapentane GED[AA/G(+)G(−)]: r(CSi)1.886(1)/1.888(1), r(CC)1.537(2)/1.539(2), r(SiH) both 1.487(4),∠(CCC)114.8(7)/118.8(7), ∠(CCSi) 114.1(4)/116.8(7),∠(SiCCC) 180.0/60.9(10); X [%, AA/AG/G(+)G(−)]28(4)/40(5)/26(6). 1,5-Disilapentane XRD: r(CSi)1.868(2), r(CC) 1.527(2), ∠(CCC)113.8(2), ∠(CCSi) 115.2(1),∠(SiCCC) 180.0(1).
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