Electron-diffraction studies of tetramethylsilane and hexamethyldisilane, and discussion of the lengths of Si-C bonds

Beagley, B.; Monaghan, John; Hewitt, T. G.

doi:10.1016/0022-2860(71)80018-2

Cited by 215 publications

(94 citation statements)

References 21 publications

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“…However, results from the MP2/aug-cc-pVTZ calculation showed that the angles average to 112.9°. This is wider than the corresponding Si-Si-C angles obtained for hexamethyldisilane (108.4±0.4°), 36 demonstrating that the trifluoromethyl groups affect the overall structure of the molecule and not just angles to fluorine atoms. 37 The longer central bond is due to the electron-withdrawing capabilities of the fluorine atoms of the two highly electronegative trifluoromethyl groups.…”

Section: Resultsmentioning

confidence: 66%

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Molecular Structure of 1,2-Bis(trifluoromethyl)-1,1,2,2-tetramethyldisilane in the Gas, Liquid, and Solid Phases: Unusual Conformational Changes between Phases

et al. 2014

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The molecular structure of 1,2-bis(trifluoromethyl)-1,1,2,2-tetramethyldisilane has been determined in three different phases (solid, liquid and gas) using various spectroscopic and diffraction techniques. Both the solid-state and gas-phase investigations revealed only one conformer to be present in the sample analyzed, while the liquid phase revealed the presence of three conformers. The data have been reproduced using computational methods and a rationale is presented for the observation of three conformers in the liquid state.

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Section: Resultsmentioning

confidence: 66%

“…36 However, the Si-C(F 3 ) bond distance shows significant elongation to 193.6(2) pm. This is a significant difference and demonstrates the electronic effects on Si-C bonds due to the addition of fluorine atoms on the ligands.…”

Section: Gas Electron Diffraction (Ged)mentioning

confidence: 98%

Molecular Structure of 1,2-Bis(trifluoromethyl)-1,1,2,2-tetramethyldisilane in the Gas, Liquid, and Solid Phases: Unusual Conformational Changes between Phases

et al. 2014

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“…We note that the Si(1)-C Me distance, at 193.3(19) pm, is approximately 5 pm longer than that in the relatively unstrained molecule Si 2 Me 6 , where an Si-C distance of 187.7(3) pm, 6 is observed by GED. It seems that for 2 the bulky substituents push this methyl group further away from the silicon backbone.…”

Section: Gas Electron Diffractionmentioning

confidence: 61%

“…For conformers 1a-1c, the Si(5)Si(1)Si (6) angles between the two symmetrically unique trimethylsilyl groups vary by several degrees, with conformer 1c having the narrowest angle at 111.6°, while conformer 1a has the widest angle at 113.5°. This narrower angle in conformer 1c results in the methyl groups on adjacent branches being closer together than in the other conformers resulting in more H···H interactions.…”

Section: Gas Electron Diffractionmentioning

confidence: 99%

“…For homoleptic disilanes general trends in the Si-Si bond lengths have been attributed on the basis of the electron-withdrawing and electron-donating character of the substituents attached to the silicon atoms. Using disilane, Si 2 H 6 , 3 as a reference the Si-Si bond is observed to shorten upon inclusion of electronegative halogen atoms to give Si 2 F 6 4 and Si 2 Cl 6 , 5 while the bond is lengthened by the inclusion of electron-donating methyl groups in Si 2 Me 6 . 6 The structures of these, as well as of the partially halogenated disilanes 1,1,2,2-tetrabromodisilane, 7 1,2-diiododisilane, 8 and 1,1,2,2-tetraiododisilane, 8 show the expected staggered conformations in the gas phase.…”

Section: Introductionmentioning

confidence: 98%

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Gas-phase structures of sterically crowded disilanes studied by electron diffraction and quantum chemical methods: 1,1,2,2-tetrakis(trimethylsilyl)disilane and 1,1,2,2-tetrakis(trimethylsilyl)dimethyldisilane

et al. 2014

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This is a repository copy of Gas-phase structures of sterically crowded disilanes studied by electron diffraction and quantum chemical methods : 1,1,2,2-tetrakis(trimethylsilyl) disilane and 1,1,2,2-tetrakis(trimethylsilyl) ReuseUnless indicated otherwise, fulltext items are protected by copyright with all rights reserved. The copyright exception in section 29 of the Copyright, Designs and Patents Act 1988 allows the making of a single copy solely for the purpose of non-commercial research or private study within the limits of fair dealing. The publisher or other rights-holder may allow further reproduction and re-use of this version -refer to the White Rose Research Online record for this item. Where records identify the publisher as the copyright holder, users can verify any specific terms of use on the publisher's website. TakedownIf you consider content in White Rose Research Online to be in breach of UK law, please notify us by emailing eprints@whiterose.ac.uk including the URL of the record and the reason for the withdrawal request. (Table S1); least-squares correlation matrices (Tables S2 and S3); calculated coordinates and energies (Tables S4-S7); descriptions of the models used for the refinements, refined (r h1 ) and calculated (r e ) parameters values and their SARACEN restraints used in the three-conformer least-squares refinements of 1 and 2 (Tables S8 and S9), amplitudes of vibration and curvilinear distance corrections (Tables S10 and S11);final GED coordinates (Tables S12 and S13); plots of the amount of conformer against R G /R G (min.) ( Figure S1); plots of molecular-scattering intensity curves ( Figure S2).3

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Rotational barriers of disilane, hexafluorodisilane, and hexamethyldisilane:Ab initio, density functional, and molecular mechanics (MM3) studies

1997

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We investigated structures, vibrational frequencies, and rotational barriers of disilane (Si2H6), hexafluorodisilane (Si2F6), and hexamethyldisilane (Si2Me6) by using ab initio molecular orbital and density functional theories. We employed four different levels of theories (i.e., HF/6–31G*, MP2/6–31G*, BLYP/6–31G*, and B3LYP/6–31G*) to optimize the structures and to calculate the vibrational frequencies (except for Si2Me6 at MP2/6–31G*). MP2/6–31G* calculations reproduce experimental bond lengths well, while BLYP/6–31G* calculations largely overestimate some bond lengths. Vibrational frequencies from density functional theories (BLYP/6–31G* and B3LYP/6–31G*) were in reasonably good agreement with experimental values without employing additional correction factors. We calculated the ΔG‡(298 K) values of the internal rotation by correcting zero‐point vibration energies, thermal vibration energies, and entropies. We performed CISD/6–31G*//MP2/6–31G* calculations and found the ΔG‡(298 K) values for the internal rotation of Si2H6, Si2F6, and Si2Me6 to be 1.36, 2.06, and 2.69 kcal/mol, respectively. The performance of this level was verified by using G2 and G2(MP2) methods in Si2H6. According to our theoretical results, the ΔG‡(298 K) values were marginally greater than the ΔE‡(0 K) values in Si2F6 and Si2Me6 due to the contribution of the entropy. In Si2H6 the ΔE‡(0 K) and ΔG‡(298 K) values were coincidently similar due to a cancellation of two opposing contributions between zero‐point and thermal vibrational energies, and entropies. Our calculated ΔG‡(298 K) values were in good agreement with experimental values published recently. In addition, we also performed MM3 calculations on Si2H6 and Si2Me6. MM3 calculated rotational barriers and thermodynamic properties were compared with high level ab initio results. Based on this comparison, MM3 calculations reproduced high level ab initio results in rotational barriers and thermodynamic properties of Si2H6 derivatives including vibrational energies and entropies, although large errors exist in some vibrational frequencies. © 1997 John Wiley & Sons, Inc. J Comput Chem 18: 1523–1533, 1997

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Electron-diffraction studies of tetramethylsilane and hexamethyldisilane, and discussion of the lengths of Si-C bonds

Cited by 215 publications

References 21 publications

Molecular Structure of 1,2-Bis(trifluoromethyl)-1,1,2,2-tetramethyldisilane in the Gas, Liquid, and Solid Phases: Unusual Conformational Changes between Phases

Molecular Structure of 1,2-Bis(trifluoromethyl)-1,1,2,2-tetramethyldisilane in the Gas, Liquid, and Solid Phases: Unusual Conformational Changes between Phases

Gas-phase structures of sterically crowded disilanes studied by electron diffraction and quantum chemical methods: 1,1,2,2-tetrakis(trimethylsilyl)disilane and 1,1,2,2-tetrakis(trimethylsilyl)dimethyldisilane

Rotational barriers of disilane, hexafluorodisilane, and hexamethyldisilane:Ab initio, density functional, and molecular mechanics (MM3) studies

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