Molecular structure of tetramethylgermane from gas electron diffraction

Csákvári, Éva; Rozsondai, B.; Hargittai, István

doi:10.1016/0022-2860(91)87109-u

Cited by 10 publications

(4 citation statements)

References 30 publications

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“…The Ge-C methyl bond length in Me 2 Ge(CCOMe) 2 is in good agreement with the corresponding bond length observed in Ge(Me) 4 , 195.8(4) pm. 15 The Ge-C ethynyl bond, as expected, is found to be considerably shorter than the Ge-C methyl bond. Similar shortening, also smaller, about 3 pm, was observed in Me 3 GeCCCl.…”

Section: Molecular Geometries and Conformationssupporting

confidence: 68%

An enormous vibrational motion: the gas-phase structure of dimethyl-bis(methoxyethynyl) germanium

et al. 2004

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The structure of dimethyl-bis(methoxyethynyl) germanium has been determined in the gas phase by electron diffraction utilising flexible restraints from quantum chemical calculations. Theoretical methods (B3LYP/6-311+G* and MP2/6-311+G*) predict a low barrier to rotation of the methoxy groups in the molecule in addition to low-frequency vibrations of the long ethynyl chains. In the equilibrium structure the Ge-C[triple bond]C angles of the two methoxyethynyl fragments in the molecule are computed to deviate by up to 4 degrees from the linear arrangement. As a consequence of low-frequency large-amplitude vibrational motion the experimental structure of these fragments without applying vibrational corrections deviates considerably from linearity, while the structure corrected for vibrational effects using the harmonic approximation and taking into account a non-linear transformation between internal and Cartesian coordinates (r(h1)) shows closer agreement with theory. The main experimental structural parameters of dimethyl-bis(methoxyethynyl) germanium (r(h1)) are: r(Ge-C)(mean), 192.5(1) pm; DeltaGeC =r(Ge-C(methyl))-r(Ge-C(ethynyl)), 4.5(5) pm, r(C[triple bond]C)(mean), 122.8(2) pm; r(C-O)(mean), 138.9(3) pm; DeltaCO =r(C(methyl)-O)-r(C(ethynyl)-O), 14.5(2) pm, r(C-H)(mean), 109.1(4) pm; [angle](X-C-H)(mean)(X = Ge,O), 109(1) degree; [angle]C(ethynyl)-Ge-C(ethynyl), 108.1(4) degree; [angle]C(methyl)-Ge-C(methyl), 113.4(5) degree; [angle]Ge-C[triple bond]C, 163(1) degree; [angle]C[triple bond]C-O, 176(2) degree; [angle]C-O-C, 115.2(6) degree; methoxy group torsion, tau, 36(9) degree from the position in which the C-O bond eclipses the further Ge-C(ethynyl) bond.

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Section: Molecular Geometries and Conformationssupporting

confidence: 68%

An enormous vibrational motion: the gas-phase structure of dimethyl-bis(methoxyethynyl) germanium

et al. 2004

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“…2,5 However, since the results from the microwave investigation are given as r s and the electron diffraction results as r g , the agreement is relatively good. The important structure parameters for (CH 3 ) 3 GeCl and (CH 3 ) 3 GeBr are compared with those obtained for (CH 3 ) 4-n GeX n (X ) F, Cl, or Br and n ) 0-4, except n ) 1 for X ) F) [1][2][3][4][5][6][7][8][9] in Table 6. For F-, Cl-, and Br-substituted germanium compounds, the Ge-C and Ge-X distances increase as the numbers of F, Cl, or Br atoms decrease.…”

Section: Discussionmentioning

confidence: 99%

“…From reports in the literature it is apparent that the Ge−X and Ge−C bond lengths in (CH 3 ) 4 - n GeX n (X = F, Cl, or Br and n = 0−4, except n = 1 for X = F) show a systematic decrease with increase in the value of n . − However, the data for the monohalo species trimethylchlorogermane and trimethylbromogermane are only partial in nature and are provided by microwave studies. , It was therefore decided to carry out full structural determinations on the molecules (CH 3 ) 3 GeX (X = Cl, Br) by gas-phase electron diffraction supported by theoretical calculations. An analogous trend in decreasing Ge−X bond length with increasing value of n has been observed for the M−Cl bond in the series of compounds (CH 3 ) 4 - n MCl n .…”

Section: Introductionmentioning

confidence: 99%

Molecular Structures of Trimethylchlorogermane, (CH₃)₃GeCl, and Trimethylbromogermane, (CH₃)₃GeBr, Obtained by Gas-Phase Electron Diffraction and Theoretical Calculations

Aarset

Page

2004

J. Phys. Chem. A

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The structures of trimethylchlorogermane ((CH3)3GeCl) and trimethylbromogermane ((CH3)3GeBr) have been determined by gas-phase electron diffraction (GED), augmented by the results from ab initio calculations employing second-order Møller−Plesset (MP2) level of theory and the 6-311+G(d) basis set. All the electrons were included in the correlation calculation. The results from the ab initio calculations indicated that these molecules have C 3 v symmetry, and models with this symmetry were used in the electron diffraction analysis. The results for the principal distances (r g) and angles (∠α) from the combined GED/ab initio study of trimethylchlorogermane (with estimated 2σ uncertainties) are: r(Ge−C) = 1.950(4) Å, r(Ge−Cl) = 2.173(4) Å, r(C−H) = 1.090(9) Å, ∠CGeC = 112.7(7)°, ∠CGeCl = 106.0(8)°, ∠GeCH = 107.8(12)°. The results for the principal distances (r g) and angles (∠α) from the combined GED/ab initio study of trimethylbromogermane (with estimated 2σ uncertainties) are: r(Ge−C) = 1.952(7) Å, r(Ge−Br) = 2.325(4) Å, r(C−H) = 1.140(28) Å, ∠CGeC = 114.2(11)°, ∠CGeBr = 104.2(13)°, ∠GeCH = 106.9(43)°. Local C 3 v symmetry and staggered conformation were assumed for the methyl groups.

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“…S2 and S8-S10 (ESI †), respectively. An inspection of Table S2 (ESI †) reveals an excellent agreement (R 2 = 0.9998) with the experimental r g bond lengths from an electron diffraction analysis of vapor-phase samples, [61][62][63][64][65] while perfect consistency (R 2 = 0.9999) was found for the carefully examined CMe 4 . 61 But such r g data 65 for PbMe 4 seem likely to be underestimated, especially for the PbÁ Á ÁH distance.…”

Section: Selection Of a Two-step Computational Protocolmentioning

confidence: 52%

¹J_CH couplings in Group 14/IVA tetramethyls from the gas-phase NMR and DFT structural study: a search for the best computational protocol

Nazarski

Makulski

2014

Phys. Chem. Chem. Phys.

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Four tetramethyl compounds EMe4 (E = C, Si, Ge, and Pb) were studied by high-resolution NMR spectroscopy in gaseous and liquid states at 300 K. Extrapolation of experimental vapor-phase C-H J-couplings to a zero-pressure limit permitted determining the (1)J(0,CH)s in methyl groups of their nearly isolated molecules. Theoretical predictions of the latter NMR parameters were also performed in a locally dense basis sets/pseudopotential (Sn, Pb) approach, by applying a few DFT methods pre-selected in calculations of other gas-phase molecular properties of all these species and SnMe4 (bond lengths, C-H stretching IR vibrations). A very good agreement theory vs. experiment was achieved with some computational protocols for all five systems. The trends observed in their geometry and associated coupling constants ((1)J(CH)s, (2)J(HH)s) are discussed and rationalized in terms of the substituent-induced rehybridization of the methyl group (treated as a ligand) carbon, by using Bent's rule and the newly proposed, theoretically derived values of the Mulliken electronegativity (χ) of related atoms and groups. All these χ data for the Group-14/IVA entities were under a lot of controversy for a very long time. As a result, the recommended χ values are semi-experimentally confirmed for the first time and only a small correction is suggested for χ(Ge) and χ(GeMe3).

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Molecular structure of tetramethylgermane from gas electron diffraction

Cited by 10 publications

References 30 publications

An enormous vibrational motion: the gas-phase structure of dimethyl-bis(methoxyethynyl) germanium

An enormous vibrational motion: the gas-phase structure of dimethyl-bis(methoxyethynyl) germanium

Molecular Structures of Trimethylchlorogermane, (CH₃)₃GeCl, and Trimethylbromogermane, (CH₃)₃GeBr, Obtained by Gas-Phase Electron Diffraction and Theoretical Calculations

¹J_CH couplings in Group 14/IVA tetramethyls from the gas-phase NMR and DFT structural study: a search for the best computational protocol

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Molecular structure of tetramethylgermane from gas electron diffraction

Cited by 10 publications

References 30 publications

An enormous vibrational motion: the gas-phase structure of dimethyl-bis(methoxyethynyl) germanium

An enormous vibrational motion: the gas-phase structure of dimethyl-bis(methoxyethynyl) germanium

Molecular Structures of Trimethylchlorogermane, (CH3)3GeCl, and Trimethylbromogermane, (CH3)3GeBr, Obtained by Gas-Phase Electron Diffraction and Theoretical Calculations

1JCH couplings in Group 14/IVA tetramethyls from the gas-phase NMR and DFT structural study: a search for the best computational protocol

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Molecular Structures of Trimethylchlorogermane, (CH₃)₃GeCl, and Trimethylbromogermane, (CH₃)₃GeBr, Obtained by Gas-Phase Electron Diffraction and Theoretical Calculations

¹J_CH couplings in Group 14/IVA tetramethyls from the gas-phase NMR and DFT structural study: a search for the best computational protocol