Issue 22, 2004

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

Abstract

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, length as m-dash]C angles of the two methoxyethynyl fragments in the molecule are computed to deviate by up to 4° 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 (rh1) shows closer agreement with theory. The main experimental structural parameters of dimethyl-bis(methoxyethynyl) germanium (rh1) are: r(Ge–C)mean, 192.5(1) pm; ΔGeC = r(Ge–Cmethyl) − r(Ge–Cethynyl), 4.5(5) pm, r(C[triple bond, length as m-dash]C)mean, 122.8(2) pm; r(C–O)mean, 138.9(3) pm; ΔCO = r(Cmethyl–O) − r(Cethynyl–O), 14.5(2) pm, r(C–H)mean, 109.1(4) pm; ∠(X–C–H)mean (X = Ge,O), 109(1)°; ∠Cethynyl–Ge–Cethynyl, 108.1(4)°; ∠Cmethyl–Ge–Cmethyl, 113.4(5)°; ∠Ge–C[triple bond, length as m-dash]C, 163(1)°; ∠C[triple bond, length as m-dash]C–O, 176(2)°; ∠C–O–C, 115.2(6)°; methoxy group torsion, τ, 36(9)° from the position in which the C–O bond eclipses the further Ge–Cethynyl bond.

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

Article information

Article type
Paper
Submitted
16 Aug 2004
Accepted
06 Oct 2004
First published
25 Oct 2004

Dalton Trans., 2004, 3878-3882

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

K. B. Borisenko, R. N. Yezhov, S. V. Gruener, H. E. Robertson and D. W. H. Rankin, Dalton Trans., 2004, 3878 DOI: 10.1039/B412565G

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