Lise Hedberg

Bond lengths in free molecules of buckminsterfullerene, c60, from gas-phase electron diffraction.

Electron diffraction patterns of the fullerene C60 in the gaseous state have been obtained by volatilizing it from a newly designed oven-nozzle at 730�C. The many peaks of the experimental radial distribution curve calculated from the scattered intensity are completely consistent with icosahedral symmetry for the free molecule. On the basis of this symmetry assumption, least-squares refinement of a model incorporating all possible interatomic distances led to the values rg(C1-C2) = 1.458(6) angstroms (�) for the thermal average bond length within the five-member ring (that is, for the bond fusing five- and six-member rings) and rg(C1-C6) = 1.401(10) � for that connecting five-member rings (the bond fusing six-member rings). The weighted average of the two bond lengths and the difference between them are the values 1.439(2) � and 0.057(6) �, respectively. The diameter of the icosahedral sphere is 7.113(10) �. The uncertainties in parentheses are estimated 2σ values.

Reinvestigation of the Molecular Structure of 1,3,5,7‐Cyclooctatetraene by Electron Diffraction

The molecular structure of 1,3,5,7‐cyclooctatetraene has been studied by a sector‐microphotometer technique using data extending to very much larger scattering angles than were obtained in earlier investigations. An application of the method of least squares to sector‐microphotometer data in electron diffraction worked out by one of us (KH) has led in three refinement stages to unusually precise values for the parameters. The following are the more interesting parameter values with standard errors. It should be noted these results do not include a possible error of up to 0.2% in the scale of the molecule because of uncertainties in the electron wavelength, nor do they include the effect of correlations among the observations on the standard errors, which we estimate might increase the standard errors by as much as the factor 2½. Molecular symmetry D2d,C=C=1.334±0.001 A,C–C=1.462±0.001 A,C–H=1.090±0.005 A,∠C=C–C=126.46∘±0.23∘,∠C=C–H=118.3∘±5.9∘,aC=C(=〈δl2〉C=C/2)=(103±7)×10−5,aC–C=(147±10)×10−5,aC1···C3=(25...

Nickel tetracarbonyl, Ni(CO)4. I. Molecular structure by gaseous electron diffraction. II. Refinement of quadratic force field

The molecular structure of gaseous nickel tetracarbonyl has been investigated by electron diffraction at room temperature. The analysis, based on an assumed Td molecular symmetry with corrections for the effects of vibrational motion, led to the following bond distances (rg) and amplitudes of vibration (l) with estimated uncertainties (2σ), all in angstroms: r (C=O) =1.141(2), r (Ni–C) =1.838(2), l (C=O) =0.039(2), l (Ni–C) =0.059(3), l (Ni⋅⋅⋅O) =0.061(3), l (C⋅⋅⋅C) =0.124(17), l (C⋅⋅⋅O) =0.176(11) and l (O⋅⋅⋅O) =0.244(34). The quadratic force field was refined using our structure and vibrational wave numbers from the literature in order to permit calculation of the distance corrections arising from vibrational averaging. The force constants are generally very similar to those from a previous spectroscopic study.

Molecular Structure of Dicyclopentadienylnickel (C5H5)2Ni

The structure of gaseous nickelocene has been determined at 110°C by electron diffraction using two independent sets of data. The molecule has the familiar ferrocenelike sandwich shape, but it differs from ferrocene in having weaker metal–carbon bonds and greater amplitudes of vibration for all distances affected by motion of the cyclopentadienyl rings as units. The simplest interpretation of the large inter‐ring amplitudes leads to the conclusion that the rings are rotating much more freely than in ferrocene. There is some slight evidence that the Ni–C bonds may not all be equivalent, corresponding to a structure that is not strictly symmetric (D2h or D2d), or alternatively that the molecular motions affecting the Ni–C bonds are unusual in a way which does not give rise to the expected essentially harmonic Ni–C amplitudes, either of which suggests the faint possibility of a Jahn–Teller effect. Based upon a symmetric sandwich conformation with freely rotating rings the principal distance (ra) and mean amp...

Molecular structure of di‐π‐cyclopentadienylcobalt, (C5H5)2Co, by gaseous electron diffraction

Gaseous cobaltocene (CoCp2) has been investigated by electron diffraction at a nozzle‐tip temperature of about 120 °C. As expected, the molecule has the sandwichlike structure previously found for ferrocene (FeCp2) and nickelocene (NiCp2). The data show that any distortion from D5h or D5d molecular symmetry arising from the degenerate electronic ground state (Jahn–Teller effect) is small. Accordingly, the structure was refined in terms of three types of symmetric models: one with an eclipsed conformation of the rings (D5h), one with a staggered conformation (D5d), and one with freely rotating rings. The best agreement was obtained with the freely rotating ring models. However, the differences are small and it is clear that if large‐amplitude torsional motion of the rings had been included in the D5h and D5d models, the agreement from them would have been about equally good. Based on the assumption that the equilibrium conformation of CoCp2 can be approximated by one of these very symmetric models, we conc...

The molecular structure of 1,1‐dichlorocyclopropane by gaseous electron diffraction using rotational constants as constraints and by abinitio gradient computation

The molecular structure of gaseous 1,1‐dichlorocyclopropane has been investigated using room‐temperature electron‐diffraction data with ground state rotational constants from published work introduced as constraints. The models of the structure were specified by parameters generating geometrically consistent distance sets of the type rz = rα0. The vibrational corrections necessary for the conversion of these to rg and to the ra set suitable to the diffraction data, and for the conversion of the observed B0 rotational constants to Bz, were calculated from a quadratic force field very similar to that deduced by others. The results leave no doubt that the unique C–C bond is significantly longer than the other C–C bonds as predicted from theoretical calculations. The important distances (rg), angles (&α), and rms amplitudes of vibration (l) with associated uncertainties estimated as 2σ are r(C–H) = 1.109(8) A, 〈r(C–C)〉 = 1.511(3) A, Δr(C–C) = 0.041(11) A, r(C–Cl) = 1.759(2) A, &Cl–C–Cl = 112.6(2)°, &H–C–H = 1...

Reinvestigation of the molecular structure of gaseous beryllium borohydride BeB2H8 by electron diffraction

The structure of beryllium borohydride has been reinvestigated by gaseous electron diffraction at a nozzle temperature of 40 °C. The experiments were characterized by unusual photographic problems which were overcome with difficulty. The structure analysis led to the unexpected result that the molecule, or at least the major part of the free molecules, has a linear heavy‐atom structure, in agreement with conclusions based on an early electron‐diffraction investigation but in disagreement with those from more recent electron‐diffraction and spectroscopic studies which have generally favored triangular configurations. Our diffraction data were satisfactorily interpreted in terms both of molecules with configuration B–Be–B and with configuration Be–B–B. The data require the peripheral atoms of the molecule, or the principal species of the molecule, to be bonded to the central one through three hydrogen bridges giving the central atom sixfold coordination; the successful models have molecular symmetries D3d a...

Gas-phase electron diffraction study of the molecular structure of tungsten oxytetrafluoride, WOF4

Abstract The molecular structure of tungsten oxytetrafluoride has been studied in the gas phase by electron diffraction. A square pyramidal model with molecular symmetry C 4v , as indicated by vibrational spectroscopy, gives a good fit to the experimental data. Least squares refinement on the molecular intensity curves gives the following results for the principal geometrical parameters (uncertainties in parentheses are 2σ): r a (W=O) = 1.666 (0.007)A, r a (W-F)= 1.847 (0.002)A, ∠OWF = 104.8 (0.6)°, ∠FWF = 86.2(0.3)°.

Monomeric bivalent group 4B metal dialkylamides M[NCMe2(CH2)3CMe2]2(M = Ge or Sn), and the structure of a gaseous disilylamide, Sn[N(SiMe3)2]2, by gas electron diffraction

Reaction of Li[[graphic omitted]Me2](LiNR2) in n-C5H12 at 20°C with GeCl2·dioxan or SnCl2 affords the corresponding coloured crystalline diamagnetic metal(II) dialkylamide, M(NR2)2, which is monomeric (cryoscopy in C6H12), has a low first ionisation potential (6·90 eV for M = Ge, 6·80 eV for M = Sn), and furnishes the 2,2,6,6-tetramethylpiperidyl radical :NR2 upon photolysis; electron diffraction analysis of gaseous Sn[N(SiMe3)2]2 shows only the monomer at ca. 100°C and 10–2 atm, which has C2v symmetry, ∠NSnN = 96·0°, and Sn–N (av.)= 2·09 A.

High-Resolution Infrared and Electron-Diffraction Studies of Trimethylenecyclopropane ([3]-Radialene)

Combined high-resolution spectroscopic, electron-diffraction, and quantum theoretical methods are particularly advantageous for small molecules of high symmetry and can yield accurate structures that reveal subtle effects of electron delocalization on molecular bonds. The smallest of the radialene compounds, trimethylenecyclopropane, [3]-radialene, has been synthesized and examined by these methods. The first high-resolution infrared spectra have been obtained for this molecule of D3h symmetry, leading to an accurate B0 rotational constant value of 0.1378629(8) cm(-1), within 0.5% of the value obtained from electronic structure calculations (density functional theory (DFT) B3LYP/cc-pVTZ). This result is employed in an analysis of electron-diffraction data to obtain the rz bond lengths (in Å): C-H = 1.072(17), C-C = 1.437(4), and C═C = 1.330(4). The results indicate that the effects of rehybridization and π-electron delocalization affects each result in a shortening of about 0.05 Å for the C-C bond in radialene compared to ethane. The analysis does not lead to an accurate value of the HCH angle; however, from comparisons of theoretical and experimental angles for similar compounds, the theoretical prediction of 117.5° is believed to be reliable to within 2°.