A. Almenningen

Structure and barrier of internal rotation of biphenyl derivatives in the gaseous state: Part 1. The molecular structure and normal coordinate analysis of normal biphenyl and pedeuterated biphenyl

Abstract The structures of the title compounds have been determined in the gaseous state. Both static and dynamic models have been applied. The structure parameters are found to be: r(C1C1′) = 1.507(4) and 1.489(4). r(C1C2) = 1.404(4) and 1.403(6), r(C2C3)= 1.395(5) and 1.396(8), r(C3C4) = 1.396(5) and 1.398(13), r(CH) = 1.102(2) and r(CD) = 1.095(2), ∠C2C1C6 = 119.4(4) and 117.9(4), ∠/C1C2C3 = 119.4(4) and 121.3(4) respectively for C12H10 and C12D10. Distances, re, are in A and angles, ∠α, in degrees. Both molecules are non planar with a torsional angle equal to 44.4(1.2) and 45.5(1.6) for C12H10 and C12D10 derived from the dynamic model using the potential function V(o) = (V2/2)(1 − cos 2o) + (V4/2)(1 − cos 4o) where V2 = 0,5(1.1) and -0.6(1.9) kJ mol−13 V4 = −6.2(2.3) and −9.5(3.6) kJ mol−1 for C12H10 and C12D10, respectively. The barriers at O° are 6.0(2.1) and 9.9(3.0) kJ mol−1, and at 90° 6.5(2.0) and 9.2 (2.6) kJ mol−1, respectively for C12H10 and C13D13. Uncertainty is one standard deviation from least-squares refinement using a diagonal weight matrix. With the exception of the torsional angles all the geometrical parameters for C12H10 and C12D10 are the same both comparing the two compounds and the results obtained in the gas phase and in the crystal, the experimental errors taken into consideration.

On the molecular structure of dicyclopentadienyllead

Abstract The electron scattering pattern from gaseous (C 5 H 5 ) 2 Pb has been recorded from s = 1.25 A −1 to 35.0 A −1 . Beyond this point the molecular intensity is lost in the background. The bond lengths are: C 1 C 2 = 1.430± 0.006 A, C 1 H 1 = 1.105±0.018 A, PbC = 2.778 ± 0.016 A. The ligand rings are not parallel, the angle between the planes being 45°±15°. The scattering pattern from (C 5 H 5 ) 2 Sn has been recorded from s = 1.25 A −1 to 24.0 A −1 . The bond lengths are C 1 C 2 = 1.431±0.009 A, C 1 H 1 = 1.142±0.056A, SnC = 2.706±0.024 A. The ligand rings are not parallel, the angle between the planes being about 55°.

The molecular structure of decamethylferrocene studied by gas phase electron diffraction. Determination of equilibrium conformation and barrier to internal rotation of the ligand rings

Abstract The molecular structure of decamethylferrocene, (η-C 5 Me 5 ) 2 Fe, has been determined by gas phase electron diffraction. The FeC and C(Cp)C(Cp) bond distances, 2.064(3) and 1.439(2) A, respectively, are indistinguishable from those in ferrocene, Cp 2 Fe. But, while the equilibrium conformation of gaseous Cp 2 Fe is eclipsed ( D 5h ), the equilibrium conformation of (C 5 Me 5 ) 2 Fe is staggered ( D 5d ) with a barrier to internal rotation of the ligand rings V 5 = 1.0(0.3) kcal mol −1 . And while the CH bonds in Cp 2 Fe are bent about 4° out of the plane of the C 5 ring towards the metal atom, the C(Cp)C(Me) bonds in (C 5 Me 5 ) 2 Fe are bent 3.4(0.5)° out of the plane in the opposite direction.

Dynamic Jahn–Teller effect and average structure of dicyclopentadienylcobalt, (C5H5)2Co, studied by gas phase electron diffraction

The molecular structure of (C5H5)2Co has been determined by gas phase electron diffraction. The best agreement between calculated and experimental intensity curves is obtained with a model with eclipsed C5H5 rings (symmetry D5h), but a model with staggered rings (symmetry D5d) cannot be ruled out. The mean CoC and CC bond distances are 2.119(3) A and 1.429(2) A respectively. The average angle between the CH bonds and the C5 ring is 2.1(0.8)°. The value obtained for the CC vibrational amplitude, l(CC) = 0.055(1) A, is significantly larger than the amplitude calculated from a molecular force field and the corresponding amplitudes in (C5H5)2Fe and (C5H5)2Ni determined by electron diffraction, and confirms the presence of a dynamic Jahn—Teller effect of the magnitude calculated from ESR data. The average structure is compared with those of the metallocenes of the other first row transition elements.

Molecular Structure of Dicyclopentadienylberyllium (C5H5) 2Be

The molecular structure of gaseous (C5H5) 2Be has been determined from electron‐scattering data. The molecule consists of two planar, symmetrical C5H5 rings. C1–C2 = 1.424±0.002 A and C1–H1 = 1.070±0.005 A. The rings are parallel and staggered with a vertical ring—ring distance h = 3.37±0.03 A. The CH skeleton thus has point group symmetry D5d. The beryllium atom may occupy two alternative positions on the fivefold rotation axis h = 1.485±0.005 A from one ring and h2 = 1.980±0.010 A from the other. The complete molecule thus has point group symmetry C5v.It appears then that the potential energy curve of the beryllium atom has two minima. This is readily understood from an ionic binding model. The discrepancy between the values found for h and h1+h2 is believed to be due to intramolecular motion.

The molecular structure of beryllocene, (C5H5)2Be. A reinvestigation by gas phase electron diffraction

Abstract The electron scattering pattern of gaseous dicyclopentadienylberyllium, Cp 2 Be, has been recorded from s = 2.00 to 39.00 A −1 with a nozzle temperature of about 120°C. Molecular models of D 5 d symmetry or models containing one π-bonded and one σ-bonded Cp ring are not compatible with the data. The possibility the gaseous Cp 2 Be consists fo a mixture D 5 d and π-Cp, σ-Cp conformers is considered and rejected. A model of C 5 v symmetry can be brought into satisfactory agreement with the data. It is also found that a slip sandwich model obtained from the C 5 v model by moving sideways the ring which is at the greatest distance from Be, while keeping the two rings essentially parallel is compatible with the electron diffraction data. The best fit between experimental and calculated intensity curves is obtained with a model with a sideways slip of 0.8(1) A. This model is similar to that indicated by the X-ray diffraction investigations by Wong and coworkers [4,5]. It is suggested that the potential energy of the molecule does not change much as the magnitude of the slip changes and that the molecule thus undergoes large amplitude vibration.

The molecular structure of di(μ-1-propynyl)bis(dimethylaluminium), [(CH3)2Al(μ-CCCH3)]2, determined by gas phase electron diffraction

Abstract The electron scattering pattern of di(μ-1-propynyl)bis(dimethylaluminium) (I) has been recorded from s = 2.50 to 36.50 A −1 with a nozzle temperature of 88±6 °C. Models of D 2h symmetry (with the CC bonds perpendicular to the Al⋯Al vector) were not compatible with the electron diffraction data. A model of C 2h symmetry could be brought into satisfactory agreement with the data. The structure parameters obtained by least squares calculations on the intensity data suggest that (I) may be regarded as consisting of two somewhat distorted (CH 3 ) 2 AlCCCH 3 units which are joined by donation of π-electrons from the CC bond of each unit into an empty atomic orbital on the Al atom of the other unit.

Cubane. molecular structure determined by gas-phase electron diffraction

Abstract The electron-diffraction data of gaseous cubane are consistent with Oh symmetry and the two geometrical parameters have been determined: τα(CC) = 157.5(1) pm and τα(CH) = 110.0(6) pm. Root-mean-square amplitudes of vibration have been determined from the electron diiffraction data and they compare well with values calculated from a symmetry force field fitted to experimental frequencies. Contribution to the intensity from multiple scattering has been shown to be small but significant. The CC bond is much longer than in cyclobutane.

The molecular structure of high- and low-spin 1,1′-dimethyl-manganocene determined by gas phase electron diffraction

Abstract The electron diffraction pattern of 1,1′-dimethyl-manganocene has been recorded from s = 3.00 to 42.00 A −1 . The gas is found to contain two geometrically distinct species. The most abundant species, mole fraction x = 0.62(4), has a MnC bond distance R(MnC) = 2.433(8) A and vibrational amplitude (MnC) = 0.111(8) A. By comparison with the structure of the essentially high-spin complex (C 5 H 5 ) 2 Mn where R(MnC) = 2.38 A, it is concluded that the most abundant species is in the high-spin, 6 A 1 g , state. The less abundant species, x = 0.38(4), has an MnC bond distance R(MnC) = 2.144(12) A and vibrational amplitude (MnC) = 0.160(16) A. This species is assumed to be in a low-spin, 2 E 2 g , state. The large MnC vibrational amplitude of the low-spin species is consistent with the existence of a dynamic Jahn-Teller effect involving the ring tilting modes.

The molecular structure of S-triazine in the gas phase determined from electron diffraction, infrared/raman data and ab initio force field calculations

Abstract The gas phase molecular structure of s-triazine has been determined from electron diffraction data. Experimental vibrational parameters proved consistent with those from the 4-21G force field after scaling onto infrared/Raman frequencies, as well as after direct scaling on electron diffraction data. The analysis resulted in the following r g / r ° α -parameters CN = 1.338(1) A, CH = 1.106(8) A, ∠CNC = 113.9(1), ∠NCN = 126.1, ∠HCN = 116.9. The (new) r g – r e (4-21G) correction for aromatic CN is 0.006(1) A.