Arne Haaland

On the molecular structure of ferrocene, Fe(C5H5)2

Abstract Electron diffraction studies of ferrocene vapor at 140° show that the free molecule has an eclipsed ( D 5 h ) equilibrium configuration with a small barrier to internal rotation. The barrier is estimated to be about 1.1 kcal/mole. The principal molecular parameters are: CC, 1.431 ± 0.005 A; FeC, 2.058 ± 0.005 A, and CH, 1.122 ± 0.020 A. The CH bonds seem to be bent about 5° out of the plane of the C 5 ring towards the iron atom.

A modification of the Schomaker—Stevenson rule for prediction of single bond distances

Abstract A modification of the Schomaker—Stevenson rule: c = 8.5 pm, n = 1.4, significantly reduces the discrepancy between experimental calculated bond lengths for every polar bonds between main group elements.

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 structures of dicyclopentadienylvanadium, (C5H5)2V, and dicyclopentadienylchromium, (C5H5)2Cr, determined by gas phase electron diffraction

The molecular structures of (C5H5)2V and (C5H5)2Cr have been determined by gas phase electron diffraction. The best agreement between calculated and experimental curves is obtained for models with eclipsed C5H5 rings (symmetry D5h), but models with staggered rings (symmetry D5d) cannot be definitely ruled out. The MC and CC bond distances are 2.169(4) and 1.431(2) A respectively in (C5H5)2Cr, and 2.280(5) and 1.434(3) A respectively in (C5H5)2V. The CH bonds in (C5H5)2Cr are bent 2.9(1.1)° out of the plane of the carbon atoms towards the metal atom. The molecular structures of the known di-π-cyclopentadienyl compounds of the first row transition elements are compared in the light of what is known about their electronic structures.

The accuracy of the pseudopotential approximation. I. An analysis of the spectroscopic constants for the electronic ground states of InCl and InCl3 using various three valence electron pseudopotentials for indium

Spectroscopic constants for InCl and InCl3 are determined by a coupled cluster procedure using relatively large basis sets and an energy‐consistent semilocal three valence electron pseudopotential for indium. Possible errors within the pseudopotential approximation are discussed in detail by comparison of available pseudopotentials adjusted through different techniques. Core‐polarization corrections and the deviation from a point core approximation are discussed. These corrections, however, do not lead to more accurate bond distances as compared to the experimental results. Differently adjusted three valence electron pseudopotentials yield quite different results for the bond distances of InCl and InCl3. The single‐electron adjusted energy‐consistent pseudopotential of Igel‐Mann et al. [Mol. Phys. 65, 1321 (1988)] yields the best results and therefore, this pseudopotential has been chosen for all further investigations on molecular properties. The Dunham parameters for InCl are calculated by solving the v...

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.

On the molecular structure of dicyclopentadienylmagnesium

Abstract The molecular structure of (C 5 H 5 ) 2 Mg has been determined by gas phase electron diffraction. The best agreement between calculated and experimental intensity curves is obtained for a model with eclipsed (C 5 H 5 ) rings (symmetry D 5h ), but a model with staggered rings (symmetry D 5d ) cannot be ruled out. The MgC and CC bond distances are 2.339(4) and 1.423(2) A respectively. The nature of the metal-to-ring bonding is discussed and it is concluded that (C 5 H 5 ) 2 Mg is best regarded as a covalent rather than an ionic compound.

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.

On the molecular structure of dimethylaluminium fluoride tetramer, [(CH3)2AIF]4

(CH3)2AlF has been studied by gas phase electron diffraction. The compound is tetrameric under the experimental conditions. The main molecular parameters are R(AlC) 1.947 (4), R(AlF) 1.810 (3) A, < CAlC 131.2 (1.9)°, < FAlF 923 (1.2)° and < AlFAl 146.1 (2.6)° the Al4F4 ring being puckered. The factors determining the degree of association of compounds of the type R2AlX (X = F,OR′, NR′2, Cl, SR′ and PR′2) are discussed, and it is suggested that Pitzer strain may be a significant factor in some cases.