Kjell-Gunnar Martinsen

The molecular structure, conformations and vibrational spectra of 2,2-di(chloromethyl)-1,3-dichloropropane and 2,2-di(bromomethyl)-1,3-dibromopropane

Abstract The IR and Raman spectra of 2,2-di(chloromethyl)-1,3-dichloropropane (C(CH2Cl)4) and 2,2-di(bromomethyl)-1,3-dibromopropane (C(CH2BR)4) were recorded as melts and as solutes in various solvents. Spectra of the solids were observed at various temperatures between the melting points and 90 K. High pressure IR spectra (0–20 kbar) of the compounds were recorded between 300 and 450 K. The crystal structures of both compounds were determined by X-ray crystallographic measurements of single crystal at ca. 130 K. In the crystalline state both compounds exist in the D2d conformer, whereas in the melt and in solution an additional conformer probably of symmetry S4 was assigned supported by force constant calculations. Unlike neopentane and various chlorinated neopentanes with one, two or three chlorine substituents, no plastic crystalline phase was detected for the title compounds. The structure of both molecules were disordered with two molecules in the monoclinic unit cell (P21/n).

Molecular structure and force field of boron tribromide as determined from combined analysis of gas electron diffraction and spectroscopic data and supported by quantum-chemical density-functional calculations

Abstract The thermal-average parameters of BBr 3 at 21(1) °C were obtained from a conventional analysis of gas electron diffraction (GED) data ( r g (BBr) = 190.0(4) pm). The equilibrium structure and the force constants were refined from a joint analysis of the GED intensities and vibrational frequencies using different approximations. The simplest approximation (quadratic potential function in rectilinear coordinates) is suitable for the refinements of the equilibrium bond length ( r h e (BBr) = 189.6(4) pm) and the force constants of BBr 3 . The molecule is planar within the error limits. Quantum-chemical density-functional calculations supported planarity of the molecule.

Molecular structures of monomeric gallium trichloride, indium trichloride and lead tetrachloride by gas electron diffraction

Gas electron diffraction data for monomeric GaCl3, monomeric InCl3 and PbCl4 have been recorded with nozzle temperatures of about 380, 480 and 20 °C respectively. The data for GaCl3 and InCl3 are consistent with equilibrium structures of D3h symmetry and bond distances ra= 210.8(3) and 228.9(5) pm respectively. The data for PbCl4 are consistent with an equilibrium structure of Td symmetry and ra= 237.3(3) pm. Bond energies and distances from the literature show that the M–Cl bonds in MCl(g) are stronger, but longer, than in MCl3(g) for M = Al, Ga or In, and that M–Cl bonds in MCl2(g) are stronger, but longer, than in MCl4(g) for M = Ge, Sn or Pb. It is suggested that the relative weakness of the bonds in group-valent chlorides is due to the energy required to promote the Group 13 metal atoms from the 2P (s2p) ground states to 4P(sp2) valence states, or to promote the Group 14 metal atoms from 3P(s2p2) ground states to 5S(sp3) valence states. Further that the decreasing stability of the group-valent relative to subvalent chlorides as the Groups are descended is due both to increasing promotional energies and to decreasing M–Cl bond strengths.

Molecular structures of the sixth period metal pentachlorides,MCl5 (M = Ta, W or Re), determined by gaselectron diffraction; is Jahn–Teller distortion of WCl5quenched by spin–orbit coupling?

The molecular structure of TaCl 5 has been optimised under D 3h symmetry by density-functional theory calculations. Calculation of the molecular force field and vibrational frequencies showed that the optimised structure corresponds to a minimum on the full potential energy surface. Gas electron diffraction data of MCl 5 (M = Ta, W or Re), recorded with nozzle temperatures ranging from 130 to 210 °C, showed that WCl 5 and ReCl 5 are trigonal bipyramidal like TaCl 5 . Structure refinements based on molecular models of D 3h symmetry lead to satisfactory agreement between experimental and calculated intensities for each compound and yield the M–Cl bond distances (ax/eq): Ta 231.3(5)/226.6(4); W 229.1(4)/224.1(5); Re 226.2(12)/223.7(7) pm. Tungsten pentachloride is a d 1 compound and might have exhibited dynamic or static Jahn–Teller distortion from D 3h symmetry; it has been suggested that such distortion is quenched by strong spin–orbit coupling.

Gas-phase vibrational spectrum and molecular geometry of TeCl4

The gas electron diffraction pattern and the infrared spectrum of gaseous TeCl 4 have been measured and ab initio molecular orbital calculations performed for the TeCl 4 molecule using second-order Moller–Plesset theory (MP2) and a relativistic effective core potential. Applying a scaled quantum mechanical (SQM) method the complete (and up to now the best) force field of the molecule has been evaluated. Based on that SQM force field the complete assignment of the vibrational spectra of TeCl 4 has been performed. The electron diffraction analysis resulted in the following geometrical parameters: r a (Te–Cl ax ) = 243.5(5), r a (Te–Cl eq ) = 229.4 (5) pm, Cl ax –Te–Cl ax = 176.4(6), Cl eq –Te–Cl eq = 103.7(7)°. The molecular geometry is consistent with valence shell electron pair repulsion theory. Comparison with the respective parameters of Te(CH 3 ) 4 supports a previous bonding model for these compounds. Both the computations and the experimental data indicate a much less flexible structure for TeCl 4 than was found for Te(CH 3 ) 4 .

The molecular structure of dimethyltellurium dichloride by gas electron diffraction and ab initio calculations at the MP2 level

Abstract Ab initio calculations at the MP2 level and gas electron-diffraction data of (CH 3 ) 2 TeCl 2 show that the molecular structure is pseudo-trigonal bipyramidal with the two methyl groups occupying equatorial positions and the two Cl atoms axial positions. The bond distances are ( GED MP 2 ): TeC = 213.2(5)/214.6 pm, TeCl = 250.4(3)/261.8 pm and the valence angles ∠ CTeC = 97(5)° 97.6° ; ∠ ClTeCl = 170(2)° 170.8° .

Molecular structure of monomeric uranium tetrachloride determined by gas electron diffraction at 900 K, gasphase infrared spectroscopy and quantum-chemical density-functional calculations

The gas electron diffraction pattern of monomeric UCl4 has been recorded with a nozzle temperature of 900 K. The data are in good agreement with a model of Td symmetry and a U–Cl bond distance of ra= 250.3(3) pm. The root-mean-square vibrational amplitudes are l(U–Cl)= 8.9(3) pm and l(Cl ⋯ Cl)= 34.3(10) pm. The gas-phase infrared absorption spectra have been recorded from 25 to 3400 cm–1 at temperatures ranging from 700 to 900 K, and the t2 stretching and deformation modes have been assigned at ν3 337.4 and ν4 71.7 cm–1 respectively. The molecular structure of UCl4 has been optimised by density-functional calculations under D2d symmetry. It is tetrahedral with bond distance re= 251 pm. The calculations yield values for the IR-active modes which are in good agreement with the experimental counterparts. The ‘best values’ for the two IR-inactive frequencies were obtained by refining a diagonal symmetry force field to the four calculated (density functional) frequencies, the two observed frequencies and the vibrational amplitudes obtained by gas electron diffraction. The entropies of gaseous UCl4 calculated from these normal modes and a symmetry number of 12 corresponding to Td symmetry are in good agreement with the experimental counterparts.

The gas electron diffraction data recorded for UCl4 cannot beascribed to the chloride oxide UOCl4

A suggestion that gas electron diffraction data previously recorded for UCl 4 and found to be consistent with a tetrahedral molecular model are due to UOCl 4 is refuted.