Showing papers on "Tetrahedral molecular geometry published in 1973"

Assignment of ν2 (E) and ν4 (F2) of tetrahedral species by the calculation of the relative Raman intensities: The vibrational spectra of VO43−, CrO42−, MoO42−, WO42−, MnO4−, TcO4−, ReO4−, RuO4, and OsO4

Abstract: A new method has been developed to assign the frequencies ν2(E) and ν4(F2) in tetrahedral molecules and ions. The method employs the calculation of the relative Raman intensities and has been applied to VO43−, CrO42−, MoO42−, WO42−, MnO4−, TcO4−, ReO4−, RuO4, and OsO4. The assignment of the frequencies has been further confirmed by measuring the infrared and Raman spectra of some of the ions and molecules in the same solvent. A more complete spectrum of TcO4− than earlier reported in the literature has been given.

Binary transition metal dinitrogen complexes. I. Matrix infrared and Raman spectra, structure and bonding of Ni(N2)n and Pd(N2)m(n = 1-4 and m = 1-3)

Abstract: The products of the cocondensation reactions of Ni and Pd atoms with N2 at 4.2-10'K are investigated by matrix isolation infrared and Raman spectroscopy and are shown to be binary dinitrogen complexes of the form of Ni(N2), and Pd(N2)m. Examination of the reaction products in pure 14N2,in 14N2/15N2, in dilute Ar/14N2, Ar/14N2/15N2 and Ar/14N5N matrices establishes the stoichiometries of the complexes to be respectively n = 1-4 and m = 1-3. Structural assignments can be made for most of the complexes on the basis of infrared and Raman activities and are found to be similar to the analogous carbonyls. Isotopic frequencies and integrated infrared absorption intensities, computed for the NN stretching modes of the individual dinitrogen complexes on the basis of the Cotton-Kraihanzel force field approximation and on isotopic intensity sum rules, are found to be in close agreement with the observed values. Ni(N2)4 in argon is a regular tetrahedral molecule with “end on bonded” dinitrogen. In nitrogen, however, it is slightly distorted. Calculations show that a substitutional site symmetry C2 for Ni(N2) satisfactorily accounts for all of the spectral lines observed for the complex in nitrogen.

Hindered rotational energy levels of a tetrahedron in a trigonal crystalline field

Abstract: The energy levels for the motion of a rigid tetrahedral molecule in a tetrahedral crystal field have been computed by the method developed by King and Hornig. The symmetry group of the Hamiltonian is T× T, where T is the tetrahedral group of rotations about body‐fixed axes and T is the tetrahedral group of rotations about space‐fixed axes.

Tetrahedral methane without 2s → 2p promotion and hybridization: Direct calculation of the effects of promotion and hybridization in CH4, NH3, H2O, and H2S

Abstract: Fairly accurate linear‐combination‐of‐atomic‐orbitals molecular‐orbital self‐consistent‐field (LCAO MO SCF) wavefunctions have been calculated for CH4, both with and without the constraint that the first two a1 MO's be the 1s and 2s SCF AO's of the C atom. The calculations were carried out for tetrahedral and distorted‐tetrahedral nuclear configurations, and it was found that the tetrahedral configuration is the most stable both with and without the constraint. To examine the effects of nonpromotional (zeroth‐order) hybridization in CH4, calculations were also carried out in which the s‐type basis functions (and four associated electrons) of the C atom were completely deleted and replaced with an appropriate effective nuclear charge. Again, a tetrahedral methane was obtained. Therefore we conclude that 2s → 2p promotion and/or hybridization does not cause the tetrahedral structure of CH4. Analogous calculations on H2O and NH3 show a decrease in bond angle due to the constraint from 106.7° to 98.1° for H2O...

A comparative quantum chemical study of ethylcarbonium ion and hydroxymethylcarbonium ion

Abstract: Nonempirical molecular orbital calculations of the energies of CH3CH (ethylcarbonium ion) and HOCH (hydroxymethylcarbonium ion) as a function of rotation about the CC or CO bonds and deviation from coplanarity at the carbonium ion center are reported. As expected, and in agreement with previous work, both carbonium centers are planar and there is no barrier to rotation in the planar ethylcarbonium ion. However, for the planar configuration at carbon, the conjugative interaction between oxygen and carbon produces a barrier to rotation about the CO bond of HOCH of 19.6 Kcal/mole. When a pyramidal geometry is imposed upon the carbonium ion center of CH3CH, a typical three-fold barrier results. As the deviation from coplanarity increases there is a regular increase in the barrier height (1.72 Kcal/mole at the tetrahedral geometry), but the energy minimum remains at the same position in each case (60°). For HOCH, imposition of a pyramidal geometry on the carbonium ion center causes a change in both rotational barriers. One decreases slightly (from 19.6 to 15.4 Kcal/mole) and the other increases to 30.5 Kcal/mole. There is an accompanying change in the position of the minimum of the rotational potential, from 90° towards the gauche structure.

X-Ray crystal structure of the thiamine hydrochloride–copper(II) complex

Abstract: In the molecular structure of the thiamine hydrochloride·CuCl2 complex, the organic cation is closely surrounded by three copper tetrachloride anions whose configurations deviate significantly from ideal tetrahedral geometry.

Single-crystal polarized electronic and electron spin resonance spectra of dichlorobis(triphenylphosphine oxide)copper(II)

Abstract: The polarized single-crystal electronic and esr spectra of dichlorobis(triphenylphosphine oxide)copper(II) have been recorded and the spectral properties have been interpreted on the basis of a compressed tetrahedral geometry in C2 symmetry

Long‐range intermolecular forces in crystalline solids

Abstract: Expressions for the multipole interaction elements of the dynamical matrix are obtained using the rigid molecule approximation and the Coulomb interaction between the composite ions of the molecules in an ionic molecular crystal. It is shown that this formulation includes the electronic polarization effects. The monopole, dipole, quadrupole, and octupole contributions are calculated for model crystals of simple cubic structure having linear and tetrahedral molecules as basis. The effect of multipole interactions is found to be very significant. The neglect of multipole interactions in the calculation of translation coefficients of the lattice with linear molecule basis introduces errors as large as 30% along the [q00] direction. A similar calculation with the more complex tetrahedral molecule basis shows an increase in the errors to as large as 240%. In general the magnitude of multipole coefficients is seen to increase with the increasing complexity of the molecular basis.

Calculation of vibrational spectra and force and vibrational-rotational constants of germanium halides of the type GeHnX4−n (X=F, Cl, Br, I; n=0 to 2)

Abstract: Calculations are made of the frequencies, the form of the normal vibrations, and the constants of the potential energy of displacements of atoms during normal vibrations of germanium halides of the type GeHnX4−n (X=F, Cl, Br, I; n=0 to 2) and their deuterium replacements. For displacements of atoms during normal vibrations a calculation is made of the constants of vibrational-rotational interaction in the molecules GeHX3 and GeX4. The validity of the calculation is confirmed by the way in which the sum rule for the ζ- and τ-constants is fulfilled. The mean-square amplitudes are calculated for tetrahedral molecules GeX4 (X=F, Cl, Br, I). An analysis is given of the strong field of germanium halides GeHnX4−n in connection with properties of the structure of the Ge-halide bond.