Orbital Valence Force Field Research Articles

Vibrations of the tetrahedral AlCl4− ion in crystals: An estimation of crystal environmental effects on the spectra of the chloroaluminate ion in crystals

AbstractForce constans for AlCl4− in a series of alkali metal compound crystals were calculated using an orbital valence force field. The calculated force constants were utilized to estimate, by empirical methods, the spreads in AlCl bond lengths and ClAlCl angles caused by crystalline environmental effects. They are of the order of few hundredths of an ångstrom and a few degrees, respectively. These variations are compared and correlated with the structure details available in the literature for these ions in crystals.

Etude comparative des hexahydrido-et des hexadeuteridoaluminates de lithium et de sodium. I - Spectres raman et infrarouge de Li 3-et Na 3AlH 6, et Li 3AlD 6

Raman and Infrared spectra of Lithium and Sodium hexahydrio- and hexadeuteridoaluminates Li 3AlH 6, Na 3AlH 6 and Li 3AlD 6 have been investigated in order to study metal-hydrogen interactions. A vibrational analysis has been performed. Several force field models (Urey-Bradley, Orbital Valence force field, Shimanouchi, Murrell).have been used in order to compute the force constants of Al-H bonds. No significative difference has been observed between the results obtained from the various models, and the environnement of aluminum has been thus well determined : AlH 6 3− ions form an almost perfect octahedron in Li 3AlH 6 and a distorted one in Na 3AlH 6.

Vibrational analysis and ab initio molecular orbital calculations of the molecular force constants of gaseous CF 4 and SiF 4

The molecular potential constants of gaseous CF 4 and SiF 4 have been evaluated using approximate force fields and ab initio quantum mechanical methods. A recently developed three-parameter approximate force field, called the adjusted valence force field (AVFF), is found to give force constants for CF 4 and SiF 4 that are in reasonably good agreement with published values based on detailed analysis of vibrational data (including isotopic frequencies and Coriolis constants) and other three-parameter approximate force fields, such as the Urey—Bradley force field (UBFF) and the orbital valence force field (OVFF). In the ab initio studies, force constants were calculated at several basis set levels; correlation effects were included by applying second-order Möller Plesset theory. At the highest level of the theory (6–31 G* basis set), the ab initio force constants for CF 4 are in very good agreement with the most accurately derived values reported in the literature. The ab initio force constants computed for SiF 4 are in reasonable accord with accurately determined values, but the agreement is not as good as that obtained for CF 4.

The calculations of orbital valency force field constants of methane, silane and germane

The Orbital Valency Force Field treatment of Tyson, Claassen and Kim has been applied to the XY 4, XY 3Z, and XY 2Z 2 isotopes of methane, silane, and germane. Four harmonic force constants of XH 4 species predict the harmonic frequencies of isotopic species within the range of their uncertainties. Four constants determined from the fundamentals of XH 4 species and small anharmonicity corrections in isotopic masses were used to calculate fundamentals of various isotopic species, and they are compared with the observed values. Good agreement obtained between the calculated and observed values, and the facility which their treatment offers for calculations of isotopically substituted species, suggest that their method can be used to predict the as yet unknown frequencies of isotopic species, thereby assisting with spectral assignments.

Effect of Environmental Cations on Force Constants, Vibrational Mean Amplitudes and Bond Order of Metaloxygen Bonds in Some Octahedral Oxyanions

Abstract The general valenoe force field (GVFF), modified orbital valence force field (MOVFF), and modified Urey-Bradley force field (MUBFF) have been employed to calculate the force constants of octahedral Te6+o6, and Ti4+o6 anions in the presence of different environmental cations. The mean amplitudes and generalized mean square amplitudes of vibrations for these anions at temperatures; O°K,298. 16°K, and 500°K have also been calculated. Further, the metaloxygen bond order was estimated with the help of general valence stretching force constants. The effects of environmental cations on the force constants, mean amplitudes and π-bonding of metal-oxygen bonds have been critically discussed. The effect of atomic masses of anions on the ooriolis coupling constants of ‘fiu species has also been outlined.

Vibrational analysis of the uranium hexachloride species in oxidation states of IV, V and VI

The i.r. and Raman data for the uranium hexachlorides (UCl 6, UCl 6 − and UCl 6 2−) are reported. The vibrational frequencies are assigned on the basis of an O h point group symmetry, and using the modified Urey-Bradely Force Field (MUBFF) and the Molecular Orbital Valence Force Field (MOVFF), a Normal Coordinate Treatment (NCT) was made. The trend of frequencies with oxidation state and counter ion, and the primary stretching force constant (K) variation with oxidation state and non-bonding valence electrons is discussed.

Intramolecular Force Field of Some Tetrahedral Thio and Seleno Anions

Abstract The orbital valence force field (OVFF) and the Urey- Bradley force field (UBFF) have been employed to evaluate the force constants of thio and seleno anions of VA, VB, VIB and VIIB group atoms of the periodic table. These constants were utilized to examine the relative strength of chemical bonds in isoelectronic sequences. Further, for these anions, the variation of the ratio L12/L21 with the mass coupling term (T = G12 √|G|) has been studied. This appears to be an excellent support to the extended L-matrix approximation **.

Force Constants and Mean Amplitudes of Vibration of Some Octahedral Anions

Abstract The modified orbital valence force field (MOVFF) has been employed to compute the force constants for FeF6 3-, GaF6 3-, InCl6 3-, SbCl6 − and M6+O6 (M = Mo, W and Te). The general valence force constants and mean amplitudes of vibration have also been calculated for M6+O6 (M = Mo, W and Te) at temperatures: T = O°K, T = 298.16°K and T = 500°K. The results have been briefly discussed. The orbital valence force field (OVFF) suggested by Heath and Linnett1 has been applied by several workers(2-5) for octahedral XY6 type systems. In some cases large discrepancy occurs between observed and calculated frequencies when four OVFF constants have been used. Recently Ramaswamy and Muthusubramanian6 have successfully applied the modified orbital valence force field (MOWF) for some complex halides of transition metals O f xY6 type. The results are very encouraging, therefore, it was thought worthwhile to apply the modified orbital valence force field (MOVFF) to some octahedral anions: FeF3- 6, GaF3- 6, InCl3-...

Normal coordinate analysis of tantalum(I) and niobium(I) hexahalide anions

Urey-Bradley force field (UBFF) and orbital valence force field (OVFF) techniques have been applied to the hexachloride and the hexabromide anions (O h symmetry) of tantalum(I) and niobium(I). Trends in stretching force constants have been discussed on the basis of (i) the periodic position of the central metal atom and (ii) the nature of the halide ligands. Comments have been made also on the suitability of the force fields used.

Intramolecular Force Field of some Tetrahedral Molecules and Ions

Abstract The orbital valence force field (OVFF), and the Urey-Bradley force field (UBFF) have been employed to calculate the force constants for six molecules and ions (AlCl4 -, AlBr4 -, AlI4 -, Til4 - , Os16O4 , and Os18O4). The results have been discussed in the light of the relative stability of the bonds. The applicability of the Lennard-Jones potential is also examined. The kinetic constants have been computed and the results have been correlated with the corresponding force constants.

Orbital Valence Force Field Constants of Tetrachlorides, Tetrabromides and Tetraiodides of Titanium, Zirconium and Hafnium

Abstract The orbital valence force field has been employed to calculate the force constants for tetra-chlorides, tetrabromides, and tetraiodides of titanium, zirconium, and hafnium making use of recent vapor-phase Raman spectral data. The results are compared with the Urey-Bradley force constants, and it has been found that these are well comparable. The applicability of the Lennard-Jones potential has been examined to understand the nature of non-bonded interactions. The force constants have also been utilized to study the relative strength of the chemical bonds in tetrahalides and hexahalide anions

Orbital valency force field: a good approximation to general valence force field for XY 4 ( Td) and XY 3 ( D3h) type molecules

Analytical expressions are derived for determining the symmetry force constants of XY 4 (T d) and XY 3 (d 3h) typs molecules in the orbital valency force field model, which proves to be very useful in the interpretation of the structure and bonding in those molecules. The results obtained are compared with the values of symmetry force constants determined using additional data. The orbital valency force field values are generally found to be in good agreement with those of the general valence force field model. The physical significance of internal force constants is discussed and a constraint for the symmetry force constants is given.

On the application of OVFF to MX6 type ions

Abstract Force constants for nine ions belonging to Oh point group have been evaluated by using Orbital Valence Force Field. The constants have been compared with their values obtained by using Urey-Bradley Force Field. The validity of the two methods has been discussed

Molecular Force Fields of Tungsten and Uranium Hexachlorides

Abstract Molecular force field studies of tungsten and uranium hexa-chloride have been carried out using the Urey-Bradley force field (UBFF) and the orbital valence force field (OVFF). Weighted least square adjustment has been used to fit the observed frequencies. Comments are also made on the suit-ability of the force fields used. The trends in stretching force constants have been discussed.

Orbital valence force field in hexahalide anions of O h symmetry

Orbital valence force field in hexahalide anions of O h symmetry

Molecular Constants of MnF6−2Anion

Abstract The normal coordinate analysis of XY6 type of anions and molecules employing different force fields is well established.1,2 Recently, the vibrational spectra and complete frequency assignment of MnF6 −2 has been reported by Flint.3 Using the available vibrational data the force constants have been evaluated employing three potential models viz. general valence force field (GVFF), Urey-Bradley force field (UBFF) and orbital valence force field (OVFF). The mean amplitudes of vibration and Bastiansen-Morino shrinkages have also been computed at two temperatures.

Normal coordinate analysis of selenium and tellurium hexahalide ions

A normal coordinate analysis has been applied to the hexachloride and hexabromide ions of tellurium and selenium, using the Urey-Bradley force field (UBFF) and the orbital valence force field (OVFF). It is observed that OVFF and UBFF are equally good for these ions. The stretching force constant K has been found to decrease as the internuclear distance increases for the hexahalide ions of the same metal, while the nonbonded repulsion force constant F is found to decrease as internuclear distance increases for the hexahalide ions containing the same halogen ligand.

Matrix-Isolation Raman and Infrared Spectra, Molecular Structure, and Force Constants for XeO3F2

Both the Raman and the infrared spectra of low-temperature matrix-isolated molecules of XeO3F2 are reported. D3h symmetry for the molecules is indicated. The observed fundamental frequencies in cm−1 are 806.7 (a1′), 567.4 (a1′), 631.7 (a2″), 375.4 (a2″), 894 (e′), 318 (e′), 190 (e′), and 361 (e″). Force constants are reported in terms of the orbital valency force field assumption.

Normal Coordinate Analysis of Some Hexahalide Anions of IV Group Elements

Abstract The normal coordinate analysis has been applied to the hexachloride and hexabromide of tin, titanium, zirconium and hafnium, using the Urey-Bradley force field (UBFF) and orbital valence force field (OVFF). It is observed that the stretching force constant increases as the oxidation number of the metal increases within isoelectronic series.

Raman Spectra for XeF2, XeF4, and XeOF4 Vapors, and Force Constant Calculations

Raman spectra of the vapor phase have been observed for XeF2, XeF4, and XeOF4. These, together with published infrared spectra, provide vapor values for all but one of the 19 vibrational frequencies of these three molecules. Normal coordinates and force constants are determined in terms of the orbital valency force field model, including repulsions between lone-pair electrons and fluorine atoms.