Vibrational Normal Coordinate Analysis Research Articles

EPR, 1H, 31P ENDOR, and IR study of Cu(II) and Ni(II)(O,O-dimethyldithiophosphate)(N,N-dimethyldithiocarbamate) complexes

Polycrystalline samples of Cu(Me 2dtp)(Me 2dtc) and Ni(Me 2dtp)(Me 2dtc) complexes are studied by means of EPR, ENDOR, and vibrational normal coordinate analysis. On the basis of EPR and ENDOR experimental results, the spin density distribution on 1H and 31P nuclei of the mixed ligand and parent copper dithiophosphate and dithiocarbamate complexes is compared. Comparison between vibrational spectra and normal coordinate analysis data on Ni(Me 2dtp)(Me 2dtc), Ni(Me 2dtp) 2 and Ni(Me 2dtc) 2 enabled the conclusion that the structure of the NiS 4 fragment in the mixed complex is retained close to that in the bis-chelate complexes.

Vibrational analysis of the trigonal bipyramidal NbCl 5 and NbBr 5 molecules

Vibrational normal coordinate analysis has been made for NbCl 5 and NbBr 5 molecules with D 3 h symmetry and using Wilson's GF matrix method. The observed frequencies are quantitatively assigned on the basis of the calculated potential energy distribution values for each vibration. The values of force constants for NbCl′ (axial) and NbCl (equatorial) bonds in NbCl 5 equal 194 and 261 Nm −1, respectively. The corresponding values for NbBr 5 are 142 and 217 Nm −1. These values are discussed in view of the bonding and structure of both compounds.

Raman studies in CuTCNQ: Resonance Raman spectral observations and calculations for TCNQ ion radicals

The Raman spectra of thin film, and powdered crystalline forms of CuTCNQ have been studied and analyzed in connection with their electronic spectra and vibrational normal coordinate analysis and molecular orbital results. Nonresonance and resonance Raman conditions have been obtained by using different sample forms and source wavelengths. Shifts of TCNQ− and TCNQ= vibrational frequencies from those of TCNQ0 due to changes in the charge on the TCNQ moiety have been calculated in terms of molecular orbital parameters and TCNQ0 vibrational frequencies. The resonance Raman enhancement of TCNQ− in the red band system is shown to be of Franck–Condon origin and its resonance Raman spectrum in this region is calculated. Transformation of CuTCNQ to TCNQ0 with different laser lines is explained on the basis of photoinduced electronic transitions.

MO and vibrational normal coordinate calculations of 1,1,4,4,-tetramethyl-1,4-diazonia-2,5-diboratacyclohexane

All-valence-electron IEHT and CNDO/2 molecular orbital calculations and an infrared vibrational normal coordinate analysis were carried out for the study of the bonding in the title compound with its six-membered ring, repeating, all-four-coordinated NBC sequence. Results of these calculations agree qualitatively with one another as well as with the residual electron density map calculated from the observed and calculated structure factors in an X-ray structure determination, which showed that the BC bond is relatively stronger than the BN bond in this molecule. The results of MO calculations also indicate that partial electron transfer from the nitrogen to the boron atom has occurred in the formation of the boronnitrogen bond. The stretching force constants for the BN and BC bonds are 2.19 and 3.33 mdyn Å −1, respectively.

The Infrared Spectra and Normal Coordinate Treatments of X3M–Mn(CO)5(X=Cl, Br, and I; M=Si, Ge, and Sn). II.

Abstract The infrared absorption spectra (2200–50 cm−1) have been measured for four metal-metal bonded molecules, Cl3Si–Mn(CO)5, Cl3Ge–Mn(CO)5, Br3Ge–Mn(CO)5, and I3Sn–Mn(CO)5. Vibrational normal coordinate analyses have been made for each of these molecules on the basis of a modified Urey-Bradley force-field. The calculated frequencies agree closely with validly-assigned frequencies. The metal-metal stretching force constant, K(M–Mn), or the F-matrix element, f(M–Mn), varies with the halogen atom, and increases as the electronegativity of X increases. The force constant, K(M–Mn), or f(M–Mn) depends also on the IVb metal atom, and increases in the order of: K(Si–Mn)≥K(Ge–Mn)>(Sn–Mn), or f(Si–Mn)≥f(Ge–Mn)>f(Sn–Mn). However, there is no clear relationship between the electronegativity of M and the K(M–Mn) or (M–Mn). These dependences of K(M–Mn) or f(M–Mn) on X and M are discussed, along with the bonding implications of the M–Mn bonds, on the basis of the sets of the force constants, or the sets of the F-matrix elements, and are interpreted in terms of the predominant σ-bonding framework of the M–Mn bonds.

A Vibrational Normal Coordinate Analysis of H(D)NCO and H(D)NCS

Abstract The infrared spectra of HNCO and HNCS are quite complicated and the band assignments are still disputed. In this note we try to add some arguments based on the normal coordinate analysis in favour of the recently proposed assignments1,2. The analysis was performed by the standard GF method with the frequency assignment due to Ashby and Werner1 for HNCO, and Durig and Wertz for HNCS2. The frequencies only were used in the iteration procedure and the results are given in the Table.