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35Cl NQR studies on molecular complexes at low temperature

Rama Basu1
16 Jan 1989-Journal of Molecular Structure (Elsevier)-Vol. 192, Iss: 3, pp 375-378

Abstract35 Cl NQR frequencies were taken for chloranil and a few complexes of chloranil with aromatic hydrocarbons at liquid nitrogen temperature The different lines are assigned to different geometrical arrangements more

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Abstract: Nuclear quadrupole coupling constants in molecules depend on the nuclear quadrupole moments and the variation in electrostatic field at the nucleus. It is shown that this variation of electric field is usually simply related to the molecular electronic structure, being primarily dependent on the way in which valence electrons fill the lowest‐energy p‐type orbits. Structural information which can consequently be obtained from known quadrupole coupling constants is discussed. Hybridization of the normal covalent bonds of N, Cl, and As with at least 15 percent s character is clearly shown. The alkali halides appear to be almost purely ionic; the quadrupole coupling data allow no more than 3 percent covalent character. In addition to molecular structure, some nuclear quadrupole moments are approximately evaluated by use of the theory developed here.

882 citations

Journal ArticleDOI
Abstract: Halogen pure electrical quadrupole resonance frequencies have been measured in the three 1:1 complexes, CBr4·p‐xylene, CCl4·p‐xylene, and Br2·benzene. From an examination of the measured frequencies of the complexes and the halogen‐containing compounds (CBr, CCl4, and Br2) together with information from the x‐ray structure determinations for two of the complexes, it has been concluded that little if any charge transfer exists in the ground state of these complexes.

53 citations

Journal ArticleDOI
Abstract: The nuclear quadrupole resonance spectrum of Cl in chloranil and in the 1: 1 complex of chloranil with hexamethylbenzene was obtained at 77 tained K and room temperature. The results are used to estimate the upper limit for charge transfer in the complex from chloranil to hexamethylbenzene. Complexes of picrylchloride: hexamethylbenzene and parachloroaniline: sym-trinitrobenzene were also studied but no resonances were detected. (D. L.C.)

27 citations

Journal ArticleDOI
Abstract: The 81Br nuclear quadrupole resonance spectra have been examined for a series of complexes of CBr4 with methyl‐substituted benzenes and pyridines. The p‐xylene−CBr4 complex gives two lines as expected from the known structure, and the benzene–CBr4 spectrum is the same, with a lower splitting. The spectra of a number of other complexes of unknown structure do not correlate simply with these. Estimates of the direct crystal‐field gradients due to the charge distribution in the aromatics suggest that the direct field gradient effects are much too low to account for observed shifts in quadrupole frequencies. The temperature dependencies of the resonances in the p‐xylene and durene complexes have been studied. The p‐xylene complex follows the Bayer equation, but the durene complex requires the inclusion of a temperature dependence of the torsional frequency. Both complexes show a fading of the resonances at about 50° below the melting points.

16 citations

Journal ArticleDOI

1 citations