Nuclear quadrupole resonance molecular complexes

Tetrachlorohydroquinone (45) is closely related to chloranil and might be expected to show overcrowding effects similar to those found in chloranil by Ueda. The crystal structure of tetrachlorohydroquinone has been investigated by Sakurai (1962) using nuclear quadrupole resonance and X-ray diffraction techniques. The crystal makes use of the molecular centre of symmetry and the asymmetric unit consists of half a molecule. The analysis shows that the C—O bond deviates by 0-9° from the aromatic plane and that the two adjacent C—Cl bonds are also bent out of the benzene plane, in the same direction, through 0-8°. (This is reminiscent of Harding and Wallwork s findings for chloranil in the hexamethylbenzene-chloranil complex.) Sakurai... 

To study the electronic structures and stereochemistries of mcthyltin halides and their molecular complexes, infrared and Raman spectroscopy, nuclear magnetic resonance, nuclear quadrupole resonance, Mossbauer spectroscopy, diffraction, and other techniques are usually employed today. Consequently, the application of these methods to the objects of interest, and the information to be gained will be discussed in this section. The conclusions made will help us to understand the behavior of specified compounds. 

Hegita H., Okuda T., Kashima M. Nuclear quadrupole resonance of antimony tribromide and its molecular complexes // J. Chem. Phys. - 1966. - Vol. 45. -P. 1076-1077. 

A third method uses data for a neutral molecular complex. Under the assumption that ferrocene and cobalticinium perchlorate have similar chemical bonding, the pure nuclear quadrupole resonance data for the latter together with the independent determination of Qg for Co from atom-beam spectroscopy data have been used to estimate 0e( Fe). The method has the advantage that the lattice sums are less than 1% of the total electric field gradient. 

R. Basu, Application of Nuclear Quadrupole Resonance in Chemical Compounds with Special Reference to Molecular Complexes (Charge-Transfer Complex) , J. Ind. Chem. Soc., 2008, 85, 975. 

If the nucleus of the acceptor atom M has a nuclear spin quantum number greater than -j, the nucleus has an electric quadrupole moment as well as a magnetic dipole moment. The quadrupole interacts with any electric field gradient at the nucleus and, in combination with the molecular motion of the complex, this can provide an important mechanism of relaxation of the M nucleus. At relaxation rates that are slow compared with Jp M, spin multiplets are observable in the spectra of M and P. As the relaxation rate increases, the multiplets broaden, but the line separations may still be used to derive 7p Mwith good accuracy. At faster relaxation rates the multiplet components of M and P coalesce into a single broadened line, and at high relaxation rates, the phosphorus resonance becomes sharp and the M resonance may become so broad as to be unobservable. 

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