NQR and NMR study of pseudorotation in solids

Abstract

Nuclear quadrupole resonance and nuclear magnetic resonance methods have been used to study the pseudorotation process in solids. In crystalline dimeric (Hal,PNR), phosphazo compounds, where Hal = CI or F, and R contains protons, the temperature dependences of the '%I, 9 and 'H spectra and the relaxation times indicate intramolecular exchange of the 'trigonal twist' type between one axial and two equatorial halogen atoms attached to the pentacoordinated phosphorus. The activation energy, E., for the exchange process is obtained from the T, temperature dependence of the 35Cl nuclei and from the T,, temperature dependence of the 9 and 'H nuclei. In the case of chlorinated phosphazo compounds, E. lies in the 59-105 kJ mol-' range, whereas in solid (F3PNCH3), E. is about 38 kJ m0l-l.