NQR and NMR study of pseudorotation in solids

Nuclear quadrupole resonance and nuclear magnetic resonance methods have been used to study the pseudorotation process in solids. In crystalline dimeric (Hal3PNR)2 phosphazo compounds, where Hal = CI or F, and R contains protons, the temperature dependences of the 35CI, 19F and 1H 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, Ea, for the exchange process is obtained from the T1 temperature dependence of the 35CI nuclei and from the T1e temperature dependence of the 19F and 1H nuclei. In the case of chlorinated phosphazo compounds, Ea, lies in the 59‐105 kJ mol−1 range, whereas in solid (F3PNCH3) Ea, is about 38 kJ mol−1.