35Cl NQR spectroscopy and pseudorotation in solid chlorophosphoranes

The 35 Cl NQR frequency ν and the spin-lattice relaxation time T 1 have been investigated in solid tetrachlorophosphoranes C 6 H 5 PCl 4 , 4-ClC 6 H 4 PCl 4 and 2,6-Br 2 -4-ClC 6 H 2 OPCl 4 at temperatures from 77 K to the melting points. The fading of the NQR signals and the exponential shortening of the T 1 time for the chlorine nuclei in the PCl bonds show the existence of the exchange motion (pseudorotation) in these solids which involves three or four chlorine atoms corresponding to their interactions with the environment. The activation energies of the motion are found to lie in the range 40–70 kJ mol −1 .