Structure and dynamics of phosphoranyl radicals. A single-crystal electron spin resonance study

The structures of phosphoranyl P/sup v/ radicals have been obtained from single-crystal ESR measurements. The radicals were prepared by x-irradiation or uv laser irradiation of their parent compounds. It is shown that phosphorus adopts a P/sup V/ trigonal-bipyramidal (TBP) structure in these radicals. The unpaired electron is located either in an apical (a) or equatorial (e) position of the TBP as a fifth ligand. Since both TBP-a and TBP-e configurations are formed in one sample of x-irradiated HP(OCH/sub 2/CH/sub 2/)/sub 3/N/sup +/BF/sub 4//sup -/, comparison of the two stereoisomers shows that the amount of s character in the apical bonds is reduced in comparison with the equatorial bonds. Besides these TBP-a and TBP-e structures the octahedral P/sup VI/ geometry of CIP(O/sub 2/C/sub 6/H/sub 4/)/sub 2//sup -/. is established, with the unpaired electron and chlorine in the axial axis. Intramolecular ligand reorganization in phosphoranyl radicals is studied in a single crystal, which reveals the exact mode of permutation: a Berry pseudoration, with the unpaired electron acting as the pivot. It is found that the intermedite square-pyramidal (SP) geometry in this process lies only slightly above the TBP-e structure in energy.