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

The structures of phosphoranyl Pv 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 Pv 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(OCH2CH2)3N+BF4-c,o mparison 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 Pvr geometry of C1P(02C6H4)pis 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 pseudorotation, with the unpaired electron acting as the pivot. It is found that the intermediate square-pyramidal (SP) geometry in this process lies only slightly above the TBP-e structure in energy.