REACTION OF R3PSE WITH I-2 - CRYSTAL-STRUCTURES OF PH3PSEI2, (ME2N)(3)PSEI2 AND (ET2N)(3)PSEI2, THE FIRST CRYSTALLOGRAPHICALLY CHARACTERIZED CHARGE-TRANSFER COMPLEXES OF TERTIARY PHOSPHINE SELENIDES WITH DIIODINE

The compounds Ph3PSeI2, (Me2N)(3)PSeI2 and (Et2N)(3)PSeI2 have been pr epared and characterised by P-31-{H} NMR and infrared spectroscopy. Th eir single crystal structures have also been determined. Interesting v ariations in d(P-Se) and d(I-I) are noted upon changing R (Ph, Me2N, E t2N). The variation in d(P-Se) for R3PSeI2 compared to the parent tert iary phosphine selenide is also discussed with respect to the degree o f retention of phosphorus selenium double-bond character upon co-ordin ation of I-2. The variations in d(P-Se) and d(I-I) are reflected in th e infrared and P-31-{H} NMR spectra of the R3PSeI2 compounds when comp ared to R3PSe (R = Ph, Me2N or Et2N). The P-Se-I geometries for all th ree compounds are bent [Ph3PSeI2, 106.0(1), (Me2N)(3)PSeI2, 100.4(2) ( average); (Et2N)(3)PSeI2, 106.4(1)degrees] whereas the Se-I-I linkages are all essentially linear [173.69(6), 174.98(8) (average); 178.04(5) degrees]. These results are interpreted as a donation of electron dens ity from the selenium atom to the sigma-antibonding orbital of the di iodine.