Reaction of R3PSe with I2;: crystal structures of Ph3PSeI2, (Me2N)3PSeI2 and (Et2N)3PSeI2, the first crystallographically characterised charge-transfer complexes of tertiary phosphine selenides with diiodine

The compounds Ph3PSeI2, (Me2N)(3)PSeI2 and (Et2N)(3)PSeI2 have been prepared and characterised by P-31-{H} NMR and infrared spectroscopy. Their single crystal structures have also been determined. Interesting variations in d(P-Se) and d(I-I) are noted upon changing R (Ph, Me2N, Et2N). The variation in d(P-Se) for R3PSeI2 compared to the parent tertiary phosphine selenide is also discussed with respect to the degree of retention of phosphorus selenium double-bond character upon co-ordination of I-2. The variations in d(P-Se) and d(I-I) are reflected in the infrared and P-31-{H} NMR spectra of the R3PSeI2 compounds when compared to R3PSe (R = Ph, Me2N or Et2N). The P-Se-I geometries for all three 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 density from the selenium atom to the sigma*-antibonding orbital of the diiodine.