NEW RESULTS ON P4SE4

Preparation of P4Se4 from the elements yields always the beta-modifica tion of P4Se4. Alpha-P4Se4 is obtained only with selenium deficient sa mples. However, it is also observed, when P4Se4 is annealed and then e xtracted with CS2. The insoluble part has the X-ray pattern of alpha-P Se4. A reversible alpha-beta transition is not observed. MAS-P-31-NMR investigations on solid P4Se4 by Eckert et al. [21 reveal P2Se4/2 buil ding units, which are, in view of our results, not dimer but linked to a polymeric network. Well-crystallized samples of beta-P4Se4 are obta ined only at measuring temperatures above 573 K. The structure is of m onoclinic symmetry with the space group P2(1)/n (a = 1141.9, b = 729.0 , c = 1211.0 pm, beta = 120.80-degrees). The reaction of alpha-P4Se3I2 with bis-(trimethyltin)selenide in CS2 at low temperature yields mole cular alpha-P4Se4, which can be detected in solution by P-31-NMR spect roscopy. Alpha-P4Se4 has D2d-symmetry like alpha-P4S4. It polymerizes at higher temperature. Alpha-P4Se3I(SeSnMe3) and alpha-P4Se3(SeSnMe3)2 were observed in the course of this reaction, too. The analogous reac tion of alpha-P4Se3I2 with bis-(trimethyltin)sulfide leads to comparab le results.