THEORETICAL AND EXPERIMENTAL STUDIES OF 6-MEMBERED SELENIUM-SULFUR NITRIDES SEXS4-XN2 (X=0-4) - PREPARATION OF S4N2 AND SES3N2 BY THE REACTION OF BIS[BIS(TRIMETHYLSILYL)AMINO]SULFANE WITH CHALCOGEN CHLORIDES

The reaction of [(Me3Si)(2)N](2)S with equimolar amounts of SCl2 and S 2Cl2 produces S4N2 in a good yield. The reaction of [(Me3Si)(2)N](2)S with a 3:1:1 mixture of S2Cl2, Se2Cl2 and SeCl4 yields a dark brown-re d insoluble material that was inferred to be mainly SSeSMSN on the bas is of the elemental analysis, mass spectroscopy, vibrational analysis, and NMR spectroscopy. Attempts to prepare selenium-rich species resul ted in the formation of elemental selenium or Se3N2Cl2. The experiment al work was supported by ab initio MO calculations which establish the structural and stability relationships of the different members of th e series 1,3-SexS4-xN2 (x = 0-4). Full geometry optimization was carri ed out for each molecular species using the polarized split-valence MI DI-4 basis sets. The effects of electron correlation were taken into account involving the second-order Moler-Plessett perturbation theory. Each molecule was found to lie in an approximate half-chair conformat ion that is well established for 1,3-S4N2 (i.e., interacting planar NE N and EEE fragments; E = S, Se). The bond parameters agree well with e xperimental information where available. Whereas the lengths of the bo nds in the NEEEN fragment approach those of the single bonds, the bond s in the NEN fragment show marked double bond character. The stabiliti es of the molecules decrease expectedly with increasing selenium conte nt as judged by the total binding energy at the MP2 level of theory. W ithin a given chemical composition, isomers containing a N=Se=N unit l ie higher in energy than those containing a N=S=N unit. These results may explain why selenium-rich SexS4-xN2 molecules have not been isolat ed.