Effects of fluorine on cyclosilazanes and cyclic silylhydrazines

Compared with organic-substituted cyclosilazanes only a few Si-N ring syste ms with inorganic substituents are known. They differ very much in molecula r structure and reaction behaviour. We succeeded in the synthesis of the fi rst (F2SiN-) cyclodi- and cyclotrisilazanes. Standard molecular orbital ab initio calculations for several cyclosilazanes were carried out for the par ent cyclodisilazane, the tetrafluoro-substituted cyclodisilazane, the disil yl-substituted cyclodisilazane, and the disilyl-, tetrafluoro-substituted c yclodisilazane in order to provide a rationalisation for the very short Si. ..Si distance in the isolated cyclodisilazanes.