title: The hexaazidosilicate(IV) ion: synthesis, properties, and molecular structure.
abstract: The reaction of SiCl4 with an excess of (PPN)N3 (PPN+ = [(Ph3P)2N]+) affords selectively (PPN)2[Si(N3)6] (1). Simultaneous thermal analysis (TG-DTA) shows that the hexaazidosilicate salt is remarkably stable, melting at Tonex = 214 degrees C. Melting of 1 is followed by two distinct exothermic decomposition processes at Ton = 256 and 321 degrees C, the first one involving elimination of N2 and the second one degradation of the PPN cations and evolution of Si(N3)4, N2, and some HN3. The crystal structure of 1 consists of discrete PPN+ cations and S2 symmetric [Si(N3)6]2- anions, which have a very rare, octahedral SiN6 framework and the highest nitrogen content (90%) among the hexaazidometallates reported so far. The IR, Raman, 29Si, and 14N NMR spectra of 1 in CH3CN suggest in combination with the calculated spectra the presence of intact [Si(N3)6]2--anions of S6 symmetry in solution. Geometry optimizations with various methods and basis sets show an S6 symmetric structure to be the most stable [Si(N3)6]2- isomer, the calculated bonding parameters comparing well with the experimental values.
authors.affiliation: Humboldt-Universität zu Berlin, Institut für Chemie, Brook-Taylor-Strasse 2, 12489 Berlin, Germany. filippou@chemie.hu-berlin.de
authors.forename: Alexander C
authors.initials: AC
authors.lastname: Filippou
authors.forename: Peter
authors.initials: P
authors.lastname: Portius
authors.forename: Gregor
authors.initials: G
authors.lastname: Schnakenburg