The novel compound SiPN3 has been prepared by reacting hexachloro-N-silylphosphinimine Cl3Si-N=PC13 with liquid ammonia a t -78 "C followed by subsequent removal of the ammonium chloride byproduct and annealing of the resulting polymeric imide at 800 "C for 12 h. The compound has been characterized by elemental analysis and 29Si and 31P MAS-NMR, as well as X-ray powder diffraction methods. The powder data suggest a defect Wurtzite type structure which is closely related to the structures of SizNzO and SiZNzNH. (Rietveld analysis data: space group CmcB1, 2 = 4, a = 902.4(4) pm, b = 527.5(2) pm, c = 469.8(2) pm; 44 reflections observed; scan range 10" < 279 < 81"; germanium monochromator, Cu Kal, R(wp) = 0.047, R(l,h,k,l) = 0.071.) At 920 "C SiPN3 decomposes into Si3N4, P4, and Nz. The Si3N4 obtained on pyrolysis of SiPN3 consists of a pure a-phase and has an extremely low oxygen content.

EinführungDer Begriff "Isosterie" hat sich zu einem der fruchtbarsten Prinzipien der anorganischen Che mie entwickelt. Viele bis dahin unbekannte Ver bindungen können mit seiner Hilfe nicht nur in ih rer Existenz, sondern sogar in ihren Eigenschaften vorausgesagt werden.Von Langm uir [1] geprägt und ursprünglich eher für Zustände benutzt, die m an heute als iso elektronisch bezeichnet, hat der Begriff Isosterie mannigfache Variationen erfahren. W ir schließen uns der klassischen Definition Josef G oubeaus [2] an, wonach zwei Verbindungen dann isoster sind, wenn sie

structure structure (solids and liquids) D 2000 -008The SiO/PN Isoelectronic Pair. Part 1. Perchlorocyclosiloxanes and Perchlorocyclophosphazenes. Vibrational Spectra and X-Ray Structure Analysis of (Cl2SiO)3 and (Cl2SiO)4.-The title compound (IV) crystallizes in space group P1 with Z = 2 and ( V) in P1 with Z = 1. The XRD data reveal that the (SiO)n rings (n = 3, 4) are planar in both compounds with average Si-O bond lengths of 1. 619 and 1.584Å, respectively. The vibrational spectra of the cyclosiloxanes (IV) and (V) are similar to that of (PNCl2)3, but clearly different from that of the puckered (PNCl2)4 molecule. -(WANNAGAT, U.; BOGEDAIN, G.; SCHERVAN, A.; MARSMANN, H. C.; BRAUER, D. J.; BUERGER, H.; DOERRENBACH, F.; PAWELKE, G.; KRUEGER, C.; CLAUS, K.-H.; Z. Naturforsch., B: Chem. Sci. 46 (1991) 7, 931-940; FB9-Anorg. Chem.

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