3: 0.09 g (0.5 mmol) Ferrocen, 0.06 g (0.25 mmol) I2 und 0.25 g (0.5 mmol) Sbl, werden nacheinander in 150 mL CH,CN unter Erwarmen gelost. Innerhalb van I d bei Raumtemperatur kristallisieren schwarze, kompakte Kristalle in 82% Ausbeute; befriedigende C,H,Fe,l-Analyse. Eingegangen am 21. Oktober 1988 [Z 30211[I] K.

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Salts of the title anion series have been prepared with the sodium-[l8]crown-6 cation (n = 1 and 2) ([18]crown-6 = 1,4,7,10,13,16-hexaoxacyclo-octadecane) or tetra-alkylammonium cations (n = 4) by addition of Br-to P(CN), or PBr,, or by Br, or BrCN oxidation of P(CN),-.Contrary to this, CN-addition to P(CN),, in a reductive elimination, gives P(CN),-. X-Ray crystal-structure determinations of the above mentioned three salts are reported and their anion structures are discussed. The P(CN),Br,-anion shows the $-trigonal-bipyramidal coordination expected on the basis of Valence Shell Electron Pair Repulsion Theory (V.S.E.P.R.), P(CN),Br-has $-octahedralco-ordination in a dimeric, bromide double-bridge structure, and PBr,-a structure intermediate between the two. Here the trigonal-bipyramidal co-ordination is distorted towards a tetrahedral geometry. This is in contradiction to V.S.E.P.R. and presumably the result of ligand-ligand repulsion. The structures are of interest as transition-state models of phosphorus(ll1) nucleophilic substitution.