Zur Chemie und Strukturchemie von Phosphiden und Polyphosphiden. 42. Trilithiumheptaphosphid Li3P7: Darstellung,Struktur und Eigenschaften

Chemistry and Structural Chemistry of Phosphides and Polyphosphides. 42. Trilithiumheptaphosphide Li₃P₇: Preparation, Structure, and Properties Trilithium heptaphosphide, Li₃P₇, has been prepared by reaction of the elements at 870 K in Nb and Ta ampoules, respectively. The bright yellow (solventfree) substance crystallizes in a new structure type (P2₁2₁2₁; a = 974.2(1) pm; b = 1053,5(1) pm; c = 759,6(1) pm; Z = 4). The structure is closely related to the plastically crystalline Rb₃P₇ type of structure (Li₃Bi variant). The heptaphosphanortricyclene anions P₇^3? are surrounded by 12 Li cations and connected one to each other in a complex manner. The anion exhibits a differentation of distances and angles typical for ionic nortricyclenes X₇^3? (P? P distances: d?(basis) = 224.9 pm; d?(basis-bridge) = 214.7 pm; d?(bridge-bridgehead) = 217.6 pm). The distances Li to P are in the range of 250 ≤ d(Li? (2b)P^?) ≤ 270 pm. The P? P and Li? P bond distances are equivalent to meaningful Pauling bond orders PBO. On heating in closed ampoules, Li₃P₇ shows an endothermic effect at 900 K, corresponding to a first order phase transition into a HT phase of unknown nature up to now. On thermal decomposition no congruent dissociative sublimation occurs in contrast to the other heptaphosphides M₃P₇, but LiP and Li₃P are formed, the latter evaporates congruently dissociative, Solutions of Li₃P₇ in en show valence fluctuation of the P₇^3? anions already at room temperature (δ ³¹P-NMR = ? 122.1). Further reactions of Li₃P₇ are reported as well as the structural differences between Li₃P₇ and the solvates Li₃P_7solv3 are discussed.