Alkali metal phosphoraneiminates. New syntheses and crystal structures of [RbNPPh3](6) and [CsNPPh3](4)

The alkali-metal phosphoraneiminates MNPPh3 with M = Na, K, Rb, Cs have bee n synthesized by reactions of Ph3PI2 with the alkali-metal amides in liquid ammonia and were obtained as pure samples by subsequent extraction with to luene. The ethyl derivative KNPEt3 has been prepared by an analogous route from Et3PBr2 and extraction with hexane. Single crystals of the phosphoraneiminates of rubidium and cesium are obtai nable by crystallization from toluene and toluene/hexane, respectively. The y were suitable for crystal structure determinations. [RbNPPh3](6). 4 1/2 toluene (1): space group P (1) over bar, Z = 2, lattice dimensions at 193 K: a = 1525.5(2); b = 1902.9(2); c = 2178.3(2) pm; alpha = 95.435(12)degrees; beta = 91.145(12)degrees; gamma = 90.448(12)degrees; R-1 = 0.0529. The compound forms a Rb6N6 skeleton of a double cube with a c ommon face of two rubidium and two nitrogen atoms, the latter being fivefol d coordinated by four rubidium atoms and the phosphorus atom. [CsNPPh3](4). 2 toluene 3 3/4hexane (2 a): space group Fd (3) over bar, Z = 8, lattice dimensions at 123 K: a = b = c = 2679.7(1) pm; R-1 = 0.0405. [CsNPPh3](4). 2 toluene (2 b): space group P2(1)/n, Z = 4, lattice dimensio ns at 193 K: a = 1418.9(1); b = 2258.9(1); c = 2497.6(1) pm; beta = 91.055( 6)degrees; R-1 = 0.0278. Both cesium compounds form Cs4N4 heterocubane stru ctures which are different by means of the packing and by different bond an gles at the cesium and nitrogen atoms.