Structure and Motion of Tetrakis(trichlorophosphazeno)phosphonium Hexachlorophosphate, [P(NPCl3)4]+PCl6 −, at 93 K

Abstract

[P(NPCl3)4]+PCl^{-}_{6}, M r = 880.02, monoclinic, P21/m, a = 7.720 (2), b = 21.235 (5), c = 8.248 (2) Å, \beta = 91.12 (2)°, V = 1351.9 (6) Å3, Z = 2, D x = 2.162 Mg m−3, \lambda(Mo K\alpha) = 0.71069 Å, T = 93 K, R = 0.0497, S = 1.007 for 4536 unique observed reflections and 140 parameters. The cations and anions show site symmetries of C s (m) and C i (\overline 1), respectively. The P—N bond lengths in the NPCl3 groups are distinctly shorter [1.515 (4)–1.532 (4) Å] than those attached to the central P atom [1.595 (2)–1.611 (4) Å], the P—Cl bond lengths are 1.961 (1)–1.975 (1) Å in the cations and 2.132 (1)–2.142  (1) Å in the anions; the P—N—P angles lie in the range 132.5 (2)–142.9 (3)°. The structure is a derivative of the CsCl structure type showing interionic distances of 3.314 (1)–3.414 (1) Å, between the Cl atoms. The differences between the angles P—Clcation...Clanion [153.38 (5)–168.28 (5)°] and P—Clanion...Clcation [102.30 (3)–116.35 (4)°] are very probably caused by the arrangement of the lone pairs at the Cl atoms. The thermal motion analysis showed that the anion behaves as a rigid body {R u = [\Sigmaw(\DeltaU)2/\Sigmaw(U obs)2]1/2 = 0.024}, whereas the cation does not (R u = 0.347). Allowing three intramolecular torsions the residual index R u for the cation could be lowered to 0.184.