research papers
[P(NPCl3)4]+PCl-6, Mr = 880.02, monoclinic, P21/m, a = 7.720 (2), b = 21.235 (5), c = 8.248 (2) Å, = 91.12 (2)°, V = 1351.9 (6) Å3, Z = 2, Dx = 2.162 Mg m-3, (Mo K) = 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 Cs(m) and Ci(), 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-ClcationClanion [153.38 (5)-168.28 (5)°] and P-ClanionClcation [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 {Ru = [w(U)2/w(Uobs)2]1/2 = 0.024}, whereas the cation does not (Ru = 0.347). Allowing three intramolecular torsions the residual index Ru for the cation could be lowered to 0.184.