The crystal structure of pentameric phosphorus nitride dichloride, (PNCl2)5

Abstract

The crystal structure of pentameric phosphorus nitride dichloride has been determined by three-dimensional, single-crystal X-ray diffraction. The crystals were orthorhombic, space-group P(2₁2₁2₁), with unit-cell dimensions a= 15·48, b= 19·44, and c= 6·26 Å and four molecules per unit cell. The structure was solved by use of Patterson superposition methods and a symmetry map generated from the three Harker sections. The positional and anisotropic thermal parameters were refined by least squares to a final agreement factor of R= 7·2% for the 1319 observed reflections.

The structure consists of very nearly planar ten-membered rings of alternating phosphorus and nitrogen atoms. The P–Cl distances and Cl–P–Cl and N–P–N angles found are in agreement with those found in other phosphorus nitride chlorides. Shortened P–N distances (average 1·521 Å) and larger P–N–P angles (average 148·6°) are found in this structure, however. In-plane d_π–p_π bonding is used to explain these features and, as well, to explain the trend of the PNCl₂ heats of formation in the cyclic phosphorus nitride chlorides.