Crystal structure of compounds with (N–P)n rings. Part 12. Decafluorocyclopentaphosphazene
Abstract
Three monoclinic crystal modifications of the title compound (m.p. –50 °C) have been obtained by low-temperature crystallization. The crystallographic data are: (1). space group P21/c, a= 11.098(19), b= 14.459(6), c= 11.784(19)Å. β= 142.4(5)°;.(2), space group P21/a, a= 15.785(12), b= 15.237(10), c= 4.919(6)Å, β= 97.4(2)°; and (3). space group P21/n, a= 14.02, b= 16.02, c= 5.24 Å, β= 99.5 °. The crystal structures of modifications (1) and (2) have been determined from low-temperature diffractometer data by the symbolic addition method and refined by block-diagdnal least-squares analysis [(1), 1 598 reflections, R 0.59; (2), 1 919 reflections, R 0.74]. The unit cell in both structures contains four molecules in a general position. In (1) the (N–P)5 ring of the molecule is somewhat boat-shaped and the molecule has a pseudo-two-fold rotation axis passing through an N and a P atom. In (2) the molecule has a rather irregular shape, which resembles to some extent the structure of N5P5Br10 Mean P–N bond lengths are 1.549(5) in (1) and 1.546(5)Å in (2). The mean P–F bond length is the same in (1) and (2)[1.528(4)Å]. The P–N–P angles range from 132.7 to 151.6 °[means 137.4(3) for (1) and 140.6(4)° for (2)]. The N–P–N angles range from 119.1 to 123.9 °[means 121.4(2) in (1) and 120.9(3)° in (2)]. The mean value of the F–P–F angles in (1) and (2) is 99.4(2)°.