Crystals of czsium and rubidium difiuorophosphates are orthorhombic, with a = 8.43,. b = 6.7g6, c = 8.06 a for the Cs salt, and a = 8.1 5, b = 6.45, c = 7.79 a for the Rb salt, Z = 4, space-group Pnma. The structure of CsPO,F, was determined by use of three-dimensional M o -K , scintillation counter data by comparison with potassium difluorophosphate, and refined by least-squares methods, the final R being 0.070 for 506 observed ref lexio ns.Potassium, rubidium, and cxsium difluorophosphates are isomorphous, and have the barium sulphate structure. The lattice parameters and interionic distances increase with increasing radius of the alkali-metal ion.POTASSIUM difluorophosphate has recently been shown to have a crystal structure similar to that of barium sul-p1~ate.l The present study indicates a similar structure for rubidium and caesium difluorophosphates, with the lattice parameters and interionic distances increasing with the radius of the cation. EXPERIMENTALRubidium and czesium difluorophosphates are prepared by reaction of the metal chlorides with difluorophosphoric acid.2 Investigation of the rubidium compound was limited to measurement of the unit-cell parameters, but a detailed X-ray analysis of the caesium compound was carried out. Crystals of CsP02F2 (from methanol) are colourless needles elongated along c. The unit-cell dimensions were measured from a c-axis rotation photograph, and by the extrapolation method of Farquhar and Lipson3 from high-angle reflexions on hkO Weissenberg photographs. The spacegroup was determined from various Weissenberg and precession films, and the density was measured by flotation in a mixture of di-iodomethane and iodoform.

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Crystals of p-chloroaniline are orthorhombic; a = 8.67, 6 = 9.28, c = 7.40 A, Z = 4, space group Pnam. The structure was determined with visual intensity data from the three-dimensional Patterson function, and refined by least-squares, with anisotropic thermal parameters for the chlorine, nitrogen, and carbon atoms, and isotropic thermal parameters for the hydrogen atoms ; the final R is 0.1 1 for 482 reflexions. The aromatic ring is planar within experimental error, but the chlorine and nitrogen are displaced from the plane in the same direction, by 0.03 and 0.06 A, respectively. The bond distances indicate electron-donation from the amino -group into the ring, the lengths being CI-C(4) = 1.75. C(l)-C(2) = 1.42, C(2)-C(3) = 1.39, C(3)-C(4) = 1.40. C(1)-N = 1.39 A.The intermolecular distances correspond to van der Waals interactions. THE C-NH, bond distances in aromatic amines are very significantly shorter than the single-bond distance, and these contractions are usually accounted for, in terms of valence-bond theory, by contributions to the f resonance-hybrid molecule of structures with a carbonnitrogen double b0nd.l This situation may be contrasted with that in nitro-compounds, where such canonical structures are " sacrificial '' and the C-N bond distances are not significantly different from the singlebond 1ength.l L4s a further contribution to these studies we have examined the structure of $-chloroaniline (I), and the results indicate C-N bond shortening, and hence contribution from structures such as (11). EXPERIMENTAL Crystals of p-chloroaniline from aqueous ethanol are colourless octahedra bounded by { 11 l } . The unit-cell and space-group data were determined from various rotation, Weissenberg, and precession photographs. Crystal Data (A, Cu-K, = 1.5418 A; A, hlo-h', = 0.7107 A) .-p-Chloroaniline, Cl-C,H4-SH,, ;14 = 127.6, m. p. 71". (all i 0 . 0 1 A), u = 595 A3, D, (flotation in aqueous KI) = 1.43, 2 = 4, D, = 1.42. Absorption coefficients, ~(CU-K,) = 47 cni.-l, p(RIo-K,) = 5 cm.-l. F(000) = 264. Absent reflexions: 0KZ absent when (k + I) = (2n + l ) , h0Z absent when h = ( 2 n + 1 ) . Space group PnaB, (CZgg) or Pnam (D2h16). Pnawz from structure analysis.The intensities of the reflexions were measured visually from Cu-K, lzKl Weissenberg films, K -1 0 7. The layers were correlated by intensity measurements of Mo-K, OkZ and kkO precession films. The crystal used was approximately spherical with diameter 0.2 mm., and no absorption corrections were considered necessary. The structure amplitudes were derived as usual; 482 reflexions were observed, Orthorhombic, a = 8.67, b = 9.28, c = 7.40 STRUCTURE ASALYSIS vectors in the three-dimensional Patterson function. These peaks could be interpreted in terms of space group Pnam, with C1, C(4), C(1), and N in positions (4(c) and the other carbon atoms in 8(d), that is, with the mean molecular plane perpendicular to the space-group mirror plane. However, to avoid any assumption about space group, the molecule was rotated about the C1-N axis, giving a structure ...

The structure of [Cu{O(CH,CO2),)],0~5H,O has been determined by Fourier and least-squares methods from diffractometer data. Crystals, all of which are twinned by reflection across the (101) twin plane or by a 90" rotation about [OlO], are orthorhombic with a = 9.263(6), b = 14.283(5), c = 9.283(6) 8, Z = 8, space group Pbcn. Volume fractions of the twin components were deduced from the ratios of intensities observed at spacegroup forbidden positions. The structure of the major component, which represents 88% of the twin volume, was refined to R 0.88 for 1042 reflections.The Cu atoms are co-ordinated by four carboxy-oxygen atoms, two from the two ends of a chelating oxydiacetate ligand and one from each of two neighbouring Cu{O(CH,CO,)) groups, with Cu-0 1.941 (9)-I .952(8) 8. Longer contacts to the ether oxygen of the chelating ligand [Cu-0 2.488(8) 8 3 and to a statistically disordered water molecule [Cu-0 2.73(2) 8 3 complete a distorted octahedral arrangement. A pseudo-mirror plane passing through Cu. H,O, and the ether 0 atom relates the halves of the oxydiacetate group and results in markedly similar packing schemes in the ab and bc unit-cell projections. Stacking faults in the packing along b account for the occurrence of the twinning.