Browsing by Author "James, R W"

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    The crystal structures of para-chloriodoxy benzene and some other aromatic compounds
    (1947) Archer, Elizabeth Muriel; James, R W
    The crystal structures of meta-dinitrobenzene, para-chloriodoxy benzene, and benzene iodo-dichloride are described. The structure of meta-dinitrobenzene, C₆H₄(NO₂)₂), was obtained from Fourier projections on the ab and bc planes. The x and y coordinates were obtained with considerable accuracy from the projection on the ab plane, and the z coordinates were obtained from a previous knowledge of the size and shape of the nitro groups and the agreement between the observed and calculated values of F(Okl). The method of three-dimensional Fourier sections was applied to the crystal para-chlor-iodoxy benzene, (ClC₆H₄IO₂), and the coordinates of all the atoms were obtained without any ambiguity. The I-O distances in the iodoxy group are short, which implies the existence of double bonding between the I and O atoms. The main binding forces in the crystal are found to be between neighbouring iodoxy groups. The structure of benzene iodo-dichloride, (C₆H₅ICl₂), has been obtained from Fourier projections on the ac and bc planes. The iodo-dichloride· group is linear. The directions of the covalent bonds of trivalent iodine in C₆H₅ICl₂ can be placed in a trigonal bipyramid, but it was impossible to fit the covalent bonds of pentavalent iodine in ClC₆H₄IO₂ into any simple geometrical figure. These iodine compounds were done in order to determine the valency directions of polyvalent iodine, and to see if there was any relationship between the directions of the covalent bonds in trivalent and pentavalent iodine. If such a relationship does exist, it has not yet been detected.
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    The crystal structure and constitution of some molecular complexes of 4:4- dinitrodiphenyl
    (1947) Saunder, Douglas Harold; Saunder, Douglas Harold; James, R W; Rapson, W S
    The crystal structures or a number of molecular complexes formed by 4:4'-dinitrodiphenyl with various diphenyl derivatives are described. The general type of structure is undoubtedly the same for all the complexes examined and the typical arrangement may be taken as that in the complex of 4:4'-dinitrodiphenyl with 4-hydroxydiphenyl, the structure of which has been fully determined. As shown in fig. 7 the dinitrodiphenyl molecules form layers in face-centred array and lie one above the other with a spacing of about 3.7 A. The arrangement of these molecules alone is such that a set of tubular cavities, also in face-centred array, run through the structure. In the complexes these cavities are occupied by the other component molecules, the hydroxydiphenyl molecules in the case considered; which thus lie nearly normal to the planes containing the dinitrodiphenyl molecules and are seen end-on in fig. 7. In the other structures examined geometrical and symmetry conditions require that the individual molecules should be tilted in varying degrees, but the type or structure still remains essentially the same. It is shown that the ratio of the components in these complexes is determined by the length of the molecule other than dinitrodiphenyl, and that in no case is it necessary for the intermolecular distances to be shorter than those found in crystals or ordinary aromatic nitro-compounds. A bonding mechanism in terms of dipole attraction between the component molecules is shown to be consistent with all the observed data. Of interest are the periodic distortions which appear to occur in the crystal lattices of the complexes or 4:4'-dinitrodiphenyl with 4-iodo-, 4-bromo- and 4-chlorodiphenyl.