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Issue 11, 1994
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The nature of halogen ⋯ halogen interactions and the crystal structure of 1,3,5,7-tetraiodoadamantane


An analysis of halogen ⋯ halogen (X ⋯ X) intermolecular interactions in crystals, using the Cambridge Structural Database (CSD). is presented. A total of 794 crystal structures yielded 1051 contacts corresponding to symmetrical and unsymmetrical X ⋯ X interactions of the type Cl ⋯ Cl, Br ⋯ Br, I ⋯ I, Cl ⋯ F, Br ⋯ F, I ⋯ F, Br ⋯ Cl, I ⋯ Cl and I ⋯ Br. These 1051 contacts are divided mainly into two categories, type I and type II depending upon the values of the two C–X ⋯ X angles θ1and θ2around the X atoms in a fragment of the type C–X ⋯ X–C. Type I contacts are defined as those in which θ12 while type II are defined as those in which θ1≅ 90° and θ2≅ 180°. Our results indicate that as the polarisability of the X atom increases, type II contacts become more significant than type I contacts and the X ⋯ X interaction may be more nearly considered to arise from specific attractive forces between the X atoms. A number of these concepts are succinctly illustrated in the crystal structure of 1,3,5,7-tetraiodoadamantane, 1. This structure has been reported to a very limited accuracy previously and the present work reveals an unusual twinned structure for this compound wherein the geometry of the stabilising I ⋯ I interactions is retained across the twin boundary. Compound 1 is tetragonal, space group I41/a, a= b = 7.1984(7) and c= 28.582(4)Å, and Z = 4. The packing of the molecules in the crystal is controlled by I ⋯ I interactions. The supramolecular network of I ⋯ I connected molecules in crystalline 1 is closely related to that in adamantane-1,3,5,7-tetracarboxylic acid. Indeed, the stabilising nature of the I ⋯ I interactions is crucial for the crystallisation of 1 in this particular structure because otherwise, it should also have formed plastic crystals as do the analogous tetrachloro and tetrabromo derivatives.

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Article type: Paper
DOI: 10.1039/P29940002353
Citation: J. Chem. Soc., Perkin Trans. 2, 1994,0, 2353-2360
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    The nature of halogen ⋯ halogen interactions and the crystal structure of 1,3,5,7-tetraiodoadamantane

    V. R. Pedireddi, D. S. Reddy, B. S. Goud, D. C. Craig, A. D. Rae and G. R. Desiraju, J. Chem. Soc., Perkin Trans. 2, 1994, 0, 2353
    DOI: 10.1039/P29940002353

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