A Study of the Molecular Structure of Diiodoethane Iodine Bond Resonance and the Molecular Structure of Diiodoethylene. Molecular Packing in Their Crystal Lattices

Abstract

Using data from an x‐ray study of the crystal structure of sym‐diiodoethane and sym‐diiodoethylene (trans form) the positions of the iodine atoms in the crystal cells were located. Iodine bond resonance is discussed and a factor of 0.92 of the length of the longer bond proposed for evaluating the interatomic distance for any resonating bond. On the basis of the concepts of tetrahedral carbon bonds, bond resonance, Pauling's normal convalent bond radii, etc., reasonable molecular models for the above substances were predicted. Comparison of these with the x‐ray data showed the iodine‐iodine distances to be in excellent agreement with certain iodine‐iodine distances within the crystal cells, thus locating the molecules within the cells. These models together with Mack's concept of the atomic domain radius of atoms in crystals permitted a consideration of the packing of the molecules in the crystal lattice, thus locating the atomic coordinates of the carbon and hydrogen atoms in the cell. The domain radii found were; iodine = 1.97A, and hydrogen = 1.23A. The resulting molecular packing is seen to explain and be in excellent agreement with observed physical properties of the two crystals.