I. The Crystal Structure of the Intermetallic Compound Mg₁₂Ce. II. Reaction Products of γ-Picoline and Iodine

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Part I: The structure of the intermetallic compound Mg12Ce has been investigated by x-ray diffraction methods. The diffraction photographs seem to indicate that the structure has hexagonal symmetry, but further considerations reveal that the true symmetry is orthorhombic, and that the space group is very probably [...]. The orthorhombic unit cell, with dimensions [...], [...], and [...], contains 156 atoms. The diffraction maxima with the Miller index 1 even can be indexed on the basis of a smaller pseudo-hexagonal unit cell containing only 13 atoms. In this subcell, the arrangement of the atoms is related to those found in the CaZn5 and TiBe12 structures. The structure of the crystal is partially disordered in a complex fashion. A theory based on crystal growth has been devised which successfully accounts for the gross features of the disorder. Part II: Two distinct addition compounds, with formulas C12H14N2I2 and C6H7NI2 have been isolated from the reaction products of iodine and [gamma]-picoline. The second of these compounds is analogous to the well-known addition compound of pyridine and iodine. It has been of interest to determine whether the complexing forces between iodine and the organic base are sufficient to break the iodine-iodine covalent bond. X-ray radial distribution analyses showed that in the first compound the covalent bond had been broken, leading to an ionic structure, whereas in the second compound the covalent bond remained intact