OPTICAL-PROPERTIES, THERMOCHROMISM, AND CRYSTAL-STRUCTURES OF THE DIMORPHS OF 2-IODOANILINIUM PICRATE

The crystals of 2-iodoanilinium picrate have three polymorphic forms. The crystal structures of the monoclinic form (form I) and the triclin ic form (form II) have been determined by the X-ray diffraction method . The crystals of the third form (form III) are unstable. In forms I a nd II, 2-iodoanilinium cation and picrate anion form a nearly planar p air of these ions with similar geometry of N-H...O hydrogen bond. In f orm I the pairs related by a translation are stacked to form the segre gated columns, in which the same kinds of ions are stacked with each o ther, while in form II the anions and cations are alternately stacked to form the continuous columns. The thermochromism of these crystals w as studied by measuring the polarized visible and IR absorption spectr a and the differential scanning calorimetry.