Iodide Chains Research Articles

Diffuse X-ray scattering and order-disorder effects in the iodide chain compounds N,N′-diethyl-N,N′-dihydrophenazinium iodide, E 2PI 1.6, and N,N′-diebenzyl-N,N′-dihydrophenazinium iodide, B 2PI 1.6

Crystals of E 2PI 1.6(C 16H 18I 1.6N 2) and B 2PI 1.6(C 26H 22I 1.6N 2) contain stacks of the organic cations which form an array of parallel channels filled with iodide anions. These anions are mainly “ordered” in channel direction. The structure of the iodine chain was derived from a quantitative analysis of the X-ray diffuse scattering. It consists of linear symmetric triiodide anions with intramolecular distances of 2.99 Å and average intermolecular distances of 3.72 Å. There is no long range order along the channel direction and the triiodide chains behave like a one-dimensional liquid or an amorphous body. The fluctuation of distances between the center of gravity of 1st neighbour I − 3 molecules is well reproduced by a gaussian distribution law of 0.30 Å mean deviation. However, at room temperature, short range interchain transverse correlations exist between the average iodine positions in E 2PI 1.6, and between the triiodide sites in B 2PI 1.6. Longitudinal and transverse correlations increase at lower temperatures. The triiodide units of B 2PI 1.6 present also a displacive modulation of their positions with a long periodicity in channel direction.

Disorder and the ground state of bis(tetrathiatetracene) triodide TTT 2I 3

The low temperature ground state of TTT 2I 3 with varying amounts of iodide chain disorder has been studied using specific heat and infrared and far infrared reflectance and absorbance. Our results support the model of TTT 2I 3 as an organic conductor at room temperature which undergoes a metal to insulator transition near 50 K. At low temperatures we find a semiconducting gap of 80 cm −1 independent of disorder.

Structural studies of (tetrathiotetracene)2(iodide)3 at room temperature and low temperatures

(Tetrathiotetracene)2(iodide)3, (TTT)2I3, is metallic and can be crystallized with varying amounts of disorder. The crystal structures of highly disordered, h.d., (TTT)2I3 and (TTT)2I3 with significant lower disorder, l.d., have been solved. For (TTT)2I3 (l.d.) the basic structure, defined primarily by the TTT molecules, was refined in the space group Cmca. The doubled cell, which includes data from the strongest diffuse layer line, was refined in Pmc21. All iodide sites in (TTT)2I3 (l.d.) have less than full occupancy, indicating that the contents of cells vary and suggesting the presence of species such as I3−, I2, and I−. The crystal structure of (TTT)2I3 (h.d.) was investigated at room temperature (∼294 °K), 164, 74, and 19 °K. At all four temperatures the symmetry of the basic structure, defined primarily by the TTT molecules, remains orthorhombic. The basic TTT structure at all four temperatures was successfully refined in the space group Cmca. During slow cooling the diffuse layer lines were carefully monitored. Even with slow cooling the iodide chains do not three dimensionally order, and no distortions occur in the basic TTT structure down to 19 °K. A model of the iodide chains is presented which explains the positions and intensities of the diffuse layer lines and the absence of three-dimensional ordering at low temperatures.

The structures of the tetraamminecopper(II)dihalocuprates(I) II. The structures of Cu(NH 3) 4(CuBr 2) 2 and Cu(NH 3) 4(CuCl 2) 2·H 2O

The structures of Cu(NH 3) 4(CuBr 2) 2 and Cu(NH 3) 4(CuCl 2) 2 · H 2O were determined by X-ray single-crystal analysis. Both compounds belong to space group I4/mmm, and there are two formula weight units per unit cell. The structures were solved by Patterson sections, Fourier and difference-Fourier analyses, and refined by block-diagonal least squares. Each copper(II) ion lies in the plane of four nitrogen atoms. The copper(I) ions are tetrahedrally coordinated to four halide ions. The tetrahedra are joined on edges and extend as infinite chains along the c axis. There are eight equally spaced halide ions about copper(II) at a distance of 4·2 Å which is much greater than those normally associated with copper(II) halide covalent bonds. The visible spectra of these compounds can be explained in terms of crystal field splittings of the d orbitals while that of the iodide complex [2] may also be due to charge transfer transitions which involve both the cupricammine plane and cuprous iodide chains.