Superstructure and modulation wave analysis for the unidimensional conductor hepta- (tetrathiafulvalene) pentaiodide
- 15 March 1976
- journal article
- research article
- Published by AIP Publishing in The Journal of Chemical Physics
- Vol. 64 (6) , 2271-2286
- https://doi.org/10.1063/1.432535
Abstract
When acetonitrile solutions of tetrathiafulvalene [i.e., (C3S2H2)2; herein called TTF] and iodine, I2, are allowed to mix by diffusion, monoclinic crystals are formed with the approximate composition (TTF)7I5. These crystals have an electrical conductivity along the needle axis c of 300 ohm−1⋅cm−1 at room temperature. A complete crystal structure analysis based on an approximate supercell with a=48.016(16) Å, b= 16.041(6) Å, c=24.877(7) Å, β=91.31(2) °, Z=12 (RRF)7I5 was carried out using space group P21/a with 225 nonhydrogen atoms in the asymmetric unit. The TTF molecules stack along c and form a TTF subcell a1=a/3, b1=b, c1=c/7, Z1=4 TTF and subcell symmetry C2/m. The iodine atoms are in chains along c and form an A‐centered sublattice complex (space group A2/m) with a2=8.213 Å, b2= b, c2=5.023 Å, β2=103.0°, and Z2=2 I. The supercell space group P21/a is the mathematical intersection of the two subcell space groups. The supercell is only approximate because 5c2=25.113(14) Å which is about 1% longer than 7 c1; consequently, the particular crystal studied has the formula (TTF) I0.7076. The crystallographic R (F2) index is 10% for the 3715 x‐ray data with intensity greater than 1 sigma and 12% for the complete set of 5733 independent reflections. The stacked TTF molecules are displaced from their ideal sublattice complex positions by displacement waves with rigid‐body translational and rotational components. One‐ and three‐dimensional Fourier analyses of the displacements show that TTF molecules are displaced predominantly by translational displacements along b and torsional rotations about c and that the periodicities are related to the iodine sublattice complex. A similar analysis for the iodine substructure show modulations related to the TTF sublattice complex; thus the modulation waves of the system are related to the dual sublattice complex geometries. Special techniques were developed for solving and refining dual‐sublattice‐complex crystal structures using a principle that interacting sublattice complexes Fourier transform as convoluting reciprocal lattices. Application of these principles to another dual‐sublattice‐complex problem, the chimney ladder structure Mn15Si26, is discussed.Keywords
This publication has 21 references indexed in Scilit:
- dc conductivity of tetrathiofulvalene bromide () and TTF-single crystalsPhysical Review B, 1975
- Amplitude and nature of the charge-density-wave displacements in Pt.3.2O (KCP) at low temperaturesPhysical Review B, 1975
- Hepta(tetrathiafulvalene) pentaiodide: the projected structureActa Crystallographica Section B: Structural Science, Crystal Engineering and Materials, 1975
- Sinusoidal structure of the 1:1 complex of phenothiazine and 7,7,8,8-tetracyanoquinodimethane, PTZ–TCNQActa Crystallographica Section B: Structural Science, Crystal Engineering and Materials, 1974
- Classifications of magnetic structuresActa Crystallographica Section A, 1971
- The crystal structure of Mn15Si26Acta Crystallographica, 1967
- The crystal structure of Rh17Ga22, an example of a new kind of electron compoundActa Crystallographica, 1967
- The Crystal and Molecular Structure of 4-Phenyl-1,2-dithiolium Iodide.Acta Chemica Scandinavica, 1966
- The accuracy of atomic co-ordinates derived from Fourier series in X-ray structure analysis. IIIProceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 1947
- The accuracy of atomic co-ordinates derived from Fourier series in X-ray structure analysisProceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 1946