All systems studied are single-carrier conductors with bulk cation conductivity and high anion disorder. The nature of disorder and its relationship to phase transitions~. as well as interchain coupling and aggregation in the cation chain, were evaluated in these compds. The nature of this transition is affected by the presence of disorder, the degree of interchain coupling, and the nature of the molecular packing along the chain (ie, eclipsed vs. sliding packing).
Since a variety of isocyanide ligands can be used, a systematic variation of electrical properties can be achieved within the series of complexes. Disorder, especially that associated with anions, is an important structural feature of all compounds. 67 at -250° K was studied in detail and the symmetry of the low-temperature phase was determined.
It appears that the Peierls transition is incomplete due to the aperiodic potential due to the iodine chain, which produces states within the energy gap. All highly conductive members of the latter group are iridium carbonyl halides or partially oxidized platinum acyanide and oxalate salts (1-6).
ML+) IHFlt1liE
CHAPTER 4
Three standard reflections and 606 were measured every 40 reflections for purposes of scale. gt;1%) significant crystal decay, although oscillation photographs taken after data collection revealed that the sharpness and intensity of the diffuse h3£ reflections of the supercell had decreased significantly. A Weissenberg photograph of the third diffuse line revealed spots with slight extension in the stick that were not significantly broadened in the 28 direction. The distribution of iodine obtained from subcell data is a smoothly varying column of electron density along (~,y,~) with a minimum of 5.15 and a maximum of 26.2 e/~3.
Differences in the absolute value of the electron density maximum are not significant, or the grid size in the Fourier maps may have been different. 1 is consistent with the arrangement of TTT molecules and the absence of systematic deficiencies for h3t reflections. The most important effect of adding the k = 3 data is to increase the electron density to two from four now.
The phase of the reflections h3t, h even, is determined by arbitrarily choosing two of the four equivalent electron density maxima for amplification. The magnitude of the displacement can be determined from the h3t, h odd reflections, but the direction of the displacement cannot be determined. Refinement of the model was performed by adjusting the populations, temperature factors, and iodine atom coordinates until the difference Fourier map was nearly flat.
Note that there is significant electron density at three of the four minima; that all maxima. The atomic coordinates and temperature factors of the TTT cation are not refined in the lower symmetry space group of the. Only iodine-iodine vectors are therefore needed for interpretation of the Patterson map, and contributions of C and S atoms from TTT.
Twofold di.order between the crystallographically different configurations shown in 4a and 4b is responsible for the fractional occupation (~.6) of two of the iodine positions (y = .28; y = .50), and the 11smearing11 of electron density in their direction. However, the very significant electron density between maxima indicates that there is exchange of iodine atoms between sites. The presence of disorder in the iodide chains of TTT2I3 has been invoked to explain the retention of conductivity at low temperature, although the nature of the disorder and its behavior on cooling are not understood (l-4,7).
CHAPTER 5
Crystals of both TMTSF salts were flat needles showing well-formed {110} and {010} faces. Unfortunately, the oxidation product also appears to be quite soluble at this temperature, even in the presence of fairly high concentrations of bromide or thiocyanate. The presence of strong satellites of the hkO layer indicates that the superperiod is due to modulation of the structure factor rather than modulation of the length of the C axis, as the latter would yield hkO satellites of vanishingly small intensity (9).
The deviation of C-H bond lengths and angles from expected values may be due to torsional motion of the methyl groups. A difference map, based on refined coordinates of non-hydrogen atoms, through the plane of the hydrogen atoms, is shown in Figure 5. The TMTSF(SCN) 0•50 data were phased by placing TMTSF molecules at positions equivalent to those in the refined.TMTSF(Br).
The electron density in the difference map also indicates the presence of a small disordered molecule similar to that seen in TMTSF(Br). In the structure modulation analysis, only hkl I and hk2' reflections (ci = 33,815 a) were used. This modulation pattern, in Space Group Cmc21, along with fitting some smaller peaks, results in R ~ .397 for 54 reflections with F2.
There are no short contacts between stacks and van der Waals contacts (3.77 ~ in the bromide) occur alone. In both compounds the anion sites are not fully occupied and there is a partially occupied site for small molecules (solvent) in the x=O plane. The period of the modulation of the (TMTSF)(SCN)0.50 structure is similar to the periods of disproportionate charge density waves observed in K2Pt(CN)4Br0_30 xH20, (TTF)(TCNQ), {TSeF )(TCNQ).
It is not unreasonable to interpret the modulation of the SCN chain as a response to a. Thiocyanate orientation disorder will also be retained, while the high thermal motion of the bromide. 50 can be expected to result in the retention of moderate conductivity to lower temperatures than in the bromide.
APPENDIX 1
Rh(CN CH CH2)4Jc104 - Structure factors, room temperature data obtained with unfiltered CuKa radiation.
APPENDIX 2
APPENDIX 3
Compare, for example, the electron density map and the ORTEP of carbon 6 in the structure [Rh(CNCHCH2) at room temperature. TTT)2I3 and (TTF)Cl 0.67 or disordered perchlorates in [Rh(CNCHCH2)4JC104, can be made in many ways that are equally valid. In all cases, the observed electron density is much more informative than the parameters used to fit it.
The types of structural disturbances and distortion that give rise to diffuse spots in the diffraction patterns of (TTF)Cl. A disturbance that appears as errors with respect to an ideal grating gives rise to a broadening of the diffraction peaks (1,2,3). This expression was used to determine the size of diffracting domains in (TTF}Cl 0.67 after rapid cooling.
It can also be used to determine the order of the chloride sublattice in (TTF)c1. This was not done quantitatively for the following reasons. a) Accurate profiles must be obtained with a very small or narrow opening for the X-ray beam. The order of iodide ions in (l.d.)(TTT) 2I3 is difficult to estimate, since part of the diffracted intensity indicates only one-dimensional order, while the spots on the diffuse third layer indicate a rather long three-dimensional order (~ 1000.
The modulation of the structures produces superperiods and leads to the observation of satellite reflections on diffraction patterns. Early treatments of this effect distinguished between modulation of unit cell parameters and structure factor amplitude (4). No attempt was made to accommodate the large decrease in intensity from the first.
