Structure of the red, semiconducting form of 4,4',5,5'-tetramethyl-Δ^2,2'-bi-1,3-diselenole-7,7,8,8-tetracyano-p-quinodimethane, TMTSF–TCNQ

Abstract

A red, semiconducting salt containing TMTSF and T_CNQ crystallizes in the triclinic system, space group P1, with one molecule of each component in a unit cell with the following crystal data: C IoHI2Se4.CI2H4N4, M r = 652.24, a = 8.096(3), b = 10.465(3), c = 6.998 (2)/k, a = 103.78 (2), /3 = 98.49 (3), ~ = 94.91 (3) ° , V = 565.0 (3) A a, D,, = 1.94 (1), D c = 1.92 g cm -3. Intensity data, collected by counter methods on an automated diffractometer operating in the 0-20 scan mode and employing monochromatized Mo Ka radiation (2 = 0.71069/~,, g = 71.2 cm-~), gave 2306 non-zero reflections which were used in the refinement of a standard heavy-atom solution by the full-matrix least-squares method. With fully anisotropic parameters for the nonhydrogen atoms and fixed, isotropic parameters for the H atoms, a final R value of 0.045 was obtained. The structure is composed of stacks of alternating TCNQ and TMTSF molecules positioned about centers of symmetry along the crystallographic c axis and separated by ~3.5 A. Each molecular component is rather planar and the TCNQ molecule is very nearly parallel to and directly centered above and below each adjacent TMTSF molecule and vice versa. The observed stacking pattern yields an excellent approximation to a mixed-stack array whose re-molecular charge-transfer integral is zero. It is estimated from vibrational frequency data and structural considerations that the degree of charge transfer is non-zero and approximately 0.2 e. The non-zero charge transfer is suggested to arise from the admixing of excited-state molecular orbitals within the mixed-stack crystal band.

Intramolecular Mixed‐Valence State Through Silicon or Germanium Double Bridges in Rigid Bis(Tetrathiafulvalenes)

“…These geometrical characteristics for 1C + , but also 2C + , combined with the analysis of the geometrical parameters of TCNQ, [19] indicating a donor-acceptor charge transfer of 1, strongly support the assumption of mixed-valence charge-transfer compounds with a mean charge of + 0.5 on each TTF unit. The donors are longitudinally shifted along the c axis and interact along the a axis in the ac plane, through a favorable axial overlap (interaction I) between the external dithiol moieties, which is characterized by an intermolecular S2···S2 contact at 3.726 , comparable with the sum of the van der Waals radii (3.70 ) of two S atoms ( Figure 7).…”

Small gap semiconducting organic charge-transfer interfaces

“…9,10 In the TMTSF-TCNQ interfaces, we observe a conductance that is thermally activated with a small ͑ϳ100 meV͒ activation energy. From the measured mobilities of charge carriers in the individual crystals in conjunction with the measured resistivity values, we estimate that the density of transferred charge is in the order of 10 11 cm −2 at room temperature, corresponding to less than 0.001 electrons per molecules, i.e., approximately three orders of magnitude smaller than what is found in the two bulk phases, [11][12][13][14][15][16] and decreasing in a thermally activated way with lowering temperature. We analyze these findings in terms of a simple band diagram, and show that our observations are consistent with a picture based on noninteracting electrons which are thermally excited from the valence band of TMTSF into the conduction band of TCNQ.…”

Structure of di(S-methylthiouronium)–tri(7,7,8,8-tetracyano-p-quinodimethane) dihydrate, (MT)2(TCNQ)3.2H2O

“…The bond lengths of molecules A and B are given in Table 2. The evaluation of the charge transfer was based on the correlation between bond distances and ionicity in the TCNQ anion (Flandrois & Chasseau, 1977;Kistenmacher, Emge, Bloch & Cowan, 1982). The calculated charge of the A molecule is -0-9 e and that of the B molecule is -0.4 e and thus the trimer has a charge -1.7 e. Further analysis of the B molecule bond lengths suggests that the charge is distributed asymmetrically and located on the part of TCNQ(B) near the cation.…”