Thomas J. Emge

Solution and Solid State Studies of Tetrafluoro-7,7,8,8-Tetracyano-p-Quinodimethane, TCNQF4. Evidence for Long-Range Amphoteric Intermolecular Interactions and Low-Dimensionality in the Solid State Structure

Solution and solid state studies of TCNQF4 are reported. The electron affinity of TCNQF4 has been derived from spectral observations of the visible-near IR charge-transfer band for the pyrene compl...

Crystal Structures for the Electron Donor Dibenzotetrathiafulavalene, DBTTF, and Its Mixed-stack Charge-transfer Salts with the Electron Acceptors 7,7,8,8-tetracyano-p-quinodimethane, TCNQ, and 2,5-difluoro-7,7,8,8-tetracyano-p-quinodimethane, 2,5-TCNQF2

Crystal structures for the electron donor DBTTF and its charge-transfer salts with the acceptors TCNQ and 2,5-TCNQF2 are reported. Crystal data for the three systems are as follows: (a) neutral DBT...

Structure of an organic charge‐transfer salt derived from dibenzotetrathiafulvalene and tetrafluorotetracyanoquinodimethane (DBTTF–TCNQF4). Observation of a high‐temperature phase transition

The crystal structure of the organic charge‐transfer salt DBTTF–TCNQF4 is reported. The structure has been determined by single‐crystal x‐ray diffraction techniques and has been shown to consist of segregated stacks of donor and acceptor molecules. Within both the donor and acceptor stacks, significant dimerization is observed at room temperature. From the geometries of the DBTTF and TCNQF4 molecules, it is concluded that the charge transfer is complete. The electrostatic contribution to the crystal cohesion for DBTTF–TCNQF4 has been calculated and compares well to those for similar salts of unit charge transfer. It is suggested that the room‐temperature structure may well be representative of the low‐temperature phase of a system affected by a Peierls instability. Based on diffraction data, a phase transition near 390 K is reported. The driving force for the transition is likely a spin–phonon instability. Crystal data for DBTTF–TCNQF4 are triclinic, space group P1; a = 13.159(3) A, b = 13.703(4) A, c = ...

Crystal Structure and Madelung Energy for the Charge-Transfer Complex Tetrathiafulvalene-2,5-Difluoro-7,7,8,8-Tetracyano-p-Quinodimethane, TTF-2,5-TCNQF2. Observations on a Dimerized Segregated Stack Motif.

Abstract The twinned crystal structure of the charge-transfer complex TTF-2,5-TCNQF2 has been determined by single-crystal X-ray diffraction techniques. From intensity measurement on one twin component, a full structural model has been developed. The model encompasses segregated stacks of TTF donors and 2,5-TCNQF2 acceptors, with each chain exhibiting significant dimerization. The alternate interplanar spacings in the TTF stack are 3.34A and 3.60A, while those in the 2,5-TCNQF2 stack are 3.23A and 3.55A. Nearly eclipsed molecular overlap patterns are found within each of the dimerized pairs. The Madelung energy of TTF-2,5-TCNQF2 has been calculated at − 2.65 eV per donor/acceptor pair for full charge transfer, utilizing partial atomic charges obtained from CNDO/INDO molecular orbital calculations. Full charge transfer is considered appropriate for this complex based primarily on the observed component molecular geometries. The dimerized structural motif observed at room temperature for the TTF-2,5-TCNQF2 ...

Synthesis of Δ2,2′-bithieno[3,4-d]-1,3-dithiole (DTTTF) and some of its charge-transfer salts

The title compound (DTTTF) was prepared by the coupling of the corresponding thieno-1,3-dithiolium salt, obtained from thieno-1, 3-dithiolane-2-thione synthesized from 3,4-dibromothiophen.

Elements of the Crystal Structure of a Solvated 1:1 Charge-Transfer Salt Derived from Tetrathiafulvalene (TTF) and Tetrafluorotetracyano-p-Quinodimethane (TCNQF4), TTF-TCNQF4

Abstract The 1:1 charge-transfer salt TTF-TCNQF4 crystallizes (from cyclohexane/acetonitrile) in the monoclinic system, space group P2/m, with a = 16.562(4) A, b = 10.728(4) A, c = 7.013(1) A, β = 97.39(2)°, V = 1235.6 A3. A structural solution has been obtained by Patterson-Fourier methods and refined (based on 2107 non-zero F 0s) to an R value of 0.18. The crystal structure of solvated TTF-TCNQF4 consists of segregated stacks of donors and acceptors propagating along the c axis. Parallel to these columnar arrays are solvent channels of unresolved composition. Disorder within these solvent channels prevents a detailed description of their contents; the basic elements of the donor and acceptor stacks are, however, well-defined. The TCNQF4 acceptor column is both distance and overlap modulated (eclipsed, dimeric interaction at a mean separation of 3.25 A, and ring-over-bond, monomeric interaction at 3.43 A). The TTF donor column shows analogous eclipsed and ring-over-bond overlap patterns; however, the di...

Crystal, Molecular and Electronic Structure of the Electron Acceptor 2,5-difluoro-7,7,8,8-Tetracyano-p-quinodimethane, 2,5-TCNQF2

Abstract The crystal structure of the electron acceptor 2,5-difluoro-7,7,8,8-tetracyano-p-quinodimethane, 2,5-TCNQF2, has been determined by single-crystal X-ray diffraction methods. The layered crystal structure is dominated by the antiparallel coupling of cyano bond moments of symmetry-related molecules. The molecular and electronic structure (INDO approximation) of 2,5-TCNQF2 are extensively compared to that of its parent TCNQ and the perfluoro analog TCNQF4. Crystal data for 2,5-TCNQF2 are as follow: monoclinic, space group C2/m, a=10.208(4) A, b=6.026(2) A, c=8.836(3) A,β=106.64(3)[ddot], V=520.8 A3. The site symmetry (2/m;C2h) in the crystal is identical to that for the free 2,5-TCNQF2 molecule

On the Crystal Structure of the Organic Charge-Transfer Salt Derived from Hexamethylenetetraselenafulvalene (HMTSF) and Tetrafluoro-7,7,8,8- Tetracyano-p-Quinodimethane (TCNQF4), HMTSF-TCNQF4

Abstract The charge-transfer salt HMTSF-TCNQF4 crystallizes in the monoclinic system, space group C2/m, with the following crystal data: a = 21.906(5) A, b = 12.918(3) A, c = 4.018(1) A, β = 91.66(1)°, V = 1136.5 A3 Z = 2, D cale, = 2.186 g cm−3 Dcale,= 2.17(2) g cm−3. A structural model was readily deduced from standard Patterson-Fourier methods and has been refined (based on 1175 counter-collected X-ray data) to an R value of 0.048. The crystalline motif is dominated by uniform, segregated stacks of donors and acceptors. Within each stack, the molecular overlap pattem is of the ring-over-bond type and the mean interplanar separations are 3.68 A (donor column) and 3.24 A (acceptor column). Principal intercolumn contacts are of two types: Se(donor) … F(acceptor) at 3.19 A and Se(donor) … N(acceptor) at 3.36 A. Comparisons are made between the crystal structure and physical properties of HMTSF-TCNQF4 and HMTSF-TCNQ (to which it is isostructural) and to those of HMTTF-TCNQ and HMTTF-TCNQF4 (to which it is c...

Crystal Structure of Monofluoro-7,7,8,8-Tetracyano-p-Quinodimethane, TCNQF. Evidence for Strong One-Dimensional Coupling of Molecular Dipole Moments

Abstract The crystal structure of the asymmetric electron acceptor TCNQF has been determined by X-ray diffraction techniques. The crystals are monoclinic, space group P21/n, with the following primary crystallographic data: a = 7.596(3)A, b = 8.204(4)A, c = 8.428(2)A, β = 90.90(3)[ddot], V = 525.3(3)A3, Z = 2, Dmeasd = 1.42(2) g cm−3, Dcalcd = 1.405 g cm−3. The presence of two molecules per cell requires 1(C1) molecular symmetry, inconsistent with the molecular structure of TCNQF. A centrosymmetrical twin model has been developed and refined by the full-matrix least-squares method based on counter-collected intensities. The dominant intermolecular interaction in the crystal is the one-dimension coupling of TCNQF molecules through their electric dipole moments. An estimation from an LCAO-MO calculation yields a molecular dipole moment of 2.0 D for TCNQF.

(TMTSF)2(2,5-Tcnqbr2): Structure and Physical Properties

Abstract The 2:1 charge-transfer salt (TMTSF)2(2,5-TCNQBr2) has been prepared and its physical properties investigated. Its crystal structure consists of segregated stacks of TMTSF donors (ring-over-bond overlap pattern; mean interplanar spacing of 3.6A) and chains of edge-on and disordered 2,5-TCNQBr2 acceptors. Infrared data are suggestive of unit charge on the 2,5-TCNQBr2 molecule and, therefore, half charge on the TMTSF donor. Resistivity data are successfully interpreted on the basis of a percolation construction. Magnetic data are also presented.