Crystal and molecular structure and ESR spectra of the 1:1 salt 5-(1-butyl)phenazinium (NBP)-2,2′-(2,3,5,6-tetrafluoro-2,5- cyclohexadiene-1,4-diylidene)-bispropanedinitrile (TCNQF4)

Abstract

The title compound C28H17F4N6, Mr=513.48, crystallizes in the monoclinic space group P21/c, with a=10.972(2) Å, b=17.557(3) Å, c=13.523(4) Å, β=111.88(2)°, V=2417.36 Å3, z=4, and dc=1.411 Mg m−3. Final refinement yielded residuals of R=0.056 and Rw=0.046. The structure consists of (NBP+)2 and (TCNQF−4)2 dimers stacked in a DDAA sequence along the c axis. The NBP+ and TCNQF−4 ions are planar, with interplanar distances of 3.54(2) Å for a donor pair and 3.15(3) Å for an acceptor pair. The angle between the NBP+ and TCNQF−4 planes is 15.8°. In the ESR experiments, two equivalent species of thermally activated Frenkel triplet spin excitons (TSE), with differently oriented fine structure tensors, are observed. They are located on two TCNQF4 molecular pairs of different orientation. A motion of the TSE in the b direction can be excluded. Additional S=1/2 lines are due to immobile doublet spins on TCNQF−4 radical ions.

Spin Multiplicity and Solid-State Electrochemical Behavior in Charge-Transfer Co-crystals of DBTTF/F4TCNQ

“…Based on these observations, the recorded doublet state can thus be assigned to isolated radical species, possibly defects, or highly localized spin 1/2 on DBTTF. Preliminary measurements on a single crystal reassure that the radical is not induced by grinding, in keeping with similar observation reported in the case of 5-alkylphenazinium–TCNQ charge-transfer crystals . Superimposed to the narrow doublet signal, a weaker six-line pattern is observed, which can be safely attributed to S = 1 species.…”

Structural and iron-57 Moessbauer characterization of 1:1 and 2:3 ferrocenium salts of 7,7,8,8-tetracyanoperfluoro-p-quinodimethane

“…The average bond distances are in excellent agreement with those previously reported for the Nbutylphenazenium salt of (TCNQ)F4, which also possesses [(TCNQ)F4]22" dimers. 27 Except for the C-CN bond, which differs by -0.012 A, the remaining distances are <0.005 A smaller. With respect to (TCNQ)F4°,29 the central and exo C=C bonds are ~0.02 and ~0.04 A longer, while the C-C(CN)2 and C-CN bonds constrict by ~0.02 and ~0.01 A, respectively.…”

“…The dimer [(TCNQ)F4]"'s are separated by 3.155 Á, which is comparable - to that reported for the W-butylphenazenium salt (i.e., 3.15 Á). 27 The metric parameters listed in ([(TCNQ)F4]-).…”

Electron Spin Resonance: A Major Probe for Molecular Conductors

“…Many TCNQ salts have a singlet (i.e., nonmagnetic) ground state. As a consequence, the magnetic susceptibility is activated and the EPR signal has been attributed to a thermally accessible triplet state. − After this pioneer work of Chesnut et al, a large number of results have been obtained in various TCNQ or related salts. − Rather than localized triplet states, the magnetic excitations should be described as triplet excitons delocalized over several TCNQ molecules. As a consequence, the triplet spin density sees a randomly changing nuclear spin environment and no hyperfine structure can be observed.…”