Crystal and molecular structure and EPR triplet spin excitons of NBP TCNQ, the 1:1 salt of 5-(1-butyl) phenazinium (NBP) with 2,2′- (2,5-cyclohexadiene-1,4-diylidene)-bispropanedinitrile (TCNQ)

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Abstract
The title compound C28H21N6, Mr=441.51 crystallizes in the triclinic space group P1̄, with lattice constants a=831.5(3), b=965.7(5), c=1638.3(8) pm, α=70.54(3)°, β=71.51(3)°, γ=76.78(3)°, V=1.165(1) nm3, Z=2, dc=1.258 Mg m−3. Final refinement yielded residuals R=0.050 and Rw=0.065. The structure consists of (NBP+)2 π-bonded dimers and (TCNQ−)2 π-bonded dimers that alternate along the [101] direction. The structure of NBP TCNQ thus is very similar to that of NBP TCNQF4 (where TCNQF4 is the 2,3,5,6-tetrafluoro derivative of TCNQ) but the latter salt belongs to the space group P21/c. The NBP+ and TCNQ− ions are planar, with interplanar distances of 344(2) pm for the donor pair, and 316(3) pm for the acceptor pair. The angle between the NBP+ and the TCNQ− planes is 5.9°. In the ESR experiments a single thermally activated ‘‘quasi-immobile’’ Frenkel triplet spin exciton (TSE) is seen, along with the usual g=2 impurity line and a second set of narrower g=2 lines that are probably due to exchange-narrowed TCNQ− radicals. The thermal activation energy for the S=1 spectrum is Ea=0.13 eV. The ESR fine structure tensor orientations and fine structure constants D/hc=±0.013 09(5) and E/hc=∓0.002 0(2) cm−1 are consistent with a model calculation using a triplet (TCNQ−)2 supermolecular state.

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