The charge-transfer complex 1-aminoanthraquinone–7,7′,8,8′-tetracyanoquinodimethane (1/1)

The reaction of 1-aminoanthraquinone with 7,7′,8,8′-tetracyanoquinodimethane yielded the title charge-transfer complex, C14H9NO2·C12H4N4. The molecules have maximum deviations from the mean planes through the non-H atoms of 0.0769 (14) Å for an oxo O atom and 0.1175 (17) Å for a cyano N atom, respectively. The dihedral angle between the two planes is 3.55 (3)°. In the crystal, molecules are stacked into columns along the a-axis direction. Pairs of N—H⋯N and N—H⋯O interactions connect the molecules perpendicular to the stacking direction. Additionally, an intramolecular N—H⋯O hydrogen-bond interaction is observed for 1-aminoanthraquinone.

The reaction of 1-aminoanthraquinone with 7,7 0 ,8,8 0 -tetracyanoquinodimethane yielded the title charge-transfer complex, C 14 H 9 NO 2 ÁC 12 H 4 N 4 . The molecules have maximum deviations from the mean planes through the non-H atoms of 0.0769 (14) Å for an oxo O atom and 0.1175 (17) Å for a cyano N atom, respectively. The dihedral angle between the two planes is 3.55 (3) . In the crystal, molecules are stacked into columns along the a-axis direction. Pairs of N-HÁ Á ÁN and N-HÁ Á ÁO interactions connect the molecules perpendicular to the stacking direction. Additionally, an intramolecular N-HÁ Á ÁO hydrogen-bond interaction is observed for 1-aminoanthraquinone.
In the title compound, the molecular structure unit matches the asymmetric unit ( Fig. 1). Both molecules show only a slight deviation from planarity. The maximal deviation from the least squares plane through all non-hydrogen atoms for the 1-aminoanthraquinone and the 7,7′,8,8′-tetracyanoquinodimethane molecule amount to 0.0769 (14) Å for O2 and 0.1175 (17) Å for N5, respectively, and the dihedral angle between the two planes is 3.55 (03)°. The bond angles suggest sp 2 hybridization for the C atoms and explain the planarity of both molecules. The structure is built from mixed stacks of donor and acceptor molecules. The stacks run the crystallographic a axis (Fig. 3). The mean distance between the molecules within the stack amounts to one half of the length of the a axis, i.e. 3.7456 (2) Å. This explains the low electrical conductivity of the compound. Above room temperature, however, a detectable electrical conductivity was observed, which reaches 4.4 × 10 -8 S/cm at 370 K. In the temperature range between 2 K and 300 K the title compound turned out as diamagnetic. The bond lengths within the dicyanomethylene groups suggest that the TCNQ units are neutral, comparing with crystal and infrared literature data (Kaim & Moscherosch, 1994). However, a small charge transfer is apparently present, since the electrical resistivity falls with increasing temperature indicating semiconducting characteristics. From the resistivity data, an Arrhenius development -ln(1/R) versus. 1/T gives a mainly linear behaviour, from which a small barrier for the thermally activated transport of 1.25 eV can be derived, according with dark brown colour of the crystals.

Experimental
Starting materials were commercially available and were used without further purification. 1-Aminoanthraquinone and 7,7′,8,8′-tetracyanoquinodimethane were dissolved in CH 2 Cl 2 separately at room temperature and equimolar concentrations. The solutions were combined and maintained for 4 h under continuous stirring. Dark brown crystals, suitable for X-ray analysis, were obtained by the slow evaporation of the solvent. Elemental analysis: Calc. 73.1 C, 3.1 H, 16.4 N; found 72.8 C, 3.4 H, 16.6 N. The melting point was determined by differential scanning calorimetry to 520 K.
Exothermic decomposition occurs at 555 K.

Refinement
All hydrogen atoms were localized in a difference density Fourier map. Their positions and isotropic displacement parameters were refined.  The molecular structure of the title compound with labelling and displacement ellipsoids drawn at the 40% probability level.   Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.