Structure and semiconducting characteristics of the CT complex 1-aminoanthraquinone–TCNQ.

What is it about?

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.

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Why is it important?

Above room temperature 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. 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.