Crystal structure of 10-(2′-pyrazyl)phenothiazine and spectroscopic identification of its radical-cations and dications

The crystal structure of 10-(2′-pyrazyl)phenothiazine has been determined by the single crystal x-ray diffraction technique. The crystal belongs to the orthorhombic system with a space group of Pbca. The unit cell parameters are a = 10.633(3), b = 7.525(2), and c = 32.984(6)Å, with eight molecules in a unit cell. The final disagreement index, R, is 0.057 for 1944 observed reflections. The central ring of the phenothiazine ring system is in a broad conformation and the 10-(2′-pyrazyl)substituent is attached to the phenothiazine central ring in a boat-axial conformation. This is the first reported phenothiazine whose 10-substituent is perpendicular to the plane bisecting the dihedral angle of the phenothiazine nucleus. Ultraviolet absorption maxima of the title compound in various oxidizing and non-oxidizing medium is reported. These data indicate that the geometry of 3 changes when it is oxidized to its radical-cations and dications.