Blackwell Publishing Acta Medica Okayama 0108-2701 63 1 2007 Hydrogen bonding in two solid phases of phenazine-chloranilic acid (1/1) determined at 170 and 93 K o17 o20 EN Kazuma Gotoh Tetsuo Asaji Hiroyuki Ishida The crystal structures in two solid phases, i.e. phase II stable between 146 and 253 K and phase IV below 136 K, of the title compound [phenazine-chloranilic acid (1/1), C12H8N2 center dot C6H2Cl2O4, in phase II, and phenazinium hydrogen chloranilate, C12H9N2+center dot C6HCl2O4-, in phase IV], have been determined. Both phases crystallize in P2(1), and each structure was refined as an inversion twin. In phase II, the phenazine and chloranilic acid molecules are arranged alternately through two kinds of O-H center dot center dot center dot N hydrogen bonds. In phase IV, salt formation occurs by donation of one H atom from the chloranilic acid molecule to the phenazine molecule; the resulting monocation and monoanion are linked by N-H center dot center dot center dot O and O-H center dot center dot center dot N hydrogen bonds. No potential conflict of interest relevant to this article was reported.