00143
Hydrogen bonding in two solid phases of phenazine-chloranilic acid (1/1) determined at 170 and 93 K

Department of Chemistry, Faculty of Science, Okayama University^* Department of Chemistry, College of Humanities and Sciences, Nihon University^**
○Kazuma Gotoh^* Tetsuo Asaji^** Hiroyuki Ishida^*

Horiuchi et al. [1, 2] have revealed that the title compound, C₁₂H₈N₂･C₆H₂O₄Cl₂, has a ferroelectric phase (space group P2₁) below 253 K, in which the phenazine and chloranilic acid molecules are arranged alternately through O-H...N hydrogen bonds to form a one-dimensional supramolecular structure. Recently, Saito et al. [3] reported two phase transitions at 136 and 146 K by heat capacity measurements. The low temperature phases were also detected by NQR measurements [4, 5]. In the present study, we have determined the crystal structure in the low-temperature phase stable below 136 K and re-determined the structure in the ferroelectric phase in order to clarify the hydrogen bonding scheme in each phase. In both phases the compound crystallizes in the space group P2₁. These structures are essentially same, except for the H atoms involved in the hydrogen bonds formed between the base and the acid. In the ferroelectric phase, H atoms in the hydrogen bonds are attached to O of the acid as reported by Horiuchi et al., but one H atom (H4) was found to have a considerably large U_iso value compared to that of the other H atom (H2), suggesting that atom H4 is disordered in the hydrogen bond. On the other hand, in the low temperature phase the H atom corresponding to atom H4 was found to be attached to N, which implies that proton transfer of one of the two H atoms of the acid to the base occurs in this phase.
[1] Horiuchi et al. (2005). Nat. Mater. 4, 163-166. [2] Horiuchi et al. (2005). J. Am. Chem. Soc. 127, 5010-5011. [3] Saito et al. (2006). J. Phys. Soc. Jpn., 75, 033601-1-3. [4] Asaji et al. (2006). J. Mol. Struct. 791, 89-92. [5] Watanabe et al. (2006). Annual Meeting of Chem. Soc. Jpn. , Tokyo, Japan, 2PC-021.