A redetermination of 2-(6-diethylamino-3-diethyliminio-3H-xanthen-9-yl)benzoate–ethyl gallate (1/1) at room temperature

Abstract

The title compound, C28H30N2O3·C9H10O5, is a well known red leuco complex of 2-(6-diethylamino-3-diethyliminio-3H-xanthene-9-yl)benzoate (rhodamine B base abbreviated to RBB: leuco dye) with ethyl gallate (EG: developer). The structure of the complex at room temperature has recently been reported by Sekiguchi, Takayama, Gotanda & Sano [(2007) Chem. Lett. 36, 1010–1011]. The RBB–EG complex forms a dimer (RBB...EG...EG...RBB) through intermolecular O—H...O hydrogen bonds. In a subsequent re-examination of the structure at room temperature, we found the RBB molecule to be disordered with a methyl group of one ethyl substituent of a diethylamino group at one extremity of the xanthene unit disordered over two positions [occupancies: 0.735 (5)/0.265 (5)]. Furthermore, at the other end of the xanthene residue, the entire diethylamino substituent (i.e. the N atom and the associated C and H atoms) was also disordered over two sites with occupancies 0.653 (7)/0.347 (7). This leads to four kinds of RBB conformations, which, in turn, results in the formation of 16 discrete RBB...EG...EG...RBB dimers in the crystal.