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

The title compound, C(28)H(30)N(2)O(3)·C(9)H(10)O(5), is a well known red leuco complex of 2-(6-diethyl-amino-3-diethyl-iminio-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 inter-molecular O-H⋯O hydrogen bonds. In a subsequent re-examination of the structure at room temperature, we found the RBB mol-ecule to be disordered with a methyl group of one ethyl substituent of a diethyl-amino 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 diethyl-amino 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.