A low-temperature phase of the 1:1 complex of 2-(6-diethylamino-3-diethyl-iminio-3H-xanthen-9-yl)benzoate with ethyl gallate at 93 K.

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-diethylamino-3-diethyl-iminio-3H-xanthen-9-yl)benzoate (rhodamine B base abbreviated to RBB, a leuco dye) with ethyl gallate (EG, developer). The structure of the complex at room temperature has recently been reported by Sekiguchi, Takayama, Gotanda & Sano [Chem. Lett. (2007 ▶), 36, 1010-1011]. We have found a new phase of the material with two discrete base/developer complexes (RBB-A/EG-A and RBB-B/EG-B) in the asymmetric unit at 93 K. There are no significant differences between the two developer mol-ecules EG-A and EG-B. The lactone ring of RBB is opened in each mol-ecule to form a zwitterionic structure. However, the xanthene system is almost flat in RBB-A (r.m.s. deviation 0.0234 Å) but is less so in RBB-B (r.m.s. deviation 0.1095 Å). Furthermore, the ethyl groups of the xanthene diethyl-amino substituents lie on the same side of the xanthene plane in RBB-A but on opposite sides in RBB-B. Dimeric dye/developer complexes are formed through inter- and intra-molecular O-H⋯O hydrogen bonds and are linked further into dimers by additional O-H⋯O hydrogen bonds involving either EG-A or EG-B developer mol-ecules.