A synchrotron-radiation study of the lactone form of rhodamine B at 120 K

The structure of the lactone form of rhodamine B, 3, 6-bis(diethylamino)-1',3'-dihydrospiro[xanthene-9, 3'-isobenzofuran]-1'-one, C(28)H(30)N(2)O(3), has been determined at 120 K using synchrotron radiation at a wavelength of 0.496 A. The structure contains two independent rhodamine B molecules with virtually identical geometry. The xanthene main planes of the molecules are inclined at an angle of 41.6 (2) degrees to one another. Molecule 2 has a statistically disordered ethyl group, with 71% in one orientation and 29% in a second orientation. The lactone C-O bonds are 1.497 (1) and 1.495 (1) A. There are no classical hydrogen bonds, but the structure is stabilized by two short C.O interactions. The crystals of the lactone form were produced by a novel hydrothermal reaction.