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, C28H30N2O3, has been d etermined at 120 K using synchrotron radiation at a wavelength of 0.496 Ang strom. The structure contains two independent rhodamine B molecules with vi rtually identical geometry. The xanthene main planes of the molecules are i nclined at an angle of 41.6 (2)degrees to one another. Molecule 2 has a sta tistically 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) Angs trom. There are no classical hydrogen bonds, but the structure is stabilize d by two short C . . . O interactions. The crystals of the lactone form wer e produced by a novel hydrothermal reaction.