title: A new polymorph of physcion.
abstract: The structure of the title compound, 7-methoxy-2-methyl-4,5-dihydroxyanthracene-9,10-dione, C(16)H(12)O(5), was originally reported by Ulický et al. [Acta Cryst. (1991). C47, 1879-1881] in the space group P2(1)2(1)2(1) [polymorph (Io)]. The new polymorph, (Im), crystallizes in the space group P2(1)/c. The molecular structures are closely similar, with both -OH groups forming intramolecular hydrogen bonds to one of the neighbouring quinone O atoms, thus slightly lengthening this C=O bond; the pattern of C-C bond lengths in the ring system is consistent with some contribution from a resonance form with a negative charge at the hydrogen-bonded quinone O atom and an aromatic region around its neighbouring C atoms. The packing of (Im) is simpler than the extensively crosslinked pattern of (Io), with molecular tapes connected by classical (but three-centre) and `weak' hydrogen bonds, parallel to [201].
authors.affiliation: Institute of Organic Chemistry, Technical University of Braunschweig, Germany.
authors.forename: Henning
authors.initials: H
authors.lastname: Hopf
authors.forename: Peter G
authors.initials: PG
authors.lastname: Jones
authors.forename: Eva
authors.initials: E
authors.lastname: Goclik
authors.forename: Pauline
authors.initials: P
authors.lastname: Aust
authors.forename: Johanna
authors.initials: J
authors.lastname: Rödiger
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D004642:Emodin / Q000031:analogs & derivatives* / Q000737:chemistry; D015394:Molecular Structure
chemical_list: C008905:physcione; D004642:Emodin