title: 1,10-Phenanthrolin-1-ium 2-carb-oxy-4,5-dichloro-benzoate.
abstract: In the structure of the 1:1 proton-transfer compound of 1,10-phenanthroline with 4,5-dichloro-phthalic acid, C(12)H(9)N(2) (+)·C(8)H(3)Cl(2)O(4) (-), determined at 130 K, the 1,10-phenanthrolinium cation and the hydrogen 4,5-dichloro-phthalate anion associate through a single N-H⋯O(carbox-yl) hydrogen bond giving discrete units which have no extension except through a number of weak cation C-H⋯O(anion) associations and weak cation-anion aromatic ring π-π inter-actions [minimum centroid-centroid separation = 3.6815 (12) Å]. The anions are essentially planar "[maximum deviation 0.214 (1) Å (a carboxyl O)] with the syn-related H atom of the carboxyl group, forming a short intra-molecular O-H⋯O(carbox-yl) hydrogen bond.
authors.forename: Graham
authors.initials: G
authors.lastname: Smith
authors.forename: Urs D
authors.initials: UD
authors.lastname: Wermuth
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: White