4-Chloro-3-fluoro-2-methylaniline–pyrrolidine-2,5-dione (1/1)

Chlorination of 3-fluoro-2-methylaniline with N-chlorosuccinimide gave one major regioisomer whose structure was determined by X-ray crystallography. The product was found to have cocrystallized with succinimide, giving the title compound, C7H7ClFN·C4H5NO2. The crystal structure is stabilized by N—H⋯O hydrogen-bonding and π–π stacking interactions with a centroid–centroid distance of 3.4501 (8) Å.

The sample was supplied in the form of large crystalline aggregates (4 mm across) coated with perfluoropolyether oil as a preservative. A large (0.8x0.8x0.4 mm) section was cut from the mass. The material did not have a strong cleavage -the crystals just fractured erratically. Because of the risk that further cutting might totally destroy the sample, an initial X-ray data set was measured from this large sample. The results confirmed the expected structure, but also showed a co-crystallized molecule of succinimide (Tukada & Mazaki, 1997).
At the end of the initial data collection, the sample was further subdivided into an irregular block approximately 0.41x0.44x0.75 mm. Prescans showed that the further cutting of the crystal had introduced fractures, but the sample was still amenable to analysis. Because of the degraded quality of the crystal, a data set with a target redundancy of 3 (as opposed to the usual 1) was collected. This highly redundant dataset would enable corrections to be made for the poor crystal quality.
Structure solution was slightly complicated because of the unexpected succinimide, but after that refinement and the location of all hydrogen atoms was normal. The two components are shown in Fig. 1. Fig. 2 shows the plane-to-plane alternate stacking of the components, with minimum inter-planar spacing of 3.37Å -presumable π -π stacking. The columns of molecules are interconnected by N-H···O hydrogen bonds which form discreet centrosymmetric 4-component clusters ( Fig. 3). mmol) was added and the mixture was allowed to warm to room temperature over 15 h (Fig. 4). Dilution with ethyl acetate, washing with water, drying (sodium sulfate), filtration and evaporation of the solvents gave a crude oil.
Crystals were grown from isopropyl ether by seeding and storing at 4°C for two weeks. The solvent was decanted and the crystals coated with 2 drops of FOMBLIN perfluoropolyether oil.

Refinement
The relatively large ratio of minimum to maximum corrections applied in the multiscan process (1:1.85) reflect the poor quality of the sample.
The H atoms were all located in a difference map, but those attached to carbon atoms were repositioned geometrically.
The H atoms were initially refined with soft restraints on the bond lengths and angles to regularize their geometry (C-H in the range 0.93-0.98, N-H in the range 0.86-0.89 N-H to 0.86 Å) and U iso (H) (in the range 1.2-1.5 times U eq of the parent atom), after which the positions were refined with riding constraints. Fig. 1. The title compound with displacement ellipsoids drawn at the 50% probability level. H atoms are shown as spheres of arbitary radius.