Multicomponent Crystalline Solid Forms of Pyridinecarboxamides and DL-2-Hydroxy-2-phenylacetic Acid

We have prepared co-crystals of racemic DL-2-Hydroxy-2-phenylacetic acid (DL-Mandelic acid, DL-H2ma) with achiral 2-Pyridinecarboxamide (picolinamide, pic), 3-Pyridinecarboxamide (nicotinamide, nam) and 4-Pyridinecarboxamide (isonicotinamide, inam); they have been characterized by elemental analysis, single crystal and powder X-ray, IR spectroscopy and 1H and 13C NMR. The crystal packing is stabilized primarily by hydrogen bonding and in some cases through π-π stacking interactions. The analysis of crystal structures reveals the existence of the characteristic heterosynthons with the binding motif R (8) 2 2 (primary amide-carboxilic acid) between pyridinecarboxamide molecules and the acid. Other synthons involve hydrogen bonds like (carboxyl)O-H···N(pyridine) and (hydroxyl)O-H···N(pyridine).