Manifestation of cocrystals and eutectics among structurally related molecules: towards understanding the factors that control their formation

Abstract

Co-crystallization among isomeric pyridinecarboxylic acids and amides was executed towards the understanding of the formation of cocrystals and eutectics in structurally related molecules. Cocrystals have formed for all amide–amide combinations (picolinamide–nicotinamide and picolinamide–isonicotinamide, with an already known nicotinamide–isonicotinamide cocrystal) and eutectics have formed for all acid–acid combinations (picolinic acid–nicotinic acid, picolinic acid–isonicotinic acid and nicotinic acid–isonicotinic acid). Among the acid–amide combinations, all three amides form cocrystals with picolinic acid, whereas only eutectics are generated with nicotinic acid and isonicotinic acid, respectively. The contest between homomeric and heteromeric interactions and the influence of the anti-NH carboxamide group in the manifestation of different adducts for varied combinations are outlined.