Stoichiomorphic Transition by Sublimation: A Case Study of 4-Aminobenzoic Acid and Isonicotinamide Cocrystals

Abstract

The abstract should be a single paragraph that summarises the content of the article This study investigates the thermal stability and gas-phase synthesis of the [PABA+iNAM] (1:1) and (2:1) cocrystals, including the first report of the 1:1 crystal structure. DSC and hot-stage microscopy identified eutectic points as the optimal window for controlled sublimation. Co-sublimation of physical mixtures, unlike separate substances, ensured phase purity by forming intermediate phases that synchronize mass transport. Transpiration measurements revealed incongruent sublimation for the 1:1 phase (5.4-fold pressure disparity) and near-congruent behavior for the 2:1 phase. QTAIMC analysis confirmed that robust homosynthons 'lock' PABA in the 2:1 lattice, aligning its volatility with iNAM, whereas an energy gap in the 1:1 phase leads to stoichiometric drift. We conclude that gas-phase synthesis success depends on the ability of intermediate solid phases to modulate volatility of the components.