Investigation on the Solvent Effect in Vanillin Habit Evolution

Rationalization of the relationship between solvents and crystal habit is of great importance to the development of crystal engineering. In this paper, the impact of different solvents on vanillin habit was investigated. The results show that the crystal habit of vanillin is closely related to the type of solvent, it was found that vanillin crystals were improved to the short and thick plate in organic acid, and the antisolvent water elongates crystals to needles, in contrast, alkane solvents could not change its habit. The molecular assembly preference of vanillin in solution and crystal was investigated by proton nuclear magnetic resonance, electrostatic potential map, noncovalent interaction plot, and crystal structure analysis. The results suggest that vanillin molecules prefer to assemble by a head-to-tail motif via the intermolecular H-bond. The underpinning mechanism of the solvent effect on the vanillin habit was further rationalized by crystal surface analysis and molecular adsorption analysis. Half-parallel-half-intercepted and all-intercepted H-bonding patterns were observed on the lateral and capped faces, respectively. Different adsorption preferences of propionic acid, water, and n-hexane on the lateral and capped faces were observed via adsorption locator analysis, the adsorbed solvent molecules might result in interference on the crystal growth of corresponding faces, and hence modify the crystal habit.

Automated summary

The relationship between solvents and crystal habit is crucial for crystal engineering. This paper investigates the impact of different solvents on the habit of vanillin crystals. The results reveal that the crystal habit of vanillin is closely related to the solvent type. Organic acids lead to short and thick plate-like crystals, while the anti-solvent water elongates crystals to needle-like shapes. In contrast, alkane solvents have no effect on the habit. The study also explores the molecular assembly preferences of vanillin and the mechanism underlying the solvent effect on crystal habit through various analytical techniques.