Urea Cocrystals for Sustainable Nitrogen Release: Design, Synthesis, and Characterization

To address the severe nitrogen leaching of urea, this study explores the role of coformer substituent effects in modulating the structure−property relationships of urea cocrystals. Guided by the ΔpKa rule and molecular electrostatic potential analysis, four urea cocrystals are synthesized. Crystal structure analysis reveals that the steric and electronic effects of the substituents regulate the hydrogen-bonding motifs and molecular packing arrangements. Computational analysis further demonstrates that the incorporation of coformers promotes the molecular assembly centered on O−H···O heterosynthons. This supramolecular restructuring enhances the phase stability of the cocrystals, reduces the maximum moisture uptake to as low as 1/10889 that of urea, and decreases the initial 15 min release of urea from 100% to as low as 3.54%. This study provides a theoretical basis for the rational design of functional agricultural materials with tailored release profiles.