Multifacial Recognition in Binary and Ternary Cocrystals from 5-Halouracil and Aminoazine Derivatives

A systematic analysis using single crystal X-ray diffraction was performed to explore the role exerted by potential intercomponent proton-transfer reactions in the supramolecular structures of A–B cocrystals formed by 5-haloderivatives of uracil (A), coupled with 2-aminoadenine simulants (aminoazines, B). Twelve new heterodimers were synthesized in different stoichiometries and cocrystallized by solvent cogrinding followed by solution crystallization. In the binary cocrystals, uracil or 1-methyluracil with halide modification at the 5 position (F, Cl, Br, I) was coupled with amino-aromatic N-heterocycles (melamine, 2,4,6-triaminopyrimidine, 2,6-diaminopyridine) as a multivalent site for pyrimidine nucleobase recognition. The crystallographic analysis showed that, next to the expected neutral three-point hydrogen bonds (TPI), ionized TPI, favored by A → B proton transfer, can be used for WC multifacial recognition. Noteworthy, the formation of the charged TPI, which depends on the acid/base properties of t...