Cocrystals of 5-fluorocytosine. I. Coformers with fixed hydrogen-bonding sites

Cocrystallization attempts with 5-fluorocytosine yielded eight cocrystals and two structures of a single compound. In six cocrystals, the expected heterodimers held together by two or three hydrogen bonds are present. Ab initio energy calculations helped to rationalize the intermolecular hydrogen-bonding patterns observed in the crystal structures.