Hydrogen bonding in proton-transfer complexes of cytosine with trimesic and pyromellitic acids

Protons-transfer complexes (1:1) of cytosine with trimesic and pyromellitic acids have been crystallized and single crystal structures have been solved by X-ray crystallography. Both cocrystals exhibit layered structures, each layer containing a plethora of N–H⋯O and O–H⋯O hydrogen bonds between the proton-transfer duplets. The cytosine–trimesic acid complex exhibits a bilayered structure (2.87 Å) in contrast to the commonly observed layered structure seen in the cytosine–pyromellitic acid complex (3.98 Å). Another layered system, an adduct of pyromellitic acid and 1,4-dihydroxy benzene, has also been studied.