Hydrogen-bonding patterns in 5-fluorocytosine- melamine co-crystal (4/1)

The asymmetric unit of the title compound, 4C4H4FN3O-C3H6N6, comprises of two independent 5-fluorocytosine (5FC) molecules (A and B) and one halfmolecule of melamine (M). The other half of the melamine molecule is generated by a twofold axis. 5FC molecules A and B are linked through two different homosynthons [R2 2(8) ring motif]; one is formed via a pair of N-H ⋯ O hydrogen bonds and the second via a pair of N-H ⋯ N hydrogen bonds. In addition to this pairing, the O atoms of 5FC molecules A and B interact with the N2 amino group on both sides of the melamine molecule, forming a DDAA array of quadruple hydrogen bonds and generating a supramolecular pattern. The 5FC (molecules A and B) and two melamine molecules interact via N- H ⋯ O, N-H ⋯ N and N-H ⋯ O, N-H ⋯ N, C-H ⋯ F hydrogen bonds forming R6 6(24) and R4 4(15) ring motifs. The crystal structure is further strengthened by C-H ⋯ F, C-F ⋯ - and -- stacking interactions.