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

Abstract

The asymmetric unit of the title compound, 4C4H4FN3O·C3H6N6, comprises of two independent 5-fluoro-cytosine (5FC) mol-ecules (A and B) and one half-mol-ecule of melamine (M). The other half of the melamine mol-ecule is generated by a twofold axis. 5FC mol-ecules A and B are linked through two different homosynthons [R 2 (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 mol-ecules A and B inter-act with the N2 amino group on both sides of the melamine mol-ecule, forming a DDAA array of quadruple hydrogen bonds and generating a supra-molecular pattern. The 5FC (mol-ecules A and B) and two melamine mol-ecules inter-act via N-H⋯O, N-H⋯N and N-H⋯O, N-H⋯N, C-H⋯F hydrogen bonds forming R 6 (6)(24) and R 4 (4)(15) ring motifs. The crystal structure is further strengthened by C-H⋯F, C-F⋯π and π-π stacking inter-actions.

Keywords: 5-fluoro­cytosine; crystal structure; homosynthons; hydrogen bonding; melamine.

Figure 1

The asymmetric unit of the title compound, showing 30% probability displacement ellipsoids. Dashed lines indicate hydrogen bonds. Atoms with the suffix a are generated by the symmetry operation 1 − x, y, {\script{1\over 2}} − z.

Figure 2

A view of the supra­molecular pattern involving two synthons formed by N—H⋯O hydrogen bonds. 5FC A mol­ecules are shown in green, 5FC B mol­ecules in blue and melamine in red. Blue dashed lines indicate hydrogen bonds. Symmetry codes are given in Table 1 ▸.

Figure 3

A view of C—F⋯π and aromatic π–π stacking inter­actions (dashed lines) between 5FC mol­ecules A and B and melamine.