Abstract
The 1:1 cocrystal of 5-fluoro-cytosine (5FC) and 4-hy-droxy-benzaldehyde (4HB), C(4)H(4)FN(3)O·C(7)H(6)O(2) has been synthesized and its structure characterized by single-crystal X-ray diffraction and Hirshfeld surface analysis. The compound crystallizes in the monoclinic P2(1)/c space group. A robust supra-molecular architecture is stabilized by N-H⋯O, N-H⋯N, C-H⋯O and C-H⋯F hydrogen bonds, forming R (2) (2)(8), R (4) (4)(22), R (6) (6)(32), and R (8) (8)(34) ring motifs. The N-H⋯O and N-H⋯N hydrogen bonds form strong directional inter-actions, contributing to the R (2) (2)(8) and R (8) (8)(34) motifs through dimeric and extended ring structures. O-H⋯O inter-actions link 5FC and 4HB mol-ecules, generating an R (6) (6)(32) ring that enhances the packing. Weaker C-H⋯F bonds help form the R (4) (4)(22) tetra-meric motif, supporting the overall three-dimensional supra-molecular framework. Additionally, C-F⋯π inter-actions between the fluorine atom and the aromatic ring add further to the crystal cohesion. Hirshfeld surface analysis and two-dimensional fingerprint plots confirm that O⋯H/H⋯O contacts are the most significant, highlighting the central role of hydrogen bonding in the stability and organization of the crystal structure.