Novel flucytosine salt: Structure, Hirshfild surface analysis, morphology, FIMs, and computational studies.

5-Flucytosine (FC) exhibits an advanced solid-state structure, which presents challenges for its pharmaceutical development. This paper presents experimental, and theoretical studies of a novel pharmaceutical salt, fluorocytosinium chloride, HFC.Cl. Single crystal X-ray diffraction (SCXRD) investigation indicates that HFC.Cl forms crystals in the monoclinic system and P2/c space group. The structure is maintained by a series of hydrogen bonding interactions, comprising N-H···Cl, N-H···O, and C-H···F. In addition, noncovalent anion···π interactions between chloride anions and HFC cations play a role in establishing a three-dimensional network. Hirshfeld surface analysis (HS) and two-dimensional fingerprinting were used to enumerate the intermolecular interactions within the crystal. The results demonstrate that the H···Cl/Cl···H, O···H/H···O, and F···H/H···F interactions are the most significant. Full Interaction Maps (FIMs) analysis predicts the positions of hydrogen bond acceptors and donors, confirming the supramolecular arrangement observed in HFC.Cl. Computational modeling studies using the Bravais-Friedel, Donnay-Harker (BFDH), and Growth Morphology (GM) methods predict the morphology of the HFC.Cl crystal. Both approaches estimate a comparable crystal shape characterized by six principal facets. Density functional theory (DFT) calculations were conducted utilizing the DMol software to investigate the electronic structure and comprehensive reactivity features of HFC.Cl. The low HOMO energy suggests significant stability against electrophilic attacks, while the high HOMO-LUMO band gap indicates high chemical hardness. Fukui functions were also calculated to identify atomic sites susceptible to nucleophilic and electrophilic attacks. This study offers a comprehensive insight into the structural and electronic properties of HFC.Cl, offering valuable information for the development of new pharmaceutical compositions.