The title compound triphenyl tetrazolium (TPT) of phenobarbital, 5-Ethyl-5-phenylbarbituric acid triphenyl tetrazolium salt (4) was prepared by the reaction of 5-Ethyl-5-phenyl-2,4,6(1H, 3H, 5H)-pyrimidinetrione, monosodium salt (1) with triphenyl tetrazolium chloride (3) in deionized water at an ambient temperature through a cation exchange reaction. Colorless crystals of compound four suitable for an X-ray structural analysis were obtained by slow evaporation from acetonitrile. Compound four had crystallized in the monoclinic space group, P21/c, with a = 15.3678 (9) Å, b = 12.2710 (7) Å, c = 21.8514 (13) Å, β = 109.867 (2)°, V = 3875.5 (4) Å3, and Z = 4. A Through density functional theory (DFT) calculations, the probable molecular association structure in the phenobarbitone -triphenyl tetrazolium solution was studied. With the 6-311G-(d,p) basis set, the gas phase features of the phenobarbital-triphenyl tetrazolium clusters with a phenobarbitone dimer and water molecules, including an optimum structure and intermolecular hydrogen bonding, were investigated in detail. In addition, the positions and strengths of the intermolecular hydrogen bond interactions between the phenobarbitone and triphenyl tetrazolium molecules were analyzed using atoms in molecule (AIM) analysis, reduced density gradient (RDG) methods, the XRD method, and the non-covalent interaction (NCI) index method. In addition, the molecular electrostatic potential (MEP) surfaces were analyzed to determine the electrophilic and nucleophilic centers.