Crystal structures of the anhydrous and two solvated forms of methyl 4-(4-fluorophenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate

Abstract

Methyl 4-(4-fluorophenyl)-6-methyl-2-oxo-1,2,3,4-tetrahydropyrimidine-5-carboxylate, (I), was found to exhibit solvatomorphism. The compound was prepared using a classic Biginelli reaction under mild conditions, without using catalysts and in a solvent-free environment. Single crystals of two solvatomorphs and one anhydrous form of (I) were obtained through various crystallization methods. The anhydrous form, C13H13FN2O3, was found to crystallize in the monoclinic space group C2/c. It showed one molecule in the asymmetric unit. The solvatomorph with included carbon tetrachloride, C13H13FN2O3·0.25CCl4, was found to crystallize in the monoclinic space group P2/n. The asymmetric unit revealed two molecules of (I) and one disordered carbon tetrachloride solvent molecule that lies on a twofold axis. A solvatomorph including ethyl acetate, C13H13FN2O3·0.5C4H8O2, was found to crystallize in the triclinic space group P\overline{1} with one molecule of (I) and one solvent molecule on an inversion centre in the asymmetric unit. The solvent molecules in the solvatomorphs were found to be disordered, with a unique case of crystallographically induced disorder in (I) crystallized with ethyl acetate. Hydrogen-bonding interactions, for example, N—H...O=C, C—H...O=C, C—H...F and C—H...π, contribute to the crystal packing with the formation of a characteristic dimer through N—H...O=C interactions in all three forms. The solvatomorphs display additional interactions, such as C—F...N and C—Cl...π, which are responsible for their molecular arrangement. The thermal properties of the forms were analysed through differential scanning calorimetry (DSC), hot stage microscopy (HSM) and thermogravimetric analysis (TGA) experiments.