Structure-forming non-covalent bonding of new 2-(4-carboxyphenylhydrazinylidene)[1,3]thiazolo[3,2-a]pyrimidines in the crystalline phase

Abstract

New 2-(4-carboxyphenylhydrazinylidene)[1,3]thiazolo[3,2-a]pyrimidine derivatives were synthesized in high yields by the reactions of 5-aryl-6-ethoxycarbonyl-7-methyl-3-oxo-2,3-dihydro-5H-[1,3]thiazolo[3,2-a]pyrimidine with 4-carboxyphenyldiazonium chloride. The azo coupling occurs at the 2 position of the substrate. Different types of intra- and intermolecular non-covalent interactions can affect the supramolecular assembly of the molecules in the crystal structures and the molecular configuration of the synthesized compounds. The combined contribution of supramolecular non-covalent interactions leads to several types of the self-assembly in the crystalline phase, such as hydrogen-, chalcogen-, and π—π-bonded racemic dimers. In the case of compounds containing the m-chlorophenyl substituent at the C(5) position of the thiazolo[3,2-a]-pyrimidine scaffold, these interactions lead to the formation of halogen-bonded homochiral chains. Due to the π—π stacking between the electron-rich thiazolopyrimidine scaffold and the electron-deficient carboxyphenyl moiety, there occurs the formation of dense layers in the solid phase when selecting the appropriate substituents at the C(5) atom. The crystallization conditions (vapor diffusion and slow evaporation) were found to influence the configuration of the C=N-arylhydrazone moiety.