Imine-tautomers of aminothiazole derivatives: intriguing aspects of chemical reactivities

Abstract

Intriguing reactivities of positional isomers 1-(5-methylthiazol-2-yl)-3-(4-nitrophenyl)thiourea (L¹) and 1-(4-methylthiazol-2-yl)-3-(4-nitrophenyl)thiourea (L²) towards environment polluting ions such as mercuric, fluoride, bromide and solvents provide scope to study various self-assemblies formed under different conditions and allied applications. The solid state structures of L¹ and L² revealed that both adopt the imine form. However, the number of symmetry independent molecules in asymmetric units as well as the packing patterns of these two compounds have distinguishable features. The asymmetric unit of L¹ has three symmetry non-equivalent molecules. The packing patterns of these two positional isomers differ as L¹ has two arrays of dimeric self-assemblies in contrast to the single array found in the packing of L². The reactivity of L¹ and L² with solvents was explored through crystal structure elucidation. The compound L¹ forms solvates with N,N′-dimethylacetamide or dimethylsulphoxide. The structural analysis of solvates of L¹ provided avenues to study conformational adjustments. An unusual example of a metastable solvate of L¹ with N,N′-dimethylacetamide was isolated. A ring-opening reaction of 1,8-diazabicyclo [5.4.0] undec-7-ene with L¹ has been observed. The compound L² underwent hydrolysis cum bromination with hydrobromic acid in dimethylsulphoxide. The reactivities of L¹ and L² towards mercuric and fluoride ions contributed to chemodosimetric signal transductions. The study establishes the impact of subtle changes in structure, reaction and crystallization conditions, which can influence pre-designed crystal engineering.