Acid–base multicomponent systems based on active pharmaceutical ingredients 2-chloro-5-nitrobenzoic acid (2Cl5NBH) and monoethanolamine were prepared by different reaction pathways. A comparative investigation of crystal structures, thermal stability and photoluminescent properties of studied molecular salts: N-(1,1-dimethyl-3-oxobutyl)monoethanolammonium 2-chloro-5-nitrobenzoate (1) and monoethanolammonium 2-chloro-5-nitrobenzoate (2), obtained in acetone and diethyl ether, was presented. In contrast to our previous results, we find that acetone acts as a reactant in the reaction of 1 forming interaction with the solute, beside diethyl ether which behaves as a solvent in the synthesis of 2. The solid-state structures of 1 and 2 were described and studied by IR spectroscopy and single-crystal X-ray diffraction. Thermogravimetric, derivative thermogravimetric and heat flow methods were used for the characterization of thermal behavior of products. It is shown that both compounds have high thermal stability until 150 °C, excepting the loss of crystallization water in compound 2. The photoluminescence properties of monoethanolammonium salts were compared to free 2Cl5NBH acid in order to examine the role of anion and cation, respectively.