The crystallization process usually implies multiple stages and is accompanied by the appearance of intermediate states. Understanding the early stages of crystallization from solution has attracted increasing attention in pharmaceutical material engineering in the last years. The objective of this study is to explore the reactivity of two different solid state forms of 4-nitrobenzoic acid with dimethylethanolamine and the evolution of crystal formation and transformation processes, under identical reaction conditions (temperature, presure and solvent). The dimethylethanolammonium 4nitrobenzoate (DMEA4NB) crystallization process occurs via two different crystal growth mechanisms. The main difference between the mechanisms of crystalliation is the formation in the first stage of microcrystalline powder suspension in a case and a clear solution in the other, which undergoes to single crystal. Thermoanalytical and infrared techniques, single crystal X-ray diffraction, hot stage microscopy and density functional theory calculations were used to investigate the time depending changes occurring in the solid phase during crystallization and the crystal stability in air (Figure 1). The structural analysis reveales the interplay of more than one type of bond in the crystal: hydrogen bonds and weak van der Waals bonds. The hydrogen bonds N–H…O and O–H…O between the organic ionic compounds contribute to the formation of molecular synthons R22(9), which are linked in chains by C–H…O bonds. The packing of these chains is stabilized by weak van der Waals bonds (Figure 2). Figure 1. Thermogravimetric curves (TG, DTG, heat flow) of DMEA4NB at heating rates of 10 ºC min-1, in air Figure 2. Chains packing in crystal