This work describes the synthesis of new 4-substituted-pyrazolo[3,4-d]pyridazinones (R= C6H5, 4-F-C6H4, benzofur-2-yl, CF3, 4-NO2-C6H4) from the reaction of dicarbonylpyrazoles with hydrazine hydrate. Solid and solution-state NMR were used to unequivocally assign the structure and identification of the byproduct formed when R=4-NO2-C6H4. Geometrical features and the intermolecular interactions of compounds were described using single crystal X-ray diffraction. The thermal behavior of the compounds was studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Kinetic parameters, such as the activation energy (E-a) and pre-exponential factor (A), were determined as a function of the conversion degree for the thermal decomposition of two compounds, by using the iso-conversional methods of Friedman and Ozawa-Flynn-Wall (OFW). The results showed that the E-a for thermal decomposition of compound with R= CF3 is always higher than for compound with R= C6H5, independent of the model used (Friedman or OFW), indicating that the former is more stable than the latter. Furthermore, the E-a values for compounds with R= C6H5 and CF3 are practically constant for all alpha values from 0.1 to 0.9, indicating the existence of a single-step degradation reaction. The kinetics results also reveal the linear dependence of E-a on the pre-exponential factor. In addition, the 4-substituted-pyrazolo[3,4-d]pyridazinones studied have two types of thermal behavior: (i) a compound that passes from the glass to a liquid phase, followed by cold crystallization, and a melting transition (R= C6H5, CF3); (ii) A compound that has no melting or freezing points, only glass-transition temperatures (R = 4-NO2-C6H4). Finally, we showed that compounds with R= C6H5 and CF3 undergo amorphization during the heating cycles, reaching 48% and 74% of amorphous content, respectively. (C) 2013 Elsevier B.V. All rights reserved.