Two polymorphs of the salicylamide cocrystal with oxalic acid have been obtained and described. Form I of the cocrystal was prepared by three alternative methods in various solvents, while formation of foxm II was achieved only by a special crystallization procedure. Single-crystal X-ray analysis has revealed that polymorphs consist of conformationally identical salicylamide and oxalic acid molecules, which are assembled into supramoleceilar units connected via a network of very similar hydrogen bonds. The packing arrangements of the cocrystal polymorphs, however, were found to be different, suggesting a rare example of packing polymorphism The stability relationship between the polymorphs has been rationalized by using a number of experimental methods, including thermochemical analysis, solubility, and solution calorimetry measurements. Similarities and differences in intermolecular contacts across two polymorphs have been visualized using the Hirshfeld surface analysis. The Bader analysis of the theoretical electron density has enabled us to quantify the pattern of noncovalent interactions in the considered cocrystals. Applicability of different theoretical schemes for evaluation of the lattice energy of the two-component organic crystals has been discussed.
