Synthesis, Crystal Structure, Hirshfeld Surface, Vibrational Thermal Analyses, and NLO Properties of a New Hybrid Material: 2,4-Diamino-6-Phenyl-1,3,5-Triazinium Perchlorate, Supported by DFT Calculations

A novel organic–inorganic ionic crystal 2,4-diamino-6-phenyl-1,3,5-triaziniumperchlorate (C9H10N5+·ClO4−) was synthesized via the reaction of benzoguanamine with perchloric acid. Its structure was affined by single-crystal XRD and characterized by UV-Vis and FT-IR spectroscopies. It crystallizes in a monoclinic system, with P21/c space group and lattice parameters of a = 13.7975 (6), b = 5.0711 (2), c = 16.6471 (9) Å, and β = 91.869 (2) ° and a cell volume of V = 1164.15 (9) Å3. Additionally, the 3D-supramolecular network illustrates a supramolecular layer-by-layer arrangement. The two-dimensional fingerprint plots and Hirshfeld surface analysis showed that H∙∙∙O/O∙∙∙H dominates the interactions, contributing with 33.4%. The UV-Vis spectrum revealed two strong absorption bands at 204 and 247nm, indicating π→π* and n→π* electronic transitions, respectively, which were corroborated by TD-DFT calculations. FT-IR spectroscopy confirmed key vibrational modes consistent with triazinium cations and perchlorate anions, demonstrating strong agreement with the affined structure. TGA/DTG demonstrated enhanced thermal stability until 290 °C compared to benzoguanamine, with a four-stage degradation profile, illustrating robust thermal resilience. Moreover, BSSE-corrected interaction-energy calculations revealed that the charge-assisted cation–anion N-H···O hydrogen bond is the main cohesive force in the crystal, with a strong stabilization energy of −248.8 kJ mol−1, while π-associated contacts mainly contribute to layered supramolecular packing. C9H10N5+·ClO4− exhibits enhanced NLO properties in comparison to urea, due to the cooperative effect of ionic hydrogen bonding and ordered π-stacking.