Structure–property relationship of a nitrogen-rich energetic salt: melamine-melaminium 3,4,5 trihydroxybenzoate dihydrate – a DFT approach

The nitrogen-rich energetic salt melamine-melaminium 3,4,5-trihydroxybenzoate dihydrate (MTBDH) has been grown by the slow evaporation method at room temperature. Single crystal X-ray diffraction studies reveal that MTBDH crystallizes in the centrosymmetric space group Pccn of the orthorhombic system with lattice parameters a = 32.878(5) Å, b = 9.392(2) Å, c = 12.785(2) Å, and V = 3947.9(12) (Å)3. The structure is stabilized by extensive N–H···N, N–H···O, O–H···O, and C–H···O hydrogen bonding, forming a three-dimensional supramolecular network. DFT calculations at the B3LYP/6–311G(d,p) level show excellent agreement with experimental data and confirm structural stability. The calculated Mulliken atomic charges reveal significant charge separation within the molecule. Nitrogen and oxygen atoms exhibit high negative charges (up to −0.82 e), whereas several carbon atoms bonded to electronegative centers display substantial positive charges (up to +0.74 e). Frontier molecular orbital analysis shows a HOMO–LUMO energy gap of 4.94 eV, indicating good molecular stability with moderate reactivity. The hardness (2.47 eV) and softness (0.20 eV) values further confirm the stable nature of MTBDH. The electronegativity (3.79 eV) and chemical potential (−3.79 eV) suggest strong electron-accepting ability, while the electrophilicity index (2.91 eV) and maximum charge (1.53 eV) transfer value indicate effective intramolecular charge redistribution within the molecule. The predicted UV–visible analysis shows an absorption maximum at 260 nm. The strong inter and intramolecular interactions were confirmed by Natural Bond Orbital (NBO) analysis. The calculated first-order hyperpolarizability (βtot) is 371.989 × 10−³1 e.s.u., which is approximately 99.87 times higher than that of urea, indicating strong nonlinear optical (NLO) behavior. Hirshfeld surface analysis identifies dominant H···H interactions (38.7%), while ELF and LOL analyses provide insight into electronic localization and non-covalent interactions.