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DFT Study on Structural, Electronic, and Nonlinear Optical Properties of Melaminium Glutarate Monohydrate
S. Akshay Kalyan, S. Sankar, K. Sivakumar, R. Gowri Shankar Rao and N. Kanaga Thara
Single crystals of melaminium glutarate monohydrate (MGM) were grown by slow evaporation at room temperature. Single-crystal X-ray diffraction analysis confirmed that the crystal belongs to the monoclinic system with a centrosymmetric space group, P21/c. Density functional theory (DFT) optimization was performed at the RB3LYP/6-311G(d,p) level using the Gaussian 09 program. The calculated FT-IR and Raman spectra are in good agreement with the observed vibrational features, while the ¹H and ¹³C NMR chemical shifts were computed using the Gauge-Including Atomic Orbitals (GIAO) method. The HOMO–LUMO energy gap was found to be 6.2439 eV, indicating good molecular stability and moderate chemical reactivity. Mulliken charge and natural bond orbital (NBO) analyses were carried out to identify the reactive sites and elucidate intramolecular charge-transfer interactions. The strongest intramolecular stabilization energies, 71.64 and 54.58 kcal mol−1, arise from hyperconjugative interactions involving donation from the lone pair of the nitrogen atom (N11) to the antibonding π∗(N3−C6) orbital. Fukui function analysis distinguished the electrophilic and nucleophilic regions of the molecule. The first-order hyperpolarizability was computed to be 118.303×10−31 esu, which is approximately 32 times greater than that of urea. Hirshfeld surface analysis was employed to investigate the intermolecular interactions present in the compound, revealing that the major contribution arises from O–H interactions (38.2%), followed by H–H (37.1%) and N–H (11.8%) interactions. Topological analysis provided further insights into the molecular structure and reactivity. The CVB index result (−0.00464) indicates the presence of strong hydrogen-bonding interactions.
Keywords: DFT, Vibrations, HOMO-LUMO, Dipole moment calculation, NBO, Hirshfeld Surface, Fukui function, Multiwfn