Structure–property correlation in a creatininium-based nonlinear optical crystal: experimental and DFT analysis

The nonlinear optical material Creatininium hydrochloride (CTHCl) was successfully synthesized as a single crystal by solvent evaporation at ambient temperature, as confirmed by XRD analysis. To deepen our understanding of the molecule’s intrinsic properties, quantum-chemical calculations were performed using density functional theory (DFT) at the B3LYP/6 − 31G(d,p) level. These theoretical approaches enabled the simulation of molecular geometries, which were then compared with their corresponding experimental crystal structures, thereby improving the accuracy of the analysis. The investigation also included Hirshfeld surface analyses, which revealed a complex network of significant intermolecular interactions contributing to the molecule’s stability. To further validate the chemical features, FT-IR and FT-Raman spectroscopy were used to record the molecular vibrational spectra, confirming the presence of various functional groups and vibrational modes, and applying second-quantization methodology for detailed spectral assignments. The insights from DFT modeling significantly supported the experimental findings, establishing a comprehensive framework for characterization. Detailed aspects examined included frontier molecular orbitals (FMOs), which illustrate reactivity patterns; natural bond orbital (NBO) analysis, which provides insights into chemical bonding; Mulliken population analysis, which shows electron distribution; and first-order hyperpolarizability, all calculated at the DFT/B3LYP/6–31G(d,p) level, consistent with the geometry optimization. This multifaceted approach not only enhances understanding of molecular behavior but also supports future research in crystal chemistry.