Synthesis, structural characterization, and Hirshfeld surface analysis of novel NLO active 1-methyl-1,3,5,7-tetraazaadamantan-1-ium 3-carboxy-5-nitrobenzoate hydrate

Abstract

Single crystals of 1-methyl-1,3,5,7-tetraazaadamantan-1-ium 3-carboxy-5-nitrobenzoate hydrate (I) were grown from an aqueous solution containing hexamethylenetetramine (HMT) and 5-nitroisophthalic acid (5NIPA) by slow evaporation solution growth technique after the mild hydrothermal process. The crystal structure is elucidated by single-crystal X-ray diffraction analysis. It crystallizes in the monoclinic system with acentric space group Cc. The cation and anion present in the adduct are bridged by a water molecule, which is interconnected with CH···O and OH···O hydrogen bonds. The relative second harmonic generation (SHG) efficiency measurements characterized by the Kurtz powder technique reveal that (I) is an active SHG material. The grown crystals were further characterized by FT-IR, UV-DRS, and photoluminescence spectral analysis. Theoretical calculations were performed using density functional theory to derive the dipole moment, polarizability, and first-order molecular hyperpolarizability (β). The intermolecular hydrogen bonding interactions are analysed by Hirshfeld surface analysis and fingerprint plots. Theoretically estimated high β rationalized by the experiment. The molecular electrostatic potential (MEP) maps and Mulliken atomic charge were calculated using density functional theory (DFT) calculations.