Experimental and theoretical studies of a new NLO active organic salt of 2-amino-4-hydroxy-6-methylpyrimidine and 4-hydroxybenzoic acid

The new monohydrate organic salt (AHMPHB) of 2-amino-4-hydroxy-6-methylpyrimidine (AHMP) with 4-hydroxybenzoic acid (HBA) was successfully synthesized and grown as an organic single crystal with characteristic optical quality using the slow evaporation technique (SET). The structural study of the grown crystal was performed using single-crystal XRD. The XRD results revealed that AHMPHB belongs to the triclinic system with space group P-1. Various functional groups of AHMPHB were identified using Raman and FTIR spectroscopic analyses. The optimized geometry and other theoretical results were determined by the DFT/B3LYP method at the 6–311++G(d,p) basis set. The H⋅⋅⋅H and O⋅⋅⋅H intermolecular forces are dominated in the crystal packing and these were explored using Hirshfeld surface and fingerprint plot analyses. TG and DTA studies demonstrate that AHMPHB remains stable up to 140 °C. According to UV–Vis spectral analysis, AHMPHB has exhibited high transparency in the visible region with a direct band gap of 4.10 eV. The NLO measurement of AHMPHB was done using the Z-scan method. The energy of the HOMO-LUMO gap of 4.37 eV was predicted using DFT calculations. NBO analysis was performed to represent the charge transfer between localized bonds and lone pairs. Moreover, the MEP maps, HOMO-LUMO profiles and theoretical NLO parameters of AHMPHB and its constituents are also obtained.