Structural, spectroscopic and second harmonic generation evaluation of 1,2,4-triazolinium tartrate - tartaric acid as a promising nonlinear optical material

Crystallization of 1,2,4-triazole with (2R,3R)-(+)-tartaric acid (L (+)-tartaric acid) in a 1:2 ratio yields the ionic co-crystals of 1,2,4-triazolium tartrate - tartaric acid (1:1), (C2H4N3) (C4H5O6)center dot C4H6O6 - (abbreviated as TATT). TATT crystallizes in the tetragonal system with a non-centrosymmetric P41212 space group of eight molecules per unit cell. Apart from ionic interaction by the building ions and N-H center dot center dot center dot O, the 1,2,4-triazolinium cation and the tartrate anion interact through hydrogen bonds and O-H center dot center dot center dot O with tartaric acid to form a supramolecular complex (C2H4N3) (C4H5O6)center dot C4H6O6 (TATT). Hydrogen bonds further organise these supramolecular complexes into a three-dimensional network. The interactions between the building blocks of the co-crystal were analyzed using Hirshfeld surface and 2D fingerprint plots. Normal coordinate force field calculations based on density functional theory (DFT) and structure optimizations were utilized to interpret the molecular structure and fundamental vibrational frequencies. The wave numbers' complete vibrational assignments were determined through potential energy distribution (PED). The HOMO and LUMO energy gap calculations explained the charge transfer interactions within the supramolecular unit. For the TATT co-crystal, the efficiency of the second harmonic generation (SHG) process was investigated under 800 nm irradiation using the Kurtz-Perry powder technique. The ionic co-crystal demonstrated a low SHG efficiency on the order of 10-1 compared to that of KDP.