Confirmation of supramolecular structure and its impact on nonlinear optical properties of Bis(4-methylbenzylammonium) tetrabromido zincate: A new semiorganic crystal

Abstract

Supramolecular structure exhibits good nonlinear optical (NLO) properties due to the enhanced proton transfer process. Semiorganic Bis(4-methylbenzylammonium) tetrabromido zincate (4MLTBZ) crystal was developed by functionalizing 4-methylbenzylamine (4MLBA) with hydrobromic acid and zinc bromide. Amine group of 4MLBA gets protonated by H+ cation of hydrobromic acid. Zinc bromide was linked with 4MLBA through CH ⋯Br and NH ⋯Br interactions which forms supramolecular structure and crystallized noncentrosymmetric space group Pna21. Raman and FTIR spectral analysis provides the evidence for the protonation of amine (NH3+) group. Raman spectrum reveals the coordination of ZnBr4 in 4MLTBZ crystal structure through the observed ZnBr vibrations between 50 and 400 cm−1. The impact over the shift in vibrational frequencies of NH and CH functional groups due to CH ⋯Br and NH ⋯Br interactions were discussed. The ‘CarbonHydrogen’ frame work of 4MLTBZ crystal was established by 1H NMR and 13C NMR spectroscopy. The UV–Vis–NIR spectrum of 4MLTBZ showed very good transparency in the region from 260 nm to 1100 nm. The enhanced SHG efficiency and third order nonlinear optical susceptibility (χ3) are interpreted through hydrogen bonds.