Synthesis, vibrational and quantum chemical investigations of hydrogen bonded complex betaine dihydrogen selenite

► The molecular complex betaine dihydrogen selenite (C5H13NO5Se) was synthesised. ► The vibrational analyses of BDHSe have been performed by FTIR, FT-Raman and far-infrared spectral studies. ► The structural parameters, energies, thermodynamic parameters and NBO charges of were determined by the DFT method. ► The 1H and 13C isotropic chemical shifts (δ ppm) with respect to TMS were also calculated. ► The efficiency of second harmonic generation for BDHSe was estimated relatively to KDP: deff = 0.97 deff (KDP).