Supramolecular structure and spectroscopic characterization of new 1,3,5-triaza-2-boracyclohex-3-en derivative formed under mild conditions between 2-imino-4-thiobiuret and boric acid

Abstract

Reaction of 2-imino-4-thiobiuret with boric acid (in molar ration of 1:1) in aqueous solution at the mild conditions leads to formation of a heterocyclic compound of 2,2-dihdroxy-4-amino-6-thio-1,3,5-trihydrotriaza-2-boracyclohex-3-en (1). This compound crystallizes directly from the reaction solution after a few days, giving light yellowish transparent monoclinic crystals (P21/n). X-ray single crystal analysis shows that the heteroring and the thio- and amine groups are co-planar, whereas the plane of hydroxyl groups linked to boron are almost perpendicular to plane of the ring. The 2,2-dihdroxy-4-amino-6-thio-1,3,5-trihydrotriaza-2-boracyclohex-3-en molecules are arrangement via O–H...S hydrogen bonds in the stacks along b-axis, and the stacks are interacting each other via N–H...O hydrogen bonds forming a three-dimensional supramolecular architecture. The qualitative and quantitative intermolecular interactions in the crystal were analyzed using the Hirshfeld surface and 2D-fingerprint plots. The compound was also characterised by the FT-IR and Raman spectroscopy. The IR and FT-Raman spectra were made for protiated (1) and its deuterated analogue (1d). The IR and FT-Raman spectra for molecule in the gas-phase were calculated using DFT. DFT calculations and the isotropic frequency shift are helpful in assignments of the vibration bands. The calculated HOMO and LUMO energy gap explain the charge transfer interactions taking place within the molecule.