Characterization of orthogonal hydrogen and halogen bonds in thiobarbituric acid complexes with halogen molecules (X = I2, Br2, and Cl2): Structural and spectroscopic study

Abstract

AbstractThe molecular complexes between thiobarbituric acid (TBA) and halogen molecules (X2 = I2, Br2, and Cl2) in different solvents are explored. Density functional theory (DFT) calculations at rwb97xd/lanl2dz were used to corroborate the experimental electronic and optical properties of the molecular adducts. Experimental results (Fourier transform infrared spectroscopy) show the stability of the complexes by halogen bonding (XB) and competitive hydrogen bonding (HB), which was supported by the DFT calculations. The molecular electrostatic potential and the frontier orbital calculations supported engagement of the thione group in XB rather than the carbonyl group. Based on the Hirshfeld atomic population, noncovalent interaction, and natural bond orbital analysis, the stability of TBAX2 adducts increases in the order TBACl2 > TBABr2 > TBAI2, where the larger charge transfer and highest stabilization energy were calculated for TBACl2 adducts.