X-ray crystal structure, spectroscopic and DFT computational studies of H-bonded charge transfer complexes of tris (hydroxymethyl)aminomethane (THAM) with chloranilic acid (CLA)

Abstract

The crystal and molecular structures of two new synthesized charge transfer complexes produced from the reaction of tris(hydroxymethyl)aminomethane, THAM and 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinone (chloranilic acid, CLA) in the mole ratios (2:1) [I] and (1:1) [II], have been studied. The; FT-IR and 1H NMR spectral data of the complexes are confirmed by single-crystal X-ray crystallography. The single-crystal X-ray crystallography, indicated the formation of both inter- and intra-molecular hydrogen bonding as well as the proton transfer from CLA to THAM. The electronic transition spectra of these two complexes as acetonitrile (AN), methanol (MeOH), ethanol (EtOH) solutions are recorded. The molecular compositions of the formed complexes in the three solvents determined by Job's method, support 1:1 mol ratio complex, whatever the polarity of the solvent. The high values of charge transfer complex formation constants, KCT determined by applying the minimum–maximum absorbance method, indicated the formation of stable CT-complexes, with the order Ethanol > Methanol ≫ Acetonitrile. Computational study incorporated the use of TD-DFT with PCM as solvation model are applied for energy minimization and estimation of the stabilization energy for the produced complexes. The geometrical parameters (bond lengths and angles) of the formed CT complexes are computed and analyzed. Furthermore, Mulliken atomic charges, molecular potential energy surface, HOMO and LUMO molecular orbitals of the formed complexes are presented. A good agreement between experimental and DFT computational analysis has been found.