Effect of anion structure on the network of hydrogen bonds formed between counter ions in salts composed of triethylamine and derivatives of 2,1-benzothiazine 2,2-dioxide and 1,2-benzoxathiine 2,2-dioxide

Abstract

The investigated symmetrical bis-adducts, i.e., bis(1-ethyl-4‑hydroxy-2,2-dioxido-1H-2,1-benzothiazin-3-yl)(furan-2-yl/phenyl)methane and bis(4‑hydroxy-2,2-dioxido-2H-1,2-benzoxathiin-3-yl)(furan-2-yl/4-methoxyphenyl)methane, essential objects for pharmacological studies, were found to exist in the liquid and solid phases in a double tautomeric enol form which allows the existence of acid-base interactions related to the proton transfer to the triethylamine and the formation of an intramolecular O―H···O− hydrogen bond between the intact OH group and the enolate O− atom. In the crystal lattice of triethylammonium salts containing 1,2-benzoxathiine 2,2-dioxide moieties in the anion molecules, counter ions are connected by N―H···O hydrogen bonds, in which the enolate O− atom plays the role of a proton acceptor. Whereas in crystals with 2,1-benzothiazine 2,2-dioxide fragments in the anion molecules cation and anion molecules are linked by N—H···O hydrogen bonds, in which the role of a proton acceptor is played by an O atom of a sulphonyl group that belongs to a bicyclic fragment which contains an enolate group. We have shown that the dipole-dipole interactions in the investigated ammonium salts may explain the orientation of the cationic N−H group once to the O− atom of the enolate group, another time to the O atom of the sulfonyl group. The effect of the structure of the anion molecule on the hydrogen bonding network in the crystals studied was analyzed by the X-ray diffraction method, the 1H and 13C NMR technique including COSY, NOESY, HSQC and HMBC two-dimensional patterns, and the Fourier transform infrared (FTIR) spectroscopy. Theoretical analysis of the interactions in the crystals was performed using Density Functional Theory (DFT) and Quantum Theory of Atoms in Molecules (QTAIM).