Tautomers of N-ethyl-3-oxopyridinium and its adduct with squaric acid studied by X-ray, Raman, FTIR, NMR and DFT methods.

The molecular complex of N -ethyl-3-hydroxypyridinium hydrogen squarate has been obtained and characterized by single-crystal X-ray diffraction, B3LYP/6-311++G(d,p) calculations, Raman, FTIR and NMR spectra. The complex is built of OH⋯O hydrogen-bonded dimer involving two anions and two cations. In order to establish a tautomeric equilibrium between 3-phenolic and 3-pyridone forms in N -ethyl-3-oxopyridinium unit in the complex, additionally N -ethyl-3-oxopyridinium has been studied by the same experimental and theoretical methods. The potential energy distributions (PED) have been used to assign the vibrational spectra. Charge delocalization has been analyzed using the Natural Bond Orbital (NBO) method. [ABSTRACT FROM AUTHOR]