Structure, electronic and vibrational spectra and aromaticity of hemiporphyrazine and its hydrates: A density functional theory study

The hemiporphyrazine molecule, its tautomer with hydrogen atoms bonded to nitrogen atoms in pyridine rings, and hemiporphyrazine monohydrate complex have been studied by density functional theory (DFT) computations using the B3LYP hybrid method and triple-ζ valence basis sets. In gas phase the hemiporphyrazine molecule has non-planar equilibrium structure of C2v symmetry, in contrast to the solid state where it is planar. Vibrational spectra (frequencies and IR intensities) of these molecules have also been calculated. UV-vis electronic spectra have been studied using time-dependent density functional theory (TDDFT). Theoretical characteristics are in good agreement with available experimental data. Aromaticity of all mentioned compounds has been evaluated using HOMA and NICS criteria. Additionally, structures of another hemiporphyrazine monohydrate with different bonding of water molecule as well as of hemiporphyrazine dihydrate were optimized in order to study hydrogen bonding in hemiporphyrazine hydrates.