Synthesis, characterization, crystal structures, and superoxide dismutase activity of copper(II) octahedral complexes containing tri- and monodentate ligands

Neutral 4-phenyl-1-[phenyl(pyridin-2-yl)methylidene]semicarbazide and its salt forms with inorganic anions

Semicarbazones can exist in two tautomeric forms. In the solid state, they are found in the keto form. This work presents the synthesis, structures and spectroscopic characterization (IR and NMR spectroscopy) of four such compounds, namely the neutral molecule 4-phenyl-1-[phenyl(pyridin-2-yl)methylidene]semicarbazide, C₁₉H₁₆N₄O, (I), abbreviated as HBzPyS, and three different hydrated salts, namely the chloride dihydrate, C₁₉H₁₇N₄O⁺·Cl^-·2H₂O, (II), the nitrate dihydrate, C₁₉H₁₇N₄O⁺·NO₃^-·2H₂O, (III), and the thiocyanate 2.5-hydrate, C₁₉H₁₇N₄O⁺·SCN^-·2.5H₂O, (IV), of 2-[phenyl({[(phenylcarbamoyl)amino]imino})methyl]pyridinium, abbreviated as [H₂BzPyS]⁺·X^-·nH₂O, with X = Cl^- and n = 2 for (II), X = NO₃^- and n = 2 for (III), and X = SCN^- and n = 2.5 for (IV), showing the influence of the anionic form in the intermolecular interactions. Water molecules and counter-ions (chloride or nitrate) are involved in the formation of a two-dimensional arrangement by the establishment of hydrogen bonds with the N-H groups of the cation, stabilizing the E isomers in the solid state. The neutral HBzPyS molecule crystallized as the E isomer due to the existence of weak π-π interactions between pairs of molecules. The calculated IR spectrum of the hydrated [H₂BzPyS]⁺ cation is in good agreement with the experimental results.