Synthesis, X-ray characterization and study of new ionic complexes of 2-pyridone, obtained by oxidation with I2

Abstract

The reaction of 2-pyridone (C₅H₅NO or PYOH) with diiodine in molar ratios of 2∶1 and 1∶2 resulted in the formation of complexes {[(PYOH)₃(PYOH)⁺]·I₃⁻} (1) and {{(PYOH)₆·[(PYOH)₂]²⁺}·0.5I⁻·1.5I₇⁻·I₂} (2), respectively. The reactions were carried out in dichloromethane solutions in air. The compounds were characterized by elemental analysis, DTA-TGA chromatography, FT-Raman, FT-IR, UV-vis and EPR spectroscopies. Crystal structures of the named complexes have been determined by X-ray diffraction at 120(1) K (1) and 293(2) K (2). Compound 1, [(C₂₀H₂₀N₄O₄)I₃], monoclinic, space group C2/c, consists of a cationic PYOH⁺ radical species and an I₃⁻ counter anion; three neutral PYOH molecules are also bound to the complex. The crystal structure of [(C₄₀H₄₀N₈O₈)I₁₃] (2) reveals a centrosymmetric P-1 triclinic space group containing two cationic PYOH⁺ species, with the anionic counterparts being one half I⁻ and three halves I₇⁻. Also, a neutral diiodine molecule I₂ is retained by weak halogen-halogen interactions to I⁻, as well as six neutral PYOH ligands. The structures of 1 and 2 consist of hydrogen-bonded pyridine layers; polyiodide fragments fill the spaces between the layers, additionally kept together by a number of weak C–H⋯I interactions.