Synthesis, X-ray characterization and DFT study of a novel Fe(III)–pyridine-2,6-dicarboxylic acid N-oxide complex with unusual coordination mode

• Synthesis of a novel Fe(III)–pyridine-2,6-dicarboxylic acid N-oxide complex.
• Confirmation of structure by XRD analysis.
• Comparison to related structures of CoII, NiII, CuII and ZnII complexes.
• Analysis of the supramolecular interactions in the solid state by DFT calculations.
• Evaluation of the energy associated with π–π and hydrogen bonding contributions.

Our synthetic approach demonstrates that pyridine-2,6-dicarboxylic acid N-oxide can form a stable FeIII complex with the rare 1:3 metal-to-ligand ratio. This study provides more information about packing features of one crystalline compound, (H9a-acr)3[Fe(pydco)3]·6H2O (1) (where H2pydco = pyridine-2,6-dicarboxylic acid N-oxide and 9a-acr = 9-aminoacridine) via proton transfer methodology. The structure of 1 was characterized by IR spectroscopy, X-ray diffraction methods and the elemental analysis was performed to check the purity of the compound. On the basis of crystallographic data, compound 1 contains a monomeric anion with distorted octahedral geometry. The metal center is coordinated to six oxygen atoms by three bidentate pyridine-2,6-dicarboxylic acid N-oxide ligands to form a ceiling fan-shaped entity in which only the N-oxide oxygen and one carboxylate oxygen generate a six-membered chelate ring as seen for other N-oxides. Furthermore, the [Fe(pydco)3]3− and (9a-acr)+ units in 1 form 2D anionic and cationic layers. The intermolecular interactions in this novel system consist of electrostatic attraction between ion pairs, different kinds of H-bonding and π-stacking all of which join the 2D layers to create 3D supramolecular architectures. Since pyridine-2,6-dicarboxylic acid N-oxide and pyridine-2,6-dicarboxylic acid have similar frameworks, we also highlighted some areas of current interest in the coordination behavior of the latter ligand in mononuclear monomeric compounds in the reported structures up to now and investigated the influence of the N-oxide moiety on the coordination mode(s) in the crystal lattice as well.

We report the synthesis and X-ray characterization of an unusual complex formed by pyridine-2,6-dicarboxylic acid N-oxide and FeIII exhibiting a rare 1:3 metal-to-ligand ratio.Figure optionsDownload as PowerPoint slide