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Open AccessArticle

Pyridine-2,6-Dicarboxylic Acid Esters (pydicR2) as O,N,O-Pincer Ligands in CuII Complexes

1
Department für Chemie, Institut für Anorganische Chemie, Universität zu Köln, Greinstraße 6, D-50939 Köln, Germany
2
Chemistry Department Faculty of Science, Shiraz University, Shiraz 71454, Iran
*
Authors to whom correspondence should be addressed.
Inorganics 2019, 7(4), 53; https://doi.org/10.3390/inorganics7040053
Received: 15 February 2019 / Revised: 31 March 2019 / Accepted: 9 April 2019 / Published: 14 April 2019
(This article belongs to the Special Issue First-Row Transition Metal Complexes)
The pyridine-2,6-carboxylic esters pydicR2 with R = Me or Ph form the unprecedented mononuclear CuII complexes [Cu(pydicR2)Cl3] in one-pot reactions starting from pyridine-2,6-carboxychloride pydicCl2, CuII chloride, and NEt3 in MeOH or PhOH solution under non-aqueous conditions. The triethylammonium salts (HNEt3)[Cu(pydicR2)Cl3] were isolated. The methyl derivative could be crystallized to allow a XRD structure determination. Both structures were optimized using DFT calculations in various surroundings ranging from gas phase and the non-coordinating solvent CH2Cl2 to the weakly coordinating acetone and well-coordinating solvents acetonitrile (MeCN) or dimethylformamide (DMF), while detailed calculation showed the charge distribution, dipole moments, and HOMO–LUMO gap energies changing upon solvation. According to these calculations, the ion pairs and the anionic CuII complexes were stable, which shows only Cu–Cl bond elongation and weakening of the charge transfer between the anionic complex and the cation as solvents become polar. Synthesis attempts in the presence of water yielded the CuII complexes [Cu(pydic)(OH2)2]n and [Cu(OH2)6][{Cu(pydic)}2(µ-Cl)2], which results from pydicCl2 hydrolysis. Alternatively, the new pydic(IPh)2 (IPh = 2-iodo-phenyl) ester ligand was synthesized and reacted with anhydrous CuCl2, which yields the new binuclear complex [{Cu(pydic(IPh)2)Cl}2(µ-Cl)2]. EPR spectroscopy of the solid compounds reveals typical axial spectra in line with the observed and DFT calculated geometries. Cyclic voltammetry and UV–vis absorption spectroscopy in solution are in line with un-dissociated complex species [Cu(pydicR2)Cl3]. View Full-Text
Keywords: oxido-pincer ligands; CuII; DFT calculations; EPR spectroscopy; electrochemistry oxido-pincer ligands; CuII; DFT calculations; EPR spectroscopy; electrochemistry
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MDPI and ACS Style

Butsch, K.; Sandleben, A.; Dokoohaki, M.H.; Zolghadr, A.R.; Klein, A. Pyridine-2,6-Dicarboxylic Acid Esters (pydicR2) as O,N,O-Pincer Ligands in CuII Complexes. Inorganics 2019, 7, 53.

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