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

Abstract

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]−.

Dinuclear Nickel(II) and Copper(II) Complexes of 8‐Quinoline‐1H‐pyrazole‐3‐carboxamide: Crystal Structure, Magnetic Properties, and DFT Calculations

“…Remarkably, we were not able to detect a half-field signal (ΔM S = � 2) which is normally observed for an anti-ferromagnetically coupled system with an S = 0 ground and S = 1 excited state. [30,47,[53][54][55][61][62][63][64][65][66][67][68] In view of the 1.7 % paramagnetic impurity concluded from the magnetic measurements, we assume that the inherently weak and broad spectrum of the dinuclear complex is merged with or even completely covered by the signal of the paramagnetic mononuclear Cu(II) impurity.…”

Synthesis, characterization, crystallographic structure, theoretical studies, and in vitro cytotoxicity assessment of two Gd(III) and Ce(IV) complexes containing pyridine-2,6-dicarboxylate

“…Accordingly, many complexes of them have been reported which were designed from various organic ligands especially multi-dentate ligands possessing oxygen and nitrogen donor atoms [8][9][10] such as pyridine-2,6-dicarboxylic acid [10][11][12][13]. The studies have shown that lanthanides complexes can bind with the biomolecular targets and cause alteration in the cellular mechanism of proliferation [14].…”

“…Also, the complex in the unit cell is observed in Fig.6. This complex with two triangle plane consist of N(3), O(9), O(11) and N(2), O(5), O(7) and O(1), Ce(1), O(3) atoms are three capped atoms. The sum of bond angles, N(2)-Ce(1)-N(3)=115.32(13), N(1)-Ce(1)-N(2)=122.50(13) and N(1)-Ce(1)-N(3)=122.18(13) equals to 360.00 which indicates that Ce(IV) is located in the center of N(1)N(2)N(3) (x,y, z-1) plane Ce(IV).…”