Carboxylate Oxygen Atom Of Ligand Research Articles

Synthesis and characterization of novel four heterodimetallic mixed metal complexes of 2,6-pyridinedicarboxylic acid

Four novel hetero dimetallic mixed metal complexes of 2,6-pyridinedicarboxylic acid (H2dipic), [Ni(H2O)5Co(dipic)2] (1), [Co(H2O)5Co(dipic)2][Ni(H2O)5Ni(dipic)2][Co(dipic)(H2O)3] (2), [Cu(H2O)5Ni(dipic)2]2[Co(dipic)(H2O)] (3) and [Ni(H2O)5Cu(dipic)2]2[Co(dipic)(H2O)] (4) have been prepared and characterized by elemental, AAS, spectral (IR and UV-Vis), and thermal analyses, as well as by using magnetic measurement and molar conductivity techniques. The results indicate that metal ions coordinate with 2,6-pyridinedicarboxylate ions (dipic2-) nitrogen atoms and carboxylate oxygen atoms of ligands. The mole ratio of dipic2- and metal ions in the complexes have been determined to be 2:2 (Co, Ni) for 1, 5:5 (3Co, 2Ni) for 2, 5:5 (Co, 2Ni and 2Cu) for 3 and 5:5 (Co, 2Ni and 2Cu) for 4 according to the results of elemental analysis. The structures of 1-4 might be proposed as octahedral ([Cu(dipic)(H2O)] unit for 2 square plane) according to results of spectroscopic analysis. The TG and DTA properties of compounds have been studied.
 
 KEY WORDS: 2,6-Pyridinedicarboxylic acid, Mixed metal, Metal complex
 
 Bull. Chem. Soc. Ethiop. 2020, 34(2), 313-321
 DOI: https://dx.doi.org/10.4314/bcse.v34i2.9

First Mononuclear Lanthanide Imidazolium Carboxylates

The synthesis and structural analysis of six new lanthanide imidazolium carboxylates are discussed. The first mononuclear lanthanide imidazolium carboxylate salts, [{(L)2M}3+{NO3−}3], M=Sm (1), Gd (2), Dy (3) and Y (4), were synthesized from the reaction between zwitterionic tris-imidazolium carboxylate and corresponding metal nitrate salts. The presence of monodentately coordinating carboxylate groups in 1–4 are confirmed by FT-IR spectra. The isostructural salts 1–4 are discrete tricationic monomer. To the best of our knowledge, the ionic salts 1–4 are the first structurally characterized mononuclear lanthanide imidazole carboxylates. The coordination environment of M(III) is fulfilled by six carboxylate oxygen atoms of ligands in distorted octahedron geometry.

Synthesis of chromium(III) complex with 1-hydroxy-2-pyridinone-6-carboxylic acid as insulin-mimetic agent and its spectroscopic and computational studies

The new complex of chromium(III) and 1-hydroxy-2-pyridinone-6-carboxylic acid was synthesized and its preparation routes were reported. Mass spectrometry and elemental analysis indicated the formation of chromium complex with the metal-to-ligand mole ratio of 1:3. Combination of spectroscopic measurement and spectral computations based on the density functional theory suggested that 1-hydroxy-2-pyridinone-6-carboxylic acid was a bidentate ligand using one oxygen atom at pyridinone carbonyl group and the other at N-oxide group as donor atoms upon chelation with chromium(III), forming the six-coordinate complex with five-membered chelate rings. Due to the enhanced stability of the chelate rings, such the pathway of chelation was theoretically predicted to be more favorable than the case where the carboxylate oxygen atom of ligand participated in the chelation. According to the preliminary tests, the chromium(III) complex with 1-hydroxy-2-pyridinone-6-carboxylic acid was found to be active in lowering plasma glucose levels in vivo.

The First Organoaluminum Derivative of a Hydroxy Carboxylic Acid. Molecular Structure of the Tetranuclear [Et2Al]4[(μ-O2C)C6H4-2-μ-O]2 Adduct

The reaction of triethylaluminum with salicylic acid in a 2:1 molar ratio results in the formation of the novel tetranuclear diethylaluminum aryloxide carboxylate adduct [Et2Al]4[(μ-O2C)C6H4-2-μ-O]2 (1). Compound 1 has been characterized by elemental analysis and 1H and 27Al NMR and IR spectroscopy, and its molecular structure has been determined by X-ray crystallography. The molecule is a centrosymmetric cluster with a skeleton framework consisting of three fused heterocycle rings, one 12- and two 6-membered. The two diethylaluminum units symmetrically join the two salicylic acid dianions by the formation of bridges between the aryloxide oxygen atom and one carboxylate oxygen atom of the second ligand. The two other diethylaluminum units are chelated by the aryloxide and second carboxylate oxygen atoms of each ligand. The carboxylate groups display a bidentate coordination mode with syn−anti conformation. The binding mode of the carboxylate and alkoxide ligands to metal centers is also discussed.