Synthesis and characterization of some coordinated metal and charge transfer complexes of isonicotinic acid hydrazide ligand with 2-hydroxyacetophenonylidene

A new series of coordinated metal (Fe(III), Co(II) and Cu(II)) and charge transfer complexes of Schiff base isonicotinic acid (2-hydroxy acetophenonylidene) hydrazide (L) have been synthesized. The ligand (L), its metals and CT complexes were characterized by UV-Vis spectra, FT-IR, 1HNMR and elemental analysis as well as conductance measurements. The pKa of L was determined in universal buffer solutions (20% v/v EtOH-H2O) with varying pH's values. The molar conductivity measurements prove the non-electrolytic nature of all metal complexes. Furthermore, the thermogravimetry (TG) and differential thermal analysis (DTA) of the synthesized complexes were carried out in the range of 30-1000 °C. In addition, interaction of (L) as an electron donor with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as π-type electron acceptor has been studied and characterized. The observed new band at 585 nm might be assigned as charge transfer (CT) absorption band. The electronic absorption spectrum of L-DDQ interaction is found to be dependent on time. The IR spectra of L with the coordinated metals and CT-complexes revealed new main IR bands, which strongly support the formation of complexes. The stoichiometry of the complexes was determined from photometric titration methods which are in accordance with the results of elemental analyses. The ratio were found to be 1:2 (metal:L) and 1:1 (L:DDQ). The spectra of L, its coordinated metals and CT complexes are fully discussed.

Recent developments in supramolecular complexes of azabenzenes containing one to four N atoms: synthetic strategies, structures, and magnetic properties

For the last couple of decades, azabenzene-based ligands have drawn much attention from inorganic chemists due to their ability to coordinate with different metal ions to form supramolecular clusters. These azabenzenes are weak σ donors and strong π acceptors and electron-deficient. Metallogrid complexes and non-grid oligomers are well-defined supramolecular clusters, formed by appropriate chelating ligands, and can show interesting optical, magnetic, and electronic properties. Self-assembly of [n × n] metallogrid complexes is dominated by the entropic factor while the formation of oligonuclear metal ion complexes is dominated by other effects like CFSE, electrostatic factors, ligand conformational characters, etc. Herein, the present article gives an overview of six-membered heterocyclic azine-based ligands and their potential for different metal ions to form polynuclear complexes. Moreover, their temperature-dependent magnetic properties and SCO phenomena are well described and tabulated.

Tetranuclear MnII, CoII, CuII and ZnII grid complexes of an unsymmetrical ditopic ligand: synthesis, structure, redox and magnetic properties

Synthesis towards the preparation of an unsymmetrical binucleating Schiff-base ligand, (H₂L) is discussed. It has been synthesized by reacting methyl 6-(hydrazinecarbonyl)picolinate with 2-hydroxy acetophenone. The ligand (H₂L) comprises two different asymmetric binding pockets; however, when reacted with Mn(ii), Co(ii), Cu(ii) and Zn(ii) salts, very stable self-assembled [2 × 2] grid complexes form regardless of the employed metal-to-ligand ratio. The obtained complexes [Mn₄L₄]·(CH₃CN) (1), [Co₄L₄]·(CHCl₃) (2), [Cu₄L₄]·(CHCl₃) (3) and [Zn₄L₄] (4) have been fully characterized by physicochemical methods, including ESI mass spectrometry and X-ray crystallographic analyses, and their EPR, magnetic and redox properties are discussed. All discussed complexes self-assembled in a 'head-to-tail' fashion leading to [2 × 2] grid architectures. Mn, Co and Cu grid complexes show weak to moderate antiferromagnetic coupling among the four metal centers. The high stability of the grid structures is in line with the lack of any observable dissociation or exchange between metal ions in solution. Complexes 1 and 2 show four quasi-reversible to irreversible oxidative responses in cyclic voltammograms at a glassy carbon working electrode in 1,2-dichlorobenzene and at a platinum working electrode in dichloromethane, respectively.