Spectroscopic studies of bridged binuclear complexes of Co(II), Ni(II), Cu(II) and Zn(II)

Binuclear cobalt(II), nickel(II), copper(II) and zinc(II) complexes of general composition [M₂L^1-2(μ-Cl)Cl₂] · nH₂O with the Schiff-base ligands (where L¹H and L²H are the potential pentadentate ligands derived by condensing 2,6-diformyl-4-methylphenol with 4-amino-3-antipyrine and 2-hydroxy-3-hydrazinoquinoxiline, respectively) have been synthesized and characterized. Analytical and spectral studies support the above formulation. ¹H-NMR and IR spectra of the complexes suggest they have an endogenous phenoxide bridge, with chloride as the exogenous bridge atom. The electronic spectra of all the complexes are well characterized by broad d–d and a high intensity charge-transfer transitions. The complexes are chloro-bridged as evidenced by two intense far-IR bands centered around 270–280 cm⁻¹. Magnetic susceptibility measurements show that complexes are antiferromagnetic in nature. The compounds show significant growth inhibitory activity against fungi Aspergillus niger and Candida albicans and moderate activity against bacteria Bacillus cirroflagellosus and Pseudomonas auresenosa.     

Synthese einiger biologisch interessanter 4′-Azaflavonoide

Zusammenfassung Verschiedene, brom-, chlor-, dichlor-, brommethoxy- und phenylsubstituierte 2-Hydroxy-4-azachalkone wurden durch basenkatalysierte Kondensation geeigneter o-Hydroxy-acetophenone mit Pyridin-4-aldehyd hergestellt und in die entsprechenden 4-Azaflavone, 4-Azaflavonole und 4-Azaflavanone umgewandelt.

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Several bromo-, chloro-, dichloro-, bromomethoxy- and phenylsubstituted 2-hydroxy-4-azachalcones have been prepared by base catalyzed condensation of the appropriate o-hydroxyacetophenones with 4-pyridinealdehyde, and subsequently converted into the corresponding 4-azaflavones, 4-azaflavonols and 4-azaflavanones.

     

Bimetallic complexes of a potentially pentadentate,acyclic, symmetrical compartmental Schiff base ligand that provides suitable topology for an exogenous bridge

The binucleating ligand LH₃, 2,6-diformyl-p-cresol-bis(phenylthioacetyldrazone), a Schiff base condensation product of 2,6-diformyl-p-cresol and phenylthioacetyldrazide forms complexes of the [M₂ClL] type with Co^II, Ni^II and Cu^II ions, which were characterized by elemental analysis, magnetic susceptibility, electronic spectra, molar conductance, i.r., n.m.r., e.p.r., t.g. and FAB mass spectral measurements. Sub-normal magnetic moments indicate the operation of antiferromagnetic coupling between the metal centres. The ligand and its copper complex show a pronounced fungistatic activity.     

Symmetric binuclear complexes with an ‘end-off’ compartmental Schiff base ligand

Four binuclear transition metal(II) complexes: [Co₂L(-Cl)Cl₂] · 2H₂O, [Ni₂L(-Cl)Cl₂(H₂O)₂] · 2H₂O, [Cu₂L(-Cl)Cl₂] · 2H₂O and [Zn₂L(-Cl)Cl₂] · 2H₂O, where LH is the binucleating ligand 2,6-diformyl-4-methylphenol bis(2-hydrazino benzothiazole), were prepared. Based on the i.r. spectra, elemental analysis, conductivity measurements and thermal analysis, we propose that these complexes contain an endogenous phenoxide bridge and an exogenous chloride bridge. Magnetic and spectral data supports the existence of a weak antiferromagnetic interaction between the metal ions, and octahedral for Ni^II and a square pyramidal environment for remaining complexes. The compounds show significant growth inhibitory activity against the fungi, Aspergillus niger and Candida albicans, as compared to antibacterial activity against Bacillus cirroflagellosus and Pseudomonas auregenosa.     

The stereochemical diversity of a new SNONS binucleating ligand towards 3d metal ions

A new binucleating ligand containing phenoxide as an endogenous bridging group, 2,6-diformyl-p-cresol bis(2-furanthiocarboxyhydrazone) and its binuclear Co(II), Ni(II), Cu(II) and Zn(II) complexes with chloride ion as an exogenous bridge, have been obtained. The complexes were characterized by elemental analysis, molar conductivities, magnetic moment measurements at room temperature, electronic, IR, 1H-NMR, EPR, FAB spectral studies and thermal data. The copper complex assumes a tetranuclear structure composed of two binuclear units related by a center of symmetry. The dimeric nature of copper(II) complex is supported by FAB. This complex is EPR silent. Room temperature magnetic moment reveals the operation of a significant antiferromagnetic spin exchange between the metal centers. Ligand and its copper and zinc complexes exhibit fluorescence at room temperature in DMF. All the compounds show an appreciable antimicrobial activity.     

Structural diversity in dinickel(II) complexes of thiosemicarbazones

2,6-Diformyl-p-cresol serves as a starting point for the generation of multidentate N/O/S chelating agents. Condensation with 4-(X-phenyl) thiosemicarbazide yields the pentadentate ligand having SNONS donor sequences, capable of holding two metal ions in close proximity. The ligands behave as mono/di/tri basic depending on the pH of the medium. Stereochemical diversity in the reaction product of such ligands with nickel(II) chloride at different pH is observed. Sterically demanding substituted ligands in association with various exogenous bridges dictate the geometry and coordination number of such complexes. The compounds were investigated by elemental analysis, molar conductivities, electronic spectra, IR, NMR, FAB mass spectra, TG-DTG, magnetic susceptibility measurements. Varieties of geometries such as square planar, square pyramidal, octahedral and square planar–square pyramidal are observed. Cryomagnetic data for the complexes (79–296 K) can be reproduced by an equation based on the Heisenberg model (H=−2JS₁S₂, S₁=S₂=1). The singlet–triplet splitting, J varies systematically with the coordination geometry about the Ni₂(SNONS) core, with the hydroxo bridged complex exhibiting the greatest degree of antiferromagnetic coupling. The coupling is somewhat weaker for the chloro-bridged complexes. None of the complexes have shown any appreciable antimicrobial activity.     

Thiocarbohydrazide as ``Diamine' to Construct Macrocyclic and Side-Off Compartmental Ligands

New dinuclear complexes of macrocycles/macroacycles/oximeshaving a reactive peripheral thioketo functional group were synthesized using2,6-diformyl-p-cresol as parent compound and thiocarbohydrazide/variousdiamines as side arms. Thioenolization and subsequent coordination to metal ionof the thio-keto sulfur is observed in asymmetric macrocycles and oxime complexes,while it is kept away from the coordination sphere in symmetric macrocycles. Magnetic susceptibility measurements over the range 7–300 K confirm that the copper(II) centersof the symmetric and asymmetric macrocycles are antiferromagnetically coupled, withvalues for the exchange coupling constant J through the phenolate oxygens of -610 to-580 cm^-1, respectively. The ligands and their complexes are found to be excellent fungistatic agents.