Coordination properties of two new Schiff-base phenoxy-carboxylates and comparative study of their antioxidant activities

Abstract

Two novel tridentate Schiff-base ligands containing carboxylate groups were obtained from the condensation of 3-amino-4-hydroxybenzoic acid with either acetylacetone (H 3 L 1 ) or salicylaldehyde (H 3 L 2 ). H 3 L 1 reacted with copper(II) acetate and pyridine (strongly coordinating solvent) to afford the C1 complex, while reaction of H 3 L 2 with nickel(II) acetate and pyridine afforded two types of complexes C2 and C3. The two ligands and their metal complexes were fully characterized by elemental analysis, XRD and spectroscopic analysis.Upon its fully deprotonated state, (L 1 ) 3coordinates in a keto-enamine fashion and acts as a ditopic binder through an ONO tridentate donor system and an O monodentate donor system (carboxylate). Upon its doubly deprotonated state, (HL 2 ) 2ligand acts either as monotopic tridentate binder (i.e. enol-imine form with an ONO donor system that lead to complex C2) or as a ditopic ligand (ONO tridentate and O monodentate donor systems to afford complex C3).The molecular structure of all the compounds were determined by single crystal X-ray diffraction studies and revealed several important characteristics. In complex C1, the Cu(II) cations are five-coordinated with a slightly distorted square pyramidal geometry, while in C2 and C3 complexes, the Ni(II) ions are four and six-coordinated with a square planar and a slightly distorted octahedral geometry, respectively. Following this structural investigation, the antioxidant activities of the free ligands and their metal complexes were then investigated and demonstrated interesting antioxidant features especially for H 3 L 2 and complex C3. Lastly, temperature dependent magnetic susceptibility measurements showed the presence of ferromagnetic interactions in C1 mediated through the phenoxido bridges.

Copper(ii) complexes with terpene derivatives of ethylenediamine: synthesis, and antibacterial, antifungal and antioxidant activity

“…Significant differences in the results depending on the method used were noted in the study of AOA Schiff-base ligands containing carboxylate groups and their copper and nickel complexes. 14 A similar result was noted for the complexes Pd( ii ), Fe( ii ), Zn( ii ), Mn( ii ), Cu( ii ) and VO( iv ) c multifunctional Schiff base. 16 Our data confirm the conclusions of other researchers 41,52,53 that for a correct assessment of AOA one should not be limited to studies of RSA alone, it is desirable to use more relevant biological test systems.…”

“…A number of works report on the AOA of copper complexes. [7][8][9][10][11][12][13][14][15][16][17] Recently, much attention has been paid to the development and use of copper complexes with the superoxide dismutase (SOD) mimetic activity. [18][19][20][21][22][23][24] To test free-radicalscavenging properties of drugs is a promising protocol for enlarging the applicability of the clinic drugs.…”

The evaluation of antioxidant and anti-inflammatory activities of Parmotrema hypotropa lichen extract

“…The extract was assessed for its ability to protect the oxidation of the carotenoid β-carotene through hydrogen-based transfer mechanism [25]. Briefly, βcarotene/linoleic acid emulsion was prepared by dissolving 0.5mg of β-carotene in 1 mL of chloroform, then 25 μL of linoleic acid and 200 mg of tween-40 were added.…”

One-Dimensional CoII and NiII Helical Coordination Polymers Exhibiting Zero-Field Splitting

“…Therefore, the synthesis of carboxylate-Schiff base ligands offers an exciting alternative to designing new and more sophisticated linkers that incorporate additional donor species or functional groups to drive the growth of extended structures. 25,26 Herein, we describe the syntheses, crystal structures, and magnetic properties of two new Co II…”

“…Thus, understanding the zfs parameters and the relationship with the geometric and electronic structure of the coordination polymers is essential to designing new magnetic materials. Therefore, the synthesis of carboxylate-Schiff base ligands offers an exciting alternative to designing new and more sophisticated linkers that incorporate additional donor species or functional groups to drive the growth of extended structures. , Herein, we describe the syntheses, crystal structures, and magnetic properties of two new Co II and Ni II 1D coordination polymers obtained from the Schiff base generated by the condensation reaction of two molecules, 4-imidazolecarbaldehyde and anthranilic acid {[M­(HL)­(EtOH) 2 ]­(ClO 4 )} n ( 1 = Co II , 2 = Ni II , and H 2 L = 2 -{[( E )-1 H -imidazol-4-ylmethylidene]­amino}­benzoic acid).…”