Co(II), Ni(II), Zn(II) and Cu(II) complexes of (3E)-3-[(2-{(E)-[1-(2,4-dihydroxyphenyl)ethylidene]amino}ethyl)imino]-1-phenylbutan-1-one (DEPH₂) derived from ethylenediamine, 2′,4′-dihydroxyacetophenone and 1-phenylbutane-1,3-dione have been synthesized and characterized by elemental analysis, FTIR, UV-Visible spectroscopy, and screened to establish their potential as antibacterial agents, antioxidants and DPPH radical scavengers. The FTIR spectra showed that the ligand behaves as a dibasic tetradentate ligand with the dioxygen-dinitrogen donor atom system oriented towards the central metal ion. The analytical and spectroscopic data suggest a square planar geometry for Cu(II) and Ni(II) complexes and an octahedral geometry for the Co(II) complex. The ligand and their metal complexes were screened for antibacterial activity against Gram (+) and Gram (−) bacteria by the agar well diffusion method. In addition, the antioxidant activities of the complexes were also investigated through their scavenging effect on DPPH and ABTS radicals. The obtained IC₅₀ value of the DPPH activity for the copper complex (2.08 ± 0.47 µM) and that of the ABTS activity for the copper complex (IC₅₀ = 2.11 + 1.69 µM) were higher than the values obtained for the other compounds.

The huge research on Schiff base coordination complexes in the past few decades has given rise to several new molecules that have been of biological importance. The ease with which the Schiff base ligands are designed and prepared and their pattern is elucidated have made them to be referred to as “fortunate ligands” possessing azomethine derivatives, the C=N linkage that is essential for biological activity, including antibacterial, antifungal, antioxidant, anticancer, and diuretic activities. A variety of Schiff base and its complexes have been studied as model molecules for biological oxygen carrier systems. The uses of Schiff bases as DNA-cleaving agents and its mode of interaction and free-radical scavenging properties are described. The review encapsulates the applications of Schiff bases and their complexes.

Co(II), Ni(II), Cu(II), and Zn(II) complexes of (4E)-4-[(2-{(E)-[1-(2,4-dihydroxyphenyl)ethylidene]amino}ethyl)imino]pentan-2-one have been synthesized and characterized by elemental analyses, molar conductance, electronic and IR spectral studies, and XRD. FTIR confirmed the ligand coordinates the metal ion to form mononuclear complex via the oxygen and nitrogen atoms of the phenolic group and azomethine group, respectively. Tetrahedral geometry is proposed for Co(II) complex and square-planar geometry for Ni(II) and Cu(II) complexes. The antibacterial studies of the compounds were determined and they show that the metal complexes are more active than the free ligands. The antioxidant activity by DPPH and ABTS method was examined and it shows Cu(II); IC₅₀= 2.31 ± 1.54 µM for DPPH and Co(II); IC₅₀= 1.83 ± 1.08 µM for ABTS were the most active.

A number of novel ruthenium(II) polypyridine complexes have been designedand synthesized for use as photosensitizers in dye-sensitized solar cells (DSSCs) due totheir rich photophysical properties such as intense absorption, long-lived lifetimes, highemission quantum yields and unique redox characteristics. Many of these complexesexhibit photophysical behavior that can be readily controlled through a careful choice ofligands and/or substituents. With this perspective, we review the design and general syntheticmethods of some polypyridine ligands based on bipyridine, phenanthroline, terpyridine andquaterpyridine with/without anchoring groups with a view to correlate functionality ofligand structures with the observed photophysical, electroredox and power conversionefficiency of some examples of Ru(II) polypyridyl complexes that have been reported andparticularly used in the DSSCs applications. The main interest, however, is focused onshowing the development of new polypyridine ligand materials containing long-rangeelectron transfer motifs such as the alkenyl, alkynyl and polyaromatic donor functionalities.