The well-known fact is that the fourteen membered tetraazamacrocycles with a 5,6,5,6 chelate ring sequence is the best fit cavity for metal ions, since this holds the four nitrogen donors in a ‘pre-oriented’ configuration which is favorable for coordination. Studies [19-23] on the four coordinated square planar copper(II) and nickel(II) and six co-ordineted cobat(III), zinc(II) cadmium(II) complexes of the concerned ligands have already been carried out by our group. But µ- peroxo binuclear cobalt(III) complexes of the concerned ligands have not been reported so far. Moreover these types of µ-peroxo complexes are rare in literature. So it was interesting to see whether µ-peroxo binuclear cobalt(III) complexes of these ligands could be prepared using cobalt(II) perchlorate hexahydrate as metal template. An effort to do so with the concerned isomeric ligands, ‘tet-a’, ‘tet-b’, L B and L C (Chart-1) was successful. But similar complex formation for
Disubstituted planar and octahedral complexes exhibit both cis and trans stereochemistry. Figure 1 shows an example of octahedral geometric isomers. Octahedral cobalt(III) complexes that are low-spin d 6 configuration are diamagnetic and considered stable,  having a filled t 2 g
Table 3.2 shows that the nature of the equatorial groups play an important role in the activity of the complexes at reducing molecular weight and hence the value of Cs for each. It is apparent from the data in table 3.2 and graphically in figure 3.2 that the Cs values for all complexes have decreased with an increase in carbons on the main skeletal carbon backbone when compared with the value obtained for CoBF, complex II. It is of course possible that catalyst purity plays an important role as the purity of the other complexes when compared to that of CoBF could differ considerably and that this could be a reason for the decrease in activity. It is also important to consider the role of isomerisation on the activity of the complex. This is important when one considers complex III as it is quite possible that there are two isomers present. The cis and trans conformations. It is quite possible that one isomer is an effective CCTA whilst the other is not. It was however not possible in this work to isolate the isomers. When one considers complexes V and VI independently of the other complexes it appears that this trend is not followed, it is in fact the opposite, i.e. an increase in Cs with an increase in skeletal backbone is observed. This could possibly be due to catalyst purity or the effect of the axial ligands which in this case are ethyl acetate for both, this is known from FAB- MS information. It is plausible that the nature of the withdrawing groups on the C=0 group of the ligand destabilises the normally stabilised complex, and allows the cobalt carbon bond to break, subsequently the forming and breaking of the cobalt (III) alkyl allowing the CCT cycle to continue. It should also be noted that other factors such as
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The continuous demand for new chemotherapeutic agents indicates that new approaches are critically needed. The current study was under taken to examine the effect of the two novel antitumor complexes namely cobalt and chromium complexes of bis-(4-bromobenzaldehydeiminoacetophenone), BBIA-Co and BBIA-Cr, on liver, kidney and heart of Ehrlich ascites carcinoma (EAC) bearing male albino mice. The effect of the two complexes on antioxidant status of the animals and histopathological examination of liver, kidney and heart tissues were also examined. Results indicated that treatment with either BBIA-Co or BBIA-Cr had ameliorated to some extent the changes in liver function exerted by EAC inoculation. Both complexes had no significant effect on kidney function, while they induced cardiac toxicity to animals. The study also showed no significant changes in the antioxidant status of EAC inoculated mice treated with BBIA-Co compared to normal animals, which was not indicated after BBIA-Cr treatment. The biochemical data results were further supported by histopathological examination.
‘Cobalt Blue’: First examples of room temperature blue emissive Co(III) complexes are presented. The low negative first reduction potential and the high excited state energies made them strong photooxidant. They are successfully adapted in the photoredox trifluoromethylation of polycyclic aromatic hydrocarbons (PAHs).
The ligand 1-amidino-O-methylurea serve as a bidentate ligand satisfying both the primary and secondary valencies with the formation of inner metallic complexes. Amino acids, on the other hand, are well known chelating agents with multifunctional groups and are biologically active, creating considerable interest in their metal complexes 2,3,4 . Because cobalt(III) is consistently hexacoordinate in its complexes, the synthesis and elucidation of the structure through elemental analysis, conductance measurements, spectral analysis and magnetic moment measurements etc. have been undertaken.
A wide variety of metal-complexes based on titanium, gallium, germanium, palladium, gold, copper, ruthenium and tin are being intensively studied as platinum replacements [4-11]. Cobalt is another option for the central metal in complex compound. Cobalt (II, III)-based complexes appear to be very promising candidates for anticancer therapy, an idea supported by a considerable number of research articles describing the synthesis and cytotoxic activities of numerous cobalt complexes . On the other hand it is very important role of the ligand in the complex, which can increase the biological activity of the complex. Semicarbazones (SC) can act as biologically active antibacterial agents and are excellent chelating ligands of different denticity resulting in the synthesis of a great number of transition metal complexes containing these ligands [13,14]. Several of these complexes, due to their stability and intense colour, have been suggested as analytical reagents . Furthermore, complexes incorporating either SC-based ligand exhibit a wide variety
or mobilizing agents, metal-containing diagnostic aids, and the medicinal recruitment of endogenous metal ions. Medicinal application of metals can be traced back almost 5000 years . The development of modern medicinal inorganic chemistry, stimulated by the discovery of cisplatin, has been facilitated by the inorganic chemist’s extensive knowledge of the coordination and redox properties of metal ions. Metal centers, being positively charged, are favored to bind to negatively charged biomolecules; In particular, Co(III) polypyridyl complexes, were found to possess some excellent DNA binding and DNA-photocleavage properties under light irradiation, and thus they have received attentions of many chemists. Recently, many Co(III) polypyridyl complexes have been synthesized and their DNA-binding and DNA-photocleavage properties were detailedly investigated in experiment [6 & 7]. The extensive studies on substitution reactions of amine complexes of Cobalt(III) have mainly dealt with acid hydrolysis, base hydrolysis and substitution by anionic ligands in different solvents. The consensus on the mechanism is that the reactions involve a dissociative activation process [8-11]. Most recently our group has been synthesized some ruthenium(II) and cobalt(III) ethylenediamine mixed- polypyridyl complexes, which bind to DNA through an intercalative and groove mode and promote cleavage of plasmid pBR 322 DNA [12-16]. In this paper, we are reporting the synthesis and characterization of the complexes 1, 2, 3 and 4 in which 4 possesses a greater binding affinity and their DNA-binding properties are revealed by electronic absorption, emission spectra, viscosity measurement and DNA melting curve. These studies are necessary for further comprehension of binding of transition metal complexes to DNA.
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Abstract: The Schiff base ligand (3-nitrobenzylidene)-1-naphthylamine was prepared by the condensation between 3- nitrobenzaldehyde and 1-naphthylamine. The Ni and Co complexes of the corresponding ligand were prepared and was characterized by different methods like Thermogravimetric analysis, CHN analysis , IR and UV spectra From CHN analysis and IR spectral data the structure of Ni complex is found to be tetrahedral and that of Cobalt complex is octahedral structure. Keywords: Schiff base, aldehyde, amine, XRD, TG
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The totalvolume of reaction mixture in the spectrophotometric cell was kept as 2.5 ml ineach kinetic run. An Evolution60Thermo spectrophotometer fitted with recording and thermosettingarrangement was used to follow the rate of thereaction.Rate of this PiDC oxidant with unbound ligand and Cobalt (III) bound complexes were calculatedfrom observed decrease in absorbance at 400nm. The excess of the reductant was used in kinetic runs.It gives pseudo first order rate constant. It was determined from the linear plot of the lnA versus time.Reproducible result obtained giving good first order plot. The stoichiometric studies for the PiDCoxidation of pentaamminecobalt (III) complexes of α-hydroxyacid and unbound ligand in the presenceof micelles were carried out at 33± 2°C. It was observed that the cobalt (II) formation was negligiblysmall.
Though iron(III) isoelectronic with manganese(II), it is difficult to have any spectra-structure correlation in the case of iron(III) complexes. There is greater tendency for iron(III) to have charge transfer bands in the ultraviolet region, which have sufficiently strong low-energy wings in the visible region to obscure almost completely the weak spin forbidden d-d bands. However spectral feature of iron(III) ion in octahedral surround are well in accordance with the theoretical predictions. All the electronic transitions are thus spin-forbidden, as well as Laporte forbidden, so that the ligand field bands in the spectrum of the iron(III) complex are very weak. In the present iron(III) complexes the weak ligand field bands are masked by the intense charge transfer band at 19600 cm -1 hence it is difficult to have any structure correlation from the spectral data. Iron(III) complexes exhibit an effective magnetic moment between 5.90-5.98 B.M which is close to the value expected for an octahedral geometry and shows absence of super exchange phenomena in the complexes. The cobalt(III) complex exhibited a strong band at 16,220 cm -1 with a shoulder at 22,100 cm -1 , arising from 1 A 1g → 1 T 1g and 1 A 1g → 1 T 2g transitions respectively. These observations along with diamagnetic
The complexes of cobalt(II), nickel(II) and copper(II) have been prepared by reacting an ethanolic solution of the ligands AQTC and ethanolic solution of corresponding metal salts in molar ratio 2:1. The resulting mixtures were heated on waterbath for 2-3 h when the compounds separated out which were filtered, washed with ethanol followed by diethyl ether and dried in an electric oven. Yield in all cases 60-70%.
(e.g. titration of Cl , E.M.F* measurements in a Cl"* concentration cell, polarography). Since aquations of cobalt(III) halo complexes are usually catalysed by these ions, the methods found useful for the present work were limited to conductivity, spectrophotometiy, and polarimetry. The less sensitive E5g(N0^)g titration of Cl was tried for some very slow reactions. Both this and conductance measure the rate of release of Cl ion from a complex, so take no account of the steric course. It is likely that high-frequency conductance or capacitance methods will be used for aquation measurements in the future, since these eliminate all
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plot of molecular rotation against wave-length - cannot as yet be firmly based on theory, and an attempt has been made to demonstrate the worth of the empirical use of this rotatory dispersion evidence. Attention has been drawn to the deviations one might expect in going from one isomer of a complex to another, or from one compound to a chemically similar one. The introduction of an asymmetrio centre into a previously inactive ligand does not greatly alter the shape of the rotatory dispersion curves of the optical isomers of the complexes it forms.
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Molar conductances of a 10 −3 M solution of the complexes were measured in DMSO at 25 o C using a 4310 Jenway model conductivity meter. The infrared spectra of the reactants and the obtained complexes were recorded using KBr discs on Perkin-Elmer 1430 ratio recording Infrared spectrometer. Elemental analyses were carried out in microanalysis unit of Cairo University, Egypt using CHNS-932 (LECO) and Vario EL elemental analysers. Thermal analyses (TG, DTG) were carried out using a Shimadzu TGA-50 H computerized thermal analysis system. The system includes program which process data from the thermal analyzer with the ChromotPac C-R3A. The rate of heating of the samples was kept at 10 o C/ min. Sample masses 1.440, 2.411, 3.053, 3.017, 3.285, 1.754, 1.964, 1.521 mg for nickel acetate tetrahydrate, H 2 salen, AAP, APDC and complexes (1,3, 3, 4), respectively were analyzed
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that the ligands coordinated to the metal ions through v(C=O), v(COO) and v(N-H) respectively due to their structural similarities. Electronic spectral data further revealed the probable geometry of Co(II) and Fe(III) complexes to be octahedral, while that of Zn(II) complex is tetrahedral. All the complexes and the ligands were screened for their biological activity on some selected bacterial species which includes:- Staphylococcus aurous, Streptococcus pyogene, Bacillus subtilis, Escherichia coli, Salmonella shigela, Klebsiella pneumoniae and Pseudomonas aeuroginosa. The results of biological activity indicated that the Co(II) and Ni(II) complexes have increased activity while Fe(III) had decreased activity. The complexes are also soluble in polar solvents.
Synthesis of metal complexes: A solution of [M (II)] salt [Cobalt (II) chloride for Co (II), Nickel (II) sulphate for Ni (II)] (5mmol) in ethanol (30ml) was added to a solution of Oxadiazole (15 mmol) in ethanol (30ml) and the mixture was boiled under reflux on a water bath for 3 – 4hrs. The solvent was then removed by vacuum distillation and the pasty residue was thoroughly washed with acetone and dry ether to remove unreacted M(II) and oxadiazole. The complex obtained was dried over P 2 O 5 in vacuum.
The kinetics and oxidation cobalt (III) of alpha Thio acids viz, Thio glycolic Thio Malic acid Thio Lactic acid acid, by 2,2’-bipyridinium bromo chromate in surfactant medium have been using a novel chromium (VI) oxidant. The rate of the reaction increase the observed presence surfactant NaLS, CTAB and TRITON-X 100. The comparison of the rate of cobalt (III) complexes bound Thio acids much more than the cobalt (III) complexes unbound Thio acid with micelles. Among the surfactant which CTAB enhances the rate much more than the TRITON-X 100, NaLS. The temperature increases the rate of the reaction increases with micelles CTAB higher than the TRITON, NaLS . Mechanism explains the synchronous C-C bond fission and electron transfer to cobalt (III) centre.
Transition metal complexes and two new Schiff bases were prepared. These compounds were evaluated by various spectroscopic techniques. The physical and spectral data revealed monobasic tridentate nature of Schiff base and ligand to metal ratio of 2:1 for cobalt complex and 1:1 for copper, zinc and nickel chelates. Octahedral arrangement for cobalt complexes, square planar geometry for nickel complexes, the distorted square planar configuration for copper complexes and tetrahedral geometry for zinc complexes have been predicted. The biological activity studies revealed the higher antibacterial and antitubercular activity of metal chelates compared to parent ligand against ESBL and MBL uropathogens and M. Tuberculosis.
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Over the last few years considerable attention has been devoted to the study of mixed-ligand complexes of metal(II) containing nitrogen, oxygen and sulphur donor ligands due to their diverse biological activities, such as antifungal[1-3] antibacterial[4-5] anti-inflammatory antipyretic, herbicidal anticancer and antiulcer activities. They also play an important role in the activation of enzymes and are used for storage as well as for transport of active materials . The study of mixed ligand complex formation is relevant in the field of analytical chemistry, where the use of mixed ligand complexes allows the development of methods with increased selectivity and sensitivity. They have also great importance in the field of biological and environmental chemistry . These facts prompted us to synthesize new mixed ligand transition metal complexes, especially biologically important cobalt, nickel and copper complexes, to study the combined antimicrobial activity effect of ligands in conjugation with the metal ions. In continuation of our previous work [12-13], in this article we have reported four new mixed ligand metal complexes with N, S and O donor ligands.