Bivalent Metal Complexes Research Articles

Uptake of Ni2+ and Cu2+ by Zn–Al layered double hydroxide intercalated with carboxymethyl-modified cyclodextrin: Equilibrium and kinetic studies

Zn–Al layered double hydroxides (Zn–Al LDHs) intercalated with carboxymethyl-modified cyclodextrin (CMCD) ions (CMCD•Zn–Al LDHs) were prepared by the co-precipitation method. The adsorption of Ni2+ by CMCD•Zn–Al LDHs followed the Langmuir-type mechanism, as evident from the adsorption isotherm. ESI-TOF-MS results implied that the uptake of Ni2+ by CMCD•Zn–Al LDHs could be attributed to the formation of chelate complexes between Ni2+ and CMCD ions in the interlayers of the CMCD•Zn–Al LDH. Kinetic studies revealed that the reaction involved in the uptake of Ni2+ by CMCD•Zn–Al LDH proceeded under mass transfer control, suggesting that the CMCD ion in the interlayer of the CMCD•Zn–Al LDH quickly formed a chelate complex with Ni2+. The transfer rate of Ni2+ through the product layer was rate-limiting. Similar results were obtained for the uptake of Cu2+ by CM-β-CD•Zn–Al LDH. It was also found that the CM-β-CD•Zn–Al LDH was more selective toward Cu2+ uptake than Ni2+ in the mixed solution. This was attributed to the Irving-Williams order of stability of bivalent transition metal complexes; Cu2+ formed a more stable chelate complex with the CM-β-CD ion in the interlayer of CM-β-CD•Zn–Al LDH as compared to Ni2+.

Spectral and Thermal Studies on Bivalent Transition Metal Complexes of Oxalic Acid with Morpholine

Morpholinium transition metal oxalates of the formula (MorpH)2[MII(ox)2 (H2O)2].2H2O, where M = Co, Ni have been prepared by the reaction of respective metal nitrates with aqueous solution of morpholinium oxalate salts in appropriate mole ratios. These compounds have been characterized by various physico-chemical techniques like elemental analysis, conductance measurements, UV-Vis, IR, TG-DTA, XRD and SEM studies. The elemental analysis confirms the desired composition of the complexes. Conductance measurements show that all the complexes behave as 2:1 electrolytes, augmenting the non-coordination of morpholiniumcation. Thermal studies show the presence of two coordinated water molecules and two lattice water molecules. Based on the above results, geometry of the complexes is assigned as octahedral. The powder X-ray diffraction patterns of these compounds are similar to one another suggesting that they are isomorphous.Scanning electron micrographs are also observed to evaluate the morphology and particle size of the complexes.

Molecular structures of some bivalent metal complexes of 1-(4-acetylphenyl)imidazole and co-ligands

A series of bivalent metal complexes having compositions [Co(L)2Cl2] (1), [Zn(L)2Cl2] (2), [Co(L)2(H2O)4](NO3)2·2H2O (3), [Zn(L)2(H2O)4](NO3)2·2H2O (4), [Co(L)2(OAc)2(H2O)]·3H2O (5), [Mn(L)2(OAc)2(H2O)]·3H2O (6) [Co(L)4(NCS)2] (7), {[Co(L)2(Fum)(H2O)2]·2H2O}n (8) and {[Mn(L)2(Fum)]}n (9) were synthesized using L {L = 1-(4-acetylphenyl)imidazole} and respective co-ligands. The mononuclear sets 1–2, 3–4 and 5–6 are isomorphous and isostructural in nature. Complex 7 is a mononuclear complex, 8 is a 1D coordination polymer and 9 is a 2D-coordination polymer. All the compounds were structurally characterized using IR spectroscopy, thermogravimetric analyses, powder X-ray and single crystal X-ray diffraction studies. In general, coordinated/lattice water molecules are found to be involved in OH⋯O hydrogen bonding and counter ions, in other weak interactions like CH⋯S, CH⋯Cl and CH⋯O. The aromatic ring of L also is involved in CH⋯π and π⋯π stacking interactions. In 3 and 4, hydrogen bonding interactions between coordinated water molecules, lattice water and nitrate ion contain cyclic hydrogen-bonded architectures. In 5 and 6, acetyl group present in L act as hydrogen bond acceptor through O⋯HO interaction. In 8 and 9 Fum coordinate to metal center in μ-η1:η1 bidentate and μ4-η1:η1:η1:η1 tetradentate fashions resulting in formation of 1D and 2D coordination polymers, respectively.

In vitro Antimicrobial Investigations of Newly Synthesized Transitional Bivalent Metal Complexes Derived from 8-Hydroxyquinoline

In vitro Antimicrobial Investigations of Newly Synthesized Transitional Bivalent Metal Complexes Derived from 8-Hydroxyquinoline

A comparative structural and property investigation of four new bivalent transition metal complexes based on 4-nitrophenylacetic acid with rigid 4-nitrobenzoate analogues

The synthesis, spectral, thermal, magnetic properties, and structural features of four new one-dimensional (1-D) polymers having formula [M(4-npa)2(μ2-H2O)(H2O)2]·2H2O where (M=Mn 1; M=Co 2; M=Zn 3; M=Ni 4; 4-npa=4-nitrophenylacetate) are investigated and compared with corresponding 4-nitrobenzoate (4-nba) analogues. The single crystal studies reveal that compounds 1–3 are isostructural and crystallize in the centrosymmetric monoclinic space group P21/c. Their structure consists of distorted octahedra of a unique central metal ion, two crystallographically unique monodentate 4-npa ligands, two terminal water molecules, a μ2-bridging bidentate water and two lattice water molecules. The central metal exhibits a distorted {MO6} octahedron with two O atoms from terminal water molecules disposed cis to each other, two O atoms from the monodentate carboxylates also disposed in a cis geometry and the remaining two O atom from the μ2-bridging bidentate water disposed trans. The μ2-brindging mode of water leads to the formation of an extended 1-D chain structure. The lattice water links parallel 1-D chains with the aid of H-bonding interactions. The IR, XRD powder pattern, thermal characterization and elemental analysis reveal that the structure of polycrystalline compound 4 is nearly identical with that of other 4-npa analogues.

Design, synthesis, spectral characterization, DNA interaction and biological activity studies of copper(II), cobalt(II) and nickel(II) complexes of 6-amino benzothiazole derivatives

Two novel Schiff bases, L1 = (2-benzo[d]thiazol-6-ylimino)methyl)-4,6-dichlorophenol), L2 = (1-benzo[d]thiazol-6-ylimino)methyl)-6-bromo-4-chlorophenol) and their bivalent transition metal complexes [M(L1)2] and [M(L2)2], where M = Cu(II), Co(II) and Ni(II) were synthesized and characterized by elemental analysis, NMR, IR, UV–visible, mass, magnetic moments, ESR, TGA, SEM, EDX and powder XRD. Based on the experimental data a square planar geometry around the metal ion is assigned to all the complexes (1a-2c). The interaction of synthesized metal complexes with calf thymus DNA was explored using UV–visible absorption spectra, fluorescence and viscosity measurements. The experimental evidence indicated that all the metal complexes strongly bound to CT-DNA through an intercalation mode. DNA cleavage experiments of metal(II) complexes with supercoiled pBR322 DNA have also been explored by gel electrophoresis in the presence of H2O2 as well as UV light, and it is found that the Cu(II) complexes cleaved DNA more effectively compared to Co(II), Ni(II) complexes. In addition, the ligands and their metal complexes were screened for antimicrobial activity and it is found that all the metal complexes were more potent than free ligands.

Determination of thermodynamic stability constant of bivalent transition metal complexes with schiffs base as ligands

Determination of thermodynamic stability constant of bivalent transition metal complexes with schiffs base as ligands

DNA Binding, Cleavage and Antibacterial Activity of Mononuclear Cu(II), Ni(II) and Co(II) Complexes Derived from Novel Benzothiazole Schiff Bases.

A series of novel bivalent metal complexes M(L1)2 and M(L2)2 where M=Cu(II), Ni(II), Co(II) and L1=2-((benzo [d] thiazol-6-ylimino)methyl)-4-bromophenol [BTEMBP], L2=1-((benzo [d] thiazol-6-ylimino)methyl) naphthalen-2-ol [BTEMNAPP] were synthesized. All the compounds have been characterized by elemental analysis, SEM, Mass, (1)H NMR, (13)C NMR, UV-Vis, IR, ESR, spectral data and magnetic susceptibility measurements. Based on the analytical and spectral data four-coordinated square planar geometry is assigned to all the complexes. DNA binding properties of these complexes have been investigated by electronic absorption spectroscopy, fluorescence and viscosity measurements. It is observed that these binary complexes strongly bind to calf thymus DNA by an intercalation mode. DNA cleavage efficacy of these complexes was tested in presence of H2O2 and UV light by gel electrophoresis and found that all the complexes showed better nuclease activity. Finally the compounds were screened for antibacterial activity against few pathogens and found that the complexes have potent biocidal activity than their free ligands.

Potentiometric, equilibrium studies and thermodynamics of novel thiosemicarbazones and their bivalent transition metal(II) complexes

Protonation constants of novel thiosemicarbazones including 2-(1-(2-phenyl-hydrazono)-propan-2-ylidene) hydrazine-carbothioamide (TPHP) and N-methyl-2-(1-(2-phenyl-hydrazono)-propan-2-ylidene)hydrazinecarbo-thioamide (MTPHP) ligands and their corresponding metal-ligand formation constants with Cu(II), Ni(II), Mn(II) and Co(II) ions were determined at 15°C, 25°C and 35°C in 50% DMSO solution at I=0.1mol·dm−3 NaNO3. The stability order of complexes with reference to the metal ions has been followed this order Cu(II)>Ni(II)>Co(II)>Mn(II) in concord with the Irving-Williams stability order. Also, chemical equilibrium studies indicated that substitution of hydrogen in thiosemicarbazone (TPHP) by methyl group causes lowering of acidity as a result of the electron-releasing effect of the methyl group in the substituted amino group of the thiosemicarbazide moiety. The speciation of different species in solution has been evaluated as a function of pH. Additionally, the effect of temperature on protonation of thiosemicarbazone ligands and formation of their M(II)-thiosemicarbazone complexes was investigated. The thermodynamic parameters (ΔH, ΔS and ΔG) were calculated and discussed. It was found that both log K1 and –ΔH1, for M(II)-thiosemicarbazone complexes are somewhat larger than log10 K2 and –ΔH2, indicating a change in the dentate character of these ligands from tridentate (SNN-donors) in 1:1 chelates to bidentate (SN-donors) in 1:2; M:L chelates. Also, the lower values of log10 K2 and –ΔH2 than log K1 and –ΔH1 may be attributed to steric hindrance produced by the entrance of a second molecule.

Preparation and Characterization of Some Bivalent Metal Complexes of Benzimidazole Derivatives

Preparation and Characterization of Some Bivalent Metal Complexes of Benzimidazole Derivatives

Bivalent transition metal complexes of ONO donor hydrazone ligand: Synthesis, structural characterization and antimicrobial activity

Mononuclear transition metal complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) with a new hydrazone ligand derived from pyrazine-2-carbohydrazide and 2-hydroxyacetophenone have been synthesized. The isolated complexes were characterized by elemental analysis, spectral and analytical methods including elemental analyses, IR, diffuse reflectance, 1H-NMR, mass spectra, molar conductance, magnetic moment, ESR, XRD, TG and SEM analysis. From the elemental analyses data, the stoichiometry of the complexes was found to be 1:1 (metal:ligand) having the general formulae [M(HL)(Cl)(H2O)2], [M=Mn(II), Co(II), Ni(II) and Cu(II)] and [M(L)(H2O)], [M=Zn(II) and Cd(II)]. The molar conductance values indicate the nonelectrolytic nature of metal complexes. The IR spectral data suggest that the ligand behaves as tridentate moiety with ONO donor atoms sequence towards central metal ion. The Mn(II), Co(II), Ni(II) and Cu(II) complexes have been assigned a monomeric octahedral geometry whereas tetrahedral to Zn(II) and Cd(II) complexes. The antibacterial and antifungal activities of the ligand and its metal complexes were studied against bacterial species Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Bacillus subtilis, Enterococcus faecalis and Streptococcus pyogenes and fungi Candida albicans, Aspergillus niger and Aspergillus clavatus. The activity data show that the metal complexes have a promising biological activity comparable with the parent ligand against all bacterial and fungal species.

Eco Friendly Microwave Assisted Rapid and Efficient Synthesis, Spectroscopic Studies and Antimicrobial Activity of Bivalent Transition Metal Complexes of Hydrazones

Two new series of Co(II), Ni(II) and Cu(II) metal complexes of the type [M(C14H10N2O3)·2H2O] and [M(C14H11N2O2)·3H2O]Ac, where M = Co(II)/Ni(II)/Cu(II) and Ac = CH3COO−, have been synthesized in good yields at less reaction time by adopting an efficient and eco friendly microwave assisted method. All the synthesized compounds were characterized by running their TLC for single spot, HPLC, elemental analyses, IR, 1H-NMR, 13C-NMR, magnetic susceptibility measurements, electronic spectral studies and screened for antimicrobial activities against two bacteria Staphylococcus aureus (gram +ve) and Escherichia coli (gram −ve) and fungi Aspergillus niger and Aspergillus flavus by adopting disc diffusion method. The antimicrobial activity results indicated that hydrazide exhibited good activity which increases in its hydrazones. However, the metal complexes exhibited maximum activity against both bacteria and fungi.

Mechanical stability of bivalent transition metal complexes analyzed by single-molecule force spectroscopy.

Multivalent biomolecular interactions allow for a balanced interplay of mechanical stability and malleability, and nature makes widely use of it. For instance, systems of similar thermal stability may have very different rupture forces. Thus it is of paramount interest to study and understand the mechanical properties of multivalent systems through well-characterized model systems. We analyzed the rupture behavior of three different bivalent pyridine coordination complexes with Cu2+ in aqueous environment by single-molecule force spectroscopy. Those complexes share the same supramolecular interaction leading to similar thermal off-rates in the range of 0.09 and 0.36 s−1, compared to 1.7 s−1 for the monovalent complex. On the other hand, the backbones exhibit different flexibility, and we determined a broad range of rupture lengths between 0.3 and 1.1 nm, with higher most-probable rupture forces for the stiffer backbones. Interestingly, the medium-flexible connection has the highest rupture forces, whereas the ligands with highest and lowest rigidity seem to be prone to consecutive bond rupture. The presented approach allows separating bond and backbone effects in multivalent model systems.

Mechanical Rupture of Mono- and Bivalent Transition Metal Complexes in Experiment and Theory

Biomolecular systems are commonly exposed to a manifold of forces, often acting between multivalent ligands. To understand these forces, we studied mono- and bivalent model systems of pyridine coordination complexes with Cu2+ and Zn2+ in aqueous environment by means of scanning force microscopy based single-molecule force spectroscopy in combination with ab initio DFT calculations. The monovalent interactions show remarkably long rupture lengths of approximately 3 A that we attribute to a dissociation mechanism involving a hydrogen-bound intermediate state. The bivalent interaction with copper dissociates also via hydrogen-bound intermediates, leading to an even longer rupture length between 5 and 6 A. Although the bivalent system is thermally more stable, the most probable rupture forces of both systems are similar over the range of measured loading rates. Our results prove that already in small model systems the dissociation mechanism strongly affects the mechanical stability. The presented approach off...

Synthesis, Characterization and Antimicrobial Activity of Isomeric Pyridyl-Tetrazole Derivative Ligands and their Bivalent Metal Complexes

Synthesis, Characterization and Antimicrobial Activity of Isomeric Pyridyl-Tetrazole Derivative Ligands and their Bivalent Metal Complexes

Synthesis, characterization, biological studies, and molecular modeling of mixed ligand bivalent metal complexes of Schiff bases based on $N$-aminopyrimidine-2-one/2-thione

New mixed Schiff bases, Cu(II), Co(II), Ni(II), and Mn(II) complexes, were synthesized derived from 5-chloro-2-hydroxyacethophenone and 1-amino-5-benzoyl-4-phenyl-1H-pyrimidine-2-one/thione. These complexes were characterized by elemental analysis, magnetic measurements, molar conductivity, IR, electronic, NMR, and mass spectral studies. All the complexes showed nonelectrolytic behavior. Moreover, the newly synthesized mixed ligand complexes were evaluated for their in vitro antimicrobial efficiency against bacteria and yeast. The compound named Co(L$_{1}$L) had good antifungal activity against Candida species, but no profound antibacterial effect against bacterial strains. In addition, the ground state geometries of the complexes were optimized using a semi-empirical method at PM6 level, which is a suitable and effective basis set for organometallic and large structures to obtain information about their 3D geometries and electronic structures.

Synthesis and Spectroscopic Study of Bivalent Metal Complexes with 4-hydroxy-6- methyl-3-((Z)-4-methylphenylazo)-2H-pyran-2-one ligand

Six chelate complexes of 4-hydroxy-6-methyl-3-((Z)-4-methylphenylazo)-2H-pyran-2-one (HL) ligand with Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) were synthesized and characterized by elemental analysis, magnetic susceptibility measurements, electronic, 1 H, 13 C NMR and IR spectral studies. The ligand is coordinated through its deprotonated pyrane-oxygen and through the azo-group to the metals. Mn(II), Co(II), Cu(II) and Ni(II) complexes have octahedral geometry around the central atoms. The molar conductance measurements on chloride-ion containing Zn(II) and Cd(II) complexes confirmed that chloride ions are bound in the coordination sphere, and the most probably geometry around the central atoms is expected to be tetrahedral.

Mixed bivalent transition metal complexes of 1,10-phenanthroline and 2-aminomethylthiophenyl-4-bromosalicylaldehyde Schiff base: Spectroscopic, molecular modeling and biological activities

Mixed ligand complexes of M(II) {M = Cu(II), Ni(II), Co(II) and Zn(II)} with 1,10-phenanthroline (1,10-Phen) and Schiff base namely 2-aminomethylthiophenyl-4-bromosalicylaldehyde (ATS) have been synthesized. These metal chelates have been characterized by elemental analyses, IR, 1 H NMR, solid reflectance, magnetic moment and molar conductance. Spectral data showed that the 1,10-phenanthroline act as neutral bidentate ligand coordinating to the metal ion through two nitrogen donor atoms and Schiff base (ATS) acts as monobasic bidentate coordinating through through azomethine- N and phenolic-oxygen groups. The geometry of the studied M(II) complexes has been fully optimized. The metal chelates have been screened for their antimicrobial activities using the disc diffusion method against different selected types of bacteria and fungi. In vitro antitumor activity assayed against two human cell lines colon (HCT116) and larynx (HEP2) cancer cells. Solution equilibrium studies were also investigated.

Spectroscopic and biological activities studies of bivalent transition metal complexes of Schiff bases derived from condensation of 1,4-phenylenediamine and benzopyrone derivatives

Many tools of analysis such as elemental analyses, infrared, ultraviolet–visible, electron spin resonance (ESR) and thermal analysis, as well as conductivity and magnetic susceptibility measurements were used to elucidate the structures of the newly prepared Co(II), Ni(II) and Cu(II) complexes with Schiff bases derived from the condensation of 1,4-phenylenediamine with 6-formyl-7-hydroxy-5-methoxy-2-methylbenzo-pyran-4-one (H2L) or 5,7-dihydroxy-6-formyl-2-methylbenzopyran-4-one (H4L). The data showed that all formed complexes are 1:1 or 2:2 (M:L) and non-electrolyte chelates. The Co(II) and Cu(II) complexes of the two Schiff bases were screened for antibacterial activities by the disk diffusion method. The antibacterial activity was screened using Escherichia coli and Staphylococcus capitis but the antifungal activity was examined by using Aspergillus flavus and Candida albicans. The Results showed that the tested complexes have antibacterial, except CuH4L, but not antifungal activities.

Bivalent transition metal complexes of cetirizine: Spectroscopic, equilibrium studies and biological activity

Metal complexes of cetirizine⋅2HCl (CTZ=2-[2-[4-[(4-chlorophenyl)phenyl methyl]piperazine-1-yl]-ethoxy]acetic acid, dihydrochloride have been prepared and characterized by elemental analyses, IR, solid reflectance, magnetic moment, molar conductance, and UV–Vis spectra. The analytical data of the complexes show the formation of 1:2 [M:L] ratio, where M represents Ni(II), Co(II) and Cu(II) ions, while L represents the deprotonated CTZ ligand. IR spectra show that CTZ is coordinated to the metal ions in a monodentate manner through carboxylate-O atom. Protonation equilibria of CTZ and its metal complexation by some divalent metal ions were determined in aqueous solution at constant ionic strength (0.1M NaCl) using an automatic potentiometric technique. Thermodynamic parameters for the protonation equilibria of CTZ were calculated and discussed. The stability order of M(II)–CTZ complexes were found to obey Mn2+<Co2+<Ni2+<Cu2+, in accordance with the Irving–Williams order. The concentration distribution of the complexes in solution is evaluated as a function of pH. The CTZ ligand and its metal complexes were screened for their biological activity against bacterial species (Bacillus subtillis RCMB 010067, Staphylococcus aureus RCMB 010028, Pseudomonas aeuroginosa RCMB 010043, and Escherichia coli RCMB 010052) and fungi as (Aspergillus flavus RCMB 02568, Pencicillium italicum RCMB 03924, Candida albicans RCMB 05031 and Geotricum candidum RCMB 05097). The activity data show that the metal complexes have antibacterial and antifungal activity more than the parent CTZ ligand against one or more bacterial or fungi species. MIC was evaluated for the isolated complexes.