A thermoanalytical study of dipicolinic acid acting as a terdentate ligand in coordination compounds of divalent metal ions

The coordination compounds obtained by reaction of hot solutions of dipicolinic acid with the carbonates of the divalent metal ions manganese(II), iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) are studied using TG, DSC and HTRS techniques. For the thermal stability a sequence Mn > Fe > Zn > Co > Ni > Cu may be observed. This series is compared with the similar series obtained with isocinchomeronic acid. The thermal stability is, for each metal of the series, isocinchomeronic > dipicolinic. Thermal stability is discussed in terms of the intermolecular bonds, of the structures and of the stability constants of the complexes examined.     

Complexes of cobalt(II), nickel(II) and copper(II) with the benzenedicarboxylic acids. Thermal properties

The thermal properties of the complexes of phthalic, isophthalic and terephthalic acid with cobalt(II), nickel(II) and copper(II) are determined by thermogravimetry (TG), differential thermogravimetry (DTG) and differential scanning calorimetry (DSC).The thermal stability of the anhydrous compounds gives, for the metal ions, a sequence Co > Ni > Cu.The thermal stability series as a function of the ligand for each metal is terephthalate > isophthalate > phthalate.     

Protonation Equilibria of Carminic Acid and Stability Constants of Its Complexes with Some Divalent Metal Ions in Aqueous Solution

The dissociation constants of carminic acid (7-D-glucopyronosyl-3,5,6,8-tetra- hydroxy-1-methyl-9,10-dioxo-anthracene-2-carboxylic acid) (CA), together with the stability constants of its Cu(II), Zn(II), Ni(II), Co(II) and Hg(II) complexes, were studied potentiometrically in aqueous medium at 25.0?(1)?°C, and at the ionic background of 0.1?mol?dm^?3 of NaCl, and determined with the SUPERQUAD computer program. It has been observed that carminic acid has five dissociation constants, and for H₅L their values are 3.39?(7), 5.78?(7), 8.35?(7), 10.27?(7), and 11.51?(7). This ligand behaves as a bi-dentate ligand, and the carboxyl and the ortho hydroxy groups of the ligand coordinate to the metal ions. Various metal complexes were produced in solution under the experimental conditions, for each metal ion used, including hydrolyzed species. The species distribution curves of the complexes formed in the solution were calculated and reviewed. The stability of the complexes was found to follow the order: Cu(II) > Zn(II) > Ni(II) > Co(II) > Hg(II).     

Pyridine-2,5-dicarboxylic acid complexes of nickel(II) with 2,2′-bipyridine and 1,10-phenanthroline coligands; syntheses,crystal structures,spectroscopic and thermal studies

Two pyridine-2,5-dicarboxylic acid (pydcH₂) complexes of nickel(II) with 2,2′-bipyridine and 1,10-phenanthroline were synthesized and characterized by elemental, spectroscopic, thermal analysis, magnetic measurements and single crystal X-ray diffraction techniques. Both [Ni(pydc)(bipy)₂]·7H₂O and [Ni(pydc)(phen)₂]·6.5H₂O crystallize in the monoclinic system and P2₁/c space group. The Ni(II) ions are coordinated by two bidentate bipy or phen ligands and one pydc dianion in a distorted octahedral geometry. The pydc ligand is coordinated through the pyridine nitrogen atom and oxygen atom of carboxyl group as a bidentate ligand. Both carboxylate groups of pydc are deprotonated but only the 2-carboxylate is coordinated to the metal. Thermal decompositions of the complexes have been studied over the range 30–600 °C on heating in a static air atmosphere.     

Thermal studies on cobalt(II), nickel(II) and copper(II) ternary complexes of N-(2-acetamido) iminodiacetic acid and imidazoles

The thermal decomposition of Co(II), Ni(II) and Cu(II) complexes has been studied using thermogravimetry (TG) and differential TG (DTG). The complexes have been characterized by IR spectroscopy. The results reveal that the decomposition of these complexes is accompanied by the formation of metal acetate as an intermediate fragments. On the basis of the applicability of a non-isothermal kinetic equations, it was demonstrated that the stability of the complexes follows the order Co(II)>Cu(II)>Ni(II). These stably correspond to the strength of chelation between the metal ions and the primary and secondary ligands. A possible mechanism of the thermal decomposition of the complexes is suggested.     

Complexes of divalent metal ions with cinchomeronic and dinicotinic acid thermal properties

The thermal properties of the complexes of cinchomeronic and dinicotinic acid with several divalent metal ions were determined by thermogravimetry (TG) and differential thermal analysis (DTA).For the thermal stability of the anhydrous compounds a sequence may be observed for the metal ions with cinchomeronic (3,4-H₂PC) and dinicotinic acid (3,5-H₂PC):

The thermal stability of the pyridine carboxylic acid for each metal of the series is: dinicotinic > cinchomeronicThe activation energy values for each thermal reaction were also calculated, using the Coats and Redfern algorism, by the Univac 1108 computer, by a program properly implemented for the statistical analysis of the data to obtain the reaction order and the activation parameters with the relative confidence limits.     

Syntheses,Spectral, Thermal and Electrochemical Studies of 3-Carboxylacetonehydroxamic Acid and its Iron(Ii), Cobalt(Ii), Nickel(Ii), Copper(Ii) and Zinc(Ii) Complexes

3-Carboxylacetonehydroxamic acid (CAHA) and its iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes were synthesized and characterized by elemental analysis, UV-Vis and IR spectra and magnetic susceptibility. The pK _a1 and pK _a2 values of the ligand in aqueous solution were found to be 6.5 ± 0.1 and 8.6 ± 0.1, which correspond to dissociation of carboxyl and hydroxamic protons, respectively. The dianion CAH acts as a tetradentate ligand through the hydroxamate and carboxylate groups and coordinates to the divalent metal ions, forming coordination polymers with a metal-to-ligand ratio of 1 : 1 in the solid state. FTIR spectra and thermal decomposition of the ligand and its metal complexes were recorded and briefly discussed. The electrochemical behavior of the complexes was investigated by square wave voltammetry and cyclic voltammetry at neutral pH. In contrast to the solid state, the iron(II) and copper(II) cations form stable complex species with a metal-to-ligand ratio of 1 : 2 in solution. The iron(II), cobalt(II) and nickel(II) complexes show two-electron irreversible reduction behavior, while the copper(II) and zinc(II) complexes undergo quasi-reversible and reversible electrode reactions, respectively. The stability constants of the complexes were determined by square wave voltammetry.     

Sorption isotherms of Nickel(II), Cobalt(II), Mercury(II), and Lead(II) ions on a phosphorus-containing polymeric sorbent

The influence of the concentration of a complexing ion on the sorption recovery of nickel, cobalt, mercury, and lead ions from aqueous solutions by a phosphorus-containing polymeric polybutadiene-based sorbent was studied. Sorption isotherms of the studied metal ions were processed by the Langmuir and Freindlich models. The affinity of metal ions to the functional groups of a sorbent and the stability of complexes were established to decrease in the order Hg(II) > Pb(II) > Co(II) > Ni(II).     

Fe2+ and Cu2+ Increase the Production of Hyaluronic Acid by Lactobacilli via Affecting Different Stages of the Pentose Phosphate Pathway

This study aimed at optimizing the production of hyaluronic acid by Lactobacillus acidophilus FTDC 1231 using response surface methodology and evaluating the effects of divalent metal ions along the production pathway using molecular docking. Among different divalent metal ions that were screened, only iron (II) sulphate and copper (II) sulphate significantly (P?<?0.05) affected the production of hyaluronic acid. Subsequent optimization yielded hyaluronic acid at concentration of 0.6152?mg/mL in the presence of 1.24 mol L^?1 iron (II) sulphate and 0.16 mol L^?1 of copper (II) sulphate (103 % increase compared to absence of divalent metal ions). Data from molecular docking showed Fe²⁺ improved the binding affinity of UDP-pyrophophorylase towards glucose-1-phosphate, while Cu²⁺ contributed towards the interaction between UDP-glucose dehydrogenase and UDP-glucose. We have demonstrated that lactobacilli could produce hyaluronic acid at increased concentration upon facilitation by specific divalent metal ions, via specific targets of enzymes and substrates along pentose phosphate pathway.     

Photometric and potentio metric study of metal com-plexes of 2-(3'-sulfobenzoyl)pyridine-2-pyridylhydrazone

The composition, formation conditions and stability constants of metal complexes of 2-(3'-sulfobenzoyl)pyridine-2-pyridylhydrazone are reported. Two types of complexes are formed having net charges of 0 and 2 - with divalent cations. The anionic form of the complex is quantitatively retained by anion-exchange resins and can be recovered by acid solution.     

Thermal studies of Co(II), Ni(II) and Cu(II) complexes of N,N′-<Emphasis Type="Italic">bis</Emphasis>(3,5-Di-<Emphasis Type="Italic">t</Emphasis>-butylsalicylidene)ethylenediamine

The thermal decomposition kinetics of sterically hindered salen type ligand (L) and its metal complexes [M=Co(II), Ni(II), Cu(II)] were investigated by thermogravimetric analysis. A direct insertion probe-mass spectrometer (DIP-MS) was used for the characterization of metal complexes of L and all fragmentations and stable ions were characterized. The thermogravimetry and differential thermogravimetry (TG-DTG) plots of salen type salicylaldimine ligand and complexes showed a single step. The kinetic analysis of thermogravimetric data was performed by using the invariant kinetic parameter method (IKP). The values of the invariant activation energy, E _inv and the invariant pre-exponential factor, A _inv, were calculated by using Coats-Redfern (CR) method. The thermal stabilities and activation energies of metal complexes of sterically hindered salen type ligand (L) were found as Co(II)>Cu(II)>Ni(II)>L and E _Cu>E _Ni>E _Co>L. Also, the probabilities of decomposition functions were investigated. The diffusion functions (D _n) are most probable for the thermal decomposition of all complexes.     

Synthesis,characterization and thermal study of some tetradentate Schiff base transition metal complexes

Several mononuclear Co(II), Ni(II), Cu(II), and Fe(II) complexes of tetradentate salpren-type diimine, obtained from 3,5-di-tert-butyl-2-hydroxybenzaldehyde and 1,3-diaminopropane have been prepared and characterized by analytical, spectroscopic (FT-IR, UV–VIS) techniques, magnetic susceptibility measurements and thermogravimetric analyses (TG). The thermodynamic and thermal properties of complexes have been investigated. For further characterization Direct Insertion Probe-Mass Spectrometry (DIP-MS) was used and the fragmentation pattern and also stability of the ions were evaluated. The characterization of the end products of the decomposition was achieved by X-ray diffraction. The thermal stabilities of metal complexes of N,N′-bis(3,5-di-t-butylsalicylidene)-1,3-propanediamine ligand (L) were found as Ni(II) > Cu(II) > Co(II) > Fe(II).     

Novel Cobalt(II), Nickel(II) and Copper(II) Complexes of Neutral Orotic Acid. Synthesis,Spectroscopic and Thermal Studies

The new orotic acid complexes, [MCl₂(H₂O)₃(H₃Or)], M=Co(II), Ni(II) and [CuCl₂(H₂O)(H₃Or)₃] · H₂O, were synthesized and characterized by elemental analysis, magnetic susceptibility, spectral (Diffuse reflectance UV–Vis and FTIR) methods, and simultaneous thermal analysis (TG, DTG and DTA) techniques. Physical measurements indicate that the neutral orotic acid ligands are bonded to metal ions through the carbonyl groups. Two thermal processes of the complexes can occur: dehydration and pyrolytic decomposition. On the basis of the DTG_max, the thermal stability of the complexes follows the order: Co(II) (122 °C) > Cu(II) (77 °C) > Ni(II) (66 °C).     

Synthesis and characterization of PVP/AAc copolymer hydrogel and its applications in the removal of heavy metals from aqueous solution

Chelating poly(vinylpyrrolidone/acrylic acid) (PVP/AAc) copolymer hydrogels were prepared by radiation-induced copolymerization. The effects of preparation parameters such as PVP content in the hydrogel and irradiation dose on the swelling behavior of the hydrogel were studied. The pH dependent swelling was investigated. The thermal stability of the prepared hydrogel and the metal chelated ones was characterized by TGA. The removal of Fe(III), Cu(II), and Mn(II) from aqueous solution by the prepared PVP/AAc chelating hydrogel was examined by batch equilibration technique. The influence of treatment time, pH, and the initial feed concentration on the amount of the metal ions removed was studied. The results show that the removal of the metal ion followed the following order: Fe(III) > Cu(II) > Mn(II). The amounts of the removed metal ions increased with treatment time and pH of the medium. To re-use the hydrogel, the metal ions were stripped by using 2 N HCl.     

Influence of d-Electron Divalent Metal Ions in Complex Formation with L-Tartaric and L-Malic Acids

Binary complexes of α-hydroxy acids (L-Tartaric acid and L-Malic acid) with d-electron metal ions (copper, cobalt, nickel) were investigated. Potentiometric measurements have been performed in aqueous solution with computer analysis of the data for determination of the stability constants of complexes formed in the studied systems. The coordination mode of the complexes was defined using spectroscopic methods: electron paramagnetic resonance (EPR), ultraviolet-visible (UV-Vis), circular dichroism (CD), and infrared (IR). Results of the equilibrium studies have provided evidence for the formation of dimers with copper(II) ions and monomers with cobalt(II) and nickel(II) ions.     

Conditional Stability Constant Determination of Metal-Fulvic Acid Complexes

Abstract

Conditional stability constants for metal complexes of a terrestrial fulvic acid were determined using an ion-exchange chromatography—atomic absorbance spectroscopy method. Employing the Scatchard model, conditional stability constants were determined for the metal (II) fulvic acid complexes of cadminum, copper, lead, nickel, manganese, and zinc. The order of metal binding by the fulvic acid was determined to be: Cu > Ni > Pb > Zn > Cd > Mn. Complexes of weakly bound metal ions were determined with an added metal ion concentration of 2 × 10^–5 M to 1 × 10^–4 M while complexes of strongly bound metal ions were determined with an added metal ion concentration of 1 × 10^–5 M to 8 × 10^–4 M. The fulvic acid concentration was kept constant at 4 × 10^–4 M. The effect of pH and ionic strength on the copper-fulvic acid complex also was investigated.     

Noncovalent interactions and copper(II) coordination in systems containing l-aspartic acid and triamines

Interactions between l-aspartic acids (Asp) and polyamines (PA): 3,3-tri (1,7-diamino-4-azaheptane) or spermidine (Spd, 1,8-diamino-4-azaoctane) are investigated in metal-free systems as well as between Cu(II) ions in ternary systems with Asp and 3,3-tri or Spd. The composition and stability constants of the complexes formed have been determined by a potentiometric method, while the centres of interactions in the ligands have been identified by NMR, UV–Vis, IR, and EPR spectroscopy. The centres are the potential sites of metal ion coordination. In the Asp/PA systems, formation of molecular complexes (Asp)H_x(PA) was observed. Comparison of the log K_e of the adducts showed that the stability of the adducts significantly depends on the steric factor contributed by the length of PA. In the (Asp)H₃(PA) species, an inversion effect was observed where one of the amine groups (deprotonated) of 3,3-tri or Spd becomes a negative reaction centre and reacts with the protonated amino group of Asp. Therefore, depending on pH, the amino group of the PA can act as a positive or negative reaction centre. In the ternary systems of Cu(II)/Asp/PA the heteroligand-protonated complexes and molecular complexes are formed. In the molecular complexes ML?L′, where L = Asp and L′ = PA, the metallation involves oxygen atoms from the carboxyl groups and the amino group of the amino acid, while the fully protonated PA is located outside the inner coordination sphere and reacts with the anchoring binary complex CuH(Asp) or Cu(Asp). Introduction of metal ions into the Asp/3,3-tri system was found to change the character of the interaction and in the Cu(Asp)H₂(3,3-tri) complex, the oxygen atoms from the Asp carboxyl groups do not take part in coordination.     

Polarographic Behavior of Manganese(II) in the Presence of Oxalate Ions in Perchlorate and Sulfate Solutions

The dc polarographic method has been applied to study coordination equilibria between Mn(II) and oxalate ions in perchlorate and sulfate solutions. The stoichiometries of complexes formed in solution and those reduced at a dropping mercury electrode were established. The stability constants of the Mn(II) oxalate and sulfate complexes, as well as their diffusion coefficients, were determined at a constant ionic strength 0.5 mol⋅L⁻¹ and 25 °C. The stabilities of these Mn(II) complexes were compared with the corresponding complexes of other divalent metal ions. The polarographic method was able to identify complexes that have not been established by other methods and to determine their stability constants with high accuracy.     

Crystal Structure of 2-pyridine-2-yl-3(pyridine-2-carboxylideneamino)quinazolin-4(3H)-one and its Ligating Diversity Towards Transition Metal(II) Ions

The synthesis of a new ligand 2-pyridine-2-yl-3(pyridine-2-carboxylideneamino)-quinazolin-4(3H)-one (PPCAQ) is described together with its manganese(II), cobalt(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes. The single crystal X-ray diffraction studies of the ligand reveal the presence of two crystallographically independent molecules in asymmetric unit cell, which exhibit N…N attractive interaction. The PPCAQ and its metal complexes were characterized by analytical, spectroscopic (i.r., n.m.r and u.v.–vis), magnetic moment, conductance and thermal studies. The i.r. spectral studies reveal the ligational diversity of the PPCAQ towards different metal ions as NNN donor in cobalt(II), copper(II), zinc(II) and cadmium(II) complexes and as ONN donor in manganese(II) and nickel(II) complexes. The antimicrobial activity of all the compounds was tested; copper(II), zinc(II) and cadmium(II) complexes show enhanced antibacterial activity compared to the free ligand.     

Coordination compounds of biological interest: Thermal properties of some compounds of saccharin (o-benzoic sulphimide) with nickel(II) and zinc(II)

The thermal properties of nickel(II) and zinc(II) complexes of saccharin (sacc) (o-benzoic sulphimide) have been studied and compared both with those of cobalt(II) and copper(II) previously studied and with those of ternary complexes of nickel(II) and zinc(II) having both saccharin and pyridine as ligands. The thermal behaviour is discussed in terms of the interaction between metal and ligands, interaction studied by IR spectroscopy, and by reflectance spectroscopy.The classical thermal stability scale Co(II) > Ni(II) > Cu(II) > Zn(II) is always obtained.