Formation Of Mixed-ligand Complexes Research Articles

Thermodynamics of mixed-ligand complex formation of copper (II) ethylenediaminetetraacetate with hexamethylenediamine in an aqueous solution

The mixed-ligand complex formation in the system Cu2+−Edta4−−(CH2)6(NH2)2 (L), where L is hexamethylenediamine has been calorimetrically, pH-potentiometrically and spectrophotometrically studied in aqueous solution at 298.15 K and the ionic strength of I = 0.5 (KNO3). The thermodynamic parameters of formation of the CuEdtaL2−, CuEdtaHL− (CuEdta)2L4− and (CuEdta)2En4− complexes have been determined. The most probable coordination mode for the complexone and the ancillary ligand in the mixed-ligand complexes was discussed.

Interaction of drug based binuclear mixed-ligand complexes with DNA

Here in we tried to increase an antibacterial activity of ciprofloxacin drug due to formation of mixed-ligand complexes. Synthesized compounds were found to be more potent compare to drugs, ligands and metal salt against selective gram (+ve) and gram (−ve) organisms. Interaction of the complexes with nucleic acid (DNA) were investigated using spectroscopic technique, viscosity measurement and gel electrophoresis and it was found that the complexes bind to DNA via intercalative mode.

Synthesis, characterization and potent superoxide dismutase-like activity of novel bis(pyrazole)-2,2'-bipyridyl mixed ligand copper(II) complexes.

Eleven new complexes of Cu(II) chloride and nitrate with bis(pyrazol-1-yl)propane and bis[2-(pyrazol-1-yl)ethyl]ether ligands were prepared and characterized by spectral and electrochemical methods. X-Ray crystal structure determination of bis[2-(3,5-dimethylpyrazol-1-yl)ethyl]etherdinitratocopper revealed a hepta-coordinated structure with the bis(pyrazole) ligand coordinated in a tridentate NNO-fashion and both of the nitrate ions in a bidentate fashion. Reaction of Cu(II) nitrate complexes with 2,2'-bipyridyl led to the displacement of one of the nitrate ions into the outer sphere and the formation of mixed-ligand complexes. Mixed-ligand bipyridyl Cu(II) complexes demonstrated the highest superoxide dismutase (SOD)-like activity in a chemical superoxide anion-generating system, with IC(50) values in the low micromolar range. Density functional theory calculations showed that introduction of a bipypidyl ligand into the complexes dramatically lowered the lowest unoccupied molecular orbital (LUMO) energy level, which explains the increased SOD-like activity of these complexes compared to non-bipy species. These bipy complexes were also effective scavengers of reactive oxygen species generated by phagocytes (human neutrophils and murine bone marrow leukocytes) ex vivo. Thus, these bipy mixed-ligand complexes represent a promising class of SOD mimetics for future development.

Mixed-ligand complex formation equilibria of CuII with glycylglycinate and guanylurea

Combined spectrophotometric and computer based pH metric investigation on the mixed ligand complex formation equilibria of Cu II with glycylglycine (H 3 N + CH 2 CONHCH 2 COO - , HGG ± ) and guanylurea [H 2 1 NC-(=O) 2 NHC(= 3 NH) 4 NH 2 , HGu] in aqueous solution at 25 ± 1 °C, at a fixed ionic strength, 1 = 0.1 mol dm -3 (NaNO 3 ), indicate variety of binary and ternary complexes: [Cu(GG) + aq], [Cu(GG-H)(H 2 O)], [Cu(GG-H)(OH)-], [Cu(Gu) + aq], [Cu(Gu)(OH)], [Cu(Gu-H)(OH) - ], [Cu(GG-H)(Gu) - ], [Cu(GG-H)(Gu-H) 2- ] and [Cu(GG-H)(Gu-2H) 3 -]. At pH ≤4.5, GG-ion provides neutral (NH 2 , C=O) bidentate chelation to Cu II and above pH 4.5 ~ 5, coordinated GG- is transformed to amide deprotonated glycylglycinate dianion, (GG-H) 2- , which provides terdentate equatorial (NH 2 , N-, COO-) chelation to Cu II . Consequently in the electronic spectra λ max of Cu II is blue shifted. λ max of the ternary complex, [Cu(GG-H)(Gu)-], indicates a square pyramidal geometry existing in a isomeric structural equilibrium, involving bidentate axial (= 3 N) and equatorial (O=C)/(H 2 1 N)/(H 1 N=C) chelation by Gu- ion. Above pH 7, [Cu(GG-H)(Gu) - ] undergoes deprotonation of the (H 1 N=) and HO-(enolic) moieties of coordinated Gu- in successive steps.

Thermodynamics of complex formation of Cu(II) ethylenediaminetetraacetate with ethylenediamine in aqueous solution

The formation of mixed-ligand complexes in the system Cu2+-Edta4−-En was studied by the calorimetric and pH-potentiometric methods at 298.15 K and I = 0.5(KNO3). The thermodynamic characteristic of the CuEdtaEn2− complex formation were determined.

Synthesis, X-ray structure and properties of a calcium(II) coordination polymer showing μ 2-η 1:η 1 and μ 3-η 2:η 1 coordination modes of 4-nitrobenzoate

The reaction of the monomeric compound [Ca(H 2O) 4(η 1-4-nba)(η 2-4-nba)] 1 (4-nba = 4-nitrobenzoate) with N-methylimidazole ( N-MeIm) or imidazole (Im) at 100 oC results in the formation of the anhydrous mixed ligand complexes of composition [Ca(L)(4-nba) 2] (L = N-MeIm 2; L = Im 3). The compounds were characterized by elemental analysis, IR, UV–Vis and 1H NMR spectra, TG-DSC thermograms, weight loss studies and the structure of 2 was determined by single crystal X-ray crystallography. Compounds 2 and 3 can be transformed into 1 by heating with water. At elevated temperatures all compounds ( 1– 3) are thermally decomposed to CaO. Compound 2 crystallizes in the centrosymmetric triclinic space group P 1 ¯ with all atoms located in general positions. The structure reveals that 2 is a polymer and can be formulated as catena-poly[[( N-methylimidazole)calcium(II)](μ 2-η 1:η 1-4-nitrobenzoato)(μ 3-η 2:η 1-4-nitrobenzoato)] . The structure of [[Ca( N-MeIm)](μ 2-η 1:η 1-4-nba)(μ 3-η 2:η 1-4-nba)] n 2 consists of a central Ca(II) ion, a terminal N-MeIm ligand and two crystallographically independent 4-nba ligands. In the crystal structure, each Ca(II) is bonded to a nitrogen atom of N-MeIm and five oxygen atoms from five symmetry related 4-nba ligands resulting in a distorted {CaO 5N} octahedron. One of the unique 4-nitrobenzoate in each formula unit functions as a bridging bidentate ligand (μ 2-η 1:η 1-4-nba) and is linked to two symmetry related Ca(II) ions leading to the formation of an infinite chain extending along a axis with a long Ca⋯Ca separation of 5.531(1) Å. The second independent 4-nba ligand (μ 3-η 2:η 1-4-nba) is coordinated to three different Ca(II) ions with both the carboxylate oxygen atoms linked to the same infinite chain formed earlier and one of the carboxylate oxygen atoms functions as a monoatomic bridge between two symmetry related Ca(II) ions. This bridge links two chains with a shorter Ca⋯Ca separation of 3.8585(7) Å resulting in the formation of a one-dimensional ladder structure. The oxygen atoms of the nitro groups are involved in C–H⋯O interactions. A comparative study of 30 Ca(II) coordination polymers is described.

Copper(I) halide complexes with 2,2′-bis(diphenylphosphano)-1,1′-binaphthyl (rac-binap) and heterocyclic thiones. Racemic compounds in chiral and achiral crystal space groups

Reactions of copper(I) halides with racemic 2,2′-bis(diphenylphosphano)-1,1′-binaphthyl (rac-binap) in 1:1 molar ratio afforded mononuclear complexes of the type [CuX(rac-binap)] (X = Cl, Br, I) which, on further treatment with 1 equiv. of pyridine-2-thione (py2SH), pyrimidine-2-thione (pymtH) or 4,6-dimethyl-pyrimidine-2-thione (dmpymtH) gave rise to the formation of mixed-ligand complexes of the formula [CuX(rac-binap)(thione)]. The molecular structures of [CuBr(rac-binap)(py2SH)] · 2CH 2Cl 2, [CuBr(rac-binap)(py2SH)] · CH 2Cl 2 and [CuBr(rac-binap)(dmpymtH)] · CH 2Cl 2 have been established by single-crystal X-ray diffraction. Each of the complexes features a distorted tetrahedral copper(I) center with the phosphane acting in a chelating fashion. The complexes are strongly luminescent in the solid state at ambient temperature. Unusually, the [CuBr(rac-binap)(py2SH)] · 2CH 2Cl 2 molecules crystallise in a chiral space group with independent S- and R-enantiomers in the asymmetric unit.

Thermochemical study of mixed-ligand complex formation in the system M2+-Nta3−-En (M = Ni, Cu, Zn, or Cd) in aqueous solution

Direct calorimetric data were used to calculate the heats of formation for mixed-ligand complexes MNtaEn−, where Nta3− is nitrilotriacetato ion, En is ethylenediamine, and M2+ = Ni2+, Zn2+, Cu2+, or Cd2+, in aqueous solution at 298.15 K and ionic strength I = 0.5 (NaNO3). The complete set of thermodynamic parameters of reaction was calculated for mixed-ligand complex formation and comproportionation.

Mixed-ligand complex formation in the copper(I)-2,9-dimethyl-1,10-phenanthroline-3,3′-bonded biquinoline system according to 1H NMR data

The reaction of the copper(I) 2,9-dimethyl-1,10-phenanthroline (neocuproine, DMP) complex with 2,3,8,9-dibenzo-4,7-dimethyl-5,6-dihydro-1,10-phenanthroline (cuprotest, DMQ) in a CD3OD solution has been studied by 1H NMR spectroscopy. The substitution of DMQ for the DMP liqand in the inner coordination sphere of the Cu+ complex has been observed. A model of the process including the formation of a mixed-ligand complex, presumably of bridged structure, is proposed to describe the observed experimental dependences of integrated intensities of the NMR signals in the spectrum on the concentrations of the components of the solution.

Isolation and single crystal study of [Nb2(μ-OMe)2(OiPr)8]. Can alcohol interchange provide the homoleptic niobium isopropoxide?

Niobium isopropoxide, Nb(OiPr)5, is an attractive precursor of simple and complex niobium oxides in sol-gel technology. This compound cannot, unfortunately, be obtained by alcohol interchange starting from linear chain homologues such as Nb(OMe)5 or Nb(OEt)5. The equilibrium in the latter reaction favours formation of mixed-ligand complexes, [Nb2(OR)2(OiPr)8], R = Me, Et. In particular, [Nb2(OMe)2(OPri)8] (1) has been isolated in high yield from repeated treatment of Nb2(OMe)10 with excess of isopropanol. The X-ray single crystal study reveals a dinuclear structure containing a pair of edge-sharing octahedra with methoxide ligands in the bridging position. Infrared (IR) and mass spectroscopy (MS) studies confirmed the incomplete ligand substitution. The 1H-NMR spectra suggest equilibrium between different molecular forms in solution. Solvothermal interaction of 1 with La chips in toluene/isopropanol media results in formation of a mixture of LaNb2(OiPr)13 and La2Nb4(μ4−O)4(OH)2(μ−OiPr)8(OiPr)8 (2).

Be2(OH)2CO3 solubility in carbonate and fluoride aqueous solutions

Beryllium is known to precipitate in the form of basic carbonates from neutral and alkaline solutions [1]; the solubility of beryllium basic carbonates is mainly due to the formation of strong hydroxide, carbonate, and mixed-ligand hydroxocarbonate complexes [2‐7]. The thermodynamic properties (solubility products) of basic carbonates and the stability constants of beryllium hydroxocarbonate complexes have not yet been determined with sufficient accuracy. The possible occurrence of strongly bonded fluorocarbonate complexes (they are also poorly studied) adds even more uncertainty to the calculations of beryllium speciation [7]. As a result, the estimation of the environmental mobility of beryllium becomes considerably less reliable, and it is more difficult to develop efficient green technologies. To partially fill in the existing gap, here we report the experimental investigation of CÂ 2 (ec) 2 ee 3 solubilities in carbonate solutions. In the experiments, we used basic beryllium carbonate CÂ 2 (ec) 2 ee 3 , which was precipitated from a boiling 0.05 M BeSO 4 solution with a twofold excess of a heated-to-boil 0.5 M Na 2 CO 3 solution. CÂ 2 (ec) 2 ee 3 solubilities were studied in 0.7 M NaClO 4 solutions that contained variable amounts of Na c CO 3 and Na 2 CO 3 with their overall concentration being less than or equal to 0.05 mol/L. In one set of runs, the solutions in addition contained NaF. The weight ratio of the solid phase to solution in all runs was 1 : 200. The run duration was 2 weeks, which was about twice as long as the period required for the solute beryllium concentration and pH to acquire constant values. The solution temperatures were within 25 ± 1°e . At the end of a run, the sample was filtered through presteamed, fine Blue Ribbon paper filters. The filtrates were colorimetrically analyzed for beryllium using Beryllon II indicator and for carbonate alkalinity using an acidometric method; the filtrate pH was determined potentiometrically. The measurement error was ± 5%, ± 2% , and ± 0.005 pH, respectively. The results of the experiments are displayed in the table. Because the concentration of free Be 2+ ions is ignorable at pH > 8 [2, 6], the CÂ 2 (ec) 2 ee 3 solubility is determined by the concentration of hydroxide, carbonate, and hydroxocarbonate complexes. In view of this, the reaction of CÂ 2 (ec) 2 ee 3 dissolution can in general be written as

Mixed ligand complexes of Cu(II)-2-(2-pyridyl)-benzimidazole and aliphatic or aromatic dicarboxylic acids: Synthesis, characterization and biological activity

The synthesis and structural characterization of mixed ligand complexes derived from 2-(2-pyridyl)-benzimidazole (PBI) (1ry ligand) and aliphatic or aromatic dicarboxylic acids (2ry ligand) are reported. Cu(II) complexes were characterized on the bases of their elemental analyses, IR, ESR and thermal analyses. The elemental analysis indicated the formation of mixed ligand complexes in a mole ratio 1:1:1 (Cu:L 1:L 2), L 1 = PBI and L 2 = oxalic acid, phthalic acid or malonic acid. IR spectra showed that PBI acts as a neutral bidentate coordinated to the Cu(II) via the pyridyl and imidazolyl nitrogen atoms. The dicarboxylic acids are bidentate with monodentate carboxylate groups. Thermal decomposition study of complexes was monitored by thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis in N 2 atmosphere. The decomposition course and steps were analysed and the activation parameters of the nonisothermal decomposition were calculated from the TG curves and discussed. The isolated metal chelates were screened for their antimicrobial activities and the results are reported, discussed and compared with some known antibiotics.

Mixed-ligand complex formation in the copper(I)-2,9-dimethyl-1,10-phenanthroline-3,3′-bridged biquinoline system as probed by 1H NMR

The interaction of the copper(I) complex of 2,9-dimethyl-1,10-phenanthroline (neocuproine, DMP) with 2,3,8,9-dibenzo-4,7-dimethyl-5,6-dihydro-1,10-phenanthroline (cuprotest, DMQ) in a CD3OD solution has been studied by 1H NMR. DMQ is substituted for the DMP ligand in the inner coordination sphere of the Cu+ complex. To describe the experimental integrated intensities of NMR signals as a function of concentrations of the components, a model of the process is proposed implying the formation of a heteroleptic complex, which, presumably, has a bridging structure.

Mixed-ligand complex formation equilibria of CuII with biguanide in presence of glycine as the auxiliary ligand

Equilibrium study on the mixed ligand complex formation of CuII with biguanide(Bg) and glycine (HG), indicated the formation of the complexes: Cu(Bg)2+, Cu(Bg) 2+2 , Cu(Bg-H)(Bg)+, Cu(Bg-H)2, Cu(Bg)(OH)+, Cu(Bg-H)(OH); Cu(G)+, Cu(G)(OH), Cu(G)2; Cu(G)(Bg)+, Cu(G)(Bg-H); (G)Cu(Bg)Cu(G)2+, (G)Cu(Bg-H)Cu(G)+, and (G)Cu(Bg-2H)Cu(G). From the deprotonation constants of coordinated biguanide (Bg) in the complexes Cu(Bg)(OH)+, Cu(Bg-H)(Bg)+ and Cu(G)(Bg)+, the Lewis basicities of the coordinated ligand species (Bg-H)-, OH- and glycinate (G-) were found to be of the order: (Bg-H)-≫ OH- > G-. Bridging (N1-N4, N2-N5) tetradentate mode of coordination by biguanide species Bg, (Bg-H)- and (Bg2H)2- was indicated from the occurrence of biguanide-bridged dinuclear mixed ligand complexes (G)Cu(Bg)Cu(G)2+, (G)Cu(Bg-H)Cu(G)+, (G)Cu(Bg-2H)Cu(G) in the complexation equilibria.

Thermodynamics of mixed-ligand complex formation of samarium(III) and cerium(III) ethylenediaminetetraacetates with various ligands in aqueous solution

The thermodynamic parameters of reaction (logK, Δr G 0, Δr H, Δr S) are determined for the mixed-ligand complex formation of SmEdta− and CeEdta− with glycinate, iminodiacetate, aspartate, and nitrilotriacetate ions in aqueous solution at 298.15 K and ionic strength of I = 0.5 (KNO3). Based on these thermodynamic data, the most likely coordination modes are suggested for the complexone and the ancillary ligand in the mixed-ligand complexes.

Reaction of zirconium(IV) with 2,3,4-trihydroxiphenylazo-5′-sulfonaphthalene in the presence of diantipyrilmethane and its homologues

The effect of diantipyrilmethane and its homologues on the complexation of zirconium(IV) with 2,3,4-trihydroxiphenylazo-5′-sulfonaphthalene is studied, and conditions for the formation of mixed-ligand complexes are determined. Correlations between the acidity constants of diantipyrilmethane and its homologues and the stability constants and the specific conductivity of complexes, and degree of contrast, and the change in the Gibbs free energy are found for the complexation reaction. A method is developed for the selective photometric determination of zirconium in pyrite containing modified quartz diorite.

Coordination properties of tridentate ( N, O, O) heterocyclic alcohol (PDC) with Cu(II) : Mixed ligand complex formation reactions of Cu(II) with PDC and some bio-relevant ligands

The formation equilibria of copper(II) complexes and the ternary complexes Cu(PDC)L (PDC = 2,6-bis-(hydroxymethyl)-pyridine, HL = amino acid, amides or DNA constituents) have been investigated. Ternary complexes are formed by a simultaneous mechanism. The results showed the formation of Cu(PDC)L, Cu(PDC, H −1)(L) and Cu(PDC, H −2)(L) complexes. The concentration distribution of the complexes in solution is evaluated as a function of pH. The effect of dioxane as a solvent on the protonation constant of PDC and the formation constants of Cu(II) complexes are discussed. The thermodynamic parameters Δ H ° and Δ S ° calculated from the temperature dependence of the equilibrium constants are investigated.

Synthesis, spectroscopic characterization and structural studies of mixed ligand complexes of Sr(II) and Ba(II) with 2-hydroxybenzophenone and salicylaldehyde, hydroxyaromatic ketones or β-diketones: Crystal structure of 2-HOC 6H 4C(O)C 6H 5

Reactions of Sr(II) and Ba(II) chlorides with 2-hydroxybenzophenone and salicylaldehyde, hydroxyaromatic ketones or β-diketones in 1:1:1 molar ratios have resulted in the formation of mixed ligand complexes of the type [MLL′(H 2O) 2] (M = Sr(II) or Ba(II); HL = 2-hydroxybenzophenone and HL′ = salicylaldehyde, 2-hydroxyacetophenone, 2-hydroxypropiophenone, pentane-2,4-dione, 1-phenylbutane-1,3-dione or 1,3-diphenylpropane-1,3-dione). These complexes have been characterized by elemental analyses, TLC, IR and 1H NMR spectroscopy.

Solution equilibria of some quaternary metal complexes involving iminodiacetic acid and L-pyrrolidine-2-carboxylic acid

Equilibrium based computer studies on quaternary complex systems, viz. Mn II /Co II /Pb II iminodiacetic acid (IMDA = A 2- ) and L-pyrrolidine-2-carboxylic acid (proline = B - ) systems demonstrate the formation of mixed-metal mixed-ligand complexes of stoichiometry M I M 2 AB and M I M 2 A 2 B in addition to MAB, M 2 A 2 B, MA and MB complexes for all metal ions. Formation constants of the complexes at 35 ± 1 °C and at fixed ionic strength, I = = 0.1 mol dm -3 (NaNO 3 ) were evaluated using SCOGS computer program and the complex formation equilibria were elucidated with the aid of speciation curves. Stability order of metal complexes and solution structure of hetrobinuclear M 1 M 2 AB complexes have been discussed.

Absorption spectra and the nature of complexes in the polyvinyl Alcohol-Nickel (II) chloride system

We have used electronic spectroscopy in the 160–1100 nm range to study the polyvinyl alcohol-nickel(II) chloride system. Based on the results obtained, we hypothesize formation of mixed-ligand complexes of the type [Ni(H2O)6-nCln]2-n (n = 0, 1,..., 5) in the polyvinyl alcohol matrix. Transformation of the coordination sphere as the NiCl2 concentration changes is apparent both in the region of the d-d transition bands (350–1100 nm) and in the region of the charge transfer bands (160–250 nm). We propose assigning the absorption bands separated by mathematical treatment to complexes of specific compositions.