Thermodynamic and NMR studies of mixed-ligand complex formation of cadmium ethylenediaminetetraacetate with diamines in an aqueous solution

The mixed-ligand complex formation in the systems Cd2 + Edta4–(CH₂) _n (NH₂)₂, n = 2 (En), 6 (L) has been NMR and calorimetrically studied in aqueous solution at 298.15 K and the ionic strength of I = 0.5 (KNO₃). The thermodynamic parameters of formation of the CdEdtaL²⁻, CdEdtaHL⁻, (CdEdta)₂L⁴⁻, and (CdEdta)₂En⁴⁻ complexes have been determined. The most probable coordination mode for the complexone and the diamine ligand in the mixed-ligand complexes was discussed.     

Thermodynamics of mixed-ligand complex formation of copper(II) ethylenediaminetetraacetate with amino acids in solution

The mixed-ligand complex formation in the systems Cu²⁺–Edta^4?–L (L = His, Lys, Orn, Arg, Im) 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 CuEdtaL, CuEdtaHL, and (CuEdta)₂L complexes have been determined. The probable coordination mode for the complexone and the ancillary ligand in the mixed-ligand complexes was discussed.     

Thermodynamics of mixed-ligand complexation of mercury(II) ethylenediaminetetraacetate with histidine and lysine in aqueous solution

The formation of mixed-ligand complexes HgEdtaIm²⁻, HgEdtaL³⁻, HgEdtaHL²⁻, and (HgEdta)₂L⁵⁻ (L is histidine, lysine; Im is imidazole) was studied by calorimetry, pH-metry, and NMR spectroscopy. The thermodynamic parameters (logK, ΔrG ⁰, ΔrH, Δr _S) for the reactions of complex formation at 298.15 K and ion strength of 0.5 (KNO₃) were determined. The most likely coordination mode for the complexone and amino acid in the mixed complexes was identified.     

Copper complexes of 1-[(2-carboxyethyl)benzene]-3-[2-pyridine]triazene

The triazenide, 1-[(2-carboxyethyl)benzene]-3-[2-pyridine]triazene (HL), has been synthesized. In the presence of Et₃N, the reaction of HL with Cu(OAc)₂·H₂O or CuCl₂·2H₂O gives the tetranuclear copper(II) complexes {Cu₄(L)₂(μ₂-OH)₂(OAc)₄} 1 and {Cu₄L₄(μ₄-O)Cl₂} 2, respectively. The X-ray crystal structures of both complexes have been obtained. Magnetic studies indicate significant antiferromagnetic coupling between the copper(II) centers for both complexes, with coupling constants (J) of −493.4 cm⁻¹ for 1 and −165 cm⁻¹ for 2.     

Synthesis,characterization, structure and magnetic properties of azido-bridged nickel(II) and copper(II) complexes with a pyridylpyrazole-based ligand

A new pyridylpyrazole-containing tetradentate ligand, namely N,N-bis(3,5-dimethylpyrazol-1-ylmethyl)aminomethylpyridine (L), and two of its binuclear azido-bridged complexes, [Ni₂(L)₂(N₃)₂](ClO₄)₂·2EtOH (1) and [Cu₂(L)₂(N₃)₂](ClO₄)₂ (2), have been synthesized and characterized by physico-chemical and spectroscopic methods. The crystal structures of both complexes are reported. Each metal atom in the complexes has a MN₆ coordination environment with distorted octahedral geometry. Variable-temperature magnetic susceptibility measurements for complex (1) show typical antiferromagnetic behavior with J value −84.5 ± 1.3 cm⁻¹, whereas complex (2) has no magnetic interactions.     

Synthesis and characterization of stable thiazolylazo anion radical complexes of ruthenium(II)

Two stable thiazolylazo anion radical complexes of ruthenium(II), [Ru(L1^•−)(Cl)(CO)(PPh₃)₂] (1) and [Ru(L2^•−)(Cl)(CO)(PPh₃)₂] (2) (where L1 = 2′-Thiazolylazo-2-imidazole and L2 = 4-(2′-Thiazolylazo)-1-n-hexadecyloxy-naphthalene), have been synthesized and characterized by spectroscopic and electrochemical techniques. The radical nature of the complexes has been confirmed from their room temperature magnetic moments and X-band ESR spectra. The radical complexes display a moderately intense (ε ~ 10⁴ M⁻¹ cm⁻¹) and relatively broad band in 430–460 nm region. In the microcrystalline state, complexes (1) and (2) display strong ESR signals at g = 1.951 and g = 1.988, respectively. In CH₂Cl₂ solution, complexes (1) and (2) show a quasireversible one-electron response near −0.64 and −0.59 V, respectively, versus Ag/AgCl due to the radical redox couple [Ru^II(L)(Cl)(CO)(PPh₃)₂]/[Ru^II (L^•−)(Cl)(CO)(PPh₃)₂].     

The thermodynamic functions of formation and transfer of copper(II) and nickel(II) ethylenediaminetetraacetate complexes with ammonia in aqueous-ethanolic solutions

The formation of mixed-ligand NiEdtaNH₃²⁻ and CuEdtaNH₃²⁻ complexes in an aqueous-ethanolic solvent with the mole fractions of ethanol 0.1 and 0.2 at 298.15 K and ionic strength I = 0.4 (KNO₃) was studied calorimetrically. The thermodynamic characteristics of formation and transfer parameters of these complexes were calculated. The influence of the mixed solvent on the thermodynamic characteristics of these reactions was studied.     

Two manganese(II) complexes based on anthracene-9-carboxylate: Syntheses,crystal structures,and magnetic properties

Abstract  To explore the influence of the anthracene ring skeleton, with a large conjugated π-system, on the structures and properties of its complexes, two Mn^II complexes with anthracene-9-carboxylate ligand were synthesized and structurally characterized: {[Mn(L)₂(H₂O)₂](H₂O)}_∞ (1) and [Mn₂(L)₄(phen)₂(μ-H₂O)](CH₃OH) (2) (L = anthracene-9-carboxylate and phen = 1,10-phenanthroline). Complex (1) has a one-dimensional (1D) chain structure that is further assembled to form a two-dimensional (2D) sheet, and then an overall three-dimensional (3D) network by π···π stacking and/or C–H···π interactions. Complex (2) makes a dinuclear structure by incorporating the chelating phen ligand, which is further interlinked via inter-molecular π···π stacking and C–H···π interactions to generate a higher-dimensional supramolecular network along the different crystallographic directions. The results reveal that the bulky anthracene ring skeleton in L, by virtue of intra- and/or inter-molecular π···π stacking and C–H···π interactions, plays an important role in the formation of complexes (1) and (2). The magnetic properties of (1) and (2) were further investigated. As expected, the very long inter-metallic separations result in weak magnetic coupling, with the corresponding coupling constant values of J = −10 cm⁻¹ for (1) and J = −2.46 cm⁻¹ for (2). Graphical abstract  The constructions of two new Mn^II complexes comprising 1D chain (1) and dinuclear subunit (2) structures have been successfully achieved by using a bulky anthracene-9-carboxylic acid (HL), together with incorporating the chelating 1,10-phenanthroline as a co-ligand for (2). The result reveals that the bulky anthracene ring skeleton of HL, by virtue of intra- and/or inter-molecular π···π stacking and C–H···π interactions, plays an important role in the formation of the supramolecular architectures of (1) and (2). Moreover, magnetic properties of the complexes have been investigated.      

Mixed-ligand complexes of tris(acetylacetonato)iridium(III) with <Emphasis Type="Italic">N</Emphasis>-heterocyclic ligands: synthesis and crystal structure

A series of mixed-ligand complexes of tris(acetylacetonato) iridium(III) with N-heterocyclic ligands, namely [bis(acac-O,O′)(acac-C³)Ir(L)], where acac = acetyacetonato; L = 2-picoline (1), 3-picoline (2), 4-picoline (3), have been synthesized via the reaction of [bis(acac-O,O′) (acac-C³)Ir(H₂O)] with the corresponding ligand, respectively. Molecular structures of all complexes were determined by using single-crystal X-ray diffraction. The results reveal that these complexes have slightly distorted octahedral coordination geometries.     

Synthesis and magnetic properties of μ-phenolato oxovanadium(IV), cobalt(II) and zinc(II) binuclear complexes

Three binuclear complexes, (VO)₂(L)OMe (1), Co₂(L)OEt·3/2H₂O (2) and Zn₂(L)OMe·H₂O (3) have been prepared, where H₃L is the binucleating ligand, 2,6-diformyl-4-methylphenol di(benzoylhydrazone). The magnetic susceptibilities of (1) and (2) were measured over the 4.2–300 K range and the observed data were fitted to the Bleaney-Bowers equation by the least-squares method, giving the exchange integral 2J = −358.5cm⁻¹ for (1) and 2J = −6.6cm⁻¹ for (2). This procedure indicates the existence of an antiferromagnetic interaction between the metals. TMC 2699     

Equilibrium study on the reactions of boric acid with some cis -diaqua CrIII-complexes

Substitution inertcis-diaqua Cr^III complexes: cis-[(L^x−)Cr^III(H₂O)₂]^(3−x)+ derived from N-donor ligands (L^x−) viz., bipyridine and 1,10-phenanthroline (x = 0) and N,O-donor ligands viz., nitrilotriacetate and anthranilate N,N-diacetate (x = 3) titrate as diprotic acids in aqueous solution and enhance the acidity of otherwise weakly acidic boric acid (H₃BO₃) producing mononuclear and binuclear mixed ligand Cr^III-borate complexes: [(L)Cr(H₂BO₄)]^x− and [(L)Cr(BO₄)Cr(L)]^(1−2x)+ respectively through coordination of the H₂O and/or OH⁻ ligands, cis-coordinated in the Cr^III-complexes on the electron deficient B^III-atom in H₃BO₃ with release of protons. Deprotonation of the parent Cr^III-complexes and their reactions with H₃BO₃ have been investigated by potentiometric method in aqueous solution,I = 0.1 mol dm⁻³ (NaNO₃) at 25 ±0.1°C. The equilibrium constants have been evaluated by computerized methods and the tentative stoichiometry of the reactions have been worked out on the basis of the speciation curves     

Thermodynamic Model for ThO<Subscript>2</Subscript>(am) Solubility in Alkaline Silica Solutions

No thermodynamic data for Th complexes with aqueous Si are available. To obtain such data, extensive studies on ThO₂(am) solubility were carried out as functions of: (1) a wide range of aqueous silica concentrations (0.0004 to 0.14 mol⋅L⁻¹) at fixed pH values of about 10, 11, 12, and 13; and (2) and variable pH (ranging from 10 to 13.3) at fixed aqueous Si concentrations of about 0.006 mol⋅L⁻¹ or 0.018 mol⋅L⁻¹. The samples were equilibrated over long periods (ranging up to 487 days), and the data showed that steady-state concentrations were reached in < 29 days. X-ray diffraction, FTIR, and Raman analyses of the equilibrated solid phases showed that the Th solids were amorphous ThO₂(am) containing some adsorbed Si. The solubility of ThO₂(am) at pH values ranging from 10 to 13.3 at fixed 0.018 mol⋅L⁻¹ aqueous Si concentrations decreases rapidly with an increase in pH, and increases dramatically with an increase in Si concentrations beyond about 0.003 mol⋅L⁻¹ at fixed pH values > 10. The data were interpreted using both the Pitzer and SIT models, and required only the inclusion of one mixed-hydroxy-silica complex of Th [Th(OH)₃(H₃SiO₄)₃²⁻]. Both models provided similar complexation constant values for the formation of this species. Density functional theory calculations predict complexes of this stoichiometry, having six-fold coordination of the Th cation, to be structurally stable. Predictions based on the fitted value of log ₁₀ K ⁰=−18.5±0.7 for the ThO₂(am) solubility reaction involving Th(OH)₃(H₃SiO₄)₃²⁻[ThO₂(am)+3H₄SiO₄+H₂O↔Th(OH)₃(H₃SiO₄)₃²⁻+2H⁺], along with the thermodynamic data for aqueous Si species reported in the literature, agreed closely with the extensive experimental data and showed that under alkaline conditions aqueous Si makes very strong complexes with Th.     

DNA-binding and nuclease activity of 1,10-phenanthroline-based thiocyanato,acetato, azido and benzoato bridged dinuclear copper(II) complexes

The mononuclear Cu(II) complex [Cu(phen)(H₂O)(NO₃)₂] (1), obtained by the reaction of 1,10-phenanthroline with Cu(NO₃)₂·3H₂O in methanol solution, reacts with anionic ligands SCN⁻, AcO⁻, N₃ ⁻ and PhCO₂ ⁻ in MeOH solution to form the stable binuclear complexes [Cu₂(H₂O)₂(phen)₂(μ-X)₂]₂ (NO₃)₂, where X = SCN⁻ (2), AcO⁻ (3), N₃ ⁻ (4) or PhCO₂ ⁻(5). The molecular structure of complex 3 was determined by single-crystal X-ray diffraction studies. These complexes were characterized by electronic, IR, ESR, magnetic moments and conductivity measurements. The electrochemical behaviour of the complexes was investigated by cyclic voltammetry. The interactions of these complexes with calf thymus DNA have been investigated using absorption spectrophotometry. Their DNA cleavage activity was studied on double-stranded pBR322 plasmid DNA using gel electrophoresis experiments in the absence and presence of H₂O₂ as oxidant.     

Carboxy Ester Hydrolysis Promoted by Two New Bimetallic Macrocyclic Complexes. Synthesis, Characterization and Catalytic Activity

A dinuclear macrocyclic ligand containing [12]aneN₃ and its two transition metal complexes, [Zn₂L(OAc)₂](ClO₄)₂ (1) and [Cu₂L(OAc)₂](ClO₄)₂ (2) have been synthesized and characterized on the basis of elemental analyses, molar conductivities, ¹H-n.m.r, IR spectra, electronic spectra and thermal analysis. In addition, the studies on the hydrolysis of a caboxy ester, 4-nitrophenyl acetate (NA), promoted by the two complexes were also investigated. The experimental results indicated that the two complexes can efficiently catalyze hydrolysis of NA, and the k_NA for complexes (1) and (2) at pH 7.25, 25 °C, were calculated to be 4.46 × 10⁻² and 4.21 × 10⁻² m⁻¹ s⁻¹, respectively, which are better than those of the corresponding mononuclear complex in the same conditions.     

A relativistic DFT study of magnetic exchange coupling in ketimide bimetallic uranium(IV) complexes

Magnetic exchange couplings in bis(ketimide) binuclear U^IV/U^IV complexes [Cp′₂UCl]₂(μ-ketimide) diuranium(IV) and [(C₅H₅)₂(Cl)An]₂(μ-ketimide) (Cp′ = C₅Me₄Et; ketimide = N=CMe-(C₆H₄)-MeC=N) have been investigated computationally using relativistic density functional theory (DFT) combined with the broken symmetry (BS) approach. Using the B3LYP hybrid functional, the BS ground state of these U^IV/U^IV 5f ²–5f ² complexes has been found of lower energy than the high spin (HS) quintet state, indicating an antiferromagnetic character (estimated coupling constant |J| < 5 cm⁻¹) which has not yet been evidenced unambiguously experimentally. On the contrary, the BP86 GGA functional overestimates greatly the antiferromagnetic character of the complexes (|J| > 100 cm⁻¹). As recently reported for para-bis(imido) [(C₅H₅)₃U]₂(μ-imido) uranium(V) complex, spin polarization is mainly responsible for the antiferromagnetic coupling through the π-network orbital pathway within the bis(ketimide) bridge. Furthermore, spin polarization is exalted by the combined roles of the 5f metal orbitals and of the π-conjugated ketimide bridging ligand which permit electronic communication between the two uranium atoms albeit separated by a distance of the order of 10 ?. The MO analysis clarifies which MOs contribute to the antiferromagnetic coupling in the binuclear complexes under consideration and brings to light the 5f orbitals driving contribution.     

Synthesis,characterization, volatilization,alcoholysis and hydrolytic studies of nonaalkoxodititanatocopper(II) complexes

Heterobimetallic alkoxides of Cu(II) of the types [Cu{η⁴-Ti₂(OEt)₉}Cl] (1) and [Cu{η³-Ti₂(OR)₉}₂] [R = Prⁱ (2), R = Et(3)] have been prepared for the first time by the reactions of CuCl₂ · xROH with KTi₂(OR)₉ in 1:1 and 1:2 molar ratios, respectively, in benzene medium. The chloro(nonaalkoxo dititanato)copper(II) complexes undergo chloride replacement reactions by a variety of monodentate alkoxo (⁻OPrⁱ, ⁻OEt) and chelating [Al(OPrⁱ) ₄ ⁻ , Al(OEt) ₄ ⁻ , Nb(OPrⁱ) ₆ ⁻ , Zr₂(OPrⁱ) ₉ ⁻ , Sn₂(OPrⁱ) ₉ ⁻ , and Sn₂(OEt) ₉ ⁻ ] ligands to form interesting hetero(bi-and tri-)metallic complexes. Alcoholysis (with methyl alcohol and tert-butyl alcohol) and hydrolytic [with Ba(OH)₂ · 8H₂O powder] reactions of a few typical compounds have also been investigated. All of these have been characterized by elemental analyses, molecular weight determinations, spectral (i.r. and visible) and magnetic studies. On attempted volatilization under reduced pressure these complexes liberated titanium alkoxides as a volatile component leaving nonvolatile residues.     

The study of the speciation of uranyl–sulphate complexes by UV–Vis absorption spectra decomposition

Uranyl–sulphate complexes are the predominant U(VI) species present in acid solutions resulting either from underground uranium ore leaching or from the remediation of leaching sites. Thus, the study of U(VI) speciation in these solutions is of practical significance. The spectra of UO₂(NO₃)₂ + Na₂SO₄ solutions of different Φ _S = [SO₄²⁻]/[U(VI)] ratio at pH = 2 were recorded for this purpose. As the presence of uranyl-nitrate complexes should be expected under these experimental conditions, the spectra of UO₂(NO₃)₂ + NaNO₃ solutions with different Φ _N = [NO₃⁻]/[U(VI)] ratio at pH = 2 were also measured. The effects of Φ _S and Φ _N ratios value were most pronounced in wavelength interval 380–500 nm. Therefore, these parts of experimental overall spectra were used for deconvolution into the spectra of individual species by the method proposed. It enabled to calculate stability constants of anticipated species at zero ionic strength. The Specific Ion Interaction Theory (SIT) was used for this purpose. Stability constants of UO₂SO₄, UO₂(SO₄)₂²⁻, UO₂NO₃ ⁺ and UO₂(NO₃)₂ coincided well with published data, but those for UO₂(SO₄)₃⁴⁻ and UO₂(NO₃)₃⁻ were significantly lower.     

Binuclear iron(III) complexes bridged by terephthalato groups

Six new μ-terephthalato iron(III) binuclear complexes have been prepared and identified: [Fe₂(TPHA)(L)₄]-(ClO₄)₄ [L = 2,2′-bipyridine (bpy); 1,10-phenanthroline (phen); 4,4′-dimethyl-2,2′-bipyridine (Me₂bpy); 5-methyl-1,10-phenanthroline (Me-phen); 5-chloro-1,10-phenanthroline (Cl-phen) and 5-nitro-1,10-phenanthroline (NO₂-phen)]; where TPHA = the terephthalate dianion. Based on the elemental analyses, molar conductance and magnetic moments of room-temperature measurements, and spectroscopic studies, extended TPHA-bridged structures consisting of two iron(III) ions, each in an octahedral environment, are proposed for these complexes. The [Fe₂(TPHA)(Me-phen)₄](ClO₄)₄ (1) and [Fe₂(TPHA)(phen)₄](ClO₄)₄ (2) complexes were characterized by variable temperature magnetic susceptibility (4–300 K) measurements and the observed data were successfully simulated by the equation based on the spin Hamiltonian operator, Ĥ = −2JŜ ₁ Ŝ ₂, giving the exchange integrals J = −1.05 cm⁻¹ for (1) and J = −9.28 cm⁻¹ for (2). This result indicates the presence of a weak antiferromagnetic spin-exchange interaction between the metal ions within each molecule. The influence of the terminal ligand methyl substituents on magnetic interactions between the metals is also discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Synthesis, characterisation and chemical reactivity of some new dioxouranium(VI) complexes of 2-aminobenzoylhydrazone of butane-2,3-dione

A new series of dioxouranium(VI) complexes of a potential ONNO tetradentate donor 2-aminobenzoylhydrazone of butane-2,3-dione (L₁H₂) have been synthesized. At pH 2·5–4·0, the donor (L₁H₂) reacts in the keto form and complexes of the type [UO₂(L₁H₂)(X)₂] (X⁻=Cl⁻, Br⁻, NO ₃ ⁻ , NCS⁻, ClO ₄ ⁻ , CH₃COO⁻, 1/2SO ₄ ²⁻ ) are obtained. At higher pH (6·5–7), the complex of the enol form having the formula [UO₂(L₁)(H₂O)] has been isolated. On reaction with a monodentate lewis base (B), both types of complexes yield adducts of the type [UO₂(L₁)(B)]. All these complexes have been characterised adequately by elemental analyses and other standard physicochemical techniques. Location of the bonding sites of the donor molecule around the uranyl ion, status of the uranium-oxygen bond and the probable structure of the complexes have also been discussed.     

Kinetic studies on H+-catalysed aquation of some chromium(III)-oxalato-amino acid complexes

The following chromium(III) complexes with serine (Ser) and aspartic acid (Asp) were obtained and characterized in solution: [Cr(ox)₂(Aa)]²⁻ (where Aa = Ser or Asp), [Cr(AspH₋₁)₂]⁻ and [Cr(ox)(Ser)₂]⁻. In acidic solutions, [Cr(ox)₂(Aa)]²⁻ undergoes acid-catalysed aquation to cis-[Cr(ox)₂(H₂O)₂]⁻ and the appropriate amino acid. [Cr(ox)(Ser)₂]⁻ undergoes consecutive acid-catalysed Ser liberation to give [Cr(ox)(H₂O)₄]⁺, and the [Cr(Asp)₂]⁻ ion is converted into [Cr(Asp)(H₂O)₄]²⁺. Kinetics of these reactions were studied under isolation conditions. The determined rate expressions for all the reactions are of the form: k _obs = a + b[H⁺]. Reaction mechanisms are proposed, and the meaning of the determined parameters has been established. Evidence for the formation of an intermediate with O-monodentate amino acid is given. The effect of the R-substituent at the α-carbon atom of the amino acid on the complex reactivity is discussed.