Formation and Stability of Cadmium(II)/Phytate Complexes by Different Electrochemical Techniques. Critical Analysis of Results

In the present work the stability constants of various cadmium(II)/phytate (Phy) species were determined at T=298.15 K in NaNO₃(aq) at I=0.1 mol⋅L⁻¹ by DP-ASV (Differential Pulse Anodic Stripping Voltammetry) and by potentiometric titrations using an ISE-Cd²⁺. Cyclic voltammograms were also recorded to check the electrochemical behavior of cadmium in the presence of phytate. The results were analyzed together with previous data determined by ISE-H⁺ measurements. Data obtained were used to provide an exhaustive speciation scheme for the phytate/cadmium(II) system at different conditions, as well as a comprehensive representation of the binding ability of phytate toward cadmium(II). Different pL₅₀ values {a previously proposed empirical parameter, expressed as −log ₁₀ C _Phy, where C _Phy is the total phytate concentration necessary to bind 50% cadmium(II)} were also calculated by modeling its dependence on pH.     

Speciation of phytate ion in aqueous solution. Alkali metal complex formation in different ionic media

The acid–base properties of phytic acid [myo-inositol 1,2,3,4,5,6-hexakis(dihydrogen phosphate)] (H₁₂Phy; Phy^12–=phytate anion) were studied in aqueous solution by potentiometric measurements ([H⁺]-glass electrode) in lithium and potassium chloride aqueous media at different ionic strengths (0<I mol L^–13) and at t=25 °C. The protonation of phytate proved strongly dependent on both ionic medium and ionic strength. The protonation constants obtained in alkali metal chlorides are considerably lower than the corresponding ones obtained in a previous paper in tetraethylammonium iodide (Et₄NI; e.g., at I=0.5 mol L^–1, logK₃^H=11.7, 8.0, 9.1, and 9.1 in Et₄NI, LiCl, NaCl and KCl, respectively; the protonation constants in Et₄NI and NaCl were already reported), owing to the strong interactions occurring between the phytate and alkaline cations present in the background salt. We explained this in terms of complex formation between phytate and alkali metal ions. Experimental evidence allows us to consider the formation of 13 mixed proton–metal–ligand complexes, M_jH_iPhy^{(12–i–j)–}, (M⁺=Li⁺, Na⁺, K⁺), with j7 and i6, in the range 2.5pH10 (some measurements, at low ionic strength, were extended to pH=11). In particular, all the species formed are negatively charged: i+j–12=–5, –6. Very high formation percentages of M⁺–phytate species are observed in all the pH ranges investigated. The stability of alkali metal complexes follows the trend Li⁺Na⁺K⁺. Some measurements were also performed at constant ionic strength (I=0.5 mol L^–1), using different mixtures of Et₄NI and alkali metal chlorides, in order to confirm the formation of hypothesized and calculated metal–proton–ligand complex species and to obtain conditional protonation constants in these multi-component ionic media.Presented at SIMEC–02, Santiago de Compostela, 2–6 June 2002     

Solvothermal synthesis and structures of three novel heterometallic microporous coordination polymers assembled from 2-hydroxy-nicotinic acid

Abstract  

Three novel heterometallic microporous coordination polymers {M(Hnico)₃M′} _n (1, M = Co, M′ = K; 2, M = Ni, M′ = K; 3, M = Co, M′ = Na, Hnico is the anion of 2-hydroxy-nicotinic acid, where the proton is transferred from the phenolate hydroxy group to the nitrogen atom of imine pyridine ring) were synthesized by hydrothermal reaction between M(Ac)₂·4H₂O, M′OH and a multifunctional organic aromatic H₂nico ligand and characterized by IR spectrum, elemental analysis, raman spectrum and the single crystal X-ray diffractions. In complexes 1–3, the M²⁺ ions linked three different Hnico ligand formed [M(Hnico)₃]⁻ subunit which further interlinked the six-coordination M′⁺ cation constructed 3D network. The network topology of 1–3 can be simplified a rare 3D (4,4)-connected (4¹²6³) net.     

A novel mononuclear square-planar copper(II) complex (Pip-H+)2[CuL4]2? with 2-cyano-3-(2,5-dimethoxyphenyl)acrylic acid as ligand: synthesis, crystal structures, spectral and thermal studies

Abstract  

2-Cyano-3-(2,5-dimethoxyphenyl)acrylic acid and its novel mononuclear square-planar copper(II) complex dipiperidinium tetrakis[2-cyano-3-(2,5-dimethoxyphenyl)acrylic acid]copper(II) ((Pip-H⁺)₂[CuL₄]²⁻) were synthesized and characterized by elemental analyses, FT–IR, UV–Vis spectroscopy, and thermogravimetric analysis. Moreover, the ligand was characterized by ¹H and ¹³C NMR spectroscopy. The structures of the ligand and its copper(II) complex were confirmed by single-crystal X-ray crystallography. Whereas the ligand crystallizes in the triclinic space group Pī with unit cell parameters a = 4.6911(2) ?, b = 9.0181(4) ?, c = 13.7084(6) ?, α = 74.946(4)°, β = 87.152(4)°, γ = 89.220(4)°, V = 559.34(4) ?³, and Z = 2, the complex crystallizes in the orthorhombic space group Pccn with unit cell parameters a = 27.5486(5) ?, b = 12.9484(2) ?, c = 15.8822(3) ?, V = 5,665.34(17) ?³, and Z = 4.     

Speciation of phytate ion in aqueous solution. Cadmium(II) interactions in aqueous NaCl at different ionic strengths

Interactions between myo-inositol 1,2,3,4,5,6-hexakis(dihydrogen phosphate) (phytic acid) and cadmium(II) were studied by using potentiometry (at 25 °C with the ISE-H⁺ glass electrode) in different metal to ligand (Phy) ratios (1:1≤Cd²⁺:Phy≤4:1) in NaCl_aq at different ionic strengths (0.1≤I/mol L⁻¹≤1). Nine Cd_iH_jPhy^{(12−2i−j)−} species are formed with i=1 and 2 and 4≤j≤7; and trinuclear Cd₃H₄Phy²⁻. Dependence of complex formation constants on ionic strength was modeled by using Specific ion Interaction Theory (SIT) equations. Phytate and cadmium speciation are also dependent on the metal to ligand ratio. Stability of Cd_iH_jPhy^{(12−2i−j)−} species was modeled as a function of both the ligand protonation step (j) and the number of metal cations bound to phytate (i), and relationships found were used for the prediction of species other than those experimentally determined (mainly di- and tri-protonated complexes), allowing the possibility of modeling Phy and Cd(II) behavior in natural waters and biological fluids. A critical evaluation of phytate sequestering ability toward cadmium(II) has been made under several experimental conditions, and the determination of an empirical parameter has been proposed for an objective “quantification” of this ability. A thorough analysis of literature data on phytate–cadmium(II) complexes has been performed. Previous contributions to this series: [1–8]     

Thermal behaviour and spectroscopic studies of complexes of some divalent transitional metals with 2-benzoil-pyridil-izonicotinoylhydrazone

New complexes of 2-benzoyl-pyridil-isonicotinoylhydrazone (L) with Cu(II), Co(II), Ni(II) and Mn(II), having formula of type [ML₂] SO₄·xH₂O (M = Cu²⁺, Co²⁺, Ni²⁺, x = 2 and M = Mn²⁺, x = 3), have been synthesised and characterised. All complexes were characterised on the basis of elemental analyses, IR spectroscopy, UV–VIS–NIR, EPR, as well as thermal analysis and determination of molar conductivity and magnetic moments. The thermal behaviour of complexes was studied using thermogravimetry (TG), differential thermal analysis (DTA) and differential scanning calorimetry (DSC). The structure of L hydrazone was established by X-ray study on single crystal. The ligand works as tridentate NNO, being coordinated through the azomethine nitrogen, the pyridine nitrogen and carbonylic oxygen. Heats of decomposition, ΔH, associated with the exothermal effects were also determined.     

Stability constants of some metal cation complexes of tetraphenyl p - tert -butylcalix[4]arene tetraketone in nitrobenzene saturated with water

Abstract  

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium \textM^{2 +} ( \textaq ) + 1 ·\textSr^{2 +} ( \textnb ) \rightleftarrows 1 ·\textM^{2 +} ( \textnb ) + \textSr^{2 +} ( \textaq ) {\text{M}}^{2 + } \left( {\text{aq}} \right) + {\mathbf{1}} \cdot {\text{Sr}}^{2 + } \left( {\text{nb}} \right) \rightleftarrows {\mathbf{1}} \cdot {\text{M}}^{2 + } \left( {\text{nb}} \right) + {\text{Sr}}^{2 + } \left( {\text{aq}} \right) taking place in the two-phase water–nitrobenzene system (M²⁺ = Ca²⁺, Ba²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, UO₂ ²⁺, Mn²⁺, Co²⁺, Ni²⁺; 1 = tetraphenyl p-tert-butylcalix[4]arene tetraketone; aq = aqueous phase, nb = nitrobenzene phase) were evaluated. Further, the stability constants of the 1 · M²⁺ complexes in water-saturated nitrobenzene were calculated; they were found to increase in the cation order Ba²⁺, Mn²⁺ < Co²⁺ < Cu²⁺, Ni²⁺ < Zn²⁺, Cd²⁺, UO₂ ²⁺ < Ca²⁺ < Pb²⁺.     

Chemistry of chromium bis-acetylide complexes

Abstract  

Stable paramagnetic Cr(II) and Cr(III) bis(alkynyl) complexes of the type [trans(RC≡C)₂Cr(dmpe)₂] ⁿ⁺ (R = Ph, SiMe₃, SiEt₃, C≡C–SiMe₃ n = 0, 1) were prepared and characterised by NMR, cyclic voltammetry, EPR, magnetic measurements, and X-ray single-crystal diffraction studies.     

Effects of the ancillary ligands of polypyridyl cobalt(II) complexes on pH-induced spectral properties and DNA binding properties

Abstract  

Two new Co(II) complexes [Co(ipH)₂(bdipH)]²⁺ and [Co(8-HQ)₂(bdipH)] (ipH = imidazo[4,5-f][1,10]phenanthroline, bdipH = 2-(benzo[d][1,3]dioxol-4-yl)-1H-imidazo[4,5-f][1,10]phenanthroline, 8-HQ = 8-hydroxyquinoline) were synthesized and characterized in detail by elemental analysis, IR, and UV–Vis spectroscopic techniques. The effects of pH on the UV–Vis absorption and emission spectra of the complex were studied. The interaction of the two complexes with calf thymus DNA was explored by using viscosity measurements, electronic absorption titration, competitive binding experiments, and cyclic voltammetry. The experimental results show that complex [Co(ipH)₂(bdipH)]²⁺ exhibits pH-sensitive emission, the two complexes can bind to DNA in an intercalation mode, and the DNA binding affinity of complex [Co(ipH)₂(bdipH)]²⁺ (K _b = 2.11 × 10⁵ M⁻¹) is greater than that of complex [Co(8-HQ)₂(bdipH)] (K _b = 1.76 × 10⁵ M⁻¹). The results show that the size and shape of the ancillary ligand have significant effects on the binding affinity of DNA and complexes.     

Synthesis, characterization, and crystal structural study of the iron(II) 4,4′-bithiazole complex [Fe(C6H4N2S2)3]2+(NO3?)2

Abstract  

The complex [Fe(C₆H₄N₂S₂)₃]²⁺(NO₃⁻)₂ was prepared from the reaction of 4,4′-bithiazole with Fe(NO₃)₃·9H₂O in methanol. It was characterized by IR, UV-Vis, luminescence, ¹H NMR and ¹³C NMR spectroscopy, and X ray crystallography. The structure was solved in the orthorhombic space group P2₁2₁2₁ with a = 12.1500(5), b = 12.8434(6), c = 16.2222(7) ?, V = 2531.43(19) ?³, Z = 4, and with wR ₂  = 0.0897.     

Synthesis, characterization, and crystal structure of two zinc(II) halide complexes with the symmetrical bidentate Schiff-base ligand (3,4-MeO-ba)2en

Abstract  

In this study two zinc(II) halide complexes with the Schiff-base ligand (3,4-MeO-ba)₂en [N,N′-bis(3,4-dimethoxybenzylidene)ethane-1,2-diamine] have been synthesized and characterized by elemental analyses (CHN), single-crystal X-ray diffraction, Fourier-transform infrared (FT-IR), and ¹H nuclear magnetic resonance (NMR) spectroscopy. The metal-to-ligand ratio was found to be 1:1 within the formula ZnX₂((3,4-MeO-ba)₂en) (X = Br, I). Crystal structure analysis reveals that the coordination geometry around the zinc(II) ions in the two isotypic complexes is distorted tetrahedral. The Schiff-base ligand (3,4-MeO-ba)₂en acts as a chelating ligand and coordinates via two N atoms to the metal center and adopts an (E,E) conformation. The coordination spheres of the metal atoms are completed by the two halide atoms, which are also involved in weak non-classical hydrogen-bonding interactions of the type C–H···X–Zn.     

Synthesis,crystal structure,and thermal decomposition kinetics of complex [Nd(BA)<Subscript>3</Subscript>bipy]<Subscript>2</Subscript>

The complex of [Nd(BA)₃bipy]₂ (BA = benzoic acid; bipy = 2,2′-bipyridine) has been synthesized and characterized by elemental analysis, IR spectra, single crystal X-ray diffraction, and TG/DTG techniques. The crystal is monoclinic with space group P2(1)/n. The two–eight coordinated Nd³⁺ ions are linked together by four bridged BA ligands and each Nd³⁺ ion is further bonded to one chelated bidentate BA ligand and one 2,2′-bipyridine molecule. The thermal decomposition process of the title complex was discussed by TG/DTG and IR techniques. The non-isothermal kinetics was investigated by using double equal-double step method. The kinetic equation for the first stage can be expressed as dα/dt = A exp(−E/RT)(1 − α). The thermodynamic parameters (ΔH ^≠, ΔG ^≠, and ΔS ^≠) and kinetic parameters (activation energy E and pre-exponential factor A) were also calculated.     

Density functional study of substituted (–SH, –S, –OH, –Cl) hydrated ions of Hg<Superscript>2+</Superscript>

Abstract  

The electronic structure of Hg(II) ions, [Hg(L) _n (H₂O) _m ] ^q (L = HO⁻, Cl⁻, HS⁻, S²⁻) has been studied. Geometries were fully optimized. The B3LYP and PBE functionals give structures in good agreement with available experimental data. Calculated stretching frequencies generally correlate well with bond lengths. The role of the water molecule(s) in the solvated Hg(II) complexes has been investigated. The solvent can act as nucleophile, as hydrogen bond acceptor or as a spectator. The trans-effect results in lengthening of the Hg–L bond length. It can be understood as a competition between ligands in trans positions for the ability to donate their electron density to the 6s AO of Hg(II). The effect of the presence of water molecules on the Hg–L bond length depends on whether or not the water molecules form a direct coordination bond with Hg(II); it will not guarantee an increase in the stability of the complexes. The interaction energy, which represents the interaction between Hg(II) and ligand L and excludes all other interactions, is nucleophilicity-dependent. The interaction energy and the strength of the ligand nucleophilicity follow the order: S²⁻ > HS⁻ > HO⁻ > Cl⁻ > H₂O. The charge transfer, ΔN, is an indication for the type and strength of the interaction between ligand and Hg(II). Increasing the positive and negative value of ΔN will decrease and increase the Hg(II) total NBO charge, respectively, while decreasing the electrophilicity of Hg(II) will decrease its charge and the charge transfer, ΔN.     

Iron Pentacarbonyl Promoted Addition of CO and MeOH to 1,4-Disubstituted-1,3-butadiyne and Formation of Vinylallyl and Butatriene Ligand Systems

Abstract  Photochemical reaction of methanol solution containing 1,4-diferrocenyl- or 1,4-diphenyl-1,3-butadiynes and iron pentacarbonyl into which CO was constantly bubbled, yielded diiron hexacarbonyl complexes of cumulene ligand systems, [η¹: η³-{RCHC₂CR(COOMe)}Fe₂(CO)₆] (1; E, R = Fc, 2; Z, R = Fc, 5; E, R = Ph, 6; Z, R = Ph) and [η³: η³-{RCHC₂CR(COOMe)}Fe₂(CO)₆] (3; E, R = Fc, 7; E, R = Ph), formed by 1,4-addition of –COOMe and –H to the butadiynes. Additionally, diferrole, [Fe(CO)₄{C(O)CC(Fc)C(O)}₂],4 was obtained in minor quantity. Compounds 1, 2, 5 and 6 contain vinylallyl carbon framework which is stabilized by MeOC=O → Fe bond along with η¹: η³ coordinated Fe₂(CO)₆ unit. Compounds 3 and 7 contain butatriene units which are stabilized by η³: η³ coordinated Fe₂(CO)₆ unit. Characterization of the new compounds was carried out by IR and ¹H and ¹³C NMR spectroscopy and by mass spectrometry. Molecular structures of 2–7 were established by single crystal X-ray diffraction methods. Graphical Abstract  Diiron hexacarbonyl complexes of cumulene ligand systems, [η¹: η³ {RCHC₂CR(COOMe)}] (1; E, R = Fc, 2; Z, R = Fc, 5; E, R = Ph, 6; Z, R = Ph) and [η³: η³-{RCHC₂CR(COOMe)}] (3; E, R = Fc, 7; E, R = Ph) were obtained from photochemical reactions between Fe(CO)₅, CO and methanol. Yield of the minor product, the diferrole, 4, was improved when the photoreaction was carried out in hexane in place of methanol      

Hydrothermal Synthesis and Crystal Structure of a New 2-D Organic–Inorganic Hybrid Wells–Dawson-Type Polyoxometalate

Abstract  

A new 2-D organic–inorganic hybrid Wells–Dawson-Type polyoxotungstate K[Cu(Im)₂]₆P₂W₁₈O₆₂·2H₂O·(OH) (Im = Imidazole) (1) has been synthesized under hydrothermal conditions and characterized by IR spectroscopy, TG, and single crystal X-ray structural analysis. Crystal data for 1: triclinic, P-1, a = 15.3676(12) ?, b = 15.5059(14) ?, c = 24.6437(19) ?, α = 98.088(2)°, β = 96.930(2)°, γ = 119.312(2)°, Z = 2. Single crystal X-ray structural analysis reveals that the [P₂W₁₈O₆₂]⁶⁻ polyoxoanion is linked by [Cu(Im)₂]⁺ cation to form a 1-D chain along the a axis which is connected by K⁺ cation down the c axis to form a 2-D layer.     

Hydroxylammonium fluorometalate: synthesis and characterisation of a new fluorozincate

Abstract  

A new coordination compound of zinc fluoride and hydroxylammonium, (NH₃OH)₂ZnF₄, was obtained after dissolving zinc powder in hydrofluoric acid (40%) and adding solid hydroxylammonium fluoride. The colourless crystals were characterised chemically, magnetically, structurally by single-crystal X-ray diffraction analysis, and thermogravimetrically by TGA and DSC analysis. The structure consists of NH₃OH⁺ cations and ZnF₆ octahedra in which the metal ion lies on the inversion centre. Each of the ZnF₆ octahedra shares four of its vertices in a way that each vertex is shared between two octahedra. Oxygen and nitrogen atoms of hydroxylammonium cations are donors of hydrogen bonds. Hydroxylamonium fluorozincate crystallizes monoclinic, P21/c, with cell parameters a = 8.1604(4) ?, b = 5.8406(3) ?, c = 5.6586(2) ? and β = 94.745(3)°. The compound decomposes above 373 K in four steps, obtaining ZnO as the final residue. Magnetic properties of the compound were studied between 2 and 300 K, giving the prevailing diamagnetic behaviour with room temperature susceptibility of −9 × 10⁻⁵ emu mol⁻¹.     

Photophysical properties of lanthanide complexes with 5-nitro-1,10-phenanthroline

Abstract  

Five novel lanthanide (Eu³⁺, Tb³⁺, Sm³⁺, Dy³⁺, and Gd³⁺) complexes with 5-nitro-1,10-phenanthroline (phenNO₂) have been synthesized and characterized by elemental analysis, IR, UV, and luminescence spectra. The triplet state energy of phenNO₂ was determined to be 20,048 cm⁻¹ via the phosphorescence spectra of phenNO₂ and its gadolinium complex. The photophysical properties of these complexes indicated that the triplet state energy of the ligand is suitable for the sensitization of the luminescence of Eu³⁺ and Sm³⁺, especially the former.     

Ruthenium complexes of 4,4′-bi-1,2,3-thiadiazole and azoimine ligands: syntheses,crystallography, and electrochemical studies

Abstract  

Five ruthenium complexes of the general type trans-[Ru^II(btd)(Azo)Cl₂] ({Azo = PhN=NC(COMe) = NC₆HY, where Y = H (a), Me (b), OMe (c), Cl (d) or Br (e)} and btd = 4,4′-bi-1,2,3-thiadiazole) have been prepared by the reaction of RuCl₃ with the ligands in the presence of LiCl. These complexes have been characterized by spectroscopic (IR, UV–Vis, and NMR) and electrochemical techniques. In addition, the complex trans-[Ru^II(btd)(L5)Cl₂] (complex 5) has been characterized by X-ray diffraction analysis. The electrochemical parameter for the π-excessive ligand (btd) is reported. The absorption spectrum of complex 5 in acetonitrile has been modeled by time-dependent density functional theory.     

Stability constants of the Li+, Na+, H3O+, NH4+, Ag+, and K+ complexes of the cone conformer of tetraethyl p-tert-butyltetrathiacalix[4]arene tetraacetate in nitrobenzene saturated with water

Abstract  

From extraction experiments in the two-phase water–nitrobenzene system and γ-activity measurements, the stability constants of the tetraethyl p-tert-butyltetrathiacalix[4]arene tetraacetate (cone)·M⁺ complexes (M⁺ = Li⁺, H₃O⁺, NH₄ ⁺, Ag⁺, or K⁺) were determined in water-saturated nitrobenzene. It was found that these constants increase in the cation order NH₄ ⁺ < K⁺ < H₃O⁺ < Ag⁺ < Li⁺ < Na⁺.