Protolitic complexing properties of acylhydrazones of substituted salicylaldehydes and stability constants of their cooper(II) complexes

The acid-base properties of acetyl-and heptoylhydrazones of substituted salicylaldehyde derivatives and the stability of their copper(II) complexes have been studied. For both sets of compounds, the ionization constants of the hydrazones and the stability constants of hydrazone complexes are linear functions of the substituent constants σ. An analogous tendency is found for the antiferromagnetic exchange interaction parameters in dimeric copper(II) nitrate complexes of heptoylhydrazones of substituted salicylaldehyde derivatives. A correlation between the protolytic properties of hydrazones and the magnetic properties of their complexes is suggested.     

Synthesis, structure, and complexing ability of hetarylhydrazones of glyoxylic acid

Benzoxazolyl-, benzthiazolyl-, 2′-quinolinyl- and 1′-phthalazinylhydrazones of glyoxylic acid (H₂L) and their complexes have been synthesized. The acid-base properties of the obtained hydrazones were studied by the methods of potentiometric titration and spectrophotometry. The hydrazones were shown to form mononuclear octahedral complexes M(HL)₂ with Ni(II) and Mn(II) acetates, whereas with Zn(II) and Cu(II) acetates binuclear complexes M₂L₂ were formed. The nature of the exchange interaction between the Cu(II) ions is discussed.     

Synthesis and magnetic properties of μ-phenolato copper (Ⅱ) binuclear complexes with different exogenous bridges

The syntheses and magnetic properties are reported for a series of copper(Ⅱ) complexes prepared from a pentadentate binucleating ligand 2,6-diformyl-4-methylphenol di(benzoyl-hydrazone) (H3L). These complexes incorporate different exogenous ions (X-) into a bridging position to form copper(Ⅱ) binuclear complexes of the formula [Cu2(H2L)X]2+, where X-= Br-(1), Cl-(2), HO-(3), C2H5O-(4) and C3H3N2- (5). The complexes have been characterized with variable temperature magnetic susceptibility (4.2-300 K) and the observed data were fit to those from a modified Bleaney-Bowers equation by least-squares method, giving the exchange integral 2J = -6.2 cm-1 for 1, -76.4 cm-1 for 2, -241.9 cm-1 for 3, -231.1 cm-1 for 4 and -343.8 cm-1 for 5. This suggested that there is an antiferromagnetic interaction between the Cu(Ⅱ) ions and the sequence of the effect of some exogenous bridging ligands on magnetic coupling is corresponding to that in spectrochemical series.     

Mononuclear copper(II) complexes of bis-triazole-based macrocyclic Schiff base hydrazones: direct synthesis,EPR studies,magnetic and thermal properties

Mononuclear copper(II) complexes of 1,2,4-triazole-based Schiff base macrocyclic hydrazones, III and IV, have been reported. The prepared amorphous complexes have been characterized by spectroscopic methods, electron spray ionization mass spectrometry, and elemental analysis data. Electrochemical studies of the complexes in DMSO show only one quasi-reversible reduction wave at +0.43 V (ΔE = 70 mV) and +0.42 V (ΔE = 310 mV) for III and IV, respectively, which is assigned to the Cu(II) → Cu(I) reduction process. Temperature dependence of magnetic susceptibilities of III and IV has been measured within an interval of 2–290 K. The values of χ_M at 290 K are 1.72 × 10^?3 cm³ mol^?1 and 1.71 × 10^?3 for III and IV, respectively, which increases continuously upon cooling to 2 K. EPR spectra of III and IV in frozen DMSO and DMF were also reported. The trend g_|| > g⊥ > g_e suggests the presence of an unpaired electron in the d_x2?y2 orbital of the Cu(II) in both complexes. Furthermore, spectral and antimicrobial properties of the prepared complexes were also investigated.     

Studies on the non‐covalent interactions between cyclodextrins and aryl alkanol piperazine derivatives by mass spectrometry and fluorescence spectroscopy

The non‐covalent complexes of α‐ and β‐cyclodextrins (α‐, β‐CDs) with two aryl alkanol piperazine derivatives (Pipe I and Pipe II) have been studied by electrospray ionization mass spectrometry (ESI‐MS) and fluorescence spectroscopy. The ESI‐MS experimental results demonstrated that Pipe I can conjugate to β‐CD and form 1:1 or 1:2 stoichiometric non‐covalent complexes, and Pipe II can only form 1:1 complexes with α‐ or β‐CD. Fluorescence spectra indicated that the fluorescence intensities of Pipe I and Pipe II can be enhanced by increasing the content of β‐CD. The mass spectrometric titration experiments showed that the dissociation constants K_d1 were 5.77 and 9.52 × 10^?4 mol L^?1 for the complexes of α‐CD with Pipe I and Pipe II, respectively, revealing that the binding of α‐CD‐Pipe I was stronger than α‐CD‐Pipe II. The K_d1 and K_d2 values were 9.81 × 10^?4 mol L^?1 and 1.11 × 10^?7 (mol L^?1)² for 1:1 and 1:2 complexes of Pipe I with β‐CD, respectively. The K_d values obtained from fluorescence spectroscopy were in agreement with those from ESI‐MS titration. Copyright © 2010 John Wiley & Sons, Ltd.     

2-Acetylbenzimidazole phthalazin-1-ylhydrazone and its complexes with transition metals

2-Acetylbenzimidazole phthalazin-1-ylhydrazone (H₂L) and its complexes with Cu(II), Ni(II), Mn(II), Zn(II), Cd(II), and Fe(III) were synthesized. The structure of the complexes was determined on the basis of their elemental compositions, IR and ESR spectra, and thermogravimetric, conductometric, and magnetochemical studies. The dinuclear copper complex [CuL]₂ was found to display strong antiferromagnetic exchange between the copper(II) ions. The ionization constants, energies of possible conformations of the hydrazone, geometric parameters of the dinuclear complex, and exchange parameters were calculated by quantum-chemical methods.     

Lanthanide complexes of D-penicillamine: formation constants,spectral and thermal properties

The complex-formation of lanthanide(III) elements with D-penicillamine have been investigated in acidic and neutral media. The macroscopic protonation constants of the ligand and the formation constants of [Ln.Pen]⁺, [Ln.Pen₂]^?, [Ln.Pen.OH] and [Ln.Pen.(OH)₂]^? complexes were determined from pH-metric data using the BEST computer program. Elemental analyses of the solid complexes indicate formation of 1?:?1 metal?:?ligand species. The binding sites in the complexes with the possible role of –COO^?, –NH₂ and –SH groups in the coordination have been discussed using infrared data. The complexes decompose in four steps as shown by their t.g. and d.t.a. analyses. A mechanism of decomposition is proposed which is supported by mass spectral data.     

Synthesis, electrochemical, magnetic, catalytic and antimicrobial studies of N-functionalized cyclam based trinuclear copper(II) and nickel(II) complexes

Trinuclear copper(II) and nickel(II) complexes have been prepared by using Schiff base ligands derived from 1,8-[bis(3-formyl-2-hydroxy-5-methyl) benzyl]-4,11-dimethyl-l,4,8,11-tetraazacyclotetradecane, and 1,8-[bis(3-formyl-2-hydroxy-5-bromo)benzyl]-4,11-dimethyl-l,4,8,11-tetraazacyclotetradecane with aliphatic and aromatic diamines. All the complexes were characterized by elemental and spectroscopic analysis. Electrochemical studies of the copper(II) complexes in DMF solution show three irreversible one electron reduction process around E _pc  ¹ = ?0.59 to ?0.80 V, E _pc  ² = ?0.89 to ?1.14 V and E _pc  ³ = ?1.17 to ?1.29 V, and for nickel(II) complexes it is around E _pc  ¹ = ?0.63 to ?0.77 V, E _pc  ² = ?1.20 to ?1.35 V and E _pc  ³ = ?1.60 to ?1.74 V. ESR spectra and magnetic moments of the trinuclear Cu(II) complexes show the presence of antiferromagnetic coupling. Cryomagnetic investigation of the trinuclear copper(II) complexes show that the observed ?2J values are in the range of 116–178 cm^?1. The rate constants for hydrolysis of 4-nitrophenylphosphate by the complexes are in the range of 2.68 × 10^?2 to 9.81 × 10^?2 min^?1. The rate constants values for the catecholase activity of the copper(II) complexes fall in the range of 3.03 × 10^?2 to 9.32 × 10^?2 min^?1. All the complexes.     

Coordination properties of N,O-carboxymethyl chitosan (NOCC). Synthesis and equilibrium studies of some metal ion complexes. Ternary complexes involving Cu(II) with (NOCC) and some biorelevant ligand

In the present study, the acid-base equilibria of N,O-carboxymethy chitosan abbreviated as (NOCC), is investigated. The complex formation equilibria with the metal ions Cu^(II), Ni^(II), Co^(II), Mn^(II), and Zn^(II) are investigated potentiometrically. The stability constant values of the binary and ternary complexes formed in solution were determined and the binding centers of the ligands were assigned. The relationships between the properties of the studied central metal ions as ionic radius, electronegativity, atomic number, and ionization potential, and the stability constants of the formed complexes were investigated in an effort to give information about the nature of chemical bonding in complexes and make possible the calculation of unknown stability constants. Cu^(II), Ni^(II), and U^(VI) complexes with NOCC are isolated as solid complexes and characterized by conventional chemical and physical methods. The structures of the isolated solid complexes are proposed on the basis of the spectral and magnetic studies. The ternary copper(II) complexes involving NOCC and various biologically relevant ligands containing different functional groups, as amino acids and DNA constituents are investigated. The stability constants of the complexes are determined and the concentration distribution diagrams of the complexes are evaluated.     

Complexation between nickel(II), cobalt(III) and hydrazones derived from pyridoxal 5′-phosphate and hydrazides of 2-,3-,4-pyridinecarboxylic acids in aqueous solution

abstract

The present work reports on stoichiometry, apparent stability constants of biologically relevant complexes of nickel(II), cobalt(III) with hydrazones derived from pyridoxal 5′-phosphate and hydrazides of 2-,3-,4-pyridinecarboxylic acids at pH 7.4, T?=?25.0?°C, I?=?0.25 determined using UV-Vis spectroscopy. The thermodynamic constants of some complexes formation (NiL, NiL₂, NiL₂H) were estimated. Cobalt(II) ion was found to be oxidized to cobalt(III). Co(II) and Co(III) form low-spin state complexes. Hydrazones binding ability (pL_0.5) in the medium mimicking biological ones towards Ni(II) and Co(III) was estimated.     

Potentiometric Studies of Ternary Complexes Involving Palladium(II) with Fluoxetine Drug and Some Bio-ligands

The complex formation equilibria of [Pd(FLX)(H₂O)₂]²⁺, where FLX = the drug fluoxetine, with the bio-ligands (L), glycine, serine, cysteine, histidine, glycylglycine and glycylvaline, were studied and their formation constants were determined. Stoichiometries and stability constants of the complexes were determined at 25 °C and at constant 0.10 mol·dm^?3 NaNO₃ ionic strength. The concentration distribution of the complexes in solution was evaluated. Palladium(II) complexes were synthesized and characterized by the ¹H NMR and electronic spectral studies. The structures consist of monomeric units in which the Pd(II) atoms exhibit square planar geometry.     

Synthesis and properties of the copper(Ⅱ) complexes with stable radical

Four novel copper(Ⅱ) complexes have been synthesized,namely Cu(hfac)2NITPhNO2 (1),Cu(hfac)2NITPhCH3 (2),Cu(pfpr)2NITPhNO2,(3) and Cu(Pfpr)2NITPhCH3 (4),where hfac= hexafluoro-acetylacetonate,pfpr=pentafluoropropionate,NITR.=2-R-4,4,5,5-tetraniethyl-4,5-dihydro-1H-imidazolyl-1-oxyl-3-oxide.(R=4-nitrophenyl,4-methylphenyl).These complexes were rharicter-ized by elemental analyses,IR,electronic spectra and molar conductance.The temperature-dependent magnetic susceptibility of complexes 1 and 3 have been studied in the 4 300 K range,giving I he exchange integral J=10.56 cm-1 for complex 1 and J =-30.9 cm-1 for complex 3.     

A correlation between spin state and electrochemical electron-transfer rate for tris(N,N-disubtituted dithiocarbamato) iron(III) complexes

The electrochemical electron-transfer rate constants for the redox systems Fe(IV)L₃⁺/Fe(III)L₃ (L=N,N-disubstituted dithicarbamate ion) and Fe(III)L₃/Fe(II)L₃^? with a variety of substituents were measured at a platinum electrode in acetonitrile with the galvanostatic double-pulse method. It is known that each of the Fe(III) complexes exists both in a highspin state ⁶A₁ and a low-spin state ²T₂ in equilibirium of which position is widely changed by a subtle change in substituent. The standard rate constants for Fe(IV)L₃⁺/Fe(III)L₃ were larger or smaller than those for Fe(III)L₃/Fe(II)L₃^? according as the Fe(III)L₃ complexes are predominantly low- or high-spin complexes. Since the Fe(IV) and Fe(II) complexes are low-and high-spin complexes respectively, these findings suggest that electrochemical electron-transfer reactions accompanied by a spin-state change are slower than those without it. Such spin-state effect on electrode reactions has rarely been discussed so far.     

Complexation Equilibria and Determination of Stability Constants of Binary and Ternary Nickel(II) Complexes with Amino Acids (Glycine, α-Alanine, β-Alanine and Proline) and Dipicolinic Acid as Ligands

In this paper we report the formation of binary and ternary nickel(II) complexes involving dipicolinic acid (H₂Dipic) as the primary ligand and some selected amino acids {glycine (HGly), ?-alanine (H?-Ala), ??-alanine (H??-Ala) and proline (HPro)} as secondary ligands. These complexes were studied at 25?°C by means of electromotive force measurements, emf(H), using 1.0?mol?dm^?3 NaCl as the ionic medium. The experimental data were analyzed by means of the computational least-squares program LETAGROP, taking into account hydrolysis of the nickel(II) cation and the acid/base reactions of the ligands whose equilibrium constants were kept fixed during the analysis. In the study of the binary nickel(II)?Camino acids systems the species [NiL]⁺, NiL₂ and [NiL₃]^? were observed, and in the case of the ternary nickel(II)?Cdipicolinic acid?Camino acids systems the complexes Ni(Dipic)HL, [Ni(Dipic)L] ^? and [Ni(Dipic)L(OH)]^2? were observed. The respective stability constants were determined, and the species distribution diagrams, as a function of pH, are briefly discussed.     

Synthesis and properties of transition and lanthanide complexes with benzyl monohydrazone-3-hydrazine- 4-benzyl-6-phenyl pyridazine ligand (BHP)

Synthesis and characterization of benzyl-monohydrazone-3-hydrazino-4-benzyl-6-phenyl pyridazine (BHP) and its complexes with copper(II), nickel(II), cobalt(II), zinc(II), manganese(II), cadmium(II), thorium(IV), dioxyuranium(VI), samarium(III) and erbium(III) are presented. The protonation equilibrium of BHP ion and complex formation equilibrium with the metal ions have been studied by potentiometry in 75% (v/v) dioxane-water and 0.10M KNO₃ at different temperatures (10, 20, 30 and 40°C). A series of mononuclear complexes [ML _n ]^{(1? z )+} (L^? =?BHP and n =?1 ??z) were found in solution and their formation constants, enthalpies and entropies were determined.

The solid metal complexes and corresponding thermal products were elucidated by elemental analysis, conductance, IR and electronic spectra, magnetic moments, ¹H NMR and TG-DSC measurements as well as by mass spectroscopy. The use of BHP as analytical reagents for the determination of copper(II), nickel(II) and cobalt(II) as well as extracting agents for these metal ions are discussed.     

Voltammetric measurement of copper(II)/organic interactions in estuarine waters

The voltammetry of copper in organic ligand/chloride media is dominated by the formation of CuCl^?₂ species and by induced adsorption of Cu(I) in organic coatings on the electrodes. These phenomena are utilised in a novel method for evaluating Cu(II)/organic ligand interactions, based on the principle of ligand exchange. The Cu(II)/organic species competes with glycine which forms copper glycinate. These two complexes can be distinguished voltammetrically: copper glycinate gives a higher surface excess of copper at a gelatin-coated hanging mercury drop electrode, partly because of the increased production of CuCl^?₂ from copper glycinate at the electrode surface. The method proved satisfactory for pure ligand/surfactant/chloride media and for estuarine waters. It is shown that there are two type of Cu(II)-binding ligand in estuarine waters: humic material (> 10^?6 mol l^?1, assuming 1:1 site binding) with polyelectrolyte-type binding, and discrete ligands (? 10^?6 M) with stability constants around 10⁹. The extent of Cu(II) binding by the humic material decreases down the estuary because of dilution and increased salinity.     

Synthesis of Two Derivatives of 3,6,9‐tri(carboxymethyl)‐3,6,9‐triazaundecanedioic Acid and the Stabilities of Their Complexes with Ca2+, Cu2+, Zn2+, Dy3+ and Gd3+

Two N‐2‐hydroxy‐1‐phenylethyl and N‐2‐hydroxy‐2‐phenylethyl derivatives of DTPA (3,6,9‐tri(carboxymethyl)‐3,6,9‐triazaundecanedioic acid), DTPA‐H1P = 3,9‐di(carboxymethyl)‐6‐2‐hydroxy‐1‐phenylethyl‐3,6,9‐triazaundecanedioic acid, and DTPA‐H2P = 3,9‐di(carboxymethyl)‐6‐2‐hydroxy‐2‐phenylethyl‐3,6,9‐triazaundecanedioic acid were synthesized. Their protonation constants were determined by Potentiometric titration in 0.10 M Me₄NNO₃ and by NMR pH titration at 25.0 ± 0.1°C. The formations of lanthanide(III), copper(II), zinc(II) and calcium(II) complexes were investigated quantitatively by potentiometry. The stability constant for Gd(III) complex is larger than those for Ca(II), Zn(II) and Cu(II) complexes with these two ligands. The selectivity constants and modified selectivity constants of the DTPA‐H1P and DTPA‐H2P for Gd(III) over endogenously available metal ions were calculated. Comparing pM values at physiological pH 7.4 assesses effectiveness of these two ligands in binding divalent and trivalent metal ions in biological media. The observed water proton relaxivity values of [Gd(DTPA‐H1P)]^? and [Gd(DTPA‐H2P)]^? became constant with respect to pH changes over the range of 4‐10. ¹⁷O NMR shifts showed that the [Dy(DTPA‐H1P)]^? and [Dy(DTPA‐H2P)]^? complexes at pH 6.30 had 1.91 and 2.28 inner‐sphere water molecules, respectively. Water proton spin‐lattice relaxation rates of [Gd(DTPA‐H1P)]^? and [Gd(DTPA‐H2P)]^? complexes were also consistent with the inner‐sphere Gd(III) coordination.     

A Method for the polarographic determination of the stability constants of mixed complexes

A new method for determining the stability constants of mixed complexes is proposed which is especially appropriate when only the mixed complex 1:1:1 is formed. In order to verify this method, the coordinate system Pb(II)-SCN^?-NO^?₃ has been studied polarographically in aqueous medium of a constant ionic strength of μ = 1.0 M. Using our knowledge of the stability constants of simple complexes and applying this method we obtain β₁₁ = 8 for the mixed complex.     

Intermolecular dynamics and paramagnetic properties of ethylenediaminetetraacetate complexes with the yttrium subgroup rare earth elements using nuclear magnetic resonance

¹H nuclear magnetic resonance (NMR) measurements are reported for the D₂O solutions of [Ln³⁺(EDTA^4?)]^? complexes, where EDTA^4? is ethylenediaminetetraacetate anion, Ln³⁺ = Tb³⁺ (I), Ho³⁺ (II), Tm³⁺ (III), Yb³⁺ (IV) and Lu³⁺ (V). Temperature dependencies of the ¹H NMR spectra of paramagnetic I–IV have been analyzed using the dynamic NMR methods. It is found that the activation free energies (ΔG^?₂₉₈ ) of the intermolecular EDTA ions exchange at [Ln³⁺(EDTA^4?)]^? complexes are 60±3 (I), 66±3 (II), 69±3 (III) and 74±3 (IV) kJ/mol (at pD = 7). A monotonic increase of the free energy of chemical exchange processes along the series of lanthanide [Ln³⁺ (EDTA^4?)]^? complexes is probably related to the lanthanide contraction. The obtained results indicate that coordination compounds I–IV may be considered as thermometric NMR sensors and lanthanide paramagnetic probes for in situ temperature control in solution. Copyright © 2012 John Wiley & Sons, Ltd.     

Anion Binding Properties of N-Confused Porphyrins at the Peripheral Nitrogen

Ni(II), Pd(II), and Cu(II) complexes of N-confused porphyrin (NCP) exhibit anion binding properties through a hydrogen bonding interaction at the peripheral NH of confused pyrrole ring. The binding constants of the tetrakis(pentafluorophenyl)-NCP metal complexes (1-M, M= Ni, Pd, Cu) for various halide anions in CH₂C1₂ increase in the order of F^? > Cl^? > Br^? > I^?, respectively. Zwitterionic resonance form of the NCP complexes as well as interactions between halide anions and a pentafluorophenyl group are suggested to be important for efficient anion binding.