Complexation dans le méthanol anhydre de Cu (II) et Zn (II) par des ligands diaza-polyoxamacrocycliques

Complexation in anhydrous methanol of Cu (II) and Zn (II) with diaza-polyoxamacrocyclic ligands Protonation of five diaza-polyoxamacrocyclic ligands, (L = [2.1], [2.2], [2.1.1.], [2.2.1], [2.2.2]), and their complexing properties towards Cu²⁺ and Zn²⁺ cations have been studied in anhydrous methanolic solutions. Potentiometric measurements have been carried out at 25°, using 5 · 10^?2MEt₄N⁺ClO as support-electrolyte, in order to determine the nature of the species formed upon complexation and their stability constants. The results were confirmed by spectrophotometry, for the cupric complexes of [2.1] and [2.2.2], and the electronic spectra of the different complexes were calculated. Comparison between complexation in aqueous and methanolic solutions have been made: as in water, ML²⁺ species and sometimes protonated MHL³⁺ species, with higher stability constants, are present in methanol; but the main difference is the formation of dinuclear complexes M₂L⁴⁺, between Cu²⁺ and all ligands except [2.1]. In these complexes the Cu²⁺ cations cannot be both ‘encaged’ in the ligand cavity because of its small size. The different possible structures are discussed in terms of the stability constants values. The protonation constants values and the existence of the binuclear complexes may indicate a possible conformational change in the complexing ligand on changing the solvent from water to methanol.     

Stabilité dans le méthanol et propriétés thermodynamiques de transfert des cryptates de certains cations de transition et de métaux lourds

Stability in Methanol and Thermodynamic Transfer Properties of the Cryptates of some Transition Cations and Heavy Metals The nature and stability of the macrocyclic and macrobicyclic complexes of Ag⁺, Cd²⁺, and Pb²⁺ (Mⁿ⁺) with 21, 22, 211, 221 and 222 in anhydrous methanol 0.05M in Et₄N⁺ClO^?₄, at 25° (see Scheme) have been determined by potentiometry and spectrophotometry. Binuclear complexes M₂L²ⁿ⁺ have been observed in all cases, besides the mononuclear MLⁿ⁺ complexes. The macrobicyclic 1:1 complexes MLⁿ⁺ exhibit an important ‘cryptate effect’ with Mⁿ⁺=Ag⁺, Pb²⁺ and Cd²⁺, but not with Cu²⁺ and Zn²⁺; their stability is in all cases maximum with 221. The applicability to our results of the recent extrathermodynamic hypothesis involving MLⁿ⁺ cryptates is examined.     

Nature et stabilité des complexes métalliques de cryptands dinucléants en solution II. Polythiamacrotricycles et monocycles apparentés

Nature and Stability of Some Metallic Complexes of Dinucleating Cryptands in Solution II. Polythiamacrotricycles and Related Monocyclic Subunits The stability constants of the Cu²⁺ and Ag⁺ complexes of the cylindrical macrotricycle 1a (1,7,13,19-tetraaza 4,16-dioxa 10,22,27,32-tetrathiatricyclo[17.5.5.5]tetratriacontane) have been determined by pH-metry, as well as those of the Cu²⁺, Co²⁺, Zn²⁺, Cd²⁺, Pb²⁺, and Ag⁺ complexes of the monocyclic subunit 2a (1,7-dimethyl-1,7-diaza 4,10-dithiacyclododecane), in aqueous solutions (NaClO₄) at 25°. In the Cu(II) systems, equilibria were reached slowly, and the results established by pH-metry were confirmed by UV/VIS spectrophotometric studies. The tricycle 1a forms dinuclear cryptates with copper and silver, with overall stability constants log β₂₁₀ (Cu₂- 1a )⁴⁺ = 18.5, log β_21-2 (Cu₂- 1a (OH)₂)²⁺ = 4.8, log β₂₁₀(Ag₂- 1a )²⁺ = 23.0. Ag⁺ also forms a mononuclear (Ag- 1a )⁺ complex, with log β₁₁₀ = 13.1, but no mononuclear species were detected in the Cu- 1a system. The absorption spectra of the bis-Cu(II) complexes of 1a and 2a in aqueous medium, MeOH and propylene carbonate (PC) are given, as well as those, in MeOH and PC, of the bis-copper complexes of the related monocycles 3 and 4 (1,7-diaza-4,10,13-trithiacyclopentadecane and 1.10-diaza 4,7,13,16-tetrathiacyclooctadecane, respectively), and tricycle 5 with two benzyl groups in the lateral chains. The complexing properties of the polyoxa- and polythia macrotricycles (Parts I and II of this series) are compared to those of other bis-chelating ligands, the bicyclic bis-tren and the monocyclic bis-dien.     

Cryptates Sphériques. Synthèse et Complexes d'Inclusion de Ligands Macrotricycliques Sphériques

Spherical Cryptates. Synthesis and Inclusion-Complexes of Spherical Macrotricyclic Ligands A general strategy for the synthesis of spherical macrotricyclic ligands has been developed. Four spherical cryptands, SC - 24 , SC - 25 , SC - 26 and SC - 27 have been obtained by this route. The synthesis and cation-complexing properties of these compounds are described in detail. Stability constants and cation exchange rates of the spherical cryptates obtained with alkali and alkaline-earth cations have been determined. Highly stable complexes are formed by SC - 24 ; the Rb⁺ and Cs⁺ cryptates of SC - 24 are the most stable complexes of these cations known to date. The size of the intramolecular cavity affects the complexation selectivity. The cation exchange rates are very slow, and the corresponding free energies of activation are even larger than, for macrobicyclic cryptates of similar stability. Both the high complex stabilities and the high activation energies required for cation exchange indicate a marked ‘spherical cryptate effect’ resulting from the highly connected nature of the molecular architecture of spherical macrotricyclic ligands.     

Stabilité en solution aqueuse de complexes de métaux lourds avec des ligands diaza-polyoxamacrocycliques

Stability in aqueous solution of some complexes of heavy metals with diaza-polyoxamacrocyclic ligands Stability of metal complexes (Mⁿ⁺ = Cu²⁺, Ni²⁺, Co²⁺, Zn²⁺, Pb²⁺, Ag⁺ and Cd²⁺) with five diaza-polyoxamacrocycles (L = [2.1.1], [2.2.1], [2.2.2], [2.1] and [2.2] ) have been determined at 25°, in 0.1 M Et₄N⁺ClO aqueous solutions, by means of potentiometric titrations. All cations form MLⁿ⁺ complexes; Cu²⁺ also forms the MHL⁽ⁿ⁺¹⁾⁺ protonated species with both [2.2.1] and [2.1.1] ligands. The stability of these complexes has been discussed in terms of structure and by considering the ionic radii of the cations together with the radii of the macrocyclic cavities. Different behaviour is observed between some of these complexes and the well known alkali and alkaline-earth cryptates, partly due to the more covalent nature of bonds formed by the investigated cations and the donor sites of the ligands. The effect of the substitution of two oxygen by two sulfur atoms in the pentadentate ligand [2.1] on the stability of the complexes is reported.     

The reducibility of Ru,Pt/Ru and Pt oxide electrocatalysts as measured by temperature-programmed reduction and cyclic voltammetry

The electrochemical reduction of alkaline cryptates (222, M)⁺ has been studied on mercury electrode by normal pulse polarography, potentiostatic coulometry and cyclic voltammetry in propylene carbonate as solvent. The corresponding kinetic parameters have been calculated and compared with those obtained on solvated alkaline cations in the same medium. A more detailed study of the electrochemical reduction mechanism of the cryptate (222, K)⁺ shows that the primary product of the reduction is the unstable (222, K^o), and that the final stable products are the free ligand (222) and the amalgam K^o (Hg). The alkaline cations, when complexed by the same (222) ligand, exhibit close values of the polarographic diffusion coefficients. The specific polarographic behaviour of the cryptate (222, Cs)⁺ is described and its stability constant calculated in propylene carbonate. An analytical application of the electrochemical reduction of cryptates is also proposed.     

Enthalpy and Entropy of Formation of Alkali and Alkaline-Earth Macrobicyclic Cryptate Complexes [1]

The enthalpies and entropies of complexation of alkali and alkaline-earth metal cations by several macrobicyclic ligands have been obtained from calorimetric measurements and from the previously determined stability constants [2]. Both enthalpy and entropy changes play an important role in the stability and selectivity of the complexes. Particularly noteworthy are the large enthalpies and the negative entropies of complexation obtained for the alkali cation complexes (Na⁺, K⁺, Rb⁺ and Cs⁺ cryptates). The Sr²⁺ and Ba²⁺ as well as [Li⁺ ? 2.1.1]

1 For use of the symbols see [2].

and [Na⁺ ? 2.2.1] cryptates are of the enthalpy dominant type with also a favourable entropy change. The Ca²⁺ and [Li⁺ ? 2.2.1] cryptates are entirely entropy stabilized with about zero heat of reaction. The high stability of the macrobicyclic complexes as compared to the macromonocylcic ones, the cryptate effect, is of enthalpic origin. The enthalpies of complexation display selectivity peaks, as do the stabilities, whereas the entropy changes do not. The high M²⁺/M⁺ selectivities found in terms of free energy, may be reversed when enthalpy is considered in view of the very different role played by the entropy term for M²⁺ and M⁺ cations. The enthalpies and entropies of ligation show that whereas the cryptate anions are similar in terms of entropy irrespective of which cation is included, the ligands, despite being more rigid than the hydration shell, are nevertheless able to adjust to some extent to the cation. This conclusion agrees with published X-rays data. The origin of the enthalpies and entropies of complexation is discussed in terms of structural features of the ligands and of solvation effects.     

Nature et stabilité des complexes métalliques de cryptands dinucléants en solution. I. Polyazapolyoxa macrotricycle cylindrique et monocycle constitutif

Nature and Stability of Some Metallic Complexes of Dinucleating Cryptands in Solution. I. A Polyazapolyoxa Cylindrical Macrotricycle and its Monocyclic Subunit pH-metry and UV spectrophotometry were used to study the complexing properties of the cylindrical macrotricycle, 1,7,13,19-tetraaza-4,16-dioxa-10,22,27,32-tetraoxatricyclo[17.5.5.5]tetratriacontane ( 1 ) and of its constitutive monocyclic subunit, 1,7-diaza-4,10-dioxacyclododecane ( 2 ) with some transition and heavy metal cations (Cu²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Ag⁺), in aqueous medium 0.1M Et₄NClO₄, at 25°. The protonation constants of the ligands as well as the nature and the stabilities of the complexes formed in the pH-regions studied were determined. The tricycle 1 only formed dinuclear M₂L complexes with Cu²⁺, Zn²⁺, and Ag⁺, accompanied in the latter case by a protonated mononuclear MLH species, and with Cu²⁺ and Zn²⁺ at high pH-values by dinuclear hydroxo complexes. Only mononuclear complexes were evidenced with the other cations, ML being accompanied either by protonated or hydroxy mononuclear species. The mononuclear complexes of 1 , when they existed, were more stable than the corresponding complexes of 2 , except for cobalt which formed complexes of comparable stability with both ligands. In the other cases (Cd²⁺, Pb²⁺, Ag⁺), the stability differences between the complexes of 1 and 2 increased with the size of the cation.     

A Study of Formation Equilibria of the Complexes of Some Metal Cations with Polyoxa Macrocyclic Ligands

Abstract

The complexes formed by the Na⁺, K⁺, Rb⁺, Ca²⁺, UO²⁺ ₂, and Ag⁺ cations with the macrocyclic polyethers 18-crown-6, benzo-15-crown-5, and dicyclohexy1-18-crown-6 are investigated. The stability constants of these complexes have been determined potentiometrically in (90% vol.) ethanol-water solutions at 25[ddot]C and an ionic strength μ= 0.1 (achieved with tetrabuty lammonium perchlorate). The stablity of the investigated complexes was interpreted in terms of “caging” the metal cation into the cavity of the macrocyclic ligand, an effect which depends on the ratio of the diameter of the complexed cation over the diameter of the cavity of the complexing ligand.     

Etude de la complexation des lanthanides trivalents par les isomères de l'acide diaminocyclohexanetétraacétique: Partie 2. Les Constantes d'Acidité et les Constantes de Formation des Complexes 1:1 avec l'Acide trans-1,4-Diaminocyclohexane-N,N,N′,N′-Tétraacétique

(Study of the complexation of trivalent lanthanides by the six isomers of diaminocyclohexanetetraacetic acid. Part 2. Acidity constants and formation constants of the 1:1 complexes of trans-1,4-diaminocyclohexane-N,N,N′,N′-tetraacetic acid)Potentiometric measurements of the acidity constants of trans-1,4-diaminocyclohexane-N,N,N′,N′-tetraacetic acid (trans-1,4-DCTA) and of the stability constants of its 1:1 complexes with the trivalent lanthanides are reported for an ionic strength of 1 (KCl) at 25°C. The behaviour of this ligand is similar to that of monoaminodiacetic acids, suggesting that only one N(CH₂COO^?)₂ group participates in chelation. The selectivity of trans-1,4-DCTA for the lanthanides is better than that reported for the monoaminodiacetic acids.     

Effect of adding ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate on the coordination environment of Li<Superscript>+</Superscript> ions in propylene carbonate,according to data from IR spectroscopy and quantum chemical modeling

The effect ionic liquid (IL) 1-ethyl-3-methylimidazolium tetrafluoroborate has on the coordination environment of Li⁺ cations in carbonate solvents is studied by means of IR spectroscopy and quantum chemical modeling using the example of propylene carbonate (PC). LiBF₄ is used as the lithium salt. This system is promising for use as an electrolyte in lithium power sources (LPSs), but the mechanism of ionic conductivity by Li⁺ ions in such systems has yet to be studied in full.     

Kinetics of substitution reactions of transition metal complexes in 1,3-dioxolan-2-one + water and 4-methyl-1,3-dioxolan-2-one + water solvent mixtures

Summary Rate constants are reported and discussed for several substitutions of inorganic complexes in ethylene carbonate (1,3-dioxolan-2-one) + water and in propylene carbonate (4-methyl-1,3-dioxolan-2-one) + water solvent mixtures. The reactions include aquation ofcis- and oftrans-[Co(en)₂Cl₂]⁺, aquation oftrans-[Cr(OH₂)₄Cl₂]⁺, bromide substitution at [Pd(Et₄dien)Cl]⁺, thiourea substitution atcis-[Pt(4-NCpy)₂Cl₂], and aquation and cyanide attack at [Fe(X-phen)₃]²⁺ cations.     

Nature et stabilité des complexes métalliques de cryptands dinucléants en solution. III. Le monocycle [22]-Py2N4

Nature and Stability of Some Metallic Complexes of Dinucleating Cryptands in Solution III. The Monocycle [22]-Py₂N₄ The nature and stability of complexes formed by a new 22-membered monocycle L = [22]-Py₂N₄ with the cations Mⁿ⁺ = Cu²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Pb²⁺, and Ag⁺ have been determined in aqueous solutions (0.01M NaClO₄, 25°) by pH-metry and also, for the copper system, by UV-absorption spectrophotometry. The stepwise protonation constants of the four amine functions of L were 9.1, 8.3, 7.1 and 3.7 logarithms units, respectively. No evidence was found for the protonation of the two pyridine nitrogen atoms. Mononuclear complexes MLⁿ⁺ were identified in all systems investigated, but the dinuclear species M₂L²ⁿ⁺ were only found with Cu²⁺ and Ag⁺. The logarithms of the overall stability constants for the copper and silver complexes are CuL²⁺, 12.9; Cu₂L⁴⁺, 18.6; Agl⁺, 6.3; Ag₂L²⁺, 10.9, respectively. Mononuclear hydroxy species MLOH^(n?1)+ were identified in all systems except those of copper and silver. No dinuclear hydroxy complexes were detected. The complexing properties of L are compared to those of the large and less rigid bis-dien.     

Complexation Studies of Bidentate Heterocyclic N-Donor Ligands with Nd(III) and Am(III)

A new bidentate nitrogen donor complexing agent that combines pyridine and triazole functional groups, 2-((4-phenyl-1H-1,2,3-triazol-1-yl)methyl)pyridine (PTMP), has been synthesized. The strength of its complexes with trivalent americium (Am³⁺) and neodymium (Nd³⁺) in anhydrous methanol has been evaluated using spectrophotometric techniques. The purpose of this investigation is to assess this ligand (as representative of a class of similarly structured species) as a possible model compound for the challenging separation of trivalent actinides from lanthanides. This separation, important in the development of advanced nuclear fuel cycles, is best achieved through the agency of multidentate chelating agents containing some number of nitrogen or sulfur donor groups. To evaluate the relative strength of the bidentate complexes, the derived constants are compared to those of the same metal ions with 2,2′-bipyridyl (bipy), 1,10-phenanthroline (phen), and 2-pyridin-2-yl-1H-benzimidazole (PBIm). At issue is the relative affinity of the triazole moiety for trivalent f element ions. For all ligands, the derived stability constants are higher for Am³⁺ than Nd³⁺. In the case of Am³⁺ complexes with phen and PBIm, the presence of 1:2 (AmL₂) species is indicated. Possible separations are suggested based on the relative stability and stoichiometry of the Am³⁺ and Nd³⁺ complexes. It can be noted that the 1,2,3-triazolyl group imparts a potentially useful selectivity for trivalent actinides (An(III)) over trivalent lanthanides (Ln(III)), though the attainment of higher complex stoichiometries in actinide compared with lanthanide complexes may be an important driver for developing successful separations.     

Thermodynamic behavior of complexation of 18-crown-6 with Tl<Superscript>+</Superscript>, Pb<Superscript>2+</Superscript>, Hg<Superscript>2+</Superscript>, and Zn<Superscript>2+</Superscript> metal cations in methanol-water binary media

The equilibrium constants and thermodynamic parameters for complex formation of 18-Crown-6 (18C6) with Tl⁺, Pb²⁺, Hg²⁺, and Zn²⁺ metal cations have been determined by conductivity measurements in methanol (MeOH)-water (H₂O) binary solutions. 18-Crown-6 forms 1:1 complexes with Hg²⁺ and Zn²⁺ cations, but in the case of Tl⁺ and Pb²⁺ cations, in addition to 1:1 stoichiometry, 1:2 (ML₂) complexes are formed in some binary solvents. The thermodynamic parameters (ΔH _c⁰ and ΔS _c⁰), which were obtained from the temperature dependences of equilibrium constants, show that in most cases the complexes are enthalpy destabilized but entropy stabilized. Non-linear behavior is observed between the equilibrium constants (log K _f ) of complexes and the composition of the mixed solvent. The selectivity of the ligand for these metal cations is sensitive to the solvent composition, and, in some cases, the selectivity order is reversed in certain compositions of the mixed solvent. The results also show that the mechanism of complexation reactions and the stoichiometry of complexes of some metal cations change with the nature and even with the composition of the mixed solvent. The article was submitted by the authors in English.     

Insertion of cations into WO<Subscript>3</Subscript> investigated by QCM techniques

The electrochemical insertion of Li⁺, Na⁺, and hydrogen ions into thin layers of WO₃ was investigated with the help of an electrochemical quartz crystal microbalance. Solutions of perchlorates in propylene carbonate were used as electrolytes, and the first cycle of coloration/discoloration cycles was studied. In both cases, insertion of cations was accompanied by a massive and partly irreversible uptake of the solvent in a molar ratio from 1:1 to 1:2 (ion vs solvent). The insertion of Na was observed for the first time. Molecules of water coinserted with H⁺ indicated that the inserted species is H₃O⁺ rather than merely a proton H⁺. Very small but observable insertion of Mg²⁺ from perchlorate/PC solution proceeded in a marginal but observable extent from ClO₄ ^-/PC solution.     

Solvation environment of lithium ion in a LiBF<Subscript>4</Subscript>–propylene carbonate system in the presence of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid studied by NMR and quantum chemical modeling

Solutions of lithium and 1-ethyl-3-methylimidazolium tetrafluoroborates ([emim][BF₄]) in propylene carbonate (PC) were studied by the high-resolution NMR method on ¹H, ⁷Li, ¹¹B, ¹³C, and ¹⁹F nuclei. The degree of solvation of lithium ions was determined by measuring selfdiffusion coefficients by pulse-field-gradient spin echo NMR method on ¹H, ⁷Li, and ¹⁹F nuclei. The hydrodynamic radii of solvated Li⁺ cations were estimated by the Stokes–Einstein equation. The model structures of the solvation complexes of Li⁺ ion with propylene carbonate molecules and BF ₄ ^– anion and their associates with ionic liquid components were calculated in terms of the density function theory. The calculated values of the chemical shifts were compared with the experimental data. PC molecules were predominantly bound to the Li⁺ cation, while LiBF₄–[emim][BF₄]–PC (1: 4: 4) electrolyte had a maximum conductivity of 9.5 mS cm^–1 at 24 °С compared to the compositions of a lower content of the solvent.     

碱金属碘化物与冠醚或穴醚的配合物中I3-和I-的氧化还原行为及其在染料敏化纳米薄膜太阳电池中的应用研究

本文利用超微铂电极和循环伏安法研究了在碱金属碘化物与冠醚或穴醚配合物的3-甲氧基丙腈(MePN)溶液中I₃^-和I^-的氧化还原行为。发现I₃^-和I^-在其中的表观扩散系数与阳离子有关，且I₃^-的表观扩散系数符合以下规律：1,2-二甲基-3-丙基咪唑阳离子(DMPI⁺)> [Na(¯¯15-C-5]⁺ > [K(¯¯18-C-6]⁺ > [Na(¯¯2.2.1-cryptand]⁺，I^-的表观扩散系数则为：[Na(¯¯2.2.1-cryptand]⁺> [Na(¯¯15-C-5]⁺ ≈[K(¯¯18-C-6]⁺> DMPI⁺。比较了由上述配合物和1,2-二甲基-3-丙基咪唑碘(DMPII)组成的染料敏化纳米薄膜太阳电池(DSC)的光伏性能，结果表明由上述配合物组成的DSC，其短路电流略高于DMPII，填充因子略低于DMPII，这与I^-和I₃^-在其中的表观扩散系数的大小是相一致的。此外，电解质溶液中的溶剂对DSC的光电转换效率也有较大影响，以MePN为溶剂，含DMPII的DSC的光电转换效率要高于[K(¯¯18-C-6]I，而以乙腈为溶剂，两者的光电转换效率并没有明显的差别。     

Relation between stability constants of metal ion cryptates in two solvents and the transfer activity coefficients of the metal ions

The extrathermodynamic assumption of Lejaille and Bessière that _1,2 log K (LM ⁿ⁺ )=–G _tr (M ⁿ⁺ ) in which K is stability constant and L is cryptand 2.2.2, 2 _B 2 _B 2, 2.2.1, or 2.1.1 has been tested in dipolar aprotic solvents for M ⁿ⁺ being Li⁺, Na⁺, K⁺, Ag⁺, Tl⁺, and Ba²⁺. The relation has been found generally acceptable for the dipolar aprotic solvents propylene carbonate, acetonitrile, N,N-dimethylformamide and dimethylsulfoxide, provided the size of the ion is equal to or smaller than the cavity of the cryptand. The relation does not hold for the hydrogen bonded donating solvents, water, and methanol.     

Electrochemistry of macrocyclic complexes of alkaline cations: Part IV. Reduction of (mnp,K)+ cryptates

The reductions of five macrobicyclic potassium cryptates (ligands (322), (222), (221), (22 C₈), (211)) and two macromonocyclic potassium complexes (ligands (22) and (18 crown 6)) are studied by polarography, coulometry and cyclic voltammetry in propylene carbonate (PC). The mechanism and the parameters of the electrochemical reduction are discussed in terms of dependence upon three important features of the macrocyclic ligands: the size of the intramolecular cavity, the number of oxygen heteroatoms in the ligand, and the number of “branches” in the ligand (cryptate effect). The electrochemical results are consistent with the other known physicochemical parameters of these complexes. The electroreduction behaviour might allow the structure and the stability constant of alkaline cryptates in a given medium (PC) to be approximated. Reciprocally, these physicochemical characteristics may lead to a rather precise prediction of the electrochemical behaviour of the corresponding macrocyclic complexes.