Etude par RMN. de polyaminocarboxylates de terres rares,II. Nitrilotriacétates de scandium,yttrium, lanthane et lutécium

Proton nuclear magnetic resonance has been used to study the chemistry of the diamagnetic nitrilotriacetate complexes of scandium, yttrium, lanthanum and lutecium in aqueous solution. Complexes with ligand-to-metal ratios of 1 and 2 are present depending of the solution conditions. The ligand exchanges by spontaneous and by acid catalysed dissociation of the metal-bis-nitrilotriacetate, and also by a bimolecular process involving the free ligand and the complex. The ligand exchange rate constants decrease with the ionic radii:lanthanum > yttrium > lutecium > scandium.     

Stabilité des carboxylates de terres,III. Maléates,méthylsuccinates et malates

The stability constants of maleates, methylsuccinates and malates of rare earths have been determined at 25.0 °C and at ionic strength 0,100 (NaClO₄) by a potentiometric method. Each ligand forms 1 : 1 and 1 : 2 complexes in aqueous solution, the malates being the most stable. The first and the second dissociation constants of the ligand acids were also measured. The 1 : 2 maleates of La, Pr, Nd, Sm, and Eu have been isolated.     

Stabilité des carboxylates de terres rares,II. Bis-hydroxyméthyl-2,2-propionates

The stability constants of 2, 2-bis-hydroxymethyl-propionates of rare earths have been determined at ionic strength 0,100 (NaClO₄) at 25.0°C by a potentiometric method. The ligand forms 1 : 1 and 1 : 2 complexes with all the rare earths and weak 1 : 3 complexes with light rare earths only. In these last complexes, it binds in a unidentate way. The dissociation constant of the acid has also been measured.     

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.     

Obtention de phosphore élémentaire et de phosphures de nickel par électrolyse de solutions de pentoxyde de phosphore dans des bains à base de cryolithe

By electrolysis of cryolitic solutions of P₂O₅, elementary pure phosphorus is obtained on carbon cathode and Ni phosphides on Ni cathode. The most probable mechanism of phosphorus formation in these conditions seems to be the final dissociation of P₂O₅ in P⁵⁺ and O^2? and the primary electrodic discharge of these ions.     

Détermination de constantes de stabilité de chélates par résonance magnétique nucléaire du proton

In a solution containing an excess of two metal ions in regard to a ligand (e.g. NTA) a competitive equilibrium is established. The measure, by proton NMR. spectroscopy, of the individual concentrations of both chelates, and eventually of the free ligand, allows to determine the ratio of the stability constants of the two complexes. As an illustration the ratios of the stability constant of the 1:1 nitrilotriacetate chelates of Pb and Zn, respectively Mo and W, were determined.     

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.     

Transition metals as electron traps. II. Structures,energetics and electron transfer dissociations of ternary Co,Ni and Zn–peptide complexes in the gas phase

Transition metal cations Co²⁺, Ni²⁺ and Zn²⁺ form 1 : 1 : 1 ternary complexes with 2,2′‐bipyridine (bpy) and peptides in aqueous methanol solutions that have been studied for tripeptides GGG and GGL. Electrospray ionization of these solutions produced singly charged [Metal(bpy)(peptide ? H)]⁺ and doubly charged [Metal(bpy)(peptide)]²⁺ ions (Metal = metal ion) that underwent charge reduction by glancing collisions with Cs atoms at 50 and 100 keV collision energies. Electron transfer to [Metal(bpy)(peptide)]²⁺ ions was less than 4.2 eV exoergic and formed abundant fractions of non‐dissociated charge‐reduced intermediates. Charge‐reduced [Metal(bpy)(peptide)]⁺ ions dissociated by the loss of a hydrogen atom, ammonia, water and ligands that depended on the metal ion. The Ni and Co complexes mainly dissociated by the elimination of ammonia, water, and the peptide ligand. The Zn complex dissociated by the elimination of ammonia and bpy. A sequence‐specific fragment was observed only for the Co complex. Electron transfer to [Metal(bpy)(peptide ? H)]⁺ was 0.6–1.6 eV exoergic and formed intermediate radicals that were detected as stable anions after a second electron transfer from Cs. [Metal(bpy)(peptide ? H)] neutrals and their anions dissociated by the loss of bpy and peptide ligands with branching ratios that depended on the metal ion. Optimized structures for several spin states, electron transfer and dissociation energies were addressed by combined density functional theory and Møller–Plesset perturbational calculations to aid interpretation of experimental data. The experimentally observed ligand loss and backbone cleavage in charge‐reduced [Metal(bpy)(peptide)]⁺ complexes correlated with the dissociation energies at the present level of theory. The ligand loss in ⁺CR^? spectra showed overlap of dissociations in charge‐reduced [Metal(bpy)(peptide ? H)] complexes and their anionic counterparts which complicated spectra interpretation and correlation with calculated dissociation energies. Copyright © 2009 John Wiley & Sons, Ltd.     

Etude cinétique des effets de fluence énergétique,de débit de fluence,et d'effacement induits par des ions lourds et des photons γ dans le triacétate de cellulose

The kinetic interpretation of the damage produced by heavy ions (Kr and Cl from 1 MeV/amu) and γ radiation in cellulose triacetate leads to an exponential dependence on the ion fluence. A comparison of the fading effect produced by heavy ions and γ rays shows that the heavy ions, unlike γ rays, cause irreversible damage. Finally, a nonlinear dependence on the flux of ions and γ rays is found in the kinetics of radiation damage. This result is contrary to the usual assumption that heavy-ion flux, like γ-ray flux, is additive, at least for the fluxes of 10⁹?2 × 10¹⁰ ions/cm²s and dose rates of 10³–10⁴ Gy/h used in this work.     

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.     

Influence of the conformers of the ligand 2-methylamino-1-phenylpropan-1-ol (HA) in the complexes (H<Subscript>2</Subscript>A)<Subscript>2</Subscript>[PdCl<Subscript>4</Subscript>] on their state in solutions and their biological activity

The systems Pd(II)-Cl^?-HA-H₂O (where HA are the conformers of 2-methylamino-1-phenylpropan-1-ol) were studied. The acid dissociation constants of the ligands HA and the resulting complexes were determined by pH-metric titration and mathematical modeling. The pH-distribution diagram of the complex species in the system containing different HA conformers was obtained. The complexes (H₂A)₂[PdCl₄] were obtained and structurally characterized; their toxicity and radioprotective effects were estimated. The biological activity of the complexes was found to depend on both the ligand basicity and the hydrogen bonding system formed by different conformers of the ligand in the cation-anion complexes.     

Etude par RMN du proton de la complexation du triéthylaluminium par l'éther diéthylique

The complex between triethylaluminium and diethylether has been studied by ¹H NMR; separate signals have been observed for free and bonded triethylaluminium. From the area ratios, a 1:1 stoichiometry is demonstrated. At higher ether concentrations, chemical shift measurements prove that other complexes do not appear.     

Complete Photochromic Structural Changes in Ruthenium(II)?Diimine Complexes,Based on Control of the Excited States by Metalation

The thermal and photochemical reactions of a newly synthesized complex, [Ru^II(TPA)(tpphz)]²⁺ ( 1 ; TPA=tris(2‐pyridylmethyl)amine, tpphz=tetrapyrido[3,2‐a:2′,3′‐c:3′′,2′′‐h: 2′′′,3′′′‐j]phenazine), and its derivatives have been investigated. Heating a solution of complex 1 (closed form) and its derivatives in MeCN caused the partial dissociation of one pyridylmethyl moiety of the TPA ligand and the resulting vacant site on the Ru^II center was occupied by a molecule of MeCN from the solvent to give a dissociated complex, [Ru^II(η³‐TPA)(tpphz)(MeCN)]²⁺ ( 1′ , open form), and its derivatives, respectively, in quantitative yields. The thermal dissociation reactions were investigated on the basis of kinetics analysis, which indicated that the reactions proceeded through a seven‐coordinate transition state. Although the backwards reaction was induced by photoirradiation of the MLCT absorption bands, the photoreaction of complex 1′ reached a photostationary state between complexes 1 and 1′ and, hence, the recovery of complex 1 from complex 1′ was 67 %. Upon protonation of complex 1 at the vacant site of the tpphz ligand, the efficiency of the photoinduced recovery of complex 1 +H⁺ from complex 1′ +H⁺ improved to 83 %. In contrast, dinuclear μ‐tpphz complexes 2 and 3 , which contained the Ru^II(TPA)(tpphz) unit and either a Ru^II(bpy)₂ or Pd^IICl₂ moiety on the other coordination edge of the tpphz ligand, exhibited 100 % photoconversion from their open forms into their closed forms ( 2′ → 2 and 3′ → 3 ). These results are the first examples of the complete photochromic structural change of a transition‐metal complex, as represented by complete interconversion between its open and closed forms. Scrutinization by performing optical and electrochemical measurements allowed us to propose a rationale for how metal coordination at the vacant site of the tpphz ligand improves the efficiency of photoconversion from the open form into the closed form. It is essential to lower the energy level of the triplet metal‐to‐ligand charge‐transfer excited state (³MLCT*) of the closed form relative to that of the triplet metal‐centered excited state (³MC*) by metal coordination. This energy‐level manipulation hinders the transition from the ³MLCT* state into the ³MC* state in the closed form to block the partial photodissociation of the TPA ligand.     

Acid Catalyzed Dissociation of 4‐Aminopyridine Complex of Pentacyanoferrate (II)

Fe(CN)₅ampy^3? (ampy = 4‐aminopyridine) complex was unstable at pH ≤ 4 with respect to the dissociation due to the protonations of the complex. The first protonation on the 4‐aminopyridine ligand at pK_a = 3.2 resulted in a ? 150‐fold in crease in rate of dissociation as compared to that of the complex in the neutral solution. However, further protonation of the complex on the cyanide ligand at pK_a = 1.5 in creased the rate only slightly. The large in crease in the rate constant of dissociation for Fe(CN)₅ampyH^2? complex suggests that in the transition state the proton is likely shifted from the amino group and becomes coordinated to a pair of dπ electrons directed at the face of the coordinated octahedron.     

Gas‐Phase Energetics of Reductive Elimination from a Palladium(II) N‐Heterocyclic Carbene Complex

Energy‐resolved collision‐induced dissociation experiments using tandem mass spectrometry are reported for an phenylpalladium N‐heterocyclic carbene (NHC) complex. Reductive elimination of an NHC ligand as a phenylimidazolium ion involves a barrier of 30.9(14) kcal mol^?1, whereas competitive ligand dissociation requires 47.1(17) kcal mol^?1. The resulting three‐coordinate palladium complex readily undergoes reductive C? C coupling to give the phenylimidazolium π complex, for which the binding energy was determined to be 38.9(10) kcal mol^?1. Density functional calculations at the M06‐L//BP86/TZP level of theory are in very good agreement with experiment. In combination with RRKM modeling, these results suggest that the rate‐determining step for the direct reductive elimination process switches from the C? C coupling step to the fragmentation of the resulting σ complex at low activation energy.     

Étude spectrophotométrique UV. de solutions diluées de chromate dans l'acide sulfurique concentré

Dilute solutions ( < 1· 10^?4M ) of CrO₄K₂ in concentrated sulfuric acid, were investigated spectrophotometrically. Spectral, kinetic and equilibrium studies confirm the instability of Cr^VI species and their conversion to Cr^V complexes, as proposed by MISHRA & SYMONS . Reaction mechanisms are proposed.     

Composés d'addition des halogénures de niobium(V) et de tantale(V). V. Stabilité relative des composés des chlorures avec quelques oxydes et sulfures organiques

The adducts of niobium(V) and tantalum(V) chlorides with some aliphatic and cyclic oxides and sulfides, studied by NMR. spectroscopy in CHCl₃, are found to have 1:1 stoechiometry, at room temperature and lower. In the thioxane complex TaCl₅ · C₄H₈OS two species are present with the ligand coordinated by the sulfur atom or by the oxygen atom, respectively, in a proportion which has been determined. The thioxane adduct of niobium(V) chloride, however, is preferentially coordinated by the sulfur atom. There is also evidence for the species 2MCl₅ · C₄H₈OS. The relative basicity of each donor atom in dioxane, thioxane and dithiane is calculated and discussed. In contrast to the nitrile adducts, whose stability was found earlier to be controlled by inductive factors, the steric factors are more important for the ether and sulfide adducts: MCl₅ · Me₂X is more stable than the corresponding MCl₅ · Et₂X (M = Nb, Ta; X = O, S). Both niobium(V) and tantalum(V) chlorides have a soft behaviour, but NbCl₅ is a weaker Lewis acid than TaCl₅ and shows also a softer behaviour.     

Über Reaktionen oxygenierter Kobalt(II)-Komplexe. V. Reaktivität diastereoisomerer μ-Peroxo-μ-hydroxo-dikobalt(III)-Ionen

On Reactions of oxygenated Cobalt(II) Complexes. V. Reactivity of diastereoisomeric μ-peroxo-μ-hydroxo-dicobalt(III) Ions The kinetics of dissociation of μ-peroxo-μ-hydroxo-dicobalt(III) chelates have been reinvestigated using a stopped flow technique. The binuclear cations [(trien)Co(O₂, OH) Co(trien)]³⁺, [(tren)Co(O₂, OH)Co(tren)]³⁺ and [(en)₂Co(O₂, OH)Co(en)₂]³⁺ dissociate on acidifying to Co²⁺ and the protonated ligand and up to 100% of the bound O₂ is evolved. The dissociation is H⁺-catalyzed and first order in complex. The observed rate constants at pH 2 are in the range of 10^?3 to 10^?1 s^?1 (20°). They depend not only on the nature of the ligand and on ligand configuration but also on the diastereoisomeric structure of the binuclear cation. In the case of trien there are 8 possible chemically different isomers. On oxygenation of Co(trien)²⁺ in dilute solution 3 of those isomers seem to be formed preferentially. Their rate constants are separated over a factor of 50. For [(en)₂ Co(O₂, OH)Co(en)₂]³⁺ there exist a meso form and a chiral structure. On oxygenation of Co(en)₂²⁺ in dilute solution the meso form and the racemate are formed to about equal amounts. The racemate dissociates about 5 times slower. Of the 3 possible achiral isomers of [(tren)Co(O₂, OH)Co(tren)]³⁺ one is formed stereoselectively by oxygenation in solution.     

Etude par Résonance Magnétique Nucléaire du carbone 13 de complexes du cobalt (III) et de la diméthylglyoxime

From a carbon magnetic resonance study of several alkylcobaloximes RCo(DMG)₂B (DMG = dimethylglyoximate monoanion), it was possible to estimate the α, β and γ effects of the Co(DMG)₂B group on the chemical shifts of the carbon atoms of various alkyl groups R. The chemical shifts of the carbon atoms belonging to the equatorial ligands and to the axial base B are not significantly affected by structural modification of the R groups. Values of δ in benzylcobaloximes XC₆H₄CH₂Co(DMG)₂B agree with a donor effect of the ? CH₂Co(DMG)₂B radical. Values of ¹J(¹³C? H) coupling constants, measured in ¹³C enriched methylcobaloximes, do not vary appreciably when B is changed (J(¹³C? H) = 137 ± 1 Hz) and are close to the value obtained for methylcobalamine.     

Chromium(III) complexes with lutidinic acid: kinetic studies in HClO<Subscript>4</Subscript> and NaOH solutions

Chromium(III)-lutidinato complexes of general formula [Cr(lutH) _n (H₂O)_6−2n ]³⁻ⁿ (where lutH⁻ is N,O-bonded lutidinic acid anion) were obtained and characterized in solution. Acid-catalysed aquation of [Cr(lutH)₃]⁰ leads to only one ligand dissociation, whereas base hydrolysis produces chromates(III) as a result of subsequent ligand liberation steps. The kinetics of the first ligand dissociation were studied spectrophotometrically, within the 0.1–1.0 M HClO₄ and 0.4–1.0 M NaOH range. In acidic media, two reaction stages, the chelate-ring opening and the ligand dissociation, were characterized. The dependencies of pseudo-first-order rate constants on [H⁺] are as follows: k _obs1 = k ₁ + k ₋₁/K ₁[H⁺] and k _obs2 = k ₂ K ₂[H⁺]/(1 + K ₂[H⁺]), where k ₁ and k ₂ are the rate constants for the chelate-ring opening and the ligand dissociation, respectively, k ₋₁ is the rate constant for the chelate-ring closure, and K ₁ and K ₂ are the protonation constants of the pyridine nitrogen atom and coordinated 2-carboxylate group in the one-end bonded intermediate, respectively. In alkaline media, the rate constant for the first ligand dissociation depends on [OH⁻]: k _obs1 = k _OH(1) + k _O[OH⁻], where k _OH(1) and k _O are rate constants of the first ligand liberation from the hydroxo- and oxo-forms of the intermediate, respectively, and K ₂ is an equilibrium constant between these two protolytic forms. Kinetic parameters were determined and a mechanism for the first ligand dissociation is proposed. The kinetics of the ligand liberation from [Cr(lut)(OH)₄]³⁻ were also studied and the values of the pseudo-first-order rate constants are [OH⁻] independent.