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 des carboxylates de terres rares I Furanne- et thiophène-carboxylates-2

The stability constants of 2-furanecarboxylates and 2-thiophencarboxylates of some rare earths have been determined at ionic strength 0.100 (NaClO₄) at 25.0°C by a potentiometric method. The ligands form 1 : 1 complexes similar to the rare earths propionates.     

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.     

Sur la séparation des terres rares XIII. Systèmes de solubilité comprenant des chlorures de terres cériques [1]

In aqueous solution, the chlorides of lanthanum, cerium and praseodymium cristallize as heptahydrates, those of the other rare earth elements as hexahydrates. Therefore, a miscibility gap exists in the solid phases in all systems comprising the two types of chlorides. Five ternary systems and a quaternary one with this behaviour have been studied.     

Les fluoronitrures de terres rares

The reaction of rare-earth nitrides with fluorides or the pyrolysis of these fluorides in gaseous ammonia atmosphere leads, in the case of lanthanum, cerium, and gadolinium, to nitride fluorides of general formula LnN_xF_3?3x. They crystallize with a fluorite-type structure which can be described in a consistent manner in terms of a Willis model. The magnetic properties of Gd₃NF₆ have been studied.     

Etude par RMN. de polyaminocarboxylates de terres rares,III. Hydroxyéthyliminodiacétates de praséodyme

¹H—NMR. has been used to study the chemistry of the hydroxyethyliminodiacetate complexes of praseodymium in aqueous solution. The ligand exchanges by spontaneous dissociation of the metal-bis-hydroxyethyliminodiacetate (1:2 complex) and of the metal-bis-hydroxyethyliminodiacetate hydroxocomplex, by acid catalysed dissociation of the 1:2 complex, and by a bimolecular process involving the free ligand and the 1:2 complex or the ternary hydroxo-complex. The ligand exchange rate constants are given and the mechanisms discussed.     

Tris-hexafluoropropyl-2-ates de terres rares

Tris-hexafluoro-2-propoxides of yttrium, lanthanum, neodymium and erbium have been prepared, by the ammonia method, directly from the hydrated rare earth chlorides, dehydrated in situ by trimethyl orthoformate. The compounds are not volatile.     

Séparation des terres rares par chromatographie sur échangeurs d'ions. I. Technique de l'éluant tamponné

A displacement chromatography technique is described for the separation of rare earths using the eluent ethylene-diaminetetraacetate buffered by ammonium acetate to have a determined pH in the separation columns. This method gives concentrations up to 20 g pure rare earth oxides per liter of eluate.     

Photochimie d'hétérocycles azotés. IV. Transposition de type photo-fries des N-acétyl benzimidazolones

The photolysis of benzene or alcoholic solutions of N-acetyl-and N,N-diacetylbenzimidazolones gave mixtures of ortho- and para-rearrangements products accompanied to some extent with de-N-acylation. The different products have been identified by means of nmr, mass spectrometry and unambiguous synthesis.     

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.     

Sur de nouveaux composés oxyfluorés des terres rares de structure pyrochlore

The action of NaF on rare earth oxides with the columbite or aeschynite structure leads to pyrochlore-type phases of formula NaTTiNbO₆F (T = Y, Ce, …, Yb). On the other hand, the substitution of cadmium by a rare earth and of oxygen by fluorine in T₂Ti₂O₇ gives isostructural phases of formula CdTTI₂O₆F (T = Y, Nd … Yb). The dielectric properties of the solid solutions between both phases and Cd₂Nb₂O₇ characterize ferroelectric-paraelectric transitions. The substitution of oxygen by fluorine brings about a decrease in the Curie temperature, but a very small substitution rate increases the dielectric constant and the spontaneous polarization.     

Composés d'addition des chlorures de terres rares avec le méthanol,l'éthanol et le propanol-2. Préparations,solubilités et réactions de transsolvatation

By reaction of hydrated rare earths chlorides (M = La, Nd, Sm, Gd, Dy, Er, Yb, Y) with orthoformates, the following adducts have been prepared: MCl₃· 4MeOH, MCl₃ ·3EtOH (M = La, Nd, Sm, Gd, Yb), MCl₄ · 4 EtOH (M = Dy, Er, Y); adducts MCl₃ · 3iso-PrOH have been prepared by successive action of methyl orthoformate and of 2-propanol. The solubilities of these adducts in the corresponding alcohols at 25° (for the lanthanum adducts equally at 0 and 50°) are given. Two examples of the transsolvatation of these compounds, yielding adducts with weakligands, are described.     

Séparation des terres rares par chromatographie sur échangeurs d'ions II. Séparation et analyse de la paire europium-gadolinium [1]

A displacement chromatography technique is described for the separation of europium and light rare earths using the eluent ethylene-diaminetetraacetate buffered by ammonium acetate giving a determined pH in the separation columns. This method gives concentrations up to 20 g of pure rare earth oxides per liter of eluate. A chromatographic method of analysis of europium in presence of other rare earths is also described.     

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

The relative stability constants of the adducts of MCl₅ (M ? Nb, Ta) with acetonitrile, halogenoacetonitriles, pivalonitrile, acrylonitrile and benzonitriles are determined in dilute solutions by NMR. methods. The stability of the adducts is controlled by inductive factors. Chemical shifts and analysis of the new compounds are reported.     

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.     

Etudes sur les composés organométalliques IV [1] Stabilité et nature des liaisons de quelques complexes organostanniques

The complexes between different diorganotin cations and substituted 1, 10-phenanthrolines in aqueous solution containing acetate ion have been investigated. Diorganotin cations can co-ordinate two acetate ions. One of these may be replaced by a 1, 10-phenanthroline derivative. A comparison of the different equilibrium constants shows that the acid hardness of diorganotin cations is markedly modified if the organic groups bound to the tin are α,β-unsaturated.     

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.     

Étude par spectrométrie infra-rouge des complexes des terres rares avec l'oxyde de tri-n-butylphosphine á l'état solide

Tri-n-butylphosphine oxide (TBPO) reacts with rare earth nitrates to form complexes of general formula Me(NO₃)₃·3 TBPO. These complexes were studied by infrared spectrometry. The coordination of the nitrates is not the same along the lanthanide series. They are bidentate for the light rare earths and monodentate for the heavy earths. The P=O frequency does not vary monotonously when Z increases; there is a break for gadolinium. This is explained by an influence of backbonding, the decrease of the ionic radius and the coordination number.     

Détermination des chaleurs de formation des orthovanadates de certains éléments des terres rares par la méthode d'analyse thermique différentielle

The heats of formation of LnVO₄-type salts (whereLn=Y, La, Sm, Nd, Gd and Dy) were determined by thermal analysis in the reactions of melts of stable lanthanides and V₂O₅ in a 1 ∶ 1 mole ratio. Heats of formation of LnVO₄-type salts can be determined using non-stoichiometric mixtures of the substrates as well. With the aid of DTA the apparent activation energies of the syntheses of the orthovanadates of these lanthanides were calculated.