Ternary Chlorides of the Trivalent Early Lanthanides. Phase diagrams,crystal structures and thermodynamic properties

A comprehensive review on phase diagrams, crystal structures and thermodynamics of ternary chlorides formed in systems ACl/LnCl₃ (A=Cs, Rb, K, Na; Ln=La−Gd) is presented. The review summarizes the author’s own studies, published since 1985, and original papers of other scientists. With the larger alkali metal ions compounds such as A₃LnCl₆, A₂LnCl₅ and ALn₂Cl₇were obtained. With sodium additional compounds NaLnCl₄ and Na₃Ln₅Cl₁₈ were obtained. The crystal structures are discussed with the concept of ionic radii, which determine the coordination numbers of Ln³⁺ and A⁺ cations against Cl⁻ anions. The formation enthalpies of the compounds from ACl and LnCl₃ were determined by solution calorimetry. Gibbs’ free energies and entropies for these reactions were obtained by e.m.f. measurements vs. temperature. The stability of a ternary chloride in a systemACl−LnCl₃ is given by the ‘free enthalpy of synproportionation’, that is, the formation of a compound from its neighbour compounds in the system. This ΔG ⁰ _syn must be negative. A surprising result is, that the highest-melting compounds in the systems, A₃LnCl₆, are formed from ACl+A₂LnCl₅ by a loss in lattice energy. They exist as high-temperature compounds due to sufficiently high gain in entropy at temperatures whereTΔS>ΔH. This revised version was published online in August 2006 with corrections to the Cover Date.     

Interaction of Thulium,Ytterbium(III) and Lutetium Chlorides with Sodium Chloride

The pseudobinary systems NaCl—LnCl₃ (Ln=Tm, Yb, Lu) were investigated by DTA and X-ray diffraction. Two types of ternary chlorides exist: congruently melting compounds Na₃LnCl₆ with the cryolite-structure, incongruently melting compounds NaLnCl₄ with the NaErCl₄-Ln (Ln=Tm) or the NaLnCl₄-structure (Ln=Yb, Lu). All these structure types contain [LnCl₆]-octahedra.By solution calorimetry and e.m.f. measurements in galvanic cells for solid electrolytes could be proved that all compounds are formed from NaCl and LnCl₃ by gain in lattice enthalpy.This revised version was published online in November 2005 with corrections to the Cover Date.     

Thermodynamic properties of dimeric molecules of lanthanum and lanthanide trichlorides Ln2Cl6(gas)

The partial pressures of dimeric molecules Ln₂Cl₆ in the saturated vapor over lanthanum and lanthanide trichlorides LnCl₃ (Ln = La, ..., Nd, Sm, Gd, ..., Lu) have been determined by high-temperature mass spectrometry. From these data, the enthalpies of the gas-phase reaction Ln₂Cl₆ = 2LnCl₃ and the enthalpies of sublimation of the compounds under consideration in the form of Ln₂Cl₆ dimers have been calculated by the third law. Analogous characteristics have also been calculated by the second and third laws from the available literature data on the partial pressures of Ln₂Cl₆ in the course of sublimation (evaporation) of LnCl₃. Taking into account typical tendencies in the standard thermodynamic characteristics of lanthanum and lanthanide compounds, a set of recommended D ₂₉₈ ⁰ (LnCl₃-LnCl₃) values has been determined. This set has been used for calculating the enthalpies of atomization Δ_at H ₂₉₈ ⁰ (Ln₂Cl₆), where Ln = La, ..., Lu.     

Ternäre Chloride in den Systemen ACl/EuCl3(A = Na?Cs)

Double Chlorides in the Systems ACl/EuCl₃ (A = Na? Cs) The phase diagrams of the pseudobinary systems ACl/EuCl₃ (A = Na? Cs) were investigated by DTA. T? and H? A₃EuCl₆ with A = Cs, Rb and T? and H? NaEuCl₄ were found in addition to other compounds already described in literature. Their powder diffractograms were indexed in analogy to known structure families. By solution calorimetry and measurements of e.m.f. = f(T) in galvanic cells for solid electrolytes the enthalpies ΔH and free enthalpies ΔG for the formation of the ternary chlorides from the compounds adjacent in the systems were determined. With KCl and NaCl only the compounds A₂EuCl₅ and NaEuCl₄ are stable at ambient temperature. Compared to the system with LnCl₃ (Ln = La? Nd) investigated previously, a tendency to structures with lower coordination numbers exists as was already detected in the systems ACl/SmCl₃.     

Synthesis and magnetic properties of ALnO2 (A=Cu or Ag; Ln=rare earths) with the delafossite structure

Synthesis, structures, and magnetic properties of ternary rare earth oxides ALnO₂ (A=Cu or Ag; Ln=rare earths) have been investigated. CuLnO₂ (Ln=La, Pr, Nd, Sm, Eu) were synthesized by the direct solid state reaction of Cu₂O and Ln₂O₃, and AgLnO₂ (Ln=Tm, Yb, Lu) were obtained by the cation-exchange reaction of NaLnO₂ and AgNO₃ in a KNO₃ flux. These compounds crystallized in the delafossite-type structure with the rhombohedral 3R type (space group: R-3m). Magnetic susceptibility measurements showed that these compounds are paramagnetic down to 1.8 K. Specific heat measurements down to 0.4 K indicated that CuNdO₂ ordered antiferromagnetically at 0.8 K.     

Ternäre Chloride in den Systemen ACl/DyCl3 (A = Cs,Rb, K)

Ternary Chlorides in the Systems ACl/DyCl₃ (A = Cs, Rb, K) The phase diagrams of the pseudobinary systems ACl/DyCl₃ (A = Cs, Rb, K) were investigated by DTA. With all alkali metals compounds A₃DyCl₆ (elpasolite family) and Ady₂Cl₇ are formed. Compounds A₂DyCl₅ exist only with Cs (Cs₂DyCl₅-type) and K (K₂PrCl₅-type). By solution calorimetry the formation enthalpies of the ternary chlorides from (nACl + DyCl₃) were measured and ‘synproportionation enthalpies’ for the formation from the compounds, adjacent in the phase diagrams, calculated. K₃DyCl₆ is the only compound, which is formed with a loss in lattice enthalpy. E.m.f. measurements in dependence on the temperature have revealed that, as for the other compounds A₃DyCl₆, a remarkable gain in entropy exists, which stabilizes K₃DyCl₆ at T ≧ 312 K. This entropy gain correlates with the existence of isolated DyCl₆^3? octahedra.     

Formation Thermodynamics of Binary and Ternary Lanthanide(III) Complexes with 1,10-Phenanthroline and Chloride in N,N-Dimethylformamide

Formation thermodynamics of binary and ternary lanthanide(III) (Ln = La, Ce, Nd, Eu, Gd, Dy, Tm, Lu) complexes with 1,10-phenanthroline (phen) and the chloride ion have been studied by titration calorimetry and spectrophotometry in N,N-dimethyl-formamide (DMF) containing 0.2 mol-dm^–3 (C₂H₅)₄NClO₄ as a constant ionic medium at 25°C. In the binary system with 1,10-phenanthroline, the Ln(phen)³⁺ complex is formed for all the lanthanide(III) ions examined. The reaction enthalpy and entropy values for the formation of Ln(phen)³⁺ decrease in the order La > Ce > Nd, then increase in the order Nd < Eu < Gd < Dy, and again decrease in the order Dy > Tm > Lu. The variation is explained in terms of the coordination structure of Ln(phen)³⁺ that changes from eight to seven coordination with decreasing ionic radius of the metal ion. In the ternary Ln³⁺-Cl^–-phen system, the formation of LnCl(phen)²⁺, LnCl₂(phen)⁺, and LnCl₃(phen) was established for cerium(III), neodymium(III), and thulium(III), and their formation constants, enthalpies, and entropies were obtained. The enthalpy and entropy values are also discussed from the structural point of view.     

Ternary molybdenum(III) chlorides

The phase diagrams of ACl/MoCl₃ (A=Na, K, Rb, Cs) were elucidated by DTA measurements in sealed quartz ampoules in the range of 0–40 mol% MoCl₃. The samples were prepared from alkali metal chlorides and the compounds A₃MoCl₆ or A₃Mo₂Cl₉. The 31 compounds withA=Na, Rb, Cs were obtained by sintering mixtures of 3ACl+MoCl₃; the enneachlorides A₃Mo₂Cl₉ withA=K, Rb, Cs were precipitated from solutions of MoCl₃·3H₂O and ACl in formic acid. Congruently melting compounds A₃MoCl₆ exist in all four systems, incongruently melting enneachlorides A₃Mo₂Cl₉ in systems withA=K, Rb, Cs. Still unknown structures were determined by analog-indexing powder patterns according to known structure families. Especially Cs₃MoCl₆ is isotypic with the recently found Cs₃CrCl₆ structure. Additionally, the unit cell parameters were determined for the compounds A₃MoCl₅·H₂O (A=K, Rb, Cs) analogous to Cs₂TiCl₅·H₂O, whose structure was determined by single crystal measurements.Dedicated to Prof. Menachem Steinberg on the occasion of his 65th birthday     

Mono and trinuclear lanthanide complexes of 13-membered tetraaza macrocycle: Synthesis and characterization

The reaction of 1,8-diamino-3,6-diazaoctane and diethyl malonate in dry methanol yielded a 13-membered macrocycle. Complexes of the type [Ln(tatd)Cl₂ (H₂O)₃]Cl [Ln^III=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy; tatd=1, 5, 8, 11-tetra-azacyclotridecane-2,4-dione] have been synthesized by template condensation. The complex [La(tatd)Cl₂ (H₂O)₃]Cl in methanol was reacted with lanthanide chlorides to yield the trinuclear complexes of type [2{La(tatd)Cl₂(H₂O)₃}LnCl₃]Cl₂ [Ln^III=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy]. The chemical compositions of mono and trinuclear complexes have been established on the basis of analytical, molar conductance, electrospray (ES) and fast atom bombardment (FAB) mass data. In mononuclear complexes the Ln³⁺ ion is encapsulated by four ring nitrogens and in trimetallic complexes the exo-carbonyl oxygens of two mononuclear units coordinate to the Ln³⁺ ions resulting in a polyhedron around the lanthanide ions. Thus the macrocycle is bonded in a tetradentate fashion in the former complexes and hexadentate in the latter. The coordination number nine around the encapsulated Ln³⁺ and seven around the exo-oxygen bonded Ln³⁺ ions are established. The symmetry of the ligand field around the metal ions is indicated from the emission spectra.     

Ln3UO6Cl3 (Ln=La,Pr, Nd) -. Die ersten Oxochlorouranate der Seltenen Erden

Ln₃UO₆Cl₃ (Ln=La, Pr, Nd) — The First Oxochlorouranates of the Rare Earths . The new compounds Ln₃UO₆Cl₃ (Ln=La, Pr, Nd) were prepared by heating stoichiometric amounts of LnOCl/Ln₂O₃/U₃O₈ (7 : 1 : 1) (Ln=La, Nd) and PrOCl/Pr₆O₁₁/U₃O₈ (12 : 1 : 2) in silica ampoules (5 d, 1000°C, Ln=La; 9 d 800°C, Ln=Pr, Nd) in the presence of an excess of chlorine [p(Cl₂, 25°C)=1 atm]. Single crystals were obtained by chemical transport reactions using chlorine [p(Cl₂, 25°C)=1 atm] as transport agent [T₂=1000°C→T₁=900°C (Ln=La); T₂=840°C→T₁=780°C (Ln=Pr, Nd)]. Crystals of Ln₃UO₆Cl₃ (Ln=La, Pr, Nd) were investigated by X-ray diffraction methods and La₃UO₆Cl₃ additionally by high resolution electron microscopy. The compounds Ln₃UO₆Cl₃ crystallize in the hexagonal spacegroup P6₃/m (No. 176) with Z=2 formula units per unit cell. Isotypical structure refinements resulted in R=3.04% respectively R_w=1.91% (Ln=La), R=4.72% respectively R_w=3.80% (Ln=Pr) and R=3.99% respectively R_w=2.49% (Ln=Nd). Uranium is coordinated with six oxygen atoms forming a trigonal prism. Lanthanide ions are 10-coordinated (6 oxygen atoms, 4 chlorine atoms).     

Synthese und Aufbau von (4-Picolinium)[LnCl4(H2O)3] (Ln = La,Ce, Pr,Nd)

Preparation and Crystal Structure of (4-Picolinium)[LnCl₄(H₂O)₃] (Ln = La, Ce, Pr, Nd) The complex water containing chlorides (4-Picolinium)[LnCl₄(H₂O)₃] (Ln = La, Ce, Pr, Nd) were prepared for the first time, and the crystal structures of (4-Picolinium)[LnCl₄(H₂O)₃] (Ln = La, Pr) were determined on single crystals by X-ray methods. The isotypic compounds crystallize with triclinic symmetry, space group P1 , Z = 2. Surprisingly there exist the dimeric complex anions [Ln₂Cl₈(H₂O)₆]^2? (Ln = La, Pr).     

Ternäre Chloride in den Systemen ACl/YCl3 (A = Cs,Rb, K,Na)

Ternary Chlorides in the Systems ACl/YCl₃ (A = Cs, Rb, K, Na) Phase diagrams of the pseudobinary systems ACl/YCl₃ (A = Cs, Rb, K, Na) were investigated by DTA and XRD. In all systems compounds of the type A₃YCl₆ and AY₂Cl₇ are formed. Furthermore the chlorides A₂YCl₅ exist with A = Cs, Rb and K, and Cs₃Y₂Cl₉ and NaYCl₄ were found. The unit cells of compounds with still unknown structure, were determined by X-ray diffraction on crystal powders. By a combination of solution calorimetry and e.m.f. measurements in galvanic cells for solid electrolytes thermodynamic functions for the formation of A_nYCl_n+3 from (nACl + YCl₃) were measured. The compounds Cs₃Y₂Cl₉, Rb₂YCl₅ and K₃YCl₆ are stable in competition with the adjacent compounds in their systems only at temperatures > 0 K. The systems ACl/YCl₃ are only gradually different from the systems ACl/HoCl₃.     

Darstellung und elektronenmikroskopische Untersuchung neuer Verbindungen des Typs Ln3MO4Cl5 (Ln = La?Nd; M = Ge,V)

Preparation and Electronmicroscopic Investigation of New Compounds Ln₃MO₄Cl₅ (Ln = La? Nd; M = Ge, V) By heating mixtures of LnOCl, LnCl₃ und GeO₂ (2:1:1) in evacuated silica tubes (Pt-shells inside) the compounds Ln₃GeO₄Cl₅ (Ln = La? Nd) were prepared. The case that the temperature of preparation (La: T = 900°C, 8d; Ce: T = 800°C, 9d; Pr, Nd: T = 650°C, 13 d) had to be reduced from Ln = La to Ln = Nd indicates a decreasing thermodynamic stability in this direction. The compound La₃VO₄Cl₅ was prepared by heating (900°C, 8d) a mixture (2:1:1) of LaOCl, LaCl₃ and VO₂ and was investigated by electronmicroscopic techniques.     

Ln2Cl 7 − ions (Ln = La and Lu): Structures and thermodynamic stability

The equilibrium geometrical parameters and frequencies of the normal vibrations of Ln₂Cl ₇ ^? ions (Ln = La and Lu) and the enthalpies of the dissociation reactions Ln₂Cl ₇ ^? → Ln₂Cl₆ + Cl^? and Ln₂Cl ₇ ^? → LnCl₃ + LnCl ₄ ^? were calculated at the MP2 and MP4 levels (with regard to single, double, triple, and quadruple perturbations). The basis set superposition errors were eliminated by using the counterpoise approach. The potential energy surface of the Ln₂Cl ₇ ^? ions was found to reach a minimum for a configuration with three bridging and four terminal Cl atoms (symmetry C ₂). The terminal fragments LnCl₂ show almost free inherent rotation. The lanthanide compression of the interatomic Ln-Cl distances differed for the bridging and terminal Ln-Cl bonds. The calculated enthalpies of dissociation of the Ln₂Cl ₇ ^? ions were compared with data from high-temperature mass spectrometry.     

Thermodynamic investigation of the systems <Emphasis Type="Italic">Ln</Emphasis>Se<Subscript>2</Subscript>–<Emphasis Type="Italic">Ln</Emphasis>Se<Subscript>1.5</Subscript> (<Emphasis Type="Italic">Ln</Emphasis> = La,Nd)

A detailed thermodynamic study of the systems LnSe₂–LnSe_1.5 (Ln = La, Nd) was performed by static method of vapour pressure measurement using quartz membrane-gauge manometers within the temperature range 713–1,395 K. The p _Se–T–x dependences obtained in this study have shown that the phase regions in composition intervals studied consist of discrete phases: LnSe_1.95 LnSe_1.90, LnSe_1.85, LnSe_1.80 (Ln = La, Nd). The enthalpies and the entropies for the stepwise dissociation process were calculated from the experimental data. The standard enthalpies of formation and the absolute entropies were estimated for the compounds investigated using literature data.     

Darstellung und Struktur von Ln3TiO4Cl5(Ln = La − Nd) - die ersten Oxochlorotitanate der Seltenen Erden

Preparation and Crystal Structure of Ln₃TiO₄Cl₅ (Ln = La?Nd) – the First Oxochlortitanates of Rare Earth The compounds Ln₃TiO₄Cl₅ have been prepared by reaction of LnCl₃/LnOCl/TiO₂ (1:2:1) (Ln = La?Nd) in evacuated silica ampoules. Single crystals of La₃TiO₄Cl₅ were obtained by chemical transport reaction (T₂ → T₁; T₂ = 1050°C, T₁ = 950°C) using chlorine (p(Cl₂; 298 K) = 1 atm) and sulfur as transport agents with La₂TiO₅ as starting material. La₃TiO₄Cl₅ crystallizes in the orthorhombic space group Pnma (No. 62) with cell-dimensions a = 16.760(2) Å, b = 4.0991(6) Å, c = 14.634(2) Å, Z = 4. The structure was refined to give R = 4.76%, R_w = 2.47%. Main building units are TiO₅ trigonal bipyramides and threefold capped trigonal prisms around La. The relationship to La₂TaO₄Cl₃ will be discussed.     

Solubility of Lanthanide Chlorides ( Ln Cl3) in Alkali Metal Chlorides ( M Cl): Thermodynamics and Electrical Conductivity of the M 3 Ln Cl6 Compounds

 Several compounds may exist in LnCl₃–MCl mixtures. Those corresponding to the M ₂ LnCl₅ and MLn ₂Cl₇ stoichiometries are formed in a few systems only, with diverse stability strongly dependent on both the corresponding lanthanide and alkali metal. On the other hand, M ₃ LnCl₆ that occur in most systems have a far larger stability range and melt congruently. These latter compounds were investigated in the present work by differential scanning calorimetry and electrical conductivity measurements. The thermodynamic and transport properties were correlated to structural features and related to the mechanism of compound formation.     

Application of rotate-bomb calorimeter for determining the standard molar enthalpy of formation of Ln(Pdc)3(Phen)

Thirteen solid ternary complexes Ln(Pdc)₃(Phen) (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu;) have been synthesized in absolute ethanol by rare-earth element chloride low hydrate reacting with the mixed ligands of ammonium pyrrolidinedithiocarbamate (APdc) and 1,10-phenanthroline · H₂O (o-Phen · H₂O) in the ordinary laboratory atmosphere without any cautions against moisture or air sensitivity. IR spectra of the complexes showed that the Ln³⁺ ion was coordinated with six sulfur atoms of three Pdc⁻ and two nitrogen atoms of o-Phen · H₂O. It was assumed that the coordination number of Ln³⁺ is eight. The constant-volume combustion energies of the complexes, Δ_c U, were determined by a precise rotate-bomb calorimeter at 298.15 K. Their standard molar enthalpies of combustion, Δ_c H _m ^o , and standard molar enthalpies of formation, Δ_f H _m ^o were calculated. The text was submitted by the authors in English.     

Rb3LnCl6 · 2 H2O (Ln = La?Nd): Darstellung,Kristallstruktur und thermisches Verhalten

Rb₃LnCl₆ · 2 H₂O (Ln = La? Nd): Preparation, Crystal Structure, and Thermal Behaviour The compounds Rb₃LnCl₆ · 2 H₂O (Ln = La? Nd) were prepared from acetic acid as powders. The preparation from aqueous solutions does not yield the pure products because RbCl precipitates as first compound. The structure of Rb₃LaCl₆ · 2 H₂O was determined by X-ray analysis of a single crystal obtained from aqueous solution. The compounds with Ln = La? Nd are isotypic. They crystallize hexagonally in the space group P6₃/m (Rb₃LaCl₆ · 2 H₂O: a = 1 220.4(2) pm, c = 1 688.6(3) (pm) with Z = 6. Anionic trimeric units [Ln₃Cl₁₂(H₂O)₆]^3? are stacked along the c-axis over the corners of the unit cell. In the stacking frequency the units are rotated by 60° with respect to each other around the c-axis. The coordination number (C. N.) of Ln³⁺ is 8, which is satisfied by four bridging and two terminal chloride ions and two water molecules. The coordination spheres of the three rubidium ions in the different atomic positions are composed differently, their C.N. are 9, 8(+1) and 6(+6). The thermal dehydration of the compounds occurs in one step. The hydrates decompose at ca. 100°C to form the anhydrous compounds Rb₂LnCl₅ und RbCl since the anhydrous chlorides Rb₃LnCl₆ are thermodynamically stable above ca. 400°C only.     

Preparation et caracterisation de complexes [cis-4,4′-dinitrodibenzo-18-couronne-6, LnCl3, 3CH3CN]

Some new complexes between thecis-4,4′-dinitrodibenzo-18-crown-6 and rare earth chlorides LnCl₃ (Ln=Nd, Gd, Yb) were synthesized in acetonitrile. Ligandcis-4,4′-dinitrodibenzo-18-crown-6 and its complexes were identified by infrared spectroscopy, X-ray diffraction and thermal analysis (TG and DTA). Acis-trans isomerisation of the complexed ligand is observed about 148°C when heating the rare earth complex.