Ternary chlorides of the trivalent late lanthanides

A comprehensive review on phase diagrams, crystal structures and thermodynamic properties of ternary chlorides formed in the systems ACl/LnCl₃ (A=Na, K, Rb, Cs) is presented. It continues an earlier review with the same contents on the lanthanides from La to Gd [1]. In both papers the author's own studies, published since 1985, together with original papers from other scientists are treated. With the three larger cations compounds of the composition A₃LnCl₆, A₂LnCl₅, ALn₂Cl₇ and beginning with holmium Cs₃Ln₂Cl₉ are formed. With sodium the compounds Na₃Ln₅Cl₁₈ (Ln=La to Sm) and NaLnCl₄ (Ln=Eu to Lu) also exist. The stability of a ternary chloride in a system ACl/LnCl₃ is given by the 'free enthalpy of synreaction', the formation of a compound from its neighbour compounds in its system. This must be negative. A surprising result is that the highest – melting compounds in the systems, A₃LnCl₆, are formed from ACl and A₂LnCl₅ with a loss of lattice energy, U. They exist as high-temperature compounds due to a sufficiently high gain in entropy at temperatures where the entropy term TΔS compensates the endothermic ΔH.     

Removal and recovery of vanadium(V) by adsorption onto ZnCl2 activated carbon: Kinetics and isotherms

Adsorption of vanadium(V) from aqueous solution onto ZnCl₂ activated carbon developed from coconut coir pith was investigated to assess the possible use of this adsorbent. The influence of various parameters such as agitation time, vanadium concentration, adsorbent dose, pH and temperature has been studied. First, second order, Elovich and Bangham’s models were used to study the adsorption kinetics. The adsorption system follows second order and Bangham’s kinetic models. Langmuir, Freundlich, Dubinin-Radushkevich and Temkin isotherms have been employed to analyze the adsorption equilibrium data. Equilibrium adsorption data followed all the four isotherms—Langmuir, Freundlich, D-R and Temkin. The Langmuir adsorption capacity (Q ₀) was found to be 24.9 mg g^{− 1} of the adsorbent. The per cent adsorption was maximum in the pH range 4.0–9.0. The pH effect and desorption studies showed that ion exchange mechanism might be involved in the adsorption process. Thermodynamic parameters such as ΔG ⁰, ΔH ⁰ and ΔS ⁰ for the adsorption were evaluated. Effect of competitive anions in the aqueous solution such as PO₄ ^{3 −}, SO₄ ²⁻, ClO₄ ⁻, MoO₄ ²⁻, SeO₃ ²⁻, NO₃ ⁻ and Cl⁻ was examined. SEM and FTIR were used to study the surface of vanadium(V) loaded ZnCl₂ activated carbon. Removal of vanadium(V) from synthetic ground water was also tested. Results show that ZnCl₂ activated coir pith carbon is effective for the removal of vanadium(V) from water.     

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.     

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.     

Studies on the electrochemical and thermodynamic behaviour of Hg-HgS electrode in the presence of sulphide ions

Mercury-mercury (II) sulphide electrode has been prepared and its electrochemical and thermodynamic behaviour has been studied in different media. The electrode is found to show Nernstian response to pS (− log [S²⁻]) over the range 5.19–10.38. In the pH range 7.96–11.98, at constant [S²⁻]_v, its response is also Nernstian. The values of thermodynamic functions, viz., ΔG⁰. ΔH⁰, and ΔS⁰ for the electrode reaction: Hg₍₃)+S²⁻ _aμ ⇌HgS_(s)+2e, have been determined. Further, the standard free energy of formation (ΔG _f ⁰ ) and solubility product constant (K _vp ) of HgS in aqueous medium at 25±0.1°C have also been determined.     

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.     

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.     

Theoretical study of the structure and stability of the Na2Cl+, NaCl 2? , Na3Cl 2+ , and Na2Cl 3? ions

The geometrical parameters, normal vibration frequencies, and thermochemical characteristics of the Na₂Cl⁺, NaCl ₂ ⁻ , Na₃Cl ₂ ⁺ , and Na₂Cl ₃ ⁻ ions in saturated vapors over sodium chloride were calculated by the ab initio methods including electron correlation. According to calculations, the Na₂Cl⁺ and NaCl ₂ ⁻ triatomic ions have a linear equilibrium D _∞h configuration. The pentaatomic ions can exist in the form of the D _∞h linear isomer, C _2v planar cyclic isomer, or D _3h bipyramidal isomer. At ∼1000 K the Na₃Cl ₂ ⁺ and Na₂Cl ₃ ⁻ ions exist predominantly in the form of the linear isomers. The energies and enthalpies of the ion-molecule reactions involving the above ions were calculated. The formation enthalpy of the ions Δ_f H ⁰(0 K) was determined: 230 ± 2 kJ/mol (Na₂Cl⁺), −96 ± 4 kJ/mol (Na₂Cl ₃ ⁻ ), −616 ± 2 kJ/mol (NaCl ₂ ⁻ ), and −935 ± 4 kJ/mol (Na₂Cl ₃ ⁻ ). Original Russian Text Copyright ? 2007 by T. P. Pogrebnaya, A. M. Pogrebnoi, and L. S. Kudin __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 48, No. 6, pp. 1053–1061, November–December, 2007.     

Thermodynamics of mixed-ligand complexation of yttrium group lanthanide ethylenediaminetetraacetates

Mixed-ligand complexation of yttrium subgroup lanthanide ethylenediaminetetraacetates with asparaginate, iminodiacetate, and nitrilotriacetate ions in aqueous solution was studied by calorimetry and pH-metry. The full set of thermodynamic parameters (logK, Δ _r G ₀, Δ _r H, Δ _r S) of the addition reactions of Asp²⁻, Ida²⁻, and Nta³⁻ to LnEdta⁻ (Ln³⁺ = Tb³⁺, Dy³⁺, Ho³⁺, Er³⁺, Tm³⁺, Yb³⁺, Lu³⁺) was determined at 298.15 K and ionic strength I = 0.5(KNO₃). The change in the thermodynamic parameters of the reactions over the series of lanthanides was discussed.     

The Effect of Temperature on the Equivalent Conductivities and Ion-Association Constants of Some Tris-(ethylenediamine)chromium(III) Complexes in N,N-dimethylformamide and N,N-dimethylacetamide

The equivalent conductivities of tris-(ethylenediamine)chromium complexes, [Cr(en)₃]X₃ (where X⁻= Cl⁻, Br⁻, I⁻; en = ethylenediamine) were measured as functions of temperature (278.15 to 328.15 K) and concentration [(1.948 ×10⁻⁴ to 10.728 ×10⁻⁴ mol⋅dm⁻³) and (2.282 ×10⁻⁴ to 11.246 ×10⁻⁴ mol⋅dm⁻³)] in N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMAC), respectively. Equivalent conductivity values for [Cr(en)₃]X₃ in DMF were found to be higher than those in DMAC. The conductivity data were analyzed with the Robinson-Stokes equations. For [Cr(en)₃]X₃, the limiting equivalent ionic conductivities of [Cr(en)₃]³⁺ and the ion-association constants (K _A) of the ion-pair between [Cr(en)₃]³⁺ and the monovalent halide anions were determined in DMF and DMAC. The values of K _A for three complex salts in DMF were higher than those in DMAC. This can be ascribed to an increase of the ion-association constants with a decrease of the relative permittivity of the solvents. The values of K _A at 298.15 K decreased in the order Cl⁻> Br⁻> I⁻ in DMF and Cl⁻> I⁻> Br⁻ in DMAC. The K _A values for [Cr(en)₃]Cl₃ increased with increasing temperature in both DMF and DMAC. For [Cr(en)₃]X₃(X⁻= Br⁻, I⁻) in both solvents, this indicates increasing disorder occurs with increasing temperature. Thermodynamic parameters (standard Gibbs energy, enthalpy and entropy changes) were determined from the temperature dependence of K _A in DMF and DMAC. These parameters were inter-compared in their dependences on temperature and solvent.     

Spin crossover in iron(II) complexes with tris(pyrazol-1-yl)methane

Mononuclear iron(II) coordination compounds with tris(pyrazol-1-yl)methane (HC(Pz)₃) described as [Fe{HC(Pz)₃}₂]A₂ × nH₂O, where A = Cl⁻, Br⁻, I⁻, 1/2 SO₄²⁻, n = 0–7, were synthesized. The compounds were studied by static magnetic susceptibility measurements, IR and UV/Vis spectroscopy, and powder X-ray diffraction. The crystal and molecular structures of all compounds were determined by single crystal X-ray diffraction.     

Thermal decomposition of complexes of cadmium(II) and mercury(II) with triphenylphosphanes

A series of substituted triphenylphosphane complexes of the type CdL₂X₂ (L= triorthotolylphosphane or trimetatolylphosphane; X=Cl⁻, Br⁻ or I⁻) and HgL₂X₂ (L=triphenylphosphane or triorthotolylphosphane) was prepared fresh. The thermal decomposition was carried out in air with heating rate programmed at 10°C min⁻¹ and it revealed that the complexes with ortho derivative were less stable and the triphenylphosphane moiety leaves along with halogen in the first step. All the complexes were stable up to 210°C. However, the stability order of the tetrahedral complexes was X=Cl>Br. Values of n, E, lnA and ΔS ^# have been approximated and compared. Complexes having Br have higher E _a, lnA and ΔS ^# values than that having Cl.     

Electrochemical behaviour of a lead electrode in phosphoric acid

 A lead electrode was studied in 6 and 12 M H₃PO₄. Oxidation of a freshly polished electrode occurred in the −0.5 to −0.3 V vs. SCE range, and led to PbHPO₄ growth on the electrode surface. The dissolution of this layer by electrochemical reduction occurred between −0.5 and −0.7 V. The influence of temperature (20 °C and 65 °C) was investigated and showed that the anodic and the cathodic peaks were increasing, and more markedly for the 12 M H₃PO₄. The ratio Q _cathodic/Q _anodic (Q=electrical charge flowing through the electrode) was equal or close to the unity at 20 °C and decreased as the temperature was increased. The influence of Cl⁻, Br⁻ and I⁻ ions was also evaluated. The addition of Cl⁻ and Br⁻ predominantly led to Pb₅(PO₄)₃Cl and Pb₅(PO₄)₃Br, respectively, while I⁻ led to a mixture of PbI₂ and PbHPO₄. Received: 18 July 1999 / Accepted: 2 November 1999     

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     

Metallosurfactants of Chromium(III) Coordination Complexes. Synthesis, Characterization and Determination of CMC Values

A number of mixed ligand chromium(III)–surfactant coordination complexes, of the type cis-[Cr(en)₂(A)X]²⁺ and cis-α-[Cr(trien)(A)X]²⁺ (A = Dodecyl or Cetylamine; X = F⁻, Cl⁻, Br⁻) were synthesized from the corresponding dihalogeno complexes by ligand substitution. These compounds form foam in aqueous solution when shaken. The critical micelle concentration (CMC) values of these surfactant metal complexes in aqueous solution were obtained from conductance measurements. Specific conductivity data (at 303, 308 and 313 K) served for evaluation of the temperature-dependent critical micelle concentration (cmc) and the thermodynamics of micellization (Δ G_m⁰, Δ H_m⁰ and Δ S_m⁰).     

4-Chloro-2-methoxybenzoates of heavy lanthanides(III) and yttrium(III)

4-Chloro-2-methoxybenzoates of heavy lanthanides(III) and yttrium(III) were obtained as mono-, di-, tri-or tetrahydrates with metal to ligand ratio of 1:3 and general formula Ln(C₈H₆ClO₃)₃·nH₂O, where n=1 for Ln=Er, n=2 for Ln=Tb, Dy, Tm, Y, n=3 for Ln=Ho and n=4 for Yb and Lu. The complexes were characterized by elemental analysis, FTIR spectra, TG, DTA and DSC curves, X-ray diffraction and magnetic measurements. The carboxylate group appears to be a symmetrical bidentate chelating ligand. All complexes are polycrystalline compounds. The values of enthalpy, ΔH, of the dehydration process for analysed complexes were also determined. The solubilities of heavy lanthanide(III) 4-chloro-2-methoxybenzoates in water at 293 K are of the order of 10⁻⁴ mol dm⁻³. The magnetic moments were determined over the range of 76–303 K. The results indicate that there is no influence of the ligand field of 4f electrons on lanthanide ions and the metal ligand bonding is mainly electrostatic in nature.     

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.     

Thermodynamics of mixed-ligand complexation of cerium group lanthanide ethylenediaminetetraacetates

The thermodynamic parameters (logK, Δ _r G ⁰, Δ _r H, and Δ _r S) for mixed-ligand complexation of LnEdta⁻ (Ln³⁺ = La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Gd³⁺) with iminodiacetate and nitrilotriacetate ions in aqueous solution at 298.15 K and ionic strength I = 0.5 (KNO₃) were determined by calorimetry and pH-metry. The variation of the thermodynamic parameters of the reactions over the lanthanide series was discussed.     

Effect of Buffer Species on the Complexation of Basic Drug Terfenadine with β-Cyclodextrin

The complexation of terfenadine (Terf) with β-cyclodextrin (β-CD) in solution and solid state has been investigated by phase solubility diagram (PSD), differential scanning calorimetry (DSC), powder X-ray diffractometry (PXD) and proton nuclear magnetic resonance (¹H-NMR). The PSD results indicated that the salt saturation with the buffer counter ion (citrate⁻², H₂PO₄⁻¹ and Cl⁻¹ ions) of Terf (pK _a = 9.5) and the hydrophobic effect play in tandem to increase the value of the complex formation constant (K₁₁) measured at different conditions of pH, ionic strength, buffer type and buffer concentration. The correlation of the free energy of complex formation (ΔG₁₁) with the free energy of inherent solubility of Terf (ΔG_So) obtained by changing the pH, ionic strength and buffer concentration was used to measure the contribution of the hydrophobic effect (desolvation) to complex formation. The hydrophobic effect was found to constitute 57.8% of the driving force for complex stability, while other factors including specific interactions contribute −13.4 kJ/mol. ¹H-NMR spectra of Terf–citrate and Terf–HCl salts gave identical chemical shift displacements (ΔΔ) upon complexation, thus indicating that the counter anions are positioned somewhere outside of the β-CD cavity. DSC, XRPD and ¹H-NMR proved the formation of solid Terf/acid/β-CD ternary complexes.     

The estimation of ether’s enthalpies of formation

Taking hydrocarbon as gerneratrix, the differences of enthalpies of formation of ether and their corresponding generatrixes were compared and concluded and the equation to estimate ether’s enthalpy of formation, which was Δ_f H _e^°/(kJ/mol) = K(Δ_f H _m^ℴ − 90 + A) was obtained. The results can be elucidated with bond dissociation energies data, bond-enthalpy of formation method, induction effect and conjugative effect. The more essential account to explain the results can be got by using quantum chemistry theories, etc. Using replacement and comparison method, the way of estimation of organic compounds’ thermodynamic properties including enthalpy of formation can be obtained either. The article is published in the original.