Stability constants of cesium complexes with 18-crown-6 in ionic liquids

The stability constants of the complex[Cs(18C6)]⁺ (18C6 is 18-crown-6 (L)) in N-butylpyridinium methyl sulfate (I) and of the complex [Cs(18C6)₂]⁺ in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (II) were measured by using ¹³³Cs NMR spectroscopy at 23°C. It was found that logK(Cs + L) in solvent I is 1.20±0.13 and logK(CsL + L) in solvent IIis 1.18±0.05. For the complex [Cs(18C6)₂]⁺, the dependence of its stability constant on the temperature in the 23–50°C range was obtained and the enthalpy change in the complexation was determined: ΔH(CsL + L)= ?47 kJ/mol. It was demonstrated that the enthalpy change is favorable for the formation of [Cs(18C6)₂]⁺, while the entropy change hinders the complexation.     

Thermodynamics of complexation of cesium ions with dibenzo-18-crown-6 in hydrophobic ionic liquids

The stability constants of the [Cs(DB18C6)]⁺ complex (DB18C6 is dibenzo-18-crown-6, L) in hydrophobic ionic liquids (room-temperature ionic liquids, RTIL) trioctylmethylammonium salicylate ([TOMA][Sal]), tetrahexylammnoium dihexylsulfosuccinate ([THA][DHSS]), and 1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ([BMIM][N(Tf)₂], as well as of the [Cs(18C6)₂]⁺ complex in [BMIM][N(Tf)₂], were measured by 133Cs NMR in the temperature range 27–57°C. The changes in the enthalpy and entropy of complex formation were determined. A linear correlation was revealed between logK ₁ and the extraction factor logD _Cs^DB18C6 for the cesium extraction from an aqueous solution into the RTIL.     

Thermodynamics of formation for the 18-crown-6-triglycine molecular complex in water-dimethylsulfoxide solvents

The effect of a water-dimethylsulfoxide (DMSO) solvent on the formation of a molecular complex of 18-crown-6 (18C6) with triglycine (diglycylglycine, 3Gly) is studied via calorimetric titration. It is found that switching from water to an H₂O-DMSO mixture with DMSO mole fraction of 0.30 is accompanied by a monotonic increase in the stability of [3Gly18C6] complex, from logK ^° = 1.10 to logK ^° = 2.44, and an increase in the exothermicity of the reaction of its formation, from ?5.9 to ?16.9 kJ/mol. It is shown that the [3Gly18C6] complex exhibits enthalpy stabilization with negative values of enthalpy and entropy over the investigated range of H₂O-DMSO solvents. Analysis of the reagents’ solvation characteristics reveals that the increase in the reaction’s exothermicity of transfer is due to differences in the solvation of [3Gly18C6] and 18C6 with a small solvation contribution from 3Gly. It is concluded that the change in the Gibbs energy of the reaction 3Gly_solv + 18C6_solv ? [3Gly18C6]_solv is due to differences in the change in the solvation state of the complex and the peptide (Δ_tr G ^°([3Gly18C6])-Δ_tr G ^°(3Gly)).     

18-crown-6 ether complexes with aralkylammonium perchlorates

Thermochemical properties of crown ether complexes have been studied by simultaneous TG-DTA (thermogravimetric analysis-differential thermal analysis) coupled with a mass spectrometer, DSC (differential scanning calorimetry) and hot stage microscopy (HSM). The examined complexes contain benzylammonium- [BA], (R)-(+)-a-phenylethylammonium- [(R)-PEA], (R)-(+)- and (S)-(-)-a-(1-naphthyl)ethylammonium perchlorate [(R)-NEA and (S)-NEA] salts as guests. In the cases of BA and (R)-PEA an achiral pyridono-18-crown-6 ligand [P18C6], and in the case of (R)-NEA and (S)-NEA a chiral (R,R)-dimethylphenazino-18-crown-6 ligand [(R,R)-DMPh18C6] was used as host molecule to obtain four different crown ether complexes. In all cases, the melting points of the complexes were higher than those of both the host and the guest compounds. The decomposition of the complexes begins immediately after their melting is completed, while the BA and (R)-PEA salts and the crown ether ligands are thermally stable by 50 to 100 K above their melting points. During the decomposition of the salts and the four complexes strongly exothermic processes can be observed which are due to oxidative reactions of the perchlorate anion. Ammonium perchlorate crystals were identified among the decomposition residues of the salts. P18C6 was observed to crystallize with two molecules of water. The studied complexes of P18C6 did not contain any solvate. BA was observed to exhibit a reversible solid-solid phase transition upon heating. The heterochiral complex consisting of (S)-NEA and (R,R)-DMPh18C6 shows a solid-solid phase transition followed by two melting points. HSM observations identified three crystal modifications, two of them simultaneously co-existing. This revised version was published online in July 2006 with corrections to the Cover Date.     

Extraction of thallium with cesium dicarbollylcobaltate in the presence of 18-crown-6

From extraction experiments with ¹³⁷Cs as a tracer, theextraction constant corresponding to the equilibrium Tl⁺ (aq)+CsL⁺ (nb) TlL ⁺ (nb) + Cs + (aq) taking place ina two-phase water-nitrobenzene system (L = 18-crown-6; aq = aqueous phase,nb = nitrobenzene phase) was determined as log K ex (Tl⁺ , CsL⁺ ) = 1.50.1. Further, the stability constant of the complex TlL⁺ in nitrobenzene saturated with water was evaluated for a temperatureof 25 °C: log ß nb (TIL⁺ ) = 9.20.1. Finally, the individualextraction constant of the TlL⁺ species in the water–nitrobenzenesystem corresponding to the equilibrium TlL + (aq) TlL + (nb)was calculated as log K TIL ⁺ i = 2.50.1.     

Complex formation of Ag+ with polyether 18-crown-6

The complex formation of Ag⁺ with polyether 18-crown-6 (18C6) and their solvation have been studied using calorimetric and potentiometric methods in H₂O-EtOH solvents in wide range of ethanol concentration. The standard enthalpies of dissolution AgNO₃, AgClO₄ and 18C6 in aqueous-ethanol solvents are obtained. The stability of a complex [Ag18C6]⁺ grows with increasing the EtOH content a solvent. Using the method based on the thermodynamic characteristics of solvation of metal-ion, ligand and complex-ion the interpretation of the results has been given. This revised version was published online in August 2006 with corrections to the Cover Date.     

Theoretical study on the complexation of the cesium cation with dibenzo-18-crown-6

Abstract  

By using quantum mechanical calculations, the most probable structures of free dibenzo-18-crown-6 ligand and the cationic complex species of Cs⁺ both with one and with two dibenzo-18-crown-6 ligands were derived. In these two complexes, the “central” cation Cs⁺ is bound by strong bond interactions to the corresponding ethereal oxygen atoms of the parent crown ligand.     

三水合高氯酸镨与18-冠-6配合的研究

采用半微量相平衡方法研究了三元体系Pr(ClO4)3.3H2O-18C6-C2H5OH在298.15K的溶解度, 测定了饱和溶液的折光率。该体系在298.15K时生成两种化学计量的配合物: Pr(ClO4)3.18C6.3H2O(1)和Pr(ClO4)3.2(18C6).3H2O(2)。制备了两种固态配合物, 用化学分析, IR, DTG和TG研究了配合物的组成和性质, 采用量热法, 测定了298.15K时18C6, 配合物1和2在乙醇中的积分溶解热, 以及Pr(ClO4)3.3H2O在18C6-C2H5OH溶液中的积分溶解热。利用本文设计的热化学循环, 求得了两种配合物的标准生成焓。     

The 1 : 1 complexes between benzo-18-crown-6, 18-crown-6 and aminosulfuric acid

The title compounds were prepared by treating a methanol solution of the corresponding crown ether with an aqueous solution of aminosulfuric acid.Crystals of [benzo-18-crown-6·H₂NSO₂OH] suitable for X-ray crystallography were obtained by recrystallization from methanol. The crystals are orthorhombic, space groupP2₁2₁2₁,a = 14.310(7),b = 12.516(4),c = 10.890(4) Å. Refinement led to a final conventionalR value of 0.051 for 909 reflections.Crystals of [18-crown-6·H₂NSO₂OH] suitable for X-ray crystallography were obtained by recrystallization from acetone. They are orthorhombic, space groupP2₁2₁2₁,a = 17.027(6),b = 14.866(5),c = 8.345(4) Å. The structure was solved by a heavy atom method and refined to an agreement value of 0.067.     

On the solid-state conformations of 18-crown-6 complexes

A procedure for displaying macrocylic torsion angles as a map on polar coordinates is discussed with reference to the solid-state conformations of l8-crown-6 and its complexes. The maps aid in comparisons of related structures, in the perception of pseudo-symmetry elements, and in the classification of the conformations of 18-crown-6. Only four conformational groups are found in the 1 : 1 complexes of 18-crown-6 with sodium, potassium, rubidium, cesium, thallium(I), calcium and strontium cations. The relationship of donor number, mean cavity radius and effective ionic radius combined with skeletal drawings of the donors and the polar map of the torsion angles provide a composite picture of the structures and insight into the balance between cation-donor interaction energy and conformational energy.This paper is dedicated to the memory of the late Dr C. J. Pedersen.     

Structural and selectivity of 18-crown-6 ligand in lanthanide-picrate complexes

The selectivity factor in the separation of lanthanide could be associated with the coordination behaviour. Thus, we observed the study in the solid phase to understand the coordination pattern of Ln(III) with the 18-crown-6 (18C6) ligand. Good selectivity of the rigid 18C6 ligand toward Ln(III) depends on gradually smaller their ionic radii of Ln(III) in the complexes formation in the presence of picrate anion (Pic⁻), i.e. lanthanide contraction and steric effects as clearly shown in the series of [Ln(Pic)₂(18C6)]⁺(Pic)⁻ {Ln = La, Ce, Pr, Nd, Sm, Gd} and [Ln(Pic)₃(OH₂)₃] · 2(18C6) · 4H₂O {Ln = Tb, Ho} complexes. The La-Gd complexes crystallized in an orthorhombic with space group Pbca, while the Ho complex crystallized in triclinic with space group . The lighter lanthanides complexes [La-Sm] had a 10-coordination number from the 18C6 ligand and the two picrates, forming a bicapped square-antiprismatic geometry. Meanwhile, the middle lanthanide complex [Gd] had a nine-coordination number from the 18C6 ligand and the two picrates, forming a tricapped trigonal prismatic geometry. The heavier lanthanide [Ho] is rather unique, since Ho(III) coordinated with nine oxygen atoms from three picrates and three water molecules in the opposite direction whereas three 18C6 molecules surrounded in the inner coordination sphere, forming a trigonal tricapped prismatic geometry. The 18C6 ligand is effective in controlling the molecular geometry and coordination bonding of Ln-O and can use a crystal engineering approach. No dissociation of Ln-O bonds in solution was observed in NMR studies conducted at different temperatures. The photoluminescence spectrum of the Pr complex has typical 4f-4f emission transitions, i.e. ³P₀ → ³F₂ (650 nm), ¹D₂ → ³F₂ (830 nm) and ¹D₂ → ³F₄ (950 nm).     

Thermodynamics of cesium cation complexation with dibenzo-24-crown-8 in mixed nonaqueous solvents

Thermodynamics of complexation of cesium cation by dibenzo-24-crown-8 was studied in three binary solvent mixtures: acetonitrile-nitromethane (AN/NM),N,N-dimethylformamide-nitromethane (DMF/NM) and acetonitrile-propylene carbonate (AN/PC) using the¹³³Cs-NMR technique. In all cases the variation of the formation constant,K _f, with the solvent composition was monotonic:K _f increased as the mole-% of the solvent of low donicity was increased. The temperature dependence ofK _f indicated that the complexes are generally enthalpy stabilized, but entropy destabilized. The enthalpy and entropy of complexation reactions are quite sensitive to the solvent composition. However, their variation with solvent composition was not monotonic but showed maxima or minima at the isosolvation points of the cation or the complexed cation. In all cases an enthalpy-entropy compensating effect was observed.