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.     

Thermodynamics of ZrO2+ cation complexation with dibenzo-18-crown-6 in mixed non-aqueous solvents

The complexation reaction of dibenzo-18-crown-6 (DB18C6) with ZrO²⁺ cation was studied in some binary solvent solutions of acetonitrile (AN), 1,2 dichloroethane (DCE), nitromethane (NM) and ethylacetate (EtOAc) with methanol (MeOH), at different temperatures by conductometry method. The stability constant of the resulting 1:1 complex at each temperature was determined using a computer fitting conductance-mole ratio data. The results revealed that, the (DB18C6·ZrO)²⁺ complex is more stable in the EtOAc–MeOH binary mixed solvents compared with the other binary mixed solvent solutions. A non-linear relationship was observed for changes of log?K_f of (DB18C6·ZrO)²⁺ complex versus the composition of the binary mixed solvents. The corresponding standard thermodynamic parameters (ΔH _c ^° , ΔS _c ^° ) were obtained from temperature dependence of the stability constant. The results show that the (DB18C6·ZrO)²⁺ complex is enthalpy destabilized but entropy stabilized and the values along with the sign of these parameters are influenced by the nature and composition of the mixed solvents.     

Photoinduced recoordination in the complexes of bis-aza-18-crown-6-containing dibenzylidenecyclobutanone with alkali and alkaline-earth metal cations

Complexation with strong competitors (i.e., Ba²⁺, Ca²⁺, and K⁺) shortens the length of the chromophore in bis-aza-18-crown-6-containing dienones of 2,4-dibenzylenecyclo-butanone series due to the weakening of π–LP conjugation as well as disruption of the quinonoid structure in the ground state of the dye (LP is the lone electron pair of the crown nitrogen atom). In the excited state, recoordination of metal cations in the crown cavity takes place. The complexation as well as the newly discovered photorecoordination in these metal complexes may be used to control the chromophore properties of the samples.     

Conductance study of the complexation of substituted and lariat 16-crown-5 derivatives with alkali metal ions in nonaqueous solvents

Formation constants (K _ML) of 1:1 complexes of 15-(2,5-dioxahexyl)-15-methyl-16-crown-5 (L16C5) and 15,15-dimethyl-16-crown-5 (DM16C5) with alkali metal ions were determined in acetonitrile (AN) and propylene carbonate (PC) by conductometry at 25°C. Except for the case of Li⁺-and K⁺-16C5 complexes in PC, the selectivity sequences of L16C5 and DM16C5 are identical with those of the parent crown ether 16-crown-5 (16C5) regardless of the solvent (AN, PC, methanol) (Na¹ > Li⁺ > K⁺ > Rb⁺ > Cs⁺), which show the size-fit correlation. The selectivities of L16C5 and DM16C5 for the alkali metal ions are governed not by the sidearms but by the cavity size. The stability of the crown ether complex is dependent not on the dielectric constant but largely on the donor number of the solvent. TheK _ML(M₁ ⁺)/K _ML(M₂ ⁺) ratio of L16C5 or 16C5 varies very much with the solvent in the cases of M₁=Na, M₂=K and M₁=Na, M₂=Li, but that of DM16C5 is almost constant regardless of the solvent.     

Thermochemistry of 18C6 complexation with alkali,alkaline earth metal cations and ammonium ion

The object of the present study is to examine the factors governing the process of 18C6 complexation in aqueous solution by interpreting of thermodynamic parameters of the reaction in terms of observed selectivity and solvation characteristics under various temperature conditions.     

Study on complexation adsorption behavior of dibenzo-18-crown-6 immobilized on CPVA microspheres for metal ions

Dibenzo-18-crown-6 (DBC) was immobilized on crosslinked polyvinyl alcohol (CPVA) microspheres, resulting in polymer-supported crown ether DBC–CPVA. The complexation adsorption behaviors of DBC–CPVA microspheres towards diverse metal ions were investigated. The experimental results show that among alkali metal ions, the complexation adsorption ability of DBC–CPVA for K⁺ ion is the strongest, and crown ether-metal complex in 1:1 ratio is formed, exhibiting a high adsorption capacity. The adsorption capacities of alkali metal ions on DBC–CPVA are in the order: K⁺ ? Na⁺ > LI⁺ > Rb⁺ > Cs⁺. Among several divalent metal ions, DBC–CPVA exhibits stronger adsorption ability towards Zn²⁺ and Co²⁺ ions, and a “sandwich”-type complex is formed probably in a molar ratio of 2:1 between the immobilized DBC and Zn²⁺ ion as well as between the immobilized DBC and Co²⁺ ion. The adsorption capacities of the several divalent metal ions on DBC–CPVA are in the order: Zn²⁺ > Co²⁺ ? Cd²⁺ > Cu²⁺ > Ni²⁺ > Pb²⁺. The complexation adsorption is exothermic physical physisorption process, and raising temperature leads to the decrease of the adsorption capacity. At the same time, the entropy during the complexation adsorption decreases, so the adsorption process is driven by the decrease of enthalpy.     

Ultraviolet photodepletion spectroscopy of dibenzo-18-crown-6-ether complexes with alkaline Earth metal divalent cations

Ultraviolet photodepletion spectra of dibenzo-18-crown-6-ether complexes with alkaline earth metal divalent cations (A(2+)-DB18C6, A = Ba, Sr, Ca, and Mg) were obtained in the gas phase using electrospray ionization quadrupole ion-trap reflectron time-of-flight mass spectrometry. Each spectrum exhibits the lowest energy absorption band in the wavenumber region of 35?400-37?800 cm(-1), which is tentatively assigned as the origin of the S(0)-S(1) transition of A(2+)-DB18C6. This origin band shows a red shift as the size of the metal dication increases from Mg(2+) to Ba(2+). The binding energies of the metal dications to DB18C6 at the S(0) state were calculated at the lowest energy structures optimized by the density functional theory and employed with the experimental energies of the origin bands to estimate the binding energies at the S(1) state. We suggest that the red shifts of the origin bands arise from the decrease in the binding energies of the metal dications at the S(1) state by nearly constant ratios with respect to the binding energies at the S(0) state, which decrease with increasing size of the metal dication. This unique relationship of the binding energies between the S(0) and S(1) states gives rise to a linear correlation between the relative shift of the origin band of A(2+)-DB18C6 and the binding energy of the metal dication at the S(0) state. The size effects of the metal cations on the properties of metal-DB18C6 complex ions are also manifested in the linear plot of the relative shift of the origin band as a function of the size to charge ratio of the metal cations, where the shifts of the origin bands for all DB18C6 complexes with alkali and alkaline earth metal cations are fit to the same line.     

A thermodynamic study of the association of alkali metal cations with dicyclohexano-18-crown-6

A thermodynamic study of the association of Na⁺, K⁺, Rb⁺, and Cs⁺ with dicyclohexano-18-crown-6 in acetonitrile has been carried out at 308, 303, 298, 293, and 288 K using a conductometric technique. The observed molar conductivities, A, were found to decrease significantly for mole ratios less than unity. A model involving 11 stoichiometry has been used to analyze the conductivity data. The stability constant,K, and the limiting molar conductivity, A _c , for each 11 complex were determined from the conductivity data by using a nonlinear least squares curve fitting procedure. The binding sequence, based on the value of logK at 298 K, as derived from this study is K⁺>Na⁺>Rb⁺>Cs⁺. Values of H ^o and S ^o are reported and their significance is discussed.     

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.     

Stability of complexes of alkali metal cations with dibenzo-24-crown-8 in water saturated nitrobenzene

From extraction experiments and γ-activity measurements, the exchange extraction constants corresponding to the general equilibrium M⁺(aq)+NaL⁺(nb)⇄ML⁺(nb)+Na⁺(aq) taking place in the two-phase water-nitrobenzene system (M⁺=Li⁺, K⁺, Rb⁺, Cs⁺; L=dibenzo-24-crown-8; aq=aqueous phase, nb=nitrobenzene phase) were evaluated. Further, the stability constants of the ML⁺ complexes in nitrobenzene saturated with water were calculated; they were found to increase in the Cs⁺Rb⁺L⁺Na⁺ order.     

A conductometric study of complexation reaction between dibenzo-24-crown-8 with yttrium cation in some binary mixed non-aqueous solvents

The complexation reaction of macrocyclic ligand, dibenzo-24-crown-8 (DB24C8) with Y⁺³ cation was studied in some binary mixtures of methanol (MeOH), ethanol (EtOH), acetonitrile (AN) and tetrahydrofuran (THF) with dimethylformamide (DMF) at different temperatures using the conductometric method. The conductance data show that in all solvent systems, the stoichiometry of the complex formed between DB24C8 and Y⁺³ cation is 1:1 (ML). The stability order of (DB24C8.Y)⁺³ complex in pure non-aqueous solvents was found to be: AN > EtOH > MeOH > DMF. A non-linear behaviour was observed for changes of log K_f of (DB24C8.Y)⁺³ complex versus the composition of the binary mixed solvents, which was explained in terms of solvent–solvent interactions and also the heteroselective solvation of the species involved in the complexation reaction. The obtained results show that the stability of (DB24C8.Y)⁺³ complex is sensitive to the mixed solvents composition. The values of thermodynamic parameters (?H°_c and ?S°_c) for formation of (DB24C8.Y)⁺³ complex were obtained from temperature dependence of the stability constant using the van’t Hoff plots. The results show that in most cases, the (DB24C8.Y)⁺³ complex is enthalpy destabilized but entropy stabilized and the values and also the sign of thermodynamic parameters are influenced by the nature and composition of the mixed solvents.     

Kinetic study of charge transfer complexes of ICl3 with DB18C6 and DC18C6 in some nonaqueous solvents

The spectrophotometric kinetic charge–transfer complex formation of iodine trichloride (ICl₃) with Dibenzo-18-crown-6 (DB18C6), Dicyclohexyl-18-crown-6 (DC18C6) has been studied in chloroform; dichloromethane and propylene carbonate solutions at different temperatures. The results indicated immediate formation of an electron donor–electron acceptor complex; which is followed by two relatively slow consecutive reactions. The pseudo-first-order rate constants for the formation of the ionic intermediate and the final product have been evaluated at various temperatures by computer fitting of the absorbance–time data to appropriate equations. The influences of both the crown’s structure and the solvent properties on the formation of donor–electron acceptor complexes and the rates of subsequent reactions are discussed.     

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.     

Thermal decomposition of metal complexes IV. Lanthanide(III) complexes with dibenzo-18-crown-6

The solid-state thermal dissociation reactions of the complexes of all the lanthanide(III) nitrates and thiocyanates (except Pm) with the cyclic polyether dibenzo-18-crown-6 were investigated. Thermal analysis was carried out in a dynamic atmosphere of dry nitrogen and under reduced pressure (5·10^?2 mm Hg). In both the conditions examined, the two series of complexes exhibit different thermal behaviours. The values of enthalpy change and “activation energy” for the dissociation reactions of the complexes with lanthanide thiocyanates show a periodic trend along the lanthanide series.     

Raman study of 12-crown-4, 15-crown-5, 18-crown-6 and their complexation with metal cations using Fourier deconvolution of CH stretching spectra

The Raman CH stretching spectra of 12-crown-4, 15-crown-5 and 18-crown-6 and their complexes with some metal cations— Li⁺, Na⁺, K⁺ and Cu⁺ in water solutions are studied. For the first time Fourier deconvolution is applied to resolve the overlapped components in the corresponding isotropic and anisotropic spectra. A model is introduced which explains the variety of components in the spectra by means of splitting of the unperturbed CH stretching frequency owing to intramolecular interactions and Fermi resonance. The coupling constants of these interactions, as well as all parameters according to the model, are calculated for studied crowns and their complexes. The differences in the number and intensity of the resolved components in the spectra of the various crowns are explained with the corresponding differences in the coupling constants and model parameters. It is established that complexation leads to some increase in the unperturbed stretching frequency, probably owing to the increase in strain of the crown molecule. It is concluded that 15-crown-5 forms 2:1 and 1:1 complexes with K⁺ and Na⁺ cations respectively and 12-crown-4 forms a 2:1 complex with the Na⁺ cation.     

Study of complexation process between N-phenylaza-15-crown-5 with yttrium cation in binary mixed solvents

The complexation reaction between Y³⁺ cation with N-phenylaza-15-crown-5(Ph-N15C5) was studied at different temperatures in acetonitrile–methanol (AN/MeOH), acetonitrile–propanol (AN/PrOH), acetonitrile–1,2 dichloroethane (AN/DCE) and acetonitrile–water (AN/H₂O) binary mixtures using the conductometric method. The results show that in all cases, the stoichiometry of the complex is 1:1 (ML). The values of formation constant of the complex which were determined using conductometric data, show that the stability of (Ph-N15C5.Y)³⁺ complex in pure solvents at 25?°C changes in the following order: PrOH?>?AN?>?MeOH and in the case of binary mixed solutions at 25?°C it follows the order: AN–DCE?>?AN–PrOH?>?AN–MeOH?>?AN–H₂O. The values of standard thermodynamic quantities (?H _c ^° and ?S _c ^° ) for formation of (Ph-N15C5.Y)³⁺ complex were obtained from temperature dependence of the formation constant using the van’t Hoff plots. The results show that in most cases, the complex is entropy and enthalpy stabilized and these parameters are influenced by the nature and composition of the mixed solvents. In most cases, a non-linear behavior was observed for variation of log K_f of the complex versus the composition of the binary mixed solvents. In all cases, an enthalpy–entropy compensation effect was observed for formation of (Ph-N15C5.Y)³⁺ complex in the binary mixed solvents.     

Study of complex formation between 18-crown-6 and diaza-18-crown-6 with uranyl cation (UO2 2+) in some binary mixed aqueous and non-aqueous solvents

The complexation reaction between UO₂ ²⁺ cation with macrocyclic ligand, 18-crown-6 (18C6), was studied in acetonitrile–methanol (AN–MeOH), nitromethane–methanol (NM–MeOH) and propylencarbonate–ethanol (PC–EtOH) binary mixed systems at 25 °C. In addition, the complexation process between UO₂ ²⁺ cation with diaza-18-crown-6 (DA18C6) was studied in acetonitrile–methanol (AN–MeOH), acetonitrile–ethanol (AN–EtOH), acetonitrile–ethylacetate (AN–EtOAc), methanol–water (MeOH–H₂O), ethanol–water (EtOH–H₂O), acetonitrile–water (AN–H₂O), dimethylformamide–methanol (DMF–MeOH), dimethylformamide–ethanol (DMF–EtOH), and dimethylformamide–ethylacetate (DMF–EtOAc) binary solutions at 25 °C using the conductometric method. The conductance data show that the stoichiometry of the complexes formed between (18C6) and (DA18C6) with UO₂ ²⁺ cation in most cases is 1:1 [M:L], but in some solvent 1:2 [M:L₂] complex is formed in solutions. The values of stability constants (log K_f) of (18C6 · UO₂ ²⁺) and (DA18C6 · UO₂ ²⁺) complexes which were obtained from conductometric data, show that the nature and also the composition of the solvent systems are important factors that are effective on the stability and even the stoichiometry of the complexes formed in solutions. In all cases, a non-linear relationship is observed for the changes of stability constants (log K_f) of the (18C6 · UO₂ ²⁺) and (DA18C6 · UO₂ ²⁺) complexes versus the composition of the binary mixed solvents. The stability order of (18C6 · UO₂ ²⁺) complex in pure studied solvents was found to be: EtOH > AN ≈ NM > PC ≈ MeOH, but in the case of (DA18C6 · UO₂ ²⁺) complex it was : H₂O > MeOH > EtOH.     

苯并-15-冠-5和二苯并-18-冠-6萃取分离铟(III)的研究

本文用斜率法、饱和法以及通过与萃取合物相对应的冠醚配合物晶体的制备及其性质研究, 探讨了In^3^+的萃取机理, 测定并计算了表观萃取平衡常数, 将此萃取体系应用于铟和某些体系应用于铟和某些金属离子的萃取分离, 亦获得较好的结果.