Chirale Gallium‐ und Indium‐Alkoxometallate

Chiral Gallium and Indium Alkoxometalates Li₂(S)‐BINOLate ((S)‐BINOL = (S)‐(–)‐2,2′‐Dihydroxy‐1,1′‐binaphthyl) generated by dilithiation of (S)BINOL with two equivalents ⁿBuLi was reacted with GaCl₃ und InCl₃ in THF to the alkoxometalates [{Li(THF)₂}{Li(THF)}₂{Ga((S)‐BINOLate)₃}] ( 1 ) and [{Li(THF)₂}₂{Li(THF)}{In((S)‐BINOLate)₃}] · [{Li(THF)₂}{Li(THF)}₂{In((S)‐ BINOLate)₃}]₂ ( 3 ), respectively. 1 and 3 crystallize from THF/toluene mixtures as 1 · 2 toluene and 3 · 8 toluene. The treatment of PhCH₂GaCl₂ with Li₂(S)‐BINOLate in THF under reflux, followed by recrystallization of the product from DME gives the gallate [{Li(DME)}₃{Ga((S)BINOLate)₃}] · 1.5 THF ( 2 · 1.5 THF). 1 – 3 were characterized by NMR, IR and MS techniques. In addition, 1 · 2 toluene, 2 · 1.5 THF and 3 · 8 toluene were investigated by X‐ray structure analyses. According to them, a distorted octahedral coordination sphere around the group 13 metal was formed, built‐up by three BINOLate ligands. The three Li⁺ counter ions act as bridging units by metal‐oxygen coordination. The coordination sphere of the Li⁺ ions was completed, depending on the available space, by one or two THF ligands ( 1 · 2 toluene, 3 · 8 toluene) and one DME ligand ( 2 · 1.5 THF), respectively. The sterical dominance of the BINOLate ligands can be shown by the almost square‐planar coordination of the Li⁺ ions in 2 · 1.5 THF giving a small twisting angle of only 17°.     

Bicyclo[6.3.0]undecapentaenyl Anion: The Next Higher Homolog of the Indenyl Anion with Exceptionally Large Ion‐Pairing Effects on its Tropicity

The title anion 1 was generated as a fairly thermally stable species in tetrahydrofuran (THF) and dimethylsulfoxide (DMSO) by the action of several bases (sodium hydride, potassium hydride, lithium diisopropylamide, and lithium hexamethyldisilazide) with appropriate bicyclo[6.3.0]undecapentaenes. Variable‐temperature ¹H NMR spectra of 1? Li⁺ in [D₈]THF reveal that the anion exhibits exceptionally large ion‐pairing effects; proton chemical shifts vary by more than 1 ppm as a function of ion‐pairing conditions. Thus, anion 1 , in a contact ion pair (Li⁺ at ambient temperature in THF), behaves as an aromatic cyclopentadienyl anion that is perturbed only slightly by the electronic effects of a paramagnetic cyclooctatetraene (COT), whereas 1 in a separated ion pair (Li⁺ at low temperatures in THF or at ambient temperature in DMSO) behaves as an overall paratropic species with a 12 π‐electron periphery. ¹³C NMR spectroscopy indicates no major skeletal rearrangement and only small variations of the electron density. The variable tropicity of 1 can be ascribed to small conformational changes of the molecule. In addition to its unusual, tunable tropicity, anion 1 can also serve as a versatile building block for the synthesis of cyclopentanoid conjugated systems fused to a fully unsaturated eight‐membered ring. A theoretical calculation predicts that the 10‐position of 1 should have the highest electron density. In agreement with this prediction, the reactions of 1 with electrophiles occur predominantly at the 10‐position. The corresponding ferrocene, two fulvenes, two diazo derivatives, and a COT‐fused azulene were obtained by the reactions of 1 with appropriate electrophiles.     

Calix[4]pyrrole‐Based Heteroditopic Ion‐Pair Receptor That Displays Anion‐Modulated,Cation‐Binding Behavior

A new ditopic ion‐pair receptor 1 was designed, synthesized, and characterized. Detailed binding studies served to confirm that this receptor binds fluoride and chloride ions (studied as their tetraalkylammonium salts) and forms stable 1:1 complexes in CDCl₃. Treatment of the halide‐ion complexes of 1 with Group I and II metal ions (Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, and Ca²⁺; studied as their perchlorate salts in CD₃CN) revealed unique interactions that were found to depend on both the choice of the added cation and the precomplexed anion. In the case of the fluoride complex [ 1? F]^? (preformed as the tetrabutylammonium (TBA⁺) complex), little evidence of interaction with the K⁺ ion was seen. In contrast, when this same complex (i.e., [ 1? F]^? as the TBA⁺ salt) was treated with the Li⁺ or Na⁺ ions, complete decomplexation of the receptor‐bound fluoride ion was observed. In sharp contrast to what was seen with Li⁺, Na⁺, and K⁺, treating complex [ 1? F]^? with the Cs⁺ ion gave rise to a stable, receptor‐bound ion‐pair complex [Cs ?1? F] that contains the Cs⁺ ion complexed within the cup‐like cavity of the calix[4]pyrrole, which in turn was stabilized in its cone conformation. Different complexation behavior was observed in the case of the chloride complex [ 1? Cl]^?. In this case, no appreciable interaction was observed with Na⁺ or K⁺. In addition, treating [ 1? Cl]^? with Li⁺ produces a tightly hydrated dimeric ion‐pair complex [ 1? LiCl(H₂O)]₂ in which two Li⁺ ions are bound to the crown moiety of the two receptors. In analogy to what was seen in the case of [ 1? F]^?, exposure of [ 1? Cl]^? to the Cs⁺ ion gives rise to an ion‐pair complex [Cs ?1? Cl] in which the cation is bound within the cup of the calix[4]pyrrole. Different complexation modes were also observed when the binding of the fluoride ion was studied by using the tetramethylammonium and tetraethylammonium salts.     

Dual influence of lithium chloride on the anionic propagation of polystyryllithium in ethereal solvents

The addition of lithium chloride (LiCl) to a solution of polystyryllithium (PStLi) in tetrahydropyran (THP) reduces the rate of propagation of PStLi at a low concentration of the latter but accelerates it at higher concentrations of PStLi. Moreover, the addition of LiCl, which is dimeric in ethereal solutions, increases the conductance of PStLi solutions in tetrahydrofuran (THF) and THP to a much greater extent than expected from the separate conductances of PStLi and LiCl, which is itself even less dissociated than PStLi. These phenomena are fully explained by the dual action of LiCl. Below a certain concentration of PStLi, the dissociation, not of LiCl as such, as claimed before, but of its solvated dimer into free Li⁺ ions and ClLiCl⁻ triple ions provides Li⁺ ions that repress the ionic dissociation of PStLi by a common ion effect. This, in turn, diminishes the concentration of free polystyryl anions, which are the dominating species responsible for the propagation of PStLi, resulting in retardation. However, at higher concentrations of PStLi, Li⁺ ions produced by its dissociation are scavenged by the scavenging action of LiCl dimers, producing quintuple cations. This reduces the concentration of free Li⁺ ions and, therefore, increases the concentration of the reactive free polystyryl anions, resulting in an acceleration of the propagation. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2148–2157, 2002     

Selective Ion Exchange in Supramolecular Channels in the Crystalline State

Artificial ion channels are of increasing interest because of potential applications in biomimetics, for example, for realizing selective ion permeability through the transport and/or exchange of selected ions. However, selective ion transport and/or exchange in the crystalline state is rare, and to the best of our knowledge, such a process has not been successfully combined with changes in the physical properties of a material. Herein, by soaking single crystals of Li₂([18]crown‐6)₃[Ni(dmit)₂]₂(H₂O)₄ ( 1 ) in an aqueous solution containing K⁺, we succeeded in complete ion exchange of the Li⁺ ions in 1 with K⁺ ions in the solution, while maintaining the crystalline state of the material. This ion exchange with K⁺ was selectively conducted even in mixed solutions containing K⁺ as well as Na⁺/Li⁺. Furthermore, remarkable changes in the physical properties of 1 resulted from the ion exchange. Our finding enables not only the realization of selective ion permeability but also the development of highly sensitive biosensors and futuristic ion exchange agents, for example.     

Oligoether‐Strapped Calix[4]pyrrole: An Ion‐Pair Receptor Displaying Cation‐Dependent Chloride Anion Transport

A ditopic ion‐pair receptor ( 1 ), which has tunable cation‐ and anion‐binding sites, has been synthesized and characterized. Spectroscopic analyses provide support for the conclusion that receptor 1 binds fluoride and chloride anions strongly and forms stable 1:1 complexes ([ 1? F]^? and [ 1? Cl]^?) with appropriately chosen salts of these anions in acetonitrile. When the anion complexes of 1 were treated with alkali metal ions (Li⁺, Na⁺, K⁺, Cs⁺, as their perchlorate salts), ion‐dependent interactions were observed that were found to depend on both the choice of added cation and the initially complexed anion. In the case of [ 1? F]^?, no appreciable interaction with the K⁺ ion was seen. On the other hand, when this complex was treated with Li⁺ or Na⁺ ions, decomplexation of the bound fluoride anion was observed. In contrast to what was seen with Li⁺, Na⁺, K⁺, treating [ 1?F ]^? with Cs⁺ ions gave rise to a stable, host‐separated ion‐pair complex, [F ?1? Cs], which contains the Cs⁺ ion bound in the cup‐like portion of the calix[4]pyrrole. Different complexation behavior was seen in the case of the chloride complex, [ 1? Cl]^?. Here, no appreciable interaction was observed with Na⁺ or K⁺. In contrast, treating with Li⁺ produces a tight ion‐pair complex, [ 1? Li ? Cl], in which the cation is bound to the crown moiety. In analogy to what was seen for [ 1? F]^?, treatment of [ 1? Cl]^? with Cs⁺ ions gives rise to a host‐separated ion‐pair complex, [Cl ?1? Cs], in which the cation is bound to the cup of the calix[4]pyrrole. As inferred from liposomal model membrane transport studies, system 1 can act as an effective carrier for several chloride anion salts of Group 1 cations, operating through both symport (chloride+cation co‐transport) and antiport (nitrate‐for‐chloride exchange) mechanisms. This transport behavior stands in contrast to what is seen for simple octamethylcalix[4]pyrrole, which acts as an effective carrier for cesium chloride but does not operates through a nitrate‐for‐chloride anion exchange mechanism.     

Highly Selective Lithium Transport through Crown Ether Pillared Angstrom Channels

Biological ion channels use the synergistic effects of various strategies to realize highly selective ion sieving. For example, potassium channels use functional groups and angstrom-sized pores to discriminate rival ions and enrich target ions. Inspired by this, we constructed a layered crystal pillared by crown ether that incorporates these strategies to realize high Li⁺ selectivity. The pillared channels and crown ether have an angstrom-scale size. The crown ether specifically allows the low-barrier transport of Li⁺. The channels attract and enrich Li⁺ ions by up to orders of magnitude. As a result, our material sieves Li⁺ out of various common ions such as Na⁺, K⁺, Ca²⁺, Mg²⁺ and Al³⁺. Moreover, by spontaneously enriching Li⁺ ions, it realizes an effective Li⁺/Na⁺ selectivity of 1422 in artificial seawater where the Li⁺ concentration is merely 25 μM. We expect this work to spark technologies for the extraction of lithium and other dilute metal ions.     

Aggregation and solvation of 9-propylfluorenyllithium and of α,ω-BIS(9-fluorenyllithium)polymethylenes in toluene

Bolaform salts of the type Li⁺,Fl^?(CH₂)_n Fl^?,Li⁺ (Fl^? = 9-fluorenyl, n = 2,4 or 6), when dissolved in toluene, were shown to be present as intramolecular aggregates (λ_m 370 nm) which can be broken up on addition of tetrahydrofuran (THF) or tetrahydropyran (THP) to form solvated tight ion pairs (λ_m 361 nm) and loose ion pairs (λ_m 386 nm). For n = 6 the ratio K₁/K₂ of the loose ion pair formation constants for the two terminal ion pairs is close to the statistical factor 4, but for n = 2 the ratio is only 0.3. This is attributed to a higher stability of the intramolecular aggregate for this compound. The data for the bolaform salts were compared with those obtained for the one ended salt 9-(n-propyl)-fluorenyllithium. For the latter compound, an equilibrium between the monomeric ion pair (λ_m 353 nm) and the dimeric ion pair aggregate (λ_m 370 nm) was found, the dissociation constant K_d being 2.9 X 10^?6M. Addition of THP produces the THP solvated tight ion pair (λ_m 361 nm) and the loose ion pair (λ_m 386 nm).     

Suitability of tetrahydofuran as a dopant and the comparison to other existing dopants in dopant‐assisted atmospheric pressure photoionization mass spectrometry in support of drug discovery

In this paper, we investigated the suitability of tetrahydofuran (THF) as a dopant and compared it against other common dopants for atmospheric pressure photoionization mass spectrometry (APPI‐MS). In a systematic analysis of 37 drug standards and 100 Wyeth proprietary drug candidates, THF was found to increase ionization efficiency as high as 33‐fold when introduced through a syringe pump at a flow rate of 20 µL/min, and as high as 114‐fold when introduced through the mobile phase at 100 µL/min. As a dopant, THF is as effective as acetone, better than anisole, and slightly less effective than toluene for the majority of the test compounds. The increase in ionization efficiency by THF was found to be compound‐dependent. THF was more effective in facilitating the ionization of polar compounds than of non‐polar compounds. With THF, toluene and acetone as dopants, a single type of molecular ion ([M+H]⁺ or M^+?) is produced for analyte molecules. However, anisole can cause the formation of an ion cluster for polar analytes. The cluster contains [M–2H+H]⁺, M^+?, and [M+H]⁺ ions with varied ratios. This complexity may make interpretation of spectra difficult for unknown compounds when complimentary data are not available. Our findings indicate that THF is a suitable dopant in the daily usage for increasing ionization efficiency, especially when THF is used as the mobile phase or as an organic modifier in the mobile phase. Copyright © 2009 John Wiley & Sons, Ltd.     

The polymerization of methyl methacrylate by ion pairs

The reactions of the polymethylmethacrylate anion have been investigated at 200 K and 250 K in both THF and 9/1 toluene/THF. Sodium-α methyl styrene tetramer and fluorenyl sodium were used as initiators. Only ion pair reactions were investigated. The rate constant of monomer addition to the ion pair at 200 K was determined to be 80 ± 6 M^?1 sec^?1. At 250 K in the presence of excess monomer, the poly MMA anion reacts with the monomer vinyl function and the monomer ester function at comparable rates. Once fully reacted, the poly MMA anion terminates very slowly in THF at 250 K by an intermolecular mechanism. This rate of termination is enhanced in the toluene/THF system. No evidence was found for different reaction mechanisms for the two initiators.     

Determination of orders of relative alkali metal ion affinities of crown ethers and acyclic analogs by the kinetic method

Ladders of relative alkali ion affinities of crown ethers and acyclic analogs were constructed by using the kinetic method. The adducts consisting of two different ethers bound by an alkali metal ion, (M₁ + Cat + M₂)⁺, were formed by using fast atom bombardment ionization to desorb the crown ethers and alkali metal ions, then collisionally activated to induce dissociation to (M₁ + Cat)⁺ and (M₂ + Cat)⁺ ions. Based on the relative abundances of the cationized ethers formed, orders of relative alkali ion affinities were assigned. The crown ethers showed higher affinities for specific sizes of metal ions, and this was attributed in part to the optimal spatial fit concept. Size selectivities were more pronounced for the smaller alkali metal ions such as Li⁺, Na⁺, and K⁺ than the larger ions such as Cs⁺ and Rb⁺. In general, the cyclic ethers exhibited greater alkali metal ion affinities than the corresponding acyclic analogs, although these effects were less dramatic as the size of the alkali metal ion increased.     

The structure of the ion pairs of the carbanion of indene with alkali metal cations

NMR spectra have been measured of the Li⁺, Na⁺ and K⁺ ion pairs of the indenyl carbanion in 1,2-dimethoxyethane and tetrahydrofuran as a function of temperature. The changes of the chemical shifts are explained in terms of the detailed structure of the ion pairs. The results in both solvents strongly suggest that in indenyl-Li⁺ the counterion is predominantly located over the six-membered ring. In THF the preferred position of the cations Na⁺ and K⁺ in the contact ion pairs seems to be the five-membered ring.     

Molecular dynamics simulation of ionic transport on molten Li–KCl interface

A molecular dynamics study is performed to determine the dynamics and transport properties of the ions on the molten interface between anode metal Li and electrolyte KCl. Radial distribution function of the ionic pair and the behavior of the mean‐square displacement (MSD) as a function of time (t) indicate that KCl and metal Li are in the molten state at 2,200 K in the canonical ensemble. The dynamics of the ionic transport are characterized by studying MSD for the centers of mass of the ions at different temperatures. Diffusion coefficient is evaluated from the linear slope of the MSD (t) function in the range of 0–500 ps. The MSD and diffusion coefficient of the Li⁺ ions are much larger than those of the Cl^? and K⁺ ions due to the difference in ionic characteristic. The transport process has been dominated by the Li⁺ ions on the molten interface and the Li⁺ ions are main charge carriers. The energy barrier of the Li⁺ ions transporting into the molten KCl is fitted to be 5.28 kcal/mol in the light of the activation model. The electrical conductivity of the Li⁺ ions transporting into the molten KCl are calculated from the Nernst–Einstein formula to be in the range of 0.2–0.3 S cm^?1. The current density resulted from the Li⁺ ions through the interface are estimated to be an order of 10⁶ A cm^?2, which may be the value corresponding to a larger concentration gradient of the Li⁺ ions. Simulated results at different temperatures show that the diffusion coefficient, conductivity and current density have increased with the temperature. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Non-ergodic effect of LiCl on the anionic polymerization of styrene in ether-solvents. Specific solvation of Li+ ions in THF solution and prevention of this effect by LiCl

In this work conductance measurements were performed on polystyryllithium PStLi in tetrahydrofuran (THF) in the concentration range of 10⁻³ mol dm⁻³ at various temperatures between −60°C and 20°C. The comparison with the other alkali salts shows that in these solutions Li⁺ gives specific interactions with partial electronic charge transfer from the solvent molecules, presumably of the formula LiS₄⁺. A quantitative treatment shows that at 25°C the extrapolated stabilization factor K_S is larger than 50000 but rapidly drops for the heavier alkali ions: 3000 for Na⁺, 200 for K⁺ and negligible for C_s⁺. Surprisingly, such a stabilization is not observed for LiCl, although the ionic radii of the anions are quite comparable. The conductances κ at given concentration C of the electrolyte are 100 times smaller. Furthermore the curves of κ² versus C exhibit in this case an important curvature whereas they are practically linear for PStLi. The absence of specific solvation for LiCl seems thus to be accompanied by the formation of triple ions. Due to the symmetry of the electrolyte the formation of both triple anions ClLiCl⁻ and cations LiClLi⁺ has to be considered. Moreover, the concentrations of these ions is then always much smaller than that of the neutral dimer LiClLiCl, even if the extent of dimerization of LiCl remains small. The triple ions therefore appear as related to the dissociation of the dimer. This means that through the intermediate formation of the neutral dimer the couples triple ion - counterfoil perpetually exchange an LiCl entity in the course of time: Li⁺ + ClLiCl⁻⇋ LiClLiCl ⇋ LiClLi⁺ + Cl⁻. Only in the dimer the central LiCl is in possession of the (negative) energy of the insertion bond. In the solution this bond can be attributed neither to ClLiCl⁻ nor to LiClLi⁺. These entities have to be considered as transient ones during the life-time of which the energy of the insertion bond is transferred to the medium or vice-versa and which possess the energy of the insertion bond only during half of their life-time. The energy of such entities is thus not unambiguously defined in the ensemble at a given time and the ergodic principle does not hold. Such transient species cannot be specifically solvated by the solvent molecules because this would prevent the necessary passage through the dimer form. It is therefore the dimerization of LiCl which opposes itself to the formation of LiS₄⁺ in the THF solutions. Quantitatively the problem can be treated by a thermodynamics based not on ensemble fractions but on time fractions. One considers that a given LiCl can only give solvated ions during a fraction ξ_C° of the time and that during the remaining fraction it participates in a dissociation process which passes through the formation of non-ergodic triple ions and neutral dimers. (1-ξ_C°)/ξ_C° is equal to K^aC^3/2/[(1 + K_S)K^do]^½ where K^a is the non-ergodic equilibrium constant governing the formation of dimers and higher aggregates and K^do the dissociation constant of LiCl in non-solvated ions. This non-ergodic treatment also allows to describe quantitatively the strange conductometric behaviour of ternary solutions of LiCl and PStLi in THF. The addition of amounts of LiCl in a mole ratio of 7/1 to a given solution of PStLi increases unexpectedly in a very spectacular way the conductivity and provokes the appearance of a non-linear term in the κ² versus concentration function. In fact this behaviour is due to the replacement of a LiCl entity in the dimers by a PStLi molecule, yielding mixed dimers LiClLiStP. The displaced LiCl molecules are again susceptible of ergodic dissociation and specific solvation of the Li⁺ ions which originate from this dissociation. Thus for the LiCl entities the time fraction ξ_C increases. Moreover, at higher concentrations the dissociation of the mixed dimers leads to an important formation of non-ergodic triple anions: Li⁺ + ClLiStP⁻ ⇋ LiClLiStP ⇋ LiClLi⁺ + StP⁻ where the entity LiCl constantly jumps in the course of time from an StP⁻ to an Li⁺ and vice-versa.     

Stable structures of 12-crown-O3N complexes with Li or Na in aqueous and acetonitrile solutions

Molecular geometries of crown ether derivatives play an important role in capturing and transporting alkali metal ions such as Li⁺ and Na⁺. As the selectivity of ions is observed in solutions, it is necessary to know their molecular structures in solutions. Recently, we investigated stable conformations of 12-crown-O₃N and its Li⁺ complex in aqueous solution by the combination of three programs, the CONFLEX, Gaussian 98, and BOSS programs. In the present study, we applied the same procedure to investigate stable structures of 12-crown-O₃N complexes with an alkali ion in aqueous and acetonitrile solutions. It was confirmed that the stable structures of Li⁺ and Na⁺ complexes in solutions are highly dependent on the polarity of the solvents.     

Amine side arm effect on the ion selectivity of 12-crown-O3N derivatives with an amine arm in aqueous and acetonitrile solutions

Molecular geometries of crown ether derivatives play an important role in capturing and transporting alkali metal ions such as Li⁺ and Na⁺. As selectivity of the ions is observed in solution, it is necessary to know their molecular structures in solutions. Recently, we investigated stable conformations of 12-crown-O₃N and its alkali ion complexes in aqueous and acetonitrile solutions. In the present study, we applied a procedure similar to that in previous papers to investigate the side arm effect of 12-crown-O₃N with an amine arm for capturing Li⁺ and Na⁺ in the two solutions. It was confirmed that the stable structures of Li⁺ and Na⁺ complexes in solutions, especially the geometry of the amine side arm, are highly solvent-dependent. This conformational difference is the key to understanding the high Li⁺ selectivity of 12-crown-O₃N derivatives with an amine side arm in acetonitrile.     

Synthesis of LiAlTiO4 and its selectivity to Li+ exchange

The ion-exchanger LiAlTiO₄ of spinel type was prepared by the common precipitation/hydrothermal crystallization method, and was acid-modified. Its ion-exchange properties for alkali ions such as saturation capacity of exchange, distribution coefficient and pH titration curve were determined. LiAlTiO₄ was characterized by the X-ray diffraction method. The acid treatment of LiAlTiO₄ caused Li⁺ extraction ratio to change from 28% to 72%, while the dissolution of Al is less than 6.8%. This inorganic ion-exchanger (LiAlTiO₄-700) has a higher saturation capacity of exchange for Li than for other alkali ions, the saturation capacity of exchange for Li⁺ reaches 4.29 mmol/g (30.03 mg/g); LiAlTiO₄-700(H) has a higher selectivity of ion exchange for Li⁺ than for other alkali ions. These results show LiAlTiO₄-700(H) has better memory and selectivity of ion exchange, and higher capacity of ion exchange for Li⁺. It is a kind of prospective ionic sieve for Li⁺. __________ Translated from Chinese Journal of Applied Chemistry, 2005, 22 (7) (in Chinese)     

Optical absorption and EPR spectroscopic studies of (30 − x)Li2O–xK2O–10CdO–59B2O3–1Fe2O3: An evidence for mixed alkali effect

Optical absorption and EPR spectroscopic studies were carried on (30 ? x)Li₂O–xK₂O–10CdO–59B₂O₃–1Fe₂O₃ (x = 0–30) glass system to understand the effect of progressive doping of Li⁺ ion with K⁺ ion. Optical absorption results show typical spectra of Fe³⁺ ions and the various optical parameters such as, optical band gap, Urbach energy, oxide ion polarizability, optical basicity and interaction parameter were evaluated from the experimental data. The observed optical band gap and Urbach energy values show large deviation from the linearity where as the other parameters show small deviation from the linearity with the progressive substitution of Li⁺ ions with K⁺ ions. The observed EPR spectra are representative of Fe³⁺ ion in octahedral and axial fields in the glass network. The number of paramagnetic centers and paramagnetic susceptibility values were evaluated at different resonance lines for all the specimens and these parameters show non-additive nature with the progressive substitution of Li⁺ ions with K⁺ ions in the glass network. This is first ever observation of mixed alkali effect (MAE) in EPR and optical parameters of mixed alkali borate glasses.     

Conductometric study of cationic and anionic complexes in propylene carbonate

Conductivity data are used to determine thermodynamic complex formation constants for cases in which both the initial electrolyte and the complexed electrolyte form ion pairs. Using the method described in the text, the complex formation constants of Li⁺, Na⁺ and K⁺ with the crown ether 18-crown-6 and of Li⁺ with the ligand triphenylphosphine oxide in propylene carbonate have been evaluated from conductance data. The complexation of AgBr in propylene carbonate solutions of n-etrabutylammonium bromide has also been studied by the measurement of molar conductivities. The results of these studies indicate that ion pairing should not be neglected, even in high permittivity solvents such as propylene carbonate, and that the ion pair association constants correlate well with structural studies on cation-crown ether molecular conformations.     

Aluminum phosphate dispersed on a cellulose acetate fiber surface: Preparation, characterization and application for Li, Na and K separation

Cellulose acetate fibers with supported highly dispersed aluminum phosphate were prepared by reacting aluminum-containing cellulose acetate (Al₂O₃=3.5 wt.%; 1.1 mmol g⁻¹ aluminum atom per gram of the material) with phosphoric acid. Solid-state NMR spectra (CPMAS ³¹P NMR) data indicated that HPO₄²⁻ is the species present on the fiber surface. The specific concentration of acidic centers, determined by ammonia gas adsorption, is 0.50 mmol g⁻¹. The ion exchange capacities for Li⁺, Na⁺ and K⁺ ions were determined from ion exchange isotherms at 298 K and showed the following values (in mmol g⁻¹): Li⁺=0.03, Na⁺=0.44 and K⁺=0.50. The H⁺/Li⁺ exchange corresponds to the model of the ideal ion exchange with a small value of the corresponding equilibrium constant K=1.1×10⁻². Due to the strong cooperative effect, the H⁺/Na⁺ and H⁺/K⁺ ion exchange is non-ideal. These ion exchange equilibria were treated with the use of models of fixed bi- or tridentate centers, which consider the surface of the sorbent as an assemblage of polyfunctional sorption centers. Both the observed ion exchange capacities with respect to the alkaline metal ions and the equilibrium constants were discussed by taking into consideration the sequence of the ionic hydration radii for Li⁺, Na⁺ and K⁺. The matrix affinity order for the ions decreases as the hydration radii of the cations increase, i.e. Li⁺>Na⁺>K⁺. The high values of the separation factors S_Na⁺/Li⁺ and S_K⁺/Li⁺ (up to several hundred) provide quantitative separation of Na⁺ and K⁺ from Li⁺ from a mixture containing these three ions.