Complexation Of Alkali Metal Cations Research Articles

Macrocyclic chemistry in the gas phase: intrinsic cation affinities and complexation rates for alkali metal cation complexes of crown ethers and glymes

Reactions of 12-crown-4, 15-crown-5, 18-crown-6, and 21-crown-7, as well as the acyclic analogs triglyme, tetraglyme, and penta(ethylene glycol), with Li + , Na + , K + , Rb + , and Cs + , are observed and characterized using Fourier transform ion cyclotron resonance mass spectrometry (FTICR/MS) and tandem quadrupole mass spectrometry in the gas phase to obtain information on intrinsic host-guest interactions in the absence of the complicating effects of solvation. Radiatively stabilized attachment of the cations to the ligands is a rapid process, with rates in some cases a factor of 2 or more times the Langevin collision rate

Solvent effects in the metal interchange of crown ether – alkali metal cation complexes. Transition from an associative exchange in nitromethane to a dissociative exchange in acetonitrile studied by 23Na nuclear magnetic resonance

The role of the solvent in the dissociation kinetics and cation exchange mechanisms of the complex sodium–monobenzo-15-crown-5 (Na: B15C5)+ was examined by 23Na NMR. In nitromethane (NM), the cationic exchange between the complexes takes place via an associative metal interchange mechanism, 1M. In acetonitrile (AN), it takes place via a dissociative (dissociation/recombination) mechanism. In AN–NM binary mixtures, the rate constant of the dissociative exchange (k−1) increases with the AN molar fraction, XAN, from 1.1 × 10−2 s−1 for XAN = 0 to 89 × 10−2 s−1 for XAN = 0.400 (corresponding to a decrease of the free energy of activation, ΔGdi≠ from 62.1 to 51.1 kJ mol−1 respectively, at 301.5 K). The activation parameters were ΔHdi≠ = 48 kJ mol−1 and ΔSdi≠ = −20 J K−1, mol−1 for XAN = 0.200. This rate increase was related to the concentration increase in solution of the AN monosolvated complex (AN: Na: B15C5)+. In the whole range of AN mole fractions studied, the rate constant of the associative exchange, k2, was not dependent upon XAN in the error limits: k2 ≈ 9 × 104 M−1 s−1 at 301.5 K (ΔGas≠ = 45 kJ mol−1). The activation parameters were determined to be ΔHas≠ = 23 kJ mol−1 and ΔHas≠ = −75 J K−1 mol−1. These findings are in good agreement with an associative exchange controlled mainly by the conformational changes of the ligand during the concerted partial decomplexation of a sodium cation and partial complexation of a second one, while solvation of the complexed cation plays a major role in the dissociative mechanism.

Standard Gibbs energies of transfer of univalent ions from water to 1,2-dichloroethane

Standard Gibbs energies of ion transfer from water to 1,2-dichloroethane have been evaluated from voltammetric measurements at the interface between two immiscible electrolyte solutions for a series of univalent ions (in kJ mol −1): H + (53), Li + (57), Na + (57), Cl − (51), Br − (43), and I − (33). Thermodynamic scales derived from solubility, partition or electrochemical measurements have been compared and found mutually consistent, except for highly hydrated cations, in which case the electrochemical scale is superior. The stability constants of crown ether complexes of alkali metal cations in 1,2-dichloroethane have been revised.

Quantitative approach to molecular interactions using the electronegativity equalization method

An internally consistent approach for describing molecular interactions is presented, based on the electronegativity equalization method (EEM). The gas-Phase complexation of alkali-metal cations by water and ammonia is taken as an example. Charge reorganisation in the molecules due to the interaction with the cations can be accurately predicted and the complexation enthalpies can be estimated. Good correlations with experimental complexation enthalpies are found (the absolute values depend on the definition of ‘charge’).

Selective alkali-metal cation complexation by chemically modified calixarenes. Part 4. Effect of substituent variation on the Na+/K+ selectivity in the ester series and X-ray crystal structure of the trifluoroethyl ester

The cation complexing abilities of a series of p-tert-butylcalix[4]arenes bearing ligating ester groups in the cone conformation have been assessed by stability constant measurements in methanol and extraction studies from water into dichloromethane. The cations studied were Na+ and K+ and variations in the ester function (CO2R) included R = methyl, ethyl, n-butyl, tert-butyl, benzyl, phenyl, phenacyl, methoxyethyl, trifluoroethyl, methylthioethyl and prop-2-ynyl. The effect of replacing one or two ester functions in the tetraethyl ester by methyl ester, carboxylic acid, ketone and amide functions was also studied. Selectivities for Na+ relative to K+ in stability constants range from 2 to 2500, the phenacyl derivative having the highest selectivity. X-Ray diffraction analysis was used to probe the conformation of the trifluoroethyl ester 11. Crystals of 11 are monoclinic, space group P21/n, in a cell of dimensions a= 13.987(2), b= 16.194(3), c= 27.630(5)A; β= 98.70(1)°; R= 0.077 for 3172 observed data. The compound possesses a distorted cone conformation.

Phosphorus-containing podands 7. Complexing properties of ortho-diphenylphosphinyl-substituted diphenyl ethers of oligoethylene glycols with respect to alkali-metal cations

Stability constants of complexes of alkali-metal cations with oligoethylene glycol diethers RO(CH2CH2O)nR (n=1–5), where R=2-Ph2P(O)C6H4 and 2-Ph2(O)-4-t-BuC6H3P, have been determined conductometrically in a tetrahydrofuran-chloroform mixture (4∶1 by volume). The dependence of complexing ability on a number of monopodand donor centers for Li+ and Na+ has multiple extrema. For K+, Rb+, and Cs+ the complexing abilities steadily increase with the length of the ligand polyether chain. Monopodands based on triethylene glycol and its pyrocatechol analog are highly effective (log K=6.7–7.0) with respect to Li+. The synthesis of ligands with a lipophilic tert-butyl substituent in the terminal group is described.

Complexation of alkali metal cations by conformationally rigid, stereoisomeric calix[4]arene crown ethers: a quantitative evaluation of preorganization

Selective bridging of p-tert-butylcalix[4]arene (1) with tetra- and pentaethylene glycol ditosylate gives the 1,3- dihydroxy-p-tert-butylcalix[4]arene crown ethers 7 and 9 in good yields. The subsequent alkylation of the two phenolic groups of 7 and 9 with substituents (R) bulkier than CH 3 gives a series of conformationally rigid 1,3-dialkoxy-p-tert-butylcalix[4]arene crown ethers.

Polycarboxylate diaza crown ethers derived from R,R-(+)-tartaric acid: synthesis and complexation of metal ions

The synthesis and complexation properties of polycarboxylate diaza crown ethers based on R,R-(+)-tartaric acid are described. Cesium carbonate mediated macrocyclization of a bis-tosylamide precursor with a bis-tosylate precursor provided the protected crown ethers. Photochemical deprotection of the tosylamides and hydrolysis of the carboxamides yielded dicarboxylic and tetracarboxylic acid derivatives of 1,10-diaza-18-crown-6. N-Methylenecarboxylate (N-acetate) derivatives were prepared by N-alkylation with bromoacetic acid. The synthetic and purification procedures developed provide samples of the ligands in a metal-free form. Acidity and stability constants for complexation of alkali metal, alkaline earth, late- and post-transition metal cations were determined by potentiometric titration. The ligands form complexes which show enhancement of stability by charge–charge and chelate interaction with the carboxylates. In comparison with crown ether polycarboxylates these aza crown ethers showed a selectivity for softer metal ions relative to alkali and alkaline earth metal ions. N-Methylenecarboxylate chelate ligands were found to bind almost all types of metal ions, due to a highly co-operative array of charge–charge, chelate and crown ether interactions. Keywords: aza crown ether synthesis, tartaric acid, potentiometric titration, cation complexation, aminocarboxylate complexone.

Electrolyte dropping electrode polarographic studies. Solvent effect on stability of crown ether complexes of alkali-metal cations

Electrolyte dropping electrode polarographic studies. Solvent effect on stability of crown ether complexes of alkali-metal cations

Lithium ion complexation kinetics by cyclic and acyclic polyethers

Abstract

Polycarboxylate crown ethers: Synthesis, complexation, applications

Crown ethers derived from tartaric acid present a number of interesting features as receptor frameworks and offer a possibility of enhanced metal cation binding due to favorable electrostatic interactions. The synthesis of polycarboxylate crown ethers from tartaric acid is achieved by simple Williamson ether synthesis using thallous ethoxide or sodium hydride as base. Stability constants for the complexation of alkali metal and alkaline earth cations were determined by potentiometric titration. Complexation is dominated by electrostatic interactions but cooperative coordination of the cation by both the crown ether and a carboxylate group is essential to complex stability. Complexes are stable to pH 3 and the ligands can be used as simultaneous proton and metal ion buffers. The low extractibility of the complexes was applied in a membrane transport system which is a formal model of primary active transport.

Flow injection analysis potentiometric selectivity study of alkali metal and alkaline earth cation complexation by 1,3-bis(tropone-2′-oxy)propane

A novel, acyclic, four-oxygen ligand for metal ion complexation has been synthesized and incorporated into poly(vinyl chloride) membrane electrodes. A flow injection analysis (FIA) study was conducted to determine the potentiometric selectivity of 1,3-bis(tropone-2′-oxy)propane for eight alkali metal and alkaline earth cations. The observed selectivity was K +, Rb +, Cs +>Na +>Li +, Sr 2+>Ca 2+>Mg 2+. Only the selectivity for Li + was altered when trioctylphosphine oxide was added to the electrode membrane matrix.

ChemInform Abstract: Synthesis and Alkali Metal Cation Complexation by Benzocrown Ethers.

AbstractAlkali metal picrate (Li, Na, K, Rb, Cs) extraction and association constants for (I)‐(III) are tabulated.

13C NMR chemical shift trends and conformational changes in alkali metal cation complexes of a series of naphthalene crown ethers

Abstract13C NMR studies of alkali metal cation complexation by six related crown ethers are described. The crown ethers (and ions studied) were 2,3‐naphtho‐20‐crown‐6 (Na+, K+, Rb+, Cs+), 2,3‐naphtho‐17‐crown‐5 (Na+, K+, Rb+, Cs+), 2,3‐naphtho‐14‐crown‐4 (Na+, K+, Rb+, Cs+), 1,8‐naphtho‐21‐crown‐6 (Na+, K+, Rb+, Cs+), 1,8‐naphtho‐18‐crown‐5 (Na+, K+, Rb+, Cs+) and 1,5‐naphtho‐22‐crown‐6 (K+, Rb+, Cs+). For each crown ethercation combination, 13C NMR spectra were obtained for a number of different ion concentrations in CD3OD. Data were analysed by a non‐linear least‐squares treatment to give complexation constants and chemical shifts that would result at the limit of complete 1:1 complexation. Analyses of the limiting chemical shifts for a number of carbons indicate regular, cation‐dependent trends (for Cs+ through Na+). Deviations from these trends are interpreted as reflecting differences in conformations of crown ether–cation complexes. Conformational differences between cation complexes that occur near the point of naphthalene attachment cause deviations from the trend in the aromatic carbon chemical shifts, while conformational differences further from the naphthalene cause trend deviations only in the crown ether carbon chemical shifts.

Interactions between metal cations and the ionophore lasalocid. Part 2.—Gibbs functions, enthalpies and entropies for complexation of alkali-metal cations by lasalocid and bromolasalocid

The nature and stability of the complexes formed in methanol through interaction of the ionophore lasalocid, and its 5-bromo-derivative, with alkali-metal cations were studied by a potentiometric method. The involvement of the salicylate group of the ionophore in the complexation process is discussed in the light of u.v.–visible spectra and of literature data. Enthalpies and (from the Gibbs functions) entropies for anionic 1 : 1 metal–ionophore complexes were obtained from calorimetric measurements. The results are discussed in terms of competition between complexation and solvation of the ions. It is shown that the variations observed with different metal cations are a fairly regular function of the size of the cation, suggesting a progressive adaptation of the ionophore with no conspicuous selectivity for any particular cation.

Synthesis and alkali metal cation complexation ofN-aryl [3.2.2] cryptands

Synthesis and alkali metal cation complexation ofN-aryl [3.2.2] cryptands

ChemInform Abstract: New Applications of Crown Ethers. Part 6. Structural Effects of Bis(benzocrown ether)s and Substituted Benzocrown Ethers on Solvent Extraction and Complexation of Alkali Metal Cations.

AbstractThe benzocrown ethers (I) and (II) and bis(benzocrown ether)s such as (III) and (IV) are prepared by reported methods (described only by a scheme).

Influence of solvent, anion and presence of nitrogen in the ring structure on the mechanism of complexation of alkali metal cations with crown ethers

The mechanism of complexation of alkali metal cations with macrocyclic ligands such as the simple crown ethers and the role of desolvation vs. ligand rearrangement are discussed. The unique role of water solvent in the rate-determining step of complexations in aqueous solutions is brought into focus. The competitive role of the anion, which becomes of paramount importance in solvents of low permittivity, is reiterated. Monoazo crown ethers are shown to possess isomeric equilibria in methanol solvent. The rate-determining process for the first step of complexation of these macrocycles with Na+ in methanol appears to be the rearrangement of the ligand through inversion to an exo position of the nitrogen lone electron pair. The rate-determining step of the overall complexation is the entrance of the Na+ into the ring with (possibly) concomitant rotation of the lone electron of the nitrogen to an endo configuration.

Extraction and transport of alkali metal salts by crown ethers and cryptands: estimation of extraction constants and their relationship to transport flux

A method is described for the estimation of two phase extraction constants from stability constants for complexation of alkali metal cations by crown ethers and cryptands. The total free energy change for extraction of alkali metal salts from water to a non-polar organic solvent is evaluated as a sum of free energy terms for complexation, transfers of cation, anion, and complex between solvents, and ion pairing in the non-polar solvent. The method gives satisfactory agreement with a variety of published extraction constants and can be used predictively. As an example, the influence of extraction constant on transport flux was examined using calculated extraction constants and the rate data of Lamb etal. (J. Am. Chem. Soc. 102, 6820 (1980)); rates are adequately modelled by a simple analysis of diffusion.

New applications of crown ethers. Part 6. Structural effects of bis(benzocrown ether)s and substituted benzocrown ethers on solvent extraction and complexation of alkali-metal cations

Bis(benzocrown ether)s consisting of benzo-15-crown-5 (B15C5), benzo-18-crown-6(B18C6) and/or benzo-21-crown-7 (B21C7) with the following linking chains, -(CH2)n-(n= 2 and 8), -(CH2)3-O-, -O-(CH2)6-O-, and -(O-CH2CH2)n-O-(n= 2–5), were prepared and their complexation behaviour was characterized using solvent extraction of alkali-metal picrates and complexation with alkali-metal chlorides. Bis(benzocrown ether)s were distinguished from the corresponding mono(benzocrown ether)s by their remarkable high extraction ability of a cation larger than the hole size of a crown unit, the so-called ‘biscrown effect’. Bis(B15C5)s (4a–h) and bis(B18C6)s (5a–h) preferentially extracted K+ and Cs+, respectively. Bis(benzocrown ether)s containing the B21C7 unit (6a)–(8a) did not show this ‘biscrown effect’ because of the large hole size of B21C7. An unsymmetrical bis(crown ether)(7b) consisting of B15C5 and B18C6 selectively extracted Rb+. The ‘biscrown effect’ was favourably exerted with the oligoethyleneglycol linkage rather than the hydrocarbon one. Little or no effect of lipophilic groups or donor oxygens in the side chain of mono(benzocrown ether)s was observed in the extraction of alkali-metal picrates. Stability constants were determined by the ion-selective electrode method in 90% methanol aqueous solution at 25 °C. In bis(B15C5)s with Na+, and bis(B18C6)s with Na+ or K+, two crown rings in one molecule acted as two individual moieties. Bis(B15C5)s bound with K+ to form preferentially an intramolecular 2 : 1 crown ether unit-K+ complex. Both bis(B15C5)s with Cs+ and bis(B18C6)s with Cs+ systems also showed the ‘biscrown effect’.