Selective Transport of Alkali Metal Cations in Solvent Extraction by Proton-Ionizable Dibenzocrown Ethers

Abstract

Lipophilic crown ethers with pendant proton-ionizable groups are novel metal complexing agents for use in solvent extraction of alkali metal cations. A variety of dibenzocrown ether carboxylic acids and dibenzo crown phosphonic acid monoesters have been examined to probe the effect of structural variation within the complexing agent upon selectivity and efficiency in solvent extraction. Results from competitive solvent extractions of alkali metal cations from aqueous solutions into chloroform are summarized.     

Determination of the Concentrations of Metal Cations in Aqueous Solutions Using Proton NMR Spectral Area Integration of the EDTA Complexes

This paper introduces an alternative method to determine the concentrations of metal cations in aqueous solutions, using area integration of proton NMR spectra of EDTA (the disodium salt of ethylenediaminetetraacetic acid) metal complexes. Using this method, a certain volume of unknown metal cation solution is added to an excess amount of standard EDTA solution, and the ratio of the remaining free EDTA and the EDTA–metal complex in the solution can be calculated from the integration areas of the proton NMR spectra. Unlike the conventional complexometric titration, where indicators need to be used to determine the endpoint, this NMR method aims to provide a simple method to eliminate the need for using indicators. This method, when EDTA is used as the standard, is valid for determining the concentrations of nonparamagnetic transition and rare earth metal cations, and for the concentrations of group IIIA and IVA metal cations.     

Formation Constants of Complexes of Monovalent Cations with Benzocrown Ethers in Nitromethane

The complexation reactions between the macrocyclic polyethers dibenzo-18-crown-6, benzo-18-crown-6, benzo-15-crown-5 and polyethers bearing a stilbene unit with alkali metal and silver cations have been studied conductometrically in nitromethane. The formation constants of 1 : 1 and 1 : 2 (metal : ligand) complexes were determined and found to decrease with increasing cation diameter. The stability of the stilbene crown – metal cation complexes is lower than for complexes of other investigated crown ethers with analogous cations. There seem to be some effects of double bond-silver ion interactions.     

Alkali Metal Complexes of the Dipeptides PheAla and AlaPhe: IRMPD Spectroscopy

Complexes of PheAla and AlaPhe with alkali metal ions Na⁺ and K⁺ are generated by electrospray ionization, isolated in the Fourier‐transform ion cyclotron resonance (FT–ICR) ion trapping mass spectrometer, and investigated by infrared multiple‐photon dissociation (IRMPD) using light from the FELIX free electron laser over the mid‐infrared range from 500 to 1900 cm^?1. Insight into structural features of the complexes is gained by comparing the obtained spectra with predicted spectra and relative free energies obtained from DFT calculations for candidate conformers. Combining spectroscopic and energetic results establishes that the metal ion is always chelated by the amide carbonyl oxygen, whilst the C‐terminal hydroxyl does not complex the metal ion and is in the endo conformation. It is also likely that the aromatic ring of Phe always chelates the metal ion in a cation‐π binding configuration. Along with the amide CO and ring chelation sites, a third Lewis‐basic group almost certainly chelates the metal ion, giving a threefold chelation geometry. This third site may be either the C‐terminal carbonyl oxygen, or the N‐terminal amino nitrogen. From the spectroscopic and computational evidence, a slight preference is given to the carbonyl group, in an RO_aO_t chelation pattern, but coordination by the amino group is almost equally likely (particularly for K⁺PheAla) in an RO_aN_t chelation pattern, and either of these conformations, or a mixture of them, would be consistent with the present evidence. (R represents the π ring site, O_a the amide oxygen, O_t the terminal carbonyl oxygen, and N_t the terminal nitrogen.) The spectroscopic findings are in better agreement with the MPW1PW91 DFT functional calculations of the thermochemistry compared with the B3LYP functional, which seems to underestimate the importance of the cation–π interaction.     

Conductometric Determination of the Stability Constants of the Inclusion Complexes of Alkali Cations with [22-DD] Diaza Crown Ether, [211] and [221] Cryptands in Acetonitrile

An equilibrium study concerning the association of Na⁺, K⁺, Rb⁺ and Cs⁺ with 4, 7, 13, 18-tetraoxa-1,10-diazabicyclo [8, 5, 5]-eicosane [211], 4, 7, 13, 16, 21-pentaoxa-1, 10-diazabicyclo [8, 8, 5]-tricosane [221] and 4, 13-didecyl-1, 7, 10, 16-tetraoxa-4, 13-diazacyclooctadecane [22-DD] in acetonitrile has been carried out at 25 °C by using a conductometric technique. The observed molar conductivity, Λ, of a test solution was found to decrease significantly for mole ratios less than 1:1 upon the addition of the complexing ligand. A model based on 1:1 stoichiometry has been used to analyze the conductivity data. The data have been fitted according to a non-linear least-squares analysis that provides the stability constant, K, and the molar conductivity, Λ_c, for each cation – ligand inclusion complex. The binding sequences were found to follow the order: Na⁺ > K⁺ > Rb⁺ ≫ Cs⁺ (K ≈ 0) for [211], Na⁺ > K⁺ > Rb⁺ > Cs⁺ for [221] and K⁺ > Na⁺ > Rb⁺ > Cs⁺ for [22-DD] complexes. Trends in ionic conductivities of complexed ions are also discussed.     

The Stability of Self-inclusion Complexes of Cyclodextrin Derivatives Bearing a p-Dimethylaminobenze Moiety

An appending moiety of modified cyclodextrins acts as an intramolecular guest and forms a self-inclusion complex in aqueous solution. In this study, the stability of self-inclusion complexes of modified cyclodextrins which have a p-dimethylaminobenzene moiety was analyzed by fluorescent decay analyses, and the factor that determines the stability of the self-inclusion complex was determined by a computational approach. The self-inclusion form is stabilized mainly due to van der Waals interaction between the appending moiety and the cyclodextrin ring.     

From CsKTaF7 to CsNaTaF7: Alkali Metal Cations Regulation to Generate SHG Activity**

Inorganic metal halides play important roles in wide range of areas including fluorescence, X-ray detection, and nonlinear-optics. Herein, two new mixed alkali metal tantalum fluorides, CsKTaF₇ and CsNaTaF₇, have been obtained based on the strategy of cations regulation in A₂MF₇ (A represents monovalent cations and M is d⁰ transition-metal cation) system by a conventional hydrothermal route. CsKTaF₇ crystallizes in the centric Pnma space group, while CsNaTaF₇ crystallizes in the polar Cmc2₁ space group and exhibits moderate and phase-matchable NLO activity. Both halides possess large optical band gaps above 5.0 eV. The crystal structure evolution, optical properties, and detailed theory calculations of these two halides were elucidated in this work.     

Record Low Ionization Potentials of Alkali Metal Complexes with Crown Ethers and Cryptands

Electronic properties of series of alkali metals complexes with crown ethers and cryptands were studied via DFT hybrid functionals. For [M([2.2.2]crypt)] (M=Li, Na, K) extremely low (1.70–1.52 eV) adiabatic ionization potentials were found. Such low values of ionization energies are significantly lower than those of alkali metal atoms. Thus, the investigated complexes can be defined as superalkalis. As a result, our investigation opens up new directions in the designing of chemical species with record low ionization potentials and extends the explanation of the ability of the cryptates and alkali crown ether complexes to stabilize multiple charged Zintl ions.     

Polarography of Alkali Metal ion Complexes of Macrotetrolides: Complex ion Size and Stability

Abstract

The stability constants of several alkali metal ion complexes with the macrotetrolides were determined polarographically in acetonitrile. For any single alkali metal ion the stability constant increased in the order nonactin < monactin < dinactin < trinactin. Their values are larger than those found in methanol. The Stoke's radii estimated from the limiting diffusion currents of the complexes increase with increasing crystallographic radius of the cation. The increasing strain on the ligand causes a decrease of stability constant for Rb⁺ and Cs⁺.     

环糊精与乙烯和三十烷醇包结物的研究

本文报道在常压下制备了α-环糊精-乙烯包结物的微细晶体,和环糊精与三十烷醇的溶胶与粉末包结物,以增加长链烷基醇的溶解度。其溶胶在室温下放置半年不凝聚。还用X-射线粉未衍射法、1~H核磁共振及差热-热重分析等方法研究了包结物的形成。     

Structural Investigation of Small Nickel-Ethanol Clusters Using Vibrational Spectroscopy in a Molecular Beam

The structural identification of small nickel clusters with ethanol can help to understand fundamental steps for heterogenous catalysis. We investigate the rows [Ni_x(EtOH)₁]⁺ with x=1–4, and [Ni₂(EtOH)_y]⁺ with y=1–3 via IR photodissociation spectroscopy in a molecular beam experiment. Analyzing the CH- and OH-stretching frequencies and comparing these experimental results with density functional theory (DFT) calculations on the PW91/6-311+G(d,p) level leads to the identification of intact motifs for all clusters and hints for C−O cleavage of the ethanol in two particular cases. Furthermore, we analyze the effects of frequency shifts with the increasing clusters sizes using the results of natural bond orbitals (NBO) analyses and an energy decomposition method.     

Intermetallic Competition in the Fragmentation of Trimetallic Au–Zn–Alkali Complexes

Cationization is a valuable tool to enable mass spectrometric studies on neutral transition‐metal complexes (e.g., homogenous catalysts). However, knowledge of potential impacts on the molecular structure and catalytic reactivity induced by the cationization is indispensable to extract information about the neutral complex. In this study, we cationize a bimetallic complex [AuZnCl₃] with alkali metal ions (M⁺) and investigate the charged adducts [AuZnCl₃M]⁺ by electrospray ionization mass spectrometry (ESI‐MS). Infrared multiple photon dissociation (IR‐MPD) in combination with density functional theory (DFT) calculations reveal a μ³ binding motif of all alkali ions to the three chlorido ligands. The cationization induces a reorientation of the organic backbone. Collision‐induced dissociation (CID) studies reveal switches of fragmentation channels by the alkali ion and by the CID amplitude. The Li⁺ and Na⁺ adducts prefer the sole loss of ZnCl₂, whereas the K⁺, Rb⁺, and Cs⁺ adducts preferably split off MCl₂ZnCl. Calculated energetics along the fragmentation coordinate profiles allow us to interpret the experimental findings to a level of subtle details. The Zn²⁺ cation wins the competition for the nitrogen coordination sites against K⁺, Rb⁺, and Cs⁺ , but it loses against Li⁺ and Na⁺ in a remarkable deviation from a naive hard and soft acids and bases (HSAB) concept. The computations indicate expulsion of MCl₂ZnCl rather than of MCl and ZnCl₂.     

Spectroscopic Study of Azo- and Azoxycrowns Binding with Cations of Similar Ionic Radius

The complexation of 13- and 16-memberedazo- and azoxycrowns with metal cations of similarionic diameter (Na⁺ and Ca²⁺; and K⁺,Ba²⁺, Ag⁺ and Pb²⁺) was studied byuv/visible spectroscopic titration in acetonitrile andMeOH. In MeOH the 13-membered azo- and azoxycrowns 1 and 2 are weakly and non-selectively bound tohard cations of similar ionic diameter, but differentcharge (Na⁺ and Ca²⁺). At the same time thebinding to the soft cation Ag⁺ of larger sizethan the macrocycle cavity is considerably stronger.In contrast to solutions in acetonitrile no bindingwith the small Li⁺ cation was found.The 16-membered azocrowns 3 and 4 alsodiscriminate silver cation in MeOH withlog K = 3.65 ± 0.1 for both compounds.Unexpectedly low bindingwith the hard barium divalent cation of similar size(log K = 1.55 ± 0.4 and 1.95 ± 0.2, respectively)was found for these compounds. Similarly to13-membered compounds no binding with the smallLi⁺ cation was detected. A reverse order ofselectivity was observed for these crowns inacetonitrile with binding constant for association of3 with Ba²⁺ (log K 5.3) considerablyhigher than for other cations. The previously observedstrong binding with the smaller Li⁺ and Na⁺cations is confirmed.     

Influence of the Cyclodextrin Size Cavity in the Complexation of Tetrahydroharmane

The interactions between cyclodextrins and tetrahydroharmane, 1-methyl-1,2,3,4-tetrahydro-9H-pyrido/3,4-b/indole, have been investigated in pH 10.1 aqueous media. Absorption and fluorescence studies, together with lifetime measurements show that tetrahydroharmane forms ground state inclusion complexes with -CD and -CD but not with -CD. Steady state experiments detect only one kind of tetrahydroharmane--CD complex, whereas time resolved measurements reveal the existence of two different types of 1:1 association complexes. The results in -CD are very similar to those in -CD, but the interactions are much weaker.     

Application of a Cation-Exchange Membrane to Determine Cations of Trace Metals in River Water

Donnan-membrane-equilibrium graphite-furnace atomic-absorption spectrophotometry (DME-GFAAS) has been developed to determine cations of trace metals in river water. The method employs a cation-exchange membrane to separate metal cations from their complexes; both total and cationic forms of metals were determined by means of GFAAS. The sensitivity of the method for the measurement of trace metal cations is determined by the detection limits of GFAAS for the metals of interest. Comparable concentrations of metal cations in water from NBS and from the Erhjen river were obtained between the DME-GFAAS and calculated (WATEQ4F) methods, indicating that the developed method is promising for natural fresh waters. The effect of pH on the distribution of metal cation in the NBS river water is significant for Cu and Pb; concentrations of these cations increase with decreasing pH. However, the concentrations of Cd and Zn cations do not vary with pH except that the concentration of the Zn cation decreases significantly as the pH value increases beyond 9. The method was applied to measure the capacity of complexing Cu in Chung-Lu river water, which was estimated to be 2.3 μM.     

An Imine‐Based Molecular Cage with Distinct Binding Sites for Small and Large Alkali Metal Cations

The synthesis of a cylindrical, imine‐based cage composed of two trimeric metallamacrocycles is described. The cage acts as a heterotopic receptor for alkali metal cations. The small cations Li⁺, Na⁺, and K⁺ bind to the outside of the cage with good selectivity for Li⁺, whereas the larger cations Rb⁺ and Cs⁺ are bound inside the cage to form unusual π complexes with a good selectivity for Cs⁺. Negative heterotopic cooperativity between the two binding sites is observed. The complexation of Cs⁺ is associated with a color change, which enables the cage to be used as a specific sensor for Cs⁺.     

Spectral Studies on the Cyclodextrin Inclusion Complexes of Toluidine Blue O and Meldola's Blue in Aqueous Solution

The absorption and emission spectral properties of toluidine blue O (TBO) and Meldola's blue (MDB) in the presence of cyclodextrins (CDs) were studied. Formation of 1 : 1 and 1 : 2 (CD-Dye) inclusion complexes were observed with -CD and -CD, respectively. An increase in the emission intensity was noticed in the presence of -CD due to the formation of 1 : 1 (CD-Dye) inclusion complexes. However, a decrease in the emission intensity was observed in the presence of -CD due to the formation of 1 : 2 (CD-Dye) inclusion complexes. Dimerization of dye molecules in the presence of -CD lead to a decrease in the emission intensity. The formation constants for the 1 : 1 and 1 : 2 (CD-Dye) inclusion complexes were calculated.     

Structures of 18-Crown-6 Complexes with Alkali Cations in Methanolic Solution as Studied by X-ray Absorption Fine Structure

The structures of 18-crown-6 (18C6) complexes with K⁺ and Rb⁺ in methanolic solutions have been studied by X-ray absorption fine structure (XAFS) at the Br K-edge as well as at the K and Rb K-edges. The XAFS spectrum at the K or Rb K-edge has indicated that either Br⁻ or solvent (methanol) molecules are present in the first coordination shell of K⁺ or Rb⁺ complexed by 18C6. However, the spectra obtained at the Br-K edge have strongly suggested that the alkali cations do not exist in the vicinity of Br⁻, indicating that no direct ion-pairing occurs between the 18C6 complex and Br⁻. The 18C6-K⁺ complex maintains D _3d symmetry even in methanol, and two methanol molecules coordinate the cation possibly from above and below the crown plane. In contrast, the corresponding Rb⁺ complex possibly forms an umbrella-shaped complex, in which Rb⁺ is situated slightly off the crown plane and three solvent molecules bind With the cation.