Interaction Of Crown Ethers Research Articles

Selective Interactions of Crown Ethers with Fluosilicic Complex Acids

.One of priority goals of supramolecular chemistryis revealing selective interactions of crown ethers( hosts ) with guest species, resulting in stabiliza-tion of unstable guest species in the form of stablecrystalline inclusion compounds [7, 8]. In this connec-tion, we examined the possibility of selective syn-thesis of crystalline supramolecular complexes ofcrown ethers with fluosilicic complex acids from solu-tions of crown ethers in aqueous HF under the condi-tions of spontaneous formation of fluosilicic acid.We found that evaporation of solutions of 1,4,7,-10,13,16-hexaoxacyclooctadecane (18C6) and

Femtosecond studies of crown ethers: supramolecular solvation, local solvent structure and cation–π interaction

We report here femtosecond studies of microsolvation, host-guest recognition, and cation–π interaction of crown ethers in organic solvents. The side-armed indole ring of the supramolecule acts as an optical probe and a π-donor. Significantly-slow solvation dynamics (e.g. 206 ps in acetonitrile) were observed, revealing ordered local solvent structures. With encapsulation of the alkali-metal cation in the macroring, solvation dynamics become much faster by one order of magnitude, reflecting significant solvent reorganization during molecular recognition. The combined data suggest a folded supramolecular structure involving intercalated solvent molecules or a sandwiched metal cation, consistent with the enhanced local polarization and the strong electrostatic interactions.

Immobilisation of ruthenium cluster catalysts via novel derivatisations of ArgoGel resinsElectronic supplementary information (ESI) available: footnotes to the text. See http://www.rsc.org/suppdata/cc/b1/b106336g/

The ruthenium cluster moiety [Ru6C(CO)17] has been attached to ArgoGel polymer beads using supported phosphine ligands and crown ether interactions with ammonium salt functionalities; these show promising results as hydrogenation catalysts for clean chemical conversions.

Study of Host‐Guest Complexation of Alkaline Earth Metal Ion, Aluminum Ion and Transition Metal Ions with Crown Ethers by Fast Atom Bombardment Mass Spectrometry

AbstractComplexations of crown ethers with alkali metal ions have been investigated extensively by FAB mass spectrometry over the past decade, but very little attention has been paid to reactions of crown ethers with other classes of metal ions such as alkaline earth metal ions, transition metal ions and aluminum ions. Although fast atom bombardment ionization mass spectrometry has proven to be a rapid and convenient method to determine the binding interactions of crown ethers with metal ions, problems in reliabilities for quantitative measurements of” binding strength for the host‐guest complexes have been described in the literature. Thus, in this paper, applications of FAB/MS for investigating the complexation of crown ethers with various classes of metal ions is discussed. Extensive fragmentations for neutral losses such as C2H4O or C2H4 molecules from the host‐guest complexes could be observed. The reason is attributed to the energetic bombardment processes of FAB occuring in the formation of these complexes. Complexes of cyclen with metal ions also show neutral losses of C2H4NH molecules leading to fragment ions. Transition metal ions usually form (Crown + MCl)+ type of ions, alkaline earth metal ions can form both (Crown + MCl)+ and (Crown + MOH)+ type of ions. But for aluminum ions, only (Crown + Al(OH)2)+ type of ions could he observed.

Free energies for association of Cs + to 18-crown-6 in water. A molecular dynamics study including counter ions

Molecular dynamics simulations have been performed to obtain free energy profiles, for the association of Cs + to 18-crown-6 in water. This is the first study of cation—crown ether interactions in aqueous solutions that explicitly includes the counter ion. This work also provides the first quantitative measurement of the influence of the counter ion on the Cs +:18-crown-6 complex potential of mean force and the related thermodynamic properties. Our results illustrate the validity of the potential function and the power of the molecular dynamics approach to the study of cation—crown ether interactions in aqueous solutions.

EXTRACTION OF Mn(II) FROM NITRIC ACID BY CROWN ETHER-SYNERGIZED CATION EXCHANGE EXTENDED EQUILIBRIUM AND INFRARED ANALYSIS*

By use of the modeling program SXLSQA, it has been possible to perform an extensive equilibrium analysis of the extraction of Mn(II) from nitric acid by didodecylnaphthalene sulfonic acid (HDDNS) in combination with either t-butylbenzo-15-crown-5 (tBB15C5) or t-butylcyclohexano-15-crown-5 (tBC15C5) in toluene. Overall, only 1:1 metal:crown ether interactions have been found, and HDDNS acts both as a cation exchanger and as a solvating agent leading to small aggregates. Used alone, HDDNS exists in the form of the fourfold aggregate (HA){sub 4} in equilibrium with the monomer HA (HA represents HDDNS with its acidic proton; associated water is omitted) and extracts Mn(II) to form the species MnH{sub 2}A{sub 4}. The crown ethers used alone extract Mn(II) weakly. When combined with HDDNS, tBB15C5 depresses the extraction of the metal compared with HDDNS used alone. In this case, the apparent antagonism is attributed to the interaction of HDDNS with tBB15C5 to give the adducts (HA)B and (HA){sub 2}B (B represents the crown ether). No complex of Mn(II) with tBB15C5 and HDDNS was found. However, tBC15C5 synergizes the extraction of Mn(II) by HDDNS with formation of a family of 1:1 metal:crown ether complexes of the form M n B H{sub a-2}A{sub a} (a = 2more » to 4). Opposing the synergistic effect was the solvation of the crown ether by HDDNS to give a family of species of the form (HA){sub a}{prime}B (a{prime} = 1, 2 and 4). 42 refs., 9 figs., 2 tabs.« less

The Interaction of Crown Ethers with B-Diketonate Complexes of f-elements

ABSTRACT The interaction of UOz z plusEu3plus, La3plus and Th4pluscomplexes of TTA with several crown ethers have been investigated in benzene and chloroform. The thermodynamic (AG, AH, AS) parameters were measured by extraction and by titration calorimetry. The hydration of the complexes were determined by Karl Fischer and fluorescence techniques. NMR (H-l and C-13) spectra were used to further clarify the nature of the complexes. These spectra indicated that the metal ion more often does not interact equally with all the ether oxygens and the “fit” of the cation to the CE cavity is not significant. The binding to the simple crowns by Ln(TTA)3and UOz(TTA)2follows the CE basicity sequence but with DChl8C6 and DB18C6, steric effects become more important. Such effects are important for Th(TTA)4interactions even in the interactions with the simple crown ether.

121Sb Mössbauer spectra for crown ether adducts of antimony(III) chloride and molecular structure of SbCl3·12-crown-4

The 121Sb Mössbauer spectra for the crown ether (12-crown-4, 15-crown-5 and 18-crown-6) adducts of antimony(III) chloride at 20 K show that the stereochemical activity of the lone pair of the SbIII atom varys with the antimony–crown ether interaction, which is strongest in the 12-crown-4 adduct having the shortest average Sb–O distance of 2.81(7)Å.

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.

Ultraviolet-visible spectroscopic study of ion-pairs of sodium and potassium monoethyl benzeneazophosphonates and their crown ether complexes in acetonitrile

The u.v.-vis spectroscopic study of ion-pairs of the sodium and potassium monoethyl ester of [α-(4-benzeneazoanilino)- N-benzyl] phosphoric acid, [α-(4-benzeneazoanilino)- N-4-hydroxybenzyl] phosphonic acid and [α-(4-benzeneazoanilino)- N-4-methoxybenzyl] phosphonic acid and their complexes with dibenzo-18-crown-6 and dibenzo-24-crown-8 is described. While the free sodium salts of monoethyl benzeneazophosphonic acids, with an extremely low solubility in acetonitrile, may be classified as tight ion-pair salts, the correspondingly more soluble potassium salts exist as solvated loose ion-pairs in acetonitrile solutions. The interaction of crown ether either with sodium or potassium monoethyl benzeneazophosphonates produces crown separated ion-pairs.