Search results for "crown ether"

Bis-cyclic Crown Ether Derived from Biphenyl. Different Behaviour in Complexing Hg(SCN)2 and Hg(CN)2

1998

Abstract A new bis-cyclic crown ether containing a biphenyl unit in its structure has been prepared. This compound shows unexpected behaviour in complexing Hg(CN)2. The new ligand transports this mercury salt across liquid membranes with great efficiency. Clear differences have been observed in the complexation of Hg(CN)2 and Hg(SCN)2. The X-ray structure of a 1:2 mercury complex with Hg(SCN)2 is also reported.

Complexation of planar, organic, five-membered cations with crown ethers

2000

Complexation of six aromatic, nitrogen-containing cations with various crown ethers has been studied using 1H NMR, mass spectrometric and crystallographic methods. Hydrogen bonding appears to be the most important interaction in complexation, but minor effects such as π-stacking or cation–π interactions have also been observed. The stability constants of five different imidazolium perchlorate ·crown ether complexes and five other similar cation·DB18C6 complexes were determined by 1H NMR titration in acetonitrile solution. The stability of these complexes in solution and in the gas phase is discussed. The crystal structures of seven complexes were determined in order to study complexation in…

Alkali metal complexation properties of resorcinarene bis-crown ethers: effect of the crown ether functionality and preorganization on complexation

2008

Abstract The synthesis and characterization of tetramethoxy resorcinarene tribenzo-bis-crown ethers, m - and p -TBBC6 , are described. The effect of the added aromatic functionality in the crown ether bridge on the alkali metal complexation properties was investigated and compared to the properties of tetramethoxy resorcinarene bis-crown-5 ( BC5 ) by means of 1 H NMR spectroscopy and X-ray crystallography. It was found that BC5 and m -TBBC6 were capable of binding alkali metal cations (K + , Rb + , and Cs + ), with the highest affinity toward Cs + cation, while no binding was observed in the case of p -TBBC6 , which confirms the significance of the complementarity and preorganization for co…

Synthesis and x-ray crystal structure of dimethyltin(IV) dithiocyanate bihydrate adduct with a crown ether

1985

Me 2 Sn(NCS) 2 (OH 2 ) 2 . 18-crown-6 cristallise dans P2 1 /n avec Z=2; affinement jusqu'a R=0,058

ChemInform Abstract: Crown Ether Substituted 1,4-Distyrylbenzenes and Their Complexation with Alkali Picrates.

2000

Synthesis, Structures and DFT Calculations on Alkaline-Earth Metal Azide-Crown Ether Complexes

2008

The first examples of azide complexes of calcium, strontium or barium with crown ethers have been prepared and fully characterised, notably [Ba([18]crown-6)(N3)2(MeOH)], [Sr([15]crown-5)(N3)2(H2O)], [Ca([15]crown-5)(N3)2(H2O)] and [Sr([15]crown-5)(N3(NO3)]. Crystal structures reveal the presence of a variety of coordination modes for the azide groups including kappa 1-, mu-1,3- and linkages via H-bonded water molecules, in addition to azide ions. The [Ba([18]crown-6)(N3)2(MeOH)].1/3 MeOH contains dinuclear cations with three mu-1,3-NNN bridges, the first example of this type in main group chemistry. The structures obtained have been compared with molecular structures computed by density fun…

Synthesis of a New pH-Dependent Ligand: Conformational and Complexation Studies

2003

A new macrocyclic ligand, 3, which exhibits pH-induced conformational changes, has been prepared. This ligand consists of a crown ether derived from a trans-anti-trans 1,2,4,5-tetrasubstituted cyclohexane. Due to the stereochemistry of the substituents on the carbocyclic ring, two different low-energy conformations of the crown ether are possible. Ligand 3 has been studied in solution by 1H NMR spectroscopy at different values of pH and temperature, showing that the conformation of the crown ether, and thus its complexing ability, is strongly pH-dependent. The solid-state structure of the ligand has been determined by X-ray diffraction.

Computational Study of Nanosized Drug Delivery from Cyclodextrins, Crown Ethers and Hyaluronan in Pharmaceutical Formulations

2015

Abstract The problem in this work is the computational characterization of cyclodextrins, crown ethers and hyaluronan (HA) as hosts of inclusion complexes for nanosized drug delivery vehicles in pharmaceutical formulations. The difficulty is addressed through a computational study of some thermodynamic, geometric and topological properties of the hosts. The calculated properties of oligosaccharides of D-glucopyranoses allow these to act as co-solvents of polyanions in water. In crown ethers, the central channel is computed. Mucoadhesive polymer HA in formulations releases drugs in mucosas. Geometric, topological and fractal analyses are carried out with code TOPO. Reference calculations are…

pH-Dependent ligands as carriers in transport experiments

2004

Abstract Conformationally pH-regulated ligands have been used as carriers in transport experiments. The experiments were carried out through bulky membranes and the pH at the source phase and at the receiving phase were modified to study the ability of ligands to act as pH-regulated carriers. The influence of pH on transport efficiency seems to be related to its influence on conformational equilibrium. X-ray determination of one precursor compound has been useful for determining the stereochemistry of one of the carriers. To cite this article: A.M. Costero et al., C. R. Chimie 7 (2004).

A neutral 2D oxalate-based soluble magnet assembled by hydrogen bonding interactions

2008

Abstract Herein we describe the synthesis, structure and magnetic properties of a novel oxalate-based layered magnetic system: {[Mn(OH2)2(S)2][Mn(S)(OH2)]2[Cr(ox)3]2(18-crown-6)}∞ (S = CH3OH; ox = C 2 O 4 2 - ; 18-crown-6 = C12H24O6) (1). In this case, no cationic templating agent is required to promote the assembling of low-dimensional oxalate-bridged metallic complexes in solution. Instead, strong enough hydrogen bonding interactions are responsible for their packing in the solid state. This magnet is soluble and presents two different types of oxalate bridges: the common bis(bidentate) and the unusual bidentate–monodentate. This structural feature has drastic consequences on the magnetis…