Comprehensive coordination chemistry of alkali and alkaline earth cations with macrocyclic multidentates: latest position

Applications of NMR spectral techniques for the study of macrocycle host‐organic guest interactions. A short review

From a comparison of transfer activity coefficients, [γ(LM+)]PC,2 between propylene carbonate and solvent S2 of alkali or silver ions complexed with dibenzo-substituted crown ethers (L=DB-18-cr-6, DB-21-cr-7, DB-24-cr-8, DB-30-cr-10) it can be concluded that in the complex LM+ both L and M+ are solvated, particularly in solvents of high donicity, e.g., N,N-dimethylformamide. From the abnormally low ionic mobility of DB-30-cr-10K+ in acetonitrile and the high value of the association constant of the ion pair DB-30-cr-10KBr it is concluded that the outer solvent shell is stripped upon formation of the ligand separated ion pair. A linear relation is found between [log γ(LM+)]PC,2 and [logγ(M+)]PC,2 only when L is 18-cr-6, B-18-cr-6, or DB-18-cr-6. Deviation from the linearity of complexes of the larger dibenzo crown ethers is attributed to the flexibility of L. It is shown that solution of 18-cr-6, DB-18-cr-6 and DB-30-cr-10 is enthalpy assisted to a greater extent in acetonitrile than in methanol, while the entropy of solution is more favorable in the latter.

Transfer activity coefficients of crown ethers and their complexes with univalent metal ions between pairs of polar organic solvents

In this paper, a series of crown ether-based liquid crystals was synthesised. The effect of different crown ether ring sizes, terminal groups and complexed salts on the mesomorphic properties was i...

Substituted crown ethers as central units in discotic liquid crystals: effects of crown size and cation uptake

The complexation of the sodium cation by a calix[4]arene tetraester, 5,11,17,23-tetra-p-tert-butyl-25,26,27, 28-tetrakis((ethoxycarbonyl)methoxy)calix[4]arene (1) was studied by 1H and 23Na NMR in a 50:50 v:v mixture of deuteriated acetonitrile and deuteriated chloroform. A 1:1 complex was formed, in very slow exchange, both on the 1H and on the 23Na NMR time scales, with solvated calixarene and sodium cation, respectively. From 1H NMR 2D exchange spectroscopy experiments and 23Na NMR line width analysis, an upper limit of the rate constant for the dissociation of the 1:1 complex was estimated to be 3 Hz. A 2:1 calixarene:sodium complex in fast exchange with the 1:1 complex was evidenced by 23Na NMR. The characteristic 23Na NMR line widths of the 1:1 and of the 2:1 complexes, determined at several temperatures, were linearly related, with a slope of 1.8 ± 0.2. This corresponds to a reorientational correlation time, characteristic of the 23Na quadrupolar relaxation, twice as large in the case of the 2:1 co...

Complexation of the Sodium Cation by a Calix[4]arene Tetraester in Solution. Formation of a 2:1 Calixarene:Sodium Complex

Structure and microdynamics in solution of the dibenzo-24-crown-8 – sodium perchlorate complex have been studied by Na-23 and C-13 nmr. In all solvents (acetone, acetonitrile, pyridine, nitromethane, propylene carbonate, and chloroform-d) and in the binary mixtures acetone/pyridine, acetonitrile/nitromethane, propylene carbonate/methanol, the crown wraps around the sodium cation and expels the conjugate anion and the solvent molecules from the cation coordination sphere. Measurements of Na-23 quadrupolar and C-13 dipole–dipole relaxation times give the effective correlation time of the complex in CDCl3 solution (65 ± 11 ps) and the Na-23 quadrupolar coupling constant in all those solvents and binary mixtures (0.8–1.2 MHz). The sodium coordination shell is completely frozen during a time superior to the reorientational correlation time.

Michel Bisnaire

Papers

L'enrobage moléculaire: complexation du cation sodium par le dibenzo-24-couronne-8