69502-28-9Relevant academic research and scientific papers
Crown Ethers of Low Symmetry. Spiro Crown Ethers and 16-Crown-5 Derivatives
Ouchi, Mikio,Inoue, Yoshihisa,Sakamoto, Hidefumi,Yamahira, Atsushi,Yoshinaga, Masanobu,Hakushi, Tadao
, p. 3168 - 3173 (2007/10/02)
Spiro crown ethers 3a-c, spiro bis(crown ethers) 5a-e, and the related 16-crown-5 derivatives 6a-d were synthesized and their cation binding abilities were evaluated by study of the extraction of aqueous alkali picrates.Crown ethers carrying 13-crown-4 and 16-crown-5 skeletons showed significant changes in cation selectivity as compared with the corresponding 12-crown-4 and 15-crown-5.Spiro-13-crown-4 3a and spiro-bis 5a showed extremely low extractabilities for all cations examined, while the 16-crown-5-derivatives, including spiro-bis 5b and spiro-bis 5c, showed anomalously high Na+ selectivity.In a quantitative study of extraction equilibrium constants (Kex), 16-crown-5 was again found to have much higher selectivity for Na+ than 15-crown-5.This result is attributed to the less symmetrical spatial arrangement of donor oxygen atoms in 16-crown-5; the symmetry-extractability relationship is discussed on the basis of the size-fit concept.
Polytopic Cation Receptors. 2. Synthesis and Selective Complex Formation of Spiro-Linked "Multiloop Crown Compounds"
Weber, Edwin
, p. 3478 - 3486 (2007/10/02)
A new type of crown compound (1-10) featuring a spiro-linked assembly of two to four individual macrorings differing in ring size, rigidity, and donor characteristics is synthesized.Syntheses were achieved by means of high-dilution techniques and blocking/deblocking procedures beginning with pentaerythritol as the basic building block.The ability of the new ligands ("multiloop crown compounds") to selectively form crystalline polyhomonuclear/heteronuclear complexes is studied.It is found that the symmetrically looped molecules (1a-c, 4a, 6, 7d) can incorporate two orthree identical metal cations well matched in their diameter (Li+, Na+, K+, Ca2+, Ba2+).Cations which are too large to fit into the crown rings of 1a-c complex in a sandwich-like manner; those which are too small effect a high hydration in their complexes.Asymmetrical 1d and 9 allow the common uptake of different metal ions, e.g., a combination of Li+ and Ba2+ or of 2K+ and Co2+.The specific occupation of the different subrings is discussed.Ligand 1b is shown to discriminate Ca2+ from Na+; 1c and 6 preferentially complex Ba2+ from a Ba2+/K+ mixture.Thus, the new ligands act as manifold selective cation receptors, corresponding to the specification of their binding compartments.
