Crown ethers—complexes and selectivity

Theoretical Study on the Extraction of Alkaline Earth Salts by 18-Crown-6: Roles of Counterions, Solvent Types and Extraction Temperatures

“…Selectivity of crown ether not only sensitive toward cation diameter, macrocycle cavity size, donor atoms, electron donating and withdrawing group substitution but also the complementary counterion, solvent types and extraction temperatures. In the case of the charged metal complex and the counterion exist mainly in the same cage solvent, the counterion effects will be observed [3]. The EXAFS experiment showed that even in highly solvated environment, counterion still has influence.…”

Molecular Tuning of Ion Binding to Calcium Signaling Proteins

“…F) Benzo[is]crown-5 and a series of derivatives modified with electron donating or withdrawing substituents. All structures are from Cox.& Schneider (1992) or from Vogtle & Weber (1980). Lehn & Sauvage (1975) and the cryptand structures are illustrated in Fig.…”

“…successively substituted with nitrogen, the cryptand affinities for Ca 2+ , Sr 2+ and Ba 2+ decrease modestly for the first nitrogen substitutions (oxygen: nitrogen ratio 5:3), but begin to drop dramatically when the subsequent nitrogen substitutions equalize the number of coordinating oxygens and nitrogens (oxygen: nitrogen ratio 4:4) (Lehn & Montavon, 1978;Arnaud-Neu et al 1977). Group la monovalent ions, including K + and Na + , exhibit even stronger preference for coordinating oxygen over nitrogen (reviewed by Vogtle & Weber, 1980). High affinity binding requires that the spatial features of the coordinating array be optimally configured in the metal binding cavity.…”

Synthesis of a diazacrown ether containing polymers and formation of complexes with alkaline earth metals

“…This is because monovalent ions usually exhibit a lower stability constant in crown ether or cryp-tand complexes. [8] Therefore, more detailed studies were focused on polymers 1 d and 1 c. The absolute molecular weight of the metal containing polymer was not determined because it is difficult to obtain reliable results for polymers that contain electronic charge on the main chain. [9] Fig.…”