Weak and Reversible Binding of Alkali Metal Ions (Na⁺/K⁺) by an Aza‐Oxa Cryptand

Abstract

A laterally asymmetric cryptand incorporating amino N and ethereal O was utilized to bind the hard alkali metal ions (Na + and K + ) in aqueous medium. Single crystal X-ray diffraction studies revealed that both Na + and K + ions were included inside the cryptand cavity. However, the trapped metal ions were weakly bound and could be released from the cavity of the cryptand. This cryptand had been used as a column chromatographic material for trapping Na + and K + ions from water as the trapped metal ion could be released back into water to extract the cryptand in its free state. Metal binding capability of the cryptand was evaluated using computational studies that revealed lower binding energy (B.E.) for the Na + and K + ions compared to first row transition metal ions. Scheme 1. Cryptand with (a) all O donors (b) all N donors and (c) mixed O and N donors.

Recent Advances in Tris‐Primary Amine Based Organic Imine Cages and Related Amine Macrocycles

“…44 provided trigonal crystallized motifs with K + and Na + and in both cases the metals were immersed into the cryptand cavity maintaining nearly same distances from all the eight donor centres. [ 31 ] During competitive study 44 disclosed preferable encapsulation for Na + over K + . The authors figured out the order of binding energies of 44 ⊂M n+ (M = K + , Na + , and transition metal ions) on the basis of DFT calculation and perceived comparatively weak and reversible bindings with K + and Na + .…”