Symmetric ethereal hosts for lithium: factors for high affinity and selectivity upon ion recognition

Since the host-guest chemistry field has been formulated, organic hosts for various ions have been studied extensively. It is now widely accepted that structural and electrostatic complementarity is very important in host-guest chemistry. However, the detailed understanding which enables the chemists to design useful hosts is still in paucity. Although the calculated gas-phase binding energy is not of direct use for many practical applications, this could provide an objective measure for the intrinsic affinity. Here, we have calculated approximate binding energies for famous organic hosts for lithium. The selectivity between lithium and sodium was also investigated. 6-311++G(d,p) basis set with B3LYP functional was used to calculate binding energy of Li+ and Na+ with four famous hosts. They are spherand, [2,1,1]cryptand, 12-crown-4 and [1(6)]starand. We examined several factors such as coordination number, partial charge of oxygen, distance from metal to its coordinating oxygen and metal-dipolar moiety interactions. Within the boundary of the chosen four symmetric hosts in this work, charge-dipolar moiety orientation was the factor that roughly explains the calculated binding affinity. [GRAPHICS]