Theoretical study of complexation of alkali metal ions in the cavity of arylazacrown ethers

Complexes of N-arylaza-15(18)-crown-5(6) ethers with K+ and Na+ are studied by the density functional method with and without regard for the specific solvation of the cation by water molecules in the macrocycle cavity. The effects of solvation on the stability of different complex conformers are studied through explicitly including up to four water molecules in the complex. Two types of conformations are considered, namely, the axial type characterized by the existence of a metal-nitrogen bond and the equatorial type, in which this bond is not formed. The selectivity of the arylaza-15(18)-crown-5(6) ethers for Na+ and K+ is estimated using the bonding energy. It is found that both azacrown ethers are selective for sodium, although interaction with water impairs the selectivity.