DFT study of a series of crown-4 ethers and their selectivity trend for alkali metal cations: Li+ and Na+.

The molecular and electronic structures for 12- to 16-crown-4 (named 12C4, 13C4, 14C4, 15C4, 16C4, respectively) and 2,3,5,6,8,9-hexahydrobenzo[b][1,4,7,10] tetraoxacyclododecine (B12C4) 3,5,6,7,9,10-hexahydro-2H-benzo[e][1,4,7,10]tetraoxacyclotridecine (B13C4) and their complexes with alkali metal cations Li+ and Na+ have been explored using the density functional theory (DFT) with B3LYP/ 6-31G* method. The nucleophilicity of crown-4 ethers has been investigated by the Fukui function. Their selectivity trend shows that of all the crown-4 ethers, 14C4 shows the highest cation selectivity for Li+ over Na+, has been achieved on the basis of thermodynamic analysis. In addition, Li+/crown-4 series are more stable than Na+/crown-4 series in the gas phase. The calculated results are in good agreement with the experimental observation.