Interaction and selectivity of 14-crown-4 derivatives with Li+, Na+, and Mg2+ metal ions

The interactions between crown ether ligands (14-crown-4, 14C4; 4,4,5,5-tetramethylbenzo-14-crown-4, BC4H12-14C4; 4,4,5,5,9,9,10,10-octamethyl-14-crown-4, C8H24-14C4; dibenzo-14-crown ether-4, DB14C4) and alkaline and alkaline earth metal ions (Li+, Na+, Mg2+) were investigated using density functional theory modeling at the M062X/def2SVP and def2TZVP level. The condensed softness analysis of crown ethers, a condensed Fukui function, a condensed dual descriptor, and frontier molecular orbital theory were used to analyze the reactivities of the complexes. The complex stability was analyzed in terms of the binding energies, standard Gibbs free energy of formation, and energy decomposition of the interaction in aqueous solution. The results show that the active sites were mainly located at the carbon atoms of the benzene ring and oxygen atoms. The reactivities of DB14C4 and BC4H12-14C4 are higher than those of 14C4 and C8H24-14C4. The electrostatic interaction is the principal factor determining the stability of the complexes. The complexes containing Li+ has the greatest stability in aqueous solution among the complexes containing Li+, Na+, and Mg2+. BC4H12-14C4 shows selective adsorption toward Li+ in a mixed solution of Li+, Na+, and Mg2+. To evaluate the stability of complexes containing Mg2+, the solvent effect must be accurately described. An energy decomposition analysis was used to evaluate the stability of complexes containing Li+, Na+, and Mg2+, and the solvent effects were considered.