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ORIGINAL PAPER

Interaction and selectivity of 14-crown-4 derivatives with Li+, Na+, and Mg2+ metal ions Yongpan Tian 1 & Wenwen Chen 1 & Zhuo Zhao 1

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Liang Xu 1 & Bihai Tong 1

Received: 21 December 2019 / Accepted: 23 February 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020

Abstract 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. Keywords Crown ether . Alkali metal cations . Alkali earth metal cations . Density functional theory (DFT) . Selectivity Highlights • M062X/def2TZVP is the proper level to calculate the Gibbs free energy of formation of these complexes composed of crown ethers and Li+, Na+, and Mg2+ metal ions with a small BSSE component. • The interactions between crown ethers and Li+, Na+, and Mg2+ ions mainly include electrostatic, dispersion, and repulsion interactions. Electrostatic interactions are principal factors in stabilizing the complexes. The interactions are also visualized using RDG and IGM functions. • The electrophilic reactivities of BC4H12-14C4 and DB14C4 are higher than those of C8H24-14C4 and 14C4 because of the presence of a benzene ring. The stability in aqueous solutions of complexes containing Li+ is the greatest among the complexes containing Li+, Na+, and Mg2+. BC4H12-14C4 shows selective adsorption toward Li+ in the mixed solution containing Li+, Na+, and Mg2+, compared with C8H24-14C4, 14C4, and DB14C4. • Energy decomposition analysis can qualitatively evaluate the stability of complexes containing Li+, Na+, and Mg2+ in aqueous solution when the solvent effect is considered. The key factor to evaluate the stabili