DFT study of the carbon- and nitrogen-pivot lariat crown ethers and their complexes with alkali metal cations: Na⁺, K⁺

In this work, a quantum mechanical research of five lariat crown ethers(LCEs), 2-methoxy-15-crown-5(A), N-methoxy-4-aza-15-crown-5(B), N-methoxy-4-aza-18-crown-6(C), N-methoxyethyl-4-aza-18-crown-6(D), N,N'-bis(2-metho xyethyl)-4,13-diaza-18-crown-6(E), which are based on either 15-crown-5 or 18-crown-6 frameworks and contain various pendant arms extending from either carbon or nitrogen atoms on the crown frameworks, had been done using density functional theory with B3LYP/6-31G* method to obtain the electronic and geometrical structures of the LCEs and their complexes with alkali metal ions: Na⁺ and K⁺. The nucleophilicity of LCEs had been investigated by the Fukui functions. For complexes, the match between the cation and cavity size, the status of interaction between alkali metal ions and donor atoms in the LCEs, and the sidearm effect of the LCEs had been analyzed through the other calculated parameters, such as, highest occupied molecular orbital energy, lowest unoccupied molecular orbital energy, and energy gaps. In addition, the enthalpies of complexation reaction had been studied by the calculated thermodynamic data (298 K). The calculated results are all in a good agreement with the experimental data for the complexes.