Structural and energetic preferences of π, σ, and bidentate cation binding (Li⁺, Na⁺, and Mg²⁺) to aromatic amines (Ph−(CH₂)_n−NH₂, n = 2−5): a theoretical study

Abstract

MP2/aug-cc-pVTZ calculations have been carried out to systematically explore three distinct binding preferences, namely, monodentate binding in π and σ fashions to aromatic and amine groups, respectively, and the bidentate mode of Li⁺, Na⁺, and Mg²⁺) ions with aromatic amines (Ph−(CH₂)_n−NH₂, n = 2−5). Several model systems were devised to examine the binding strength of the interactions where the aromatic and amine motifs are not interconnected. The sensitivity of structures and energetics to the basis set superposition error (BSSE) was examined by doing the geometry optimization with a counterpoise option at the MP2/6-31G(d) and MP2/cc-pVDZ levels. Variations in the binding affinities of Li⁺, Na⁺, and Mg²⁺ metals to π systems and −NH₂ groups are observed. The effects of the spacer chain orientation and its length on the binding of metal ions and protons to aromatic amines are studied. It is observed that Mg²⁺ binding is sensitive to the spacer chain orientation and its length, whereas Li⁺ or Na⁺ binding is independent of spacer chain orientation and length. Reorganization energies are estimated for the complexation of metal ions to aromatic amines. It is observed that the reorganization energy for the complexation of Mg²⁺ is slightly higher than that of Li⁺, Na⁺, and H⁺.