Fourier-transform infrared study of intramolecular O–Li+⋯ ON ⇌ O–⋯ Li+ON bonds with large Li+ polarizability in 4-substituted 2-diethylaminomethylphenolate N-oxides

Abstract

Six Li⁺ complexes of 4-substituted 2-diethylaminomethylphenolate N-oxides have been synthesized and studied in 0.1 mol dm^–3 CHCl₃ solutions using Fourier transform infrared spectroscopy as a function of the basicity of the phenolate group. In the case of compound 1(R = Bu^t) a relatively asymmetrical Li⁺ potential is present in the O^–Li⁺⋯ ON ⇌ O^–⋯ Li⁺ON bonds, with a deeper well the phenolate groups. However, this bond still shows a large Li⁺ polarizability. In the case of compounds 2(R = Me), 3(R = F) and 4(R = C₆H₅) double minimum Li⁺ potentials are present and are, on average, relatively symmetrical. These bonds show a large Li⁺ polarizability as indicated by intense far-infrared continua. With compounds 5(R = CO₂C₂H₅) and 6(R = NO₂) the basicity of the phenolate group is much less. The spectral feature in the far-infrared has changed completely. Now a broad flat single minimum Li⁺ potential is present in the Li⁺ bonds, with the minimum near the N-oxide group. In these cases the bonds are probably much stronger and shorter.