The effect of lithium triflate and lithium bromide on the vibrational frequencies of DMEDA

Abstract

An experimental and computational investigation of the structures and vibrational frequencies of N,N′-dimethylethylenediamine–lithium triflate (DMEDA–LiTf; Tf ^– = CF ₃ SO ₃ ^– ) has been done using a combination of hybrid Hartree–Fock/density functional calculations and Raman and IR spectroscopy. Band assignments for DMEDA–LiBr were made by comparing the experimental Raman and IR spectra of a 5 ∶ 1 DMEDA–LiBr sample with the calculated vibrational frequencies of the DMEDA–Li ⁺ and DMEDA–LiBr complexes. Band assignments for DMEDA–LiTf were made by comparing the experimental spectra of samples over a composition range of 20 ∶ 1 to 1.5 ∶ 1 with calculations done on the DMEDA–LiTf complexes. The effect of the lithium cation and lithium triflate on the geometries and vibrational frequencies of the DMEDA will be examined. The combined experimental data and computational results clearly show that the intramolecular hydrogen bonding in pure DMEDA is broken upon addition of lithium bromide or lithium triflate.