Infrared studies of complexes between carboxylic acids and tertiary amines in argon matrices

Abstract

The infrared spectra of the complexes formed between acetic and trifluoroacetic acids and tertiary amines [N(CH₃)₃, N(C₂H₅)₃] in argon matrices and for two-component solid mixtures of acid and amine have been recorded. The spectra show that both 1 : 1 and 2 : 1 complexes of acetic acid and amine isolated in argon matrices have molecular forms characterized by broad v_OH absorption at ≈ 2000 cm^–1. In an acidic environment in both highly concentrated argon matrices and in two-component solid mixtures the proton transfer form CH₃CO^–₂⋯H⁺NR₃ was identified. The 2 : 1 complexes of trifluoroacetic acid and amine isolated in argon matrices have an ionic form as identified by the appearance of characteristic carboxylate group absorption. The spectra also suggest that the 1 : 1 complex forms an ion pair in an argon matrix but this is not conclusive.