Structure of 1:1 and 1:2 complexes formed by aromatic NH and OH proton donors with aliphatic amines. Possibility of homoconjugated NHN cation formation

Structure of the complexes with NHN hydrogen bond formed by bis(2,3,5,6-tetrafluoro-4-trifluoromethyl-phenyl)-amine ((4-CF₃C₆F₄)₂NH, FA) as proton donor with aliphatic amines (dibutyl-, tributyl- and trimethylamines) as proton acceptors in aprotic solvents (isooctane and methylene chloride) in a wide range of concentrations and temperatures have been studied by IR and UV spectra. Quantitative treatment of the spectra by a computer program based on factor analysis reveals the equilibrium between free molecules and FA–aliphatic amine complexes of 1:1 and 1:2 composition, the latter having an ionic structure with proton transferred from FA to the aliphatic amine. Thermodynamic characteristics of the 1:1 and 1:2 complexes for FA+dibutylamine system have been measured. Appearance of IR bands indicating formation of NHN⁺ homoconjugated cation has been detected in FA+trimethylamine solution in methylene chloride at temperatures 190–150 K. Spectral manifestations of the complexes containing the (trimethylamine-H-trimethylamine)⁺ cation, formed by FA and OH proton donor (pentachlorophenol) are compared.