Nitrogen inversion in the solid state: characterization of a conformational process in crystalline 1,3,5-tribenzyl-1,3,5-triazacyclohexane by X-ray analysis at several temperatures

Abstract

The occupation of the axial and equatorial sites at the N atoms of crystalline 1,3,5-tribenzyl-1,3,5-triazacyclohexane changes with temperature, consistent with dynamic nitrogen inversion in the solid, below ca. 250 K the molecules adopting a single conformation, eaa(e= equatorial, a= axial), but at higher temperatures the equatorial component increasing markedly; from the X-ray results, ΔH° for the a⇌e process is –54 kJ mol^–1 for N(1) and 36 and 37 kJ mol^–1 for N(3) and N(5), while ΔS° is -173 J K^–1 mol^–1 for N(1) and 121 and 118 J K^–1 mol^–1 for N(3) and N(5).