The 1 : 1 and 1 : 2 salts of 1,4-diazabicyclo[2.2.2]octane and bis(trifluoromethylsulfonyl)amine: thermal behaviour and polymorphism

Abstract

The salts of 1,4-diazabicyclo[2.2.2]octane (DABCO) and bis(trifluoromethylsulfonyl)amine (in 1 : 1 and 1 : 2 stoichiometry, 1 and 2, respectively) were investigated by DSC, TGA, PXRD and single crystal X-ray diffraction. Thermal analysis of the two compounds revealed reversible phase transitions, indicating enantiotropic relationships between all the polymorphs. Compound 1 can exist as a room-temperature form 1L and as a high-temperature modification 1H. By contrast, 2 forms a low- (2L), an intermediate- (2I) and a high-temperature (2H) polymorph. The structures of 1L and 2L were determined by single crystal X-ray crystallography. N–H⋯O bonded cations of 1L are arranged in a staggered fashion and form infinite chains. The crystal contains two sets of symmetry related H-bonded chains, which are in an inclined orientation relative to one another. In the structure of 2L, the cation is N–H⋯O bonded to two neighbouring triflimide anions. The discrete H-bonded structure fragments resulting from these interactions assemble to a layer structure. The structure determination of the high-temperature forms 1H and 2H from PXRD data was negatively affected by a high degree of disorder of the triflimide anions. All N–H⋯O bonded DABCO chains in 1H adopt a parallel orientation, which is in contrast to the inclined orientation found in 1L.