Crystal structure of poly(ethylenimine)-hydrogen chloride complex

Linear poly(ethylenimine) was found to form a crystalline complex with hydrogen chloride when poly(ethylenimine) in the state of its anhydrate or hydrates was immersed in concentrated hydrochloric acid or exposed to HCl vapour. The crystal structure of the HCl complex was determined by X-ray diffraction. The crystals are metrically tetragonal with cell constants a = b = 5.06 A ̊ and c ( chain axis) = 7.57 A ̊ and the unit cell includes one planar zigzag polymer chain (two monomeric units) and two HCl molecules (the molar ratio is 1:1). The space group of the crystals is, however, not of the tetragonal system: the structure determined can be expressed in terms of any of the following crystal systems and space groups: orthorhombic P222 1, orthorhombic Pcm2 1, orthorhombic Pc2 m, and monoclinic P2 1 m ( c unique). The Cl···N distance of 3.05 Å strongly indicates that every NH and HCl hydrogen atom participates in hydrogen bondings between nitrogen and chlorine atoms. The HCl complex has a fairly high melting temperature of 265°C, which is about 200°C higher than those of the anhydrate and hydrates.