Open Accessp ‐Phenylenediamine and its dihydrate: two‐dimensional isomorphism and mechanism of the dehydration process, and N—H...N and N—H...π interactions
Author(s) -
Czapik Agnieszka,
Konowalska Hanna,
Gdaniec Maria
Publication year - 2010
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
eISSN - 1600-5759
pISSN - 0108-2701
DOI - 10.1107/s010827011000541x
Subject(s) - dehydration , isomorphism (crystallography) , process (computing) , mechanism (biology) , chemistry , mathematics , crystallography , combinatorics , physics , computer science , crystal structure , biochemistry , quantum mechanics , operating system
p ‐Phenylenediamine can be obtained as the dihydrate, C 6 H 8 N 2 ·2H 2 O, (I), and in its anhydrous form, C 6 H 8 N 2 , (II). The asymmetric unit of (I) contains one half of the p ‐phenylenediamine molecule lying about an inversion centre and two halves of water molecules, one lying on a mirror plane and the other lying across a mirror plane. In (II), the asymmetric unit consists of one molecule in a general position and two half molecules located around inversion centres. In both structures, the p ‐phenylenediamine molecules are arranged in layers stabilized by N—H...π interactions. The diamine layers in (I) are isostructural with half of the layers in (II). On dehydration, crystals of (I) transform to (II). Comparison of their crystal structures suggests the most plausible mechanism of the transformation process which requires, in addition to translational motion of the diamine molecules, in‐plane rotation of every fourth p ‐phenylenediamine molecule by ca 60°. A search of the Cambridge Structural Database shows that the formation of hydrates by aromatic amines should be considered exceptional.