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HBr or not HBr? That is the question: crystal structure of 6‐hydroxy‐1,4‐diazepane‐1,4‐diium dibromide redetermined
Author(s) -
Piontek Mateusz,
Morgenstern Bernd,
Steinbrück Nils,
Oberhausen Bastian,
Kickelbick Guido,
Hegetschweiler Kaspar
Publication year - 2019
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 17
ISSN - 2053-2296
DOI - 10.1107/s2053229619005321
Subject(s) - chemistry , crystal structure , crystallography
Liu et al. [ Chin. J. Struct. Chem . (1996). 15 , 371–373] reported the structure of 6‐hydroxy‐1,4‐diazepane di(hydrogen bromide), C 5 H 12 N 2 O·2HBr, which was interpreted in terms of neutral diazepane and HBr molecules. We found, however, ample evidence that the formation of an organic salt, consisting of a diammonium cation and two bromide anions, is more plausible. This interpretation is also in agreement with thermogravimetric analysis and with the observed solution behaviour. The crystal structure of 6‐hydroxy‐1,4‐diazepane‐1,4‐diium dibromide, C 5 H 14 N 2 O 2+ ·2Br − , measured at 142 K, crystallized in the orthorhombic space group P 2 1 2 1 2 1 . The structure displays O—H…Br and N—H…Br hydrogen bonding. Contact distances are given. A search in the Cambridge Structural Database for the singly‐bonded H—Br moiety revealed a total of 69 structures. The question, whether these structures really include HBr as neutral molecules or rather Br − anions and a protonated substrate such as an amine, is addressed.