A. Katrusiak et al., Stereochemistry and transformations of NH-N hydrogen bonds - Part II. Proton stability in the monosalts of 1,4-diazabicyclo[2.2.2]octane, J MOL STRUC, 474, 1999, pp. 135-141
Crystal structures of three monosalts of 1,4-diazabicyclo[2.2.2]octane, per
chlorate, tetrafluoroborate and bromide, have been studied by X-ray diffrac
tion. The orthorhombic perchlorate and tetrafluoroborate salts are isostruc
tural, while the bromide salt crystallizes in the hexagonal system. Varying
stabilities of the acidic proton in the NH-N hydrogen bonds, linking the c
ations into chains, have been observed: in the perchlorate salt the H-atom
is ordered, in the tetrafluoroborate it is 0.75:0.25 disordered at two N-si
tes, and in the hydrobromide the H-atom is 50:50 disordered between the sym
metry-related sites. Possible mechanisms leading to the disorder of the pro
tons and their stabilizing factors are discussed. (C) 1998 Elsevier Science
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