Secondary interactions in n-(chloromethyl)pyridinium chlorides (n=2, 3, 4)

Abstract

In the isomeric title compounds, viz. 2-, 3- and 4-(chloromethyl)pyridinium chloride, C6H7ClN+.Cl-, the secondary interactions have been established as follows. Classical N-H...Cl- hydrogen bonds are observed in the 2- and 3-isomers, whereas the 4-isomer forms inversion-symmetric N-H(...Cl-...)(2)H-N dimers involving three-centre hydrogen bonds. Short Cl...Cl contacts are formed in both the 2-isomer (C-Cl...Cl-, approximately linear at the central Cl) and the 4-isomer (C-Cl...Cl-C, angles at Cl of ca 75degrees). Additionally, each compound displays contacts of the form C-H...Cl, mainly to the Cl- anion. The net effect is to create either a layer structure (3-isomer) or a three-dimensional packing with easily identifiable layer substructures (2- and 4-isomers).