Bispyridinium salts: Examining water-to-salt ratio in methylenebispyridinium dichloride and derivatives

Bispyridinium salts (BPS) are a class of organic compounds that are highly effective antimicrobial agents. Whilst effective in such treatments, BPS pose environmental risks as they persist in and are toxic to aquatic and terrestrial ecosystems. Accurate chemical characterisation data is therefore essential when assessing the environmental footprint of processes involving these ubiquitous chemicals. Consequently, historic work presents the formation of white crystals identified as 1,1’-methylenebispyridinium dichloride or the corresponding derivative. However, the inclusion of stoichiometric amounts of water in these crystals went unnoticed, which has implications for accurate quantification of the compound namely the molar mass (261.14 g mol −1 ). Here in this work, we present the X-ray structure of 1,1’-methylenebispyridinium dichloride hydrate to show that water and its hydrogen-bonding capacity facilitate crystallisation. We also analysed infrared data to show that previously reported analogues all contain water. • Novel characterisation aspects of these wastewater pollutants are presented. • Crystallographic and computational evidence show structural inclusion of water. • Included water affects overall bispyridinium mass and related calculations. • Essential in calculations that assess environmental footprint of Bispyridinium salts.