Anion-directed architectures in amine halide peroxosolvates: role of H2O2/H2O competition in crystal engineering

Abstract

Peroxosolvates have found wide application as a source of hydrogen peroxide for bleaching and disinfecting agents in industry, medicine, household use and organic synthesis. The key problem in their industrial production from aqueous H₂O₂ solutions is the isomorphic substitution of H₂O₂ for H₂O during crystallization, driven by the similarity of hydrogen bonding networks. We report the first crystalline H₂O₂ adducts of primary, secondary and tertiary amine halides, synthesized from 5–97% w/w H₂O₂ solutions. These include peroxosolvates of aminoadamantane hydrochloride, ethylenediammonium dichloride, piperazinium dichloride and dibromide and triethylenediaminium dichloride, characterized by single crystal X-ray diffraction, elemental analysis, powder diffraction, IR spectroscopy and thermal analysis. Single-crystal XRD revealed structures stabilized by charge-assisted H-bond networks between H₂O₂, halide anions and organic ammonium cations. An unprecedented degree of isomorphic substitution of hydrogen peroxide by water, exceeding 50%, was discovered. The formation of peroxosolvates with H₂O₂/H₂O isomorphous substitution was observed for all organic diammonium dihalides, suggesting a potential general trend for such coformers. Solid-state DFT calculations indicate H₂O₂ forms stronger H-bonds than H₂O due to torsional adaptability to the distances between hydrogen bond acceptors. The synthesized peroxosolvates demonstrate relatively high thermal stability (up to 110–140 °C). The monoperoxosolvates of piperazinium dichloride and triethylenediaminium dichloride remain stable under ambient conditions, with a loss in relative H₂O₂ content of only 9.7% and 12.3%, respectively, over three months.