High pressure used for producing a new solvate of 1,4-diazabicyclo[2.2.2]octane hydroiodide

Abstract

High pressure efficiently induces polymorphic transformations and various solvates of 1,4-diazabicyclo[2.2.2]octane hydroiodide (dabcoHI). However, it has defied the formation of solvates with methanol. In this article we report on the isochoric crystallization method of producing dabcoHI from methanol:ethanol:water solution above 3 GPa leading to the mixed solvate with methanol, albeit with water as well. A single crystal of dabcoHI·H₂O·CH₃OH has been grown in situ in a diamond-anvil cell, and its structure determined by X-ray diffraction. In its structure the NH⁺⋯N hydrogen bonds, which link the dabco cations into chains in all 10 unsolvated dabcoHI polymorphs, are replaced by H-bonds NH⁺⋯OH⋯N analogous to those in two high-pressure polymorphs of monohydrate dabcoHI·H₂O. The pressure-induced solvation of dabcoHI has been linked to the dimension of voids in the neat compound, and the systematic pressure effect destabilizing the NH⁺⋯N bonds has been demonstrated for the series of dabcoHI polymorphs and solvates.