Crystal structure of 1,4-diazoniabicyclo[2.2.2]octane diiodide monohydrate

1,4-diazoniabicyclo[2.2.2]octane diiodide monohydrate was synthesized by protonation of 1,4-diazabicyclo[2.2.2]octane (DABCO) with an excess of concentrated hydroiodic acid in water. It forms colourless rod-like crystals. At room temperature an orthorhombic unit cell, space group Cmc21, a = 7.781(2) Å, b = 13.010(3) Å, c = 11.610 (2) Å, V = 1175.3(4) Å3, Z = 4, is observed. Both nitrogen atoms bear a proton. The hydrate water ämolecule within the compound is statistically disordered on a site besides a crystallographic mirror plane at room temperature. DSC measurements indicate a phase transition at about –10 °C. A single crystal X-ray diffraction measurement at 123 K reveals a primitive unit cell, space group Pca21, a = 12.8835(2) Å, b = 7.6819(1) Å, c = 11.4392(2) Å, V = 1132.16(3) Å3, Z = 4. The water molecule with its hydrogen atoms is well ordered at this temperature. Two almost linear hydrogen bonds O—H···I are formed. The formation of hydrogen bonds is also detected by IR-spectroscopy with O—H stretching frequencies at -v = 3403 cm–1 and -v = 3354 cm–1, respectively.