Synthesis and crystal structure of 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane bis(hydrogen oxalate)

A crystalline salt of 2.2.2-cryptand and oxalic acid, 4,7,13,16,21,24-hexaoxa-1,10-diazoniabicyclo[8.8.8]hexacosane bis(hydrogen oxalate), [H₂(Crypt-222)]²⁺·2(C₂HO₄)^?, was synthesized and studied by single crystal X-ray diffraction. In the crystal structure of this salt, the 2.2.2-cryptand cation has a rare conformation of the exo-exo type in which the H atoms at the two protonated N atoms are oriented outside the cryptand cavity. The geometric parameters (bond lengths, bond angles, torsion angles) of the [H₂(Crypt-222)]²⁺ cation and two independent C₂HO ₄ ^? anions were found with a fairly high accuracy, and the crystal packing was determined. These ions are linked by interionic hydrogen bonds to form thick infinite layers parallel to the (xz) plane.