4,7,13,16,21,24-Hexaoxa-1,10-diazoniabicyclo[8.8.8]-hexacosane Bis(nitrate-hydrogennitrate): Synthesis and crystal structure

A crystalline adduct of 2.2.2-cryptand and nitric acid, H₂(Crypt-222)]²⁺·2(NO ₃ ^? ·HNO₃) (I), is synthesized and studied using X-ray diffraction analysis. The monoclinic structure of compound I (space group C2/c, a = 13.326 Å, b = 15.262 Å, c = 15.020 Å, β = 98.96°, Z = 4) is solved by a direct method and refined by the full-matrix least-squares method in the anisotropic approximation to R = 0.067 for 2647 independent reflections (CAD4 automated diffractometer, λMoK _α radiation). In the structure of compound I, the 2.2.2-cryptand dication lies on an axis 2 and has an endo-endo conformation, for which two H atoms at two protonated N atoms are directed inside the cavity. One of the NO ₃ ^? ·HNO₃ dimers is situated in the inversion center, and the other dimer lies on another axis 2 and is disordered over three orientations. All H atoms in the NO ₃ ^? ·HNO₃ dimers are equiprobably disordered over two close sites. Each of the two NO ₃ ^? ·HNO₃ dimers is formed by the very strong disordered N-O-H···O=N hydrogen bond between the nitric acid molecule and nitrate anion.