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C. Knoll, D. Müller, G. Giester, J. Ofner, B. Lendl, P. Weinberger, G. Steinhauser:
"An unusually water-poor 5,5´-azobistetrazolate of dysprosium: stabilization of a nitrogen-rich heterocycle by a minimum of hydrogen bonds";
New Journal of Chemistry, 37 (2013), 3840 - 3844.

In inorganic 5,5´-azobistetrazolate (C₂N₁₀^2- ; ZT) compounds, the energetic ZT moiety is usually stabilized by H-bonds to lattice H₂O and/or coordination of an N-atom of the tetrazole ring to the metal ion. Here we present the synthesis and characterization of a novel, salt-like compound [Dy(H₂O)₈]₂ZT₃, which constitutes a unique exception to the above rule. We used supercritical CO₂ as an unconventional desiccant in a straightforward metathesis reaction without abstaining from the benefits aqueous chemistry offers. It caused the crystallization of the title compound with a complex system of H-bonds between [Dy(H₂O)₈]³⁺ and ZT^2- that involves almost every N-atom of the ZT^2- anions as H-bond acceptors, which sufficiently stabilizes the energetic ZT despite the lack of lattice H₂O or a coordinative bond to the metal ion.

dysprosium(III), 5,5´-azo-bistetrazolate, crystal structure

http://dx.doi.org/10.1039/c3nj00492a