catena-Poly[[bis-(di-aqua-lithium)]-μ4-3,3',5,5'-tetra-nitro-4,4'-bi-pyrazole-1,1'-diido]: a new moisture-insensitive alkali-metal energetic salt with a well-defined network structure

Kostiantyn V Domasevitch; Ganna A Senchyk; Harald Krautscheid

doi:10.1107/S2056989023005339

catena-Poly[[bis-(di-aqua-lithium)]-μ₄-3,3',5,5'-tetra-nitro-4,4'-bi-pyrazole-1,1'-diido]: a new moisture-insensitive alkali-metal energetic salt with a well-defined network structure

Acta Crystallogr E Crystallogr Commun. 2023 Jun 20;79(Pt 7):657-663. doi: 10.1107/S2056989023005339. eCollection 2023 Jun 1.

Authors

Kostiantyn V Domasevitch¹, Ganna A Senchyk¹, Harald Krautscheid²

Affiliations

¹ Inorganic Chemistry Department, National Taras Shevchenko University of Kyiv, Volodymyrska Str. 64/13, 01601 Kyiv, Ukraine.
² Institute of Inorganic Chemistry, Leipzig University, Johannisallee 29, D-04103 Leipzig, Germany.

Abstract

In the structure of the title salt, [Li₂(C₆N₈O₈)(H₂O)₄]_n, the 3,3',5,5'-tetra-nitro-4,4'-bi-pyrazole-1,1'-diide dianion [{TNBPz}^2-] is situated across the twofold axis. The distorted coordination octa-hedra around Li⁺ involve four short bonds with two pyrazolate N atoms and two aqua ligands [Li-N(O) = 1.999 (3)-2.090 (2) Å] and two longer contacts with nitro-O atoms [2.550 (2), 2.636 (2) Å]. When combined with μ₄-{TNBPz}^2-, this generates a mono-periodic polymeric structure incorporating discrete centrosymmeric [(H₂O)₂Li-(di-nitro-pyrazolato)₂-Li(H₂O)₂] units. The three-dimensional stack of mutually orthogonal coordination chains is reminiscent of a Lincoln log pattern. It is influenced by conventional hydrogen bonding [O⋯O = 2.8555 (17)-3.0010 (15) Å] and multiple lone pair-π hole inter-actions of the nitro groups [N⋯O = 3.0349 (15) and 3.0887 (15) Å]. The Hirshfeld surface and two-dimensional fingerprint plots also support the significance of non-covalent bonding. Coordinative saturation and a favorable geometry at the Li⁺ ions, dense packing of the polymeric subconnectivities and particularly extensive inter-anion inter-actions may be involved in the stabilization of the structure. The title salt is a rare example of an energetic Li nitro-azolate, which nicely crystallizes from aqueous solution and is neither hygroscopic nor efflorescent. The TG/DTA data reveal total dehydration in the range of 330-430 K and stability of the anhydrous material up to 633-653 K.

Keywords: crystal structure; energetic materials; hydrogen bonding; lithium; nitropyrazoles.

Grants and funding

This work was supported by the Ministry of Education and Science of Ukraine (Project No. 22BF037–11) and the National Research Foundation of Ukraine (Project No. 2020.02/0071).