Abstract
In the structures of the title salts, poly[[μ4-4-(3,5-di-nitro-pyrazol-4-yl)-3,5-di-nitro-pyrazol-1-ido]rubidium], [Rb(C6HN8O8)] n , (1), and its isostructural caesium analogue [Cs(C6HN8O8) n , (2), two independent cations M1 and M2 (M = Rb, Cs) are situated on a crystallographic twofold axis and on a center of inversion, respectively. Mutual inter-molecular hydrogen bonding between the conjugate 3,5-dinito-pyrazole NH-donor and 3,5-di-nitro-pyrazole N-acceptor sites of the anions [N⋯N = 2.785 (2) Å for (1) and 2.832 (3) Å for (2)] governs the self-assembly of the translation-related anions in a predictable fashion. Such one-component modular construction of the organic subtopology supports the utility of the crystal-engineering approach towards designing the structures of polynitro energetic materials. The anionic chains are further linked by multiple ion-dipole inter-actions involving the 12-coordinate cations bonded to two pyrazole N-atoms [Rb-N = 3.1285 (16), 3.2261 (16) Å; Cs-N = 3.369 (2), 3.401 (2) Å] and all of the eight nitro O-atoms [Rb-O = 2.8543 (15)-3.6985 (16) Å; Cs-O = 3.071 (2)-3.811 (2) Å]. The resulting ionic networks follow the CsCl topological archetype, with either metal or organic ions residing in an environment of eight counter-ions. Weak lone pair-π-hole inter-actions [pyrazole-N atoms to NO2 groups; N⋯N = 2.990 (3)-3.198 (3) Å] are also relevant to the packing. The Hirshfeld surfaces and percentage two-dimensional fingerprint plots for (1) and (2) are described.
Highlights
In the structures of the title salts, poly[[4-4-(3,5-dinitropyrazol-4-yl)-3,5dinitropyrazol-1-ido]rubidium], [Rb(C6HN8O8)]n, (1), and its isostructural caesium analogue [Cs(C6HN8O8)n, (2), two independent cations M1 and M2 (M = Rb, Cs) are situated on a crystallographic twofold axis and on a center of inversion, respectively
Many issues of crystal engineering, in regard to control over bonding patterns, supramolecular topologies, molecular packing, and crystal morphologies are highly relevant to the area of energetic materials
We describe the synthesis and structure of rubidium and caesium 4-(3,5-dinitropyrazol4-yl)-3,5-dinitropyrazolates M{H(TNBP)} [M = Rb (1) and Cs (2)], incorporating the peculiar half-deprotonated bipyrazole tectons
Summary
Many issues of crystal engineering, in regard to control over bonding patterns, supramolecular topologies, molecular packing, and crystal morphologies are highly relevant to the area of energetic materials. A more severe limitation is associated with the need for direct bonding between the nitro-rich functionalities only, since the incorporation of any low-energetic component or solvent molecules is an inevitable penalty to the performance Such dilution of the energetic moieties in the crystals is relevant, for example, to a series of hydrogenbonded solids prepared by Aakeroy et al (2015) with acidic ethylenedinitramine and common bitopic pyridine-N bases. Double functionality of the wellperforming material 3,30,5,50-tetranitro-4,40-bipyrazole [H2(TNBP)] (Domasevitch et al, 2019) grants synthetic access either to singly or doubly anionic species [{H(TNBP)}À and {TNBP}2À, respectively] The former combine conjugate dinitropyrazole donor and dinitropyrazolate acceptor sites for sustaining strong N—HÁ Á ÁN bonding. These materials may give an insight into the development of flame colorants in pyrotechnics: rubidium and caesium compounds exhibit, respectively, purple and orange colors when burned
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