catena-Poly[[bis­(di­aqua­lithium)]-μ(4)-3,3′,5,5′-tetra­nitro-4,4′-bi­pyrazole-1,1′-diido]: a new moisture-insensitive alkali-metal energetic salt with a well-defined network structure

In the structure of the title salt, [Li(2)(C(6)N(8)O(8))(H(2)O)(4)]( n ), the 3,3′,5,5′-tetra­nitro-4,4′-bi­pyrazole-1,1′-diide dianion [{TNBPz}(2−)] is situated across the twofold axis. The distorted coordination octa­hedra 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 μ(4)-{TNBPz}(2−), this generates a mono-periodic polymeric structure incorporating discrete centrosymmeric [(H(2)O)(2)Li–(di­nitro­pyrazolato)(2)–Li(H(2)O)(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 inter­actions 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 inter­anion inter­actions may be involved in the stabilization of the structure. The title salt is a rare example of an energetic Li nitro­azolate, 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.