catena-Poly[[bis­(di­aqua­lithium)]-μ4-3,3′,5,5′-tetra­nitro-4,4′-bi­pyrazole-1,1′-diido]: a new moisture-insensitive alkali-metal energetic salt with a well-defined network structure

Domasevitch, K.V.; Senchyk, G.A.; Krautscheid, H.

doi:10.1107/S2056989023005339

research communications

CRYSTALLOGRAPHIC
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ISSN: 2056-9890

Volume 79| Part 7| July 2023| Pages 657-663

https://doi.org/10.1107/S2056989023005339

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catena-Poly[[bis(diaqualithium)]-μ₄-3,3′,5,5′-tetranitro-4,4′-bipyrazole-1,1′-diido]: a new moisture-insensitive alkali-metal energetic salt with a well-defined network structure

Kostiantyn V. Domasevitch,^a ^* Ganna A. Senchyk ^a and Harald Krautscheid ^b

^aInorganic Chemistry Department, National Taras Shevchenko University of Kyiv, Volodymyrska Str. 64/13, 01601 Kyiv, Ukraine, and ^bInstitute of Inorganic Chemistry, Leipzig University, Johannisallee 29, D-04103 Leipzig, Germany
^*Correspondence e-mail: dk@univ.kiev.ua

Edited by S. Parkin, University of Kentucky, USA (Received 2 June 2023; accepted 14 June 2023; online 20 June 2023)

In the structure of the title salt, [Li₂(C₆N₈O₈)(H₂O)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 μ₄-{TNBPz}²⁻, this generates a mono-periodic polymeric structure incorporating discrete centrosymmeric [(H₂O)₂Li–(dinitropyrazolato)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 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.

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

CCDC reference: 2269963

1. Chemical context

Red-light-emitting technical or military pyrotechnics traditionally concern the utilization of Sr salts (Sabatini, 2018 ). However, there is a growing interest for alternative red-flame colorants since strontium is potentially harmful to human health, specifically replacing calcium in bone and affecting skeletal development (Glück et al., 2017 ). Recent works by Klapötke suggest significant potential for lithium-based systems, in particular those incorporating energetic nitropyrazole species (Dufter-Münster et al., 2022 ; Dufter et al., 2020 ). The accumulation of nitro groups enhances acidity (pK_a = 3.14 for 3,5-dinitropyrazole vs 14.63 for the parent pyrazole; Janssen et al., 1973 ) for producing hydrolytically stable salts, while the incorporation of energy-rich nitropyrazolates contributes to oxygen balance of the formulations. In addition, the high nitrogen content and N—N linkage within the pyrazole ring inherently facilitate the release of nitrogen gas when burned. This meets the needs for cooling the flame for improving the color purity (Glück et al., 2017).

However, most of the examined salts are still not suited for applications in spite of such valuable pre-requisites. The nitropyrazolates crystallize with difficulty (Drukenmüller et al., 2014 ) and their Li salts are commonly hygroscopic and deliquescent (Dufter-Münster et al., 2022). In the present work, we address this problem with a crystal-engineering approach. The recently introduced bifunctional tecton 3,3′,5,5′-tetranitro-4,4′-bipyrazole [H₂(TNBPz)] readily affords a range of salts with alkali metal ions (Domasevitch & Ponomarova, 2021 ) and nitrogen bases (Gospodinov et al., 2020 ) and supports either coordination or hydrogen-bonded arrays in a very predictable fashion. One can anticipate that the doubled nitropyrazolate functionality could grant the connection of the Li⁺ ions and generation of a relatively robust polymer, whereas the extended molecular framework of {TNBPz}²⁻ is particularly beneficial for the dense anion–anion interactions because of a larger contribution of dispersion forces. An appropriate set of binding sites for such interactions may be found with four NO₂ functions, which commonly act as self-complementary donor and acceptor groups for non-covalent lone pair–π hole bonds (Bauzá et al., 2017 ). With this in mind, we prepared the new energetic salt catena-poly[[bis(diaqualithium)]-μ₄-3,3′,5,5′-tetranitro-4,4′-bipyrazole-1,1′-diido] and report its structure here.

2. Structural commentary

The molecular structure of the title compound is shown in Fig. 1, with the asymmetric unit comprising one metal ion, two aqua ligands and half a molecule of the organic dianion {TNBPz}²⁻, which is situated across the twofold axis passing through the center of the C—C bond between two pyrazole rings.

Figure 1
The molecular structure of the title compound with displacement ellipsoids drawn at the 50% probability level. Dotted lines indicate distal Li—O(nitro) interactions. Two out of four H atoms of the aqua ligands are equally disordered over two positions (H2A, H2B and H4A, H4B). [Symmetry codes: (i) −x + 1, −y + 1, −z; (ii) −x + $[{1\over 2}]$ , −y + $[{1\over 2}]$ , z.]

The coordination around the Li⁺ ion may be regarded as distorted octahedral, with four relatively short bonds with two pyrazole-N atoms [2.086 (2) and 2.090 (2) Å], two aqua-O atoms [1.999 (3) and 2.027 (3) Å] and two elongated bonds with nitro-O atoms [2.550 (2) and 2.636 (2) Å] (Table 1). A very comparable pattern for lithium 4-amino-3,5-dinitropyrazolate retained only one Li—O(nitro) bond, which was slightly shorter [2.441 (4) Å; Dufter-Münster et al., 2022]. Although the distorted octahedral geometries themselves are well known for Li⁺ (Olsher et al., 1991 ), the spread of the bond lengths is usually narrower. For example, the citrate salt exhibits six Li—O bonds in the range of 1.998 (2)–2.222 (3) Å (Rossi et al., 1983 ). The exceedingly long bonds with nitro groups may be described rather as very weak ion-dipole contacts, while the remaining four shorter bonds almost perfectly match the sum of the corresponding ionic radii for 4-coordinate Li⁺ ions [which are Li—O = 1.94 Å and Li—N = 2.05 Å; Shannon, 1976 ]. Nevertheless, the weak Li—O(nitro) interactions are presumably important for a more effective shielding of the cations against hydration when exposed to moist air. Unlike many related systems, crystals of the title compound are not hygroscopic. A second issue is the saturation of the Li⁺ environment with an appropriate number of aqua ligands. This is contrary to the structures of far more moisture-sensitive 3,4-, 3,5-dinitropyrazolates and 4-amino-3,5-dinitropyrazolate, where the diaqualithium moieties were recognized as local fragments of 1:1 aqualithium chains –Li–[(μ-H₂O)Li]_n– (Dufter-Münster et al., 2022).

Table 1
Selected geometric parameters (Å, °)

Li1—O5	1.999 (3)	Li1—N2ⁱ	2.090 (2)
Li1—O6	2.027 (3)	Li1—O3ⁱ	2.550 (2)
Li1—N1	2.086 (2)	Li1—O1	2.636 (2)

O5—Li1—O6	145.63 (13)	N1—Li1—O3ⁱ	170.20 (11)
O5—Li1—N1	98.49 (10)	N2ⁱ—Li1—O3ⁱ	68.60 (7)
O6—Li1—N1	101.69 (11)	O5—Li1—O1	80.47 (8)
O5—Li1—N2ⁱ	100.84 (11)	O6—Li1—O1	81.94 (9)
O6—Li1—N2ⁱ	101.22 (11)	N1—Li1—O1	67.50 (7)
N1—Li1—N2ⁱ	103.29 (10)	N2ⁱ—Li1—O1	170.76 (11)
O5—Li1—O3ⁱ	78.28 (8)	O3ⁱ—Li1—O1	120.49 (9)
O6—Li1—O3ⁱ	85.66 (8)
Symmetry code: (i) .

The geometric parameters of the {TNBPz}²⁻ dianion are consistent with the data for neutral H₂(TNBPz) (Domasevitch et al., 2019 ) or singly charged species {H(TNBPz)}⁻ (Domasevitch & Ponomarova, 2021). The ion adopts a twisted conformation with two pyrazole rings rotated by 54.48 (4)° (Fig. 1). Although this twist is larger than 42.99 (8)° for Rb{H(TNBPz)} (Domasevitch & Ponomarova, 2021), it is still unusually small, as may be compared with the even less hindered 3,3′,5,5′-tetramethyl-4,4′-bipyrazole analogs (65–90°; Ponomarova et al., 2013 ). In fact, the intramolecular interactions of NO₂ groups, with a shortest contact N3⋯O4ⁱⁱ = 2.9199 (15) Å [symmetry code: (ii) −x + $[{1\over 2}]$ , −y + $[{1\over 2}]$ , z], are likely attractive, as a kind of lone pair–π hole bonding (Bauzá et al., 2017). The central C2—C2ⁱⁱ bond is insensitive to the protolytic effects [1.463 (2) Å vs 1.4644 (15) and 1.462 (2) Å for H₂(TNBPz) and Rb{H(TNBPz)}, respectively], which indicates a lack of essential conjugation between two pyrazolate rings. Shortening of the C-NO₂ bonds upon deprotonation is also minor [mean 1.4308 (16) Å vs 1.439 (2) Å for H₂(TNBPz)], while a certain increase in conjugation is reflected rather by a perceptible flattening of the dinitropyrazole fragments. For the latter, the NO₂ groups are nearly coplanar with the ring, the two dihedral angles are 1.35 (8) and 11.66 (8)°, for N4O3O4 and N3O1O2 groups, respectively. In the case of H₂(TNBPz), the twist comes to 22.8 (2)°. The most appreciable consequence of the dianionic structure is similarity of bond angles at the ring-N atoms: N2—N1—C1 = 107.11 (9)° and N1—N2—C3 = 106.93 (9)°. For the neutral dinitropyrazole rings, the parameters for N- [103.9 (2)°] and NH-sites [112.0 (2)°] are clearly different (Domasevitch et al., 2019).

3. Supramolecular features

The title compound adopts a mono-periodic polymeric structure with the {TNBPz}²⁻ anions acting as tetradentate bridging ligands. Two dinitropyrazolate groups of the anions and two diaqualithium fragments compose the cyclic pattern (Fig. 2), which is reminiscent of the dimers in lithium 3,5-dinitro-4-amino- and 3,4-dinitropyrazolates (Dufter-Münster et al., 2022). Unlike these monofunctional prototypes, with the C2—C2ⁱⁱ bond linking the two pz halves of the bipyrazole core, these dimers are connected into linear chains, with a distance of 9.06 Å between the centroids of the Li₂(pz)₂ cycles (pz is pyrazole).

Figure 2
(a) View of the coordination chains with hydrogen-bond interactions between pairs of symmetry-related aqua ligands that afford layers parallel to the ab plane. The Li⁺ ions are represented by coordination tetrahedra, while considering only the four shortest coordination bonds. (b) Projection of the structure on the ab plane with two successive layers indicated in blue and red. (c) Packing of the coordination chains following a Lincoln log pattern. The chain nodes represent the dilithium units and the chain links are bridging {TNBPz}²⁻ anions. [Symmetry code: (vii) −x + $[{3\over 2}]$ , −y + $[{1\over 2}]$ , z.]

Adjacent chains are linked by a set of conventional hydrogen bonds O—H⋯O, which involve either aqua or nitro-O acceptors. The geometric parameters for five types of such interactions are very comparable (Table 2), with the range of O⋯O separations [2.8555 (17)–3.0010 (15) Å] and nearly straight angles at the H atoms [153 (2)–177 (4)°] indicating directional hydrogen bonding. Bonds of the type O6—H4A⋯O6^vii [symmetry code: (vii) −x + $[{3\over 2}]$ , −y + $[{1\over 2}]$ , z; the H atom is equally disordered over two symmetry-related O atoms] are important for the connection of the chains into layers, which are parallel to the ab plane, whereas the second aqua/aqua bond O5—H⋯O6^v [symmetry code: (v) −x + $[{3\over 2}]$ , y, z + $[{1\over 2}]$ ] and all three aqua/nitro hydrogen bonds actualize between the layers (Fig. 3).

Table 2
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
O5—H1⋯O4ⁱⁱ	0.87 (2)	2.02 (2)	2.8818 (14)	174 (2)
O5—H2A⋯O2ⁱⁱⁱ	0.87 (2)	2.13 (2)	3.0010 (15)	177 (4)
O5—H2B⋯O6^iv	0.87 (2)	2.02 (2)	2.8555 (17)	163 (3)
O6—H3⋯O1^v	0.82 (3)	2.24 (3)	2.9995 (17)	153 (2)
O6—H4A⋯O6^vi	0.92 (4)	2.01 (4)	2.905 (2)	163 (4)
O6—H4B⋯O5^vii	0.95 (5)	1.93 (5)	2.8555 (17)	164 (4)
Symmetry codes: (ii) $[-x+{\script{1\over 2}}, y, z+{\script{1\over 2}}]$ ; (iii) $[-x+1, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]$ ; (iv) $[-x+{\script{3\over 2}}, y, z+{\script{1\over 2}}]$ ; (v) $[x, -y+{\script{1\over 2}}, z-{\script{1\over 2}}]$ ; (vi) $[-x+{\script{3\over 2}}, -y+{\script{1\over 2}}, z]$ ; (vii) $[-x+{\script{3\over 2}}, y, z-{\script{1\over 2}}]$ .

Figure 3
The hydrogen bonding between adjacent coordination chains, which is shown by the dotted red lines. Two successive layers are marked in blue and gray and the Li⁺ ions are presented as coodination tetrahedra, while considering only the four shortest coordination bonds for clarity. The purple lines identify the directions of the coordination chains, which coincide with the crystal directions (110) and ( $[\overline{1}]$ 10). [Symmetry codes: (vi) x, −y + $[{1\over 2}]$ , z − $[{1\over 2}]$ ; (vii) −x + $[{3\over 2}]$ , −y + $[{1\over 2}]$ , z; (ix) x + 1, y, z; (x) x + $[{1\over 2}]$ , y + $[{1\over 2}]$ , −z.]

The coordination chains of two successive layers are inclined, one in relation to the other, and adopt an angle of 78.9° [which is the angle between the (110) and ( $[\overline{1}]$ 10) directions in the crystal]. This nearly orthogonal mutual orientation conditions a very simple packing pattern, in the form of Lincoln log-like stacks (Fig. 2). The {TNBPz}²⁻ anions are situated exactly one on the top of the other at the distances of 4.71 Å corresponding to one half of the c parameter of the unit cell. In spite of the twisted conformation of the bipyrazole, such stacking is geometrically favorable, with every pair of molecules within the stack mutually fitting like puzzles. The resulting interactions are particularly extensive, with four pairs of symmetry-related short contacts N3⋯O4ⁱⁱⁱ = 3.0349 (15) Å and N2⋯O2^vi = 3.0887 (15) Å [symmetry codes: (iii) −x + $[{1\over 2}]$ , y, z + $[{1\over 2}]$ ; (vi) x, −y + $[{1\over 2}]$ , z − $[{1\over 2}]$ ] established by every {TNBPz}²⁻ anion (Fig. 4). For the mutually bonded nitro groups, i.e. N3O1O2 and (N4O3O4)ⁱⁱⁱ, the latter is lone-pair donor and the former one is π-hole acceptor, which combine to create a very characteristic stack (Veluthaparambath et al., 2023 ). The planes of the two groups subtend a dihedral angle of 34.16 (15)°, but the N3⋯O4ⁱⁱⁱ axis is nearly orthogonal to the acceptor plane, as indicated by a slippage angle of 8.6 (2)°. The second type of interaction of is a lone pair–π-hole bond with the dinitropyrazolate ring system. Similar interactions are well known for electron-deficient N-heterocycles and they are most pronounced for 1,2,4,5-tetrazines (Gural'skiy et al., 2009 ). In this case, the interplanar [49.96 (10)°] and slippage angles [13.98 (15)°, with respect to the centroid of the pyrazole ring] are slightly larger. This non-covalent bonding is clearly traced in every structure adopted by H₂(TNBPz) [with very short mutual nitro contacts down to N⋯O = 2.9115 (15) Å; Domasevitch et al., 2019] and its anions (Domasevitch & Ponomarova, 2021) and in fact it may be regarded as a prominent feature for the crystal chemistry of such systems. These close interactions of shape-complementary twisted molecules contribute to the relatively high packing index of 75.8%, which is at the top of the 65–75% range expected for organic solids (Dunitz, 1995 ).

Figure 4
Lone pair-π–hole interactions of the {TNBPz}²⁻ anions. The stacking axis is indicated by the purple line and it coincides with the c-axis direction. [Symmetry codes: (iii) −x + $[{1\over 2}]$ , y, z + $[{1\over 2}]$ ; (vi) x, −y + $[{1\over 2}]$ , z − $[{1\over 2}]$ ; (xi) x, −y + $[{1\over 2}]$ , z + $[{1\over 2}]$ ; (xii) −x + $[{1\over 2}]$ , y, z − $[{1\over 2}]$ .]

4. Hirshfeld analysis

The supramolecular interactions in the title structure were further assessed by Hirshfeld surface analysis (Spackman & Byrom, 1997 ; McKinnon et al., 2004 ; Hirshfeld, 1977 ; Spackman & McKinnon, 2002 ) performed with CrystalExplorer17 (Turner et al., 2017 ). The Hirshfeld surface of the individual {TNBPz}²⁻ anion mapped over d_norm, using a fixed color scale of −0.73 (red) to 1.14 a.u. (blue), indicates a set of red spots associated with the interaction sites (Fig. 5). Two pairs of the most intense spots (−0.72 a.u.) are associated with the Li—N coordination, while the hydrogen bonding is also visualized as prominent features (−0.38 to −0.44 a.u.). The lone pair–π-hole interactions of NO₂ groups are less visible, but they are still detectable on the surface as a set of very diffuse spots (−0.04 a.u.).

Figure 5
Hirshfeld surface of the individual {TNBPz}²⁻ anion, mapped over d_norm (the C—H distances are normalized) in the color range −0.73 (red) to 1.14 a.u. (blue), with the red regions indicating the sites of intermolecular interactions.

The two-dimensional fingerprint plots (Fig. 6) are even more informative. They suggest the significance of coordination and hydrogen-bonding interactions, which are reflected as two sharp spikes pointing to the lower left with the shortest contacts N⋯Li = 2.1 Å and O⋯H = 2.0 Å. One can note a similar indication of N⋯Li (9.6%) and O⋯Li (4.5%) contacts, but the fraction of the latter is significantly less and the corresponding short spike is diffuse. This agrees with the weakness of the coordination bonds adopted by the nitro-O atoms. O⋯H interactions account for 40.1% of the entire number of contacts. This is complemented by a 10.2% contribution of N⋯H contacts, but there are no signs of any O—H⋯N bonding. The plot represents a rather diffuse collection of points with the shortest N⋯H = 2.8 Å. The large fraction of O⋯N/N⋯O and O⋯C/C⋯O contacts (in total over 20%) is a primary indicator for extensive anion–anion interactions. The nature of these contacts is similar and they appear in the plots as nearly symmetrical (about the diagonal where d_i = d_e) pairs of features. Therefore, either donor or acceptor sites of the bonds are found within the individual anions supporting the shortest contacts O⋯N = 3.0 Å and O⋯C = 3.1 Å. It may be postulated that the accessibility of aqua hydrogen-bond donors does not disrupt the main anion–anion interactions, but rather governs elimination of less favorable nitro O⋯O contacts. The total contributions of the C(N)⋯C(N,O) contacts in the title structure and in the very similar unsolvated Rb{H(TNBPz)} (Domasevitch & Ponomarova, 2021) are nearly identical (33.4% and 31.9%, respectively), while the impact of hydrogen bonding is best illustrated by the pronounced contraction of the O⋯O fraction (37.4% to 11.2% in the present case). Moreover, the asymmetry of the O⋯O plot is contrary to the patterns for the O⋯N/N⋯O and O⋯C/C⋯O contacts. This witnesses the prevalence of the nitro/aqua contacts, instead of direct nitro O⋯O interactions.

Figure 6
Two-dimensional fingerprint plots for the individual {TNBPz}²⁻ anion, and delineated into the principal contributions of N⋯Li, O⋯Li, O⋯H, N⋯H, O⋯N/N⋯O, O⋯C/C⋯O and O⋯O contacts. Other contributors are: C⋯N/N⋯C, 1.8%; N⋯N, 0.5% and C⋯C, 0.1% contacts.

5. Synthesis and crystallization

3,3′,5,5′-Tetranitro-4,4′-bipyrazole monohydrate [H₂(TNBPz)·H₂O] is readily available by nitration of 4,4′-bipyrazole in mixed acids (yield 92%) and subsequent crystallization from water (Domasevitch et al., 2019).

For the preparation of the title compound, 0.294 g (7.0 mmol) of LiOH·H₂O was dissolved in 10 ml of water at 333–343 K and then 1.162 g (3.5 mmol) of solid H₂(TNBPz)·H₂O was added with stirring. The mixture was stirred for 30 min and the resulting clear deep-yellow solution was cooled to r.t. Slow evaporation to a minimum volume over 8–10 d led to crystallization of the product as well-developed large lemon-yellow prisms. The crystals were removed and dried on a filter paper in air. The yield was 1.25 g (90%). The material shows neither signs of hygroscopy nor efflorescence when exposed to ambient air for months.

Analysis (%) calculated for C₆H₈Li₂N₈O₁₂: C 18.10, H 2.03, N 28.15; found: C 18.45, H 1.99, N 28.42. IR (KBr, cm⁻¹): 564 m, 636 m, 698 m, 716 m, 773 w, 853 s, 1006 m, 1021 s, 1189 w, 1284 w, 1308 s, 1321 s, 1353 s, 1381 s, 1410 s, 1484 s, 1540 s, 1641 m, 1658 m, 3460 br, 3580 br.

The FT–IR spectrum reveals a distinctive pattern, which is characteristic for hydrated nitropyrazolates. The peaks, which are associated with the aqua ligands, appear at 3460 and 3580 cm⁻¹ (O—H stretching), 1641, 1658 cm⁻¹ (bend) and 564 cm⁻¹ (libration). The peaks for symmetric and asymmetric NO₂ stretching (1351, 1381 and 1484, 1540 cm⁻¹, respectively) are very similar to the spectra of comparable 3,5-dinitropyrazole (Ravi, 2015 ). These double peaks originate in coupling of the NO₂ vibrations with the ring motions. The intense and sharp band at 853 cm⁻¹ is ν(C—NO₂), and its shift, with respect to the band for H₂(TNBPz)·H₂O (839 cm⁻¹; Domasevitch et al., 2019), suggests a certain increase of conjugation of the nitro groups with the carrier aromatic ring upon deprotonation. For Rb{H(TNBPz)}, both these frequencies were present (839 and 852 cm⁻¹; Domasevitch & Ponomarova, 2021).

Preliminary assays for safety of the title compound and its suitability for pyrotechnic formulations were performed by thermal analysis (OZM Research DTA 552-Ex). There are two partially separated stages for nearly identical weight losses in the temperature range of 330–430 K (Fig. 7), which correspond to total dehydration of the salt (in total, −18.49 mass %; −4H₂O: calculated −18.09%). The anhydrous material is stable up to 633 K, with the very minor exothermic event at 597 K possibly indicating a phase transition. Exothermic decomposition proceeds above 653 K, with instantaneous loss of any remaining weight and a sharp exothermic effect at ca 700 K suggesting an explosion. For comparison, typical onset temperatures for decomposition of energetic Li nitropyrazolates are 400–500 K, and only 3,5-dinitropyrazolate is stable up to 600 K (Dufter-Münster et al., 2022).

Figure 7
Combined DTA (red) and TGA (blue) plots for the title compound, in the temperature range of 273–873 K (air, heating rate 5 K min⁻¹).

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. The hydrogen atoms were located and then refined with isotropic thermal parameters. For both aqua ligands, one of the H atoms is equally disordered over two positions, which were refined with 0.5 partial contribution factors and with soft similarity restraints applied to O—H bond lengths [O—H = 0.82 (3)–0.95 (5) Å].

Table 3
Experimental details

Crystal data
Chemical formula	[Li₂(C₆N₈O₈)(H₂O)₄]
M_r	398.08
Crystal system, space group	Orthorhombic, Pccn
Temperature (K)	213
a, b, c (Å)	11.5094 (9), 13.9839 (8), 9.4247 (5)
V (Å³)	1516.87 (17)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	0.17
Crystal size (mm)	0.25 × 0.22 × 0.20

Data collection
Diffractometer	Stoe Image plate diffraction system
No. of measured, independent and observed [I > 2σ(I)] reflections	10855, 1817, 1225
R_int	0.049
(sin θ/λ)_max (Å⁻¹)	0.660

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.030, 0.072, 0.88
No. of reflections	1817
No. of parameters	151
No. of restraints	4
H-atom treatment	All H-atom parameters refined
Δρ_max, Δρ_min (e Å⁻³)	0.28, −0.14
Computer programs: IPDS Software (Stoe & Cie, 2000 ), SHELXS97 (Sheldrick, 2008 ), SHELXL2014/7 (Sheldrick, 2015 ), Diamond (Brandenburg, 1999 ) and WinGX (Farrugia, 2012 ).

Supporting information

CCDC reference: 2269963

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S2056989023005339/pk2688sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989023005339/pk2688Isup2.hkl

checkCIF report

Computing details top

Data collection: IPDS Software (Stoe & Cie, 2000); cell refinement: IPDS Software (Stoe & Cie, 2000); data reduction: IPDS Software (Stoe & Cie, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015); molecular graphics: Diamond 2.1e (Brandenburg, 1999); software used to prepare material for publication: WinGX 1.70.01 (Farrugia, 2012).

catena-Poly[[bis(diaqualithium)]-µ₄-3,3',5,5'-tetranitro-4,4'-bipyrazole-1,1'-diido] top

Crystal data top

[Li₂(C₆N₈O₈)(H₂O)₄]	D_x = 1.743 Mg m⁻³
M_r = 398.08	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pccn	Cell parameters from 8000 reflections
a = 11.5094 (9) Å	θ = 2.9–28.0°
b = 13.9839 (8) Å	µ = 0.17 mm⁻¹
c = 9.4247 (5) Å	T = 213 K
V = 1516.87 (17) Å³	Prism, yellow
Z = 4	0.25 × 0.22 × 0.20 mm
F(000) = 808

Data collection top

Stoe Image plate diffraction system diffractometer	R_int = 0.049
φ oscillation scans	θ_max = 28.0°, θ_min = 2.9°
10855 measured reflections	h = −15→15
1817 independent reflections	k = −16→18
1225 reflections with I > 2σ(I)	l = −12→11

Refinement top

Refinement on F²	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F² > 2σ(F²)] = 0.030	Hydrogen site location: difference Fourier map
wR(F²) = 0.072	All H-atom parameters refined
S = 0.88	w = 1/[σ²(F_o²) + (0.0455P)²] where P = (F_o² + 2F_c²)/3
1817 reflections	(Δ/σ)_max < 0.001
151 parameters	Δρ_max = 0.28 e Å⁻³
4 restraints	Δρ_min = −0.14 e Å⁻³

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Li1	0.62380 (18)	0.42289 (16)	0.0859 (2)	0.0258 (5)
O1	0.57465 (8)	0.25173 (7)	0.18668 (12)	0.0401 (3)
O2	0.42324 (9)	0.16320 (7)	0.21808 (12)	0.0357 (3)
O3	0.17428 (9)	0.50551 (7)	−0.11938 (11)	0.0341 (3)
O4	0.08500 (8)	0.37055 (7)	−0.08988 (11)	0.0327 (3)
O5	0.62403 (9)	0.45230 (8)	0.29341 (11)	0.0336 (3)
O6	0.69704 (11)	0.34427 (9)	−0.07111 (14)	0.0361 (3)
N1	0.44846 (8)	0.38814 (7)	0.06362 (11)	0.0196 (2)
N2	0.36602 (8)	0.43947 (7)	−0.00029 (12)	0.0191 (2)
N3	0.47107 (9)	0.23391 (7)	0.16949 (12)	0.0236 (3)
N4	0.17120 (9)	0.42244 (8)	−0.07765 (11)	0.0212 (2)
C1	0.40259 (10)	0.30164 (9)	0.09198 (13)	0.0187 (3)
C2	0.28824 (10)	0.29180 (9)	0.04627 (13)	0.0176 (3)
C3	0.27171 (10)	0.38324 (8)	−0.01021 (13)	0.0178 (3)
H1	0.5584 (14)	0.4317 (13)	0.327 (2)	0.071 (7)*
H2A	0.608 (3)	0.5133 (13)	0.289 (4)	0.064 (13)*	0.5
H2B	0.671 (2)	0.409 (2)	0.326 (4)	0.047 (10)*	0.5
H3	0.651 (2)	0.3349 (17)	−0.136 (3)	0.089 (9)*
H4A	0.724 (4)	0.284 (3)	−0.053 (4)	0.062 (13)*	0.5
H4B	0.749 (4)	0.390 (3)	−0.108 (5)	0.081 (15)*	0.5

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Li1	0.0233 (10)	0.0256 (12)	0.0285 (13)	−0.0004 (9)	0.0005 (9)	0.0042 (10)
O1	0.0233 (5)	0.0431 (6)	0.0540 (7)	−0.0006 (4)	−0.0134 (5)	0.0113 (5)
O2	0.0439 (6)	0.0233 (5)	0.0397 (6)	−0.0057 (4)	−0.0055 (5)	0.0132 (4)
O3	0.0329 (5)	0.0264 (5)	0.0431 (7)	0.0014 (4)	−0.0059 (4)	0.0133 (5)
O4	0.0219 (5)	0.0358 (6)	0.0406 (6)	−0.0075 (4)	−0.0109 (4)	0.0059 (5)
O5	0.0371 (6)	0.0374 (7)	0.0264 (6)	−0.0090 (5)	−0.0017 (5)	0.0036 (5)
O6	0.0336 (6)	0.0380 (7)	0.0369 (7)	0.0057 (5)	−0.0007 (5)	−0.0095 (5)
N1	0.0195 (5)	0.0176 (5)	0.0218 (6)	−0.0027 (4)	−0.0024 (4)	0.0020 (4)
N2	0.0190 (5)	0.0186 (5)	0.0197 (5)	−0.0032 (4)	0.0003 (4)	0.0014 (4)
N3	0.0257 (6)	0.0221 (6)	0.0229 (6)	−0.0016 (4)	−0.0038 (5)	0.0016 (5)
N4	0.0207 (5)	0.0226 (6)	0.0204 (6)	−0.0010 (4)	−0.0013 (4)	0.0016 (5)
C1	0.0187 (6)	0.0178 (6)	0.0195 (6)	−0.0028 (5)	−0.0011 (5)	0.0014 (5)
C2	0.0184 (6)	0.0178 (6)	0.0167 (6)	−0.0026 (5)	0.0008 (5)	−0.0013 (5)
C3	0.0177 (6)	0.0183 (6)	0.0174 (6)	−0.0021 (5)	−0.0006 (5)	−0.0007 (5)

Geometric parameters (Å, º) top

Li1—O5	1.999 (3)	O5—H2B	0.866 (17)
Li1—O6	2.027 (3)	O6—H3	0.82 (3)
Li1—N1	2.086 (2)	O6—H4A	0.92 (4)
Li1—N2ⁱ	2.090 (2)	O6—H4B	0.95 (5)
Li1—O3ⁱ	2.550 (2)	N1—N2	1.3336 (14)
Li1—O1	2.636 (2)	N1—C1	1.3465 (16)
O1—N3	1.2287 (14)	N2—C3	1.3435 (15)
O2—N3	1.2209 (14)	N2—Li1ⁱ	2.090 (2)
O3—N4	1.2270 (14)	N3—C1	1.4324 (16)
O3—Li1ⁱ	2.550 (2)	N4—C3	1.4292 (16)
O4—N4	1.2346 (13)	C1—C2	1.3917 (16)
O5—H1	0.869 (15)	C2—C3	1.3981 (17)
O5—H2A	0.874 (17)	C2—C2ⁱⁱ	1.463 (2)

O5—Li1—O6	145.63 (13)	H3—O6—H4A	102 (3)
O5—Li1—N1	98.49 (10)	Li1—O6—H4B	99 (3)
O6—Li1—N1	101.69 (11)	H3—O6—H4B	105 (3)
O5—Li1—N2ⁱ	100.84 (11)	N2—N1—C1	107.11 (9)
O6—Li1—N2ⁱ	101.22 (11)	N2—N1—Li1	127.46 (10)
N1—Li1—N2ⁱ	103.29 (10)	C1—N1—Li1	124.64 (10)
O5—Li1—O3ⁱ	78.28 (8)	N1—N2—C3	106.93 (9)
O6—Li1—O3ⁱ	85.66 (8)	N1—N2—Li1ⁱ	129.06 (9)
N1—Li1—O3ⁱ	170.20 (11)	C3—N2—Li1ⁱ	123.87 (10)
N2ⁱ—Li1—O3ⁱ	68.60 (7)	O2—N3—O1	123.53 (11)
O5—Li1—O1	80.47 (8)	O2—N3—C1	118.60 (10)
O6—Li1—O1	81.94 (9)	O1—N3—C1	117.84 (10)
N1—Li1—O1	67.50 (7)	O3—N4—O4	123.35 (11)
N2ⁱ—Li1—O1	170.76 (11)	O3—N4—C3	118.83 (10)
O3ⁱ—Li1—O1	120.49 (9)	O4—N4—C3	117.81 (10)
N3—O1—Li1	110.17 (9)	N1—C1—C2	113.46 (11)
N4—O3—Li1ⁱ	111.00 (9)	N1—C1—N3	118.65 (10)
Li1—O5—H1	106.9 (14)	C2—C1—N3	127.80 (11)
Li1—O5—H2A	99 (3)	C1—C2—C3	98.98 (10)
H1—O5—H2A	99.0 (19)	C1—C2—C2ⁱⁱ	130.38 (13)
Li1—O5—H2B	102 (2)	C3—C2—C2ⁱⁱ	130.46 (12)
H1—O5—H2B	100.4 (19)	N2—C3—C2	113.51 (10)
Li1—O6—H3	111.1 (18)	N2—C3—N4	117.41 (10)
Li1—O6—H4A	121 (2)	C2—C3—N4	129.07 (10)

C1—N1—N2—C3	−0.25 (13)	N1—C1—C2—C3	−0.92 (14)
Li1—N1—N2—C3	169.92 (12)	N3—C1—C2—C3	175.50 (12)
C1—N1—N2—Li1ⁱ	−176.01 (12)	N1—C1—C2—C2ⁱⁱ	174.43 (9)
Li1—N1—N2—Li1ⁱ	−5.8 (2)	N3—C1—C2—C2ⁱⁱ	−9.15 (19)
Li1—O1—N3—O2	−173.04 (11)	N1—N2—C3—C2	−0.36 (14)
Li1—O1—N3—C1	4.91 (15)	Li1ⁱ—N2—C3—C2	175.68 (11)
Li1ⁱ—O3—N4—O4	−175.74 (11)	N1—N2—C3—N4	−179.10 (11)
Li1ⁱ—O3—N4—C3	4.81 (14)	Li1ⁱ—N2—C3—N4	−3.07 (17)
N2—N1—C1—C2	0.78 (14)	C1—C2—C3—N2	0.76 (14)
Li1—N1—C1—C2	−169.73 (11)	C2ⁱⁱ—C2—C3—N2	−174.58 (10)
N2—N1—C1—N3	−175.99 (10)	C1—C2—C3—N4	179.32 (13)
Li1—N1—C1—N3	13.49 (18)	C2ⁱⁱ—C2—C3—N4	4.0 (2)
O2—N3—C1—N1	166.52 (12)	O3—N4—C3—N2	−2.02 (17)
O1—N3—C1—N1	−11.53 (18)	O4—N4—C3—N2	178.50 (11)
O2—N3—C1—C2	−9.7 (2)	O3—N4—C3—C2	179.46 (12)
O1—N3—C1—C2	172.21 (13)	O4—N4—C3—C2	0.0 (2)

Symmetry codes: (i) −x+1, −y+1, −z; (ii) −x+1/2, −y+1/2, z.

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
O5—H1···O4ⁱⁱⁱ	0.87 (2)	2.02 (2)	2.8818 (14)	174 (2)
O5—H2A···O2^iv	0.87 (2)	2.13 (2)	3.0010 (15)	177 (4)
O5—H2B···O6^v	0.87 (2)	2.02 (2)	2.8555 (17)	163 (3)
O6—H3···O1^vi	0.82 (3)	2.24 (3)	2.9995 (17)	153 (2)
O6—H4A···O6^vii	0.92 (4)	2.01 (4)	2.905 (2)	163 (4)
O6—H4B···O5^viii	0.95 (5)	1.93 (5)	2.8555 (17)	164 (4)

Symmetry codes: (iii) −x+1/2, y, z+1/2; (iv) −x+1, y+1/2, −z+1/2; (v) −x+3/2, y, z+1/2; (vi) x, −y+1/2, z−1/2; (vii) −x+3/2, −y+1/2, z; (viii) −x+3/2, y, z−1/2.

Funding information

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).

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