Energetic alliance of tetrazole-1-oxides and 1,2,5-oxadiazoles

Abstract

The connection of highly endothermic heterocycles with high nitrogen as well as oxygen content is a recent trend in the development of new energetic materials in order to increase densities and stabilities. Bis(1-hydroxytetrazolyl)furazane (9) and bis(1-hydroxytetrazolyl)furoxane (10) were synthesized for the first time from dicyanofurazane and dicyanofuroxane, respectively. Several nitrogen-rich compounds (e.g. ammonium and hydroxylammonium) and metal salts thereof were prepared. Most compounds were characterized by single crystal X-ray diffraction. In addition all compounds were analyzed by vibrational spectroscopy (IR and Raman), multinuclear NMR spectroscopy, elemental analysis and DSC measurements. The heats of formation of 4, 5, 15–16, 20 and 24 were calculated using the atomization method based on CBS-4M enthalpies. With these values and the experimental (X-ray) densities several detonation parameters such as the detonation pressure, velocity, energy and temperature were computed using the EXPLO5 code (V.5.05). In addition, the sensitivities towards impact, friction and electrical discharge were tested using the BAM drop hammer and friction tester as well as a small scale electrical discharge device.

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Introduction

Research towards insensitive replacements for hexogen (RDX), octogen (HMX) and nitropenta (PETN) is still of particular interest in our and many other research groups worldwide. RDX has been identified as toxic and possibly carcinogenic.¹ Several attempts to synthesize appropriate replacements for RDX have been made in the recent past using tetrazole oxides.^2–4 The purpose of this study was to combine furazanes (1,2,5-oxadiazoles) and furoxanes (1,2,5-oxadiazole-2-oxides) with tetrazole oxides. The connection of highly endothermic heterocycles with high nitrogen as well as oxygen content is a recent trend in the development of new energetic materials in order to obtain powerful materials with great density and appropriate oxygen balance on the one hand, and perfect stability on the other hand. Tetrazoles (without N-oxide) have already been attached to furazanes⁵ and furoxanes.⁶ The resulting literature known compounds 24 and 25 as well as the new ones 9 and 10 are displayed in Fig. 1.

Fig. 1 Compounds 9 and 10 and the literature known compounds 24⁵ and 25.⁶

Various nitrogen rich salts of 9 and 10 as well as metal salts were synthesized to investigate their properties as potential energetic ingredients. The resulting 3,4-(1-oxidotetrazolyl)-furoxanes and furazanes are capable and fairly stable compounds in their deprotonated form.

Results and discussion

Synthesis

Compounds 9 and 10 were synthesised using a similar protocol from dicyanofurazane⁷ and dicyanofuroxane⁸ as depicted in Scheme 1.

Scheme 1 Synthetic protocol for 9 and 10.

Hydroximoylamines 3 and 4 are made from the nitriles by exothermic addition of aqueous hydroxylamine in ethanol in about 85% yield. Hydroximoyl chlorides 5 and 6 were synthesized from 3 and 4 by diazotization in 15% HCl and subsequently extracted into diethyl ether. The reaction of 5 and 6 with sodium azide in aqueous ethanol affords hydroximoylazides 7 and 8, respectively, which are also extracted into diethyl ether. The dried ether phase was saturated with gaseous HCl at 0 °C and stirred for 24 h in order to close the desired aromatic tetrazole-oxide rings. Compounds 9 and 10 are obtained as slightly yellow sticky oils after removal of the ethereal HCl solution.

Salts of compounds 9 and 10 could be easily prepared by the addition of a base or the corresponding carbonates/bicarbonates to aqueous solutions of 9 and 10. The silver salt of 10 precipitated upon the addition of aqueous silver nitrate. An overview of the salts prepared in this work is given in Scheme 2.

Scheme 2 Synthesis of salts 11–23.

Crystal structures

Single crystals for XRD of compounds 3–6, 11, 12, 14–17, 20 and 23 could be obtained during this work. Crystallographic data and parameters as well as CCDC numbers are given in Tables S1 and S2 in the ESI.‡

In general, all bond lengths and angles were observed as expected and are comparable to similar crystal structures of furazanes,⁹ furoxanes,¹⁰ and tetrazole-oxides¹¹ in the literature. Compound 3 crystallizes in the monoclinic space group C2/c with four molecules in the unit cell. The molecular unit is generated by C₂ symmetry through atom O1 and bond C1–C1ⁱ. The density (1.667 g cm⁻³ at 100 K) of 3 is significantly smaller than that of the corresponding furazane 7 (1.780 g cm⁻³ at 173 K). Compound 4 crystallizes in the monoclinic space group P2₁/n. The molecular moieties are depicted in Fig. 2.

Fig. 2 Molecular moieties of 3 and 4 thermal ellipsoids are drawn at the 50% probability level. 3: Symmetry code: 1 − x, y, 1.5 − z. Selected bond lengths (Å): O2–N3 1.4194(18), N3–C2 1.291(2), N2–C2 1.351(2); 4: Selected bond lengths (Å): O2–N1 1.224(2), N4–C3 1.354(3), N4–C3 1.354(3), O3–N3 1.418(3).

Hydroximoyl chlorides 5 and 6 crystallize in the monoclinic (P2₁/n) and orthorhombic (P2₁2₁2₁) crystal systems with four molecules in the unit cell. The molecular units are shown in Fig. 3. The density of furazane (1.909 g cm⁻³ at 100 K) again is slightly lower than that of furoxane (1.949 g cm⁻³ at 100 K).

Fig. 3 Molecular moiety of 5 and 6. Thermal ellipsoids are drawn at the 50% probability level.

Crystal structures of both potassium salts were obtained. The structure of furazane 11, which crystallizes in the monoclinic space group P2₁/c, contains two crystal water molecules resulting in a lower density of 1.926 g cm⁻³ (at 100 K). For furoxane 12 (triclinic, P1̄) a density of 2.156 g cm⁻³ at 100 K has been calculated. In both structures two rings (containing atoms C1 and C2/C3) are almost in plane while the third one is significantly deviated. Molecular moieties of 11 and 12 are depicted in Fig. 4.

Fig. 4 Molecular moiety of 11 and 12. Thermal ellipsoids are drawn at the 50% probability level. Selected bond lengths of 11/12 (Å): O1 N1 1.297(2), N1 N2 1.340(2), N1 C1 1.360(2), N2 N3 1.321(2), N3 N4 1.344(2) O2 N5 1.3822(19), O2 N6 1.430(2), O3 N6 1.2343(19)

Compound 14·H₂O could only be obtained in the crystalline form with inclusion of one crystal water molecule (Fig. 5). It crystallizes in the monoclinic space group P2₁ with a density of 1.794 g cm⁻³ at 173 K.

Fig. 5 Molecular moiety of 14·H₂O. Thermal ellipsoids are drawn at the 50% probability level.

Bisammonium salt 15 crystallizes in the orthorhombic space group Pbca with a calculated density of 1.686 g cm⁻³ at 298 K. The corresponding bisammonium furoxane salt 16 crystallizes with a higher density of 1.748 g cm⁻³ (at 293 K) in the monoclinic space group P2₁/c. Both structures shown in Fig. 6 are dominated by strong hydrogen bonds involving all NH₄⁺ protons.

Fig. 6 Molecular moiety of ammonium salts 15 and 16. Thermal ellipsoids are drawn at the 50% probability level. 15: Selected bond lengths (Å): C1–C2 1.455(3), C2–C3 1.432(3), C3–C4 1.457(3), O1–N1 1.327(2), O3–N7 1.327(2); 16: Selected bond lengths (Å): C1–C2 1.450(3), C3–C2 1.423(3), C3–C4 1.449(3), O1–N1 1.3187(19), O2–N5 1.323(2), O4–N10 1.231(2).

The products of deprotonation of 9 with hydrazine and different guanidinium bases have not been obtained as single crystals. The hydrazinium salt of 9 crystallizes in the triclinic (P1̄) crystal system and with a density of 1.727 g cm⁻³ at 236 K without inclusion of crystal water. The molecular moiety is shown in Fig. 7.

Fig. 7 Molecular moiety of hydrazinium salt 17. Thermal ellipsoids are drawn at the 50% probability level.

The bisguanidinium salt 20 (Fig. 8) crystallizes in the monoclinic space group C2/c and with a density of 1.739 g cm⁻³ at 100 K (Fig. 8).

Fig. 8 Molecular moiety of guanidinium salt 20. Thermal ellipsoids are drawn at the 50% probability level. Symmetry code: (i) 1 − x, y, 0.5 − z.

In contrast to 20, the aminoguanidinium salt 23 shows a slightly lower crystal density of 1.692 g cm⁻³. The asymmetric unit of the monoclinic (P2₁/c) cell is shown in Fig. 9.

Fig. 9 Molecular moiety of aminoguanidinium salt 23. Thermal ellipsoids are drawn at the 50% probability level.

NMR spectroscopy

All ¹H NMR and ¹³C NMR shifts of compounds 1–23 are gathered in Table 1. The ¹H NMR spectra of 9 and 10 exhibit both a broad singlet at around 7 ppm although 10 has no C_2V symmetry anymore. The oximes in compounds 3–8 are observed in low field regions from 10.33 to 13.00 ppm. In the case of the oxime and amide protons splitting of the signals of the furoxane compounds can be observed because of the lower symmetry. In the ¹³C NMR spectrum 9 exhibits two resonances at 142.1 ppm caused by furazane and 136.6 ppm caused by 1-hydroxytetrazole. 10 shows four resonances in the ¹³C NMR spectra because of the lower symmetry at 136.8 and 134.4 ppm for the tetrazole oxides and at 143.4 and 103.4 ppm for the furoxane ring. Upon deprotonation the furazane signal of 9 is shifted towards lower fields up to 148.7 ppm and the tetrazole-oxide signal is shifted towards higher fields down to 132.8 ppm. The same trend was observed for 10. Deprotonation led to a shift towards lower fields up to 149.4 and 107.7 ppm for furoxane but to a shift towards higher fields down to 133.2 and 130.3 ppm for the tetrazole-oxide resonances. The ¹⁵N NMR spectrum of 9 is depicted in Fig. 10. The chemical shifts are assigned to the particular nitrogen atoms.

Table 1 ¹H NMR and ¹³C NMR shifts of all compounds

C	^1H NMR shift [ppm]	^13C NMR shift [ppm]
1	—	136.3, 106.7
2	—	134.7, 106.8, 105.0, 99.5
3	10.33, 6.20	148.7, 142.1
4	10.64, 10.08, 6.98, 6.08	151.6, 142.5, 139.8, 109.9
5	13.61	148.7, 122.9
6	13.78, 13.58	150.6, 124.8, 120.3, 110.2
7	12.85	147.1, 132.6
8	13.00, 12.75	149.4, 133.7, 130.4, 107.7
9	9.02	142.1, 136.6
10	6.67	143.4, 136.8, 134.4, 103.4
11	—	145.0, 132.8
12	—	147.7, 133.2, 130.3, 106.5
13	10.22	144.2, 133.9
14	10.27	146.4, 134.3, 131.5, 105.6
15	7.18	144.8, 133.1
16	7.22	147.2, 133.5, 130.7, 106.1
17	7.09	144.8, 133.1
18	7.16	147.1, 133.7, 130.9, 106.1
19	6.63	158.1, 144.2, 132.9
20	6.99	158.5, 146.9, 133.8, 130.9, 105.9
21	—	146.2, 133.2, 130.4, 105.4
22	6.36	158.4, 145.6, 135.1, 132.5, 105.0
23	8.70, 7.26, 6.90, 4.51	159.4, 147.0, 133.8, 130.9, 106.0

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Fig. 10 ¹⁵N{¹H} NMR spectrum of 9.

The carbon signals of the salts 11–23 are shifted to lower fields in comparison with their acids. No irregularities in the ¹H NMR and ¹³C NMR shifts of the nitrogen-rich cations were observed.

Energetic properties

Thermal behavior (DSC). The thermal behaviour of the most important salts (with respect to their energetic behavior) of 9 and 10 is depicted in Fig. 11. The highest thermal stabilities of bis(1-oxidotetrazolyl)furaz(ox)anes are reached by the potassium salts at 277 °C (11) and 265 °C (12), respectively.

Fig. 11 DSC plots of compounds 11, 12, 15, 16, 17 and 18 at 5 °C min⁻¹.

Heats of formation, sensitivities and detonation parameters. Gas phase heats of formation (Δ_fH°_(g,M,298)) were calculated theoretically using the atomization eqn (1) and CBS-4M electronic enthalpies. Details of the computations and the conversion of gas phase values into solid state values are given in the ESI.‡

Δ_fH°_(g,M,298) = H_(M,298) − ΣH°_(atoms,298) + ΣΔ_fH°_(atoms,298) (1)

Sensitivities were measured using a BAM drop hammer, a BAM friction tester¹² and a OZM electrostatic discharge device¹³ (see also the Experimental part, General methods).

Detonation parameters were calculated using the computer code EXPLO5.05¹⁴ using X-ray densities which were converted to room temperature values according to eqn (2). A coefficient of volume expansion¹⁵α_v of 1.5 × 10⁻⁴ K⁻¹ was used. The structures of 15 and 16 were already measured at room temperature. Further explanations are gathered in the ESI.‡

ρ_298K = ρ_T/(1 + α_v(298 − T₀)) (2)

Only the physicochemical properties of compounds 4, 5, 15–16, 20 and 23 are discussed since (i) they consist only of CHNO atoms and (ii) anhydrous crystal structures were obtained. The energetic parameters in comparison with RDX (cyclotrimethylene-trinitramine) are summarized in Table 2. All compounds investigated show improved sensitivities to RDX (IS 7.4 J, FS 120 N). Especially 20 is classified as insensitive towards impact and friction. The highest heat of formation was calculated for hydrazinium salt 17 (Δ_fH°_(s) = 947.5 kJ mol⁻¹). For energetic materials it is more convenient to look for mass based enthalpies or energies. Also the highest mass based energy of formation value (Δ_fU° 3245.4 kJ kg⁻¹) was calculated for 17. The most important detonation parameters (heat of detonation, detonation temperature, pressure, velocity of detonation, and volume of detonation gases) were calculated with the EXPLO5.05 code and are summarized in Table 2. Based on these computations, compound 17 (8843 m s⁻¹) has higher velocity of detonation than RDX (8763 m s⁻¹). However, with respect to the synthetic expenditures and the assessment of all important energetic properties (sensitivities, stabilities and performance) probably none of the compounds will be used as an explosive filler by itself.

Table 2 Energetic properties of 3, 4, 15–17, 20 and 23

	3	4	15	16	17	20	23	RDX
a Impact sensitivity (BAM drophammer (1 of 6)). b Friction sensitivity (BAM friction tester (1 of 6)). c Electrostatic discharge device (OZM research). d Nitrogen content. e Oxygen balance (Ω = (xO − 2yC − 1/2zH)M/1600). f Start of decomposition temperature from DSC (β = 5 °C). g From X-ray diffraction, values for 298 K were calculated with ρ298K = ρT/(1 + αv(298 − T)),^15αv = 1.5 × 10^−4 K^−1. h Calculated enthalpy of formation. i Calculated energy of formation. j Energy of explosion. k Explosion temperature. l Detonation pressure. m Detonation velocity. n Volume of detonation gases (assuming only gaseous products).
Formula	C4H6N6O3	C4H6N6O4	C4H8N12O3	C4H8N12O4	C4H10N14O3	C6H12N16O4	C6H14N18O4	C3H6N6O6
FW/g mol^−1	186.13	202.13	272.18	288.18	302.21	372.26	402.29	222.12
IS/J^a	>40	10	9	10	7	30	8	7.4^16
FS/N^b	>360	240	>360	240	>360	>360	>360	120^16
ESD/J^c	>1.5	0.25	1.5	1	1.5	n.d.	n.d.	0.2
N/%^d	45.15	41.58	61.75	58.32	64.89	60.20	62.67	37.84
Ω CO2/%^e	−68.76	−55.40	−52.90	−44.41	−52.94	−60.17	−59.65	−21.61
T Dec./°C^f	198	180	259	234	211	197	165	205
ρ/g cm^−3^g	1.668(100 K)	1.781(173 K)			1.727(236 K)	1.739(100 K)	1.692(100 K)	1.858(90 K)^17
	1.64(298 K)	1.75(298 K)	1.686(293 K)	1.748(293 K)	1.71(298 K)	1.69(298 K)	1.64(298 K)	1.806(298 K)^18
ΔfHm°/kJ mol^−1^h	150.2	159.3	625.6	621.7	947.5	638.3	885.4	66.6^16
ΔfU°/kJ kg^−1^i	907.1	886.4	2402.8	2260.2	3245.4	1820.8	2311.2	400.2^16
EXPLO5.05:
−ΔExU°/kJ kg^−1^j	4713	5323	5122	5530	5779	4532	4884	6110
T det/K^k	3286	3631	3582	3841	3813	3193	3340	4224
P CJ/kbar^l	229	287	279	313	318	261	261	351
V Det./m s^−1^m	7727	8312	8364	8671	8843	8161	8224	8763
V o/L kg^−1^n	720	719	769	772	793	764	782	739

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Conclusions

From this combined experimental and theoretical study the following conclusions can be drawn.

– The combination of furazanes or furoxanes with tetrazole-1-oxides is a suitable strategy in order to generate new triheterocyclic high-performing energetic materials due to their large positive heats of formation and appropriate densities.

– Generally the investigated furoxanes show mostly higher densities but lower thermal stabilities than the corresponding furazanes. Therefore, furazanes mostly are the better choice as energetic backbone heterocycles.

– The thermal stability of the tetrazole oxide anions attached to a furoxane or furazane ring is sufficient to reach decomposition temperatures above 200 °C.

Experimental part

For general methods, please see the ESI.‡

Syntheses

Bisaminohydroximoylfurazane (3). 10.8 g (90 mmol) of 1 was dissolved in 45 mL of ethanol and added within 15 min to 22.2 g (336 mmol) of 50% hydroxylamine solution, which was diluted with 90 mL of ethanol. The solvent was removed under reduced pressure until crystallization started. Upon filtering 9.3 g (50 mmol, 55%) of 3 were obtained as a yellowish powder. DSC (5 °C min⁻¹): 193 (mp.), 198 °C (dec.). Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 3162 (6), 1651 (71), 1592 (17), 1535 (35), 1513 (100), 1374 (43), 1282 (6), 1126 (6), 1040 (16), 984 (32), 956 (9), 923 (8), 826 (4), 761 (6), 488 (14) cm⁻¹. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 10.33, 6.20 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 148.7, 142.1 ppm.

Bisaminohydroximoylfuroxane (4). 1.4 g of dicyanofuroxane (10 mmol) was dissolved in 30 mL of ethanol and 1.3 g of 50% hydroxylamine solution in 10 mL of ethanol was added. After stirring for 30 min the solvent was removed and the residue was suspended in 20 mL of diethyl ether. The solid was filtered yielding 1.7 g (8.4 mmol, 84%) of the yellowish product. DSC (5 °C min⁻¹): 180 (dec.)°C. IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3463 (w), 3371 (w), 3309 (w), 1668 (m), 1647 (s), 1579 (s), 1539 (w), 1504 (m), 1418 (m), 1360 (m), 1311 (m), 1229 (w), 1082 (w), 1021 (w), 951 (s), 929 (s), 858 (w), 810 (m), 744 (vs), 688 (s) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 3372 (12), 1671 (39), 1651 (34), 1582 (13), 1542 (100), 1507 (12), 1421 (20), 1310 (14), 1232 (14), 1107 (10), 1066 (10), 1021 (10), 956 (9), 933 (11), 860 (6), 756 (10), 639 (6), 480 (24), 370 (5), 330 (11), 299 (5), 263 (6) cm⁻¹. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 10.64, 10.08, 6.98, 6.08 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 151.6, 142.5, 139.8, 109.9 ppm. EA (C₄H₆N₆O₄, 202.13 g mol⁻¹) calc. (found): C 23.77 (23.99), H 2.99 (2.86), N 41.58 (41.45)%. IS: 10 J (<100 μm). FS: 240 N. ESD: 0.25 J.

Bischlorohydroximoylfurazane (5). 6.9 g (37 mmol) of 3 was dissolved in 200 mL of semi-conc. hydrochloric acid. A solution of 6.3 g (92 mmol) of sodium nitrite in 30 mL of water was added dropwise within one hour while maintaining the temperature below 0 °C. The solution was stirred for one hour, allowed to come to ambient temperature, diluted with 200 mL of water and was extracted with 4 × 35 mL of diethyl ether. The organic phase was dried over magnesium sulfate and the solvent was removed under reduced pressure to obtain 7.97 g (35 mmol, 96%) of 5 as an oily liquid which partially started to crystallize.

DSC (5 °C min⁻¹): 115 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3502 (m), 3388 (m), 2991 (w), 2877 (w), 1731 (w), 1607 (m), 1561 (w), 1507 (w), 1499 (w), 1397 (m), 1390 (m), 1376 (m), 1359 (m), 1343 (m), 1265 (m), 1193 (w), 1094 (vw), 1057 (s), 1032 (s), 999 (s), 962 (s), 900 (s), 887 (vs), 863 (s), 818 (m), 795 (w), 749 (vw), 664 (m) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 3397 (6), 2944 (9), 2245 (3), 1626 (9), 1611 (100), 1563 (14), 1509 (89), 1396 (16), 1374 (3), 1361 (2), 1273 (3), 160 (8), 1002 (3), 968 (4), 889 (18), 864 (2), 666 (29), 655 (6), 616 (5), 601 (7), 499 (7), 430 (13), 413 (3), 366 (4), 325 (7), 296 (9), 241 (19), 226 (10), 182 (8), 151 (10), 102 (55), 76 (11), 67 (6) cm⁻¹. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 13.61 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 148.7, 122.9 ppm. EA (C₄H₂N₄O₃Cl₂, 224.99 g mol⁻¹) calc. (found): C 21.35 (23.19), H 0.90 (1.53), N 24.90 (22.76)%.

Bischlorohydroximoylfuroxane (6). 4 (34.8 g, 0.2 mol) was dissolved in 500 mL of 34% hydrochloric acid (595 g, 6.0 mol). The solution was cooled with a salt-ice bath and additionally 500 g of ice was added to the solution. Sodium nitrite (31.1 g, 0.5 mol) was dissolved in little water and added dropwise over 1 h while keeping the temperature below 0 °C. Afterwards the solution was allowed to warm to ambient temperature and diluted by addition of 1 L of ice water. The product was extracted three-times with 200 mL of diethyl ether and dried over magnesium sulfate. 6 was obtained as a slightly yellow oily liquid which partially started to crystallize to give a total yield of 41.1 g (170 mmol, 81%). ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 13.78, 13.58 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 150.6, 124.8, 120.3, 110.2 ppm.

Bisazidohydroximoylfurazane (7). 7.96 g (35 mmol) of 5 was dissolved in 50 mL of ethanol and 6.53 g (100 mmol) of sodium azide in 50 mL water was added at 0–5 °C. The suspension was stirred for 1 h on ice, diluted with 100 mL of water and brought to pH 2 using 2 M hydrochloric acid. The product was extracted with 5 × 30 mL of diethyl ether. The organic phase was dried over magnesium sulfate. The product does not need to be isolated for the continuing steps. If the solvent is removed a yellowish oil is obtained in approx. 80% yield which partially starts to crystallize on standing. IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3258 (m), 3035 (w), 2981 (w), 2855 (w), 2361 (vw), 2325 (vw), 2132 (s), 1733 (w), 1614 (m), 1558 (vw), 1516 (w), 1445 (w), 1389 (m), 1340 (s), 1272 (s), 1223 (m), 1108 (vw), 1093 (w), 1026 (s), 976 (vs), 936 (s), 899 (m), 855 (s), 819 (w), 781 (vw), 753 (w), 668 (vw) cm⁻¹. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 12.85 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 147.1, 132.6 ppm.

Bisazidohydroximoylfuroxane (8). 6 (3.9 g, 16 mmol) was dissolved in 20 mL of ethanol and cooled with an ice bath while an aqueous solution of sodium azide (2.6 g, 40 mmol) was added in small portions. After the addition of sodium azide, the mixture was stirred for 1 h. The yellowish solution was diluted with 70 mL of ice water, adjusted to pH 1 by addition of concentrated hydrochloric acid and extracted with 3 × 30 mL and 1 × 10 mL of diethyl ether. The organic phase was dried over magnesium sulfate and the solvent was removed under reduced pressure. 8 was obtained as a yellowish oil in approx. 80% yield. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 13.00, 12.75 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 149.4, 133.7, 130.4, 107.7 ppm.

Bis(1-hydroxytetrazolyl)furazane (9). The ethereal solution of 7 was saturated with gaseous HCl below 5 °C, the reaction flask was sealed and was then allowed to come to ambient temperature and stirred overnight. The solvent was removed under reduced pressure and bis(1-hydroxytetrazolyl)furazane was obtained as a yellowish oily liquid. DSC (5 °C min⁻¹): 91 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3404 (w), 2255 (w), 2128 (w), 1713 (w), 1660 (m), 1463 (m), 1344 (m), 1246 (m), 1197 (m), 1103 (m), 1053 (s), 1022 (s), 1005 (s), 982 (s), 922 (s), 895 (s), 819 (vs), 758 (s), 729 (s), 709 (m), 686 (m), 673 (m) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 2982 (8), 2940 (70), 2878 (14), 1618 (100), 1453 (10), 1387 (7), 1261 (30), 1205 (6), 1111 (5), 1011 (8), 907 (10), 764 (5), 736 (15), 711 (5), 455 (10), 92 (38) cm⁻¹. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 9.02 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 142.1, 136.6 ppm. ¹⁵N{¹H} NMR (400 MHz, DMSO-d₆, 25 °C), δ: 38.39, −2.1, −17.4, −51.1, −111.1 ppm.

Bis(1-hydroxytetrazolyl)furoxane (10). The oily compound 8 (3.3 g, 13 mmol) was dissolved in 100 mL of diethyl ether. Gaseous HCl was passed through the reaction mixture until saturation was reached at 0–5 °C and the reaction flask was sealed. After stirring overnight at room temperature the solvent was removed and bis(1-hydroxytetrazolyl)furoxane remained as a yellowish resinous substance. IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3423 (w), 2460 (w), 1607 (vs), 1461 (w), 1402 (w), 1369 (m), 1301 (m), 1259 (m), 1223 (m), 1194 (w), 1135 (w), 1091 (w), 1000 (m), 965 (s), 816 (s), 762 (w), 744 (w), 728 (w), 696 (w) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 2997 (2), 2990 (2), 2982 (7), 2943 (44), 1612 (100), 1463 (12), 1309 (14), 1265 (35), 1227 (31), 1201 (6), 1138 (6), 1003 (12), 820 (8), 765 (9), 747 (13), 733 (14), 700 (7), 526 (7), 453 (10), 414 (6), 388 (6), 358 (8) cm⁻¹. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 6.67 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 143.4, 136.8, 134.4, 103.4 ppm.

Dipotassium bis(1-oxidotetrazolyl)furazane (11). An aqueous solution of 9 was brought to pH 8 with 2 M potassium hydroxide solution. The solution was left for crystallization and the dihydrate of 11 was obtained as a crystalline solid. The anhydrous compound was obtained by pouring a hot concentrated aqueous solution of 11 into the five-fold volume of ethanol and filtering. DSC (5 °C min⁻¹): 87 °C (dehy), 277 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3552 (w), 3357 (m), 3242 (w), 1665 (w), 1635 (m), 1592 (m), 1574 (w), 1542 (w), 1471 (s), 1437 (m), 1407 (s), 1372 (m), 1362 (m), 1286 (s), 1239 (s), 1173 (w), 1118 (m), 1084 (w), 1033 (m), 1015 (w), 1000 (s), 983 (vs), 912 (s), 896 (m), 834 (w), 803 (w), 771 (m), 751 (w), 727 (w), 692 (w), 664 (w) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 1594 (26), 1575 (100), 1473 (6), 1374 (13), 1240 (11), 1176 (12), 1145 (8), 1121 (4), 1085 (3), 1017 (5), 1004 (3), 774 (5), 457 (5), 98 (13), 79 (5) cm⁻¹. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 145.0, 132.8. EA (K₂C₄H₄N₁₀O₅, 386.37 g mol⁻¹) calc. (found): C 12.43 (13.60), H 1.04 (1.22), N 36.25 (36.72)%. MS (FAB⁺) m/z: 39.0 [K⁺], (FAB⁻) m/z: 237.2 [C₄HN₁₀O₃⁻]. IS: 35 J (<100 μm), FS: >360 N. ESD: 1.5 J.

Dipotassium bis(1-oxidotetrazolyl)furoxane (12). The total amount of 10 was suspended in 50 mL of ethanol and an aqueous solution of potassium hydroxide was added until pH 7 was reached. The potassium salt started to precipitate. After addition of 20 mL of diethyl ether more precipitate could be obtained. Filtration of the mixture and air drying led to 4.9 g (15 mmol, 94% based on step 6) of a white powder. DSC (5 °C min⁻¹): 265 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3376 (w), 3142 (w), 3087 (w), 2841 (w), 2799 (w), 2652 (w), 2449 (w), 2357 (w), 2343 (w), 2167 (w), 2000 (w), 1799 (w), 1703 (w), 1670 (w), 1648 (w), 1609 (s), 1575 (s), 1546 (s), 1464 (m), 1450 (s), 1427 (s), 1421 (s), 1396 (s), 1370 (s), 1297(m), 1231 (vs), 1195 (w), 1167 (m), 1156 (w), 1144 (w), 1115 (w), 1095 (m), 1035 (w), 1017 (m), 988 (s), 964 (s), 879 (w), 836 (s), 792 (w), 767 (s), 754 (m), 731 (m), 711 (m), 705 (w), 693 (m), 682 (m), 654 (w) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 1616 (22), 1576 (100), 1549 (35), 1449 (11), 1403 (11), 1372 (3), 1299 (5), 1235 (24), 1195 (29), 1170 (19), 1158 (6), 1147 (6), 1098 (6), 1021 (6), 992 (18), 838 (8), 769 (16), 734 (3), 713 (3), 696 (7), 685 (3), 595 (4), 558 (5), 511 (13), 456 (13), 442 (5), 411 (5), 368 (6), 341 (3), 297 (2), 260 (4), 240 (4), 166 (34), 137 (46), 122 (24), 101 (36), 77 (27) cm⁻¹. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 147.7, 133.2, 130.3, 106.5. MS (FAB⁺): 39.0 [K⁺], (FAB⁻): 253.1 [C₄HN₁₀O₄⁻]. EA (K₂C₄N₁₀O₄, 330.30 g mol⁻¹) calc. (found): C 14.55 (14.64), H 0.00 (0.00), N 42.41 (41.38)%. Found: C 14.64, H 0.00, N 41.38%. IS: 10 J (<100 μm). Friction tester: 48 N (<100 μm).

Dihydroxylammonium bis(1-oxidotetrazolyl)furazane (13). 3.2 g (10 mmol) of 11 was dissolved in 20 mL of 2 M hydrochloric acid. The solution was extracted with 5 × 30 mL of diethyl ether and the solvent was removed under reduced pressure. The residue was dissolved in 20 mL of ethanol. 2.2 eq. of 50% hydroxylamine solution was added under vigorous stirring. The solution was stirred for additional 30 min, the solvent was then removed under reduced pressure and the precipitate was filtered off. 2.9 g (9.6 mmol, 95%) of 13 was obtained as a white crystalline powder. DSC (5 °C min⁻¹): 170 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3210 (w), 3043 (w), 2885 (w), 2663 (m), 1992 (w), 1623 (w), 1602 (w), 1497 (m), 1473 (s), 1434 (m), 1429 (m), 1404 (s), 1376 (w), 1361 (s), 1285 (s), 1245 (s), 1230 (s), 1197 (m), 1180 (m), 1126 (w), 1035 (w), 1009 (m), 1000 (s), 986 (vs), 894 (m), 878 (w), 773 (m), 748 (w), 694 (w) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 1606 (15), 1588 (100), 1477 (5), 1439 (2), 1376 (14), 1289 (2), 1249 (13), 1236 (4), 1183 (16), 1147 (8), 1128 (4), 1089 (5), 1012 (16), 903 (7), 776 (4), 750 (6), 686 (2), 556 (4), 462 (10), 46 (2), 349 (2), 309 (2), 98 (14) cm⁻¹. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 10.22 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 144.2, 133.9 ppm. EA (C₄H₈N₁₂O₅, 304.18 g mol⁻¹) calc. (found): C 15.79 (16.39), H 2.65 (2.67), N 55.26 (54.23)%. IS: 7 J (<100 μm). FS: 216 N (<100 μm). ESD (<100 μm): 1 J.

Dihydroxylammonium bis(1-oxidotetrazolyl)furoxane monohydrate (14). 1.7 g of 12 (5 mmol) was dissolved in 20 mL of 2 M hydrochloric acid and extracted with 4 × 20 mL of diethyl ether. The ether was removed under reduced pressure and the residue was dissolved in a few milliliters of water. Hydroxylamine (661 mg of 50% solution in H₂O, 0.61 mL, 10 mmol) was added while stirring. The solution was left for crystallisation. Compound 14 crystallized to give 1.7 g (4.9 mmol, 98%) yield. DSC (5 °C min⁻¹): 135 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 2976 (m), 2709 (m), 1696 (w), 1625 (s), 1591 (s), 1559 (s), 1461 (s), 1426 (m), 1399 (m), 1376 (m), 1300 (m), 1232 (vs), 1187 (m), 1020 (m), 996 (s), 964 (s), 822 (m), 757 (m), 704 (w) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 2986 (13), 1630 (27), 1590 (100), 1567 (29), 1495 (6), 1463 (8), 1398 (14), 1300 (8), 1235 (15), 1212 (44), 1186 (6), 1137 (10), 1102 (5), 1018 (14), 1001 (33), 833 (4), 756 (8), 707 (3), 684 (3), 506 (4), 460 (7). ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 10.27 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 146.4, 134.3, 131.5, 105.6 ppm. EA (C₄H₁₀N₁₂O₇, 338.20 g mol⁻¹) calc. (found): C 14.21 (14.30), H 2.98 (2.90), N 49.70 (48.43)%. IS: 10 J (100–500 μm). FS: 240 N (100–500 μm).

Diammonium bis(1-oxidotetrazolyl)furazane (15). 3.1 g (10 mmol) of 11 was dissolved in 20 mL of 2 M hydrochloric acid. The solution was extracted with 5 × 30 mL of diethyl ether and the solvent was removed under reduced pressure. The residue was dissolved in 20 mL of water. 2.2 eq. of ammonium hydroxide was added under vigorous stirring. The solvent was then removed under reduced pressure. The crude product was recrystallized from methanol, 2.66 g (8.8 mmol, 87%) of 11 was obtained as colorless crystals. DSC (5 °C min⁻¹): 259 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3134 (w), 3000 (w), 2881 (w), 2796 (w), 1665 (w), 1604 (w), 1594 (w), 1469 (m), 1440 (s), 1405 (s), 1366 (s), 1283 (s), 1229 (vs), 1181 (w), 1133 (w), 1122 (m), 1031 (m), 1014 (w), 1003 (m), 983 (s), 905 (s), 889 (m), 765 (w), 748 (s), 731 (w), 716 (w), 696 (w) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 1606 (31), 1594 (100), 1482 (4), 1373 (11), 1235 (20), 1182 (16), 1136 (12), 1123 (4), 1015 (6), 1005 (3), 906 (7), 767 (4), 750 (7), 612 (3), 461 (10), 305 (2), 163 (5), 129 (6), 102 (42). ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 7.18 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 144.8, 133.1 ppm. EA (C₄H₈N₁₂O₃, 272.19 g mol⁻¹) calc. (found): C 17.65 (17.93), H 2.96 (2.95), N 61.75 (61.00)%. IS: 9 J (<100 μm). FS: >360 N (<100 μm). ESD (<100 μm): 1.5 J.

Diammonium bis(1-oxidotetrazolyl)furoxane (16). 1.7 g of 12 (5 mmol) was dissolved in 20 mL of 2 M hydrochloric acid and extracted with 4 × 20 mL of diethyl ether. The solvent was removed under reduced pressure and the residue was dissolved in a few milliliters of water. The solution was adjusted to pH 7 by addition of 2 M NH₃. The solvent was removed under reduced pressure and 16 precipitated as a colorless solid to give 1.2 g (4.2 mmol, 84%) yield. Crystals of 16 were obtained from water. DSC (5 °C min⁻¹): 230 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3166 (w), 3010 (w), 2892 (w), 2801 (w), 1622 (s), 1583 (m), 1555 (m), 1462 (s), 1426 (s), 1399 (s), 1374 (m), 1297 (m), 1228 (vs), 1181 (w), 1020 (w), 996 (m), 964 (s), 832 (s), 760 (m), 744 (w), 733 (w), 706 (w), 688 (w) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 3031 (3), 1622 (29), 1585 (100), 1556 (20), 1398 (10), 1297 (4), 1229 (14), 1207 (28), 1182 (4), 1134 (9), 1102 (4), 1025 (4), 999 (8), 832 (3), 761 (4), 711 (2), 687 (2), 553 (2), 500 (4). ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 7.22 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 147.2, 133.5, 130.7, 106.1 ppm. EA (C₄H₈N₁₂O₄, 288.18 g mol⁻¹) calc. (found): C 16.67 (16.88), H 2.80 (2.82), N 58.32 (56.18)%. IS: 10 J (<100 μm). FS: 240 N (<100 μm). ESD (<100 μm): 1 J.

Dihydrazinium bis(1-oxidotetrazolyl)furazane (17). 3.2 g (10 mmol) of 11 was dissolved in 20 mL of 2 M hydrochloric acid. The solution was extracted with 5 × 30 mL of diethyl ether and the solvent was removed under reduced pressure. The residue was dissolved in 20 mL of ethanol and 2.2 eq. of hydrazine hydrate was added under vigorous stirring. The solution was stirred for additional 30 min, the solvent was then concentrated under reduced pressure and the precipitate was filtered off. The crude product was recrystallized from methanol, 2.9 g (9.4 mmol, 94%) of 17 was obtained as yellowish crystals. DSC (5 °C min⁻¹): 175 °C (mp.), 211 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3323 (w), 3187 (w), 2839 (m), 2710 (m), 2640 (m), 1604 (m), 1537 (m), 1471 (m), 1422 (w), 1402 (s), 1374 (w), 1361 (m), 1285 (s), 1232 (m), 1222 (s), 1173 (w), 1141 (m), 1115 (s), 1093 (s), 1078 (s), 1009 (w), 999 (m), 982 (s), 962 (vs), 897 (s), 874 (m), 768 (w), 758 (m), 747 (m), 731 (w), 716 (w), 697 (w), 689 (w) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 3326 (3), 3188 (4), 1609 (57), 1587 (100), 1473 (8), 1376 (15), 1235 (16), 1174 (18), 1150 (9), 1137 (5), 1087 (7), 1004 (7), 963 (10), 901 (9), 772 (7), 749 (5), 620 (3), 464 (14), 171 (4), 141 (5), 104 (9), 92 (16). ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 7.09 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 144.8, 133.1 ppm. EA (C₄H₁₀N₁₄O₃, 302.21 g mol⁻¹) calc. (found): C 15.90 (16.36), H 3.34 (3.27), N 64.89 (64.45)%. IS: 7 J (<100 μm). FS: >360 N (<100 μm). ESD (<100 μm): 1.5 J.

Dihydrazinium bis(1-oxidotetrazolyl)furoxane (18). 1.7 g of 12 (5.6 mmol) was dissolved in 20 mL of 2 M hydrochloric acid and extracted four-times with 20 mL of diethyl ether. The solvent was removed under reduced pressure and the residue was dissolved in a few milliliters of water. Hydrazinium hydroxide (0.5 g, 0.5 mL, 10 mmol) was added to the colorless solution, the solvent was removed under reduced pressure and 18 precipitated as a colorless solid to give 1.5 g (4.8 mmol, 96%) yield. DSC (5 °C min⁻¹): 160 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3563 (w), 3461 (w), 3344 (m), 3331 (m), 3285 (m), 2833 (m), 2725 (m), 2606 (m), 2105 (m), 1613 (s), 1580 (s), 1551 (s), 1512 (s), 1455 (s), 1426 (s), 1413 (s), 1391 (s), 1371 (s), 1345 (m), 1292 (m), 1230 (s), 1108 (m), 1088 (s), 1018 (m), 984 (s), 956 (s), 942 (vs), 820 (s), 773 (m), 760 (s), 746 (m), 732 (m), 704 (m), 688 (m), 679 (m) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 1613 (19), 1583 (100), 1554 (12), 1457 (4), 1396 (9), 1295 (3), 1237 (11), 1209 (30), 1181 (7), 1152 (7), 1137 (7), 1096 (7), 1018 (4), 989 (11), 946 (4), 764 (10), 734 (3), 707 (3), 692 (3), 556 (4), 500 (7), 456 (11), 439 (5), 366 (3), 324 (6), 295 (2), 159 (14), 110 (46), 88 (45) cm⁻¹. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 7.16 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 147.1, 133.7, 130.9, 106.1 ppm. MS (FAB⁺): 33.0 [N₂H₅⁺], (FAB⁻): 253.1 [C₄HN₁₀O₄⁻]. EA (C₄H₁₀N₁₄O₄, 318.21 g mol⁻¹) calc. (found): C 15.10 (15.56), H 3.17 (3.24), N 61.62 (59.96)%. IS: 5 J (<100 μm). FS: 96 N (<100 μm). ESD (<100 μm): 0.5 J.

Diguanidinium bis(1-oxidotetrazolyl)furazane (19). 3.1 g (10 mmol) of 11 was dissolved in 20 mL of 2 M hydrochloric acid. The solution was extracted with 5 × 30 mL of diethyl ether and the solvent was concentrated under reduced pressure. The residue was dissolved in 5 mL of water. 1.1 eq. of a solution of guanidinium carbonate in water was added under vigorous stirring. The solution was stirred for additional 30 min, the solvent was then removed under reduced pressure and the precipitate was filtered off. The crude product was recrystallized from methanol, 3.4 g of 19 was obtained as pale yellow crystal rods. DSC (5 °C min⁻¹): 124 (mp.), 264 (dec.) °C. IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3360 (s), 3206 (m), 3119 (s), 2813 (w), 1691 (w), 1656 (vs), 1591 (m), 1582 (m), 1469 (s), 1432 (w), 1404 (s), 1363 (m), 1291 (s), 1237 (s), 1140 (m), 1126 (m), 1040 (m), 1001 (m), 987 (s), 899 (m), 882 (m), 770 (w), 750 (w), 696 (w) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 3370 (2), 3229 (9), 1597 (9), 1578 (100), 1470 (5), 1368 (19), 1243 (9), 1180 (16), 1151 (6), 1128 (4), 1099 (7), 1010 (24), 906 (5), 777 (6), 752 (2), 542 (6), 462 (10), 293 (6), 136 (2), 106 (2) cm⁻¹. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 6.63 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 158.1, 144.2, 132.9 ppm. EA (C₆H₁₂N₁₆O₃, 356.27 g mol⁻¹) calc. (found): C 20.23 (19.56), H 3.40 (3.63), N 62.90 (59.68)%. IS: >40 J (<100 μm). FS: >360 N (<100 μm). ESD (<100 μm): 1.5 J.

Diguanidinium bis(1-oxidotetrazolyl)furoxane (20). 1.7 g of 12 (5.1 mmol) was dissolved in 20 mL of 2 M hydrochloric acid and extracted four-times with 20 mL of diethyl ether. The solvent was removed under reduced pressure and the residue was dissolved in a few milliliters of water. Guanidinium carbonate (0.9 g, 5.2 mmol) was added and the solution was heated while stirring. After filtration the mixture was cooled down to ambient temperature and 20 precipitated to give 1.8 g (4.8 mmol, 96%) of colorless, crystalline blocks. DSC (5 °C min⁻¹): 197 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3428 (s), 3342 (s), 3161 (s), 2793 (m), 2202 (w), 1999 (w), 1640 (vs), 1590 (s), 1553 (s), 1458 (m), 1423 (s), 1400 (m), 1335 (s), 1303 (s), 1243 (s), 1226 (s), 1180 (s), 1134 (m), 1106 (m), 1089 (m), 1026 (m), 1010 (m), 986 (s), 964 (s), 846 (w), 818 (s), 763 (s), 735 (s), 726 (s), 700 (m), 692 (m) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 3267 (2), 1623 (42), 1594 (100), 1558 (40), 1460 (22), 1434 (12), 1338 (3), 1307 (27), 1234 (9), 1210 (64), 1183 (7), 1136 (15), 1109 (8), 1092 (5), 1028 (7), 1009 (69), 989 (18), 967 (3), 823 (8), 761 (12), 729 (8), 704 (9), 592 (4), 564 (11), 529 (14), 494 (11), 448 (14), 421 (14), 368 (23), 286 (7), 230 (26), 163 (26) cm⁻¹. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 6.99 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 158.5, 146.9, 133.8, 130.9, 105.9 ppm. MS (FAB⁺): 60.1 [CH₆N₃⁺], 373.1 [M + H⁺], (FAB⁻): 253.1 [C₄HN₁₀O₄⁻]. EA (C₆H₁₂N₁₆O₄, 372.26 g mol⁻¹) calc. (found): C 19.36 (19.74), H 3.25 (3.22), N 60.20 (59.93)%. IS: 30 J (100–500 μm). FS: 360 N (100–500 μm). ESD (<100 μm): 1.5 J.

Disilver bis(1-oxidotetrazolyl)furoxane (21). 0.5 g of 11 (1.5 mmol) was dissolved in 20 mL of water and an aqueous solution of silver nitrate (0.5 g, 3.0 mmol) was added, the silver salt precipitated immediately. After stirring and heating until boiling for a short time, the colorless solid was filtered off and air dried to give 0.7 g (1.4 mmol, 90%) of Ag₂BOTFOX as a monohydrate. DSC (5 °C min⁻¹): 221 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3365 (w), 3155 (w), 1628 (s), 1584 (s), 1462 (s), 1432 (s), 1397 (s), 1372 (m), 1302 (m), 1231 (vs), 1185 (m), 1092 (w), 1027 (w), 990 (m), 967 (s), 818 (s), 765 (s), 747 (m), 726 (m), 696 (m), 677 (m) cm⁻¹. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 146.2, 133.2, 130.4, 105.4 ppm. MS (DEI⁺): 107.0 [Ag⁺]. EA (Ag₂C₄H₂N₁₀O₅, 485.86 g mol⁻¹) calc. (found): C 9.89 (10.09), H 0.41 (0.41), N 28.83 (28.47)%. IS: 3 J (<100 μm). FS: 16 N (<100 μm).

Diaminouronium bis(1-oxidotetrazolyl)furoxane dihydrate (22). 1.7 g of 12 (5 mmol) was dissolved in 20 mL of 2 M hydrochloric acid and extracted four-times with 20 mL of diethyl ether. The solvent was removed under reduced pressure and the residue was dissolved in a few milliliters of water. Diaminourea (0.9 g, 10 mmol) was added and the solution was heated while stirring. After filtration the mixture was cooled down to ambient temperature and 22 precipitated as a colorless solid to give 1.8 g (4.8 mmol, 96%) yield. DSC (5 °C min⁻¹): 156 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3288 (w), 2964 (m), 2683 (m), 2133 (w), 1693 (m), 1618 (s), 1575 (s), 1557 (s), 1454 (s), 1427 (m), 1396 (m), 1377 (m), 1297 (m), 1233 (vs), 1180 (m), 1106 (w), 1014 (w), 990 (m), 965 (s), 826 (s), 750 (s), 734 (m), 678 (m) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 1618 (20), 1586 (100), 1557 (20), 1453 (2), 1400 (11), 1298 (6), 1248 (9), 1209 (33), 1180 (5), 1145 (8), 1104 (5), 1016 (6), 993 (19), 830 (7), 769 (7), 736 (3), 711 (3), 691 (3), 591 (2), 502 (8), 453 (8), 407 (3), 670 (3), 242 (6), 154 (31), 102 (47) cm⁻¹. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 6.36 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 158.4, 145.6, 135.1, 132.5, 105.0. MS (FAB⁻): 253.1 [C₄HN₁₀O₄⁻], EA (C₅H₁₂N₁₄O₇, 380.24 g mol⁻¹) calc. (found): C 15.79 (16.23), H 3.18 (2.99), N 51.57 (51.47)%. IS: 40 J (<100 μm). FS: 216 N (<100 μm). ESD (<100 μm): 1.5 J.

Di(aminoguanidinium) bis(1-oxidotetrazolyl)furoxane (23). 1.7 g of 11 (5 mmol) was dissolved in 20 mL of 2 M hydrochloric acid and extracted four-times with 20 mL of diethyl ether. The solvent was removed under reduced pressure and the residue was dissolved in a few milliliters of water. Aminoguanidinium bicarbonate (1.4 g, 10 mmol) was added and the solution was heated while stirring. After filtration the mixture was cooled down to ambient temperature and 23 crystallized to give 1.9 g (4.7 mmol, 94%) of colorless blocks. DSC (5 °C min⁻¹): 165 °C (dec.). IR (ATR, 25 °C), [small nu, Greek, tilde] (rel. int.): 3424 (w), 3359 (m), 3303 (m), 3241 (m), 3101 (w), 1668 (vs), 1620 (s), 1585 (m), 1560 (s), 1455 (m), 1428 (m), 1400 (m), 1363 (m), 1301 (m), 1238 (s), 1227 (s), 1193 (m), 1168 (m), 1095 (m), 1077 (m), 1056 (m), 1024 (w), 1009 (w), 990 (m), 961 (s), 910 (s), 823 (s), 771 (m), 758 (s), 732 (m), 710 (m) cm⁻¹. Raman (1064 nm, 400 mW, 25 °C), [small nu, Greek, tilde] (rel. int.): 3363 (6), 3263 (5), 1622 (31), 1588 (100), 1562 (30), 1456 (9), 1430 (6), 1397 (7), 1365 (5), 1303 (15), 1215 (69), 1170 (10), 1138 (14), 1107 (10), 1025 (6), 1011 (5), 992 (33), 966 (14), 824 (13), 773 (8), 752 (9), 735 (5), 711 (3), 687 (2), 624 (4), 591 (4), 557 (10), 501 (16), 460 (11), 434 (6), 405 (2), 375 (12), 342 (3), 285 (3), 260 (6), 231 (20), 155 (49), 138 (64), 127 (60), 100 (77), 89 (91) cm⁻¹. ¹H NMR (270 MHz, DMSO-d₆, 25 °C), δ: 8.70, 7.26, 6.90, 4.51 ppm. ¹³C{¹H} NMR (270 MHz, DMSO-d₆, 25 °C), δ: 159.4, 147.0, 133.8, 130.9, 106.0 ppm. MS (FAB⁺): 75.1 [CH₇N₄⁺], 403.2 [M + H⁺], (FAB⁻): 253.1 [C₄HN₁₀O₄⁻]. EA (C₆H₁₄N₁₈O₄, 402.29 g mol⁻¹) calc. (found): C 17.91 (18.17), H 3.51 (3.47), N 62.67 (61.54)%. IS: 8 J (<100 μm). FS: 360 N (<100 μm).

Acknowledgements

Financial support of this work by the Ludwig-Maximilian University of Munich (LMU), the U.S. Army Research Laboratory (ARL) under grant no. W911NF-09-2-0018, the Armament Research, Development and Engineering Center (ARDEC) under grant no. W911NF-12-1-0467, and the Office of Naval Research (ONR) under grant nos. ONR.N00014-10-1-0535 and ONR.N00014-12-1-0538 is gratefully acknowledged. The authors acknowledge collaborations with Dr Mila Krupka (OZM Research, Czech Republic) in the development of new testing and evaluation methods for energetic materials and with Dr Muhamed Suceska (Brodarski Institute, Croatia) in the development of new computational codes to predict the detonation and propulsion parameters of novel explosives. We are indebted to and thank Drs Betsy M. Rice and Brad Forch (ARL, Aberdeen, Proving Ground, MD) for many inspired discussions. We also thank Mr Stefan Huber for sensitivity measurements.

Notes and references

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Footnotes

† Dedicated to Dr. Klaus Römer on the occasion of his 75th birthday.

‡ Electronic supplementary information (ESI) available: X-ray diffraction data, computations, and general experimental methods. CCDC 988403–988414. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c4nj01351d

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