Stabilization of the Pentazolate Anion in Three Anhydrous and Metal‐Free Energetic Salts

Abstract

According to previous reports, metal cations or water molecules are necessary for the stabilization of pentazolate anion (cyclo-N ) at ambient temperature and pressure. Seeking a new method to stabilize N is a big challenge. In this work, three anhydrous, metal-free energetic salts based on cyclo-N 3,9-diamino-6,7-dihydro-5 H-bis([1,2,4]triazolo)[4,3-e:3',4'-g][1,2,4,5] tetrazepine-2,10-diium, N-carbamoylguanidinium, and oxalohydrazinium (oxahy ) pentazolate were synthesized and isolated. All salts were characterized by elemental analysis, IR spectroscopy, H, C, and (in some cases) N NMR spectroscopy, thermal analysis (TGA and DSC), and single-crystal XRD analysis. Computational studies associated with heats of formation and detonation performance were performed by using Gaussian 09 and Explo5 programs, respectively. The sensitivity of the salts towards impact and friction was determined, and overall the real N explosives showed promising energetic properties.

Novel All‐Nitrogen Molecular Crystals of Aromatic N10

“…This is much higher than those typical energetic materials, such as TATB, RDX, and HMX, which have energy densities around 1–3 kJ g −1 . [ 30 ] In addition, due to the instability of a single cyclic N 5 ring, nonenergetic ions are required to stabilize them in the complexes in previous works, [ 9–12,31,32 ] which reduces the energy density of the materials. In our predicted three polynitrogen crystals, the covalent bond between the two cyclic N 5 rings naturally stabilize each other and thus form stable bispentazole molecular crystals even at ambient pressure.…”

Syntheses of Energetic cyclo‐Pentazolate Salts

“…Compound 2 has the highest heat of formation of 746.4 kJ mol À1 .T he other two compounds also show positive heats of formation with values of 95.2 (1)t o5 56.1 (3)kJmol À1 ,r espectively.A sc an be seen from Ta ble 1, the heat of formation of 1 is lowest among all selected cyclo-N 5 À -containing compounds. The heats of formation of 2 and 3 are higher than those of GU + N 5 À (203.4 kJ mol À1 ), [12] NH 3 OH + N 5 À (327.6 kJ mol À1 ), [15] NH 4 + N 5 À (269.1 kJ mol À1 ), [15] and AG + N 5 À (392.1 kJ mol À1 ). [15] Based on the calculated densities( 298 K) and solid-state heats of formation,t he detonationp erformances of these salts were calculated using the EXPLO5 program (version6 .01).…”

“…Up to now,s odium,m agnesium, and silver pentazolate salts have been reported as precursors to synthesize non-metallice nergetic salts of cyclo-N 5 À .E arliest, three anhydrous energetic salts DABTT 2 + (N 5 À ) 2 ,G u + N 5 À ,O xahy + N 5 À were synthesized by our group via the metathesis reaction of sodiump entazolate with the respective chloride salts. [12] This work opens the door to the exploration of more pentazolate salts. Then this metathesis reactionw as improved and two salts (C 4 H 9 N 10 + )(N 5 À )·3 H 2 Oa nd (C 5 H 9 N 10 + ) 2 (Cl À )(N 5 À )·3.5 H 2 Ow ere successfully synthesized.…”

“…The heat of formation of cyclo-N 5 À anionw as referenced from the literature. [12] The heats of formation of other cations were calculated by the Guassian 09 (Revision A.02) suite of programs. [21] The lattice energies and solid-state heats of formation for cyclo-N 5 À salts were calculated according to the Born-Haber energy cycle [22] (More details can be found in the Supporting Information.).…”

“…[15] However,a ll the newly synthesized cyclo-N 5 À salts show higher detonation velocities (> 6896 ms À1 )t han TNT (6881 ms À1 ) and the three-dimensional framework [Na 8 (N 5 ) 8 (H 2 O) 3 ] n (5011ms À1 ). [5] In particular,the energetic performances of compound 1 are superiort ot hose of [Ag(N 5 )] n , [8] GU + N 5 À , [12] DABTT 2 + (N 5 À ) 2 , [12] NH 4 + N 5 À , [15] AG + N 5 À , [15] DAT + N 5 À , [15] and TATT + N 5 À [15] (Table 1).…”