Roads to pentazolate anion: a theoretical insight

Abstract

The formation mechanism of pentazolate anion (PZA) is not yet clear. In order to present the possible formation pathways of PZA, the potential energy surfaces of phenylpentazole (PPZ), phenylpentazole radical (PPZ-R), phenylpentazole radical anion (PPZ-RA), PPZ and m-chloroperbenzoic acid (m-CPBA), p-pentazolylphenolate anion (p-PZPolA) and m-CPBA, and p-pentazolylphenol (p-PZPol) and m-CPBA were calculated by the computational electronic structure methods including the hybrid density functional, the double hybrid density functional and the coupled-cluster theories. At the thermodynamic point of view, the cleavages of C–N bonds of PPZ and PPZ-R need to absorb large amounts of heat. Thus, they are not feasible entrance for PZA formation at ambient condition. But excitation of PPZ and deprotonation of PPZ-RA probably happen before cleavage of C–N bond of PPZ at high-energy condition. As to the radical anion mechanism, the high accuracy calculations surveyed that the barrier of PZA formation is probably lower than that of dinitrogen evolution, but the small ionization potential of PPZ-RA gives rise to the unstable ionic pair of sodium PPZ at high temperature. In respect of oxidation mechanism, except for PPZ, the reactions of p-PZPolA and p-PZPol with m-CPBA can form PZA and quinone. The PZA formations have the barriers of about 20 kcal mol−1 which compete with the dinitrogen evolutions. The stabilities of PZA in both solid and gas phases were also studied herein. The proton prefers to transfer to pentazolyl group in the (N5)6(H3O)3(NH4)4Cl system which leads to the dissociation of pentazole ring. The ground states of M(N5)2(H2O)4 (M = Co, Fe and Mn) are high-spin states. The pentazolyl groups confined by the crystal waters in the coordinate compounds can improve the kinetic stability. As to the reactivity of PZA, it can be persistently oxidized by m-CPBA to oxo-PZA and 1,3-oxo-PZA with the barriers of about 20 kcal mol−1.

Bipentazole (N10): A Low-Energy Molecular Nitrogen Allotrope with High Intrinsic Stability

“…An important question arises: how can bipentazole be obtained experimentally? We speculate that the most probable way for obtaining this nitrogen allotrope is electrolysis of ammonium pentazolate salts. − Recently, a simple and versatile method for preparation of such salts was reported. , It is worth noting that the USPEX method applied in this work demonstrated success in prediction of the structure of such salts. − …”

To Be or Not To Be Protonated: cyclo-N5– in Crystal and Solvent

“…It is noteworthy that very recently Yu et al investigated the stabilities and possible formation pathways of the pentazolate anion at the B3LYP/6-311+ +G** and CCSD(T)/CBS levels. 17 These results have been illuminating the paths of theoretical and experimental studies on pentazolate.…”

“…− have been protonated to HN 5 at the beginning of the simulations, as illustrated in Movie 1. In o ther words, t he prot onation of cyclo-N 5 − in (N 5 ) 6 (H 3 O) 3 (NH 4 ) 4 Cl at 123 K is spontaneous (Figure1b), which is qualitatively in agreement with Huang's conclusion obtained by using a static gas-phase cluster model 17 and indicates that the extensive hydrogen-bonding interactions between the cations and anions in the crystal 19 are not sufficient to retain all hydrogen atoms in H 3 O + (see the detailed trajectory in the Supporting Information).…”

Unraveling the Mechanism of cyclo-N5– Production through Selective C–N Bond Cleavage of Arylpentazole with Ferrous Bisglycinate and m-Chloroperbenzonic Acid: A Theoretical Perspective

“…11−17 Nevertheless, the way to the bulk synthesis of cyclo-N 5 − is unexpectedly difficult. 18 For the whole 20th century, the stable existing cyclo-N 5 was in the form of arylpentazoles with the N 5 group bonded to aromatic rings. 19−22 In 2002, cyclo-N 5 − was first detected through the cleavage of the C−N bond of arylpentazole using electrospray ionization mass spectrometry.…”

“…However, the development and synthesis of energetic polynitrogen compounds have always been a great challenge due to the inherent instability that arises from the large thermodynamic driving force toward the N 2 production . For a long time, only N 3 – was known, but over the last two decades, more polynitrogen species have been discovered, such as the chainlike N 5 + cation, the pentazolate anion ( cyclo -N 5 – ), , as well as the cubic gauche polymetric nitrogen atoms­(cg-N). − Among those, cyclo -N 5 – is becoming one of the central concerns in the field of energetic materials driven by the possibility of a large energy release upon the decomposition and its stability toward fragmentation to N 3 – and N 2 with an activation barrier of 27 kcal/mol. − Nevertheless, the way to the bulk synthesis of cyclo -N 5 – is unexpectedly difficult . For the whole 20th century, the stable existing cyclo -N 5 was in the form of arylpentazoles with the N 5 group bonded to aromatic rings. − In 2002, cyclo -N 5 – was first detected through the cleavage of the C–N bond of arylpentazole using electrospray ionization mass spectrometry .…”