Reaction Mechanism and Energetics of Decomposition of Tetrakis(1,3-dimethyltetrazol-5-imidoperchloratomanganese(II)) from Quantum-Mechanics-based Reactive Dynamics

Abstract

Energetic materials (EMs) are central to construction, space exploration, and defense, but over the past 100 years, their capabilities have improved only minimally as they approach the CHNO energetic ceiling, the maximum energy density possible for EMs based on molecular carbon–hydrogen–nitrogen–oxygen compounds. To breach this ceiling, we experimentally explored redox-frustrated hybrid energetic materials (RFH EMs) in which metal atoms covalently connect a strongly reducing fuel ligand (e.g., tetrazole) to a strong oxidizer (e.g., ClO4). In this Article, we examine the reaction mechanisms involved in the thermal decomposition of an RFH EM, [Mn­(Me2TzN)­(ClO4]4 (3, Tz = tetrazole). We use quantum-mechanical molecular reaction dynamics simulations to uncover the atomistic reaction mechanisms underlying this decomposition. We discover a novel initiation mechanism involving oxygen atom transfer from perchlorate to manganese, generating energy that promotes the fission of tetrazole into chemically stable species such as diazomethane, diazenes, triazenes, and methyl azides, which further undergo exothermic decomposition to finally form stable N2, H2O, CO, CO2, Mn-based clusters, and additional incompletely combusted products.

High-Energy-Density Material with Magnetically Modulated Ignition

“…The Goddard group pioneered the use of QM-MD pyrolysis simulations to determine the Chapman–Jouguet conditions of energetic materials (RDX, HMX, and CL-20) and accurately predicted the detonation properties at 150 ps. These studies correctly predicted the initial decomposition steps in these materials in simulations of less than 20 ps. − Previously, our QM-MD simulations of Mn 4 (μ 3 -NTzMe 2 ) 4 (ClO 4 ) 4 pyrolysis (using the PBE-D3 − 44–46 functional with spin-polarized GGA to allow unrestricted spin change in the reactions) revealed that starting with the ferromagnetic ground-state coupling between the high-spin manganese centers of the tetranuclear heterocubane cluster and heating it to 2000 K leads to spin flips as the reaction initiate to transfer oxygen atom from perchlorate to manganese . These oxygen atom transfer events decrease the quantum spin of oxidized manganese ions, leading to antiferromagnetic coupling via superexchange across the bridging oxide ligands.…”

“…47−51 Previously, our QM-MD simulations of Mn 4 (μ 3 -NTzMe 2 ) 4 (ClO 4 ) 4 pyrolysis (using the PBE-D3 44−4644−46 functional with spin-polarized GGA to allow unrestricted spin change in the reactions) revealed that starting with the ferromagnetic ground-state coupling between the high-spin manganese centers of the tetranuclear heterocubane cluster and heating it to 2000 K leads to spin flips as the reaction initiate to transfer oxygen atom from perchlorate to manganese. 32 These oxygen atom transfer events decrease the quantum spin of oxidized manganese ions, leading to antiferromagnetic coupling via superexchange across the bridging oxide ligands. In this report, our QM-MD simulations on the dimethyl analogue of 1, hexanuclear cluster Mn 6 (μ 3 -NTzMe 2 ) 6 (ClO 4 ) 6 (2), show a similar decrease in overall spin as the reaction proceeds.…”

“…31 We recently determined the novel mechanism of decomposition of this material using quantum mechanics-based reactive molecular dynamics simulations (QM-MD). 32 However, this material does not explode due to the low oxygen balance (%OB) of −107%, meaning an additional 107 mass % of O 2 is required to fully combust this material. In this report, we improved the oxygen balance by substitution of one tert-butyl group with a methyl group, which leads to a larger hexanuclear cluster: Mn 6 (μ 3 -NTz t BuMe) 6 (ClO 4 ) 6 (1, Figure 1).…”

“…We showed that this material has an unusually high energy density that we attribute to the large amount of redox frustration . We recently determined the novel mechanism of decomposition of this material using quantum mechanics-based reactive molecular dynamics simulations (QM-MD) . However, this material does not explode due to the low oxygen balance (%OB) of −107%, meaning an additional 107 mass % of O 2 is required to fully combust this material.…”

Theoretical investigation on intermolecular interactions, co-crystal structure, thermal decomposition mechanism, and shock properties of 3-nitro-1,2,4-triazol-5-one (NTO) and ammonium perchlorate

“…Therefore, theoretical calculations have become a common part of energetic materials research. 4–6 In the case of DFT and AIMD methods, which are considered to be able to accurately describe atoms and electrons, these methods have been used in various fields of energetic materials research, such as intermolecular interactions between explosives, 7–10 impact behavior of plastic bonded explosives (PBX), 11 thermal decomposition of explosive molecules or crystal, 12–15 and crystal structure. 16 These research methods have been proven to be effective and reliable, and can even obtain theories that are difficult to be achieved by experiments alone, which will provide guidance for the design and understanding of the internal mechanism of energetic materials in the future.…”