Di(1H-tetrazol-5-yl)methane as Neutral Ligand in Energetic Transition Metal Complexes

Vapochromic effect in switchable molecular-based spin crossover compounds

Coordination complexes based on transition metal ions displaying [Ar]3d⁴-3d⁷ electronic configurations can undergo the likely most spectacular switchable phenomena found in molecular coordination chemistry, the well-known Spin Crossover (SCO). SCO phenomena is a detectable, reproducible and reversible switch that occurs between the high spin (HS) and low spin (LS) electronic states of the transition metal actuated by different stimuli (i.e. light, temperature, pressure, the presence of an analyte). Moreover, the occurrence of SCO phenomena causes different outputs, one of them being a colour change. Altogether, an analyte in gas form could be detected by naked eye once it has triggered the corresponding HS ↔ LS transition. This vapochromic effect could be used to detect volatile molecules using a low-cost technology, including harmful chemical substances, gases and/or volatile organic compounds (VOCs) that are present in our environment, in our home or at our workplace. The present review condenses all reported iron coordination compounds where the colour change induced by a given molecule in its gas form is coupled to a HS ↔ LS spin transition. Special emphasis has been made on describing the nature of the post-synthetic modification (PSM) taking place in the material upon the analyte uptake. In this case, three types of PSM can be distinguished: based on supramolecular contacts and/or leading to a coordinative or covalent bond. In the latter, a colour change not only indicates the switch of the spin state in the material but also the formation of a new compound with different properties. It is important to indicate that some of the SCO coordination compounds discussed in the current report have been part of other spin crossover reviews, that have gathered thermally induced SCO compounds and the influence of guest molecules on the SCO behaviour. However, in the majority of examples in these reviews, the change of colour upon the uptake of analytes is not associated with a spin transition at room temperature. In addition, the observed colour variations have been mainly discussed in terms of host-guest interactions, when they can also be induced by a PSM taking place in different sites of the molecule, like the Fe(II) coordination sphere or by chemically altering its inorganic and/or organic linkers. Therefore, we present here for the first time an exhaustive compilation of all systems in which the interaction between the coordination compounds and the vapour analytes leads to a colour change due to a spin transition in the metal centre at room temperature.

Alkaline metal and alkaline earth metal salts of di(1H-tetrazol-5-yl)methanone (DTO): energetic catalysts for ammonium perchlorate decomposition

Six new coordination complexes were obtained and fully characterized; complexes 4 and 5 exhibit good catalytic performances on AP.

Low-Power Laser Ignition of an Antenna-Type Secondary Energetic Copper Complex: Synthesis, Characterization, Evaluation, and Ignition Mechanism Studies

In recent years, development of new energetic compounds and formulations, suitable for ignition with relatively low-power lasers, is a highly active and competitive field of research. The main goal of these efforts is focused on achieving and providing much safer solutions for various detonator and initiator systems. In this work, we prepared, characterized, and studied thermal and ignition properties of a new laser-ignitable compound, based on the 5,6-bis(ethylnitroamino)-N'2,N'3-dihydroxypyrazine-2,3-bis(carboximidamide) (DS3) proligand. This new energetic proligand was prepared in three steps, starting with 5,6-bis(ethylamino)-pyrazine-2,3-dicarbonitrile. Crystallography studies of the DS3-derived Cu(II) complex (DS4) revealed a unique stacked antenna-type structure of the latter compound. DS4 has an exothermal temperature of 154.5 °C and was calculated to exhibit a velocity of detonation of 6.36 km·s^-1 and a detonation pressure of 15.21 GPa. DS4 showed properties of a secondary explosive, having sensitivity to impact, friction, and electrostatic discharge of 8 J, 360 N, and 12 mJ, respectively. In order to study the mechanism of ignition by a laser (using a diode laser, 915 nm), we conducted a set of experiments that enabled us to characterize a photothermal ignition mechanism. Furthermore, we found that a single pulse, with a time duration of 1 ms and with a total energy of 4.6 mJ, was sufficient for achieving a consistent and full ignition of DS4. Dual-pulse experiments, with variable time intervals between the laser pulses, showed that DS4 undergoes ignition via a photothermal mechanism. Finally, calculating the chemical mechanism of the formation of the complex DS4 and modeling its anhydrous and hydrated crystal structures (density functional theory calculations using Gaussian and HASEM software) allowed us to pinpoint a more precise location of water molecules in experimental crystallographic data. These results suggest that DS4 has potential for further development to a higher technology readiness level and for integration into small-size safe detonator systems as for many civil, aerospace, and defense applications.

Synthesis and characterization of promising insensitive energetic salts based on 3-amino-5-hydrazinopyrazole

The development of green energetic materials is based on environmental friendliness, safety and performance improvement. It is of great significance to design and synthesize new nitrogen rich salts for a new generation of green energetic materials. In the present work, a series of 3-amino-5-hydrazinopyrazole energetic salts comprising energetic anions were synthesized and were characterized using elemental analysis, IR spectroscopy and differential scanning calorimetry (DSC). Compounds 1-5 were further confirmed by single crystal X-ray diffraction and the sensitivities were measured by the standard BAM methods. Additionally, the structure-property relationship was elucidated from the experimental results and theoretical calculations. Energetic salts of 2 and 5 exhibited high heat of formation (5, 1160.06 kJ mol-1), high decomposition temperature (2, 172 °C; 5, 186 °C), excellent detonation performance (2, Dv, 9076 m s-1, P 34.1 GPa; 5, Dv, 8974 m s-1, P 31.9 GPa), moderate sensitivity towards outer stimuli and high nitrogen contents (2, 41.03%; 5, 63.84%). This work increases future prospects for the design of insensitive and novel high-energy green energetic material.

Imino-bridged N-rich energetic materials: C4H3N17 and their derivatives assembled from the powerful combination of four tetrazoles

Imino-bridged symmetric N-rich energetic materials with high energetics and good stability.

Insensitive energetic compounds: alkaline earth metal salts of 5,5′-dinitramino-3,3′-methylene-1H-1,2,4-bistriazolate

Three insensitive energetic alkaline earth metal salts based on 5,5′-dinitramino-3,3′-methylene-1H-1,2,4-bistriazolate were synthesized. All the salts exhibit explosive properties comparable to TNT, and are suggested as potential energetic materials.

Crystal structure of 1,4-bis-[5-(2-meth-oxy-phen-yl)-2H-tetra-zol-2-yl]butane

The title compound, C20H22N8O2, was synthesized by the coupling reaction of a sodium tetra-zolate salt and di-bromo-butane in a molar ratio of 2:1. The reaction can produce several possible regioisomers and the title compound was separated as the major product. The X-ray crystallographic study confirmed that the title compound crystallizes in the monoclinic P21/c space group and possesses a bridging butyl-ene group that connects two identical phenyl tetra-zole moieties. The butyl-ene group is attached not to the first but the second nitro-gen atoms of both tetra-zole rings. The dihedral angles between the phenyl groups and the adjacent tetra-zolyl rings are 5.32 (6) and 15.37 (7)°. In the crystal, the mol-ecules form centrosymmetric dimers through C-H⋯O hydrogen bonds between a C-H group of the butyl-ene linker and the O atom of a meth-oxy group.

Highly Stable Energetic Coordination Polymer Assembled with Co(II) and Tetrazole Derivatives

A solvothermal reaction of Co(CH₃COO)₂·4H₂O and 5-mercapto-1-methyl-tetrazole (Hmmtz) in methanol (MeOH) yielded a one-dimensional solvent-free energetic coordination polymer, namely, [Co(mmtz)₂] _n 1, which was structurally characterized. The enthalpy of formation (Δ_f H°) of 1 (907 kJ mol^-1) is much larger than that of commercial 2,4,6-trinitrotoluene (-59 kJ mol^-1). The impact sensitivity and the friction sensitivity are greater than 40 J and 360 N, respectively, indicating that compound 1 exhibits a potential application as a safe explosive. Temperature-dependent molar magnetic susceptibilities show that weak antiferromagnetic behavior exists in 1.

Energetic Metal-Organic Frameworks Incorporating NH3OH+ for New High-Energy-Density Materials

Energetic metal-organic frameworks (E-MOFs) have witnessed increasing development over the past several years. However, as a highly energetic cation, NH₃OH⁺ has never been explored to construct transition-metal-based E-MOFs. Herein, we report the first examples of NH₃OH⁺-containing E-MOFs with bis(tetrazole)methane (H₂btm) as a ligand and copper and manganese as central metal ions, [(NH₃OH)₂(Cu(btm)₂)]_n and [(NH₃OH)₂(Mn(btm)₂)]_n. Crystal structure determinations reveal that both E-MOFs show two-dimensional layered structures. Experimental results suggest that they have high thermal decomposition temperatures (>200 °C). Among them, Cu-based E-MOFs possesses outstanding thermal stability (T_dec = 230.3 °C), which surpasses those of known NH₃OH⁺-containing compounds. They also have high energy density; in particular, the Cu-based E-MOF affords a high heat of combustion (11447 kJ kg^-1) and high heat of detonation (713.8 kJ mol^-1) beyond the most powerful organic explosives in use today. Additionally, the two E-MOFs show completely different sensitivity properties: the Mn-based E-MOF is an insensitive high-energy-density material (IS > 40 J; FS > 360 N; EDS > 20 J), while the Cu-based E-MOF can be classified as a sensitive energetic material (IS = 13 J; FS = 216 N; EDS = 10.25 J), demonstrating their diverse applications in different fields. Our research proposes a unique class of high-energy-density materials.

2-Methyl-substituted monotetrazoles in copper(ii) perchlorate complexes: manipulating coordination chemistry and derived energetic properties

Several new energetic coordination compounds (ECC) have been prepared using two 2-methyl-substituted tetrazoles. By simply changing the reaction conditions, the coordination sphere of the metal center can be manipulated in order to obtain different complexes with varying energetic properties.

Improving the density and properties of nitrogen-rich scaffolds by the introduction of a C–NO2 group

5,5′-(Nitromethylene)bis(1H-tetrazole) and 5,5′-(2-(nitromethyl)-2H-1,2,3-triazole-4,5-diyl)bis(1H-tetrazole) were synthesized by introducing a C–NO₂ group to increase the density and detonation performance.

Gem-diol and Ketone Crystal-to-crystal Transition Phenomena

The generally thought unstable diol compound tetrazyl gem-diol (1, H₂DTMdiol·2H₂O), was firstly obtained in crystalline form by culturing the filtrate for ten days after acidification and filtration of aqueous solution of potassium salt of ketone (2, [K(HDTMone)·2H₂O]_n). The stability of this novel gem-diol compound is found owning to the hydrogen bonds with lattice water molecules and electrophilic tetrazolyl groups. Meanwhile, the undissolved ketone (3, H₂DTMone) was separated during the filtration in the process of gem-diol compound production. Surprisingly, the crystal-to-crystal perfect transition phenomena from gem-diol (1) to ketone (3) were firstly observed after heating up to 120^°C as evidenced by X-ray single crystal diffraction and powder X-ray diffraction. These results found here might open new revenues for methylene oxidation and alkanediol chemistry.