Cupric coordination compounds with multiple anions: a promising strategy for the regulation of energetic materials.

To seek new high energetic materials, N-methylene-C-bridged nitrogen-rich heterocycle 1-((4,5-diamino-4H-1,2,4-triazol-3-yl)methyl)-1H-1,2,4-triazol-3,5-diamine (DATMTDA) (2) was first synthesized, and two copper coordination compounds ([Cu12(OH)4(ClO4)4(H2O)4(DATMTDA)12](ClO4)16·12H2O (3) and [Cu3(OH)(ClO4)(DATMTDA)3](ClO4)3(NO3) (4)) based on 2 were formed by introducing different anions. These compounds were characterized by elemental analysis, IR spectroscopy and single-crystal X-ray diffraction analysis. The crystal structures of compounds 3 and 4 are similar and crystallize in monoclinic systems with the P21/c space group, while the central copper atoms show different coordination behaviors. However, the structure of compounds 3 and 4 is analogous to a three dimensional structure owing to the O atom of OH-, forming coordinate bonds with three copper cations. The NBO charge of 2 was calculated using density functional theory to understand its coordination modes. The Hirshfeld surface calculation reveals that 3 and 4 have strong intermolecular interactions. The thermal decomposition processes, non-isothermal kinetics, and enthalpies of formation and sensitivities of these compounds were investigated. By introducing one NO3- of compound 4 to replace one ClO4- in compound 3, compound 4 shows lower density and lower decomposition peak temperature but lower sensitivity and a higher formation enthalpy than compound 3. The complex 4 possesses an outstanding catalytic effect for the decomposition of AP than that of complex 3. The results illustrate the possibility of introducing various anions into energetic coordination compounds for the regulation of energetic materials.

Theoretical study of the reduction in sensitivity of copper azide following encapsulation in carbon nanotubes.

Research aimed at reducing the sensitivity of primary explosives with excellent ignition performance is of great significance for their practical application. In this work, we theoretically studied the effect of inserting the primary explosive copper azide (Cu(N3)2) into single-walled carbon nanotubes (SWCNTs) on the sensitivity of the explosive to changes in hydrostatic pressure. The electronic structure of Cu(N3)2 was found to be more sensitive to external pressure than lead azide, which is consistent with their experimental impact sensitivities. A composite of Cu(N3)2 molecules and SWCNTs (Cu(N3)2/CNTs) was prepared in which the components mainly interacted electrostatically and the Cu(N3)2 molecules formed semi-arc structures along the nanotube walls, rather than exhibiting their usual planar structure. The electrostatic potential and electronic structure of the composite indicate that it is more stable than crystalline Cu(N3)2. Notably, combining the Cu(N3)2 with the SWCNTs reduces the sensitivity of the Cu(N3)2 to external pressure, implying that carbon nanotubes can reduce the sensitivity of Cu(N3)2. This work should aid the development of highly efficient green primary explosives.

Carbonyl-bridged energetic materials: biomimetic synthesis, organic catalytic synthesis, and energetic performances.

In order to obtain high-performance energetic materials, in this work, carbonyl groups (C[double bond, length as m-dash]O) have been newly introduced as sole bridging groups in the field of energetic materials. To this end, two tailored green methods for the synthesis of carbonyl-bridged energetic compounds have been developed for the first time. One is a biomimetic synthesis, in which the conversion route of heme to biliverdin has been used to obtain metal-containing energetic compounds. The other one is an organocatalysis, in which guanidinium serves as an energetic catalyst to afford other energetic compounds. Experimental studies and theoretical calculations have shown that carbonyl-bridged energetic compounds exhibit excellent energetic properties, which is promising for the carbonyl group as a new important and effective linker in energetic materials.

Energetic Salts Based on Tetrazole N-Oxide.

Energetic materials (explosives, propellants, and pyrotechnics) are used extensively for both civilian and military applications and the development of such materials, particularly in the case of energetic salts, is subject to continuous research efforts all over the world. This Review concerns recent advances in the syntheses, properties, and potential applications of ionic salts based on tetrazole N-oxide. Most of these salts exhibit excellent characteristics and can be classified as a new family of highly energetic materials with increased density and performance, alongside decreased mechanical sensitivity. Additionally, novel tetrazole N-oxide salts are proposed based on a diverse array of functional groups and ions pairs, which may be promising candidates for new energetic materials.

Controllable explosion: fine-tuning the sensitivity of high-energy complexes.

Tuning the sensitivity of energetic materials has always been a research topic of interest. A lot of attention has been paid on changing the ligands previously used in traditional high energy density materials (HEDMs). Recently, we have stepped further along this path by thinking from another angle, i.e., changing the metal centre. Herein, we report 4 transition metal complexes bearing the 1,5-diaminotetrazole ligand, which have similar structures but drastically different sensitivities. These differences are apparently due to the different metal centres used.

Combination multinitrogen with good oxygen balance: molecule and synthesis design of polynitro-substituted tetrazolotriazine-based energetic compounds.

We investigated 5,8-dinitro-5,6,7,8-tetrahydrotetrazolo[1,5-b][1,2,4]triazine (short for DNTzTr (1)) using various ab initio quantum chemistry methods. We proposed an additional three novel polynitro-substituted tetrazolotriazine-based compounds with exceptional performance, including 5,8-dinitro-5,6-dioxotetrazolo[1,5-b][1,2,4]triazine, DNOTzTr (2), 4,5,9,10-tetranitro[1,2,4,5]tetrazolo[3,4-b][1,2,4,5]tetrazolo[3',4':5,6]triazino[2,3-e]triazine, TNTzTr (3), and 4,5,6,10,11,12-hexanitro-bis[1,2,4,5]tetrazolo[3',4':5,6]triazino[2,3-b:2',3'-e]triazine, HNBTzTr (4). The optimized structure, electronic density, natural bond orbital (NBO) charges and HOMO-LUMO orbitals, electrostatic potential on surface of molecule, IR- and NMR-predicted spectra, as well as thermochemical parameters were calculated with the B3LYP/6-311+G(2d) level of theory. Critical parameters such as density, enthalpy of formation (EOF), and detonation performance have also been predicted. Characters with positive EOF (1386.00 and 1625.31 kJ/mol), high density (over 2.00 g/cm(3)), outstanding detonation properties (D = 9.82 km/s, P = 45.45 GPa; D = 9.94 km/s, P = 47.30 GPa), the perfect oxygen balance set to zero, and acceptable impact sensitivity led novel compounds 3 and 4 to be very promising energetic materials. This work provides the theoretical molecule design and a reasonable synthesis path for further experimental synthesis and testing.

Extensive theoretical studies on two new members of the FOX-7 family: 5-(dinitromethylene)-1,4-dinitramino-tetrazole and 1,1'-dinitro-4,4'-diamino-5,5'-bitetrazole as energetic compounds.

Two novel compounds 5-(dinitromethylene)-1,4-dinitramino-tetrazole (DNAT) and 1,1'-dinitro-4,4'-diamino-5,5'-bitetrazole (DNABT) were suggested to be potential candidates of high energy density materials (HEDMs). The optimized geometry, NBO charges and electronic density, HOMO-LUMO, electrostatic potential on the surface of molecules, the IR spectrum and thermochemical parameters were calculated for inspecting the electronic structure properties at B3LYP/6-311++G** level of theory. Meanwhile, the solid states of DNAT and DNABT were studied using the crystal packing models by the plane-wave periodic local-density approximation density functional theory. Four stable polymorphous cells have been found including P212121, P21/c, P1̄ and Pbca, assigned to the orthorhombic, monoclinic and triclinic lattice systems. In addition, properties such as density, enthalpy of formation and detonation performance have also been predicted. As a result, the detonation velocity and pressure of two compounds are found to be very remarkable (DNAT: D = 9.17 km s(-1), P = 39.23 GPa; DNABT: D = 9.53 km s(-1), P = 40.92 GPa). Considering the tetrazole rings with energetic groups and the insensitive fragment of FOX-7, high positive heat of formation (583.50 kJ mol(-1) and 1081.39 kJ mol(-1)) and eminent performance render DNAT and DNABT to be very promising powerful energetically insensitive compounds. This work provides theoretical support for further experimental synthesis.

Theoretical study on the tautomerization of 1,5-diaminotetrazole (DAT).

The tautomerization pathways and kinetics of 1,5-diaminotetrazole (DAT) have been investigated by means of second-order Møller-Plesset perturbation theory (MP2) and coupled-cluster theory, with single and double excitations including perturbative corrections for triple excitations (CCSD(T)). Five possible tautomers, namely 4-hydro-1-amino-5-imino-tetrazole (a), 2,5-diamino-tetrazole (b), 1,5-diamino-tetrazole (c), 2-hydro-1-imino-5-amino-tetrazole (d), and 2,4-dihydro-1,5-diimino-tetrazole (e) were identified. The structures of the reactants, transition states, and products along with the tautomerism pathways were optimized by the MP2 method using the 6-311G** basis set, and the energies were refined using CCSD(T)/6-311G**. The minimum-energy path (MEP) information for DAT was obtained at the CCSD(T)/6-311G**//MP2/6-311G** level of theory. Therein, reaction 2 (c → b) is an amino-shift reaction, while reaction 1 (c → a), reaction 3 (c → d), reaction 4 (a → e), and reaction 5 (d → e) are reactions of hydrogen-shift tautomerization. The calculated results show that 2,5-diaminotetrazole (b) with the minimum energy (taking c as a standard) among five tautomers, is the energetically preferred tautomer of DAT in the gas phase. In addition, the energy barrier of reaction 2 is 71.65 kcal · mol(-1) in the gas phase, while reaction 1 takes place more easily with an activation barrier of 61.53 kcal · mol(-1) also as compared to 63.71 kcal · mol(-1) in reaction 3. Moreover, the tautomerization of reaction 4 requires the largest energy barrier of 83.29 kcal · mol(-1), which is obviously bigger than reaction 5 with a value of 73.78 kcal · mol(-1). Thus, the hydrogen-shift of c to a is the easiest transformation, while the tautomerization of a to e is the hardest one. Again, the rate constants of tautomerization have been obtained by TST, TST/Eckart, CVT, CVT/SCT, and CVT/ZCT methods in the range 200-2500 K, and analysis indicated that variational effects are small over the whole temperature range, while tunneling effects are significant in the lower temperature range.

Theoretical study on novel nitrogen-rich energetic compounds of bis(amino)-azobis(azoles) with tetrazene unit.

Six stereoisomers of 5,5'-bis(amino)-1,1'-azobis(tetrazoles) and 30 other structures, including all possible bis(amino)-azobis(azoles) with an N-N=N-N unit, were designed. The molecular geometries were fully optimized at the DFT-B3LYP level with the 6-31++g (d, p) basis set. From the absence of any imaginary frequency in the infrared vibration frequency spectrum, it is predicted that all these studied structures may exist in stable forms. The results of the total energies of the stereoisomers of 5,5'-bis(amino)-1,1'-azobis(tetrazoles) indicate that the two symmetric trans-form structures are more likely to exist than the other four. The pyrolysis process, chemical stability and molecular electrostatic potential were studied via the investigation of their electronic structure. Heats of formation (HOFs) were calculated using the atomization energy method based on the results of the harmonic vibration frequencies, and a linear relationship was found between the HOF and nitrogen chain or nitrogen content. Densities of the title compounds were predicted with the Monte Carlo method. Finally, according to the results of the calculated HOFs and densities, the explosive parameters of these compounds were calculated using the Kamlet-Jacobs formula. 5,5'-Bis(amino)-1,1'-azobis(tetrazoles) and its isomer 5,5'-bis(amino)-2,2'-azobis(tetrazoles) may have potential for use as energetic compounds.

Theoretical study of the decomposition mechanisms and kinetics of the ingredients RDX in composition B.

RDX as a component in composition B (TNT + RDX) was first studied by us on its mechanism and kinetics of decomposition reactions in this paper. We have pointed out three possible pathways and found a new low-energy process of its decomposition. The N-N bond cleavage in composition B has higher dissociation energies than the monomer, but it is also the initial step. The optimized structures and the frequencies of all the stationary points were calculated at the B3LYP/6-31G(d) level. The minimum-energy paths were obtained by using the intrinsic reaction coordinate (IRC) theory, and the reaction potential energy curve was corrected with zero-point energy. Finally, the rate constants were calculated in a wide temperature region from 200 to 2500 K using TST, TST/Eckart theories. The obtained results also indicate that the tunneling effects are remarkable at low temperature (200 K

First-principles study of energetic complexes (II): (5-cyanotetrazolato-N2) pentaammine cobalt (III) perchlorate (CP) and Ni, Fe and Zn analogues.

First-principles methods using the TPSS density functional level of theory with the basis set 6-31G** were applied to study (5-cyanotetrazolato-N(2)) pentaammine cobalt (III) perchlorate (CP) and Ni, Fe and Zn analogues in the gas phase. The optimized lowest-energy geometry of CP was calculated from reported experimental structural data using the TPSS method. The calculated values are in good agreement with those measured by X-ray diffraction. Ni, Fe and Zn analogues were constructed and calculated on the same basis. NBO results showed that the metal-ligand interactions have covalent character. Donor-acceptor analyses predicted that the delocalization energy E(2) decreases from Co to Zn, so the covalent nature of the complexes increases in the order Co>Fe>Ni>Zn. In addition, HOMO-LUMO composition was investigated to determine the stability of the title compounds.

Synthesis, structural investigation and thermal properties of a novel manganese complex Mn2(DAT)2Cl4(H2O)4 (DAT=1,5-diaminotetrazole).

A novel manganese complex Mn(2)(DAT)(2)Cl(4)(H(2)O)(4), where DAT is 1,5-diaminotetrazole, was synthesized by the reaction of manganese(II) chloride tetrahydrate and 1,5-diaminotetrazole (DAT) in ethanol, and characterized by elemental analysis, FT-IR spectroscopy. The crystal structure was determined through X-ray single crystal diffraction. The molecular unit of Mn(2)(DAT)(2)Cl(4)(H(2)O)(4) has a distorted octahedral structure, containing two central manganese cations, which coordinated by a mono-dentate terminal chloride, a bulky DAT ligand and two water molecules, and linked by two bidentate bridging chloride ligands. There are two main exothermic peaks and one endothermic peak in the thermal decomposition process, investigated by differential scanning calorimetry (DSC) and thermo-gravimetric analysis (TGA), the final residue of the title compound at 600 degrees C is MnO. The kinetic parameters of the endothermic process and two main exothermic processes were studied by applying the Kissinger's and Ozawa-Doyle's methods.

Theoretical studies on the tautomerism and intramolecular hydrogen shifts of 5-amino-tetrazole in the gas phase.

The tautomerism and intramolecular hydrogen shifts of 5-amino-tetrazole in the gas phase were studied in the present work. The minimum energy path (MEP) information of 5-amino-tetrazole was obtained at the CCSD(T)/6-311G**//MP2/6-311G** level of theory. The six possible tautomers of 1H, 4H-5-imino-tetrazole (a), 1H-5-amino-tetrazole (b), 2H-5-amino-tetrazole (c), 1H, 2H-5-imino-tetrazole (d), the mesoionic form (e) and 2H, 4H-5-imino-tetrazole (f) were investigated. Among these tautomers, there are 2 amino- forms, 3 imino- forms, and 1 mesoionic structure form. In all the tautomers, 2-H form (c) is the energetically preferred one in the gas phase. In the imino- tautomers, the energy value of the compound d is similar as that of the compound f but it is higher than the energy value of the compound a. The potential energetic surface (PES) and kinetics for five reactions have been investigated. Reaction 2 (b-->c) was hydrogen shifts only in which the 1-H and 2-H rearrangement. This means that the reaction 2 (b-->c) is energetically favorable having an activation barrier of 45.66 kcal.mol(-1) and the reaction energies (DeltaE) is only 2.67 kcal.mol(-1). However, the reaction energy barrier for tautomerism of reaction 1 (b-->e) is 54.90 kcal.mol(-1). Reaction 1 (b-->a), reaction 3 (c-->d), and reaction 5 (c-->f) were amino- -->imino- tautomerism reactions. The energy barriers of amino- -->imino- tautomerism reactions required are 59.39, 65.57, 73.61 kcal.mol(-1) respectively in the gas phase. The calculated values of rate constants using TST, TST/Eckart, CVT, CVT/SCT and CVT/ZCT methods using the optimized geometries obtained at the MP2/6-311G** level of theory show the variational effects are small over the whole temperature range, while tunneling effects are big in the lower temperature range for all tautomerism reactions.

The mechanism and kinetics of decomposition of 5-aminotetrazole.

The pathway and ab initio direct kinetics of the decomposition 5-aminotetrazole (5-ATZ) to HN(3) and NH(2)CN was investigated. Reactant, products and transition state were optimized with MP2 and B3LYP methods using 6-311G** and aug-cc-pVDZ basis sets. The intrinsic reaction coordinate curve of the reaction was calculated using the MP2 method with 6-311G** basis set. The energies were refined using CCSD(T)/6-311G**. Rate constants were evaluated by conventional transition-state theory (CVT) and canonical variational transition-state theory (TST), with tunneling effect over 300 to 2,500 K. The results indicated that the tunneling effect and the variational effect are small for the calculated rate constants. The fitted three-parameter expression calculated using the CVT and TST methods are k(T) = 4.07 x 10(11) x T(0.84) x e((-2.42 x 10(4))/T)s(-1) and k(T) = 2.09 x 10(11) x T(0.89) x e((-2.36 x 10(4))/T)s(-1), respectively.