Taming the Dragon: Complexation of Silver Fulminate with Nitrogen-Rich Azole Ligands.

The almost ancient and very sensitive silver fulminate (SF), which was involved in the establishment of fundamental chemical concepts, was desensitized for the first time with different nitrogen-rich triazoles and tetrazoles, yielding SF complexes [Agx(CNO)x(N-Ligand)y] (x = 1-4; y = 1-3). These were accurately characterized (X-ray diffraction, scanning electron microscopy, IR, elemental analysis, differential thermal analysis, and thermogravimetric analysis) and investigated concerning their energetic character. The highly energetic coordination compounds suddenly show, in contrast to SF, sensitivities in a manageable range and are therefore safer to handle. In particular, compounds [Ag4(CNO)4(BTRI)] [3; BTRI = 4,4'-bis(1,2,4-triazole)] and [Ag4(CNO)4(2,2-dtp)] [8; 2,2-dtp = 1,3-di(tetrazol-1-yl)propane] show values in the range of desired lead styphnate alternatives with similar energetic performances. The crystal structure experiments reveal silver cluster formation in all complexes with distinct argentophilic interactions close to 2.77 Å. Furthermore, it was possible to synthesize 8 in a one-pot reaction, avoiding the isolation of highly sensitive SF.

Refinement of Copper(II) Azide with 1-Alkyl-5H-tetrazoles: Adaptable Energetic Complexes.

A concept for stabilizing highly sensitive and explosive copper(II) azide with 1-N-substituted tetrazoles is described. It was possible to stabilize the system by the use of highly endothermic, nitrogen-rich ligands. The sensitivities of the resulting energetic copper coordination compounds can be tuned further by variation of the alkyl chain of the ligands and by phlegmatization of the complexes with classical additives during the synthesis. It is demonstrated, using the compound based on 1-methyl-5H-tetrazole ([Cu(N3 )2 (MTZ)], 1) that this class of complexes can be applied as a potential replacement for both lead azide (LA) and lead styphnate (LS). The complex was extensively investigated according to its chemical (elemental analysis, single-crystal and powder X-ray diffraction, IR spectroscopy, scanning electron microscopy) and physico-chemical properties (differential thermal analysis, sensitivities towards impact, friction, and electrostatic discharge) compared to pure copper(II) azide.

Comparison of 1-Ethyl-5H-tetrazole and 1-Azidoethyl-5H-tetrazole as Ligands in Energetic Transition Metal Complexes.

Energetic coordination compounds (ECC) based on 3d or 4d transition metals show promising characteristics to be used as potential replacements for highly toxic lead-containing primary explosives. Herein we report the synthesis of 12 new ECC based on 1-azidoethyl-5H-tetrazole (AET) or 1-ethyl-5H-tetrazole (1-ETZ) as nitrogen-rich ligands as well as various central metals (Cu2+ , Fe2+ , Zn2+ , Ag+ ) and anions such as perchlorate and nitrate. The influence of the increased endothermicity by adding an additional azide group was studied by comparing analogous ECC based on AET and 1-ETZ. Furthermore, the compounds were extensively analyzed by XRD, IR, EA, solid-state UV/Vis, and DTA as well as their sensitivities toward impact and friction were determined with BAM standard techniques, together with their sensitivity against electrostatic discharge. The sensitivities were compared with the one toward ball drop impact measurements. Classical initiation tests (nitropenta filled detonators) and ignition by laser irradiation highly prove the potential use of the most promising compounds in lead-free initiation systems.

1-AminoTriazole Transition-Metal Complexes as Laser-Ignitable and Lead-Free Primary Explosives.

This unique complex study describes two isomeric aminotriazoles as auspicious nitrogen-rich ligands for energetic coordination compounds (ECCs) to replace the commonly used highly poisonous and environmentally harmful lead-based primary explosives. The triazoles were obtained by easily scalable and convenient synthetic routes starting solely from commercially available starting materials. 1-Amino-1,2,3-triazole (1, 1-ATRI) and, for the first time, 1-amino-1,2,4-triazole (2, 1A-1,2,4-TRI) were employed as ligands to form highly energetic transition-metal(II) complexes. The desired characteristics could be altered successively by using various nonpoisonous metal(II) centers (Cu2+ , Mn2+ , Fe2+ , and Zn2+ ) and anions (Cl- , NO3 - , ClO3 - , ClO4 - , picrate, styphnate, 2,4,6-trinitro-3-hydroxyphenolate, and 2,4,6-trinitro-3,5-dihydroxyphenolate). The 14 synthesized coordination compounds were characterized comprehensively by XRD, IR and UV/Vis spectroscopy, elemental analysis, and differential thermal and thermogravimetric analyses. Ball-drop impact, electrostatic discharge (ESD), and mechanical (impact and friction) sensitivities were determined according to BAM standard methods. In addition to laser ignition experiments, selected ECCs were evaluated in classical secondary explosive initiation tests (detonators filled with pentaerythritol tetranitrate (nitropenta)), which revealed their enormous potential and proved them to be very attractive for future applications in explosives.

Nitrogen-Rich Copper(II) Bromate Complexes: an Exotic Class of Primary Explosives †.

Because of the ongoing very challenging search for potential replacements of the currently used toxic lead-based primary explosives, new synthetic strategies have to be developed. In particular, the smart concept of energetic coordination compounds (ECC) has proven to hold great potential to solve this difficult and complex problem. The herein-described approach combines the exotic and neglected class of copper(II) bromate ECC with different environmentally friendly nitrogen-rich heterocycles, which exhibit the energetic properties of powerful primary explosives. The concept is the simple adjustment of the energetic properties of the complexes through alteration of the corresponding azoles. Six new copper(II) bromate complexes with reasonable sensitivities are featured in this study, which were synthesized in a practical and straightforward fashion, assured through easy access to copper(II) bromate obtained by metathesis reaction. Obtained compounds were comprehensively characterized through various analytical methods such as low-temperature X-ray diffraction, IR spectroscopy, and elemental analysis. Their sensitivities toward impact and friction were assessed through BAM standard techniques, together with their sensitivity against electrostatic discharge. Evaluation of the energetic properties of the newly synthesized compounds included examination of the respective thermal stabilities by differential thermal analysis. Furthermore, the complexes were tested regarding their behavior toward laser irradiation. Additionally, to receive insight into a possible correlation between the laser-investigated compounds' optical absorption and their ability to ignite by exposure to laser irradiation, UV-vis-near-IR spectra were recorded.

Copper(II) Chlorate Complexes: The Renaissance of a Forgotten and Misjudged Energetic Anion.

A convenient synthetic route toward new copper(II) chlorate complexes with potential use in modern advanced ignition or initiation systems is described. Obtained compounds were not only accurately characterized (XRD, IR, UV/Vis EA and DTA) but also investigated for their energetic character (sensitivities, initiation capability and laser ignition). The copper 4-aminotriazolyl chlorate complex showed excellent initiation of PETN, while also being thermally stable and safe to handle. Solid-state UV-Vis measurements were performed to get a possible insight toward the laser initiation mechanism. In contrast to expectations, the presented copper(II) chlorate energetic coordination compounds show manageable sensitivities that can be tamed or boosted by the appropriate choice of nitrogen-rich ligands.

Methylsemicarbazide as a Ligand in Late 3d Transition Metal Complexes.

Most ignition and initiation systems nowadays still contain poisonous chemicals such as lead styphnate and lead azide but also chromates and other compounds of high concern. Therefore, methylsemicarbazide (1, MSC), which can be prepared in a one-step reaction and in an extraordinary high yield of 95 %, has been evaluated as ligand in energetic coordination compounds. For the first time 25 new transition metal complexes (Mn2+ , Ni2+ , Co2+ , Cu2+ , and Zn2+ ) using methylsemicarbazide (1) as the ligand were prepared and comprehensively analyzed by, for example, XRD, IR, EA, UV/Vis and DSC/DTA/TGA. Many show a strong energetic character, which can be tuned by using different anions such as Cl- , SO42- , NO3- , ClO4- , picrate or styphnate. Selected compounds were additionally evaluated as lead-free primary explosives in initiation tests (nitropenta filled detonators) and in laser ignition systems. Especially compound 7 showed very promising results during these tests and could be a potential candidate for future applications.

Synthesis and Characterization of Nitro-, Trinitromethyl-, and Fluorodinitromethyl-Substituted Triazolyl- and Tetrazolyl-trihydridoborate Anions.

The problem of preparing energetic, exclusively mono-azolyl substituted hydridoborate anions in high yield and purity from [BH4 ]- and nitroazoles by hydrogen elimination was overcome by reacting the corresponding nitroazolate anions with the BH3 adducts BH3 ⋅S(CH3 )2 or BH3 ⋅THF. The highly-energetic, nitro-, trinitromethyl-, and fluorodinitromethyl- substituted triazolyl- and tetrazolyl-trihydridoborate anions were synthesized in this manner and characterized by vibrational and multinuclear NMR spectroscopy and their crystal structures. The use of excess BH3 resulted in some cases in the addition of a second BH3 molecule bound more-weakly to one of the nitrogen atoms of the azole ring. All monoazolyl-trihydridoborates were thermally less stable than the parent azolate anions. A decomposition product of tetraphenylphosphonium (5-(trinitromethyl)-5H-2λ4 -tetrazol-2-yl)trihydridoborate, the tetraphenyl-phosphonium (dinitro-1H-tetrazol-5-yl)methanide monohydrate, was also structurally characterized, providing some insight into the decomposition pathways of the nitromethyl-substituted azolyltrihydridoborate anions.

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

The synthesis of di(1H-tetrazol-5-yl)methane (1, 5-DTM), starting from commercially available sodium azide and malononitrile, is described. This tetrazole was characterized and investigated for use as a neutral nitrogen-rich ligand in various energetic transition metal complexes: ([CuCl2(5-DTM)2]·2H2O (2), [Co(H2O)2(5-DTM)2]Cl2 (3), [Ni(H2O)2(5-DTM)2]Cl2 (4), [Co(H2O)2(5-DTM)2](NO3)2 (6), [Ni(H2O)2(5-DTM)2](NO3)2 (7), [Zn(H2O)2(5-DTM)2](NO3)2 (8), {[Cu3(SO4)2(5-DTM-H)2(H2O)4(5-DTM)2]·2H2O}∞ (9), [Cu(H2O)2(5-DTM)2](NO3)2 (11), [Cu(NO3)2(5-DTM)2]·2H2O (12), [Cu(NO3)2(5-DTM)2] (13), [Cu(H2O)2(5-DTM)2](ClO4)2 (14), and [Cu(ClO4)2(5-DTM)2] (15). Obtained coordination compounds were characterized using single crystal X-ray diffraction (except for 7 and 13), IR spectroscopy, elemental analysis, and differential thermal analysis. The sensitivities to external stimuli (impact, friction, electrostatic discharge) were determined. Complexes 12 and 13 were tested for their ignitability by laser irradiation.

Metal salts and complexes of 1,1'-dinitramino-5,5'-bitetrazole.

Potassium 1,1'-dinitramino-5,5'-bitetrazolate is one of the most promising primary explosives which is currently under investigation for different applications. This is due to its high initiation power and the exclusion of heavy metals. To close the gap, the remaining alkali metal salts such as the lithium 6, sodium 7, rubidium 8 and cesium 9 salts were synthesized by reaction of the highly soluble ammonium salt 5 with its corresponding metal hydroxide solutions. In addition, the highly explosive silver salt 10 as well as several other transition metal(ii) amine complexes with nickel(ii) 11, copper(ii) 12 and zinc(ii) 13 were prepared in a similar manner. The structure of all compounds was determined by X-ray diffraction. The sensitivities toward impact, friction, heat and electrostatic discharge as well as their behavior on laser irradiation of the transition metal complexes were explored.

1,1'-Nitramino-5,5'-bitetrazoles.

1,1'-Dinitramino-5,5'-bitetrazole and 1,1'-dinitramino-5,5'-azobitetrazole were synthesized for the first time. The neutral compounds are extremely sensitive and powerful explosives. Selected nitrogen-rich salts were prepared to adjust sensitivity and performance values. The compounds were characterized by low-temperature X-ray diffraction, IR and Raman spectroscopy, multinuclear NMR spectroscopy, elemental analysis, and DTA/DSC. Calculated energetic performances using the EXPLO5 code based on calculated (CBS-4M) heats of formation and X-ray densities support the high performances of the 1,1'-dinitramino-5,5'-bitetrazoles as energetic materials. The sensitivities toward impact, friction, and electrostatic discharge were also explored. Most of the compounds show sensitivities in the range of primary explosives and should only be handled with great care!

Synthesis and characterization of various photosensitive copper(II) complexes with 5-(1-methylhydrazinyl)-1H-tetrazole as ligand and perchlorate, nitrate, dinitramide, and chloride as anions.

The preparation of 5-(1-methylhydrazinyl)-1H-tetrazole monohydrate (1⋅H2O) and various copper(II) complexes with perchlorate (2 and 3), nitrate (4, 5, and 6), dinitramide (7), and chloride (8) is described. The coordination compounds (monomers, dimers, and polymers) were characterized through infrared spectroscopy and elemental analysis. Further, the structures of 2 and 4-8 were determined by single-crystal X-ray diffraction. Compound 1 can act as a bidentate ligand in its neutral form (HMHT) and as a µ2- or µ3-bridging ligand in its deprotonated form (MHT). The energetic properties of the synthesized complexes, such as their sensitivities toward impact and friction, were determined, and laser ignition tests were performed. New information about the laser initiation process and the role of the anion in the initiation criterion was obtained. The perchlorate complexes 2 (T(decomp)=217 °C) and 3 (T(decomp)=206 °C) are potential primary explosives.