The Chemistry of 5‐(Tetrazol‐1‐yl)‐2H‐tetrazole: An Extensive Study of Structural and Energetic Properties

5‐(Tetrazol‐1‐yl)‐2H‐tetrazole ( 1 ), or 1,5′‐bistetrazole, was synthesized by the cyclization of 5‐amino‐1H‐tetrazole, sodium azide and triethyl orthoformate in glacial acetic acid. A derivative of 1 , 2‐methyl‐5‐(tetrazol‐1‐yl)tetrazole ( 2 ) can be obtained by this method starting from 5‐amino‐2‐methyl‐tetrazole. Furthermore, selected salts of 1 with nitrogen‐rich and metal (alkali and transition metal) cations, including hydroxylammonium ( 4 ), triaminoguanidinium ( 5 ), copper(I) ( 8 ) and silver ( 9 ), as well as copper(II) complexes of both 1 and 2 were prepared. An intensive characterization of the compounds is given, including vibrational (IR, Raman) and multinuclear NMR spectroscopy, mass spectrometry, DSC and single‐crystal X‐ray diffraction. Their sensitivities towards physical stimuli (impact, friction, electrostatic) were determined according to Bundesamt für Materialforschung (BAM) standard methods. Energetic performance (detonation velocity, pressure, etc.) parameters were calculated with the EXPLO5 program, based on predicted heats of formation derived from enthalpies computed at the CBS‐4M level of theory and utilizing the atomization energy method. From the analytical and calculated data, their potential as energetic materials in different applications was evaluated and discussed.     

1D Structure Sodium Coordination Anion based on [5‐(Dinitromethylene)‐4,5‐dihydro‐1H‐tetrazole]: Syntheses,Structures, and Thermal Behavior

The ten‐coordinate complex, (HATr)[Na(DNMz)] · H₂O ( 1 ) was synthesized by reaction of 5‐(dinitromethylene)‐4,5‐dihydro‐1H‐tetrazole (DNMz), sodium hydroxide, and 3‐hydrazinium‐4‐amino‐1,2,4‐1H‐triazolium dichloride (HATr) in aqueous solution and characterized by various physico‐chemical techniques. Complex 1 is an energetic material with a nitrogen content of 51.2 % and a decomposition temperature of 128.9 °C. The molecular structure of complex 1 crystallizes in the monoclinic system with P2(1)/c group and shows an infinite 1D chain structure. The heat of formation was determined as –122.27 kJ · mol^–1 by using bomb calorimetry. In addition, the kinetic parameters were studied by Kissinger's and Ozawa‐Doyle's methods.     

A Study of 5‐(1,2,4‐Triazol‐C‐yl)tetrazol‐1‐ols: Combining the Benefits of Different Heterocycles for the Design of Energetic Materials

The synthesis and full structural and spectroscopic characterization of three 5‐(1,2,4‐triazol‐C‐yl)tetrazol‐1‐ol compounds with selected energetic moieties including nitrimino ( 5 ), nitro ( 6 ) and azido ( 7 ) groups are reported. The influence of those energetic moieties as well as the C? C connection of a tetrazol‐1‐ol and a 1,2,4‐triazole on structural and energetic properties has been investigated. All compounds were well characterized by various means, including IR and multinuclear NMR spectroscopy, mass spectrometry, and DSC. The molecular structures of 5 – 8 were determined in the solid state by single‐crystal X‐ray diffraction. The standard heats of formation were calculated on the CBS‐4M level of theory utilizing the atomization energy method, revealing highly positive values for all compounds. The detonation parameters were calculated with the EXPLO5 program and compared to the common secondary explosive RDX. Additionally, sensitivities towards impact, friction and electrostatic discharge were determined.     

Two derivatives of 5‐amino­tetrazole: 5‐amino‐1‐phenyl­tetrazole and 5‐amino‐1‐(1‐naphthyl)­tetrazole

In the mol­ecules of 5‐amino‐1‐phenyl­tetrazole, C₇H₇N₅, (I), and 5‐amino‐1‐(1‐naphthyl)­tetrazole, C₁₁H₉N₅, (II), the tetrazole rings and aryl fragments are not coplanar; corresponding dihedral angles are 50.58 (5) and 45.19 (7)° for the two independent mol­ecules of (I), and 64.14 (5)° for (II). Intermolecular N—H⋯N hydrogen bonds between the amino groups and tetrazole N atoms are primarily responsible for formation of two‐dimensional networks extending parallel to the bc plane in both compounds. The presence of the amino group has a distinct effect on the geometry of the tetrazole rings in each case.     

New Nitriminotetrazoles – Synthesis,Structures and Characterization

The reactions of 5‐nitriminotetrazole ( 4 ) with 1‐methyl‐5‐aminotetrazole ( 2 ) as well as 2‐methyl‐5‐aminotetrazole ( 3 ) were investigated. In the first reaction 2 was protonated yielding 1‐methyl‐5‐aminotetrazolium 5‐nitrimino‐1H‐tetrazolate monohydrate ( 7 ). In the latter case no protonation could be observed and a co‐crystallization of 5‐nitraminotetrazole and 2‐methyl‐5‐aminotetrazole was obtained. In this compound a new tautomer of 4 could be found. Both products were determined by low temperature single crystal X‐ray diffraction, IR, Raman and multinuclear (¹H, ¹³C, ¹⁵N) NMR spectroscopy, elemental analysis as well as differential scanning calorimetry. In addition the heats of formation were calculated using experimentally obtained heats of combustion. With these and the X‐ray densities several detonation parameter were computed using the EXPLO5 software. In addition the sensitivities towards impact, friction and electrostatic discharge were determined. Further, two crystal structures of the important starting materials in energetic research 5‐nitriminotetrazole monohydrate ( 4 ·H₂O) and 1‐methyl‐5‐nitriminotetrazolemonohydrate ( 5 ·H₂O) are presented and compared with the water‐free compounds. The heats of formation of 4 , 4 ·H₂O, 5 , 5 ·H₂O have been calculated by the atomization method using the CBS basis set. Inclusion of crystal water decrease heats of formation about 265 kJ mol^?1. Also the influence of crystal water on sensitivities (impact, friction, electrostatic discharge) but also performance is discussed.     

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.     

Synthesis and Characterization of the New Heterocycle 5‐(4‐Amino‐1,2,4‐triazol‐3‐on‐5′‐yl)‐1H‐tetrazole and Some Ionic Nitrogen‐Rich Derivatives

A new heterocycle consisting of a tetrazole ring attached to an amino‐triazolone ring, namely 5‐(4‐amino‐1,2,4‐triazol‐3‐on‐5′‐yl)‐1H‐tetrazole ( 3 ) as well as its ammonium ( 2 ), hydroxylammonium ( 3 ), and sodium salt ( 4 ), is introduced. Its ammonium salt ( 2 ) is formed starting from tetrazole‐5‐carboxamide oxime ( 1 ), which is reacted with diaminourea (carbonyldihydrazide) in aqueous media. All compounds 2 , 3 , 4 , 5 were structurally characterized by single crystal X‐ray diffraction. The thermal behavior was investigated using differential scanning calorimetry, and the sensitivities towards impact, friction, and electrostatic discharge were determined. Furthermore, several detonation parameters were calculated with the program EXPLO5 to determine the potential use of these compounds as highly energetic materials.     

Synthesis and Comprehensive Characterization of Hydrated Alkaline Earth Metal Salts of 5‐Amino‐1H‐tetrazole

Hydrated alkaline earth metal salts of 5‐amino‐1H‐tetrazole ( B ) were synthesized by reaction of B with a suitable metal hydroxide in water. All compounds were fully characterized by analytical (elemental analysis and mass spectrometry) and spectroscopic (IR, Raman, ¹H and ¹³C NMR) methods. Additionally, the crystal structures of the magnesium [ 1· 4H₂O: triclinic, P$\bar {1}$ , a = 5.940(1) Å, b = 7.326(1) Å,c = 7.383(1) Å, α = 106.10(1)°, β = 106.51(1)°, γ = 111.85(1)°, V = 258.0(1) ų], calcium [ 2· 6H₂O: monoclinic, P2₁/m, a = 6.904(1) Å,b = 6.828(1) Å, c = 10.952(2) Å, β = 94.50(2)°, V = 514.6(1) ų], and strontium [ 3· 6H₂O: orthorhombic, Cmcm, a = 6.987(1) Å, b = 28.394(2) Å, c = 7.007(1) Å, V = 1390.3(2) ų] were determined by low temperature X‐ray diffraction. Additionally, the (gas phase) structure of the 5‐amino‐1H‐tetrazole anion ([ B ]^–) was also studied by natural bond orbital (NBO) analysis [B3LYP/6‐31+G(d,p)]. Lastly, standard tests were used to determine the sensitivity towards impact, friction, and electrostatic discharge of the compounds and the thermal stability was assessed by differential scanning calorimetry (DSC) analysis.     

A new three‐dimensional CdII supramolecular framework constructed from the 1‐[(1H‐tetrazol‐5‐yl)methyl]‐1,4‐diazoniabicyclo[2.2.2]octane ligand

A new tetrazole–metal supramolecular compound, di‐μ‐chlorido‐bis(trichlorido{1‐[(1H‐tetrazol‐5‐yl‐κN²)methyl]‐1,4‐diazoniabicyclo[2.2.2]octane}cadmium(II)), [Cd₂(C₈H₁₆N₆)₂Cl₈], has been synthesized and structurally characterized by single‐crystal X‐ray diffraction. In the structure, each Cd^II cation is coordinated by five Cl atoms (two bridging and three terminal) and by one N atom from the 1‐[(1H‐tetrazol‐5‐yl)methyl]‐1,4‐diazoniabicyclo[2.2.2]octane ligand, adopting a slightly distorted octahedral coordination geometry. The bridging bicyclo[2.2.2]octane and chloride ligands link the Cd^II cations into one‐dimensional ribbon‐like N—H...Cl hydrogen‐bonded chains along the b axis. An extensive hydrogen‐bonding network formed by N—H...Cl and C—H...Cl hydrogen bonds, and interchain π–π stacking interactions between adjacent tetrazole rings, consolidate the crystal packing, linking the poymeric chains into a three‐dimensional supramolecular network.     

Reactions of Imidoyl Isoselenocyanates with Aromatic 2‐Amino N‐Heterocycles and 1‐Methyl‐1H‐imidazole

The reaction of N‐phenylimidoyl isoselenocyanates 1 with 2‐amino‐1,3‐thiazoles 10 in acetone proceeded smoothly at room temperature to give 4H‐1,3‐thiazolo[3,2‐a] [1,3,5]triazine‐4‐selones 13 in fair yields (Scheme 2). Under the same conditions, 1 and 2‐amino‐3‐methylpyridine ( 11 ) underwent an addition reaction, followed by a spontaneous oxidation, to yield the 3H‐4λ⁴‐[1,2,4]selenadiazolo[1′,5′:1,5] [1,2,4]selenadiazolo[2,3‐a]pyridine 14 (Scheme 3). The structure of 14 was established by X‐ray crystallography (Fig. 1). Finally, the reaction of 1‐methyl‐1H‐imidazole ( 12 ) and 1 led to 3‐methyl‐1‐(N‐phenylbenzimidoyl)‐1H‐imidazolium selenocyanates 15 (Scheme 4). In all three cases, an initially formed selenourea derivative is proposed as an intermediate.     

Nitrogen‐Rich Energetic Dianionic Salts of 3, 4‐Bis(1H‐5‐­tetrazolyl)furoxan with Excellent Thermal Stability

Nitrogen‐rich 3, 4‐bis(1H‐tetrazol‐5‐yl)furoxan (H₂BTF, 2 ) and its energetic salts with excellent thermal stability were successfully synthesized and fully characterized by ¹H, and ¹³C NMR, and IR spectroscopy, differential scanning calorimetry (DSC), and elemental analyses. Additionally, the structures of barium ( 3 ) and 1‐methyl‐3, 4, 5‐triamino‐triazolium ( 10 ) salts were confirmed by single‐crystal X‐ray diffraction. The densities of the energetic salts paired with organic cations range between 1.56 and 1.85 g · cm^–3 as measured by a gas pycnometer. Based on the measured densities and calculated heats of formation, the detonation pressures and velocities are calculated to be in the range 23.4–32.0 GPa and 7939–8915 m · s^–1, which make them competitive energetic materials.     

Synthesis of (3,5‐Aryl/methyl‐1H‐Pyrazol‐1‐yl)‐(5‐Arylamino‐2H‐1,2,3‐Triazol‐4‐yl)Methanone

Some new (3,5‐aryl/methyl‐1H‐pyrazol‐1‐yl)‐(5‐arylamino‐2H‐1,2,3‐triazol‐4‐yl)methanones were synthesized and characterized by ¹HNMR, ¹³C NMR, MS, IR spectra data and elemental analyses or high resolution mass spectra (HRMS). During the procedure, Dimroth rearrangement was used in this synthesis.     

Synthesis and Characterization of 5‐(1,2,4‐Triazol‐3‐yl)tetrazoles with Various Energetic Functionalities

In this contribution the synthesis and full structural as well as spectroscopic characterization of three 5‐(1,2,4‐triazol‐3‐yl)tetrazoles along with selected energetic moieties like nitro, nitrimino, and azido groups are presented. The main goal is a comparative study on the influence of those variable energetic moieties on structural and energetic properties. A complete characterization including IR and Raman as well as multinuclear NMR spectroscopy of all compounds is presented. Additionally, X‐ray crystallographic measurements were performed and reveal insights into structural characteristics as well as inter‐ and intramolecular interactions. The standard enthalpies of formation were calculated for all compounds at the CBS‐4M level of theory and reveal high positive heats of formation for all compounds. The calculated detonation parameters (using the EXPLO5.05 program) are in the range of 8000 m s^?1 (8097 m s^?1 ( 5 ), 8020 m s^?1 ( 6 ), 7874 m s^?1 ( 7 )). As expected, the measured impact and friction sensitivities as well as decomposition temperatures strongly depend on the energetic moiety at the triazole ring. The C? C connection of a triazole ring with its opportunity to introduce a large variety of energetic moieties and a tetrazole ring, implying a large energy content, leads to the selective synthesis of primary and secondary explosives.     

Two derivatives of 1,5‐disubstituted tetrazoles: 1‐(4‐nitrophenyl)‐1H‐tetrazol‐5‐amine and {(E)‐[1‐(4‐ethoxyphenyl)‐1H‐tetrazol‐5‐yl]iminomethyl}dimethylamine

The geometric features of 1‐(4‐nitrophenyl)‐1H‐tetrazol‐5‐amine, C₇H₆N₆O₂, correspond to the presence of the essential interaction of the 5‐amino group lone pair with the π system of the tetrazole ring. Intermolecular N—H...N and N—H...O hydrogen bonds result in the formation of infinite chains running along the [110] direction and involve centrosymmetric ring structures with motifs R₂²(8) and R₂²(20). Molecules of {(E)‐[1‐(4‐ethoxyphenyl)‐1H‐tetrazol‐5‐yl]iminomethyl}dimethylamine, C₁₂H₁₆N₆O, are essentially flattened, which facilitates the formation of a conjugated system spanning the whole molecule. Conjugation in the azomethine N=C—N fragment results in practically the same length for the formal double and single bonds.     

Novel Bis(2‐(5‐((5‐phenyl‐1H‐tetrazol‐1‐yl)methyl)‐4H‐1,2,4‐triazol‐3‐yl)phenoxy)Alkanes: Synthesis and Characterization

In this study, 10 different substituted aromatic bis‐benzaldehydes were synthesized by treating hydroxy benzaldehydes with various dihaloalkanes. Bis aldehydes 5a , 5b , 5c , 5d , 5e , 5f , 5g , 5h , 5i , 5j were treated with 2‐(5‐phenyl‐1H‐tetrazole‐1‐yl)acetohydrazide ( 3 ) in acidic medium and in the presence of ammonium acetate to yield a series of new isomeric bis(2‐(5‐((5‐phenyl‐1H‐tetrazol‐1‐yl)methyl)‐4H‐1,2,4‐triazol‐3‐yl)phenoxy)alkanes ( 6a , 6b , 6c , 6d , 6e , 6f , 6g , 6h , 6i , 6j ) in excellent to good yield. The newly synthesized compounds were characterized by the available spectroscopic analysis.     

Synthesis of some new 1‐acyl‐5‐aryl‐3‐(5‐methyl‐1‐p‐tolyl‐1H‐1,2,3‐triazol‐4‐yl)‐4,5‐dihydro‐1H‐pyrazole

Some new compounds (E)‐3‐aryl‐1‐(5‐methyl‐1‐p‐tolyl‐1H‐1,2,3‐triazol‐4‐yl)‐prop‐2‐en‐1‐ones 5a–e were prepared by 1‐(5‐methyl‐1‐p‐tolyl‐1H‐1,2,3‐triazol‐4‐yl)‐ethanone and various aromatic aldehydes. Then one pot reaction was happened by compounds 5a–e with hydrazine hydrate in acetic acid or propionic acid, respectively, to give the title compounds 1acyl‐5‐aryl‐3‐(5‐methyl‐1‐p‐tolyl‐1H‐1,2,3‐triazol‐4‐yl)‐4,5‐dihydro‐1H‐pyrazoles 6a–i . All structures were established by MS, IR, CHN, ¹H‐NMR and ¹³C‐NMR spectral data. J. Heterocyclic Chem., (2012).     

A one‐dimensional zinc(II) coordination polymer with a three‐dimensional supramolecular architecture incorporating 1‐[(1H‐benzimidazol‐2‐yl)methyl]‐1H‐tetrazole and adipate

The synthesis of coordination polymers or metal–organic frameworks (MOFs) has attracted considerable interest owing to the interesting structures and potential applications of these compounds. It is still a challenge to predict the exact structures and compositions of the final products. A new one‐dimensional coordination polymer, catena‐poly[[[bis{1‐[(1H‐benzimidazol‐2‐yl)methyl]‐1H‐tetrazole‐κN³}zinc(II)]‐μ‐hexane‐1,6‐dicarboxylato‐κ⁴O¹,O^1′:O⁶,O^6′] monohydrate], {[Zn(C₆H₈O₄)(C₉H₈N₆)₂]·H₂O}_n, has been synthesized by the reaction of Zn(Ac)₂ (Ac is acetate) with 1‐[(1H‐benzimidazol‐2‐yl)methyl]‐1H‐tetrazole (bimt) and adipic acid (H₂adi) at room temperature. In the polymer, each Zn^II ion exhibits an irregular octahedral ZnN₂O₄ coordination geometry and is coordinated by two N atoms from two symmetry‐related bimt ligands and four O atoms from two symmetry‐related dianionic adipate ligands. Zn^II ions are connected by adipate ligands into a one‐dimensional chain which runs parallel to the c axis. The bimt ligands coordinate to the Zn^II ions in a monodentate mode on both sides of the main chain. In the crystal, the one‐dimensional chains are further connected through N—H…O hydrogen bonds, leading to a three‐dimensional supramolecular architecture. In addition, the title polymer exhibits fluorescence, with emissions at 334 and 350 nm in the solid state at room temperature.     

A tetrazol‐5‐yl analogue of glycine, 5‐ammoniomethyl‐1H‐tetrazolide,and its copper(II) complex

A nonclassical tetrazole isostere of glycine, viz. zwitterionic 5‐ammoniomethyl‐1H‐tetrazolide, C₂H₅N₅, (I), crystallizes in the chiral P3₁ space group, similar to γ‐glycine. The crystal packing of (I) is determined by a set of classical hydrogen bonds, forming a three‐dimensional network that is practically the same as that in γ‐glycine. The Cu^II complex of (I), poly[[bis(μ₂‐5‐aminomethyl‐1H‐tetrazolido‐κ³N¹,N⁵:N⁴)copper(II)] dihydrate], {[Cu(C₂H₄N₅)₂]·2H₂O}_n, (II), is a layered coordination polymer formed as a result of tetrazole ring bridges. The Cu^II cations lie on inversion centres, are surrounded by four anions and adopt elongated octahedral coordination. Water molecules are located in the interlayer space and connect the layers into a three‐dimensional network via a system of hydrogen bonds.