A New Route to Metal Azides

Constructing Highly Reliable and Adaptive Primary Explosive Composites for Micro-Initiator Assisting by a Hybrid Template of Metal-Organic Frameworks and Cross-Linked Polymers

Primary explosive, as a reliable initiator for secondary explosives, is the central component of micro-initiators for modern aerospace systems and military operations. However, they are typically prepared as powders, posing potential safety risks because of the inevitable particles scattering issues in the actual working environments. Here, the fabrication of a highly adaptive bulk material of copper azide (CA)-based safe primary explosive for micro-initiators is demonstrated. This bulk material, as derived by a complete azidation reaction of the carbonized metal-organic framework/cross-linked polymer hybrid template, enables the firm embedding of active CA species in a cross-linked carbon network (denoted as CA-C). Interestingly, this CA-C bulk material demonstrates multifarious mechanical stabilities (e.g., good shock and vibration resistance, and anti-overload capacity) in the simulated working conditions. Meanwhile, the CA contents in the CA-C bulk material reached as high as 70.3%, ensuring its detonation power. As a proof of concept, CA-C bulk material assembling in a micro-detonator can efficiently detonate the secondary explosive of CL-20 under laser irradiation. This work hereby advances the fabrication of safe and powerful primary explosives for the fulfillment of safe micro-initiator in a broad range of applications in aerospace systems.

Rare Earth Starting Materials and Methodologies for Synthetic Chemistry

The number of rare earth (RE) starting materials used in synthesis is staggering, ranging from simple binary metal-halide salts to borohydrides and "designer reagents" such as alkyl and organoaluminate complexes. This review collates the most important starting materials used in RE synthetic chemistry, including essential information on their preparations and uses in modern synthetic methodologies. The review is divided by starting material category and supporting ligands (i.e., metals as synthetic precursors, halides, borohydrides, nitrogen donors, oxygen donors, triflates, and organometallic reagents), and in each section relevant synthetic methodologies and applications are discussed.

Recent developments in the chemistry of metal oxopolyazides

The recent acomplished syntheses of novel metal oxopolyazides VO(N3)3, NbO(N3)3, NbO(N3)3·2CH3CN, MoO(N3)3, MoO(N3)3·2CH3CN, WO(N3)4, WO(N3)4·CH3CN, MoO2(N3)2, MoO2(N3)2·2CH3CN, WO2(N3)2, WO2(N3)2·2CH3CN and UO2(N3)2·CH3CN by the author is reviewed. The conversion of the compounds into 2,2'-bipyridine donor adducts and oxaazido metallates is discribed. The properties and X-ray crystal structures of the metal oxopolyazides are compared and discussed.

Nanoscale Homogeneous Energetic Copper Azides@Porous Carbon Hybrid with Reduced Sensitivity and High Ignition Ability

Research on green primary explosives with lead-free and excellent ignition performance is of significance for practical applications. In this work, we have developed a novel, green, and facile strategy for synthesizing copper azide@porous carbon hybrids (CA@PC) based on ionic cross-linked hydrogel with low-cost cellulose derivatives as the starting material, in which the CA nanoparticles are uniformly distributed in the porous carbon skeletons. The detailed characterizations and control experiments demonstrated that such an outstanding performance originates from the excellent electric conductivity of nanoscale carbon cages. With the favorable unique structures, the as-prepared hybrids can greatly benefit a new type of energetic materials, which exhibit a very low electrostatic sensitivity of 1.06 mJ. Interestingly, the hybrids possess a high ignition ability, and the flame sensitivity can even achieve 47 cm, superior to those well-developed CA-based materials reported previously. This work paves the way toward the design and development of next-generation highly efficient energetic materials.

Labile Low-Valent Tin Azides: Syntheses, Structural Characterization, and Thermal Properties

The first two examples of the class of tetracoordinate low-valent, mixed-ligand tin azido complexes, Sn(N₃)₂(L)₂, are shown to form upon reaction of SnCl₂ with NaN₃ and SnF₂ with Me₃SiN₃ in either pyridine or 4-picoline (2, L = py; 3, L = pic). These adducts of Sn(N₃)₂ are shock- and friction-insensitive and stable at r.t. under an atmosphere of pyridine or picoline, respectively. A new, fast, and efficient method for the preparation of Sn(N₃)₂ (1) directly from SnF₂, and by the stepwise de-coordination of py from 2 at r.t., is reported that yields 1 in microcrystalline form, permitting powder X-ray diffraction studies. Reaction of 1 with a nonbulky cationic H-bond donor forms the salt-like compound {C(NH₂)₃}Sn(N₃)₃ (4) which is comparably stable despite its high nitrogen content (55%) and the absence of bulky weakly coordinating cations that are conventionally deemed essential in related systems of homoleptic azido metallates. The spectroscopic and crystallographic characterization of the polyazides 1-4 provides insight into azide-based H-bonded networks and unravels the previously unknown structure of 1 as an important lighter binary azide homologue of Pb(N₃)₂. The atomic coordinates for 1 and 2-4 were derived from powder and single crystal XRD data, respectively; those for 1 are consistent with predictions made by DFT-D calculations under periodic boundary conditions.

NH3 and (NH2)1− as ligands in yttrium metallocene chemistry

First crystallographically-characterized yttrium metallocene with an (NH₂)¹⁻ ligand.

An unusual nitride network of aluminum-centered octahedra and phosphorus-centered tetrahedra and structure determination from microcrystalline samples

Aluminum coordinated by six nitrogen atoms was realized in a new highly condensed network which was obtained via HP–HT synthesis at 5 GPa.

Introducing a Hydrogen-Bond Donor into a Weakly Nucleophilic Brønsted Base: Alkali Metal Hexamethyldisilazides (MHMDS, M=Li, Na, K, Rb and Cs) with Ammonia

Alkali metal 1,1,1,3,3,3-hexamethyldisilazide (MHMDSs) are one of the most utilised weakly nucleophilic Brønsted bases in synthetic chemistry and especially in natural product synthesis. Like lithium organics, they aggregate depending on the employed donor solvents. Thus, they show different reactivity and selectivity as a function of their aggregation and solvation state. To date, monomeric LiHMDS with monodentate donor bases was only characterised in solution. Since the first preparation of LiHMDS in 1959 by Wannagat and Niederprüm, all efforts to crystallise monomeric LiHMDS in the absence of chelating ligands failed. Herein, we present ammonia adducts of LiHMDS, NaHMDS, KHMDS, RbHMDS and CsHMDS with unprecedented aggregation motifs: 1) The hitherto missing monomeric key compound in the LiHMDS aggregation architectures. Monomeric crystal structures of trisolvated LiHMDS (1) and NaHMDS (2), showing unique intermolecular hydrogen bonds, 2) the unprecedented tetrasolvated KHMDS (3) and RbHMDS (4) dimers and 3) the disolvated CsHMDS (5) dimer with very close intermolecular Si-CH3 ⋅⋅⋅Cs s-block "agostic" interactions have been prepared and characterised by single-crystal X-ray structure analysis.

Metal-Organic Framework Templated Synthesis of Copper Azide as the Primary Explosive with Low Electrostatic Sensitivity and Excellent Initiation Ability

A powerful yet safe primary explosive, embedded in a conductive carbon scaffold, is prepared by using a metal-organic framework as precursor. It simultaneously possesses low electrostatic sensitivity, good flame sensitivity, and excellent initiation ability. This method is simple, scalable, and provides a new platform for the development of energetic materials especially those employed in miniaturized explosive systems.

Taming Tin(IV) Polyazides

The first charge-neutral Lewis base adducts of tin(IV) tetraazide, [Sn(N3)4(bpy)], [Sn(N3)4(phen)] and [Sn(N3)4(py)2], and the salt bis{bis(triphenylphosphine)iminium} hexa(azido)stannate [(PPN)2Sn(N3)6] (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline; py = pyridine; PPN = N(PPh3)2) have been prepared using covalent or ionic azide-transfer reagents and ligand-exchange reactions. The azides were isolated on the 0.3 to 1 g scale and characterized by IR and NMR spectroscopies, microanalytical and thermal methods and their molecular structures determined by single-crystal XRD. All complexes have a distorted octahedral Sn[N]6 coordination geometry and possess greater thermal stability than their Si and Ge homologues. The nitrogen content of the adducts of up to 44% exceed any Sn(IV) compound known hitherto.

Synthesis, structure, and properties of SrC(NH)3 , a nitrogen-based carbonate analogue with the trinacria motif

Strontium guanidinate, SrC(NH)3 , the first compound with a doubly deprotonated guanidine unit, was synthesized from strontium and guanidine in liquid ammonia and characterized by X-ray and neutron diffraction, IR spectroscopy, and density-functional theory including harmonic phonon calculations. The compound crystallizes in the hexagonal space group P63 /m, constitutes the nitrogen analogue of strontium carbonate, SrCO3 , and its structure follows a layered motif between Sr(2+) ions and complex anions of the type C(NH)3 (2-) ; the anions adopt the peculiar trinacria shape. A comparison of theoretical phonons with experimental IR bands as well as quantum-chemical bonding analyses yield a first insight into bonding and packing of the formerly unknown anion in the crystal.

Homoleptic low-valent polyazides of group 14 elements

First examples of coordinatively unsaturated, homoleptic azido complexes of low-valent group 14 elements are reported. A simple strategy uses low-valent precursors, ionic azide transfer reagents and bulky cations to obtain salt-like compounds containing E(N3)3(-) of Ge(II)/Sn(II) which are fully characterised, including XRD. Remarkably, these compounds are kinetically stable at r.t. and isolable in sub-gram quantities.