Binary Bismuth(III) Azides: Bi(N3)3 , [Bi(N3)4]−, and [Bi(N3)6]3−

Dihalo bismuth cations: unusual coordination properties and inverse solvent effects in Lewis acidity

A series of well-defined cationic hepta-coordinate bismuth halides [BiX₂(py)₅][B(3,5-(CF₃)₂-C₆H₃)₄] (X = Cl, Br, I), stabilized only by substitutionally labile solvent molecules, were synthesized and fully characterized. Their apparent D_5h symmetry with a lone pair at the central atom is unprecedented for main group compounds. The potential of BiX₃ to show unexpectedly high Lewis acidities in moderately polar solvents is likely due to the formation of [BiX₂(solv)₅]⁺ and related ionic species.

Isolation of unique heterocycles formed from pyridine-thiocarboxamides as diiodine, iodide, or polyiodide salts

The reaction of pyridine-thiocarboxamides with I2 provided a variety of novel heterocyclic products as iodide, triiodide, and/or pentaiodide salts. Bismuth triiodide was incorporated as a crystallization aid to access other structural types.

Synthesis and characterization of phosphorous(III) diisocyanate and triisocyanate

Two phosphorous(iii) isocyanates, ClP(NCO)2 and P(NCO)3 were isolated as neat substances and characterized with IR (gas-phase and Ne-matrix), Raman (solid), and 31P NMR spectroscopy. Their vibrational spectra were analyzed in terms of a single conformer with the aid of quantum chemical computations at the B3LYP/6-311+G(3df) level of theory. In line with the theoretically computed favorable syn-configuration of the NCO ligands with the sterically active lone-pair electrons on the central phosphorous atom (nP), low-temperature single-crystal X-ray diffraction (XRD) of solid ClP(NCO)2 reveals a Cs symmetric syn-configuration for both NCO ligands with weak CO (r = 2.9692(4) Å) van der Waals (vdW) interactions. In the binary isocyante P(NCO)3, all the three NCO ligands adopt similar syn-configuration with nP, leading to a propeller-shaped structure with slightly distorted C3v symmetry due to steric repulsion of the NCO ligands and the PO vdW interactions (r = 3.1901(1) Å) in the solid state.

Identification of octahedral coordinated ZrN12+ cationic clusters by mass spectrometry and structure searches

Cationic zirconium-doped nitrogen clusters were produced by laser ablation of a Zr : BN mixture target and were detected by TOF mass spectrometry. It is found that the mass peak of the ZrN12+ cluster is dominant in the spectrum. The ZrN12+ cluster was further dissociated with 266 nm photons. Extensive structure searches of a cationic ZrN12+ cluster indicate that the ground state structure of ZrN12+ consists of a central Zr atom and six N2 pairs with Oh symmetry. The calculated binding energy of the ZrN12+ cluster is about 0.96 eV, which is in accordance with the result of the photodissociation experiment. The neutral ZrN12 cluster has almost the same geometry, but with D3h symmetry. NBO analysis showed that the molecular orbitals of ZrN12+/0 clusters are mainly composed of Zr 4d and N 2p orbitals. These findings provide rich information for understanding the geometries and the electronic properties of zirconium-doped N clusters, which will offer valuable guidance for the exploration of other metal doped nitrogen clusters.

Properties and Promise of Catenated Nitrogen Systems As High-Energy-Density Materials

The properties of catenated nitrogen molecules, molecules containing internal chains of bonded nitrogen atoms, is of fundamental scientific interest in chemical structure and bonding, as nitrogen is uniquely situated in the periodic table to form kinetically stable compounds often with chemically stable N-N bonds but which are thermodynamically unstable in that the formation of stable multiply bonded N₂ is usually thermodynamically preferable. This unique placement in the periodic table makes catenated nitrogen compounds of interest for development of high-energy-density materials, including explosives for defense and construction purposes, as well as propellants for missile propulsion and for space exploration. This review, designed for a chemical audience, describes foundational subjects, methods, and metrics relevant to the energetic materials community and provides an overview of important classes of catenated nitrogen compounds ranging from theoretical investigation of hypothetical molecules to the practical application of real-world energetic materials. The review is intended to provide detailed chemical insight into the synthesis and decomposition of such materials as well as foundational knowledge of energetic science new to most chemists.

Heavy Neutral and Anionic Pnictogen Thiocyanates

When [PPN]SCN (1; PPN = [Ph₃P-N-PPh₃]) is treated with Me₃Si-SCN in methanol, [PPN][H(NCS)₂] (2), a hydrogen diisothiocyanate salt bearing the [H(NCS)₂]^- anion, was generated, isolated, and fully characterized. Pure heavy E(NCS)₃ [E = Sb (3), Bi (4)] species were obtained from the reaction of EF₃ and an excess of Me₃Si-SCN, while the tetrahydrofuran (THF) solvates E(NCS)₃·THF were isolated when the product was recrystallized from THF. When 2 equiv of 1 was combined with Me₃Si-SCN and SbF₃, [PPN]₂[Sb(NCS)₅] (5) could be isolated. When 1 was added to BiF₃, [PPN]₂[Bi(NCS)₃(SCN)₂·THF] (6·THF), containing three SCN^- ions coordinating via the N atom and two coordinating via the S atom, was isolated after recrystallization from THF. The structures of 1, 2, 3·THF, 4·THF, 5, and 6·THF were determined. 3·THF displayed a typical [3 + 3] coordination mode with a trigonal-pyramidal environment in the first coordination sphere of the Sb³⁺ ion, and the dianion of 5, [Sb(NCS)₅]^2-, featured a classical square-pyramidal molecular geometry around the Sb³⁺ ion with one additional Menshutkin-type interaction to one aryl ring of the [PPN]⁺ cation. 4·THF exhibited a distorted pentagonal-bipyramidal structure within a two-dimensional network, while in 6·THF, an octahedrally surrounded Bi³⁺ ion was observed.

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.

Structural evolution of LiNn+ (n = 2, 4, 6, 8, and 10) clusters: mass spectrometry and theoretical calculations

Mixed nitrogen-lithium cluster cations LiN_n⁺ were generated by laser vaporization and analyzed by time-of-flight mass spectrometry. It is found that LiN₈⁺ has the highest ion abundance among the LiN_n⁺ ions in the mass spectrum. Density functional calculations were conducted to search for the stable structures of the Li–N clusters. The theoretical results show that the most stable isomers of LiN_n⁺ clusters are in the form of Li⁺(N₂)_n/2, and the order of their calculated binding energies is consistent with that of Li–N₂ bond lengths. The most stable structures of LiN_n⁺ evolve from one-dimensional linear type (C_∞v, n = 2; D_∞h, n = 4), to two-dimensional branch type (D_3h, n = 6), then to three-dimensional tetrahedral (T_d, n = 8) and square pyramid (C_4v, n = 10) types. Further natural bond orbital analyses show that electrons are transferred from the lone pair on N_α of every N₂ unit to the empty orbitals of lithium atom in LiN_2–8⁺, while in LiN₁₀⁺, electrons are transferred from the bonding orbital of the Li–N_α bonds to the antibonding orbital of the other Li–N_α bonds. In both cases, the N₂ units become dipoles and strongly interact with Li⁺. The average second-order perturbation stabilization energy for LiN₈⁺ is the highest among the observed LiN_n⁺ clusters. For neutral LiN_2–8 clusters, the most stable isomers were also formed by a Li atom and n/2 number of N₂ units, while that of LiN₁₀ is in the form of Li⁺(N₂)₃(η¹-N₄).

LiN_n⁺ clusters were generated by laser ablation and the LiN₈⁺ with tetrahedral Li⁺(N₂)₄ structure has the highest ion abundance.

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.

The vibrational spectroscopy of the coordinated azide anion; a theoretical study

The vibrational behaviour of the azide anion in a variety of environments has been examined by DFT methods. The frequency is sensitive to polar, dipolar and quadrupolar fields. The frequency is also dependent on the metal to which it is bonded and thus to the details of that bonding. Several azides within one molecule can be strongly vibrationally coupled, a coupling which carries with it a transfer of spectral activity. It is suggested that whilst absolute vibrational frequencies carry little immediately accessible information, a combination of infrared and Raman data for the antisymmetric stretch region might give limited structural insights.

A new linear bismuth coordination polymer based on 1,10-phenanthroline-2,9-dicarboxylic acid: ionothermal synthesis, crystal structure and fluorescence properties

A new linear bismuth(III) coordination polymer, catena-poly[[chloridobismuth(III)]-μ3-1,10-phenanthroline-2,9-dicarboxylato-κ(6)O(2):O(2),N(1),N(10),O(9):O(9)], [Bi(C14H6N2O4)Cl]n, has been obtained by an ionothermal method and characterized by elemental analysis, energy-dispersive X-ray spectroscopy, IR spectroscopy, thermal stability studies and single-crystal X-ray diffraction. The structure is constructed by Bi(C14H6N2O4)Cl fragments in which each Bi(III) centre is seven-coordinated by one Cl atom, four O atoms and two N atoms. The coordination geometry of the Bi(III) cation is distorted pentagonal-bipyramidal (BiO4N2Cl), with one bridging carboxylate O atom and one Cl atom located in the axial positions. The Bi(C14H6N2O4)Cl fragments are further extended into a one-dimensional linear polymeric structure via subsequent but different centres of symmetry (bridging carboxylate O atoms). Neighbouring linear chains are assembled via weak C-H···O and C-H···Cl hydrogen bonds, forming a three-dimensional supramolecular architecture. Intermolecular π-π stacking interactions are observed, with centroid-to-centroid distances of 3.678 (4) Å, which further stabilize the structure. In addition, the solid-state fluorescence properties of the title coordination polymer were investigated.

Experimental observation of TiN12+ cluster and theoretical investigation of its stable and metastable isomers

TiN n+ clusters were generated by laser ablation and analyzed experimentally by mass spectrometry. The results showed that the mass peak of the TiN12+ cluster is dominant in the spectrum. The TiN12+ cluster was further investigated by photodissociation experiments with 266, 532 and 1064 nm photons. Density functional calculations were conducted to investigate stable structures of TiN12+ and the corresponding neutral cluster, TiN12. The theoretical calculations found that the most stable structure of TiN12+ is Ti(N2)6+ with Oh symmetry. The calculated binding energy is in good agreement with that obtained from the photodissociation experiments. The most stable structure of neutral TiN12 is Ti(N2)6 with D3d symmetry. The Ti-N bond strengths are greater than 0.94 eV in both Ti(N2)6+ and its neutral counterpart. The interaction between Ti and N2 weakens the N-N bond significantly. For neutral TiN12, the Ti(N3)4 azide, the N5TiN7 sandwich structure and the N6TiN6 structure are much higher in energy than the Ti(N2)6 complex. The DFT calculations predicted that the decomposition of Ti(N3)4, N5TiN7, and N6TiN6 into a Ti atom and six N2 molecules can release energies of about 139, 857, and 978 kJ mol-1 respectively.

Binary polyazides of cadmium and mercury

Following our interest in binary element-nitrogen compounds we report here on the synthesis and comprehensive characterization (M.p., IR/Raman, elemental analysis, (14)N/(133)Cd/(199)Hg NMR) of tri- and tetraazido cadmate and mercurate anions [E(N3)(2+n)](n-) (E = Cd, Hg; n=1, 2) in a series of [Ph4P](+) and [PNP](+) ([PNP](+) = bis(triphenylphosphine)iminium) salts. The azide/chloride exchange in CH2Cl2 as well as the formation of tetrazolate salts in CH3CN solutions of the polyazido mercurates were investigated. Single crystal X-ray structures of all new compounds, and for comparison [Ph4P][Cd2(N3)5(H2O)], were determined. Moreover, the synthesis of anhydrous cadmium(II) azide and its DMSO adduct is presented for the first time. For a better understanding of structure and bonding in E(N3)2, [E(N3)3](-) and [E(N3)4](2-), theoretical calculations at the M06-2X/aug-cc-pVDZ level were carried out.

Preparation of the first manganese(III) and manganese(IV) azides

Fluoride-azide exchange reactions of Me3SiN3 with MnF2 and MnF3 in acetonitrile resulted in the isolation of Mn(N3)2 and Mn(N3)3 ⋅CH3CN, respectively. While Mn(N3)2 forms [PPh4]2[Mn(N3)4] and (bipy)2Mn(N3)2 upon reaction with PPh4N3 and 2,2'-bipyridine (bipy), respectively, the manganese(III) azide undergoes disproportionation and forms mixtures of [PPh4]2[Mn(N3)4] and [PPh4]2[Mn(N3)6], as well as (bipy)2Mn(N3)2 and (bipy)Mn(N3)4. Neat and highly sensitive Cs2[Mn(N3)6] was obtained through the reaction of Cs2MnF6 with Me3SiN3 in CH3CN.

A novel dinuclear bismuth(III) coordination compound: bis(μ-pyridine-2,6-dicarboxylato)-κ4O2,N,O6:O6′;κ4O2:O2′,N,O6-bis[(azido-κN)(1,10-phenanthroline-κ2N,N')bismuth(III)] tetrahydrate

A novel dinuclear bismuth(III) coordination compound, [Bi2(C7H3NO4)2(N3)2(C12H8N2)2]·4H2O, has been synthesized by an ionothermal method and characterized by elemental analysis, energy-dispersive X-ray spectroscopy, IR, X-ray photoelectron spectroscopy and single-crystal X-ray diffraction. The molecular structure consists of one centrosymmetric dinuclear neutral fragment and four water molecules. Within the dinuclear fragment, each Bi(III) centre is seven-coordinated by three O atoms and four N atoms. The coordination geometry of each Bi(III) atom is distorted pentagonal-bipyramidal (BiO3N4), with one azide N atom and one bridging carboxylate O atom located in axial positions. The carboxylate O atoms and water molecules are assembled via O-H···O hydrogen bonds, resulting in the formation of a three-dimensional supramolecular structure. Two types of π-π stacking interactions are found, with centroid-to-centroid distances of 3.461 (4) and 3.641 (4) Å.