The Uranium(VI) Oxoazides [UO2 (N3 )2 ⋅CH3 CN], [(bipy)2 (UO2 )2 (N3 )4 ], [(bipy)UO2 (N3 )3 ]- , [UO2 (N3 )4 ]2- , and [(UO2 )2 (N3 )8 ]4

Temperature induced single-crystal to single-crystal transformation of uranium azide complexes

The monomeric and dimeric uranium azide complexes {[(CH3)2NCH2CH2NPiPr2]2U(N3)2} (2) and {[(CH3)2NCH2CH2NPiPr2]2U(N3)2}2 (3) were synthesized by treating complex 1 with NaN3 at 60 and -20 °C, respectively. A temperature-induced single-crystal to single-crystal transformation of 3 to 2 was observed. The reduction of either 2 or 3 with KC8 yields a uranium nitride complex {[(CH3)2NCH2CH2NPiPr2]4U2(μ-N)2} (4).

Np(V) azide complexes with electroneutral N-donor ligands

Two new Np(V) azide complexes with electroneutral N-donor ligands of terpyridine derivatives have been synthesized and structurally characterized: [(NpO2)(Cl-Terpy)(N3)(H2O)] (1) and a centrosymmetric dimer [(NpO2)(EtO-Terpy)(N3)]2·2CH3OH (2). The coordination polyhedra of Np atoms in compounds are pentagonal bipyramids with “yl” oxygen atoms in apical positions. The equatorial plane of the bipyramid in complex 1 is formed by: a nitrogen atom from an anion, three nitrogen atoms from an electroneutral Cl-Terpy ligand and an oxygen atom of a water molecule. The equatorial plane of bipyramids in dimer 2 is formed by five nitrogen atoms: two atoms from two anions [N3]− and three atoms from EtO-Terpy. In compound 1, the anion [N3]− acts as a monodentate ligand, and in compound 2, the anion [N3]− is a bidentate-bridging ligand.

The First Alkaline-Earth Azidoaurate(III), Ba[Au(N3 )4 ]2 ⋅ 4 H2 O

Transparent, dark orange Ba[Au(N₃ )₄ ]₂  ⋅ 4 H₂ O was synthesized by reaction of Ba(N₃ )₂ and AuCl₃ or HAuCl₄ in aqueous solution. The novel barium tetraazidoaurate(III) tetrahydrate crystallizes in the monoclinic space group Cc (no. 9) with a=1813.68(17) pm, b=1737.95(11) pm, c=682.04(8) pm and β=108.849(4)°. The predominant structural features of Ba[Au(N₃ )₄ ]₂  ⋅ 4 H₂ O are two crystallographically independent discrete anions [Au(N₃ )₄ ]^- with gold in a tetragonal planar coordination by nitrogen. Vibrational spectra show good agreement with those of other azidoaurates(III). Upon drying, this salt was shown to be a highly explosive material.

Dinitrogen cleavage and hydrogenation to ammonia with a uranium complex

The Haber-Bosch process produces ammonia (NH₃) from dinitrogen (N₂) and dihydrogen (H₂), but requires high temperature and pressure. Before iron-based catalysts were exploited in the current industrial Haber-Bosch process, uranium-based materials served as effective catalysts for production of NH₃ from N₂. Although some molecular uranium complexes are known to be capable of combining with N₂, further hydrogenation with H₂ forming NH₃ has not been reported to date. Here, we describe the first example of N₂ cleavage and hydrogenation with H₂ to NH₃ with a molecular uranium complex. The N₂ cleavage product contains three uranium centers that are bridged by three imido μ ₂-NH ligands and one nitrido μ ₃-N ligand. Labeling experiments with ¹⁵N demonstrate that the nitrido ligand in the product originates from N₂. Reaction of the N₂-cleaved complex with H₂ or H⁺ forms NH₃ under mild conditions. A synthetic cycle has been established by the reaction of the N₂-cleaved complex with trimethylsilyl chloride. The isolation of this trinuclear imido-nitrido product implies that a multi-metallic uranium assembly plays an important role in the activation of N₂.

The Cluster Polyazide Complexes: Synthesis, Crystal Structures, and 14N NMR Studies of [{Re3(μ-X)3}(N3)9]3- (X = Br or I)

Azide cluster complexes [{Re₃(μ-Br)₃}(N₃)₉]^3- and [{Re₃(μ-I)₃}(N₃)₉]^3- were obtained by reaction of Re₃X₉ (X = Br or I, respectively) with sodium azide in methanol. The complexes were crystallized as cesium salts of the compositions Cs₃[{Re₃(μ-Br)₃}(N₃)₉]·H₂O (1) and Cs₃[{Re₃(μ-I)₃}(N₃)₉]·H₂O (2) and characterized by X-ray single-crystal diffraction and elemental analyses, mass spectrometry, ¹⁴N NMR spectroscopy, and DFT calculations. In the anions, each rhenium atom is coordinated by three azide ligands. To the best of our knowledge, these compounds represent the first case of metal cluster polyazide complexes (i.e., where each metal atom bears more than one azide ligand). Both complexes are stable in air but are very shock sensitive, and spontaneous explosive decomposition is also possible.

Facile N-functionalization and strong magnetic communication in a diuranium(v) bis-nitride complex

Uranium nitride complexes are of high interest because of their ability to effect dinitrogen reduction and functionalization and to promote magnetic communication, but studies of their properties and reactivity remain rare. Here we have prepared in 73% yield the diuranium(v) bis-nitride complex [K2{[U(OSi(O t Bu)3)3]2(μ-N)2}], 4, from the thermal decomposition of the nitride-, azide-bridged diuranium(iv) complex [K2{[U(OSi(O t Bu)3)3]2(μ-N)(μ-N3)}], 3. The bis-nitride 4 reacts in ambient conditions with 1 equiv. of CS2 and 1 equiv. of CO2 resulting in N-C bond formation to afford the diuranium(v) complexes [K2{[U(OSi(O t Bu)3)3]2(μ-N)(μ-S)(μ-NCS)}], 5 and [K2{[U(OSi(O t Bu)3)3]2(μ-N)(μ-O)(μ-NCO)}], 6, respectively. Both nitrides in 4 react with CO resulting in oxidative addition of CO to one nitride and CO cleavage by the second nitride to afford the diuranium(iv) complex [K2{[U(OSi(O t Bu)3)3]2(μ-CN)(μ-O)(μ-NCO)}], 7. Complex 4 also effects the remarkable oxidative cleavage of H2 in mild conditions to afford the bis-imido bridged diuranium(iv) complex [K2{[U(OSi(O t Bu)3)3]2(μ-NH)2}], 8 that can be further protonated to afford ammonia in 73% yield. Complex 8 provides a good model for hydrogen cleavage by metal nitrides in the Haber-Bosch process. The measured magnetic data show an unusually strong antiferromagnetic coupling between uranium(v) ions in the complexes 4 and 6 with Neel temperatures of 77 K and 60 K respectively, demonstrating that nitrides are attractives linkers for promoting magnetic communication in uranium complexes.

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.

Monomeric thorium chalcogenolates with bipyridine and terpyridine ligands

Thorium chalcogenolates Th(ER)4 react with 2,2'-bipyridine (bipy) to form complexes with the stoichiometry (bipy)2Th(ER)4 (E = S, Se; R = Ph, C6F5). All four compounds have been isolated and characterized by spectroscopic methods and low-temperature single crystal X-ray diffraction. Two of the products, (bipy)2Th(SC6F5)4 and (bipy)2Th(SeC6F5)4, crystallize with lattice solvent, (bipy)2Th(SPh)4 crystallizes with no lattice solvent, and the selenolate (bipy)2Th(SePh)4 crystallizes in two phases, with and without lattice solvent. In all four compounds the available volume for coordination bounded by the two bipy ligands is large enough to allow significant conformational flexibility of thiolate or selenolate ligands. 77Se NMR confirms that the structures of the selenolate products are the same in pyridine solution and in the solid state. Attempts to prepare analogous derivatives with 2,2',6',2''-terpyridine (terpy) were successful only in the isolation of (terpy)(py)Th(SPh)4, the first terpy compound of thorium. These materials are thermochromic, with color attributed to ligand-to-ligand charge transfer excitations.

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.