The structure and reactivity of iron nitride complexes

The structure and reactivity of discrete iron nitride complexes is described. Six-coordinate, four-fold symmetric nitrides are thermally unstable, and have been characterized at cryogenic temperatures by an arsenal of spectroscopic methods. By contrast, four-coordinate, three-fold symmetric iron nitrides can be prepared at room temperature. A range of diamagnetic iron(IV) nitrides have been reported and in some cases, isolated. Among these are the isolable, yet reactive, tris(carbene)borate iron(IV) nitrides. These complexes can effect two-electron nitrogen atom transfer to a range of substrates, in some cases with complete atom transfer occuring through Fe-N bond cleavage. These nitrides are also active in single electron pathways, including the synthesis of ammonia by a mechanism involving hydrogen atom transfer to the nitride ligand. One-electron oxidation of a tris(carbene)borate iron(IV) nitride leads to an isolable iron(V) complex that is unusually reactive for a metal nitride.     

Analysis of uranium azide and nitride complexes by atmospheric pressure chemical ionization mass spectrometry

Atmospheric pressure chemical ionization mass spectrometry (APCI-MS) has been used to characterize the air-sensitive paramagnetic organouranium azide and nitride complexes [(C5Me5)2UN3(mu-N3)]3 and [(C5Me5)U(mu-I)2]3N, respectively. The trimetallic complex [(C5Me5)U(mu-I)2]3E had been identified by X-ray crystallography, but the data did not definitively identify E as N3- versus O2- or (OH)-, a common problem in heavy-element nitride complexes involving metals with variable oxidation states. A comparison of the 250 degrees C APCI-MS spectra of products made from NaN3 and Na15NNN showed mixed [M]+ and [M + H]+ envelopes at expected ion intensities for the 14N and 15N isotopomers. A compilation of U-C(C5Me5) and U-I bond distance data for U3+ and U4+ is also reported that shows that the ranges for the two oxidation states have significant overlap.     

The synthesis of transition metal nitrides via thermolysis of metal-ammine complexes, Part I: Chromium nitride

The thermal decomposition of a CrN precursor, hexaammine chromium(II) chloride, in ammonia has been investigated via a combination of thermogravimetric analysis, differential thermal analysis, Fourier transform infrared spectroscopy, and X-ray diffraction. Upon heating, [Cr(NH₃)₆]Cl₂ sequentially loses ammonia ligands, ultimately forming CrCl₂·NH₃ at ∼400 °C. When heat-treated to 500 °C in ammonia, this compound ammonolyzes to form nanocrystalline CrN.     

Terminal, anionic carbide, nitride, and phosphide transition-metal complexes as synthetic entries to low-coordinate phosphorus derivatives

Anionic terminal one-atom nitride, phosphide, and carbide complexes are excellent starting materials for the synthesis of ligands containing low-coordinate phosphorus centers in the protecting coordination sphere of the metal complex. Salt-elimination reactions with chlorophosphanes lead to phosphaisocyanide, iminophosphinimide, and diorganophosphanylphosphinidene complexes in which the unusual phosphorus ligands are stabilized by coordination. X-ray structure analyses and density-functional calculations illuminate the bonding in these compounds.     

Computational chemistry of the silicon nitride surface. 2. Binary hydroxylamine complexes. Geometry and bond energies

In order to study the silicon nitride surface it is interesting to consider hydrogen-bonded complexes with hydroxyl and amine key groups (OH...O, OH...N, NH...O, and NH...N). To investigate the behavior of the above bonds, we considered the water, ammonia, and hydroxylamine dimers and the binary hydroxylamine complexes with water and ammonia. The results of this work are compared with the data obtained by an ab initio method. Russian University of Peoples' Frienfship. Translated fromZhurnal Strukturnoi Khimii Vol. 37, No. 1, pp. 29–47, January–February, 1996. Translated by I. Izvekova     

Aluminum nitride nanotubes

An AlN nanotube (AlNNT) was theoretically predicted in 2003. In comparison with the carbon nanotubes, the AlNNTs are wide-band-gap nanostructures with high reactivity, high thermal stability and sharp electronic sensitivity toward some chemicals. The B3LYP predicts an HOMO–LUMO gap of 3.74–4.27 eV for zigzag AlNNTs, while the experimental bad gap of bulk AlN is about 6.28 eV. The lowest strain energy of AlNNTs relative to its AlN nanosheet compared to the nanosheets of carbon and BN nanotubes with an equivalent diameter suggests the feasibility of AlNNT synthesis from its nanosheet. Theoretical methods predict a Young’s Modulus of about 453 GPa for AlNNTs that is smaller than that of carbon (1 TPa), BN (870 GPa) and GaN (796 GPa) nanotubes. In 2003, the faceted single-crystalline hexagonal AlNNTs were synthesized and extensively explored by means of density functional theory calculations. Several works have suggested different potential applications for AlNNTs including chemical sensors, hydrogen storage, gas adsorbent, and electron field emitter. This review is a comprehensive study on the latest achievements in the structural analyses, synthesis, and property evaluations based on the computational methods on the AlNNTs in the light of the development of nanotubes.     

Mixed amido/imido/guanidinato complexes of niobium: potential precursors for MOCVD of niobium nitride thin films

Novel mixed amido/imido/guanidinato complexes of niobium are reported. The complexes were synthesized by insertion of two equivalents of di-isopropylcarbodiimide (i-Pr-cdi) or bis-cyclohexylcarbodiimide (Cy-cdi) respectively, into the niobium-amido bonds of [Nb(NR(2))(3)(N-t-Bu)] (, R = Me; , R = Et) starting out from [NbCl(3)(N-t-Bu)(py)(2)] and the respective LiNR(2) reagent (py = pyridine). Four representative examples of these mixed ligand amido/imido/guanidinato compounds were synthesized and were characterized by (1)H-NMR, (13)C-NMR, (15)N-NMR, CHN-analysis, mass spectrometry and infra-red spectroscopy. The molecular structures of [Nb(NR(2)){eta(2)-(i-Pr-N)(2)C(NR(2))}(2)(N-t-Bu)] (, R = Me; , R = Et) in the solid state were determined by single-crystal X-ray diffraction studies and are discussed together with the molecular structure of the starting compound [Nb(NMe(2))(3)(N-t-Bu)] (). The thermal properties of the new compounds depend on the substitution at the guanidinato ligand. Complexes of i-Pr-cdi are significantly more volatile than complexes of Cy-cdi as revealed by thermogravimetric analysis. Preliminary experiments using as a single-molecule source for metal-organic chemical vapour deposition (MOCVD) in the absence of ammonia indicate the formation of the stoichiometric, and surprisingly carbon-free, cubic niobium nitride phase.     

Mixed hydrazido amido/imido complexes of tantalum, hafnium and zirconium: potential precursors for metal nitride MOCVD

The coordination chemistry of the hydrazine derivatives dimethylhydrazine (Hdmh) and N-trimethylsilyl-N'N'-dimethylhydrazine (Htdmh) at Ta, Zr and Hf was investigated aiming at volatile mixed ligand all-nitrogen coordinated compounds. The hydrazido ligands were introduced either by salt metathesis employing the Li salts of the hydrazines and the tetrachlorides MCl(4) (M = Zr, Hf) or by amine substitution using M(NR(2))(4) (R = Me, Et) and [(t-BuN)Ta(NR(2))(3)]. The new complexes were fully characterised including (1)H/(13)C NMR, mass spectrometry and a study of their thermal behaviour. The crystal structures of [ZrCl(tdmh)(3)] and the all-nitrogen coordinated complex [Ta(N-t-Bu)(NMe(2))(2)(tdmh)] are discussed as well as the structure of the by-product [Li(tdmh)(py)](2). Preliminary MOCVD experiments of the liquid compound [Ta(NEt(2))(2)(N-t-Bu)(tdmh)] were performed and the deposited TaN(Si) films were analysed by RBS and SEM.     

Magnetic iron nitride nanodendrites

We report the synthesis of Fe₃N nanodendrites directly by reduction-nitriding of α-Fe₂O₃ nanopine dendrites in a mixed stream of H₂-NH₃. Fe₃N basically retains dendritic morphology of the starting material α-Fe₂O_3. It is found that nanorod branches of Fe₃N dendrites have relatively uniform diameters and are evenly distributed at both sides of the stem with a periodicity of about 50 nm. The diameters of the nanorods are about 50 nm, and their lengths range from 50 to 1000 nm. Fe₃N nanodendrites show a rapid saturation of magnetization of 104 emu/g at 300 K, as expected for a magnet.     

Polyhedral boron nitride molecules

The geometrical and electronic structures of two isomers (1 and2) of the polyhedral boron nitride molecule, B₁₂N₁₂, have been calculated using the MNDO method. Structure1 having the form of a truncated octahedron is more energetically preferable (ΔH _f ⁰=−128 kcal mol⁻¹) than isomer2, which hasC _6v symmetry. The equilibrium geometries of the N₆B₆(CH₂)₆ isomers (3 and4), which simulate fragments of structure2, have been calculated. The stabilization mechanism of the N₆ nitrogen cluster (hexaazabenzene) in polyhedral structures is discussed. The parameters calculated for molecules1 and2 have been correlated with the corresponding characteristics of their carbon analogs. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1712–1714, October, 1993.     

Photoluminescent carbon nitride films grown by vapor transport of carbon nitride powders

The thermal vapor transport of nitrogen-rich carbon nitride powders produces carbon nitride films on substrates that retain significant nitrogen content, have conjugated bond character, and show blue photoluminescent emission near 450 nm.     

Zirconium nitride as a highly efficient nitrogen source to synthesize the metal nitride clusterfullerenes

Metal nitride clusterfullerenes(NCFs)have significant applications in molecular electronics,biomedical imaging,and nonlinear optical devices due to their unique structures.However,their wide applications are limited by the production quantity.In this work,the yields of metal nitride clusterfullerenes M3N@C80(M=Y,Sc,Gd)were greatly enhanced by utilizing zirconium nitride(Zr N)as an efficient nitrogen source for the arc-discharge method.Compared with the traditional synthetic route using N2gas as nitrogen source,the Zr N inside graphite tube can be vaporized simultaneously with metal and graphite,and then afford the high concentration of nitrogen atoms in the arc region,which will promote the formation of metal nitride clusterfullerenes finally.The Zr N can promote the yields of Y3N@C80,Sc3N@C80and Gd3N@C80,revealing the universal applicability of Zr N as a highly efficient nitrogen source.Specifically,the yield of Sc3N@C80was greatly improved when adding Zr N,and it shows over double yield compared to traditional synthetic route using N2gas.In addition,Zr N can also enhance the yields of paramagnetic azametallofullerene M2@C79N due to the high concentration of nitrogen atoms in the arc region.This new method enhances the production quantity of metal nitride clusterfullerenes and azametallofullerenes,and it will greatly promote the research and application of these molecular carbon materials.     

Technetium-99m nitride radiopharmaceuticals

Following the introduction of an efficient method for the preparation of technetium-99m complexes containing a terminal Tc-N multiple bond, under conditions suitable for nuclear medicine applications, new radiopharmaceuticals for heart and brain imaging have been discovered. These compounds belong to the class of bi-substituted, square-pyramidal nitride TcV complexes with dithiocarbamate ligands, and are the first examples of radiopharmaceuticals of this type exhibiting interesting biological properties. The peculiar chemical characteristics of the Tc-N core can also be conveniently utilized for the design of radiopharmaceuticals incorporating bioactive peptides and having definite structural features.     

Infrared studies of silicon nitride

The FTS measurements of silicon nitride Si₃N₄ in the range 100–1400 cm⁻¹ have been made. There have been several varieties of IR spectra which can be ascribed to alpha silicon nitride. Tentative explanation of this effect suggesting a complex structure of alpha phase is proposed.     

Pathways to metastable nitride structures

The structure types of spinel and willemite-II are related by a Bain correspondence. γ-Si₃N₄ can, therefore, transform into wII-Si₃N₄ by a diffusionless mechanism. We calculate the activation barrier for this process from the spinel into the energetically more favorable wII modification of Si₃N₄ and Ge₃N₄ to and , respectively. We predict that the spinel modification is a suitable precursor for the synthesis of the wII modification, which otherwise is metastable throughout the enthalpy-pressure phase diagram of Si₃N₄ and Ge₃N₄ and thus not accessible via standard pressure techniques using equilibrium thermodynamics. To allow a phase identification we provide the calculated Raman-spectra of both wII-Si₃N₄ and wII-Ge₃N₄ and compare them with those of the spinel modifications.