Rhenium Nitride Research Articles

Exploring chemical bonding nature, weak exciton effect, electronic, optical and thermoelectric properties of NaReN2 via DFT computations

We performed first principles calculations on the recently synthesized NaReN2. This compound is the main product of the reaction between Re and NaN3 in forming the super hard material ReN2. Theoretical calculations of sodium rhenium nitride, such as band structure and density of states (DOS) were performed. The partial density of states (PDOS) was also included to determine the contribution of individual atoms to the electronic states. The theoretical data reveal that the material possesses a rather narrow bandgap of 0.26 eV. Semi-conducting materials with such low bandgap values have interesting applications in various fields. The optical properties were also studied indicating possible application of NaReN2 in opto-electronic devices. Excitonic study reveals the weak excitonic behavior of this material. Thus, first principles calculations on this material provide necessary theoretical information on physicochemical properties of NaReN2.

Microstructure, chemical composition and mechanical properties of rhenium nitride hard coating deposited by reactive magnetron sputtering

Rhenium nitride coatings were deposited by reactive magnetron sputtering technique on H13 steel and polished silicon substrates. To vary the nitrogen content in the ReNx coatings, flow rates of 2, 6, and 8 sccm were used in the nitrogen line gas, while argon flow was kept constant (40 sccm). Different substrate temperatures of 100 °C, 175 °C, and 250 °C were also evaluated. A stack of four Ti/TiN bilayers with a total thickness of 200 nm was deposited, in order to improve the adhesion of the rhenium nitride top layer. X- ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and X- ray diffraction (XRD) analysis of the coatings confirmed the formation of ReNx compounds with a face-centered cubic (FCC) structure for all samples produced, together with the formation of rhenium oxides and metallic rhenium. The nanohardness of the coating, measured by atomic force microscopy (AFM), reached values up to 24 GPa. The coating design and hardness value obtained have not been previously reported for ReN synthesized by physical vapor deposition (PVD) and represent an important contribution to the current state of knowledge and a relevant database for future research projects on ReN.

Photoelectrochemical Conversion of Dinitrogen to Benzonitrile: Selectivity Control by Electrophile- versus Proton-Coupled Electron Transfer.

Nitride complexes are key species in homogeneous nitrogen fixation to NH3 via stepwise proton‐coupled electron transfer (PCET). In contrast, direct generation of nitrogenous organic products from N2‐derived nitrides requires new strategies to enable efficient reductive nitride transfer in the presence of organic electrophiles. We here present a 2‐step protocol for the conversion of dinitrogen to benzonitrile. Photoelectrochemical, reductive N2 splitting produces a rhenium(V) nitride with unfavorable PCET thermochemistry towards ammonia generation. However, N‐benzoylation stabilizes subsequent reduction as a basis for selective nitrogen transfer in the presence of the organic electrophile and Brønsted acid at mild reduction potentials. This work offers a new strategy for photoelectrosynthetic nitrogen fixation beyond ammonia—to yield nitrogenous organic products.

Photoelectrochemical Conversion of Dinitrogen to Benzonitrile: Selectivity Control by Electrophile‐ versus Proton‐Coupled Electron Transfer

AbstractNitride complexes are key species in homogeneous nitrogen fixation to NH3via stepwise proton‐coupled electron transfer (PCET). In contrast, direct generation of nitrogenous organic products from N2‐derived nitrides requires new strategies to enable efficient reductive nitride transfer in the presence of organic electrophiles. We here present a 2‐step protocol for the conversion of dinitrogen to benzonitrile. Photoelectrochemical, reductive N2splitting produces a rhenium(V) nitride with unfavorable PCET thermochemistry towards ammonia generation. However,N‐benzoylation stabilizes subsequent reduction as a basis for selective nitrogen transfer in the presence of the organic electrophile and Brønsted acid at mild reduction potentials. This work offers a new strategy for photoelectrosynthetic nitrogen fixation beyond ammonia—to yield nitrogenous organic products.

Materials synthesis at terapascal static pressures

Theoretical modelling predicts very unusual structures and properties of materials at extreme pressure and temperature conditions1,2. Hitherto, their synthesis and investigation above 200 gigapascals have been hindered both by the technical complexity of ultrahigh-pressure experiments and by the absence of relevant in situ methods of materials analysis. Here we report on a methodology developed to enable experiments at static compression in the terapascal regime with laser heating. We apply this method to realize pressures of about 600 and 900 gigapascals in a laser-heated double-stage diamond anvil cell3, producing a rhenium–nitrogen alloy and achieving the synthesis of rhenium nitride Re7N3—which, as our theoretical analysis shows, is only stable under extreme compression. Full chemical and structural characterization of the materials, realized using synchrotron single-crystal X-ray diffraction on microcrystals in situ, demonstrates the capabilities of the methodology to extend high-pressure crystallography to the terapascal regime.

Thermodynamic and electronic properties of ReN2 polymorphs at high pressure

High pressure synthesis of rhenium nitride pernitride ReN$_2$ with crystal structure unusual for transition metal dinitrides and high values of hardness and bulk modulus attracted significant attention to this system. We investigate the thermodynamic and electronic properties of the P2$_1$/c phase of ReN$_2$ and compare them with two other polytypes, C2/m and P4/mbm phases suggested in the literature. Our calculations of the formation enthalpy at zero temperature show that the former phase is the most stable of the three up to pressure p=170 GPa, followed by the stabilization of the P4/mbm phase at higher pressure. The theoretical prediction is confirmed by diamond anvil cell synthesis of the P4/mbm ReN$_2$ at $\approx$175 GPa. Considering the effects of finite temperature in the quasi-harmonic approximation at p=100 GPa we demonstrate that the P2$_1$/c phase has the lowest free energy of formation at least up to 1000 K. Our analysis of the pressure dependence of the electronic structure of the rhenium nitride pernitride shows a presence of two electronic topological transitions around 18 GPa, when the Fermi surface changes its topology due to an appearance of a new electron pocket at the high-symmetry Y$_2$ point of the Brillouin zone while the disruption of a neck takes place slightly off from the $\Gamma$-A line.

Growth and characterization of Rhenium Nitride coatings produced by reactive magnetron sputtering

In this work, thin rhenium nitride (ReNx) films were deposited by reactive radio frequency (R. F.) magnetron sputtering on H13 steel and polished silicon substrates. To improve adhesion to the substrates, a Ti/TiN bilayer was deposited before the ReNx films. Substrate temperature, R.F. power, Ar and N2 gas flow, negative bias voltage, and working pressure were varied in the experiments when synthesizing the ReNx coatings. It was found that lower process pressure and nitrogen flow rate negatively affect the stabilization of coatings and lead to their delamination after they are extracted from the vacuum chamber. Meanwhile, higher nitrogen flow rate and work pressure increase the stability of the coatings by up to several days. Additionally, when the nitrogen flow rate and the negative bias voltage were increased, changes in the crystalline structure of the coatings were observed. However, when the work pressure and N2/Ar ratio were increased and the bias voltage was decreased, the stability of ReNx coatings continued even several weeks after their deposition. X-ray Photoelectron Spectroscopy (XPS) and X-Ray Diffraction (XRD) measurements validated the formation of ReN compound. The more stable deposited rhenium nitride coatings exhibited lower hardness values than the theoretical predictions for this compound, possibly due to the presence of metallic rhenium and thereby rhenium oxides, as seen in the XRD and XPS characterizations.

Electronic and Spin-State Effects on Dinitrogen Splitting to Nitrides in a Rhenium Pincer System.

Bimetallic nitrogen (N2) splitting to form metal nitrides is an attractive method for N2 fixation. Although a growing number of pincer-supported systems can bind and split N2, the precise relationship between the ligand properties and N2 binding/splitting remains elusive. Here we report the first example of an N2-bridged rhenium(III) complex, [(trans-P2tBuPyrr)ReCl2]2(μ-η1:η1-N2) (P2tBuPyrr = [2,5-(CH2PtBu2)2C4H2N]-). In this case, N2 binding occurs at a higher oxidation level than that in other reported pincer analogues. Analysis of the electronic structure through computational studies shows that the weakly π-donor pincer ligand stabilizes an open-shell electronic configuration that leads to enhanced binding of N2 in the bridged complex. Utilizing SQUID magnetometry, we demonstrate a singlet ground state for this Re-N-N-Re complex, and we offer tentative explanations for antiferromagnetic coupling of the two local S = 1 sites. Reduction and subsequent heating of the rhenium(III)-dinitrogen complex leads to chloride loss and cleavage of the N-N bond with isolation of the terminal rhenium(V) nitride complex (P2tBuPyrr)ReNCl.

Thermal atomic layer deposition of rhenium nitride and rhenium metal thin films using methyltrioxorhenium.

The growth of rhenium nitride and rhenium metal thin films is presented using atomic layer deposition (ALD) with the precursors methyltrioxorhenium and 1,1-dimethylhydrazine. Saturative, self-limiting growth was determined at 340 °C for pulse times of ≥4.0 s for methyltrioxorhenium and ≥0.1 s for 1,1-dimethylhydrazine. An ALD window was observed from 340 to 350 °C with a growth rate of about 0.60 Å per cycle. Films grown at 340 °C revealed a root mean square surface roughness of 2.7 nm for a 70 nm thick film and possessed a composition of ReN0.14 with low O and C content of 1.6 and 2.6 at%, respectively. Enhanced nucleation on in situ grown TiN, relative to thermal SiO2, enabled a conformality of 98% on high aspect ratio trenched structures. Subjecting the ReN0.14 thin films to thermal or chemical and thermal treatments reduced the nitrogen content to ≤1.6 at%, yielding a film purity of about 96 at% rhenium and resistivities as low as 51 μΩ cm. The Re metal film thicknesses on the trenched structures remained intact during the post-deposition annealing treatments and the films did not delaminate from the substrate surfaces.

Volatile Rhenium(I) Compounds with Re-N Bonds and Their Conversion into Oriented Rhenium Nitride Films by Magnetic Field-Assisted Vapor Phase Deposition.

New heteroleptic rhenium(I) compounds, [fac-Re(I)(CO)3(L)] (e.g., L= tfb-dmpda, (N,N-(4,4,4-trifluorobut-1-en-3-on)-dimethyl propylene diamine)), containing anionic and neutral ligands act as efficient precursors to grow polycrystalline rhenium nitride (ReN) films by their vapor phase deposition at 600 °C. Deposition of ReN films under an external magnetic field showed an orientation effect with preferred growth of crystallites along ⟨100⟩ direction. Rhenium complexes reported here unify high stability and reactivity in a single molecule through a Janus-type coordination around a Re center, constituted by a chelating tridentate ligand and three carbonyl groups imparting a facial geometry. Single-crystal diffraction analysis confirmed the structural integrity of the new rhenium compounds. The rigidity of molecular framework was validated in solution via 1D and 2D NMR spectroscopy, in the gas phase via mass spectrometry, and in the solid-state by thermogravimetric analysis and differential scanning calorimetry studies. The analytical data showed that pre-existent Re-N bonds in [fac-Re(I)(CO)3(L)] facilitated low-temperature formation of crystalline ReN deposits confirmed by grazing angle X-ray diffraction analysis. The surface chemical composition and the uniformity of microstructure were provided by X-ray photoelectron spectroscopy (XPS) and scanning and transmission electron microscopy (SEM/TEM), respectively.

High-pressure synthesis of ultraincompressible hard rhenium nitride pernitride Re2(N2)(N)2 stable at ambient conditions

High-pressure synthesis in diamond anvil cells can yield unique compounds with advanced properties, but often they are either unrecoverable at ambient conditions or produced in quantity insufficient for properties characterization. Here we report the synthesis of metallic, ultraincompressible (K0 = 428(10) GPa), and very hard (nanoindentation hardness 36.7(8) GPa) rhenium nitride pernitride Re2(N2)(N)2. Unlike known transition metals pernitrides Re2(N2)(N)2 contains both pernitride N24− and discrete N3− anions, which explains its exceptional properties. Re2(N2)(N)2 can be obtained via a reaction between rhenium and nitrogen in a diamond anvil cell at pressures from 40 to 90 GPa and is recoverable at ambient conditions. We develop a route to scale up its synthesis through a reaction between rhenium and ammonium azide, NH4N3, in a large-volume press at 33 GPa. Although metallic bonding is typically seen incompatible with intrinsic hardness, Re2(N2)(N)2 turned to be at a threshold for superhard materials.

Rhenium Metal and Rhenium Nitride Thin Films Grown by Atomic Layer Deposition

AbstractRhenium is both a refractory metal and a noble metal that has attractive properties for various applications. Still, synthesis and applications of rhenium thin films have been limited. We introduce herein the growth of both rhenium metal and rhenium nitride thin films by the technologically important atomic layer deposition (ALD) method over a wide deposition temperature range using fast, simple, and robust surface reactions between rhenium pentachloride and ammonia. Films are grown and characterized for compositions, surface morphologies and roughnesses, crystallinities, and resistivities. Conductive rhenium subnitride films of tunable composition are obtained at deposition temperatures between 275 and 375 °C, whereas pure rhenium metal films grow at 400 °C and above. Even a just 3 nm thick rhenium film is continuous and has a low resistivity of about 90 μΩ cm showing potential for applications for which also other noble metals and refractory metals have been considered.

Rhenium Metal and Rhenium Nitride Thin Films Grown by Atomic Layer Deposition.

Rhenium is both a refractory metal and a noble metal that has attractive properties for various applications. Still, synthesis and applications of rhenium thin films have been limited. We introduce herein the growth of both rhenium metal and rhenium nitride thin films by the technologically important atomic layer deposition (ALD) method over a wide deposition temperature range using fast, simple, and robust surface reactions between rhenium pentachloride and ammonia. Films are grown and characterized for compositions, surface morphologies and roughnesses, crystallinities, and resistivities. Conductive rhenium subnitride films of tunable composition are obtained at deposition temperatures between 275 and 375 °C, whereas pure rhenium metal films grow at 400 °C and above. Even a just 3 nm thick rhenium film is continuous and has a low resistivity of about 90 μΩ cm showing potential for applications for which also other noble metals and refractory metals have been considered.

Novel rhenium(V) nitride complexes with dithiocarbimate ligands – A synchrotron X-ray and DFT structural investigation

Abstract The application of rhenium complexes as therapeutic agents in nuclear medicine has propelled research into the chemistry of these compounds. In our effort to develop and investigate new therapeutic radiopharmaceuticals based on the complexes of rhenium we have investigated the nitride core, [ReN]2+. This work looks at the behavior of sulfonamide based dithiocarbimates towards the rhenium(V) nitride core. The aim here was to prepare anionic complexes with aromatic as well as fluorescent aromatic groups in the sulfonamide substituent located on the dithiocarbimate backbone. We envisaged that the polar sulfonamide and dianionic charge would confer solubility in water. Here we report the reactions of the dithiocarbimate ligands towards the rhenium(V) precursors: [ReNCl2(PPh3)2] and [ReNCl2(PMe2Ph)3]. These reactions proceeded with bis-substitution by the dithiocarbimate ligand, resulting in the formation of a dianionic rhenium(V) complex, of the type [ReN(S-S)2]2−, where (S-S) denotes the sulfonamide-tagged dithiocarbimato unit. Spectroscopic characterization data, as well as the synchrotron X-ray diffraction structure of the metal complex with the phenyl sulfonamide backbone shed light into the structural features of this interesting class of ligands and opens up opportunities for further studies in molecular imaging and therapeutic arenas.

Thermal Dehydrogenation of Methane by [ReN]+

The thermal reaction of the diatomic rhenium nitride cation [ReN]+ with methane has been explored using FT-ICR mass spectrometry complemented by high-level quantum chemical calculations. Mechanistic aspects of the reaction have been addressed to uncover scenarios for the competitive generation of a methylene and a hydrogen cyanide ligand attached to the rhenium center. The role the nitrogen atom plays in the reactive [ReN]+ /CH4 couple is elucidated, and the cause of the rather different reactivities of [ReN]+ and its lighter congener [MnN]+ is revealed.

High-pressure and high-temperature synthesis of rhenium carbide using rhenium and nanoscale amorphous two-dimensional carbon nitride

Both Re2C and Re2N are ultra incompressible and have a bulk modulus of about 400 GPa. These materials are synthesized under high pressure and high temperature. The synthesis pressures are about 10 GPa or below for Re2C and 20–30 GPa for Re2N. If the synthesis pressure of Re2N was about 10 GPa or below, a large volume high-pressure cell like a multi-anvil apparatus can be used to synthesize Re2N. To realize this, a proper solid nitrogen source is needed instead of liquid or gas nitrogen. We used a precursor of a mixture of rhenium and home-made nanoscale amorphous two-dimensional carbon nitride as a solid nitrogen source. Consequently, the synthesis reaction produced Re2C but not Re2N. We characterized the synthesized Re2C by various techniques including high-pressure x-ray diffraction (XRD). The bulk modulus B0 of the synthesized Re2C under hydrostatic conditions was estimated to be 385.7 ± 18.0 GPa. This value is a little smaller than the previous data. When the pressure medium became non-hydrostatic, the peculiar compression behaviour occurred; the rate of broadening of XRD lines increased and the compression became negligible in the range of a few GPa. The reason for this peculiar behaviour is not known.

Dinitrogen splitting and functionalization in the coordination sphere of rhenium.

[ReCl3(PPh3)2(NCMe)] reacts with pincer ligand HN(CH2CH2PtBu2)2 (HPNP) to five coordinate rhenium(III) complex [ReCl2(PNP)]. This compound cleaves N2 upon reduction to give rhenium(V) nitride [Re(N)Cl(PNP)], as the first example in the coordination sphere of Re. Functionalization of the nitride ligand derived from N2 is demonstrated by selective C-N bond formation with MeOTf.

The Denitridation of Nitrides of Iron, Cobalt and Rhenium Under Hydrogen

The denitridation behaviour of binary iron, cobalt and rehnium nitrides under H2 /Ar has been investigated. The iron nitride was found to lose over 70 % of its as prepared nitrogen content at 400 °C. The cobalt nitride was completely denitrided at 250 °C. Rhenium nitride lost close to 90 % of its nitrogen at 350 °C. In addition, Co-Re4 prepared by ammonolyis was investigated, whilst only traces of NH3 were lost from this material under H2/Ar at 400 °C, with H2/N2 it proved to be an active ambient pressure ammonia synthesis catalyst in accordance with previous literature.

Does the real ReN2have the MoS2structure?

Rhenium nitride (ReN(2)) with the hexagonal MoS(2) structure was recently synthesized by metathesis reaction under high pressure. Here the calculated elastic and thermodynamic stabilities and chemical bonding show that the MoS(2) phase is unstable based on first-principles calculations. Meanwhile, the MoS(2)-type ReN(2) compound may be stabilized by nitrogen-vacancies from X-ray diffraction and supercell calculations. Structure searches identify a monoclinic C2/m phase for ReN(2), which is energetically more stable than previous predictions and MoS(2) structure over a wide range of pressures. Above 130 GPa, a tetragonal P4/mbm phase becomes favorable from enthalpy calculations. Both phases have superior mechanical properties, and their syntheses would have important applications fundamentally and technologically.

Experimental evidence for the structural models of Re2N and Re2C from micro-Raman spectroscopy

The vibrational properties of the high-pressure, high-temperature phases of hexagonal Re${}_{2}$N rhenium nitride and Re${}_{2}$C rhenium carbide are reported from micro-Raman spectroscopy at ambient and high pressure and from theoretical calculations based on density functional theory. These data confirm the structural model of Re${}_{2}$N proposed recently. The ambiguity of the location of the carbon position in Re${}_{2}$C is resolved. We show that the structures of Re${}_{2}$N and Re${}_{2}$C are isotypic, with the N and C atoms occupying the same trigonal prismatic voids in the hexagonal stacking of Re atoms. The effect of pressure on vibrational properties is investigated, and mode Gr\"uneisen parameters of the Raman-active modes are found to be between 1.1 and 1.6 for both Re${}_{2}$N and Re${}_{2}$C.