Hydride Chemistry Research Articles

Ultrafast Yttrium Hydride Chemistry at High Pressures via Non-equilibrium States Induced by an X-ray Free Electron Laser.

Controlling the formation and stoichiometric content of the desired phases of materials has become of central interest for a variety of fields. The possibility of accessing metastable states by initiating reactions by X-ray-triggered mechanisms over ultrashort time scales has been enabled by the development of X-ray free electron lasers (XFELs). Utilizing the exceptionally high-brilliance X-ray pulses from the EuXFEL, we report the synthesis of a previously unobserved yttrium hydride under high pressure, along with nonstoichiometric changes in hydrogen content as probed at a repetition rate of 4.5 MHz using time-resolved X-ray diffraction. Exploiting non-equilibrium pathways, we synthesize and characterize a hydride in a Weaire-Phelan structure type at pressures as low as 125 GPa, predicted using a crystal structure search, with a hydrogen content of 4.0-5.75 hydrogens per cation, that is enthalpically metastable on the convex hull.

Low-Coordinate Iron Hydride Chemistry at an N,N,C-Heteroscorpionate Platform.

Locally high-spin iron hydrides are proposed to play a critical role as intermediates in iron-molybdenum cofactor (FeMoco)-catalyzed N2 fixation. Inspired by these biological systems, we report herein our initial investigations into low-coordinate iron hydride chemistry supported by our N,N,C-heteroscorpionate ligands. Those ligands with smaller steric profiles are unable to completely suppress the formation of a binuclear [Fe(μ2-H)]2 complex; however, the incorporation of more substantial steric bulk allows for the isolation of a rare example of a terminal, high-spin (S = 2) Fe2+ hydride. Fourier transform infrared spectroscopy suggests an unusually weak Fe-H bond in the latter molecule. Mössbauer spectroscopies, coupled with density functional theory calculations, highlights the substantial influence of the terminal hydride ligand on 57Fe isomer shift.

Global Minimum Search and Bonding Analysis of Tl2 Hx and Tl3 Hy (x=0-6; y=0-5) Series.

A remarkable distinction between boron and carbon hydrides lies in their extremely different bonding patterns and chemical reactivity, resulting in diverse areas of application. Particularly, carbon, characterized by classical two-center - two-electron bonds, gives rise to organic chemistry. In contrast, boron forms numerous exotic and non-intuitive compounds collectively called non-classical structures. It is reasonable to anticipate that other elements of Group 13 exhibit their own unusual bonding patterns; however, our knowledge of the hydride chemistry for other elements in Group 13 is much more limited, especially for the heaviest stable element, thallium. In this work, we performed a conformational analysis of Tl2 Hx and Tl3 Hy (x=0-6, y=0-5) series via Coalescence Kick global minimum search algorithm, DFT, and ab initio quantum chemistry methods; we investigated the bonding pattern using the AdNDP algorithm, thermodynamic stability, and stability toward electron detachment. All found global minimum structures are classified as non-classical structures featuring at least one multi-center bond.

ReH3 (PPh3 )4 ] - A Key Compound in the Rhenium Hydride Chemistry.

The chemistry of the rhenium trihydrido complex [ReH3 (PPh3 )4 ] (1) has been reinvestigated. An improved synthesis and the solid-state structure of the compound as well as several reactions are reported. The solid-state structure of 1 is similar to that of [TcH3 (PPh3 )4 ] having a capped-octahedral coordination sphere. The PPh3 ligands surround the Re atom in a trigonal-pyramidal mode with a short apical Re-P bond (2.300(2) Å) and three longer basal bonds (2.429(2)-2.449(2) Å). Reactions of 1 with monodentate phosphines such as PMe3 or PBu3 give the mono-substituted complexes [ReH3 (PPh3 )3 (PMe3 )] (2) and [ReH3 (PPh3 )3 (PBu3 )] (3) under retention of the apical PPh3 ligand and substitution of one of the basal PPh3 ligands. The stability of the phosphine trihydride complexes decreases in the order PPh3 >PMe3 >PBu3 . Treatment of [ReH3 (PPh3 )4 ] with trityl hexafluorophosphate in CH3 CN does not result in a hydride abstraction, but gives the tetrahydrido cation [ReH4 (NCCH3 )(PPh3 )3 ]+ (4), while reactions with nitriles give unstable azavinylidene complexes of the composition [ReH2 (PPh3 )3 (NC(H)R)] (5). They are formed by an insertion of the nitrile into a Re-H bond. The solid-state structure of the methyl derivative [ReH2 (PPh3 )3 (NC(H)CH3 )] (5 a) was determined showing a linear Re-N-C unit with rhenium-nitrogen and nitrogen-carbon double bonds, while the N=CH-C bond is clearly bent with an angle of 124°. Two previously unknown polymorphs of [ReH5 (PPh3 )3 ] were isolated from reactions of 1 with HOC6 H3 (CH3 )2 and thiourea after prolonged heating in toluene and characterized by IR spectroscopy and X-ray diffraction.

Hydrogen induced structural phase transformation in ScNiSn-based intermetallic hydride characterized by experimental and computational studies

Understanding an interrelation between the structure, chemical composition and hydrogenation properties of intermetallic hydrides is crucial for the improvement of their hydrogen storage performance. Ability to form the hydrides and to tune the thermodynamics and kinetics of their interaction with hydrogen is related to their chemical composition. Some features of the metal–hydrogen interactions remain however poorly studied, including chemistry of Sc-containing hydrides. ZrNiAl-type ScNiSn-based intermetallic hydride has been probed in the present work using a broad range of experimental techniques including Synchrotron and Neutron Powder Diffraction, 119Sn Möessbauer Spectroscopy, hydrogenation at pressures reaching several kbar H2 and hydrogen Thermal Desorption Spectroscopy studies. Computational DFT calculations have been furthermore performed. This allowed to establish the mechanism of the phase-structural transformation and electronic structure changes causing a unique contraction of the metal lattice of intermetallic alloy and the formation of the ...H-Ni-H-Ni… chains in the structure with H atoms carrying a partial negative charge. Such hydrogen absorption accompanied by a formation of a covalent Ni-H bonding and causing an unusual behavior contracts to the conventionally observed bonding mechanism of hydrogen in metals as based on the metallic bonding frequently accompanied by a jumping diffusion movement of the inserted H atoms – in contrast to the directional Metal-Hydrogen bonding observed in the present work. At high applied pressures ScNiSnH0.83 orthorhombic TiNiSi type hydride is formed with H atoms filling Sc3Ni tetrahedra. Finally, this study shows that scandium closely resembles the behavior of the heavy rare earth metal holmium.

Orthogonal Access to α‐/β‐Branched/Linear Aliphatic Amines by Catalyst‐Tuned Regiodivergent Hydroalkylations

AbstractLinear, α‐branched, and β‐branched aliphatic amines are widespread in pharmaceuticals, agrochemicals, and fine chemicals. Thus, the development of direct and efficient methods to these structures in a tunable manner is highly desirable yet challenging. Herein, a catalyst‐controlled synthesis of α‐branched, β‐branched and linear aliphatic amines from Ni/Co‐catalyzed regio‐ and site‐selective hydroalkylations of alkenyl amines with alkyl halides is developed. This catalytic protocol features the reliable prediction and control of the coupling position of alkylation to provide orthogonal access to α‐branched, β‐branched and linear alkyl amines from identical starting materials. This platform unlocks orthogonal reactivity and selectivity of nickel hydride and cobalt hydride chemistry to catalytically repurpose three types of alkyl amines under mild conditions.

Theory-directed discovery of high-temperature superconductivity in clathrate hydrides at high pressure

Theory-directed discovery of high-temperature superconductivity in clathrate hydrides at high pressure

Tuning chemical precompression: Theoretical design and crystal chemistry of novel hydrides in the quest for warm and light superconductivity at ambient pressures

Over the past decade, a combination of crystal structure prediction techniques and experimental synthetic work has thoroughly explored the phase diagrams of binary hydrides under pressure. The fruitfulness of this dual approach is demonstrated in the recent identification of several superconducting hydrides with Tcs approaching room temperature. We start with an overview of the computational procedures for predicting stable structures and estimating their propensity for superconductivity. A survey of phases with high Tc reveals some common structural features that appear conducive to the strong coupling of the electronic structure with atomic vibrations that leads to superconductivity. We discuss the stability and superconducting properties of phases containing two of these—molecular H2 units mixed with atomic H and hydrogenic clathrate-like cages—as well as more unique motifs. Finally, we argue that ternary hydride phases, whose exploration is still in its infancy, are a promising route to achieve simultaneous superconductivity at high temperatures and stability at low pressures. Several ternary hydrides arise from the addition of a third element to a known binary hydride structure through site mixing or onto a new site, and several more are based on altogether new structural motifs.

Accessing the main-group metal formyl scaffold through CO-activation in beryllium hydride complexes

Carbon monoxide (CO) is an indispensable C1 building block. For decades this abundant gas has been employed in hydroformylation and Pausen-Khand catalysis, amongst many related chemistries, where a single, non-coupled CO fragment is delivered to an organic molecule. Despite this, organometallic species which react with CO to yield C1 products remain rare, and are elusive for main group metal complexes. Here, we describe a range of amido-beryllium hydride complexes, and demonstrate their reactivity towards CO, in its mono-insertion into the Be-H bonds of these species. The small radius of the Be2+ ion in conjunction with the non-innocent pendant phosphine moiety of the developed ligands leads to a unique beryllium formyl complex with an ylidic P-COC fragment, whereby the carbon centre, remarkably, datively binds Be. This, alongside reactivity toward carbon dioxide, sheds light on the insertion chemistry of the Be-H bond, complimenting the long-known chemistry of the heavier Alkaline Earth hydrides.

Thermodynamics of the elementary steps of organic hydride chemistry determined in acetonitrile and their applications

This review focuses on the thermodynamics of the elementary step of 421 organic hydrides and unsaturated compounds releasing or accepting hydride or hydrogen determined in acetonitrile as well as their potential applications.

Fred Hawthorne, inorganic chemist, dies

M. Frederick Hawthorne, who established the field of boron chemistry almost single-handedly and won countless awards for his research, including the Priestley Medal in 2009 and the National Medal of Science in 2011, died July 8. He was 92. “He became the master of boron hydride chemistry—that will forever be linked with the name of Hawthorne,” says J. Fraser Stoddart , a chemist at Northwestern University and corecipient of the 2016 Nobel Prize in Chemistry. Hawthorne was born in Fort Scott, Kansas, in 1928. He got his bachelor’s degree in chemistry at Pomona College in 1949 and his PhD in 1953 at the University of California, Los Angeles. Hawthorne began investigating boron chemistry shortly after finishing his doctorate, as a researcher at Rohm & Haas’s Redstone Arsenal research division in Huntsville, Alabama. In 1969, after a few academic hops, Hawthorne returned to UCLA as a full professor. By then, he

Bottlenecks to interstellar sulfur chemistry

Hydride molecules lie at the base of interstellar chemistry, but the synthesis of sulfuretted hydrides is poorly understood and their abundances often crudely constrained. Motivated by new observations of the Orion Bar photodissociation region (PDR) – 1″ resolution ALMA images of SH+; IRAM 30 m detections of bright H232S, H234S, and H233S lines; H3S+ (upper limits); and SOFIA/GREAT observations of SH (upper limits) – we perform a systematic study of the chemistry of sulfur-bearing hydrides. We self-consistently determine their column densities using coupled excitation, radiative transfer as well as chemical formation and destruction models. We revise some of the key gas-phase reactions that lead to their chemical synthesis. This includes ab initio quantum calculations of the vibrational-state-dependent reactions SH+ + H2(v) ⇄ H2S+ + H and S + H2 (v) ⇄ SH + H. We find that reactions of UV-pumped H2(v ≥ 2) molecules with S+ ions explain the presence of SH+ in a high thermal-pressure gas component, Pth∕k ≈ 108 cm−3 K, close to the H2 dissociation front (at AV < 2 mag). These PDR layers are characterized by no or very little depletion of elemental sulfur from the gas. However, subsequent hydrogen abstraction reactions of SH+, H2S+, and S atoms with vibrationally excited H2, fail to form enough H2S+, H3S+, and SH to ultimately explain the observed H2S column density (~2.5 × 1014 cm−2, with an ortho-to-para ratio of 2.9 ± 0.3; consistent with the high-temperature statistical value). To overcome these bottlenecks, we build PDR models that include a simple network of grain surface reactions leading to the formation of solid H2S (s-H2S). The higher adsorption binding energies of S and SH suggested by recent studies imply that S atoms adsorb on grains (and form s-H2S) at warmer dust temperatures (Td < 50 K) and closer to the UV-illuminated edges of molecular clouds. We show that everywhere s-H2S mantles form(ed), gas-phase H2S emission lines will be detectable. Photodesorption and, to a lesser extent, chemical desorption, produce roughly the same H2S column density (a few 1014 cm−2) and abundance peak (a few 10−8) nearly independently of nH and G0. This agrees with the observed H2S column density in the Orion Bar as well as at the edges of dark clouds without invoking substantial depletion of elemental sulfur abundances.

Proton Transfer Mechanisms in Bimetallic Hydrogenases.

Hydrogenases are metalloenzymes that catalyze proton reduction and H2 oxidation with outstanding efficiency. They are model systems for bioinorganic chemistry, including low-valent transition metals, hydride chemistry, and proton-coupled electron transfer. In this Account, we describe how photochemistry and infrared difference spectroscopy can be used to identify the dynamic hydrogen-bonding changes that facilitate proton transfer in [NiFe]- and [FeFe]-hydrogenase.[NiFe]-hydrogenase binds a heterobimetallic nickel/iron site embedded in the protein by four cysteine ligands. [FeFe]-hydrogenase carries a homobimetallic iron/iron site attached to the protein by only a single cysteine. Carbon monoxide and cyanide ligands in the active site facilitate detailed investigations of hydrogenase catalysis by infrared spectroscopy because of their strong signals and redox-dependent frequency shifts. We found that specific redox-state transitions in [NiFe]- and [FeFe]-hydrogenase can be triggered by visible light to record extremely sensitive "light-minus-dark" infrared difference spectra monitoring key amino acid residues. As these transitions are coupled to protonation changes, our data allowed investigation of dynamic hydrogen-bonding changes that go well beyond the resolution of protein crystallography.In [NiFe]-hydrogenase, photolysis of the bridging hydride ligand in the Ni-C state was followed by infrared difference spectroscopy. Our data clearly indicate the formation of a protonated cysteine residue as well as hydrogen-bonding changes involving a glutamic acid residue and a "dangling water" molecule. These findings are in excellent agreement with crystallographic analyses of [NiFe]-hydrogenase. In [FeFe]-hydrogenase, an external redox dye was used to accumulate the Hred state. Infrared difference spectra indicate hydrogen-bonding changes involving two glutamic acid residues and a conserved arginine residue. While crystallographic analyses of [FeFe]-hydrogenase in the oxidized state failed to explain the rapid proton transfer because of a breach in the succession of residues, our findings facilitated a precise molecular model of discontinued proton transfer.Comparing both systems, our data emphasize the role of the outer coordination sphere in bimetallic hydrogenases: we suggest that protonation of a nickel-ligating cysteine in [NiFe]-hydrogenase causes the notable preference toward H2 oxidation. On the contrary, proton transfer in [FeFe]-hydrogenase involves an adjacent cysteine as a relay group, promoting both H2 oxidation and proton reduction. These observations may guide the design of organometallic compounds that mimic the catalytic properties of hydrogenases.

Deuterium fractionation of nitrogen hydrides: detections of NHD and ND2

ABSTRACT Although ammonia is an abundant molecule commonly observed towards the dense interstellar medium, it has not yet been established whether its main formation route is from gas-phase ion–molecule reactions or grain-surface hydrogen additions on adsorbed nitrogen atoms. Deuterium fractionation can be used as a tool to constrain formation mechanisms. High abundances of deuterated molecules are routinely observed in the dense interstellar medium, with the ratio between deuterated molecules and the main isotopologue enhanced by several orders of magnitude with respect to the elemental D/H ratio. In the case of ammonia, the detection of its triply deuterated isotopologue hints at high abundances of the deuterated intermediate nitrogen radicals, ND, NHD, and ND2. So far however, only ND has been detected in the interstellar medium. In this paper, to constrain the formation of ammonia, we aim at determining the NHD/NH2 and ND2/NHD abundance ratios, and compare them with the predictions of both pure gas-phase and grain-surface chemical models. We searched for the fundamental rotational transitions of NHD and ND2 towards the class 0 protostar IRAS16293−2422, towards which NH, NH2 and ND had been previously detected. Both NHD and ND2 are detected in absorption towards the source. The relative abundance ratios NH2:NHD:ND2 are close to 8:4:1. These ratios can be reproduced by our gas-phase chemical model within a factor of 2–3. Statistical ratios as expected from grain-surface chemistry are also consistent with our data. Further investigations of the ortho-to-para ratio in ND2 , both theoretical and observational, could bring new constraints to better understand nitrogen hydride chemistry.

A Search for Light Hydrides in the Envelopes of Evolved Stars

Abstract We report a search for the diatomic hydrides SiH, PH, and FeH along the line of sight toward the chemically rich circumstellar envelopes of IRC+10216 and VY Canis Majoris. These molecules are thought to form in high-temperature regions near the photospheres of those stars, and may then further react via gas-phase and dust-grain interactions leading to more complex species, but have yet to be constrained by observation. We used the German Receiver for Astronomy at Terahertz Frequencies spectrometer on the Stratospheric Observatory for Infrared Astronomy to search for rotational emission lines of these molecules in four spectral windows ranging from 600 to 1500 GHz. Although none of the targeted species was detected in our search, we report their upper limit abundances in each source and discuss how they influence the current understanding of hydride chemistry in dense circumstellar media. We attribute the nondetections of these hydrides to their compact source sizes, high barriers of formation, and proclivity to react with other molecules in the winds.

Spectroscopic investigations under whole-cell conditions provide new insight into the metal hydride chemistry of [FeFe]-hydrogenase.

Hydrogenases are among the fastest H2 evolving catalysts known to date and have been extensively studied under in vitro conditions. Here, we report the first mechanistic investigation of an [FeFe]-hydrogenase under whole-cell conditions. Functional [FeFe]-hydrogenase from the green alga Chlamydomonas reinhardtii is generated in genetically modified Escherichia coli cells by addition of a synthetic cofactor to the growth medium. The assembly and reactivity of the resulting semi-synthetic enzyme was monitored using whole-cell electron paramagnetic resonance and Fourier-transform Infrared difference spectroscopy as well as scattering scanning near-field optical microscopy. Through a combination of gas treatments, pH titrations, and isotope editing we were able to corroborate the formation of a number of proposed catalytic intermediates in living cells, supporting their physiological relevance. Moreover, a previously incompletely characterized catalytic intermediate is reported herein, attributed to the formation of a protonated metal hydride species.

Flexible Coordination of N,P-Donor Ligands in Aluminum Dimethyl and Dihydride Complexes.

Aluminum hydrides, once a simple class of stoichiometric reductants, are now emerging as powerful catalysts for organic transformations such as the hydroboration or hydrogenation of unsaturated bonds. The coordination chemistry of aluminum hydrides supported by P donors is relatively underexplored. Here, we report aluminum dihydride and dimethyl complexes supported by amidophosphine ligands and study their coordination behavior in solution and in the solid state. All complexes exist as κ2-N,P complexes in the solid state. However, we find that for amidophosphine ligands bearing bulky aminophosphine donors, aluminum dihydride and dimethyl complexes undergo a “ligand-slip” rearrangement in solution to generate κ2-N,N complexes. Thus, importantly for catalytic activity, we find that the coordination behavior of the P donor can be modulated by controlling its steric bulk. We show that the reported aluminum hydrides catalyze the hydroboration of alkynes by HBPin and that the variable coordination mode exhibited by the amidophosphine ligand modulates the catalytic activity.

Chemistry of 11-Vertex Polyhedral Boron Hydrides (Review)

The current state of chemistry of 11-vertex polyhedral boron hydrides is considered. Their synthesis and interconversions, the substitution reactions of their terminal hydrogen atoms, and the insertion reactions with the closure of the icosahedral cage are discussed.

Identifying the Role of Dynamic Surface Hydroxides in the Dehydrogenation of Ti-Doped NaAlH4.

Solid-state metal hydrides are prime candidates to replace compressed hydrogen for fuel cell vehicles due to their high volumetric capacities. Sodium aluminum hydride has long been studied as an archetype for higher-capacity metal hydrides, with improved reversibility demonstrated through the addition of titanium catalysts; however, atomistic mechanisms for surface processes, including hydrogen desorption, are still uncertain. Here, operando and ex situ measurements from a suite of diagnostic tools probing multiple length scales are combined with ab initio simulations to provide a detailed and unbiased view of the evolution of the surface chemistry during hydrogen release. In contrast to some previously proposed mechanisms, the titanium dopant does not directly facilitate desorption at the surface. Instead, oxidized surface species, even on well-protected NaAlH4 samples, evolve during dehydrogenation to form surface hydroxides with differing levels of hydrogen saturation. Additionally, the presence of these oxidized species leads to considerably lower computed barriers for H2 formation compared to pristine hydride surfaces, suggesting that oxygen may actively participate in hydrogen release, rather than merely inhibiting diffusion as is commonly presumed. These results demonstrate how close experiment-theory feedback can elucidate mechanistic understanding of complex metal hydride chemistry and potentially impactful roles of unavoidable surface impurities.

Fabrication and characterization of a coplanar nickel-metal hydride microbattery equipped with a gel electrolyte

The growing utilization of portable and autonomous micro devices results in a need for novel integrated power supplies with low power densities and energy contents. We report on a rechargeable thin-film microbattery which is manufactured using typical microfabrication methods. In detail, the microbattery is based on the nickel-metal hydride chemistry and fabricated with a coplanar design on a glass wafer. Ionic conductivity is enabled with a gel electrolyte that is sealed with a polymer to prevent dessication. We compare the electrode characteristics in the gel electrolyte and in a corresponding liquid electrolyte. Charge-discharge measurements at different currents are performed to evaluate the performance of the microbattery. The capacity is found to be 2.8 μAh cm−2 μm−1 at a current density of 1 mA cm−2. We also investigate the microbattery degradation over the number of charge-discharge cycles using electrochemical impedance spectroscopy. The results reveal that the capacity after 100 cycles decreases to around half of the initial value which is mainly attributed to the gel electrolyte degradation.