High pressure synthesis of phosphine from the elements and the discovery of the missing (PH3)2H2 tile

I Single-Atom Doped P-Rich CoPn Nanocluster@CoP with Enhanced HER

Constructing I single-atom (ISA) doped CoP electrocatalyst for HER is extremely challenging and has not been reported to date. Herein, an ISA doping-phosphatization strategy is proposed to prepare a novel I single-atom doped P-rich CoPn nanocluster@CoP electrocatalyst (ISA-CoPn/CoP) with enhanced HER performance first. ISA-CoPn/CoP shows a low overpotential of only 44 and 81 mV in 0.5 m H2SO4 solution, to drive a current density of 10 and 100 mA cm-2. ISA and P-rich CoPn nanocluster show unique synergies, which can optimize the H adsorption energy and accelerate the kinetics of HER in the CoP system. The intermediate I─H bond vibration peak is directly observed through in situ Raman testing, demonstrating that ISA doping helps accelerate the HER process. Additionally, the ΔGH of ISA-CoPn/CoP is only 0.05 eV by density functional theory (DFT) calculation, which is conducive to H2 evolution.

Stability, Chemical Bonding, and Electron Lone Pair Localization in AsN at High Pressure by Density Functional Theory Calculations

The covalent bonding framework of crystalline single-bonded cubic AsN, recently synthesized under high pressure and high temperature conditions in a laser-heated diamond anvil cell, is here studied by means of density functional theory calculations and compared to single crystal X-ray diffraction data. The precise localization of the nonbonding electron lone pairs and the determination of their distances and orientations are related to the presence of characteristic structural motifs and space regions of the unit cell dominated by repulsive electronic interactions, with the relative orientation of the electron lone pairs playing a key role in minimizing the energy of the structure. We find that the vibrational modes associated with the expression of the lone pairs are strongly localized, an observation that may have implications for the thermal conductivity of the compound. The results indicate the thermodynamic stability of the experimentally observed structure of AsN above ∼17 GPa, provide a detailed insight into the nature of the chemical bonding network underlying the formation of this compound, and open new perspectives to the design and high pressure synthesis of new pnictogen-based advanced materials for potential applications of energetic and technological relevance.

Structure and Bonding in Amorphous Red Phosphorus

Amorphous red phosphorus (a-P) is one of the remaining puzzling cases in the structural chemistry of the elements. Here, we elucidate the structure, stability, and chemical bonding in a-P from first principles, combining machine-learning and density-functional theory (DFT) methods. We show that a-P structures exist with a range of energies slightly higher than those of phosphorus nanorods, to which they are closely related, and that the stability of a-P is linked to the degree of structural relaxation and medium-range order. We thus complete the stability range of phosphorus allotropes [Angew. Chem. Int. Ed. 2014, 53, 11629] by now including the previously poorly understood amorphous phase, and we quantify the covalent and van der Waals interactions in all main phases of phosphorus. We also study the electronic densities of states, including those of hydrogenated a-P. Beyond the present study, our structural models are expected to enable wider-ranging first-principles investigations-for example, of a-P-based battery materials.

Solid-State Investigation, Storage, and Separation of Pyrophoric PH3 and P2 H4 with α-Mg Formate

Phosphane, PH₃ -a highly pyrophoric and toxic gas-is frequently contaminated with H₂ and P₂ H₄ , which makes its handling even more dangerous. The inexpensive metal-organic framework (MOF) magnesium formate, α-[Mg(O₂ CH)₂ ], can adsorb up to 10 wt % of PH₃ . The PH₃ -loaded MOF, PH₃ @α-[Mg(O₂ CH)₂ ], is a non-pyrophoric, recoverable material that even allows brief handling in air, thereby minimizing the hazards associated with the handling and transport of phosphane. α-[Mg(O₂ CH)₂ ] further plays a critical role in purifying PH₃ from H₂ and P₂ H₄ : at 25 °C, H₂ passes through the MOF channels without adsorption, whereas PH₃ adsorbs readily and only slowly desorbs under a flow of inert gas (complete desorption time≈6 h). Diphosphane, P₂ H₄ , is strongly adsorbed and trapped within the MOF for at least 4 months. P₂ H₄ @α-[Mg(O₂ CH)₂ ] itself is not pyrophoric and is air- and light-stable at room temperature.

Taming PH3: State of the Art and Future Directions in Synthesis

Appetite for reactions involving PH₃ has grown in the past few years. This in part is due to the ability to generate PH₃ cleanly and safely via digestion of cheap metal phosphides with acids, thus avoiding pressurized cylinders and specialized equipment. In this perspective we highlight current trends in forming new P–C/P–OC bonds with PH₃ and discuss the challenges involved with selectivity and product separation encumbering these reactions. We highlight the reactivity of PH₃ with main group reagents, building on the early pioneering work with transition metal complexes and PH₃. Additionally, we highlight the recent renewal of interest in alkali metal sources of H₂P^– which are proving to be useful synthons for chemistry across the periodic table. Such MPH₂ sources are being used to generate the desired products in a more controlled fashion and are allowing access to unexplored phosphorus-containing species.

High-Pressure and High-Temperature Chemistry of Phosphorus and Nitrogen: Synthesis and Characterization of α- and γ-P3N5

The direct chemical reactivity between phosphorus and nitrogen was induced under high-pressure and high-temperature conditions (9.1 GPa and 2000–2500 K), generated by a laser-heated diamond anvil cell and studied by synchrotron X-ray diffraction, Raman spectroscopy, and DFT calculations. α-P₃N₅ and γ-P₃N₅ were identified as reaction products. The structural parameters and vibrational frequencies of γ-P₃N₅ were characterized as a function of pressure during room-temperature compression and decompression to ambient conditions, determining the equation of state of the material up to 32.6 GPa and providing insight about the lattice dynamics of the unit cell during compression, which essentially proceeds through the rotation of the PN₅ square pyramids and the distortion of the PN₄ tetrahedra. Although the identification of α-P₃N₅ demonstrates for the first time the direct synthesis of this compound from the elements, its detection in the outer regions of the laser-heated area suggests α-P₃N₅ as an intermediate step in the progressive nitridation of phosphorus toward the formation of γ-P₃N₅ with increasing coordination number of P by N from 4 to 5. No evidence of a higher-pressure phase transition was observed, excluding the existence of predicted structures containing octahedrally hexacoordinated P atoms in the investigated pressure range.

The α- and γ-P₃N₅ phosphorus nitride polymorphs have been obtained by direct chemical reactivity between phosphorus and molecular nitrogen under high pressure (9.1 GPa) and high-temperature (2000−2500 K) conditions, generated using a laser heated diamond anvil cell. Insights on the reaction mechanism, involving the preliminary formation of α-P₃N₅, and on the structural properties of γ-P₃N₅ have been evinced by synchrotron X-ray diffraction, Raman spectroscopy and DFT calculations.

Formation and Stability of Dense Methane-Hydrogen Compounds

Through a series of x-ray diffraction, optical spectroscopy diamond anvil cell experiments, combined with density functional theory calculations, we explore the dense CH_{4}-H_{2} system. We find that pressures as low as 4.8 GPa can stabilize CH_{4}(H_{2})_{2} and (CH_{4})_{2}H_{2}, with the latter exhibiting extreme hardening of the intramolecular vibrational mode of H_{2} units within the structure. On further compression, a unique structural composition, (CH_{4})_{3}(H_{2})_{25}, emerges. This novel structure holds a vast amount of molecular hydrogen and represents the first compound to surpass 50 wt % H_{2}. These compounds, stabilized by nuclear quantum effects, persist over a broad pressure regime, exceeding 160 GPa.

Single-Bonded Cubic AsN from High-Pressure and High-Temperature Chemical Reactivity of Arsenic and Nitrogen

Chemical reactivity between As and N2 , leading to the synthesis of crystalline arsenic nitride, is here reported under high pressure and high temperature conditions generated by laser heating in a diamond anvil cell. Single-crystal synchrotron X-ray diffraction at different pressures between 30 and 40 GPa provides evidence for the synthesis of a covalent compound of AsN stoichiometry, crystallizing in a cubic P21 3 space group, in which each of the two elements is single-bonded to three atoms of the other and hosts an electron lone pair, in a tetrahedral anisotropic coordination. The identification of characteristic structural motifs highlights the key role played by the directional repulsive interactions between non-bonding electron lone pairs in the formation of the AsN structure. Additional data indicate the existence of AsN at room temperature from 9.8 up to 50 GPa. Implications concern fundamental aspects of pnictogens chemistry and the synthesis of innovative advanced materials.