Abstract
High pressure reactivity of phosphorus and hydrogen is relevant to fundamental chemistry, energy conversion and storage, and materials science. Here we report the synthesis of (PH3)2H2, a crystalline van der Waals (vdW) compound (I4cm) made of PH3 and H2 molecules, in a Diamond Anvil Cell by direct catalyst-free high pressure (1.2 GPa) and high temperature (T ≲ 1000 K) chemical reaction of black phosphorus and liquid hydrogen, followed by room T compression above 3.5 GPa. Group 15 elements were previously not known to form H2-containing vdW compounds of their molecular hydrides. The observation of (PH3)2H2, identified by synchrotron X-ray diffraction and vibrational spectroscopy (FTIR, Raman), therefore represents the discovery of a previously missing tile, specifically corresponding to P for pnictogens, in the ability of non-metallic elements to form such compounds. Significant chemical implications encompass reactivity of the elements under extreme conditions, with the observation of the P analogue of the Haber-Bosch reaction for N, fundamental bond theory, and predicted high pressure superconductivity in P-H systems.
Highlights
High pressure reactivity of phosphorus and hydrogen is relevant to fundamental chemistry, energy conversion and storage, and materials science
Bridgman, who may be considered the founder of high pressure science, first synthesized black phosphorus (Pblack), whose characteristic crystalline layered structure corresponds to the thermodynamically stable allotrope of the element[2]
In this paper we report a synchrotron X-ray diffraction (XRD)
Summary
High pressure reactivity of phosphorus and hydrogen is relevant to fundamental chemistry, energy conversion and storage, and materials science. We report the synthesis of (PH3)2H2, a crystalline van der Waals (vdW) compound (I4cm) made of PH3 and H2 molecules, in a Diamond Anvil Cell by direct catalyst-free high pressure (1.2 GPa) and high temperature (T ≲ 1000 K) chemical reaction of black phosphorus and liquid hydrogen, followed by room T compression above 3.5 GPa. Group 15 elements were previously not known to form H2-containing vdW compounds of their molecular hydrides. A high pressure study, based on synchrotron X-ray diffraction (XRD) in Diamond Anvil Cell (DAC), has made another mark in the history of the layered structures of phosphorus, providing a clear insight about the mechanism of interlayer bond formation and significantly raising the pressure limit for the existence of the phosphorus layers up to ~30 GPa at room T4,5. The combination of pressure with high temperature or electronic photo-excitation has been shown to be a very effective and extremely powerful tool for opening selective reactive paths[10,11], activating chemical reactivity in notoriously non interacting systems at ambient conditions[12], like here P and H, and for synthesizing new unexpected compounds[13,14], suggesting the idea of investigating the so far unexplored chemistry of the phosphorus-hydrogen system under high pressure conditions
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