Examination of the Crystal Structures of PH3, AsH3, SbH3 and their polymorphism with Neutron Diffraction

• Applicant: Dr. Frank Tambornino
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation ; Solid State and Surface Chemistry, Material Synthesis
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 553943492

The hydrogen compounds of the lighter Group 15 elements PnH3 (Pn = N, P, As) have been important starting materials for industrial processes for many decades. Their use in the chemical industry, e.g. ammonia in the Ostwald process or the Raschig synthesis for the large-scale synthesis of nitric acid or hydrazine or phosphane and arsane in the production of modern semiconductor materials, has become indispensable in today's world. Furthermore, ammonia as well as phosphane and arsane are well-established compounds which play an important role in current research in various fields. In addition to the lighter homologs of pnictogens, which are well established in research and industry, stibane as a higher homolog has also come to the forefront of research in recent years. In particular, research into the structure of these compounds in the solid state has revealed major discrepancies. For example, at least five polymorphs are known for the lighter homolog ammonia. For the higher homologs phosphane, arsane and stibane, only one crystal structure is known. The aim of our project is to elucidate the missing solid-state structures of these compounds. The high-purity synthesis of these compounds, which are gaseous under normal conditions, is well established in our working groups. In the course of the planned research, in addition to the high-temperature modifications, the modifications that these compounds assume shortly after solidification, possible low-temperature phases are also to be elucidated. We have already been able to carry out successful measurements as part of our previous investigations using X-ray structure analysis on single crystals. Due to the insufficiency of this analytical method to clearly localize hydrogen atoms, and the fact that the low-temperature modifications of these compounds are not accessible to us as single crystals by crystallization, it is necessary at this point to carry out powder neutron diffraction on the above-mentioned compounds. This analytical method enables us to elucidate these previously unknown structures beyond doubt and to draw conclusions about the properties of these compounds in solid form. This applies both to the high-temperature modifications and to the low-temperature modifications of these compounds that we have already postulated by X-ray structure analysis of the single crystal. These investigations also make it possible to study the hydrogen bonds formed by the heavier main group elements, which have hardly been investigated to date. The measurement of the phase transitions allows conclusions to be drawn about the bond strength of these exotic bonds.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Carsten von Hänisch