Periodic Reporting for period 1 - NgCHEM (Noble-Gas Compounds meet X-ray Charge Density and High-Pressure Research)
Reporting period: 2023-06-01 to 2024-05-31
The project “Noble-Gas Compounds meet X-ray Charge Density and High-Pressure Research˝ addresses the need for more experimental studies in the field of noble-gas and fluorine chemistry, due to the decreasing number of active research groups in this field. By focusing on contemporary methods such as X-ray charge-density analysis and high-pressure studies, this research not only contributes to advancing the current state of knowledge but also serves to strengthen this specialized field of chemistry. The primary outcome of the project is the first systematic experimental charge-density study on noble-gas compounds, offering a detailed examination of their electronic structure and intermolecular interactions. This investigation addresses a shortcoming in the field, as most theoretical studies on noble-gas compounds lack experimental confirmation. In addition to studying the electronic structure and intermolecular interactions of noble-gas compounds, the project is also dedicated to discovering new chemical species and reactivity phenomena through synthetic research efforts. Typically, noble-gas atoms are bonded to fluorine atoms, with a smaller proportion of examples where they are bonded to other atoms, such as oxygen and nitrogen. This project aims to identify novel xenon–oxygen-bonded species and investigate oxygen-transfer reaction methodologies. By expanding the scope of noble-gas chemistry, we hope to uncover unique chemical species and reactions that will contribute to our understanding of this intriguing field. The high-pressure structural study was focused on compounds that are reactive and air sensitive, which is experimentally demanding area of research. The objective of this project was also to perform high-pressure structural studies of selected fluoride compounds in the GPa range. Through this research, the project aims to generate valuable results that will widen our understanding of chemistry under extreme pressure conditions.
The research of the project was carried out through four work packages (WP1–WP4). WP1 included the synthesis and single-crystal growth of novel noble-gas compounds. This package focused on the application of well-established techniques in the host laboratory: handling fluorine gas, anhydrous hydrogen fluoride, and fluorides; employing specialized synthetic experimental techniques; and utilizing low-temperature single-crystal growth methods. We synthesized a novel xenon–oxygen-bonded compound and characterized it by low-temperature single-crystal X-ray diffraction analysis, low-temperature Raman spectroscopy and quantum-chemical calculations. In addition, several possible reactions for the synthesis of novel xenon species were tested and thoroughly investigated. WP2 comprised measurements of experimental X-ray charge-density analysis of noble-gas compounds. This work package involved the use of low-temperature crystal selection and mounting techniques, as well as the measurement of high-angle, high-redundancy, low-temperature single-crystal X-ray diffraction data using a microfocus Ag Kα radiation. High-quality experimental datasets of several compounds were measured, suitable for multipole refinement. WP3 included a high-pressure study of a selected compounds in diamond anvil cells (DAC). The aim of this work package was to provide training in DAC procedures, including anvil alignment, gasket indentation, hole drilling, loading, and ruby fluorescence measurements. Training also covered DAC loading with air-sensitive compounds in a glovebox, as well as crystal structure determinations of the selected compounds under high pressure in the DAC. We successfully loaded the DAC with a main-group fluoride and measured several single-crystal X-ray diffraction datasets in the pressure range of 0.1 GPa to 4.5 GPa. The results of high-pressure crystal structure determinations research reveal an interesting effect of pressure on the intramolecular and intermolecular bonding. This work continues beyond the MSCA fellowship through ongoing collaboration between the fellow and the host laboratory. WP4 involved a secondment at Politecnico di Milano. Within this work package, training on advanced charge-density (CD) analysis and multipole refinement using the program XD2016 was conducted. This training was complemented by guidance and advising on CD experimental design, data collection, and data analysis. A detailed analysis of the bonding situation in noble-gas compounds was performed and compared with theoretical calculations.
This project pushed the limits of experimental X-ray charge-density analysis, utilizing advanced methodology and cutting-edge equipment. The new findings from this project provide insights into the unique chemical bonding of noble-gas compounds. Experimental X-ray charge-density analysis of noble-gas compounds represents a significant advance beyond the current state-of-the-art. Furthermore, the research carried out within this project resulted in a discovery of new chemical species and explored reactivity of noble-gas compounds. This included the synthesis, isolation and full characterization of a new rare example of xenon–oxygen-bonded species. The effect of high-pressure on the structure of a main-group fluoride afforded new insights into the nature of intermolecular interactions present in this and similar compounds. Communication activities were aimed at increasing the awareness about noble-gas chemistry, a fascinating yet often overlooked and underrepresented field of main-group chemistry.