What is the discovery?
Density functional theory (DFT) calculations have proven invaluable in the study of transition metal catalysis. They can predict both the geometric and electronic structures of active catalysts and their intermediates. However, although platinum-based catalysts are used extensively in industrial processes, a systematic understanding of how well DFT methods can predict the structures of Pt-containing species has been lacking. Now, in a new publication, the team of Louise Debefve and Chris Pollock (both at the PIPOXS beamline at CHEXS) have evaluated 80 different DFT methods to reproduce the experimental geometries of Pt complexes, using a diverse training set of 14 platinum-containing species with varying sizes, oxidation states, and number and type of ligands. The team determined a recipe for best performance (PBE0 functional, def2-TZVP basis set for the ligand atoms, the ZORA relativistic approximation, and solvation and dispersion corrections). The accuracy of the predictions made using Debefve and Pollock’s methodology was confirmed experimentally, by comparing the DFT optimized geometry of a previously uncharacterized complex to EXAFS data newly collected at PIPOXS, which showed excellent agreement.
Why is it important?
Platinum is used extensively as a catalyst for a wide variety of chemical reactions, though its scarcity and price present limitations to expansions of its use. Chemists hope to understand the origin of platinum's versatility in order to both improve the efficiency of existing catalysts and to mimic its reactivity with more abundant metals. To do so, we must figure out the mechanisms of platinum-catalyzed chemical reactions via structural and spectroscopic characterization of these catalysts under operando conditions; unfortunately, such data typically involve looking at complex mixtures of species and are often challenging to interpret. Chemical theory, such as DFT, is often used to help interpret complex data sets, and the ability to accurately predict the structures of Pt-containing species is a critical first step to leveraging computational chemistry to help understand reactivity of Pt-based catalysts.
Why did this research need CHEXS?
This research took place at the PIPOXS beamline at CHEXS, which is optimized to study the geometric and electronic structures of operando catalysts using x-ray spectroscopic methods. EXAFS studies of transition metal catalysts are a core capability of the beamline. Additionally, this work also leveraged the dedicated computational resources at the PIPOXS beamline to perform the thousands of DFT calculations used in this study.
How was the work funded?
This work is based upon research conducted at the Center for High Energy X-ray Sciences (CHEXS) which is supported by the National Science Foundation under award DMR-1829070. This work was also supported by NSF-PREM: Center for Interfacial Electrochemistry of Energy Materials (CiE2M) under award DMR-1827622.
Systematic assessment of DFT methods for geometry optimization of mononuclear platinum-containing complexes
Louise M. Debefve and Christopher J. Pollock
Phys. Chem. Chem. Phys., Advance Article( 2021); https://doi.org/10.1039/d1cp01851e