Project A – Disentangling catalysis at real surfaces

Bench Project AThe project involves a new approach to the measurement of chemical reaction rates at surfaces, a topic of great relevance to heterogeneous catalysis. We have recently succeeded in measuring the rates of reactions at specific active sites on a catalytic surface - see Nature, (2018) DOI : 10.1038/s41586-018-0188-x, where we report step and terrace specific reaction rate constants for CO oxidation on Pt. We intend to systematically obtain kinetic data for important catalytic reactions involving multiple reaction sites and in cooperation with theoretical collaborators construct accurate atomic scale dynamical descriptions and detailed maps of the elementary steps of the reaction mechanisms.

Supervisor: Prof. Dr. Alec Wodtke (enquire about current or future availability - Email contact)

Collaborators (Göttingen): Prof. Dr. Jörg Behler

Collaborators (external): Prof. Dr. Charles Campbell (U Washington)

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See also: [1]

Project B – Barriers of protonation reactions of organometallics

Bench Project BTypical organometallics, such as Grignard reagents RMgX, are notorious for their complexity in solution: they easily switch between different aggregation and coordination states (so-called Schlenk equilibria). This dynamic behavior severely complicates any kinetic analysis in solution. For ionic species, the latter problem can be circumvented by transferring them into the gas phase via electrospray ionization and isolating them by tandem mass spectrometry. The project will use this approach for examining the microscopic reactivity of a wide range of organometallic ions toward proton donors as model electrophiles. The experimentally obtained rate constants shall then serve as benchmarks for theory. In combination, experiment and theory, thus, promise to unravel the mechanism of prototypical organometallic reactions and afford fundamental insight relevant to synthesis and catalysis.

Supervisor: Prof. Dr. Konrad Koszinowski (enquire about current or future availability - Email contact)

Collaborators (Göttingen): Prof. Jörg Behler, Prof. Sven Schneider, Prof. Dietmar Stalke

Collaborators (external): Riccardo Spezia (LAMBE)

See also: [1], [2]

Project C – Thermochemistry of proton-coupled electron transfer reactions involving 3d metal ions

Bench Project CRedox reactions are often, if not most often, coupled to proton transfer events. Such proton-coupled electron transfer (PCET) reactions are important in chemical energy conversion reactions as the water oxidation reaction or in fuel cells, which are usually mediated by metal compounds. The underlying elementary steps are also commonly subject to quantum chemical benchmarking, from ionization to electron attachment, or even hydrogen atom transfer. The latter reference data are, however, far from the systems and the conditions commonly featured in catalysis, focusing on gas phase reactivity with light main-group elements. In the BENCh project, we will explore PCET reactions involving 3d metal/ligand reactivity in solution. The solution thermochemistry of the elementary steps of formally spin forbidden and spin allowed PCET reactions will be investigated in different, aprotic solvents as well as the solution BDFE of the HAT reaction.

Supervisor: Prof. Dr. Inke Siewert (enquire about current or future availability - Email contact)

Collaborators (Göttingen): Prof. Dr. Ricardo Mata, Prof. Dr. Sven Schneider, Prof. Dr. Martin Suhm

Collaborators (external): Prof. Dr. Jeremy Harvey (Leuven)

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See also: [1], [2]

Project D – Hydrogen atom transfer reactivity of 5d oxo- and nitrene species

Bench Project DHeavy (5d) transition metals (TM) are important for many catalytic transformations, such as oxo/nitrene transfer. Owing to the transient character of the TM oxo/nitrene key intermediates, mechanistic evaluation of such reactions heavily relies on computational analysis. We want to benchmark the thermochemistry of 5d TM complexes relevant to catalysis, specifically with respect to spin-orbit relativistic contributions, which can be as large as 50 kcal/mol for bare transition metal ions in the gas phase. We will systematically evaluate the thermochemistry of hydrogen atom transfer to late 5d TM oxo/imido complexes as a key reaction to oxo/nitrene transfer catalysis via a radical rebound mechanism. This will allow for assessing the relevance of relativistic spin-orbit effects in the condensed phase and benchmarking of the computational methods.

Supervisor: Prof. Dr. Sven Schneider (enquire about current or future availability - Email contact)

Collaborators (Göttingen): Prof. Dr. Inke Siewert

Collaborators (external): Prof. Dr. Max Holthausen (Frankfurt), Prof. Dr. Bas de Bruin (Amsterdam)

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Project E – Tailoring and exploiting magnetic anisotropy in low-coordinate 3d transition metal complexes

Bench Project EA key requirement for molecules to behave as single-molecule magnets (SMMs) is the presence of magnetic anisotropy, characterized by a negative axial zero-field splitting (ZFS) parameter D, which creates an energy barrier inhibiting reversal of the magnetisation. Since SMM properties are extremely sensitive to changes in structure and bonding, they provide ideal data for the critical analysis of dynamic and static electron correlation effects. The focus of this study will be on (mostly low-coordinate) 3d SMMs with targeted variations in geometry, metal-ligand covalency, etc., translating into tunable variations of the magnetic anisotropy. Ligands will be synthesized to conformationally restrict the complex and lead to enforced coordination modes, such as macrocyclic systems with two N-heterocyclic carbene units. These will be studied by SQUID magnetometry and by a bouquet of spectroscopic methods, including high-field EPR and Mössbauer spectroscopy (where applicable); the latter also provides information about internal magnetic fields.

Supervisor: Prof. Dr. Franc Meyer (enquire about current or future availability - Email contact)

Collaborators (Göttingen): Prof. Dr. Dietmar Stalke

Collaborators (external): Prof. Dr. Frank Neese (Mülheim), Prof. Dr. Mihail Atanasov (Mülheim), Prof. Dr. Eckhard Bill (Mülheim)

Project F – Dependencies of Thermochemical Observables from the Electronic Ground State

ProjectFBoroles are often brightly coloured, unsaturated five-membered heterocycles containing one boron-atom and feature four electrons in the cyclic π-system. This projects seeks to probe influence of the substitution pattern on the reactivity and spectroscopic properties of these main-group heterocycles with a rather unusual and reactive π-system. Their spectroscopic, kinetic and thermodynamic properties will serve as benchmark for theoretical modelling of the electronic ground-state and linear free enthalpy relationships and thus accessing synthetic blueprints for property customised systems. Collaboration with the Schneider group allows us to obtain experimental data on thermochemical properties using a microcalorimetry set-up.

Supervisor: Dr. Christian Sindlinger (enquire about current or future availability - Email contact)

Collaborators (Göttingen): Prof. Dr. Sven Schneider, Prof. Dr. Ricardo A. Mata

Collaborators (external): Prof. Dr. Leticia González (Vienna)

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Project G – Benchmarking luminescence to structural features in substituted anthracene host-guest excimers

Bench Project GIn daily life dyes and optoelectronics like OLEDs and OFETs are either employed as thin films or single crystals. Despite the various applications the effects causing solid-state luminescence are not yet fully understood. Aggregation-caused quenching, as well as aggregation-induced emission, are currently qualitatively scaled to a variety of weak non-covalent interactions, which one can steer by substitution and conformation. The use of photochromic coordination cages proved to be particularly interesting for light-triggered guest uptake and release. In this project, we will conduct structural measurements on a full cornucopia of asymmetrically substituted anthracenes crystallizing with numerous different arenes. The resulting luminescent host-guest complexes will provide a basis for challenging theoretical benchmarks.

Supervisor: Prof. Dr. Dietmar Stalke (enquire about current or future availability - Email contact)

Collaborators (Göttingen): Prof. Dr. Ricardo Mata, Prof. Dr. Konrad Koszinowski, Prof. Dr. Martin Suhm

Collaborators (external): Prof. Dr. Carlo Gatti (Milan)

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Project H – Chirality recognition as an experimental benchmarking tool

Bench Project HChiral molecules recognize the relative chirality of partner molecules through subtle intermolecular interactions. This molecular handshake has spectroscopic, thermodynamic and kinetic implications for the molecular pairs that are best explored at low temperature in the gas phase. By studying these molecular recognition effects using unique vibrational spectroscopy setups in the Suhm group, one can test the performance of electronic structure methods quite rigorously, down to the sub-kJ/mol level. It has even been speculated that there may be new kinds of chirality-dependent forces based on spin polarization. In any case, there are intriguing competitions between attractive and repulsive forces to be discovered and concepts like chirality discrimination, chirality induction and chirality synchronization to be dissected using terpenes, lactates, and other chiral model systems. This has practical implications - e.g. one can even smell the chirality of molecules in favorable cases.

Supervisor: Prof. Dr. Martin Suhm (enquire about current or future availability - Email contact)

Collaborators (Göttingen): Prof. Dr. Ricardo Mata, Prof. Dr. Konrad Koszinowski and Prof. Dr. Dietmar Stalke

Collaborators (external): Prof. Dr. Melanie Schnell (Hamburg)

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Project I – Understanding environmental effects on molecules – step by step

Bench Project IQuantum chemistry is best at calculating isolated molecules at 0 K. Chemists like to study them with some thermal excitation, embedded in a solvent. We aim to provide bridges between these two worlds. Supersonic jet spectroscopy offers rigorous answers for well-defined partial problems such as stepwise solvation and mode-selective thermal excitation. In this project, interesting model systems are put under spectroscopic scrutiny by adding weak solvent perturbations and by exciting selected vibrational modes. Weak hydrogen bonding, vibrational mode coupling and shock heating will be explored to tame the complexity of environmentally influenced molecules and to benchmark both electronic structure and nuclear dynamics theory.

Supervisor: Prof. Dr. Martin Suhm (enquire about current or future availability - Email contact)

Collaborators (Göttingen): Prof. Dr. Jörg Behler, Prof. Dr. Alec Wodtke, Prof. Dr. Ricardo Mata and Prof. Dr. Sven Schneider

Collaborators (external): Prof. Dr. Deborah Crittenden (Christchurch, NZ)

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Project J – Non-covalent interactions in energy storage materials

BENCh PROJECT JContributing to the greater quest for environmentally sustainable technology, this project seeks to understand the interactions of hydrogen with potential storage materials. Using small mimics and analogs of the well-studied covalent organic frameworks (COF), we study the properties of hydrogen complex formation in the gas-phase. The Obenchain group uses rotational spectroscopy, which allows for a high-quality structure determination of the hydrogen position. This technique is sensitive enough to determine favored hydrogen binding sites and can even detect the subtle differences in the binding caused by the behavior of the ortho/para forms of hydrogen. The majority of our targets contain quadrupolar nuclei, which act as local probes to changes in the electronic structure of a molecule upon hydrogen absorption. Our targets are small enough to compare to both DFT and WFT predictions. In the end, we gain a multifaceted set of experimentally determined properties for benchmarking to a wide-range of theoretical methods.

Supervisor: Jun.-Prof. Dr. Daniel Obenchain (enquire about current or future availability - Email contact)

Collaborators (Göttingen): Prof. Dr. Martin Suhm, Prof. Dr. Ricardo Mata

Collaborators (external): Prof. Dr. Melanie Schnell (Kiel), Prof. Dr. Jens-Uwe Grabow (Hannover)

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Project T1 – New approaches to electronic structure diagnostics

Bench Project T1How can one work towards a more predictive, robust use of computational procedures for chemical simulations? Part of the solution is understanding the caveats of current methods, starting with the electronic structure. In this project, we explore a series of local orbital descriptions to analyze and diagnose wave function and density functional theory approaches in the computation of a wide range of properties and systems, ranging from non-covalent interactions in the gas phase to chemical reactivity in solution. Successful applicants will come in contact with state-of-the-art electronic structure methods and embedding techniques for the description of molecules in condensed phases.

Supervisor: Prof. Dr. Ricardo Mata (enquire about current or future availability - Email contact)

Collaborators (Göttingen): Prof. Dr. Martin Suhm, Prof. Dr. Inke Siewert, Prof. Dr. Jörg Behler and Prof. Dr. Dietmar Stalke

Collaborators (external): Prof. Dr. Jeremy Harvey (Leuven), Prof. Dr. Melanie Schnell (Hamburg)

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Project T2 – Molecular Dynamics with Machine Learning Potentials

Bench Project T2The simulation of dynamical processes in chemistry is still a substantial challenge because of the high complexity of realistic structural models and because of the need to reach statistically converged results. In spite of the availability of high performance supercomputers the use of ab initio molecular dynamics simulations is still prohibitively expensive for many interesting problems. In recent years, machine learning potentials have become promising new tools to transfer the accuracy of first principles methods to larger time and length scales. In this project we seek candidates to develop and apply high-dimensional neural network potentials to solve chemical problems in different fields like heterogeneous catalysis, vibrational spectroscopy and chemistry in solution.

Supervisor: Prof. Dr. Jörg Behler (enquire about current or future availability - Email contact)

Collaborators (Göttingen): Prof. Dr. Alec Wodtke, Prof. Dr. Martin Suhm, Prof. Dr. Ricardo Mata and Prof. Dr. Konrad Koszinowski

Collaborators (external): Prof. Dr. Geert-Jan Kroes (Leiden)

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