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Relativistic Effects on Electronic Structure and Nuclear Magnetic Resonance Shifts in Heavy Metal Systems

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Relativistic Effects on Electronic Structure and Nuclear Magnetic Resonance Shifts in Heavy Metal Systems Relativistic Effects on Electronic Structure and Nuclear Magnetic Resonance Shifts in Heavy Metal Systems vorgelegt von M. Sc. Anja Helene Greif geb. in Berlin Von der Fakultät II – Mathematik und Naturwissenschaften der Technischen Universität Berlin zur Erlangung des akademischen Grades Doktor der Naturwissenschaften – Dr. rer. nat. – genehmigte Dissertation Promotionsausschuss: Vorsitzender: Prof. Dr. rer. nat. Arne Thomas Gutachter: Prof. Dr. rer. nat. Martin Kaupp Gutachter: Prof. Dr. rer. nat. Stephan P. A. Sauer Tag der wissenschaftlichen Aussprache: 14. September 2017 Berlin 2017 "Der Forscher fühlt sich dann dem noch nicht Erkannten gegenüber wie ein Kind, das der Erwachsenen überlegenes Walten zu begreifen sucht." Albert Einstein Zusammenfassung Untersucht wird der Einfluss relativistischer Effekte auf die Elektronen- struktur und die chemische Verschiebung von NMR Kernen in diamagneti- schen 5d Übergangsmetall- und Uran-Hydriden wie auch metallorganischen Uran-Komplexen. Neue Trends und Bereiche im NMR Spektrum dieser Ver- bindungen werden aufgezeigt basierend auf voll- und quasi-relativistischen Dichtefunktionalrechnungen, die an experimentell bekannten NMR Daten für Pt(II) und U(VI) Komplexen evaluiert wurden. Es zeigt sich, dass für die akkurate relativistische Berechnung der Ab- schirmungskonstante die Verwendung des Austausch-Korrelations-Kernels sowie PBE0-Hybridfunktionals notwendig ist. Die NMR Signale in den unter- suchten Komplexen werden durch beträchtliche relativistische Beiträge domi- niert, welche durch Spin-Bahn (SB) Kopplung am schweren Atom bedingt werden und sowohl entschirmend als auch abschirmend sein können. Die wie- derholt beobachteten qualitativen Unterschiede zwischen d6/d8 und d10 Kom- plexen hinsichtlich der Größe und des Vorzeichens von SB-induzierter NMR Abschirmung an einem benachbarten 1H Atom können auf einen auffallend allgemeingültigen trans-Liganden Einfluss zurück geführt werden, der die Me- tallorbitalbeteiligung in relevanten Molekülorbitalen sowie deren Energie mo- duliert. Die daraus resultierenden Unterschiede für die σ-/π-Spinor- Vermischung durch die SB Kopplung führen zu unterschiedlich effizienten magnetischen Kopplungen der metallbasierten Orbitale. Stark abschirmende Beiträge von vorrangig -artigen Spinoren für schwache trans-Liganden sind für starke trans-Liganden vermindert oder sogar verschwunden infolge einer Destabilisierung von besetzen -Orbitalen, was schließlich zur Vorzeichen- änderung für die SB-induzierten NMR Verschiebungen führt. Ähnliche Effekte können auch für andere NMR Kerne festgestellt werden. Im Gegensatz zu früheren Annahmen lässt sich die Veränderung der 1H NMR Verschiebung nicht durch die Änderung der M-1H Bindungslänge in einem gegebenen Komplex begründen. Für die 1H und 13C NMR Signale für Ligandenatome an einem U(VI) Zent- rum werden sehr hohe Resonanzfrequenzen vorhergesagt, die bis zu +170 ppm für 1H und über +550 ppm für 13C betragen können und damit außerhalb der normalen Messbereiche für die jeweiligen Kerne liegen. Der Ursprung der enormen SB-Beiträge zur NMR Verschiebung steht in Verbindung mit der Po- sition des Liganden im Komplex sowie der allgemeinen Elektronenstruktur. Abstract The role of relativistic effects on the electronic structure and ligand NMR chemical shifts in diamagnetic 5d transition-metal and uranium hydrides as well as organometallic uranium complexes is investigated. New NMR trends and spectral regions for these compounds are suggested based on fully and quasi-relativistic density functional theory calculations carefully calibrated on the experimentally known NMR data for Pt(II) and U(VI) complexes. For accurate relativistic shielding computations, the exchange-correlation kernel on NMR chemical shifts and the use of the PBE0 hybrid functional is found to be mandatory. The NMR signals in the investigated complexes are dictated by sizable relativistic contributions due to spin−orbit (SO) coupling at the heavy atom and can be highly shielding and deshielding, as well. The fre- quently observed qualitative differences between d6/d8 and d10 complexes in the magnitude and the sign of SO-induced nuclear magnetic shielding at a vicinal 1H atom are found to be dominated by surprisingly general trans ligand effects modulating the metal orbital participations in relevant MOs as well as their energy. The resulting changes in σ-/π-spinor mixing by SO coupling modify the efficiency of metal-based orbital magnetic couplings. Large shielding contributions from predominantly -type spinors for weak trans ligands are diminished or even removed for strong trans ligands due to a destabilization of occupied levels, causing a sign change from shielding to deshielding of the dominant SO-induced shifts. Similar effects are operative also for other NMR nuclei. In contrast to previous assumptions, the change of the M−H distances for given complexes does not allow correlations with the hydride shifts. The 1H and 13C NMR signals of ligand atoms directly bonded to U(VI) cen- ters are predicted to resonate at very high frequencies, up to +170 ppm for 1H and above +550 ppm for 13C, outside the usual measurement area for the given type of nuclei. The origin of the vast SO contributions to the NMR shift is traced to the ligand position in the complex, and on the overall electronic struc- ture. Danksagung Große Dankbarkeit gilt meinem Doktorvater Prof. Dr. Martin Kaupp, der mir die Möglichkeit gegeben hat, mich an verschiedenen Projekten auszupro- bieren, Anregungen und Hilfestellungen gab und mir immer unterstützend zur Seite stand. Bei allen Mitgliedern der Arbeitsgruppe Kaupp bedanke ich mich ebenfalls. Besonders hervorheben möchte ich meine Bürokollegen Dr. Matthias Parthey, Dr. Toni Maier und Sascha Klawohn. Außerdem danke ich unserer stets hilf- reichen IT-Managerin Heidi Grauel sowie unserer Sekretärin Nadine Rechen- berg, ohne die wohl kaum etwas im Alltag funktionieren würde. Dr. Peter Hrobárik und Prof. Dr. Jochen Autschbach gilt mein Dank für die Zusammenarbeit an verschiedenen Projekten. Vielen Dank auch an Dr. Michal Repisky, der meinen Forschungsaufenthalt jenseits des Polarkreises betreute. Herzlichen Dank möchte ich meinen lieben Freunden aussprechen, allen voran Marcel Schmidt, der nicht nur während des Studiums sondern auch auf dem Weg zur Promotion mein treuer Mitstreiter war und mir den Alltag stets versüßte. Für ihre Liebe und Unterstützung danke ich meiner Familie, insbesondere meinen Eltern. Zu guter Letzt möchte ich mich bei meinem Mann Ludwig bedanken. Es ist mir kaum möglich, den Beistand, das Verständnis und die Geduld, welche er mir entgegenbrachte auch nur annähernd in Worte zu fassen. List of Publications Publications included in the thesis Paper I: A relativistic quantum-chemical analysis of the trans influence on 1H NMR shifts in square-planar Pt(II) complexes A. H. Greif, P. Hrobárik, V. Hrobáriková, A. V. Arbuznikov, J. Autschbach and M. Kaupp, Inorg. Chem., 2015, 54, 7199–7208. DOI: 10.1021/acs.inorgchem.5b00446 Paper II: Insights into trans-Ligand and Spin-Orbit Effects on electronic Structure and Ligand NMR Shifts in Transition-Metal Complexes A. H. Greif, P. Hrobárik and M. Kaupp, Chem. Eur. J., 2017, 23, 9790. DOI: 10.1002/chem.201700844 Paper III: Giant Spin-Orbit Effects on 1H and 13C NMR Shifts for Urani- um(VI) Complexes Revisited: Role of the Exchange-Correlation Response Kernel, Bonding Analyses, and New Predictions A. H. Greif, P. Hrobárik, J. Autschbach and M. Kaupp, Phys. Chem. Chem. Phys., 2016, 18, 30462-30474. DOI: 10.1039/C6CP06129J Non-contributing Publication Giant Spin-Orbit Effects on NMR Shifts in Diamagnetic Actinide Complexes: Guiding the Search of Uranium(VI) Hydride Complexes in the Correct Spectral Range P. Hrobárik, V. Hrobáriková, A. H. Greif, M. Kaupp, Angew. Chem. Int. Ed. 2012, 51, 10884–10888. DOI: 10.1002/anie.201204634 Contents Zusammenfassung v Abstract vii Danksagung ix List of Publications xi Contents xiii List of Abbreviations xv 1 General Introduction 1 1.1 Contributing Publications 3 1.2 Personal Contribution to the Publications 4 1.3 Outline 5 2 Theoretical Background 6 2.1 Molecular Quantum Mechanics 6 2.1.1 Hartree-Fock Theory 8 2.1.2 Density Functional Theory 9 2.1.3 Localized Molecular Orbitals 10 2.2 Special Relativity 11 2.3 Relativistic Quantum Mechanics 12 2.3.1 Four-Component Dirac Equation 12 2.3.2 Two-Component Approximation 14 2.3.3 Relativistic Effective Core Potentials 15 2.4 Consequences of Special Relativity in Chemistry 16 2.4.1 Dirac Quantum Numbers 17 2.4.2 Relativistic Effects on the Periodic Table 18 2.4.3 Gold Maximum of Relativistic Effects 20 2.4.4 Relativistic Effects for Molecular Properties and Chemistry 21 2.5 Nuclear Magnetic Resonance 23 2.5.1 NMR Shielding Contributions 25 2.5.2 Non-Relativistic Computation of NMR Shielding 25 2.5.3 The Buckingham-Stephens Effect 27 2.5.4 Relativistic Computation of NMR shieldings 28 2.5.5 Relativistic Effects on NMR Shifts 32 3 Results and Discussion 35 3.1 Evaluation of Methods 35 3.1.1 Structure Optimization 36 3.1.2 NMR Calculation 36 3.2 Role of SO Effects for the trans Influences in TM Hydrides 40 3.2.1 General trans Ligand Influences on Bonds and NMR Shifts 41 3.2.2 Analysis of Shielding Tensor Contributions and Components 43 3.2.3 Analysis of the Electronic Structure 45 3.2.4 MO Analysis of p+SO Contributions to 1H Shielding 47 3.2.5 Relations to Magnetically Induced Current Loops 50 3.3 Role of SO Effects for Uranium(VI) Complexes 52 3.3.1 Predictions of 13C and 1H Shifts 52 3.3.2 General Ligand
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