Spin and orbital magnetic moments of isolated single molecule magnets and transition metal clusters

In the present work, magnetic moments of isolated Single Molecule Magnets (SMMs) and transition metal clusters were investigated. Gas phase X‐ray Magnetic Circular Dichroism (XMCD) in combination with sum rule analysis served to separate the total magnetic moments of the investigated species into their spin and orbital contributions. Two different mass spectrometry based setups were used for the presented investigations on transition metal clusters (GAMBIT‐setup) and on single molecule magnets (NanoClusterTrap). Both experiments were coupled to the UE52‐PGM beamline at the BESSY II synchrotron facility (Helmholtz Zentrum Berlin) which provided the necessary polarized X‐ray photons. The investigation of the given compounds as isolated molecules in the gas phase enabled a determination of their intrinsic magnetic properties void of any influences of e.g. a surrounding bulk or supporting surfaceIn der vorgelegten Arbeit wurden die magnetischen Momente von isolierten Einzelmolekülmagneten (SMMs, Single Molecule Magnets) und von Übergangsmetallclustern untersucht. Gasphasen röntgenstrahlinduzierter magnetischer Zirkulardichroismus (XMCD, X‐ray Magnetic Circular Dichroism) in Kombination mit der sogenannten Summenregelanalyse diente zur Bestimmung der Anteile der spin‐ und bahnmagnetischen Momente zum totalen magnetischen Moment der untersuchten Substanzen. Zwei unterschiedliche, auf Massenspektrometrie basierende, Instrumente wurden für die genannten Untersuchungen verwendet. Im Falle der Übergangsmetallcluster war dies das GAMBIT‐Setup und im Falle der Einzelmolekülmagnete handelte es sich um die NanoClusterTrap. Beide Instrumente waren an der UE52‐PGM Beamline am BESSY II Synchrotron (Helmholtz Zentrum Berlin) angebracht, welche die benötigte zirkular polarisierte Röntgenstrahlung lieferte. Die Untersuchungen der genannten Substanzen als isolierte Moleküle in der Gasphase ermöglichte die Bestimmung ihrer intrinsischer magnetischer Momente ohne den Einfluss etwaiger benachbarter Festkörper‐ oder tragender Oberflächenmoleküle

Spin and orbital magnetic moments of isolated single molecule magnets and transition metal clusters

In the present work, magnetic moments of isolated Single Molecule Magnets (SMMs) and transition metal clusters were investigated. Gas phase X‐ray Magnetic Circular Dichroism (XMCD) in combination with sum rule analysis served to separate the total magnetic moments of the investigated species into their spin and orbital contributions. Two different mass spectrometry based setups were used for the presented investigations on transition metal clusters (GAMBIT‐setup) and on single molecule magnets (NanoClusterTrap). Both experiments were coupled to the UE52‐PGM beamline at the BESSY II synchrotron facility (Helmholtz Zentrum Berlin) which provided the necessary polarized X‐ray photons. The investigation of the given compounds as isolated molecules in the gas phase enabled a determination of their intrinsic magnetic properties void of any influences of e.g. a surrounding bulk or supporting surfaceIn der vorgelegten Arbeit wurden die magnetischen Momente von isolierten Einzelmolekülmagneten (SMMs, Single Molecule Magnets) und von Übergangsmetallclustern untersucht. Gasphasen röntgenstrahlinduzierter magnetischer Zirkulardichroismus (XMCD, X‐ray Magnetic Circular Dichroism) in Kombination mit der sogenannten Summenregelanalyse diente zur Bestimmung der Anteile der spin‐ und bahnmagnetischen Momente zum totalen magnetischen Moment der untersuchten Substanzen. Zwei unterschiedliche, auf Massenspektrometrie basierende, Instrumente wurden für die genannten Untersuchungen verwendet. Im Falle der Übergangsmetallcluster war dies das GAMBIT‐Setup und im Falle der Einzelmolekülmagnete handelte es sich um die NanoClusterTrap. Beide Instrumente waren an der UE52‐PGM Beamline am BESSY II Synchrotron (Helmholtz Zentrum Berlin) angebracht, welche die benötigte zirkular polarisierte Röntgenstrahlung lieferte. Die Untersuchungen der genannten Substanzen als isolierte Moleküle in der Gasphase ermöglichte die Bestimmung ihrer intrinsischer magnetischer Momente ohne den Einfluss etwaiger benachbarter Festkörper‐ oder tragender Oberflächenmoleküle

Inverse H/D Isotope Effects in Benzene Activation by Cationic and Anionic Cobalt Clusters

Reactions under single collision conditions with benzene C₆H₆ and with benzene-<i>d</i>₆ C₆D₆ of size selected cationic cobalt clusters Co_<i>n</i>⁺ and of anionic cobalt clusters Co_<i>n</i>^– in the cluster size range <i>n</i> = 3–28 revealed that dehydrogenation by cationic clusters is sparse, whereas it is ubiquitous in reactions by anionic clusters. Kinetic isotope effects (KIE) in total reaction rates are inverse and, in part, large. Dehydrogenation isotope effects (DIE) are normal. A multistep model of adsorption and stepwise dehydrogenation from the precursor adsorbate unravels a possible origin of the inverse KIE: Single step C–H bond activation is swift (no KIE in forward direction) and largely reversible (normal KIE backward) whereas H/D tunneling is likely to contribute (backward). DFT calculations of the structures and energetics along the reaction path in [Co₁₃C₆H₆]⁺ lend support to the proposed multistep model. The observed effects on rates and KIEs of cluster charges and of cluster sizes are noted to elucidate further

The spin and orbital contributions to the total magnetic moments of free Fe, Co, and Ni clusters

We present size dependent spin and orbital magnetic moments of cobalt (Co$_{n}$$^{+}$, 8 ≤ n ≤ 22), iron (Fe$_{n}$$^{+}$, 7 ≤ n ≤ 17), and nickel cluster (Ni$_{n}$$^{+}$, 7 ≤ n ≤ 17) cations as obtained by X-ray magnetic circular dichroism (XMCD) spectroscopy of isolated clusters in the gas phase. The spin and orbital magnetic moments range between the corresponding atomic and bulk values in all three cases. We compare our findings to previous XMCD data, Stern-Gerlach data, and computational results. We discuss the application of scaling laws to the size dependent evolution of the spin and orbital magnetic moments per atom in the clusters. We find a spin scaling law “per cluster diameter,” ~n$^{−1/3}$, that interpolates between known atomic and bulk values. In remarkable contrast, the orbital moments do likewise only if the atomic asymptote is exempt. A concept of “primary” and “secondary” (induced) orbital moments is invoked for interpretation