Paul Kögerler
English Website

Current Highlights

Hypersensitive Polyoxovanadate Spin Clusters

Polyoxovanadate host-guest complexes are known since ages (read: 20 years). Especially mixed-valent species display a pronounced tendency towards structural complementarity, where the shape of the guest determines the host cluster type, despite very weak, purely electrostatic host-guest interactions. A closer look at the {V22O54(X)} family revealed a bunch of surprises linked to the intricate distribution of vanadium 3d electron density and its ultra-sensitive response to perturbations. See:

K.Yu. Monakhov, O. Linnenberg, P. Kozłowski, J. van Leusen, C. Besson, T. Secker, A. Ellern, X. López, J.M. Poblet, P. Kögerler, "Supramolecular Recognition Influences Magnetism in [X@HVIV8VV14O54]6- Self-Assemblies with Symmetry-Breaking Guest Anions", Chem. Eur. J. 2014, accepted, doi:10.1002/chem.201403858.

Counting on Neodynium for Molecular Spintronics

Quantum charge transport through single-molecule magnets is at the heart of molecular spintronics. However, the magnetically active orbitals need to be at the right energy so that they can actually interact with the electrons tunneling through the molecule. We discovered that early lanthanide ions such as Nd(III) fullfil these requirements. This allows, for the first time, the direct observation of molecular 4f-states by scanning tunneling microscopy. See our work in collaboration with our physics partners at Research Center Jülich:

S. Fahrendorf, N. Atodiresei, C. Besson, V. Caciuc, F. Matthes, S. Blügel, P. Kögerler, D. E. Bürgler, C. M. Schneider, "Accessing 4f-states in Single-Molecule Spintronics", Nature Commun. 2013, 4, 2425 (doi:10.1038/ncomms3425).

This work was also highlighted in Nature Nanotechnology (doi:10.1038/nnano.2013.245).

COST Action "Polyoxometalate Chemistry for Molecular Nanoscience" (PoCheMoN) approved

Paul Kögerler will act as Vice Chair for the COST Action CM1203 which aims to consolidate and communicate the efforts in polyoxometalate chemistry in 21 European countries as well as several near-neighbor and international partner countries. The EU-funded Action will run until November 2016.

Stabilization and Control of Fe-Pt Nanoparticles with Polyoxometalates

Magnetic metal nanoparticles of a few nm fill the gap between the magnetism of single or few metal atoms and cooperative phenomena of condensed phases. Yet, the stabilization and the controlled synthesis of mono-disperese ultra-small nanoparticles (less than 5 nm) remain tricky. Fortunately, functionalized polyoxometalates of the Keggin type can stabilize the surface of such nanoparticles, yielding water-soluble core-shell systems. For our results on such POM-nanoparticle hybrids based on technologically important, hard ferromagnetic FePt phases see:

K.M. Seemann, A. Bauer, J. Kindervater, M. Meyer, C. Besson, M. Luysberg, P. Durkin, W. Pyckhout-Hintzen, N. Budisa, R. Georgii, C.M. Schneider, P. Kögerler, "Polyoxometalate-stabilized, water dispersible Fe2Pt magnetic nanoparticles", Nanoscale 2013, 5, 2511-2519 (doi:10.1039/c3nr33374d).

Getting Polyoxometalate Nanoreactors to Work

Spherical oxomolybdate clusters of the Keplerate type provide highly defined interior cavities (with a volume of approx. 1.5 nm3) as well as pores. We were able to demonstrate that these systems can indeed function as nanoreactors in which steric confinement translates into specific regioselectivies. At the same time, running an organic cycloaddition reaction within this nanoreactor shields the reactants from catalytically active species in the solution surrounding the Keplerate clusters.

C. Besson, S. Schmitz, K.M. Capella, S. Kopilevich, I.A. Weinstock, P. Kögerler, "A regioselective Huisgen reaction inside a Keplerate polyoxomolybdate nanoreactor", Dalton Trans. 2012, 41, 9852-9854 (doi:10.1039/c2dt30502j).

Prof. Kögerler receives ERC Starting Grant (Consolidator Level) "MOLSPINTRON"

Revolutionary innovations in microelectronics mandate new materials: molecular magnets, used as integral transistor components, are expected to offer several decisive advantages, such as extremely low energy consumption and highly complex switching functions that are hard to realize using conventional semiconductor logic devices. The foundation for these characteristics is the joint utilization of magnetic and electronic quantum states of individual magnetic molecules.

In our ERC project 'Synthetic Expansion of Magnetic Molecules Into Spintronic Devices' (11/2012-10/2017), we aim to tackle one of central difficulties in molecular spin electronics: precise and reproducible contacts of the particle. We utilize highly stable magnetic metal oxide nanomolecules and exploit their versatile surface chemistry. Thus, contacts can be made synthetically, i.e., with atomic precision, creating both conductive and nonconductive interfaces.

Alternative Metal Oxide Cluster Chemistry: The Dark Secrets of Cerium

Classical polyoxometalates are typically based on group 5/6 transition metals (V, Nb, Mo, W). What about their communist left-leaning neighbors with less valence electrons? Surprisingly, high-nuclearity molecular cerium oxides can indeed be formed via controlled condensation reactions. Read how their chemistry and structures mimic that of archetypal polyoxometalates in:

I.L. Malaestean, A. Ellern, S. Baca, P. Kögerler, "Cerium oxide nanoclusters: Commensurate with concepts of polyoxometalate chemistry?", Chem. Commun. 2012, 48, 1499-1501 (doi:10.1039/c1cc14725k).
Communication. A polyoxometalate-based single-molecule magnet with an S = 21/2 ground state. X. Fang, P. Kögerler, M. Speldrich, H. Schilder, M. Luban, Chem. Commun. 2012, 48, 1218-1220. DOI: 10.1039/C1CC15520B
Perspective. Structure-related frustrated magnetism of nanosized polyoxometalates: aesthetics and properties in harmony. P. Kögerler, B. Tsukerblat, A. Müller, Dalton Trans. 2010, 39, 21-36. DOI: 10.1039/B910716A

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