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Molecular Magnetism

The central field of research of the group "Molecular Magnetism" are single- and oligonuclear complexes of the 3d, 4d, 5d transition metals, the 4f (lanthanides) and 5f (actinide) elements. We focus on the application of ab-initio wave function-based quantum chemical methods for the computation, ligand field analysis, interpretation and prediction of the spectroscopic and magnetic properties of open-shell systems. The aim of our studies is to increase the magnetic anisotropy - the predominantly uniaxial magnetic moments - from the one side and from the other side to decouple the magnetic moments of the single spin centers from each other. Our calculations and analyzes focus on concrete systems in close cooperation with internal and external synthetic and spectroscopic working groups.

  • Ab initio wave function based methods for computing the electronic structure of well-defined dn and fn configured open-shell complexes.
  • Ligand field theory for single and binuclear complexes based on ab initio procedure (AILFT) - application and further development.
  • Correlations between the electronic and geometric structure and the magnetic and spectroscopic properties as predictive tools.
  • Coupling between nuclei and electrons - Jahn-Teller and Pseudo-Jahn Teller coupling effects and their influence on the structure, magnetic and spectroscopic properties.
  • In the context of the ORCA Program Developer Group (F.Neese, F.Wennmohs): Suggestions for the improvement and further development of multireference correlation methods for the description and prediction of the magnetic and spectroscopic properties of complexes of transition metals, lanthanides and actinides.


Mihail Atanasov

Prof. Dr. Mihail Atanasov

2018
Group leader at the Max-Planck-Institut für Kohlenforschung
4/2017
Group leader *Molecular Magnetism* at the MPI CEC
2014-2017
Project leader *Molecular Magnetism* at the MPI CEC
2011-2014
Staff scientist at the MPI CEC
2010-2011
Guest professor at the University of Bonn
2009-2010
Guest professor at the Paul-Scherrer-Institut, Villigen, Schweiz
2005-2007
Guest professor at the University of Heidelberg
2004-2005
Guest professor at the University of Fribourg
1999-2004
Guest professor at the University of Marburg
1998
Guest professor at the University of Bern
1998
Guest professor at the University of Fribourg
seit 1996
Associate Professor at the Bulgarian Academy of Science
1996
Habilitation at the Institute of General and Inorganic Chemistry at the Bulgarian Academy of Sciences
1986-1996
Scientific coworker at the Institute of General and Inorganic Chemistry at the Bulgarian Academy of Sciences
1985-1986
Postdoc at the Institute for Theoretical Chemistry, Heinrich-Heine Universität, Düsseldorf
1984
Ph.D. (Chemistry) at the Institute of General and Inorganic Chemistry at the Bulgarian Academy of Sciences
1977
Diplom (Chemistry), University of Sofia, Bulgarien

 

  • Synthesis, Detailed Characterization, and Theoretical Understanding of Mononuclear Chromium(III)-Containing Polyoxotungstates [CrIII(HXVW7O28)2]13− (X = P, As) with Exceptionally Large Magnetic Anisotropy; LiuW.; Christian, J. H.; Al-Oweini, R.M.; Bassil, B.S.; vanTol, J.; Atanasov, M.; Neese, F.; Dalal, N. S.; Kortz, U.; Inorg. Chem. 2014, 53, 9274-9283.
  • Kβ Mainline X‑ray Emission Spectroscopy as an Experimental Probe of Metal−Ligand Covalency; Pollock, C.J.; Delgado-Jaime, M.U.; Atanasov, M.; Neese, F.; DeBeer, S.; J. Am. Chem. Soc.; 2014, 136, 9453-9463. 
  • Electronic Structures of Octahedral Ni(II) Complexes with “Click” Derived Triazole Ligands: A Combined Structural, Magnetometric, Spectroscopic, and Theoretical Study; Schweinfurth, D.; J. Krzystek, J.; Schapiro, I.; Demeshko, S.; Klein, J.; Telser, J., Ozarowski, A.; Su, C.-Y.;  Meyer, F.; Atanasov, M.; Neese,F.; Sarkar. B.; Inorg. Chem. 2013,52, 6880-6892.
  • Mössbauer Spectroscopy as a Probe of Magnetization Dynamics in the Linear Iron(I) and Iron(II) Complexes [Fe(C(SiMe3)3)2]1−/0; Zadrozny, J.M.; Xiao, D.J.; Long, J.R.; Atanasov, M.; Neese, F.; Grandjean, F.; Long, G.J.; Inorg. Chem, 2013, 52, 13123-13131.
  • Magnetic blocking in a linear iron(I) complex, Zadrozny, J.M.; Xiao, D.J.; Atanasov, M.; Long, G. J.; Granjean, F.; Neese, F.; Long, J.R. Nature Chemistry, 2013, 5, 577-581.  
  • A theoretical analysis of chemical bonding, vibronic coupling, and magnetic anisotropy in linear iron(II) complexes with single-molecule magnet behavior, Atanasov, M.; Zadrozny, J.M.;Long, J.R.; Neese, F.; Chem. Science, 2013, 139-156.
  • Slow magnetization dynamics in a series of two-coordinate iron(II) complexes; Zadrozny, J.M.;  Atanasov, M.; Bryan, A.M.; Lin, C.-Y.; Rekken, B.D.; Power, P.P.; Neese, F.; Long, Jeffrey R.; Chem. Science, 2013, 4,125-138.  
  • Zero-Field Splitting in a Series of Structurally Related Mononuclear NiII−Bispidine Complexes; Atanasov, M.; Comba, P.; Helmle, S.; Müller, D.; Neese, F.; Inorg. Chem. 2012, 51, 12324−12335.

Full publicationlist

Researchers discover previously unknown anion[U2F12] 2- in the compound Sr[U2F12]. The complex was characterized magnetically and spectroscopically.

Mihail Atanasov's team shows that quantum chemical methods implemented in the ORCA program allow the interpretation and prediction of magnetic and spectroscopic properties of uranium dimers. The results were published in issue 11 of March 5, 2018 in the"Angewandte Chemie Internationale Edition".

In this paper, the researchers at Philipps-Universität Marburg and the Department of Molecular Theory and Spectroscopy at the Max-Planck-Institut für Kohlenforschung in Mülheim describe their evidence and a detailed description of the previously unknown dinuclear[U2F12] 2- anion in the salt Sr[U2F12]. The anion has the special structure of a trigonal monocapped prism around each uranium (V) center, which could not be observed in complex anions with similar binding characteristics so far. The crystalline anion was first detected by X-ray analysis, its binding symmetry and other properties were precisely defined by the use of extended analytical instruments and the ORCA software. "The special thing about the theoretical side is our methodological expertise, which allowed us to fully describe this dimer," says Mihail Atanasov, who was involved in the work as group leader molecular magnetism. The simplicity of the proven structure could serve as a benchmark for further quantum chemical considerations of UV-UV interactions; further investigations of uranium complexes have already been started.

Research Topics

Molecular Magnetism
Molecular Magnetism

Molecular Magnetism

Molecular magnetism is a multidisciplinary field that combines synthesis of molecules with desired magnetic properties and theoretical analysis aiming at mechanistic understanding of the relation of these properties with the electronic structure. Spectacular advances in the development and implementation in the program ORCA of spin-dependent relativistic correlated electronic structure methods for larger systems by Prof. Dr. Frank Neese and his developer team supplied the infrastructure and serves as a firm theoretical basis for this project. The combination of experiment and theory on a one-to-one basis allows to both interpret and to predict (rationally design) magnetic properties of target magnetic materials. Molecular magnetism has a big impact on closely related disciplines such as molecular electronics and chemical reactivity (homogeneous and heterogeneous catalysis). The latter has been inspired by the action of transition metal spin centers at the active sites in enzymes such as the spitting of water on a four nuclear mixed-valence manganese complex (Photosystem II) and oxygen and hydrogen atom transfer in heme and non-heme high-valence iron enzymes leading to molecules for energy storage. All this motivated the creation in 2013 of a group on molecular magnetism at the institute. Basic tools in the work on this project have been: i) computational protocols allowing to extract magnetic and spin-Hamiltonian (SH) parameters from ab intio correlated wave functions [1a], and ii) an ab initio based ligand field theory (AILFT) that allows to relate the magnetic parameters with the nature of the metal-ligand bonds and the complex geometries [1b].

Open d- or f-shell transition metal or lanthanides and actinides in complexes  give rise to an unique response to an external magnetic field governed by the preferred alignments of their magnetic moments. This property is termed magnetic anisotropy. In axial symmetry this anisotropy is described by one parameter D which  quantifies  the zero-field splitting of the 2S+1 sublevels M ( -S<M<S )  of the spin S (E=DM2) of the non-relativistic ground state.  Magnetic anisotropy arises from coupling between orbital and spin angular momenta.  Below a given temperature (called the blocking temperature, TB) the resulting total angular momentum and its magnetization induced by an external magnetic  field  may persists after switching off  the field. The specific  life-time of  this magnetic state  -the  relaxation time depends on the magnitude of the orbital angular momentum and its coupling to its dissipative surrounding (thermal bath). Orbital momenta are maximal in atoms and ions with orbitally degenerate ground states, such as FeI 4F(d7) or FeII 2D(d6). However, because of their spherical symmetry, such orbital moments are isotropic.  Anisotropic magnetic moments are intrinsic for  molecules possessing axial (four of threefold) symmetries, which in addition, are in orbitally degenerate or nearly-denerate ground states. Spin-orbit coupling  introduces atomic like orbital moments which couple with the spin and this leads to an entirely anisotropic magnetization (Ising anisotropy).  This magnetization  is maximal along the axis of quantization  (the easy axis, D<0)  and (in weak magnetic fields) very small in directions perpendicular to it.

The project focuses on magnetic properties of transition metal complexes with open d-shells. Open d- or f-shell transition metal or a lanthanide complex can give rise to an unique response to an external magnetic field governed by the preferred alignments of their magnetic moments. This property is termed magnetic anisotropy. In axial symmetry this anisotropy is described by one parameter D which quantifies the zero-field splitting of the 2S+1 sublevels M ( -S≤M≤S ) of the spin S (E=DM2) within a given electronic state (normally the non-relativistic ground state). Magnetic anisotropy arises from coupling between orbital and spin angular momenta. Below a given temperature (called the blocking temperature, TB) the resulting total angular momentum and its magnetization induced by an external magnetic field may persist after switching off the field. The specific life-time of this magnetic state -the relaxation time depends on the magnitude of the orbital angular momentum and its coupling to its dissipative surrounding (thermal bath). Orbital momenta are maximal in atoms and ions with orbitally degenerate ground states, such as Co(II) 4F or Fe(II) 2D. However, because of the spherical symmetry, such orbital moments are isotropic and do not create magnetic anisotropies. Anisotropic magnetic moments are intrinsic for molecules possessing axial four of threefold symmetries, which in addition, are in orbitally degenerate ground states. First order spin-orbit coupling in such systems introduces atomic like orbital moments which couple with the spin and this leads to an entirely anisotropic magnetization. This magnetization is maximal along the axis of quantization (the easy axis, D<0) and (in weak magnetic fields) very small in directions perpendicular to it (Ising type anisotropy). A series of pseudo-tetrahedral Fe(II) complexes of this type has been theoretically predicted [1] by first principles calculations and synthesized and magnetically characterized [2,3] at about the same time (see Figure 1). These were shown to display slow relaxation of the magnetization and were termed single ion magnets (SIM). These discoveries opened a new field in magneto chemistry. The ultimate goal of the studies carried out within this project is to increase the blocking temperature and the relaxation time making such systems potential candidates for magnetic memory devices. Systems with magnetically bi stable ground states in molecules well isolated from their dissipative surroundings can also display quantum coherence and are therefore of potential interest in future quantum computers.

Based on the infrastructure given by the development and implementation of multi reference electronic structure methods in the ORCA program by Prof. Frank Neese and his group, we developed and tested computational protocols for first principles computations of the magnetic and spectroscopic properties of SIM which allow to both interpret and predict such phenomena [4]. We applied these tools to the interpretation of existing SIM and to assist rational design of novel ones with improved magnetic properties. We studied trigonal four coordinate (Figure 1, [4]) and pseudo linear two coordinate Fe(II) complexes (Figure 2, [5,6]) the latter displaying magnetic anisotropies on unprecedented size.

A fruitful scientific exchange with our collaborators (Prof. J. Long, Berkeley, USA) culminated in understanding of the magnetic properties of these class of compounds and the first SIM displaying a magnetic hysteresis and magnetic blocking temperature TB=4K (Figure 3) [7].

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  • Prof. Dr. Mihail Atanasov

    Prof. Dr. Atanasov, Mihail

    +49 (0)208 306 - 3886

    mihail.atanasov((atsign))kofo.mpg.de

     

  • Dr. Saurabh Kumar Singh

    Dr. Singh, Saurabh Kumar

    +49 (0)208 306 - 3886

    saurabh-kumar.singh((atsign))kofo.mpg.de

     

  • Dr. Willem Van den Heuvel

    Dr. Van den Heuvel, Willem

    +49 (0)208 306 - 3893

    willem.van-den-heuvel((atsign))kofo.mpg.de