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Magnetic Exchange Coupling in Transition Metal Complexes

The magnetic properties of bridged bi- and polynuclear transition metal complexes are characterized by
  1. the exchange coupling constant J, which describes the coupling of the spins at the transition metal ions
  2. the g tensor, which describes the splitting of degenerate electronic levels in external magnetic fields
  3. the zero-field splitting tensor D, which contains information on local anisotropies and spin-orbit interactions
Experimentally, most bi- and polynuclear transition metal complexes exhibit antiferromagnetic coupling (J<0), but ferromagnetic (J>0) and paramagnetic coupling (J=0) is also observed. Several mechanisms contribute to the exchange interaction: direct exchange, superexchange, double exchange.

We use our wavefunction based quantum chemical ab initio program package (ROHF, CAS-SCF, CAS-CI, SOC-CI, MC-CEPA) to calculate the energy levels of the transition metal compounds. Electron correlation effects and spin-orbit interactions are included if necessary. From the calculated energy levels and their splitting in external magnetic fields, the parameters J, g, D can be derived. Alternatively, the magnetic susceptibility of the complex can be directly calculated as a function of the temperature.

Similar studies are also performed for transition metal oxides and for Fe2S2 clusters in biological molecules. In combination with molecular dynamics simulations this provides a detailed understanding of the magnetostructural dynamics in such systems.

Recent publications in this field:
Nr. 157,161,166,167 in Volker Staemmler's list of publications .


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