Quantum Chemical Calculations on the Electronic Structure an Magnetism of Heterometallic Multinuclear Complexes and Clusters

Based on quantum chemical calculations, we shall develop concepts for a rational design of transition metal compounds with high magnetic Anisotropy, high spin and strong exchange couplings.

To this end, the different properties of light and heavy transition metals cooperate within multinuclear heterometallic transition metal complexes. We will focus on structural motifs which are amenable to experimental realization (synthesis). Smaller model systems allow for wave function based ab initio calculations which will be useful for the validation and calibration of density functional approaches that have to be used for the very large systems.

Electronic Theory of Magnetic Multicenter Complexes as Logic-Elements

In today's computers only hard disks are magnetic. Substituting optical spin manipulation for conventional semiconductor technology in processors and main memory can increase information density and speed. The goal of the present project is to theoretically investigate two-, three- and four-center molecular systems with Ni, Co and/or Fe as electronically and magnetically active centers using quantum-mechanical wavefunction methods, with regard to (a) geometrical structure, (b) electronic-level schemes, (c) optically induced spin flip and spin transfer, and (d) functionalization.

Di- to Tetranuclear Compounds Incorporating Highly Anisotropic Paramagnetic Metal Ions

The aim of this project is to synthesise and characterise small coordination clusters with two to four metal centres as well as metal/radical systems showing cooperativity resulting from the presence of mobile electrons subject to very strong orbital contributions. Highly anisotropic molecular systems have largely been avoided because of the inherent difficulties in quantifying the magnetic and electronic behaviour. However, anisotropic molecular systems can show highly interesting physical properties, such as the observation of single-molecule magnet (SMM) behaviour and molecular-based double-exchange phenomena. The project will provide theoretical chemists and physical experimentalists with completely new systems with challenging electronic structures.

Conventional and Synchrotron-Based Mössbauer Spectroscopy of Oligonuclear Spin Crossover Complexes

The aim of the project is to prepare new oligonuclear spin crossover(SCO) iron complexes and to study their interaction with light. The focus of the project is the development of potential molecular switches on the basis of SCO processes, also in combination with valence tautomerism. Of special interest is the investigation of the influence between the SCO and non-SCO metal centers in these complexes (cooperativity). For the characterization of the magnetic and dynamic properties of their ground states and their light induced excited states conventional as well as synchrotron-based Mössbauer-Spectroscopy will be used. 

Magnetism of Isolated Multinuclear Transition Metal Complexes within Ion Traps

Spin and orbit momenta of trinuclear cobalt complexes, of ligand stabilized manganese complexes, and of endohedral silicon cages [Co₂@Si_16+x ]⁺ shall determine from X-ray induced magnetic circular dichroism (XMCD, GAMBIT experiment at BESSY). A complementary view arises from vibrational spectra through infrared induced multi photon dissociation (IR-MPD) and from adsorption-desorption equilibria under single collision conditions (FRITZ experiment at the RPTU). Rotationally resolved IR-MPD spectra allow for exact temperature calibration.