(Half-)Sandwich Complexes as Valence Tautomeric Spin Switches

• Applicant: Professor Dr. Rainer Winter
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 557181785

The aim of the project “(Half-)Sandwich Complexes as Valence Tautomeric Spin Switches” is the synthesis and comprehensive characterization of dyads composed of the organometallic donors ferrocene or cymantrene [C5H4-nRn)Mn(CO)3-m(PR3)m] (n = 0-4,; m = 0, 1, 2) and triarylmethylium acceptors. These are designed in such a way that they exist as mixtures of two different isomers (so-called valence tautomers), of which the isomer Donor-Linker-CAr2+ is diamagnetic, whereas the other isomer Donor•+ -Linker-CAr2• is paramagnetic and has an unpaired spin on each of the two redox-active subunits. This makes such dyads spin-state switches whose magnetic properties can be reversibly altered by an external stimulus. Such systems are of great current interest with regard to applications in spintronics. To achieve this, a fine balancing of the intrinsic redox potentials of the two chemically different redox-active units is required. Conceptually, this can be achieved by varying the substituents on the triarylmethylium acceptor and the coligands on the organometallic donor moiety.On the way to stable, easy-to-characterize complexes with balanced ratios between the two possible isomers, we have to master the following challenges: i) maximizing electronic decoupling between donor and acceptor; ii) preventing the dimerization of the paramagnetic isomer with formation of a C-C bond between the trityl radicals; iii) increasing their general chemical stability; iv) making them amenable to the broadest possible methodological arsenal for the quantitative analysis of the equilibria between the valence tautomers. We will address these challenges in subproject 1 by separating the donor and acceptor via sterically demanding anthryl or triptycenediyl linkers. These linkers disrupt conjugation by inducing strong twisting between the donor and acceptor units and prevent dimerization. In subproject 2 we will replace the ferrocenyl donor with electron-rich half-sandwich complexes of the cymantrene type. The cymantrene donors will provide us with a straightforward means for simple quantitative analysis of the valence tautomerism equilibria using IR spectroscopy, since the positions of the CO stretching bands in the Mn0 and MnI forms differ significantly from each other. Furthermore, particularly electron-rich donor units of this type allow the use of weaker triarylmethylium acceptors, which increases the stability of such dyads.

• DFG Programme: Research Grants
• Major Instrumentation: leistungsfähiger Kryostat
• Instrumentation Group: 8520 Kryostaten, Tauchkühler (bis -100 Grd C)