Synthesis and spin structure of trinuclear metal complexes with bridging ligands based on the triaminoguanidine framework

• Applicant: Professor Dr. Winfried Plass
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 549658201

The project aims to develop new magnetic molecules with spin structures useful for spintronics applications. In this context, spin-frustrated systems and complexes with competing magnetic exchange interactions have been proposed as suitable candidates. A key advantage of such molecular nanomagnets is the potential interaction of their spin structure with electric fields, a unique property that is particularly attractive since electric fields can be applied with much higher spatial precision than magnetic fields. Therefore, one of the primary goals of this project is to generate examples of corresponding nanomagnets to experimentally demonstrate that the spin structure can be influenced by electric fields, even without the need for additional contributing effects such as spin-orbit coupling. Previous results have shown that triaminoguanidine-based ligands with their rigid threefold molecular symmetry represent a perfect bridging framework for the efficient transfer of magnetic exchange interactions. On this basis, we propose to use this bridging unit for the synthesis of new triangular nanomagnets to investigate (i) the influence of the electronic configuration of the transition metal ions used and (ii) the possibility of generating higher nuclear aggregates with competing magnetic interactions between the spin centers. The use of electron-poor transition metal ions should lead to ferromagnetic interactions within the triangular assemblies and thus provide a basis for new molecules with a high spin ground state, while the systems with competing magnetic exchange should show the desired spin-electric effects. To investigate the latter, non-standard techniques for the inclusion of electric fields in ESR spectroscopy will be implemented by in-house developed solutions and used to characterize the new compounds. Since the absence of crystallographic inversion symmetry is a prerequisite for the observation of spin-electric effects on single crystals by electric-field-modulated (EFM) ESR spectroscopy, we will investigate ways for the deliberate generation of acentric crystals. A complete magnetic characterization of the new compounds will be performed, that besides ESR spectroscopy includes the full set magnetic susceptibility and magnetization measurements. Additional insights into the electronic structure of the new compounds will be gained through quantum mechanical calculations. The molecular nanomagnets synthesized in this project offer options for fundamentally new approaches in molecular spintronics through the possible interaction of their spin structure with electric fields.

• DFG Programme: Research Grants