Innovative Sulfur-Nitrogen Ligands for Promising Ln3+ Single Molecule Magnets

• Applicant: Professor Dr. Dietmar Stalke
• Subject Area: Inorganic Molecular Chemistry - Synthesis and Characterisation
• Term: from 2019 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 419278547

The main objective of the proposal is the synthesis and characterisation of lanthanide organometallic SMM complexes comprising sulfur-nitrogen ligands together with a deeply-rooted X-ray and neutron diffraction based charge and spin density investigation. We will synthesize, characterize, structurally and magnetically investigate f-element complexes containing the sulfur-centred polyimido ligands S(NR)32–, S(NR)42–, RS(NR)2–, RS(NR)3–, (R2C)S(NR)22–, and (R2C)S(NR)32–. The ligand portfolio will be completed by the scorpionates Ph2PCH2S(NR)2–, Ph2PCH2S(NR)3– and (NR)2SCH2Py–, (Py = 2-pyridyl). Easy adaptable N-S-N bond angels together with the soft sulfur atom promise large magnetic anisotropy and slow magnetic relaxation, inevitable for good SMMs. In addition to these mono- and dianionic ligands we will employ our radical monoanionic S(NR)3•– ligand to evaluate how much of the spin density is metal- and ligand-centred and what the effect is on the magnetic properties. This of course should matter in the design of SMMs. Currently from the EPR spectra we know the radical to be N-centred and certainly will affect the spin density at the lanthanide atom. As metal sources we will use the lanthanide trihalides LnHal3, Ln = Gd, Tb, Dy, Ho, Er, triacetylacetonates Ln(acac)3 and triamides Ln{N(SiMe3)2}3. The structural determinations and investigations concerning the localisation of electrons in the proposed compounds will go far beyond the classical single crystal structure analysis. We will investigate them from high-resolution diffraction data and their structures will be modelled along the multipole model. Their properties will be analysed along the quantum theory of atoms in molecules. In addition to the electron density determination we plan to experimentally determine the spin density. Hence we need to employ neutron diffraction, either to determine the nuclei position precisely and to determine the magnetic moment. This will hopefully be facilitated from polarised neutron diffraction experiments. The determined charge density enables the direct deduction of physically meaningful atomic and bond properties. Further chemical and physical properties like the reactive surface and the electrostatic potential are accessible, crucial for the design of building blocks to give SMMs. To conclude we got the ligands and the methods in hand to further develop that most fruitful field.

• DFG Programme: Research Grants