Pyrrolyl-Bridged Metallocene Complexes: From Synthesis, Electronic Structure, to Single-Molecule Magnetism

Area of Science:

• Coordination Chemistry
• Organometallic Chemistry
• Materials Science

Background:

• The pyrrolyl ligand exhibits diverse coordination modes due to its π- and σ-basicity.
• Sterically demanding coordination environments can induce novel ligand behaviors.
• Rare earth metal complexes are of interest for their unique electronic and magnetic properties.

Purpose of the Study:

• To synthesize and characterize new dinuclear rare earth complexes with pyrrolyl ligands.
• To investigate the coordination modes of the pyrrolyl ligand in sterically hindered environments.
• To explore the magnetic properties of these novel complexes, particularly for single-molecule magnet applications.

Main Methods:

• Protonolysis reaction between allyl complexes and H-pyrrole.
• X-ray crystallography for structural determination.
• Electrochemical and spectroscopic characterization (UV-Vis, IR, NMR).
• Density Functional Theory (DFT) and Complete Active Space Self-Consistent Field (CASSCF) calculations.

Main Results:

• Three dinuclear rare earth complexes, [Cp*₂RE(μ-pyr)]₂ (RE = Y, La, Dy), were successfully synthesized.
• An unprecedented asymmetric coordination mode of the pyrrolyl ligand, [((η⁵-Cp*)₂RE)₂(μ-1η²-pyr-2κN)(μ-2η²-pyr-1κN)], was observed and structurally confirmed.
• Complex 3 (Dy) demonstrated slow magnetic relaxation under zero dc field, characteristic of single-molecule magnets, with U_eff = 98.9(7) cm^-1 and τ_o = 6.7(1) × 10^-8 s.
• DFT and CASSCF calculations provided insights into the electronic structure and magnetic properties.

Conclusions:

• Steric pressure from pentamethylcyclopentadienyl (Cp*) ligands dictates the unusual coordination of the pyrrolyl ligand in these dinuclear rare earth complexes.
• The synthesized dinuclear dysprosium complex represents a promising new addition to the field of single-molecule magnets.
• This work expands the understanding of rare earth coordination chemistry and the development of advanced magnetic materials.