A linear cobalt(II) complex with maximal orbital angular momentum from a non-Aufbau ground state

Area of Science:

• Inorganic Chemistry
• Materials Science
• Quantum Mechanics

Background:

• Orbital angular momentum is crucial for magnetic anisotropy in transition metal complexes.
• Typically, the ligand field in these complexes quenches orbital angular momentum.
• Understanding these properties is key to designing novel magnetic materials.

Purpose of the Study:

• To synthesize a cobalt(II) complex with a weak ligand field.
• To investigate the role of interelectron repulsion and spin-orbit coupling in determining the electronic ground state.
• To explore magnetic anisotropy and relaxation dynamics in this unique complex.

Main Methods:

• Synthesis of a cobalt(II) dialkyl complex, Co(C(SiMe2ONaph)3)2, featuring reduced basicity alkyl ligands.
• Characterization using dc magnetic susceptibility, experimental charge density mapping, and ab initio calculations.
• Analysis of magnetic relaxation via variable-field far-infrared spectroscopy and ac magnetic susceptibility measurements.

Main Results:

• A weak ligand field was achieved in the cobalt(II) complex, allowing orbital angular momentum to persist.
• A non-Aufbau electron configuration (dxy)3(dxz,dyz)3(dz2)1 was assigned, supported by experimental and computational data.
• Slow magnetic relaxation was observed, attributed to a magnetic excited state at 450 cm-1.

Conclusions:

• The synthesized cobalt(II) complex demonstrates the importance of weak ligand fields for magnetic anisotropy.
• The study highlights the dominant roles of interelectron repulsion and spin-orbit coupling in this system.
• The findings provide insights into the design of molecular magnets with tailored magnetic relaxation properties.