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Air-Stable Chiral Four-Coordinate Cobalt(II) Guanidinium BINOLate Single-Molecule Magnets
Tingting Feng1,2, Xu Ying1,3, Chun-Yang Gu4
1State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China.
Inorganic Chemistry
|May 25, 2026
Summary
New cobalt(II) complexes with enhanced air stability exhibit distinct magnetic properties. These compounds function as single-molecule magnets, offering insights into designing stable magnetic materials.
Area of Science:
- Coordination Chemistry
- Materials Science
- Magnetochemistry
Background:
- Development of air-stable mononuclear cobalt(II) complexes is crucial for advancing molecular magnetism.
- Tuning ligand substituents significantly impacts the geometry and magnetic properties of coordination compounds.
- Four-coordinate cobalt(II) complexes with a CoO4 motif are of interest for single-molecule magnet applications.
Purpose of the Study:
- To construct enantiopure mononuclear cobalt(II) complexes with a CoO4 coordination motif using BINOLate ligands.
- To investigate the effect of different substituents on BINOLate ligands on the molecular geometry and magnetic anisotropy.
- To evaluate the single-molecule magnet behavior of the synthesized cobalt(II) complexes.
Main Methods:
- Synthesis of two pairs of enantiopure mononuclear Co(II) complexes: (S/R-F2BINOL)2Co[TMG-H+]2 (S/R-Co-F) and (S/R-N2BINOL)2Co[TMG-H+]2 (S/R-Co-N).
- Characterization of structural differences, including dihedral and bite angles, influenced by ligand substituents.
- Magnetic property measurements and theoretical calculations (CASSCF/RASSI-SO) to determine magnetic anisotropy and zero-field splitting (ZFS) parameters.
Main Results:
- The introduction of TMG-H+ cations enhanced air stability through intramolecular hydrogen bonding.
- S/R-Co-F exhibited a distorted tetrahedral geometry, while S/R-Co-N displayed a distorted seesaw geometry due to bulkier naphthyl substituents.
- Distinct magnetic anisotropies were observed: S/R-Co-F showed easy-plane anisotropy, and S/R-Co-N displayed easy-axis anisotropy, confirmed by ZFS parameter D.
- Both S/R-Co-F and S/R-Co-N demonstrated single-molecule magnet behavior with varying effective energy barriers.
Conclusions:
- The study successfully synthesized air-stable four-coordinate Co(II) complexes with tunable magnetic properties.
- Ligand design, specifically the substituents at the 3,3'-positions of BINOLate, plays a critical role in controlling molecular geometry and magnetic anisotropy.
- These findings provide valuable insights for the rational design of novel air-stable single-molecule magnets based on cobalt(II) complexes.
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