Heterometallic Ru₂Co₂ [2 × 2] Grid with Localized Single Molecule Magnet Behavior

Area of Science:

• Coordination Chemistry
• Materials Science
• Molecular Nanotechnology

Background:

• Gridlike metal complexes are crucial building blocks in materials chemistry, particularly for molecular nanotechnology and electronics.
• While homometallic grids are common, heterometallic grids offer enhanced functionalities but are synthetically challenging.
• Existing heterometallic [n × n] grids are rare due to complex synthesis.

Purpose of the Study:

• To synthesize and characterize a new heterometallic [2 × 2] grid complex.
• To investigate the magnetic and redox properties of the synthesized complex and its oxidized form.
• To explore the potential of this heterometallic grid as a single-molecule magnet.

Main Methods:

• Stepwise synthesis involving an inert Ruthenium(II) precursor followed by Cobalt(II) addition to prevent metal scrambling.
• Single crystal X-ray diffraction for structural confirmation of the [2 × 2] grid with anti-topology.
• 1H NMR spectroscopy and ESI mass spectrometry to confirm grid integrity in solution.
• Magnetic susceptibility measurements and analysis of zero-field splitting to determine magnetic properties.

Main Results:

• Successful synthesis of the heterometallic [2 × 2] grid complex [L4Ru2Co2](BF4)4 (2) and its oxidized congener [L4Ru2Co2](BF4)6 (3).
• Structural analysis confirmed the desired anti-topology with Ruthenium(II) and Cobalt(II) ions at opposite corners.
• Complex 2 exhibits low-spin Ruthenium(II) and high-spin Cobalt(II) ions, while complex 3 contains low-spin Ruthenium(II) and low-spin Cobalt(III) ions.
• Complex 2 displays single-molecule magnet (SMM) behavior with a significant axial zero-field splitting (D = -64 cm-1), a spin inversion barrier (Ueff = 8.8 cm-1), and a single relaxation process.

Conclusions:

• A novel heterometallic 3d/4d [2 × 2] grid complex has been synthesized using a controlled stepwise approach.
• The complex demonstrates unique magnetic properties, including single-molecule magnet behavior, which is rare for such systems.
• This work presents the first heterometallic 3d/4d grid system exhibiting SMM characteristics, highlighting its potential in advanced materials and molecular magnetism.