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Preparation, Purification, and Characterization of Lanthanide Complexes for Use as Contrast Agents for Magnetic Resonance Imaging
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Magnetic Blocking in Fluoflavine Radical-Bridged Dilanthanide Complexes
Florian Benner1, Saroshan Deshapriya1, Jakub Hrubý2
1Department of Chemistry, Michigan State University, East Lansing, Michigan 48824, United States.
Journal of the American Chemical Society
|December 10, 2025
Summary
Researchers developed new lanthanide (Ln) complexes with radical bridges, creating the first single-molecule magnets (SMMs) with radicals in distinct oxidation states. Complex 3-Dy shows record magnetic blocking temperatures for SMMs with organic radical bridges.
Area of Science:
- Coordination Chemistry
- Materials Science
- Magnetism
Background:
- Fostering magnetic exchange coupling in lanthanide (Ln) complexes is challenging due to weak interactions via closed-shell ligands.
- Open-shell ligands enhance coupling, leading to single-molecule magnets (SMMs) with potential for magnetic memory.
- The effect of radical bridges in different oxidation states on magnetic blocking in Ln SMMs remains unexplored.
Purpose of the Study:
- To synthesize and characterize novel dilanthanide complexes featuring fluoflavine (flv) radical bridges in distinct oxidation states.
- To investigate the magnetic properties, particularly single-molecule magnet behavior, of these complexes.
- To explore the influence of radical bridge oxidation states on magnetic blocking and SMM performance.
Main Methods:
- Synthesis of dilanthanide complexes with fluoflavine bridges in z=1-•, z=2-, and z=3-• oxidation states.
- Structural characterization using single-crystal X-ray diffraction (SCXRD).
- Magnetic property measurements including SQUID magnetometry and high-field electron paramagnetic resonance (HF-EPR) spectroscopy.
- Computational analysis using broken-symmetry density functional theory (BS-DFT).
Main Results:
- First report of dilanthanide complexes with fluoflavine radical bridges in two distinct oxidation states (flv1-• and flv3-•).
- Complexes 1-Dy and 3-Dy are the first SMMs incorporating radicals in differing oxidation states.
- Complex 3-Dy exhibits a significantly enhanced spin-reversal barrier (Ueff = 143(2) cm-1) and record magnetic hysteresis up to 9.5 K for dilanthanide SMMs with organic radical bridges.
- Complex 1-Dy shows a Ueff of 28.36 cm-1 with hysteresis below 3 K.
Conclusions:
- The study demonstrates the successful synthesis of dilanthanide complexes with tunable radical bridges, enabling the creation of advanced SMMs.
- The oxidation state of the radical bridge critically influences SMM performance, with the flv3-• bridge yielding superior magnetic blocking properties.
- The enhanced performance in 3-Dy is attributed to spin-phonon coupling and optimized frontier orbital structure, paving the way for rational design of polynuclear Ln SMMs.
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