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Structure, Stability, and Spin Resonance in Dicopper(II) Complexes
Ökten Üngör1, Nicholas Yiching Chiang1, Alexander Yu Sokolov1
1Department of Chemistry and Biochemistry, The Ohio State University, Columbus, Ohio 43210, United States.
Inorganic Chemistry
|July 6, 2026
Summary
This study explores dinuclear copper(II) complexes for quantum information science. Researchers found that varying ligands and counterions robustly tune magnetic properties, offering insights for designing molecular spin systems.
Area of Science:
- Coordination Chemistry
- Quantum Information Science
- Magnetochemistry
Background:
- Designing molecular systems for quantum sensing and information science requires accessing entangled spin states.
- Spin-forbidden transitions are crucial for these applications but remain a significant challenge in molecular design.
Purpose of the Study:
- To investigate a family of dinuclear copper(II) complexes, [L₂Cu₂(μ-CA)]X₂, to understand how ligand and counterion variations influence their spin states and magnetic properties.
- To explore the potential of these complexes as platforms for quantum sensing and information science.
Main Methods:
- Systematic variation of cyclic (Me₃tacn, tmchd) and polypyridyl ligands (4'-Br/Cl-terpy, tpa), along with counteranions (ClO₄⁻, CF₃SO₃⁻, Cl⁻).
- Structural analysis using X-ray diffraction.
- Magnetic susceptibility measurements to determine exchange coupling and singlet-to-triplet energy gaps.
- Electron Paramagnetic Resonance (EPR) spectroscopy, including low-temperature and frozen-solution EPR, to study spin states and transitions.
- Comparison with mononuclear analogues.
- Multireference calculations to model g-anisotropy.
Main Results:
- Distorted octahedral to trigonal-bipyramidal Cu(II) environments were observed.
- Moderate antiferromagnetic coupling was established, with singlet-to-triplet energy gaps ranging from 2J = -1.26 to -30.68(3) cm⁻¹.
- Well-resolved half-field (ΔMs = ±2) transitions in the S = 1 manifold were observed in EPR spectra.
- The dinuclear core structure ([L₂Cu₂(μ-CA)]²⁺) was confirmed to persist in frozen solutions.
- A robust magnetic core was identified, showing resilience to changes in counterions and ligand shells.
- Subtle influences of chemical modifications on the intensity of forbidden ΔMs = ±2 transitions were noted.
- A remarkable absence of the singlet/triplet transition was observed.
Conclusions:
- The study demonstrates that systematic chemical modifications of dinuclear copper(II) complexes can tune their magnetic properties, including exchange coupling and EPR spectral features.
- The identified robust magnetic core provides a stable platform for further development in molecular quantum technologies.
- The absence of the singlet/triplet transition offers valuable insights for future molecular design strategies aimed at controlling spin dynamics and accessing specific entangled states.
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