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In complexation reactions, metal cations are the electron pair acceptors, and the ligands are the electron pair donors. The stability of the metal complexes depends primarily on the complexing ability of the central metal ion and the nature of the ligands. Generally, the complexing ability of the metal ion depends on the size and charge of the ion. As the metal ion size increases, the stability of the metal complexes decreases, provided that the valency of the metal ion and the ligands remain...
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Ligand Modifications Produce Two-Step Magnetic Switching in a Cobalt(dioxolene) Complex.

Khadanand Kc1, Toby Woods2, Lisa Olshansky1

  • 1Department of Chemistry, Center for Biophysics and Quantitative Biology, Materials Research Laboratory, University of Illinois, Urbana-Champaign, Urbana, Illinois, 61801, USA.

Angewandte Chemie (International Ed. in English)
|September 21, 2023
PubMed
Summary

Researchers developed a new cobalt complex with a modified ligand, enabling two-step magnetic switching. This breakthrough offers a third magnetic state and potential for advanced molecular switches.

Keywords:
Cobalt DioxoleneMolecular SwitchSpin CrossoverValence Tautomerism

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Area of Science:

  • Coordination Chemistry
  • Materials Science
  • Molecular Magnetism

Background:

  • Mononuclear cobalt complexes with monodioxolene ligands exhibit valence tautomerism (VT) between low-spin (l.s.) CoIII (catecholato) and high-spin (h.s.) CoII (seminquinonato) states.
  • The tetradentate ligand framework typically supports these states, influencing the temperature of the VT transition.
  • Accessing intermediate magnetic states in these systems is challenging.

Purpose of the Study:

  • To investigate the effect of ligand modification on the magnetic properties of mononuclear monodioxolene cobalt complexes.
  • To explore the possibility of accessing new magnetic states beyond typical valence tautomerism.
  • To develop novel multi-state molecular switches.

Main Methods:

  • Synthesis and characterization of novel cobalt complexes featuring a modified tetradentate ligand (tris(2-pyridylmethyl)amine with an ortho-anisole moiety).
  • Variable temperature crystallographic, magnetic, calorimetric, and spectroscopic studies.
  • Analysis of electron transfer and spin crossover phenomena.

Main Results:

  • A third magnetic state, consistent with l.s. CoII (seminquinonato), was accessed by modifying the ligand.
  • The modified complex exhibits a two-step magnetic switching behavior: VT from l.s. CoIII (catecholato) to l.s. CoII (seminquinonato), followed by spin crossover from l.s. CoII (seminquinonato) to h.s. CoII (seminquinonato).
  • This represents the first observation of two-step magnetic switching in a mononuclear monodioxolene cobalt complex.

Conclusions:

  • Ligand design, specifically incorporating flexibility or weaker field moieties, can facilitate access to rarely observed intermediate magnetic states.
  • The observed two-step magnetic switching behavior highlights a new pathway for creating advanced stimulus-responsive molecular switches.
  • Ligand dynamicity is proposed as a key factor in accessing the l.s. CoII state, suggesting a new design criterion for molecular switches.