# Switchable Valence States in Dinuclear Cobalt Complexes: The Role of Halogenated Catecholates and Counterions

## TL;DR

This paper explores how different ligands and counterions affect the valence states and magnetic properties of dinuclear cobalt complexes.

## Contribution

The study demonstrates how electron-deficient ligands and counterions can tune cobalt valence tautomerism and redox behavior.

## Key findings

- Sulfate-based complexes show thermally induced valence tautomerism above room temperature.
- Electron-deficient tetrahalogenated catecholates stabilize the low-spin state of cobalt complexes.
- Counterions and solvent molecules influence intermolecular interactions in the solid state.

## Abstract

We present the synthesis and comprehensive characterization
of
a series of eight dinuclear cobalt complexes, C1–C8, with the general formula [Co2(L)­(X4cat)2]2+(A)1–
2, wherein X = Br or Cl, A = SO4
2–, ClO4
–, PF6–, or
B­(Ph)4
–, and L denotes a
redox inactive bis-tetradentate bridging ligand. Single-crystal X-ray
diffraction at 120 K confirms a low-spin Co­(III) configuration in
all compounds. SQUID magnetometry also shows that the complexes remain
diamagnetic below room temperature. However, the complexes bearing
sulfate anions, C1 and C5, exhibit a distinct
thermally induced valence tautomeric transition above room temperature,
marked by an increase in magnetic moment. The temperature of this
transition is strongly influenced by the electronic properties of
the catecholate (cat) ligands, with electron-deficient tetrahalogenated
catecholates stabilizing the low-spin state. In addition, counterions
and solvent molecules are found to modulate intermolecular interactions
in the solid state. Comparative cyclic voltammetry with previously
reported ditert-butyl catecholate (dbucat) complex C9 highlights the influence of ligand electronics on redox
potentials, with electron-deficient catecholates shifting redox processes
to higher potentials. These results highlight the tunability of cobalt
valence tautomerism and redox behavior through strategic ligand and
counterion selection.