# Solvatochromism and Redox Multi‐Switch in a Trinuclear Cobalt(II) Complex

## TL;DR

A new cobalt complex with a special ligand shows multiple redox states and color changes, enabling advanced magnetic and optical switching.

## Contribution

The study introduces a trinuclear cobalt(II) complex with enhanced redox and solvatochromic properties due to ligand field tuning.

## Key findings

- The complex exists in two redox states enabled by solvatochromism.
- Six reversible one-electron processes are achieved through ligand field tuning.
- Redox processes involve the HHTP ligand and possibly the Co(II) centers.

## Abstract

A trinuclear cobalt(II) complex incorporating the redox‐active hexahydroxytriphenylene (H6HHTP) ligand was prepared and isolated in two different redox states: [CoII
3(sq‐sq‐sq)]3+ (1) and [CoII
3(cat‐sq‐sq)]2+ (2) (sq = semiquinone; cat = catecholate), enabled by its remarkable solvatochromic behavior. The ligand field tuning of the Co(II) centers through the ancillary ligand Me3TPA (tris(6‐methyl‐2‐pyridylmethyl)amine) allowed accessing six reversible one‐electron processes instead of only three with the parent TPA ligand, therefore increasing the range of redox‐coupled magnetic and optical switching in this system. Upon reduction, the three redox processes are ligand‐centered and involve the three sq•−/cat2− couples of hexahydroxytriphenylene (HHTP), while we hypothesize that some of the oxidation processes may involve the Co(II) metallic species.

A trinuclear cobalt(II) complex incorporating the redox‐active H6HHTP ligand is isolated in two redox states: [CoII3(sq‐sq‐sq)]3+ and [CoII3(cat‐sq‐sq)]2+ (sq = semiquinone; cat = catecholate), enabled by its remarkable solvatochromic behavior. The ligand field tuning of the Co(II) centers through the ancillary ligand allows accessing six reversible one‐electron processes, increasing the range of redox‐coupled magnetic and optical switching in this system.