Low-spin to low-spin valence tautomeric transition in cobalt bis-dioxolenes.

Cobalt dioxolenes are a well-known class of switchable coordination compounds showing intramolecular electron transfer, which is always accompanied by a spin state change at the cobalt center. Here, we present the first example of thermally switchable cobalt bis-dioxolenes where intramolecular electron transfer seems to take place, but the spin state change is suppressed. This leads to the detection of thermal transition between a common ls-Co III (SQ˙ - )(Cat 2- ) and an extremely rare ls-Co II (SQ˙ - ) 2 electronic state (hs - high-spin, ls - low-spin, SQ˙ - - benzosemiquinonate(1-) radical and Cat 2- - catecholate(2-)). Parallel to the present work, a similar work but on cobalt mono -dioxolenes has just appeared ( Chem. Eur. J. , 2023, 29 , e202300091), suggesting thermal transition between ls-Co III (Cat 2- ) and ls-Co II (SQ˙ - ) electronic states.