Ligand Modifications Produce Two‐Step Magnetic Switching in a Cobalt(dioxolene) Complex
Khadanand KC, Toby J. Woods, Lisa Olshansky
Abstract
Abstract Mononuclear monodioxolene valence tautomeric (VT) cobalt complexes typically exist in their low spin (l.s.) Co III (cat 2− ) and high spin (h.s.) Co II (sq⋅ − ) forms (cat 2− =catecholato, and sq⋅ − =seminquinonato forms of 3,5−di− t Bu‐1,2‐dioxolene), which reversibly interconvert via temperature‐dependent intramolecular electron transfer. Typically, the remaining four coordination sites on cobalt are supported by a tetradentate ligand whose properties influence the temperature at which VT occurs. We report that replacing one chelating pyridyl arm of tris(2‐pyridylmethyl)amine (tpa) with a weaker field ortho ‐anisole moiety facilitates access to a third magnetic state, and examine a series of related complexes. Variable temperature crystallographic, magnetic, calorimetric, and spectroscopic studies support that this third state is consistent with l.s. Co II (sq⋅ − ). Thus, our ligand modifications not only provide access to the VT transition from l.s. Co III (cat 2− ) to l.s. Co II (sq⋅ − ), but at higher temperatures, the complex undergoes spin crossover from l.s. Co II (sq⋅ − ) to h.s. Co II (sq⋅ − ), representing the first example of two‐step magnetic switching in a mononuclear monodioxolene cobalt complex. We hypothesize that ligand dynamicity may facilitate access to the rarely observed l.s. Co II (sq⋅ − ) intermediate state, suggesting a new design criterion in the development of stimulus‐responsive multi‐state molecular switches.