Kc K, Woods T, Olshansky L. Ligand Modifications Produce Two-Step Magnetic Switching in a Cobalt(dioxolene) Complex.
Angew Chem Int Ed Engl 2023;
62:e202311790. [PMID:
37733206 PMCID:
PMC10615740 DOI:
10.1002/anie.202311790]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2023] [Revised: 09/20/2023] [Accepted: 09/21/2023] [Indexed: 09/22/2023]
Abstract
Mononuclear monodioxolene valence tautomeric (VT) cobalt complexes typically exist in their low spin (l.s.) CoIII (cat2- ) and high spin (h.s.) CoII (sq⋅- ) forms (cat2- =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. CoII (sq⋅- ). Thus, our ligand modifications not only provide access to the VT transition from l.s. CoIII (cat2- ) to l.s. CoII (sq⋅- ), but at higher temperatures, the complex undergoes spin crossover from l.s. CoII (sq⋅- ) to h.s. CoII (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. CoII (sq⋅- ) intermediate state, suggesting a new design criterion in the development of stimulus-responsive multi-state molecular switches.
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