Tuning the magnetic properties of dinuclear cobalt-tetraoxolene compounds: from valence tautomerism to ferromagnetic coupling

The reaction of a non-innocent ligand 2,7-di-tert-butyl-pyrene-4,5,9,10-tetraone (pyreneQ-Q, Q = quinone), Co2(CO)8, and tris(2-pyridylmethyl)amine derivatives (Mentpa) gave rise to a series of dinuclear cobalt-tetraoxolene compounds formulated as {[Co(Mentpa)]2(pyreneSq-Sq)}[Co(CO)4]2 center dot S (Sq = semiquinone; n = 0, S = 2C6H5CH3 for 3; n = 1 for 4; n = 2, S = 2CHCl3 for 5). Magnetic measurements and single-crystal X-ray diffraction studies revealed that compound 3 underwent incomplete valence tautomeric transition, while compounds 4 and 5 maintained in the steady electronic structure of {CoII-HS-pyreneSq-Sq-CoII-HS} in the whole temperature range. Remarkably, strong ferromagnetic interactions in both 4 and 5 were confirmed by experimental and theoretical studies. Theoretical calculations showed that the successive introduction of methyl groups enhanced the steric rigidity of tpa, and hence the {CoII-HS-pyreneSq-Sq-CoII-HS} state was stabilized sterically and electronically, which in turn altered the energetic order and gap among the different electronic states, which resulted in distinct magnetic properties. The reaction of ligand pyreneQ-Q, Co2(CO)8, and Mentpa gave rise to a series of dinuclear cobalt-tetraoxolene compounds formulated as {[Co(Mentpa)]2(pyreneSq-Sq)}[Co(CO)4]2 center dot S (Sq = semiquinone; n = 0, S = 2C6H5CH3 for 3; n = 1 for 4; n = 2, S = 2CHCl3 for 5).

Automated summary

The reaction of a non-innocent ligand with cobalt resulted in a series of dinuclear cobalt-tetraoxolene compounds, and it was found that two of these compounds exhibited strong ferromagnetic interactions.