Octahedral cobalt(ɪɪɪ) compounds are almost exclusively diamagnetic (S = 0). In a square-planar environment, however, sizable dz²-orbital stabilization occurs, enabling an intermediate spin state (S = 1). Such an open-shell electron configuration, which is unprecedented in organocobalt(ɪɪɪ) chemistry, has now been substantiated in homoleptic [NBu₄][CoR₄] compounds (R = C₆F₅, C₆Cl₅). See M. A. García-Monforte, I. Ara, A. Martín, B. Menjón, M. Tomás, P. J. Alonso, A. B. Arauzo, J. I. Martínez, C. Rillo, Inorg. Chem. 2014, 53, 12384.
These results are particularly significant, given the diamagnetic character of the heavier-metal isoleptic species [Rhɪɪɪ(C₆Cl₅)₄]⁻ previously reported by our colleague Mª Pilar García Clemente, to whose Memory the current work is warmly dedicated.
