Probing Magnetic-Exchange Coupling in Supramolecular Squares Based on Reducible Tetrazine-Derived Ligands.

Reducible 3,6-bis(3,5-dimethyl-pyrazolyl)1,2,4,5-tetrazine was employed to isolate supramolecular air-stable [Co4 ] and [Zn4 ] squares, which were achieved via careful selection of counterions rather than the use of reducing agents. Magnetic susceptibility studies revealed a strong radical-CoII exchange coupling (Jrad-Co /hc=-118 cm-1 , -2J formalism) with a spin ground state of ST =4, whereas the unreduced analogue revealed negligible coupling between the Co centers (JCo-Co /hc=-0.64 cm-1 ). Radical-radical coupling was also probed in the [Zn4 ] congener, which led to Jrad-rad /hc=-15.9(5) cm-1 . These results highlight the versatile air-stable coordination chemistry of tetrazine and the importance of exploiting easily reducible delocalized radical to promote strong exchange coupling between spin carriers.