Reducible 3,6-bis(3,5-dimethyl-pyrazolyl)1,2,4,5- tetrazine was employed to isolate supramolecular airstable [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.