A Redox‐Active Bridging Ligand to Promote Spin Delocalization, High‐Spin Complexes, and Magnetic Multi‐Switchability

A dinuclear Co II complex, [Co 2 (tphz)(tpy) 2 ] n + ( n =4, 3 or 2; tphz: tetrapyridophenazine; tpy: terpyridine), has been assembled using the redox‐active and strongly complexing tphz bridging ligand. The magnetic properties of this complex can be tuned from spin‐crossover with T 1/2 ≈470 K for the pristine compound ( n =4) to single‐molecule magnet with an S T =5/2 spin ground state when once reduced ( n =3) to finally a diamagnetic species when twice reduced ( n =2). The two successive and reversible reductions are concomitant with an increase of the spin delocalization within the complex, promoting remarkably large magnetic exchange couplings and high‐spin species even at room temperature.