The redox non-innocent ligand 2,2'-bipyrimidine (bpym) reacted with two molar equivalents of LCo(tol) (L = CH(MeC[double bond, length as m-dash]NAr)2, Ar = 2,6-iPr2C6H3) to afford the binuclear CoII complex (LCo)2(μ-bpym) (1), in which the bpym moiety accepts two electrons from the metal centers and in the dianion state. Complex 1 readily underwent one-electron oxidation when treated with [Cp2Fe]+[BPh4]- affording the cation salt [(LCo)2(μ-bpym)][BPh4] (2) with the bpym moiety in the radical anion state. Meanwhile, complex 2 could be converted back to 1 with elemental potassium. The magnetic studies revealed that complex 2 is a single molecular magnet (SMM) under a small external field, while 1 has no SMM activity. This represents a new example of a SMM exhibiting a fully reversible 'on/off' switching ability in anodic and neutral states.