Coordination-Induced Spin-State Switching of an Aminyl-Radical-Bridged Nickel(II) Porphyrin Dimer between Doublet and Sextet States.

A bis(NiII -porphyrinyl)aminyl radical with meso-C6 F5 groups was prepared as a spin-delocalized stable aminyl radical with a doublet spin state. Upon addition of pyridine, both NiII centers became hexacoordinated by accepting two axial pyridines, which triggered a spin-state change of the NiII centers from diamagnetic (S=0) to paramagnetic (S=1). The resulting high-spin NiII centers interact with the aminyl radical ferromagnetically to give rise to an overall sextet state (S=5/2). Importantly, this coordination-induced spin-state switching can be conducted in a reversible manner, in that washing of the high-spin radical with aqueous hydrochloric acid regenerates the original doublet radical in good yield.