Persistent Metal Bis(Hexafluoroacetylacetonato) Complexes Featuring a 2,2′-Bipyridine Substituted Triarylamminium Radical Cation

Herein, we describe the preparation of a 2,2'-bipyridine derivative containing a redox-active N,N-(4,4'-dimethoxydiphenylamino) substituent (1), which readily coordinates M(hfac)(2) salts [M = Mn (2), Ni (3), Cu (4)] to generate stable, neutral, and pseudo-octahedral coordination complexes, which have been fully characterized. Cyclic voltammetry and spectroelectro-chemical measurements on complexes 2-4 indicate stable one-electron oxidation processes, and the formation of persistent radical cation complexes. The neutral complexes (M = Mn or Ni) were subject to one-electron oxidation with NOPF6 in acetonitrile, and magnetic moments of the resulting solutions were obtained using the Evans method at different temperatures. Our experimental results suggest that the first reported ferromagnetically coupled metal-triarylamminum radical cation complex is obtained when M = Mn2+, and antiferromagnetic coupling results when M = Ni2+. These results are supported by results from density functional theory calculations, which indicate that a pi spin polarization mechanism for magnetic exchange coupling is operative in singly oxidized complexes, 2-4.