Pentanuclear Heterometallic String Complexes with High‐Bond‐order Units [Ni23+−Mo24+−Ni2+(bna)4X2]3+ (X = Cl, NCS)

Abstract

Our quest for ligands toward the synthesis of functional metal string complexes started from α‐pyridylamido anions. With the modulation of naphthyridylamido anions, the ligands carry less negative charge to be balanced and, thus, to some extent, can tune the oxidation state of the metal centers and the strength of metal–metal interactions. For example, the formation of Ni23+, a mixed‐valence moiety, has been demonstrated. In this paper, high‐bond‐order units of M2 (Mo2 or Ru2) and Ni23+ are introduced and supported by four equatorial ligands of the bisnaphthyridylamido anion (bna−). The resulting compounds are [Ni2Mo2Ni(bna)4Cl2](PF6)3 (1), [Ni2Mo2Ni(bna)4(NCS)2](PF6)3 (2), and [Ni2Ru2Ni(bna)4Cl2](ClO4)3 (3). X‐ray crystallography reveal quadruply bonded characteristics with Mo–Mo distances of 2.133(2) and 2.109(2) Å for 1 and 2, respectively. The Ni2 moieties have a short Ni–Ni distance of 2.331(5) for 1 and 2.334(4) Å for 2, suggesting the formation of mixed‐valence Ni23+ units. It appears that there are no significant metal–metal interactions between Mo2 and its neighboring Ni centers. Characterization using magnetism, voltammetry, electronic absorption, and single‐molecule conductance, however, shows significant influence of Mo2 on the properties of the metal string complexes.