Probing the electronic communication of linear heptanickel and nonanickel string complexes by utilizing two redox-active [Ni2(napy)4]3+ moieties.

Two extended nickel string complexes, [Ni7(bnapy)4Cl2](Cl)2 (2) and [Ni9(bnapya)4Cl2](PF6)2 (3) (bnapy2− = 2,6-bis(1,8-naphthyridylamido)pyridine and bnapya3- = bis(6-(1,8-naphthyridylamido)pyridyl)amido), which possess two redox-active [Ni2(napy)4]3+ units, were synthesized and characterized. The electronic communication between the two redox-active units in both complexes can be investigated not only by magnetic measurements but also by analyzing the difference between two consecutive one-electron oxidation peaks (ΔE1/2) of 2 and 3. The antiferromagnetic coupling between the two [Ni2(napy)4]3+ fragments become weaker as the metal frameworks are elongated (J = −13.21 and −1.48 cm−1 for 2 and 3, respectively). Moreover, the ΔE1/2 values of 2 and 3 are 110 and 84 mV, respectively, which are smaller than that (300 mV) of their pentanickel analogue [Ni5(bna)4(Cl)2](PF6)2 (bna− = bisnaphthyridylamido) (1). These ΔE1/2 values indicate that the electronic communication decreases with increasing number of inner diamagnetic nickel ions in nickel string complexes.