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, [Ni(7)(bnapy)(4)Cl(2)](Cl)(2) (2) and [Ni(9)(bnapya)(4)Cl(2)](PF(6))(2) (3) (bnapy(2-) = 2,6-bis(1,8-naphthyridylamido)pyridine and bnapya(3-) = bis(6-(1,8-naphthyridylamido)pyridyl)amido), which possess two redox-active [Ni(2)(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 (DeltaE(1/2)) of 2 and 3. The antiferromagnetic coupling between the two [Ni(2)(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 DeltaE(1/2) values of 2 and 3 are 110 and 84 mV, respectively, which are smaller than that (300 mV) of their pentanickel analogue [Ni(5)(bna)(4)(Cl)(2)](PF(6))(2) (bna(-) = bisnaphthyridylamido) (1). These DeltaE(1/2) values indicate that the electronic communication decreases with increasing number of inner diamagnetic nickel ions in nickel string complexes.