Effect of axial anthracene ligands on the luminescence of trinickel molecular wires

Abstract

Two nickel compounds having extended metal atom chains (EMACs) with the Ni 3(dpa) 4L 2 core, where dpa is the anion of 2,2′-dipyridylamine and L represents an anthracene derivative, have been synthesized in good yield and excellent purity by reaction of Ni 3(dpa) 4Cl 2 and the respective anthracene derivatives. For the compound Ni 3(dpa) 4(AnCC) 2 ( 1) AnCC is the anion of 9-ethynylanthracene and for Ni 3(dpa) 4(AnCOO) 2 ( 2) AnCOO is anthracene-9-carboxylate. The two compounds have been characterized by X-ray crystallography and other techniques. The cyclovoltammograms (CVs) of 1 and 2 display reversible redox processes at E 1/2 = 0.911 V and 1.020 V, respectively (vs. Ag/AgCl). The magnetic data suggest that the terminal Ni atoms are in a high spin state while the central Ni atom is diamagnetic, in agreement with other trinickel molecular wires. Although compound 1 is strongly luminescent, and represents the first such example in an EMAC, 2 does not display luminescence. The strong emission in 1 is related to donor–acceptor interactions between the Ni⋯Ni⋯Ni wire, the triply bonded C C linking unit, and the conjugated aromatic anthracene derivative, a process that is unavailable for 2 because the carboxylate group is almost perpendicular to the anthracene moiety.