Tetrapalladium(II) Bisazobenzene and Azoazoxybenzene Complexes: Syntheses, Electronic Structures, and Optical Properties

Abstract

Three new tetranuclear, chloride-bridged PdII complexes have been prepared by using 1,4-bis[(E)-phenylazo]benzenes (BPABs) and an azoazoxybenzene derivative. The latter was obtained unexpectedly by reacting N,N-dimethyl-4-nitrosoaniline with 2,3,5,6-tetramethylphenylenediamine in glacial acetic acid. Characterization includes 1H NMR and UV–vis spectroscopies, and single-crystal X-ray structures have been obtained for two of the proligands and one complex. As expected, the methyl groups on the central aryl rings cause severe departures from planarity. The proligands show an intense UV absorption (λmax ≈ 350 nm) due to π → π* intramolecular charge transfer, together with weaker n → π* bands in the visible region. The complexes display an intense visible band (λmax = 449–475 nm) and multiple near-UV absorptions. While the electronic absorption spectra of the BPAB complexes are quite similar, the azoazoxybenzene complex shows a doubly intense visible band. Dichroic ratios (DRs) measured in two different liqui...