Redox modification of EMACs through the tuning of ligands: Heptametal(II) complexes of pyrazine-modulated oligo-α-pyridylamido ligands
Resource
European Journal of Inorganic Chemistry 2009 (14): 2110-2120
Journal
European Journal of Inorganic Chemistry
Journal Issue
14
Pages
2110-2120
Date Issued
2009
Author(s)
Abstract
Using pyrazine-modulated oligo-α-pyridylamido ligands N 2-(pyrazin-2-yl)-N6-[6-(pyrazin-2-ylamino)pyridin-2-yl] pyrid-ine-2,6-diamine (H3pzpz) and N2-(pyrazin-2-yl)- N6-[6-(pyr-idin-2-ylamino)pyridin-2-yl]pyridine-2,6-diamine (H 3tpz), linear heptametal(II) extended metal atom chains (EMACs) [M7(μ7-L)4X2] [L = pzpz 3-, M = NiII, X = Cl- (1), NCS- (2); M = CrII, X = Cl- (3), NCS- (4); L = tpz 3-, M = CrII, X = Cl- (5), NCS- (6)] were synthesized and structurally characterized. Electrochemical studies showed that heptanickel(II) complexes can undergo one reversible oxidation at +0.46 V for 1 and +0.52 V for 2. Chromium(II) species 3 exhibited two reversible, one-electron oxidation peaks at +0.61 and +0.88 V, and 5 exhibited three reversible, one-electron oxidation peaks at +0.40, +0.68 and +1.07 V. The redox peaks shifted positively when axial ligands changed from chloride to thiocyanate anions, at +0.67 and +0.92 V for 4 and +0.44, +0.73 and +1.11 V for 6. The introduction of electron-withdrawing pyrazine rings to the spacer ligand retarded oxidation of the heptametal EMACs and stabilized the complexes. In nickel(II) species 1 and 2, both terminal nickel atoms exist in spin state S = 1 whereas all the inner nickel atoms exist in spin state S = 0. Temperature-dependent magnetic research revealed an antiferromagnetic interaction between the two terminal atoms through a superexchange pathway along metal cores with a parameter of about -4 cm-1. Chromium(II) species 3-6 showed a localized structure consisting of three quadruple Cr-Cr bonds and a single terminal CrII atom. Magnetic study revealed a quintet ground state resulting from the isolated, high-spin CrII atom. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA.
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journal article
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