American Chemical Society
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Dinuclear Cyano-Bridged CoIII−FeII Complexes as Precursors for Molecular Mixed-Valence Complexes of Higher Nuclearity

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posted on 2006-01-09, 00:00 authored by Paul V. Bernhardt, Fernando Bozoglián, Gabriel González, Manuel Martínez, Brendan P. Macpherson, Beatriz Sienra
The preparation and characterization of a series of trinuclear mixed-valence cyano-bridged CoIII−FeII−CoIII compounds derived from known dinuclear [{LnCoIII(μ-NC)}FeII(CN)5]- complexes (Ln = N5 or N3S2 n-membered pendant amine macrocycle) are presented. All of the new trinuclear complexes were fully characterized spectroscopically (UV−vis, IR, and 13C NMR). Complexes exhibiting a trans and cis arrangement of the Co−Fe−Co units around the [Fe(CN)6]4- center are described (i.e., cis/trans-[{LnCoIII(μ-NC)}2FeII(CN)4]2+), and some of their structures are determined by X-ray crystallography. Electrochemical experiments revealed an expected anodic shift of the FeIII/II redox potential upon addition of a tripositively charged {CoIIILn} moiety. The CoIII/II redox potentials do not change greatly from the di- to the trinuclear complex, but rather behave in a fully independent and noncooperative way. In this respect, the energies and extinction coefficients of the MMCT bands agree with the formal existence of two mixed-valence FeII−CN−CoIII units per molecule. Solvatochromic experiments also indicated that the MMCT band of these compounds behaves as expected for a class II mixed-valence complex. Nevertheless, its extinction coefficient is dramatically increased upon increasing the solvent donor number.