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Iron versus Ruthenium: Clarifying the Electronic Differences between Prototypical Mixed-Valence Organometallic Butadiyndiyl Bridged Molecular Wires

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posted on 2018-04-30, 12:04 authored by Simon Gückel, Josef B. G. Gluyas, Sarah El-Tarhuni, Alexandre N. Sobolev, Mark W. Whiteley, Jean-François Halet, Claude Lapinte, Martin Kaupp, Paul J. Low
The electronic structures of the prototypical bimetallic buta-1,3-diyn-1,4-diyl-bridged radical cation complexes [{M­(dppe)­Cp′}2(μ-CCCC)]+ (M= Fe, Cp′ = Cp* (1a), Cp (1b); M = Ru, Cp′ = Cp* (2a), Cp (2b)) have been (re)­investigated using a combination of UV–vis–NIR and IR spectroelectrochemistry, and quantum chemical calculations based on both dispersion-corrected global (BLYP35-D3) and local (Lh-SsirPW92-D3) hybrid functionals. Following analysis of new and existing data, including the IR-active ν­(CC) bands, the iron compounds [1]+ are reclassified as valence-trapped (Robin and Day Class II) mixed-valence complexes, in contrast to the ruthenium complexes [2]+, which are delocalized (Robin and Day Class III) systems. All members of the series exist as a thermally populated distribution of conformers in solution, and the overlapping spectroscopic profiles make the accurate extraction of the parameters necessary for the analysis of [1]+ and [2]+ within the framework of the Marcus–Hush model extremely challenging. Analysis of the spin-density distributions from a range of conformational minima provides an alternative representation of the degree of charge localization, and a comparison between members of the series is presented.

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