Octahedral clusters of the type [Co6Se8(L’)(PEt3)5]n, where L’ = CO or PBu3 for n = 0 and +1, have been synthesized and characterized for their mixed valence properties. Formally the cluster core is described as [4CoIII2CoII]; nonetheless the observation of large ΔE1/2 in the cyclic voltammograms of these species suggest a strong electron delocalization. The extent of delocalization was also investigated via near infrared absorption studies and heteronuclear NMR; however, none of these techniques provide delocalization information at the single metal sites level. Conveniently, we took advantage of the asymmetric ligand environment, enforced by monoligation of CO or PBu3, and analyzed these clusters via multiple wavelength anomalous (MAD) diffraction. From this analysis, site-specific relative oxidation states were extracted by obtaining the anomalous scattering factors for each atom in the [Co6Se8] cluster core. In the CO-ligated species all the PEt3-bound Co sites display superimposable f’ curves while the Co site with CO-bound displays its f’ curve shifted towards higher energy. This can be interpreted as the former five Co sites residing at the same oxidation level while the latter Co–CO site settling at slightly higher relative oxidation. This finding corroborates the chemical intuition. Furthermore, it is remarkable that when the ligand field around the Co sites is almost identical, as in [Co6Se8(PBu3)(PEt3)5]n, the electron density adopts a mer-type distribution. Thus, two sets of three Co atoms each are observed. Co sites within each set display superimposable f’ curves and the set containing the Co–PBu3 site have f’ curves shifted slightly to higher energies. In this report the site-specific findings will be discussed and correlated with the overall bulk-like electron delocalization information.

Deconvoluting the relative oxidation states in hexanuclear cobalt clusters

253rd National Meeting (2017)

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