The hydrated crystal structure of a polymeric manganese citrate cubane complex suggests at least three specific mechanisms involving coordinated water molecules, by which proton transfer occurs within the crystal. [Mn(H2O)6]2n{[Mn(H2O)5][�-Mn(H2O)4]Mn4(citr)4}n�8nH2O was observed to permit proton transport via a Grotthuss-like mechanism (Proton Cascade in a Molecular Solid: H/D Exchange on Mobile and Immobile Water, Capelli, S. C.; Falvello, L. R.; Forc�n-V�zquez, E.; McIntyre, G. J.; Palacio, F.; Sanz, S.; Tom�s, M., Angew. Chem. Int. Ed. 2013 , 52, 13463-13467,DOI: 10.1002/anie.201307994 and 10.1002/ange.201307994). The details of the water structure in these molecular crystals, which was reported on the basis of single-crystal neutron diffraction analysis, include a series of fully and partially occupied hydrogen-atom sites that readily suggest the proton hopping and water-molecule rotation that constitute the Grotthuss mechanism. In this presentation the details of three distinct local proton transfer pathways are described -- (1) transfer between two aqua ligands bound to the same Mn(II) center, mediated by a free water molecule; (2) transfer between aqua ligands bound to distinct Mn(II) centers, with no mediating group; and (3) transfer between aqua ligands of distinct Mn(II) complexes, mediated by a free water. The geometric details of these pathways, along with other, localized pathway fragments that reveal the potential and limitations of this type of explanation are discussed.

Proton transport mechanisms in crystals of aquo complexes

248th National Meeting (2014)

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