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Issue 26, 2009
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Molybdenum-oxide based unique polyprotic nanoacids showing different deprotonations and related assembly processes in solution

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Abstract

We report the self-assembly processes in solution of three Keplerate-type molybdenum-oxide based clusters {Mo72V30}, {Mo72Cr30} and {Mo72Fe30} (all with diameters of ∼2.5 nm). These clusters behave as unique weak polyprotic acids owing to the external water ligands attached to the non-Mo metal centers. Whereas the Cr and Fe clusters have 30 water ligands attached at the 30 M3+ centers pointing outside, {Mo72V30} has 20 water ligands coordinated to vanadium atoms, of which only 10 are pointing outside. The self-assembly processes of the Keplerates leading to supramolecular blackberry-type structures are influenced by the effective charge densities on the cluster surfaces, which can be tuned by the pH values and solvent properties. As expected, {Mo72Cr30} and {Mo72Fe30} behave similarly in aqueous solution due to their analogous structures and in both cases the self-assembly follows the partial deprotonation of the external water ligands attached to the non-Mo metal centers. However, the M-OH2 functionalities differ not only in acidity but also lability, i.e. in different residence times of the H2O ligands. In contrast to {Mo72Cr30} and {Mo72Fe30}, the {Mo72V30} clusters carry a rather large number of negative charges so that their solution properties are different. They exist as discrete macroions in dilute aqueous solution, and form only in mixed water/organic solvent (like acetone) blackberry-type structures whose size increases with acetone content. The comparison of the properties of the clusters allows more general information about the interesting self-assembly phenomenon to be unveiled.

Graphical abstract: Molybdenum-oxide based unique polyprotic nanoacids showing different deprotonations and related assembly processes in solution

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Publication details

The article was received on 23 Jan 2009, accepted on 03 Apr 2009 and first published on 14 May 2009


Article type: Paper
DOI: 10.1039/B901505A
Citation: Dalton Trans., 2009,0, 5094-5100
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    Molybdenum-oxide based unique polyprotic nanoacids showing different deprotonations and related assembly processes in solution

    M. L. Kistler, T. Liu, P. Gouzerh, A. M. Todea and A. Müller, Dalton Trans., 2009, 0, 5094
    DOI: 10.1039/B901505A

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