Deprotonations and Charges of Well-Defined {Mo72Fe30} Nanoacids Simply Stepwise Tuned by pH Allow Control/Variation of Related Self-Assembly Processes
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- 作者：Tianbo Liu ; Brandon Imber ; Ekkehard Diemann ; Guang Liu ; Katrina Cokleski ; Huilin Li ; Zhiqiang Chen ; Achim Mü ; ller
- 刊名：Journal of the American Chemical Society
- 出版年：2006
- 出版时间：December 13, 2006
- 年：2006
- 卷：128
- 期：49
- 页码：15914 - 15920
- 全文大小：164K
- 年卷期：v.128,no.49(December 13, 2006)
- ISSN：1520-5126
文摘
The solution behavior of the largest inorganic acid known thus far, the neutral, spherical iron/molybdenum/oxide nanocluster {Mo72Fe30} (
{(MoVI) MoVI5}12FeIII30 1a), including the pH-controlleddeprotonation, is reported. The acidic properties are due to the 30 peripheral, weakly acidic FeIII(H2O)groups that form a unique Archimedean solid with all edges and dihedral angles being equal, theicosidodecahedron, and therefore an "isotropic" surface. Interestingly, the aqueous solutions are stableeven for months because of the inertness of the spherical solutes and the presence of the hard FeIII andMoVI centers. The stability can be nicely proven by the very characteristic Raman spectrum showing, becauseof the (approximately) icosahedral symmetry, only a few lines. Whereas the {Mo72Fe30} clusters exist asdiscrete, almost neutral, molecules in aqueous solution at pH < 2.9, they get deprotonated and self-associateinto single-layer blackberry-type structures at higher pH while the assembly process (i.e., the size of thefinal species) can be controlled by the pH values; this allows the deliberate generation of differently sizednanoparticles, a long-term goal in nanoscience. The average hydrodynamic radius (Rh) of the self-assembledstructures decreases monotonically with increasing number of charges on the {Mo72Fe30} macroanions(from ~45 nm at pH 
3.0 to ~15 nm at pH 6.6), as studied by laser light scattering and TEM techniques.The {Mo72Fe30} macroions with high-stability tunable charges/surfaces, equal shape, and masses providemodels for the understanding of more complex polyelectrolyte solutions while the controllable associationand dissociation reported here of the assembled soft magnetic materials with tuneable sizes could beinteresting for practical applications.
{(MoVI) MoVI5}12FeIII30 1a), including the pH-controlleddeprotonation, is reported. The acidic properties are due to the 30 peripheral, weakly acidic FeIII(H2O)groups that form a unique Archimedean solid with all edges and dihedral angles being equal, theicosidodecahedron, and therefore an "isotropic" surface. Interestingly, the aqueous solutions are stableeven for months because of the inertness of the spherical solutes and the presence of the hard FeIII andMoVI centers. The stability can be nicely proven by the very characteristic Raman spectrum showing, becauseof the (approximately) icosahedral symmetry, only a few lines. Whereas the {Mo72Fe30} clusters exist asdiscrete, almost neutral, molecules in aqueous solution at pH < 2.9, they get deprotonated and self-associateinto single-layer blackberry-type structures at higher pH while the assembly process (i.e., the size of thefinal species) can be controlled by the pH values; this allows the deliberate generation of differently sizednanoparticles, a long-term goal in nanoscience. The average hydrodynamic radius (Rh) of the self-assembledstructures decreases monotonically with increasing number of charges on the {Mo72Fe30} macroanions(from ~45 nm at pH 3.0 to ~15 nm at pH 6.6), as studied by laser light scattering and TEM techniques.The {Mo72Fe30} macroions with high-stability tunable charges/surfaces, equal shape, and masses providemodels for the understanding of more complex polyelectrolyte solutions while the controllable associationand dissociation reported here of the assembled soft magnetic materials with tuneable sizes could beinteresting for practical applications.