Unraveling Water Structure Inside and Between Nanocapsules |
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Authors: | Marc Henry |
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Affiliation: | (1) Solid State Molecular Tectonics, UMR CNRS/ULP 7140, Institut Le Bel, Université Louis Pasteur, 4, Rue Blaise Pascal, 67070 Strasbourg Cedex, France |
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Abstract: | Among Achim Müller's prolific crystal structure database, we have selected two crystalline phases in order to perform a whole and complete characterization of water structure at the nanometer scale. The first chosen example involves the Na3(NH4)12[Mo57Fe6(NO)6O174(OH)3(H2O)24] 76H2O compound synthesized and characterized in 1994. Some very interesting yet unnoticed water clusters may be evidenced in the voids generated by the stacking of the polyanionic units. Among them, we have been able to characterized a pure water crown (H2O)18, a loose association of three strongly solvated ammonium ions [H3N–H![sdot](/content/w651q527g43r7557/xxlarge8901.gif) ![sdot](/content/w651q527g43r7557/xxlarge8901.gif) OH2]+ mediated by two water dimers and one water molecule, a perfectly planar alternating six-member ring [(NH4)3(H2O)3]3+, a puckered chair-shaped hexagonal ring [(NH4)2(H2O)4]3+ and two triangular pyramidal water tetramers (H2O)4. It was also shown that the crown and the chair ring was involved through further hydrogen bonding into the formation of a quite novel supramolecular layer modeling the structure of water in contact with a polyelectrolyte. The second example involves the (gua)32[Mo132O372(H2O)72(SO4)10(H2PO2)20(gua)20] nH2O compound synthesized and characterized in 2002. Here, we provide for the first time a complete structural analysis of all the various hydrogen bond patterns encountered in this system. Among them we may cite, an intramolecular web covering the internal cavity, an intramolecular finite system involving the guanidinium cations and the nine-member ring pores of the Mo132 shell and a central pure water cluster of one hundred water molecules. In this last case, the evolution of the hydrogen bond strengths on a per H-bond basis or within supramolecular aggregates ([H2O]20, [H2O]40, and [H2O]100) is quantitatively studied from standpoints involving both geometry (H–O![sdot](/content/w651q527g43r7557/xxlarge8901.gif) ![sdot](/content/w651q527g43r7557/xxlarge8901.gif) O bond angles distribution) and energy (partition functions). A survey of other crystalline phases involving water clusters is also presented. It is hoped that the study of these new clusters in a very next future will allow us to solve the well-known water puzzling behaviors. |
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