Nanoparticles with atomic precision
Research in the recent past has resulted in a large number of nanoparticles whose properties depend on the number and spatial arrangement of their constituent atoms. This distinct atom-dependence of properties is particularly noticeable in ligand protected atomically precise clusters of noble metals. They behave indeed likemolecules. They show unusual properties such as luminescence in the visible and near-infrared regions. Their molecule-like behavior is most elegantly shown by atom and structure conserving chemical reactions between them. Several clusters, which are archetypal nanoparticles, Ag25(SR)18 and Au25(SR)18 (-SR = alkyl/aryl thiolate) have been used for such reactions. Despite their geometric robustness and electronic stability, reactions between them in solution at room temperature produce alloysAgmAun(SR)18 (m+n=25), keeping their M25(SR)18 composition, structure and topology intact. We captured one of the earliest events of the process, namely the formation of the dianionic adduct, [Ag25Au25(SR)36]2-, by electrospray ionization mass spectrometry. Molecular docking simulations and density functional theory (DFT) calculations also suggest that metal atom exchanges could occur through the formation of adducts. Such isomorphous transformations between nanoparticles imply that microscopic pieces of matter can be transformed completely to chemically different entities, preserving their structures, at least in the nanometric regime.Intercluster interactions can also produce cluster dimers and unusual, well-defined alloys.They reflect the shell structure of certain reactants. Atom exchanges suggest interesting dynamics in solution, early results of these investigations will be presented. New experiments in this subject area confirm the fascinating chemical diversity possible in such systems. They are shown to exhibit properties useful for applications.
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