Authors: Ott, Lisa Starkey; Finke, Richard G.

Source: Journal of Nanoscience and Nanotechnology, Volume 8, Number 3, March 2008 , pp. 1551-1556(6)

Publisher: American Scientific Publishers

Abstract:

A supersensitivity of the formation and stabilization of transition-metal nanoclusters to the initial nanocluster concentration and temperature synthesis conditions is reported, then probed, herein for the specific case of prototype Ir(0)_n nanoclusters prepared from the organometallic precursor [Bu₄N]₅Na₃[(1,5-COD)Ir·P₂W₁₅Nb₃O₆₂] by reduction with H₂ in propylene carbonate solvent. Fully isolable, redissolvable, near-monodisperse (i.e., ≤± 15% size distribution) and thus excellent Ir(0)_n nanoclusters are formed using low temperature (22 °C) and moderate precursor concentration (1.2 mM) in propylene carbonate solvent. However, inferior, polydisperse (±40% size distribution), non-redispersable nanoclusters are formed at the seemingly only moderately different conditions of 38 °C higher temperature (i.e., 60 °C) and 5-fold lower precursor concentration (0.24 mM). Investigation of this supersensitivity to the nanocluster synthesis conditions reveals that it derives from the dissociation of (1,5-COD)Ir(solvent)⁺₂ from the P₂W₁₅Nb₃O⁹⁻₆₂ polyanionic ligand/stabilizer, subsequently resulting in a too fast, kinetically uncontrolled reduction of the quickly reduced (1,5-COD)Ir(solvent)⁺₂ as the cause of the inferior synthesis of polydisperse, non-isolable, non-redissolvable nanoclusters. The results are significant in that they illustrate that understanding the mechanism of nanocluster formation, and then performing the nanocluster synthesis under kinetically carefully controlled, understood conditions, is necessary for the formation of superior nanoclusters in this, and by implication probably many other, cases.

Keywords: TRANSITION-METAL NANOCLUSTERS; KINETICS; NANOCLUSTER NUCLEATION AND GROWTH; NANOCLUSTER SYNTHESIS; SUPERSENSITIVITY TO NANOCLUSTER SYNTHESIS CONDITIO

Document Type: Short communication

DOI: http://dx.doi.org/10.1166/jnn.2008.089

Publication date: 2008-03-01

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