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Title: Nanoparticle Nucleation Is Termolecular in Metal and Involves Hydrogen: Evidence for a Kinetically Effective Nucleus of Three {Ir 3 H 2x ·P 2 W 15 Nb 3 O 62 } 6– in Ir(0) n Nanoparticle Formation From [(1,5-COD)Ir I ·P 2 W 15 Nb 3 O 62 ] 8– Plus Dihydrogen

The nucleation process yielding Ir(0) ~300 nanoparticles from (Bu 4N) 5Na3[(1,5-COD)Ir·P 2W 15Nb 3O 62] (abbreviated hereafter as (COD)Ir·POM 8-, where POM 9- = the polyoxometalate, P 2W 15Nb 3O 62 9-) under H 2 is investigated to learn the true molecularity, and hence the associated kinetically effective nucleus (KEN), for nanoparticle formation for the first time. Recent work with this prototype transition-metal nanoparticle formation system ( J. Am. Chem. Soc. 2014, 136, 17601 - 17615) revealed that nucleation in this system is an apparent second-order in the precatalyst, A = (COD)Ir·POM 8-, not the higher order implied by classic nucleation theory and its nA ⇌ A n, “critical nucleus”, A n concept. Herein, the three most reasonable more intimate mechanisms of nucleation are tested: bimolecular nucleation, termolecular nucleation, and a mechanism termed “alternative termolecular nucleation” in which 2(COD)Ir + and 1(COD)Ir·POM 8- yield the transition state of the rate-determining step of nucleation. The results obtained definitively rule out a simple bimolecular nucleation mechanism and provide evidence for the alternative termolecular mechanism with a KEN of 3, Ir 3. All higher molecularity nucleation mechanisms were also ruled out. Further insights into the KEN and its more detailed composition involving hydrogen,more » {Ir 3H 2xPOM} 6-, are also obtained from the established role of H 2 in the Ir(0) ~300 formation balanced reaction stoichiometry, from the p(H 2) dependence of the kinetics, and from a D 2/H 2 kinetic isotope effect of 1.2(±0.3). Eight insights and conclusions are presented. A section covering caveats in the current work, and thus needed future studies, is also included.« less
Authors:
 [1] ; ORCiD logo [2]
  1. Middle East Technical Univ., Ankara (Turkey). Dept. of Chemistry
  2. Colorado State Univ., Fort Collins, CO (United States). Dept. of Chemistry
Publication Date:
Grant/Contract Number:
FG02-03ER15453
Type:
Published Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 15; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
Colorado State Univ., Fort Collins, CO (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1415068
Alternate Identifier(s):
OSTI ID: 1473888

Özkar, Saim, and Finke, Richard G. Nanoparticle Nucleation Is Termolecular in Metal and Involves Hydrogen: Evidence for a Kinetically Effective Nucleus of Three {Ir 3 H 2x ·P 2 W 15 Nb 3 O 62 } 6– in Ir(0) n Nanoparticle Formation From [(1,5-COD)Ir I ·P 2 W 15 Nb 3 O 62 ] 8– Plus Dihydrogen. United States: N. p., Web. doi:10.1021/jacs.7b00958.
Özkar, Saim, & Finke, Richard G. Nanoparticle Nucleation Is Termolecular in Metal and Involves Hydrogen: Evidence for a Kinetically Effective Nucleus of Three {Ir 3 H 2x ·P 2 W 15 Nb 3 O 62 } 6– in Ir(0) n Nanoparticle Formation From [(1,5-COD)Ir I ·P 2 W 15 Nb 3 O 62 ] 8– Plus Dihydrogen. United States. doi:10.1021/jacs.7b00958.
Özkar, Saim, and Finke, Richard G. 2017. "Nanoparticle Nucleation Is Termolecular in Metal and Involves Hydrogen: Evidence for a Kinetically Effective Nucleus of Three {Ir 3 H 2x ·P 2 W 15 Nb 3 O 62 } 6– in Ir(0) n Nanoparticle Formation From [(1,5-COD)Ir I ·P 2 W 15 Nb 3 O 62 ] 8– Plus Dihydrogen". United States. doi:10.1021/jacs.7b00958.
@article{osti_1415068,
title = {Nanoparticle Nucleation Is Termolecular in Metal and Involves Hydrogen: Evidence for a Kinetically Effective Nucleus of Three {Ir 3 H 2x ·P 2 W 15 Nb 3 O 62 } 6– in Ir(0) n Nanoparticle Formation From [(1,5-COD)Ir I ·P 2 W 15 Nb 3 O 62 ] 8– Plus Dihydrogen},
author = {Özkar, Saim and Finke, Richard G.},
abstractNote = {The nucleation process yielding Ir(0)~300 nanoparticles from (Bu4N)5Na3[(1,5-COD)Ir·P2W15Nb3O62] (abbreviated hereafter as (COD)Ir·POM8-, where POM9- = the polyoxometalate, P2W15Nb3O629-) under H2 is investigated to learn the true molecularity, and hence the associated kinetically effective nucleus (KEN), for nanoparticle formation for the first time. Recent work with this prototype transition-metal nanoparticle formation system ( J. Am. Chem. Soc. 2014, 136, 17601 - 17615) revealed that nucleation in this system is an apparent second-order in the precatalyst, A = (COD)Ir·POM8-, not the higher order implied by classic nucleation theory and its nA ⇌ An, “critical nucleus”, An concept. Herein, the three most reasonable more intimate mechanisms of nucleation are tested: bimolecular nucleation, termolecular nucleation, and a mechanism termed “alternative termolecular nucleation” in which 2(COD)Ir+ and 1(COD)Ir·POM8- yield the transition state of the rate-determining step of nucleation. The results obtained definitively rule out a simple bimolecular nucleation mechanism and provide evidence for the alternative termolecular mechanism with a KEN of 3, Ir3. All higher molecularity nucleation mechanisms were also ruled out. Further insights into the KEN and its more detailed composition involving hydrogen, {Ir3H2xPOM}6-, are also obtained from the established role of H2 in the Ir(0)~300 formation balanced reaction stoichiometry, from the p(H2) dependence of the kinetics, and from a D2/H2 kinetic isotope effect of 1.2(±0.3). Eight insights and conclusions are presented. A section covering caveats in the current work, and thus needed future studies, is also included.},
doi = {10.1021/jacs.7b00958},
journal = {Journal of the American Chemical Society},
number = 15,
volume = 139,
place = {United States},
year = {2017},
month = {4}
}