Speaker
Chris Whitehead
Speaker's Institution
Colorado State University
Date
2/26/19
Time
4:00 PM
Location
Chemistry A101
Mixer Time
3:45 PM
Mixer Location
Chemistry B101E
Additional Information

Research Seminar Abstract

The kinetics and molecular mechanism of nucleation are investigated in molecular detail starting from [(1,5-COD)IrI(NCCH3)2][BF4], 1, which upon addition of HPO42– to 1 forms a neutral, phosphate-bridged species, {[(1,5-COD)IrI(NCCH3)]2•HPO4}0, 2, en route to {[(1,5-COD)IrI•HPO4]2[Bu4N]2}, 3. 1H NMR solution speciation and Signer apparatus solution molecular weight studies establish that in situ prepared {[(1,5-COD)IrI•HPO4]2}2–, 3, exists predominantly in its indicated, dimeric form. The NMR studies also identify {[(1,5-COD)IrI(NCCH3)]2•HPO4}0, 2, as an important, meta-stable species with one less HPO42–, formed in a dissociative equilibrium of 3 to 2 plus HPO42–. Kinetic studies reveal a first-order dependence of nucleation on the concentration of 3, and, hence, rule out the higher-order dependence implied by Classical Nucleation Theory. Additional kinetic studies reveal a telling, inverse, quadratic dependence on added HPO42–, results that unveil the previously unavailable insights that a simple bimetallic, Ir2 precursor is sufficient to enable low molecularity nucleation via {[(1,5-COD)IrI(NCCH3)]2•HPO4}0, 2, as a kinetically competent intermediate—a unique example of a nucleation mechanism in molecular detail from a precisely defined molecular precursor that also includes spectroscopic detection of a kinetically competent intermediate. The state-of-the-art nucleation results presented provide insights that promise to help the drive towards a deeper understanding of nucleation not just in transition-metal nanoparticle formation, but hopefully more broadly across nature.

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