One can nowadays
readily generate monodisperse colloidal nanocrystals,
but a retrosynthetic analysis is still not possible since the underlying
chemistry is often poorly understood. Here, we provide insight into
the reaction mechanism of colloidal zirconia and hafnia nanocrystals
synthesized from metal chloride and metal isopropoxide. We identify
the active precursor species in the reaction mixture through a combination
of nuclear magnetic resonance spectroscopy (NMR), density functional
theory (DFT) calculations, and pair distribution function (PDF) analysis.
We gain insight into the interaction of the surfactant, tri-
n
-octylphosphine oxide (TOPO), and the different precursors.
Interestingly, we identify a peculiar X-type ligand redistribution
mechanism that can be steered by the relative amount of Lewis base
(L-type). We further monitor how the reaction mixture decomposes using
solution NMR and gas chromatography, and we find that ZrCl
4
is formed as a by-product of the reaction, limiting the reaction
yield. The reaction proceeds via two competing mechanisms: E1 elimination
(dominating) and S
N
1 substitution (minor). Using this new
mechanistic insight, we adapted the synthesis to optimize the yield
and gain control over nanocrystal size. These insights will allow
the rational design and synthesis of complex oxide nanocrystals.
One can nowadays readily generate monodisperse colloidal nanocrystals, but a retrosynthetic analysis is still not possible since the underlying chemistry is often poorly understood. Here, we provide insight into the reaction mechanism of colloidal zirconia and hafnia nanocrystals synthesized from metal chloride and metal isopropoxide. We identify the active precursor species in the reaction mixture through a combination of nuclear magnetic resonance spectroscopy (NMR), density functional theory (DFT) calculations, and pair distribution function (PDF) analysis. We gain insight into the interaction of the surfactant, tri-n-octylphosphine oxide (TOPO), and the different precursors. Interestingly, we identify a peculiar X-type ligand redistribution mechanism that can be steered by the relative amount of Lewis base (L-type). We further monitor how the reaction mixture decomposes using solution NMR and gas chromatography, and we find that ZrCl4 is formed as a by-product of the reaction, limiting the reaction yield. The reaction proceeds via two competing mechanisms: E1 elimination (dominating) and SN1 substitution (minor). Using this new mechanistic insight, we adapted the synthesis to optimize the yield and gain control over nanocrystal size. These insights will allow the rational design and synthesis of complex oxide nanocrystals.
Iron−sulfur clusters have been reported to catalyze various redox transformations, including the multielectron reduction of CO 2 to hydrocarbons. Herein, we report the design and assembly of an artificial [Fe 4 S 4 ]-containing Fischer− Tropschase relying on the biotin−streptavidin technology. For this purpose, we synthesized a bis-biotinylated [Fe 4 S 4 ] cofactor with marked aqueous stability and incorporated it in streptavidin. The effect of the second coordination sphere provided by the protein environment was scrutinized by cyclic voltammetry, highlighting the accessibility of the doubly reduced [Fe 4 S 4 ] cluster. The Fischer−Tropschase activity was improved by chemo-genetic means for the reduction of CO 2 to hydrocarbons with up to 14 turnovers.
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