Dear all,
Recently I have been working on direct ligand exchange on the surface of Ge nanoparticles.
The experimental part is done, now I'm trying to rationalize the observed efficiency of these exchanges according to different parameters, electric neutrality, chelate and steric effect, and HSAB theory.
The latter is proving to be more tricky than I expected.
I've performing exchanges with 1-Undecedoic acid (UDA), Oleylamine(OAm),1-octadecene (ODE), octanethiol (OT), and 1-dodecyne (DODY).
I know that the metallic core of my NPs is made out of germanium, which is considered a mild hard acid, and that's enough.
Regarding the ligands, I more or less know what is what, but I'm trying to arrange them in series. So far, I came up with this:
UDA as carboxylate in solution the R-COO- is a definitely hard base
OAm neutral primary amine in solution is a hard base but not that much
DODY alkynes in solution are harder than alkenes but softer than amines?
ODE as before, definitely softer than DODY, but not sure in respect to amines or acid
OT as thiolate in solution the R-S- I think should be the softer.
This list has been built based on the HSAB theory and chemical intuition, thinking about polarizability, electronegativity, atomic radii, and such. Still, I'm struggling to find a confirmation of my hypothesis.
Does any of you know better? Can anybody point me toward some references I can lookup?
Thanks in advance for any feedback
Bruno
Dear Bruno Pescara many thanks for asking this very interesting technical question. In general I think that your proposed "hardness ladder of different ligands" sounds reasonable as it is not based only on intuition but on the HSAB principle. I'm just not sure how the alkyne would fit into this series. In organometallic chemistry alkynes could coordinate to metal atoms via the triple bond or as alkynyide anions, R-CC–. I assume that the latter bonding mode will prevail in your case.
For a successful lignad exchange reaction on the surface of germanium nanocrystals please have a look at the following relevant article:
Thiol-Capped Germanium Nanocrystals: Preparation and Evidence for Quantum Size Effects
Article Thiol-Capped Germanium Nanocrystals: Preparation and Evidenc...
In this study the authors successfully replaced oleylamine ligands on the surface of Ge nanocrystals with dodecanethiol.
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