Fatty acid capped, metal oxo clusters as the smallest conceivable nanocrystal prototypes

Van den Eynden, Dietger and Pokratath, Rohan and Mathew, Jikson Pulparayil and Goossens, Eline and De Buysser, Klaartje and De Roo, Jonathan. (2023) Fatty acid capped, metal oxo clusters as the smallest conceivable nanocrystal prototypes. Chemical Science, 14 (3). pp. 573-585.

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Official URL: https://edoc.unibas.ch/94144/

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Metal oxo clusters of the type M6O4(OH)4(OOCR)12 (M = Zr or Hf) are valuable building blocks for materials science. Here, we synthesize a series of zirconium and hafnium oxo clusters with ligands that are typically used to stabilize oxide nanocrystals (fatty acids with long and/or branched chains). The fatty acid capped oxo clusters have a high solubility but do not crystallize, precluding traditional purification and single-crystal XRD analysis. We thus develop alternative purification strategies and we use X-ray total scattering and Pair Distribution Function (PDF) analysis as our main method to elucidate the structure of the cluster core. We identify the correct structure from a series of possible clusters (Zr3, Zr4, Zr6, Zr12, Zr10, and Zr26). Excellent refinements are only obtained when the ligands are part of the structure model. Further evidence for the cluster composition is provided by nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR), thermogravimetry analysis (TGA), and mass spectrometry (MS). We find that hydrogen bonded carboxylic acid is an intrinsic part of the oxo cluster. Using our analytical tools, we elucidate the conversion from a Zr6 monomer to a Zr12 dimer (and vice versa), induced by carboxylate ligand exchange. Finally, we compare the catalytic performance of Zr12-oleate clusters with oleate capped, 5.5 nm zirconium oxide nanocrystals in the esterification of oleic acid with ethanol. The oxo clusters present a five times higher reaction rate, due to their higher surface area. Since the oxo clusters are the lower limit of downscaling oxide nanocrystals, we present them as appealing catalytic materials, and as atomically precise model systems. In addition, the lessons learned regarding PDF analysis are applicable to other areas of cluster science as well, from semiconductor and metal clusters, to polyoxometalates.
Faculties and Departments:05 Faculty of Science > Departement Chemie > Chemie > Nanomaterials (De Roo)
UniBasel Contributors:De Roo, Jonathan and Van den Eynden, Dietger and Pokratath, Rohan and Pulparayil Mathew, Jikson
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:Royal Society of Chemistry
Note:Publication type according to Uni Basel Research Database: Journal article
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Last Modified:03 Apr 2023 06:59
Deposited On:03 Apr 2023 06:59

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