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Insights into the Ligand Shell, Coordination Mode, and Reactivity of Carboxylic Acid Capped Metal Oxide Nanocrystals
Author(s) -
De Roo Jonathan,
Baquero Edwin A.,
Coppel Yannick,
De Keukeleere Katrien,
Van Driessche Isabel,
Nayral Céline,
Hens Zeger,
Delpech Fabien
Publication year - 2016
Publication title -
chempluschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.801
H-Index - 61
ISSN - 2192-6506
DOI - 10.1002/cplu.201600372
Subject(s) - chemistry , carboxylate , ligand (biochemistry) , carboxylic acid , ionic bonding , oxide , metal , catalysis , hydrogen bond , coordination complex , inorganic chemistry , photochemistry , polymer chemistry , stereochemistry , organic chemistry , molecule , ion , biochemistry , receptor
A detailed knowledge of surface chemistry is necessary to bridge the gap between nanocrystal synthesis and applications. Although it has been proposed that carboxylic acids bind to metal oxides in a dissociative NC(X) 2 binding motif, this surface chemistry was inferred from indirect evidence on HfO 2 nanocrystals (NCs). Here, a more detailed picture of the coordination mode of carboxylate ligands on HfO 2 and ZrO 2 NC surfaces is shown by direct observation through solid‐state NMR techniques. Surface‐adsorbed protons are clearly distinguished and two coordination modes of the carboxylic acid are noted: chelating and bridging. It is also found that secondary ligands penetrate the ligand shell and have the same orientation with respect to the surface as the primary ligands, indicating that the ionic or hydrogen‐bonding interactions with the surface are more important than the van der Waals interactions with neighboring ligands. During ligand exchange with amines, the chelating carboxylate is removed preferentially. Finally, it is shown that the HfO 2 and ZrO 2 NCs catalyze imine formation from acetone and oleylamine. Together with the previously reported catalytic activity of HfO 2 , these results put colloidal metal oxide nanocrystals squarely in the focus of catalysis research.