resolver

Chapter 4 61
active catalytic centers were generated through fast precipitation and partial substitution
of dicarboxylic by mono-carboxylic acid linkers. Interestingly, the obtained in this manner
defect-engineered Zn-MOFs show shape selectivity in catalyzing alkylation of large
aromatics molecules. [144] Furthermore, by using CF3COOH and HCl during the synthesis,
Vermoortele et al. demonstrated that UiO-66(Zr) can be modified via partial substitution
of terephthalates by trifluoroacetate. Interestingly, subsequent thermal activation lead to
post-synthetic removal of the trifluoroacetate groups in addition to the dehydroxylation
of the hexanuclear Zr-clusters. All together, this yielded more open defect framework with
a large number of open sites. Remarkably, produced defects at metal sites enhanced UiO-
66(Zr) activity in several Lewis acid catalyzed reactions(Figure 4.3). [141] As a result, better
catalytic performance in several Lewis-acid catalyzed reactions was observed for the
DEMOFs. Controlled introduction and characterization of specific defects into MOFs is
quite a challenge including the comparison with the parent (more or less) “defect-free”
reference samples.
Figure 4.3. The generation of defects in UiO-66(Zr). Reprinted with permission from F.
Vermoortele, B. Bueken, G. Le Bars, B. Van de Voorde, M. Vandichel, K. Houthoofd, A. Vimont, M.
Daturi, M. Waroquier, V. Van Speybroeck, C. Kirschhock and D. E. De Vos, J. Am. Chem. Soc., 2013,
135, 11465-11468. Copyright (2013) American Chemical Society. [141]
[Cu3(BTC)2]n (also known as HKUST-1) [35] as well as the isostructural family [M3(BTC)2]n
(M = Mo, [81, 83] Cr, [78, 83] Ni, [79, 83] Ru, [82-83, 198] Zn, [77, 83] , BTC = benzene-1,3,5-tricarboxylate)
attracted considerable attention over last years, mainly due to presence of coordinatively
unsaturated metal-sites (M-CUS), as has been already introduced in Chapter 3. Intentional
defect generation in [Cu3(BTC)2]n was initially reported by Baiker et al. who studied