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Chapter 4 59<br />
This is the most straightforward way and commonly used to incorporate some specific<br />
functionality, decorate the walls of a framework with particular (active) organic groups .<br />
Thus, Yaghi’s multivariate MOFs (MTV-MOF-5) are typical representatives of such solid<br />
solutions. [123] In fact, by mixing the terephthalic acid and its derivatives in various<br />
combinations, eighteen single phased MTV-MOFs-5 were prepared and, remarkably,<br />
demonstrated the enhancement of H2 storage capacity as well as adsorption selectivity for<br />
CO2 over CO. Furthermore, Baiker et al. reported mixed-linker amine-functionalized MOFs<br />
(MIXMOFs) with the general formula Zn4O(bdc)x(abdc)3–x (bdc = benzene-1,4-<br />
dicarboxylate; abdc = 2-aminobenzene-1,4-dicarboxylate). Notably, obtained solid<br />
solution materials could be used as both nucleophilic catalysts [124] and support to<br />
immobilize Pd-species for Pd-catalyzed cross-coupling reactions. [212]<br />
ii) truncated mixed-linker (TML) approach, in which one linker is truncated in comparison<br />
with the other.<br />
Figure 4.2. Schematic illustration of the formation of the MOF-5 analogs: spng-MOF-5 and pmg-<br />
MOF-5. Reprinted with permission from K. M. Choi, H. J. Jeon, J. K. Kang and O. M. Yaghi, J. Am.<br />
Chem. Soc., 2011, 133, 11920-11923. Copyright (2011) American Chemical Society. [215]<br />
This strategy is strongly related to the modulation approach, whereby a monocarboxylic<br />
acid is commonly added during the MOF synthesis to influence crystal growth and<br />
morphology. For instance, Kitagawa et al. used acetic acid as a modulator to directly affect<br />
the coordination equilibrium, which in turn controls the crystal growth of nanosized
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