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16 Chapter 2<br />
Expansion of this structures (i.e. isoreticular series of HKUST-1) could be obtained via<br />
employing other tritopic linkers of various lengths such as TATB 3- (4,4’,4’’-(s-triazine-<br />
2,4,6-triyl-tribenzoate) [61] and BBC 3- (4,4’,4’’-(benzene-1,3,5-triyl-tris(benzene-4,1-<br />
diyl))tribenzoate), for example (Figure 2.10). [62] In facts, the cell volume of the largest<br />
reported member of this series (MOF-399 ([Cu3(BBC)2]n)) is 17.4 times than that of<br />
HKUST-1. Moreover, the isoreticular construction of MOFs to enlarge the pores is also<br />
implemented through the expansion of the original phenylene unit of MOF-74-M [63] or<br />
CPO-27-M (M2(dobdc), dobdc = 2,5-dioxido-1,4-benzenedicarboxylate; M = Mg, Mn, Fe,<br />
Co, Ni, Zn, etc.). [64-65]<br />
Synthesis of MOFs, especially reticular synthesis, has earlier mainly focused on the<br />
preparation of new frameworks with new topologies and open structures with high<br />
porosity which are aimed for the gas storage capacities such as hydrogen, methane and<br />
carbon dioxide. [25, 60] Nowadays, the applications of MOFs have been more widely<br />
explored, including some fields of physics and biology. Consequently, modification of<br />
MOFs towards targeted applications has been more widely developed as well.<br />
2.3.3 Way to the modification of MOFs<br />
Beyond the traditional synthesis approaches, controlled modifications of MOFs at the<br />
organic linkers and/or at the metal nodes, could be mainly realized in several approaches:<br />
2.3.3.1 Direct decoration on the utilized linkers<br />
Ligands are often decorated with various organic groups to provide guest-accessible<br />
functional sides. [67-69] For example, Kitagawa et al. reported [Cd(4-<br />
btapa)2(NO3)2]n∙6H2O∙2DMF (4-btapa = 1,3,5-benzene tricarboxylic acid tris[N-(4-<br />
pyridyl)amide]) framework with amide-functionalized linker, where the highly ordered<br />
amide groups play an important role in the interaction with the guest molecules. [68]<br />
Moreover, the material shows selective base catalytic activity in the Knoevenagel<br />
condensation reaction. Furthermore, introduction of the thioether side CH3SCH3CH3Schain<br />
to the 2,5-position of 1,4-bdc and its co-assembly with Zn(II) ions lead to porous<br />
cubic network [Zn4O(L)3], whose topology is the same as MOF-5. [69] The obtained material<br />
exhibits a notable sensing response to nitrobenzene in the form of fluorescence<br />
quenching. Besides, it is able to absorb HgCl2 from the ethanol solution at low
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