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8 Chapter 2
2.2.2 MOF features
Advantages of MOFs combining the features of CPs and porous solids
MOFs (i.e. porous coordination networks) could be considered like a combination of both
CPs and porous solids. As a subclass of CPs, MOFs feature even more diverse and robust
structures. The construction of MOFs is commonly realized by the connection of “rigid”
secondary building units (SBUs) rather than the simple linking of node and spacer in
coordination networks where usually single atoms are joined by ditopic linkers. On the
other hand, the feature of being microporous compounds, which is very important
motivation to design MOFs, should not be underrated. Classical porous solids including
zeolites, silica, alumina, carbon-based materials, etc. are known in various research fields
of not only chemistry but also physical and material science due to their versatile
application related to separation, storage and heterogeneous catalysis. For example,
zeolites can be effectively utilized as molecular sieves for adsorbent of gases and liquids,
builders for the production of laundry detergents, etc. Moreover, the usage of activated
carbon in air filters and gas masks is seen in our daily life. MOFs as a novel class of porous
solids are expected to behave in a similar manner as other mentioned porous solids. In
fact, they exhibit uniform pores or open channels which might be preserved upon careful
removal of the guest molecules. Compared to the CPs of 1 st generation, this essential
characteristic allows MOFs to hold huge potential for a wide variety of applications such
as gas sorption/separation, [22-23] gas storage [24-26] and catalysis, [27-29] for which previously
only conventional purely inorganic (e.g. zeolites, alumina, silica) or purely organic porous
solids (e.g. activated carbons) were suitable.
Features highlight 1 –Structure diversity and porosity
As mentioned above, MOFs are constructed from metal nodes (also known as inorganic
building blocks or SBUs) and multidentate organic linkers (e.g. carboxylates, [13, 30]
azolates, [31-33] etc.). One of the common clusters, the octahedral Zn4O(CO2)6 cluster(Figure
2.4) composed of four ZnO4 tetrahedra with a common vertex and six carboxylate C atoms
can be as SBUs and further joined together by the benzene links, which leads to a 3D MOF
Zn4O(bdc)3∙(DMF)8(C6H5Cl) (known as MOF-5, bdc = 1,4-benzenddicarboxylate, DMF =
N,N-Dimethylformamid), where the vertices are the octahedral SBUs and the edges are
the benzene struts. [18] The obtained framework exhibit high thermal stability(300 °C) and
porosity (Brunauer-Emmett-Teller (BET) surface area well above 3500 m 2 /g). The same