resolver

60 Chapter 4
framework [Cu2(ndc)2(dabco)]n (ndc=1,4-naphthalene dicarboxylate; dabco=1,4-
diazabicyclo[2.2.2]octane). [213] Subsequently, similar morphological control of
[Cu3(BTC)2]n (BTC = 1,3,5-benzenetricarboxylate) from octahedral to cuboctahedral to
cubic by addition of lauric acid has been achieved. [214] Moreover, by utilizing various
amounts of dodecyloxybenzoic acid, Yaghi and co-workers have modified the crystals of
MOF-5 to develop isostructural sponge-/pomegranate- like crystal analogs featuring
meso- and macropores, respectively(Figure 4.2). [215]
iii) heterostructural mixed-linker (HML) strategy, where the employed mixed linkers bear
different linkage geometries. [142, 216-219]
UMCM-1 (University of Michigan Crystalline Material-1) reported by Matzger et al. is a
first rigorous example derived following this approach by the usage of dicarboxylate and
tricarboxylate linkers. This MOF contains 3.1 nm mesoporous hexagonal channels
surrounded by 1.4 nm microporous cages and exhibits exceptionally high surface area. [217]
Thus, variation of the relative lengths of the linkers mixed (di- and trifunctional linkers)
may result frameworks of different topologies. [218] In this manner, HML strategy has
paved up a way to unavailable topologies and larger pore sizes which are not easily
achieved in single-component frameworks. However, careful control over MOF synthesis
to avoid the formation of physical mixtures of different phases needs to be considered.
The latter two synthetic strategies, especially TML approach, can be successfully
employed to prepare defect-engineered MOFs (DEMOFs), which will be described in this
Chapter below.
4.1.2 Defects in MOFs and its “engineering”
It has been recognized that MOFs, similar to other (crystalline) solid-state materials, are
typically not perfect crystals with infinite periodic repetition or ordering of the identical
groups of atoms in space. In fact, defects of various types and length scales (even more
generally: structural heterogeneity) cannot be rigorously avoided during synthesis and
crystal growth and often play an important role for the material properties. [220-222] The
diversity of MOF structures connected with the issues of intrinsic and intentional
structural defects, non-stoichiometry and heterogeneity suggests a much broader
approach for understanding and tailoring their chemical and physical properties. [137] In
fact, Ravon and co-workers has reported MOFs featuring structural defects in which acidic