Chemistry Reference
In-Depth Information
generally speaking, the building blocks should be conformationally rigid, and the
bond formation direction must be discrete. To satisfy these requirements, a series
of building blocks are designed, which are distinguished according to their direc-
tional symmetry of the reactive groups.
How to select building units to construct COFs? Two requirements should be
considered: one is that the monomers should contain the above-mentioned reac-
tive groups which are suitable for DCC reactions; the other is that the geometries
of monomers should match with the regular structures. Theoretically, the building
blocks could be designed on the basis of the requirements. However, in the actual
experimental procedure, the feasibility of preparing monomers should be consid-
ered. As simplified symmetry notation, these 2D or 3D monomers are referred to
as 2D-
C
2
, 2D-
C
3
, 2D-
C
4
, and 3D-
T
d
.
Through carefully analyzing the geometry of monomers and the constructing
reactions, the forming process of COFs could be discussed in detail. (1) Along
with the reactions occur new types of connection forms; (2) the topological struc-
tures do not change during bond formation. Regarding (1), the reactions of borate
anhydride formation and ZnCl
2
mediated nitrile cyclotrimerization could offer
newly formed triangular connections. Thus, even the monomers are 2D-
C
2
types,
the resulting discrete linkers provide favorable conditions for the formation of
COF networks. Therefore, for these 2D-
C
2
types' relations, the reactive groups
of the monomers are fixed on the borate acid and nitrile groups. As shown in
Fig.
2.10
, the representative samples are COF-1 and CTF-1 [
8
].
Fig. 2.10
Schematic representation of COF-1 and CTF-1
