Polymorphism of 2D Imine Covalent Organic Frameworks

Article abstract of DOI:10.1002/anie.202015130

We designed and synthesized A₂B₂ type tetraphenyl benzene monomers (p-, m-, and o-TetPB) which have the para-, meta, and ortho-substituted isomeric structures, for the direct construction of isomeric frameworks. Interestingly, both kagome (kgm) and monoclinic square (sql) framework isomers are produced from either p-TetPB (C_2h symmetry) or m-TetPB (C_2v symmetry) by changing reaction solvents, while their isomeric structures are characterized by X-ray diffraction, computational simulation, microscopy, and sorption isotherm measurements. Only sql frameworks was formed for o-TetPB (C_2v symmetry), irrespective of reaction solvents. These results disclose a unique feature in the framework structural formation, that is, the geometry of monomers directs and dominates the lattice growth process while the solvent plays a role in the perturbation of chain growth pattern. The isomeric frameworks exhibit highly selective adsorption of vitamin B₁₂ owing to pore shape and size differences.

Full text of DOI:10.1002/anie.202015130

A Journal of the Gesellschaft Deutscher Chemiker
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Accepted Article
Title: Polymorphism of 2D Imine Covalent Organic Frameworks
Authors: Yusen Li, Linshuo Guo, Yongkang Lv, Ziqiang Zhao, Yanhang
Ma, Weihua Chen, Guolong Xing, Donglin Jiang, and Long
Chen
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.202015130
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RESEARCH ARTICLE
Polymorphism of 2D Imine Covalent Organic Frameworks
+
+
Yusen Li, Linshuo Guo, Yongkang Lv, Ziqiang Zhao, Yanhang Ma, Weihua Chen, Guolong Xing,
Donglin Jiang, and Long Chen*
Abstract: Isomerism is widely observed in chemistry but it has
covalent bonds across the material while covalent bond usually
lacks precise spatial directivity.
scarcely been identified in crystalline porous covalent organic
frameworks. Herein, we designed and synthesized a series of A
2
B
2
Covalent organic frameworks (COFs) are a class of crystalline
porous polymers which have recently drawn even increasing
research interest.[9] COFs have been rapidly developed owing to
type tetraphenyl benzene monomers (p-, m-, and o-TetPB) which
have the para-, meta, and ortho-substituted isomeric structures, for
the direct construction of isomeric frameworks. Interestingly, both
kagome (kgm) and monoclinic square (sql) framework isomers are
produced from either p-TetPB (C2h symmetry) or m-TetPB (C2v
symmetry) by simply changing reaction solvents, while their isomeric
structures are unambiguously characterized by X-ray diffraction,
computational simulation, microscopy, and sorption isotherm
measurements. In contrast, only sql frameworks was formed for o-
TetPB (C2v symmetry), irrespective of reaction solvents. These results
disclose a unique feature in the framework structural formation, i.e.
the geometry of monomers directs and dominates the lattice growth
process while the solvent plays a role in the perturbation of chain
growth pattern. The isomeric frameworks exhibit highly selective
adsorption of vitamin B12 owing to a great difference in their pore
shape and size. These results open the possibility of selective
crystallization of COFs and topological engineering of the
polymorphism of 2D organic materials.
[
10]
their fascinating designable topologies
and broad application
prospects in catalysis, photoelectric devices,[12] drug delivery,[13]
energy storage,[ and sensors.[15] The topology of COFs can be
well regulated by changing the building blocks, so that various
COFs with different topologies have been designed.[10] However,
the investigation of the isomerism of COFs remains to be well
explored. Examples are limited to only 3D COF-300[ , 2D COF-
ED[16b] and on-surface synthesized single-layered COFs.[16c] The
typical 3D COF-300 with a dia-c5 topology[17] can be converted to
an interpenetration isomer with a dia-c7 topology when an
additional aging process was performed ahead of the
conventional synthetic procedure,[16a] and this is based on the
interpenetration isomerism.[16a] Co-condensation of D2h symmetric
4′,4″′,4″″′,4″″″′-(ethene-1,1,2,2-tetrayl)tetrakis([1,1′-biphenyl]-4-
[11]
14]
16a]
2
carbaldehyde]) (ETTBC) and C symmetric 2,5-diaminotoluene
(DAT) yields dual-pore kagome or single-pore rhombic
frameworks in different solvents.[16b] Theoretically, co-
2
condensation of D2h and C symmetric monomers can generate
both kagome and rhombic isomers. However, experimentally
most cases yield only one of the isomers.[18]
Introduction
Isomerism is a common phenomenon in chemistry, as it has been
developed in small molecules,[1] nanoclusters,[2] porous organic
cages (POCs),[3] and metal organic frameworks (MOFs)[4-8]. It has
been demonstrated that isomerism is closely correlated to the
synthetic conditions including solvents, temperature, nucleation
kinetics, and other factors.[1-4] The isomers usually feature
significant differences in both structure and function which greatly
enhance the structure diversity and application scope.
Nevertheless, how to control the isomerism or, in other words, to
produce the desired isomer in a selective way remains a
challenging goal. This becomes far much difficult in the case of
polymer networks, as it requires the same confined growth for all
[*]
Y. Li,[+] Y. Lv, Z. Zhao, G. Xing, Prof. L. Chen
Department of Chemistry, Institute of Molecular Plus and Tianjin Key
Laboratory of Molecular Optoelectronic Science, Tianjin University,
Tianjin 300072, China.
E-mail: long.chen@tju.edu.cn (L. Chen)
[
+]
L. Guo, Prof. Y. Ma
School of Physical Science and Technology, Shanghai Tech
University, Shanghai 201210, China.
Prof. W. Chen
College of Chemistry and Green Catalysis Center, Zhengzhou
University, Henan 450001, China.
Chart 1. Possible topologies constructed by A
TetPB, and o-TetPB.
2 2
B monomers of p-TetPB, m-
Prof. D. Jiang
Department of Chemistry, Faculty of Science, 3 Science Drive,
Singapore 117543, Singapore
These authors contributed equally to this work.
Except boroxine-linked COFs[19a] and covalent triazine
frameworks (CTFs),[19b] most COFs are constructed by
polycondensation of at least two monomers with different reactive
groups. Thus, screening specific mixed-solvent systems is a must
[
+]
Supporting information for this article is given via a link at the end of
the document.
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Angewandte Chemie International Edition
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RESEARCH ARTICLE
for balancing reaction and crystallization to synthesize high
regulate the polymorph of COFs in a selective manner while
enhancing the structural complexity and function scope.
quality crystalline COFs.[9,10] Meanwhile,
a
relative high
temperature and long reaction time are generally required to allow
the error correction of dynamic covalent linkages.[9e] We recently
developed a “two-in-one” molecular design strategy for the high
throughput synthesis of COFs via self-polycondensation of
Results and Discussion
2 2
bifunctional A B monomers. A distinct feature is that high quality
2 2
Three A B monomers (p-TetPB, m-TetPB and o-TetPB) were
COFs can be synthesized in various solvents even including low
boiling point solvents like dichloromethane (DCM) or methanol.[20]
Interestingly, the monomer concentration exerts a minimal
influence on the crystallinity of COFs.[20b] Therefore, we envision
that the excellent adaptability of this “two-in-one” strategy toward
solvents, temperature, and concentration might provide a new
possibility for exploring unprecedented isomerism of COFs.
synthesized via stepwise Suzuki coupling (Scheme S1-S3) and
unambiguously characterized by NMR (Figure S34-S48), high
resolution ESI mass (Figure S49-S51), and the detailed synthetic
procedures were summarized in the Supplementary Information.
TetPB-COFs were synthesized as light-yellow powders in high
yields (> 85%) from various organic solvents such as dioxane,
tetrahydrofuran (THF), n-butanol (n-BuOH), DCM, etc. (Figure S1,
S5 and S9). These as-synthesized TetPB-COFs exhibit similar
Fourier transform infrared spectra (FT-IR). The characteristic
stretching vibration bands for amino and formyl groups were
significantly attenuated or even disappeared while the
Herein, we elaborately designed and synthesized three A
isomeric monomers to construct imine-linked 2D COFs via self-
polycondensation. These three A monomeric isomers feature
2 2
B
2
B
2
same tetraphenyl benzene core (TetPB) but with formyl and
amino substituents aligned at different positions (relative to the
central benzene ring), named as p-TetPB, m-TetPB and o-TetPB,
respectively (Chart 1). DFT calculation revealed that the dihedral
angles between the 4-aminophenyl and 4-formylphenyl groups
and the central benzene core caused by the steric hindrance
between the adjacent phenyl rings were in the range of
−1
characteristic signals of C=N newly appeared around 1618 cm
after self-condensation (Figure 1a and S13), indicating these
TetPB-COFs feature the same chemical constitution with high
13
polymerization degree. Solid state C CP-MAS NMR spectra of
these isomeric TetPB-COFs are similar and the characteristic
resonance signals around 156 ppm are observed in all TetPB-
COFs (Figure 1b and S14), which further confirm the same
chemical constitutions and the presence of C=N linkages.
Thermogravimetric analysis (TGA) confirmed all TetPB-COFs did
o
o
4
7.6 ~52.3 , and are nearly identical to each other among the
three isomeric TetPB monomers. Regarding the symmetries of p-
TetPB (C2h) and m-TetPB (C2v), both of them are able to assemble
into two possible topologies of hexagonal kagome (kgm) net and
monoclinic square (sql) framework (Chart 1, Scheme S4 and S5).
These two monomers exhibit similar Gibbs free energy with
negligible difference of ΔG = 0.6124 kcal/mol (ESI), suggesting a
comparable thermodynamic stability. In contrast, although o-
TetPB possess the same symmetry with m-TetPB (C2v), it can
only afford sql net due to the configuration mismatch (Chart 1 and
Scheme S6). Actually, crystalline TetPB-COFs can be readily
synthesized in at least eight different solvents (Figure S1, S5 and
S9) to show a good solvent adaptability similar to our previous
studies.[20] Moreover, the kgm p-TetPB-COF-K and m-TetPB-
COF-K were readily formed in some aprotic solvents such as THF
and dioxane while the sql p-TetPB-COF-M and m-TetPB-COF-M
were usually obtained in protic alcohols and the optimal solvents
for kgm and sql frameworks were determined to be THF and n-
BuOH, respectively as judged by the higher surface areas and
better PXRD patterns (Figure S1 and S5).
not exhibit significant weight loss until 535 oC under N
2
atmosphere (Figure 1c and S15), revealing excellent thermal
stabilities. The solid-state diffuse reflectance K–M spectra
revealed that these TetPB-COFs showcased nearly identical
broad bands around 396 nm (Figure 1d and S16). Therefore,
these TetPB-COFs exhibit almost the same thermal stability and
electronic absorption features.
The resulted TetPB-COFs with same chemical constitutions
but different topologies are unambiguously characterized and
confirmed powder X-ray diffraction (PXRD), high-resolution
transmission electron microscope (HRTEM), and pore-size
distribution analysis. Theoretically, both p-TetPB and m-TetPB
can yield kgm (denote as: TetPB-COF-K, K refers to Kagome)
and monoclinic sql topologies (denote as: TetPB-COF-M, M
stand for monoclinic), while o-TetPB only affords a monoclinic sql
product. We emphasize that it is impossible to obtain framework
isomers by the conventional [C
tetrakis-(4-formylphenyl)benzene (TetPB-4CHO) and 1,2,4,5-
tetrakis-(4-aminolphenyl)benzene (TetPB-4NH ) (Scheme S9).
Moreover, the TetPB-COFs with different pore shape and size
were employed to adsorb vitamin B12 and demonstrated that
these isomeric COFs enable selective adsorption and separation.
The successful synthesis of COF isomers with different structures
and properties from isomeric monomers provide an approach to
4 4
+ C ] co-condensation of 1,2,4,5-
2
Figure 1. (a) FT-IR spectra comparison of p-TetPB-COF-K (orange), p-TetPB-
COF-M (violet), and p-TetPB monomer (pink); (b) Solid-state 13C CP/MAS NMR
spectra of p-TetPB-COF-K (orange) and p-TetPB-COF-M (violet); (c)
Thermogravimetric analysis for p-TPB-COF-K (pink) and p-TetPB-COF-M
(violet); (d) UV-visible spectra of p-TetPB-COF-K (pink) and p-TetPB-COF-M
(violet).
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Figure 2. (a) Experimental PXRD patterns of p-TetPB-COF-K (black), Pawley refinement (red dot), their difference (green), simulated profiles for kagome kgm-AA
model (orange), kgm-AB model (dark yellow) monoclinic sql-AA model (pink) and sql-AB model (purple); (b) Top and (c) across views of kgm-AA model; (d) Top
and (e) across views of sql-AA model; (f) Experimental PXRD patterns of p-TetPB-COF-M (black), Pawley refinement (red dot), their difference (green), simulated
profiles for monoclinic sql-AA model (pink), sql-AB model (purple), kagome kgm-AA model (orange), kgm-AB model (dark yellow).
PXRD analysis and structural simulation were performed to
assess the crystalline structures of these TetPB-COFs. Taking p-
TetPB-COFs (Figure 2) as examples to briefly illustrate the
structural analysis. The p-TetPB-COF-K showcases diffraction
exclusive sql topological o-TetPB-COF was obtained when o-
TetPB was utilized as the building unit (Scheme S6). The
corresponding PXRD pattern exhibited characteristic peaks at
o
o
o
o
o
6.42 , 8.02 , 12.95 , 16.36 , and 20.12 (Figure S27) and agreed
well with the eclipsed AA-stacking monoclinic model with a unit
o
o
o
o
peaks at 3.45 , 7.16 , 10.95 and 21.46 , which was consistent
well with the simulated eclipsed AA-stacking kgm topology and
the optimized unit cell parameters are a = b = 30.04 Å, c = 4.27 Å,
α = β = 90 , and γ = 120o (Figure S22 and table S1). The
o
cell of a = 16.95 Å, b = 24.84 Å, c = 4.51 Å, α = γ = 90 , and β =
o
p
deviations of Pawley refinement were negligible (R = 1.90%, Rwp
=
2.96%) and the diffraction peaks were related to (100), (200),
(
300), and (001) lattice planes, respectively (Figure 2a, b, c). In
o
contrast, p-TetPB-COF-M exhibits diffraction peaks at 6.36 ,
8
o
o
o
o
.03 , 12.74 , 16.30 , and 20.06 , which was in accordance with
the eclipsed AA-stacking sql net. Pawley refinement of the
experiment PXRD pattern yielded a unit cell of a = 17.05, b =
o
o
2
4.85 Å, c = 4.51 Å, α = γ = 90 , and β = 103.36 (Figure S23 and
Table S2) with good agreement factors (R = 2.84%, Rwp = 4.08%),
and the diffraction peaks were ascribed to (110), (020), (220),
040), and (001) lattice planes (Figure 2d, e, f). Notably, a mixed-
phase product could be obtained in propanol which shown both
p
(
o
o
characteristic PXRD signals at 3.45 and 6.36 (Figure S1, dark
yellow line).
On the other hand, the kagome and monoclinal m-TetPB-
COFs exhibited nearly identical PXRD patterns with that of p-
TetPB-COFs which indicates they possess almost same crystal
structures (Figure S24~26, Table S4~S5). The simulated unit
cells are a = b = 30.06 Å, c = 4.27 Å, α = γ = 90°, β = 120° for m-
TetPB-COF-K and a = 16.95 Å, b = 24.96 Å, c = 4.52 Å, α = γ =
9
0o, and β = 103.67o for m-TetPB-COF-M. The deviations of
Pawley refinement with the experimental results were negligible
as well (R = 2.06% and Rwp = 3.02% for m-TetPB-COF-K, R
.26% and Rwp = 5.99% for m-TetPB-COF-M). In contrast,
Figure 3. Nitrogen adsorption (solid) and desorption (open) isotherms at 77 K
for (a) p-TetPB-COF-K synthesized in THF and (c) p-TetPB-COF-M synthesized
in n-BuOH; Pore size distribution curves based on NLDFT calculation for (b) p-
TetPB-COF-K and (d) p-TetPB-COF-M.
p
p
=
4
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Figure 4. (a) SEM image of p-TetPB-COF-K; (b-c) HRTEM images of p-TetPB-COF-K, inset pattern is diffractogram obtained from the yellow square area; (d)
denoised image of the green square area in image (c) by ABSF filter; (e) SEM image of p-TetPB-COF-M; (f-g) HRTEM images of p-TetPB-COF-M, inset pattern is
diffractogram obtained from the yellow square area; (h) denoised image of the green square area in image (g) by ABSF filter; (i) SEM image of m-TetPB-COF-K; (j-
k) HRTEM images of m-TetPB-COF-K, inset pattern is diffractogram obtained from the yellow square area; (l) denoised image of the green square area in image
(k) by ABSF filter; (m) SEM image of m-TetPB-COF-M; (n-o) HRTEM images of m-TetPB-COF-M, inset pattern is diffractogram obtained from the yellow square
area; (p) denoised image of the green square area in image (o) by ABSF filter; (q) SEM image of o-TetPB-COF; (r-s) HRTEM images of o-TetPB-COF, inset pattern
is diffractogram obtained from the yellow square area; (t) denoised image of the green square area in image (s) by ABSF filter.
1
04.32o (Figure S28 and Table S7). The residuals for Pawley
refinement were R = 3.95% and Rwp = 5.37%, and the diffraction
(Figure S21a) resemble that of p-TetPB-COF-M. Brunauer–
Emmett–Teller (BET) surface areas for kgm topological p-TetPB-
p
2
2
peaks can be reasonably ascribed to the (110), (020), (220), (040), COF-K and m-TetPB-COF-K are 1580 m /g and 1770 m /g which
and (001) lattice planes, respectively.
The intrinsic porosity of these isomeric TetPB-COFs was
evaluated by nitrogen sorption isotherm measurements at 77 K.
As shown in Figure 3a, the isotherms of p-TetPB-COF-K
exhibited rapid uptake at low pressure (P/P
obvious step behind P/P = 0.1, which suggesting the coexistence
of micropores and mesopores. In sharp contrast, p-TetPB-COF-
M showcased typical type I sorption isotherms (Figure 3c)
indicating the exclusive presence of micropore. The pore volume
for m-TetPB-COF-K (1.493 cm /g calculated at P/P
Figure S20a) is greater than that of p-TetPB-COF-K (1.158 cm /g,
Figure 3a), but the isotherms of them are similar. Moreover, the
isotherms for m-TetPB-COF-M (Figure S20c) and o-TetPB-COF
2
are higher than their sql topological isomers (957 m /g for p-
2
TetPB-COF-M, 991 m /g for m-TetPB-COF-M) and o-TetPB-COF
2
(1080 m /g). These results are comparable to the theoretical
2
2
values (ca. 1728 m /g for TetPB-COF-K and 1267 m /g for TetPB-
COF-M) calculated by HT-CADSS approach.9d Moreover, the
pore size distribution profiles simulated by the nonlocal density
functional theory (NLDFT) further clarified the different structures
of TetPB-COFs. As shown in Figure 3b, p-TetPB-COF-K
exhibited a micropore of 7.0 Å and a mesopore of 23.3 Å which
agree with the geometrical values (7.2 Å and 23.5 Å). In contrast,
p-TetPB-COF-M (Figure 3d) only possesses a micropore of 11.3
Å, which is closed to the simulated pore size (12.7 Å). In addition,
the pore sizes calculated from the sorption isotherms of m-TetPB-
0
< 0.05) and an
0
3
0
= 0.93,
3
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COF-K (7.3 Å and 24.5 Å), m-TetPB-COF-M (12.3 Å) and o-
TetPB-COF (12.1 Å) are all consistent well with the theoretical
values (Figure S20b, d and S21b). These results further verified
the successful construction of the isomeric kgm and sql TetPB-
COFs.
the HRTEM images of p-TetPB-COF-M (Figure 4f,g) and the
denoised pattern (Figure 4h) shows good bright and dark
contrasts. Similarly, the regular kagome and rhombic pore
structures of m-TetPB-COF-K (Figure 4j-l), m-TetPB-COF-M
(Figure 4n-p), and o-TetPB-COF (Figure 4r-t) also can be directly
observed in their corresponding HRTEM images.
The morphologies and pore structures of TetPB-COFs were
examined by scanning electron microscopy (SEM) and
transmission electron microscopy (TEM) (Figure 4, S17, S18 and
S19), respectively. Interestingly, the kgm topological p-TetPB-
COF-K (Figure 4a and S17a,b) and m-TetPB-COF-K (Figure 4i
and S18a,b) exhibited flake-like morphology while sql p-TetPB-
COF-M (Figure 4e and S17c,d), m-TetPB-COF-M (Figure 4m and
S18c,d), and o-TetPB-COF (Figure 4q and S19) assume regular
rhombic shape which is rather rare for 2D COFs. The distinct
To provide more insights into the isomerism, the influences of
reaction time, temperature and concentration on the
crystallization process were systematically investigated. The time
dependent PXRD patterns revealed that both TetPB-COF-K and
TetPB-COF-M were directly formed without obvious crystal phase
transformation processes (Figure S3 and S7). Crystalline p-
TetPB-COF-K and m-TetPB-COF-K were generated at about 1 h
(Figure S3a) and 3h (Figure S7a). However, it required at least 9
h to form ordered structure of p-TetPB-COF-M (Figure S3b) and
m-TetPB-COF-M (Figure S7b) which demonstrating the
nucleation rate of TetPB-COF-K is faster than that of TetPB-COF-
M. On the other hand, as shown in Figure S2a and Figure S6a,
crystalline kgm p-TetPB-COF-K and m-TetPB-COF-K were
readily synthesized in THF over a wide temperature range (from
morphologies are probably related to the different reaction
solvents.[
21]
Furthermore, the crystalline structures of these
isomeric TetPB-COFs were confirmed by HRTEM. As illustrated
in Figure 4, the HRTEM images of p-TetPB-COF-K taken along
the [001] direction revealed a clear hexagonal honeycomb
structure (Figure 4b-c). The denoised image provides clearer
bright and dark contrasts which can be attributed to the open
channels of the kgm network (Figure 4d). On the other hand, the
uniform rhombic pore structure can also be clearly visualized in
o
R.T. to 120 C). In contrast, highly ordered sql p- TetPB-COF-M
and m-TetPB-COF-M could only be obtained at relative high
temperature (120 oC) in n-BuOH. Oligomers or amorphous
polymers were generated when the reaction temperature was
o
below 80 C (Figure S2b and S6b). This phenomenon may be
ascribed to the lower relative total energy of the kgm networks
than that of the sql frameworks (Table S3 and S6). Similarly, the
sql topological o-TetPB-COF also cannot be obtained at relative
low temperatures (Figure S10), which indicates the synthetic
solvents exert a profound effect on the nucleation process.
Moreover, once the synthetic solvent is fixed, the concentration of
these isomeric monomers has been demonstrated to exert
minimal influence on the topological structures of the
corresponding TetPB-COFs (Figure S4, S8 and S12).
To differentiate the characteristic features of these isomeric
TetPB-COFs, adsorption experiments of vitamin
B12 were
performed considering the significant difference of the pore size
and pore shape of the kagome and monoclinic TetPB-COFs. The
molecular dimension of vitamin B12 is 14.12 Å×18.35 Å×11.4
Å,[ which is accessible to the hexagonal mesoporous channels
of p-TetPB-COF-K and m-TetPB-COF-K (~23.5 Å) but should not
be compatible to the triangular micropores (~7.2 Å) and
inaccessible to these monoclinic frameworks with rhombic
micropores (~12.7 Å). The adsorption experiments of vitamin B12
were performed by soaking the five different TetPB-COF isomers
22]
(
15 mg) in an aqueous solution of vitamin B12 (30 μg/mL, 50 mL),
while the loading amounts of vitamin B12 were determined by UV-
Vis spectroscopy. As expected, both p-TetPB-COF-K and m-
TetPB-COF-K adsorb vitamin B12 because the characteristic
absorbance at 361 nm was continued to decline after immersing
the kgm TetPB-COFs into the solution (Figure 5a, c, f). However,
almost no adsorption was observed in the case of sql p-TetPB-
COF-M, m-TetPB-COF-M, and o-TetPB-COF (Figure 5b-5f).
Consequently, the drastic difference in pore characters renders
TetPB-COF isomers able to selective adsorb or separate specific
guest molecules even though they possess the same chemical
composition.
Figure 5. UV−Vis absorption spectra of the aqueous solutions of vitamin B12 in
the presence of (a) p-TetPB-COF-K, (b) p-TetPB-COF-M, (c) m-TetPB-COF-K,
(d) m-TetPB-COF-M, and (e) o-TetPB-COF at different time intervals. Almost
no adsorption in sql TPB-COFs systems after 60 min; (f) Adsorption isotherms
of vitamin B12 for p-TetPB-COF-K (black), p-TetPB-COF-M (pink), m-TetPB-
COF-K (dark cyan), m-TetPB-COF-M (violet), and o-TetPB-COF (orange).
Conclusion
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In summary, we have shown the selective growth of isomeric
covalent organic lattices to create specific topologies by designing
monomer isomers and tuning reaction conditions. Systematic and
comparative studies on three monomer isomers with tetraphenyl
H. Lin, S.-L. Wang, S. J. L. Billinge, K.-L. Lu, Y. J. Chabal, X. Zou, H.-C.
Zhou, Nat. Chem., 2020, 12, 90–97.
[
9]
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This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.202015130
RESEARCH ARTICLE
Layout 2:
RESEARCH ARTICLE
+
+
Y. Li, L. Guo, Y. Lv, Z. Zhao, Y. Ma,
W. Chen, G. Xing, D. Jiang, L. Chen*
Page No. – Page No.
Polymorphism of 2D Imine Covalent
Organic Frameworks
An efficient strategy was developed for selective growth of isomeric covalent organic frameworks by designing monomer isomers and
tuning reaction conditions. Three elaborately designed A type tetraphenyl benzene monomers (p-, m-, and o-TetPB) successfully
2
B
2
afford the corresponding five different 2D TetPB-COF isomers in a pre-designable yet synthetically controllable manner, which exhibit
selective adsorption of vitamin B12 owing to a great difference in their pore shape and size.
This article is protected by copyright. All rights reserved.