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CrystEngComm
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attractions and C-H
dehydrated, ensuring the stability of the dehydrated crystal.
…
Br HBs after the PMC-bpy was novel PMCs. The dehydrated crystal can returnViteow AirttsicleinOintliinael
state when rehydrated, illustrating DOI: 10.1039/C6CE02197B
reversible and
a
Another point that deserves comment is that PXRD pattern reproducible performance for water uptake and removal.
of the rehydrated crystal is much similar to that of the initial
crystal. This illustrates that the dehydrated crystal would
return to the initial structure, to some extent, upon the
Conclusions
rehydration. This is consistent with the water
adsorption/desorption results.
FT-IR spectra. The temperature-dependent in situ FT-IR spectra
In summary, we have successfully constructed a porous
molecular crystal by means of discrete metal complexes. The
resulting PMCs are of porosity, verified by water sorption
experiments. We have not only confirmed that there are
various crystal water existing in adsorption and desorption
processes, which can stabilize the crystal structure with 2D
hydrogen bond network, but also demonstrated that the
were used to provide the experimental evidences for C–H⋯O
interactions and structural change of alkyl chains in crystals.
The PMC-bpy samples, identical to the species for PXRD, were
used for FT-IR measurements. FT-IR spectra of PMC-bpys in the
process of the dehydration together with more details are
dehydrated crystal can still retain
structures. Specially, such PMC-bpys show
a
typical crystalline
great
given in Figure S10
attributed to the C-H stretching vibration and bending
vibration of the bipyridine ring caused by C–H O interactions
†. On one hand, the blue-shifting peaks
a
reproducibility for the water adsorption/desorption. Our
findings indicate that the metal-ligand coordination complex
can be utilized as a building block to construct PMCs, since it
can provide various additional interacting sites and cohesions,
favoring an enhanced stability of crystal structures.
⋯
between bipyridine ring and water, 34-36 gradually diminish or
disappear as the temperature is elevated. This confirms that
the crystal water decreases with the increasing temperature in
the dehydration process. On the other hand, a structural
change in alkyl chains takes place in the dehydration process,
confirmed by the blue shifts of methylene stretching vibration
peaks37 and the change in the -CH2- scissoring vibration
band.38,39
Acknowledgements
This work is supported by the National Natural Science
Foundation of China (No.21273074, 91334203, 21576079), the
111 Project of China (No.B08021) and the Fundamental
Research Funds for the Central Universities of China
(WK1213003).
FT-IR absorption spectra of dehydrated PMC-bpys during
cooling in air atmosphere were also investigated by the
temperature-dependent in situ FT-IR, as shown in Figure S11†.
A notable feature is that all characteristic peaks return to their
initial state after this cooling process. All changes of such
peaks in FT-IR spectra mentioned in the heating/cooling cycles
are reversible, which implies that in the cooling process the
dehydrated crystal could rapidly rehydrate in the air. This
result confirms that the dehydrated crystal has a sensitive
response to external moisture. More importantly, FT-IR results
of both dehydration and rehydration lend support for the
presence of the change in the crystal structure upon the water
removal/uptake, namely that the PMC-bpy shows a reversible
water adsorption-desorption characteristic.
Taken together, all results show that the introduction of
coordinative metals plays two important roles in tuning the
structure and the stability of porous molecular crystals. Firstly,
it favors the formation of the 2D HB network in the water-
included crystal. Here, the unique 2D HB network can be
attributed to the fact that the host scaffold provides various
interacting sites for crystal water, including the CHX groups, μ-
OH, counter ions and the coordinating metal ion Cu (II) as well.
Secondly, the dehydrated crystal can maintain a relatively
stable crystal structure as a result of the additional interaction
of the coordinative metal ion and its counterion with host
molecules, instead of collapsing into or forming an amorphous
substance, compared with 12-2Ar crystal. The PMC-bpy
presents an enhanced stability of crystal structures due to the
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