Dalton Transactions
Communication
SHU-1b is higher than those of commercial activated carbon
and natural zeolite, and very close to that of MIL-53, but
lower than those of chitosan bead and MIL-100(Fe)
(Table S3, ESI†).11
Notes and references
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The selective adsorption of MG on SHU-1, SHU-1a and
SHU-1b may be attributed to the synergistic effect of size
exclusion and acid–base interaction. The hollow layered struc-
ture may accommodate the MG molecule, and MG could
partially insert its phenyl group into the windows of the layer.
Furthermore, this kind of insertion may be favored by the π–π
interaction between the phenyl group of MG and the aromatic
backbone of SHU-1, SHU-1a and SHU-1b. The Lewis acid–base
interaction may also play an important role in the selective
adsorption. The Lewis acid site of the Ca2+ atom could interact
with the Lewis base group –N(CH3)2 of MG after the replace-
ment of coordinated solvents. More open metal sites could be
obtained in water for SHU-1b, therefore SHU-1b showed
higher adsorption capacity than those of SHU-1 and SHU-1a.
The geometry size and ionic strength of MG may match well
with the specific void structure of SHU-1, SHU-1a and SHU-1b,
and contribute to the selective adsorption. Besides,
a
preliminary study revealed that an ion-exchange mechanism
may be involved in the process of adsorption for SHU-1
(Fig. S10 and S13, ESI†).
In conclusion, we have disclosed solvent-induced structural
transformations that take place among rigid 2D MOFs. Drastic
changes in the layered structure have been observed during
the SC–SC transformation process from SHU-1 to SHU-1a,
meanwhile a reversible structural transformation has been dis-
covered between SHU-1a and SHU-1b. Furthermore, SHU-1,
SHU-1a and SHU-1b have shown the void accessibility by selec-
tive adsorption towards MG. More investigations on tuning the
structure diversity of spirobifluorene-based MOFs via the
adjustment of ligand rigidity and flexibility remain to be
conducted.
This work was financially supported by the National
Natural Science Foundation of China (21201118 & 61371021).
Dr Min Shao, Dr Hongmei Deng, Dr Hui Zhang and Dr Bo Lu
at the Instrumental Analysis and Research Center of Shanghai
University are acknowledged for their assistance with measure-
ments. We thank Prof. Zengqiang Gao from the Institute of
High Energy Physics, Chinese Academy of Sciences for his
kind help on synchrotron data reduction. We also thank 10 (a) D. Chen, W. Shi and P. Cheng, Chem. Commun., 2015,
the staff from beamlines 3W1A and 1W2B at the Beijing
Synchrotron Radiation Facility (BSRF) for their assistance with
data collection of SHU-1a.
51, 370; (b) R. Hailili, L. Wang, J. Qv, R. Yao, X.-M. Zhang
and H. Liu, Inorg. Chem., 2015, 54, 3713.
11 S.-H. Huo and X.-P. Yan, J. Mater. Chem., 2012, 22, 7449.
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Dalton Trans., 2017, 46, 8350–8353 | 8353