Structural diversity and luminescent sensing of three coordination polymers based on the hydrolysates of N,N′-bis(3,5-dicarboxylatophenyl)pyromelliticdi-imide)

Article abstract of DOI:10.1016/j.molstruc.2018.05.092

Based on the hydrolysates of N,N′-bis(3,5-dicarboxylatophenyl)pyromelliticdi-imide) (H₄L) and 1,3-bis(imidazol-1-ylmethyl)benzene (bimb), three coordination polymers, namely, {[Zn(BTC)_0.5(bimb)]·4H₂O}_n (1), [Cu(BTC)_0.5(bimb)]_n (2), and {[Cd(AIP)(H₂O)]·H₂O}_n (3), have been obtained under solvothermal conditions. The possible hydrolysis mechanism of H₄L was investigated here. Structural analyses reveal that complex 1 is a 3D (4,4)-c {6⁴.8²}{6⁶}₂-bbf net. Complex 2 displays a 2D 4-c {3².6².7²}-kgm sheet. While complex 3 exhibits a 3D (3,6)-c {4.6²}₂{4².6¹⁰.8³}-rtl net based on binuclear {Cd₂(COO)₄} SBUs. Besides, luminescent sensing investigation indicated that 1 and 3 exhibit highly sensitive and selective sensing of chromate anions in aqueous solution.

Full text of DOI:10.1016/j.molstruc.2018.05.092

Journal of Molecular Structure 1171 (2018) 54e61
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Structural diversity and luminescent sensing of three coordination
polymers based on the hydrolysates of N,N0-bis(3,5-
dicarboxylatophenyl)pyromelliticdi-imide)
,
*
Liming Fan a, Jiang Wang a, Li Zhao a, Yujuan Zhang a, Xiaoqing Wang a, Tuoping Hu a
,
,
**
Xiutang Zhang b
a Department of Chemistry, College of Science, North University of China, Taiyuan 030051, China
b Advanced Material Institute of Research, College of Chemistry and Chemical Engineering, Qilu Normal University, Jinan, 250013, China
a r t i c l e i n f o
a b s t r a c t
Based on the hydrolysates of N,N0-bis(3,5-dicarboxylatophenyl)pyromelliticdi-imide) (H4L) and 1,3-
bis(imidazol-1-ylmethyl)benzene (bimb), three coordination polymers, namely, {[Zn(BTC)0.5(bimb)]$
4H2O}n (1), [Cu(BTC)0.5(bimb)]n (2), and {[Cd(AIP)(H2O)]$H2O}n (3), have been obtained under sol-
vothermal conditions. The possible hydrolysis mechanism of H4L was investigated here. Structural an-
alyses reveal that complex 1 is a 3D (4,4)-c {64.82}{66}2-bbf net. Complex 2 displays a 2D 4-c {32.62.72}-
kgm sheet. While complex 3 exhibits a 3D (3,6)-c {4.62}2{42.610.83}-rtl net based on binuclear
{Cd2(COO)4} SBUs. Besides, luminescent sensing investigation indicated that 1 and 3 exhibit highly
sensitive and selective sensing of chromate anions in aqueous solution.
Article history:
Received 20 March 2018
Received in revised form
16 May 2018
Accepted 28 May 2018
Available online 31 May 2018
Keywords:
Hydrolysis mechanism
In-situ reaction
© 2018 Elsevier B.V. All rights reserved.
Structural diversity
Self-assembly
Luminescent sensing
1. Introduction
of organic linkers, including decarboxylation, cycloaddition,
oxidation/reduction, hydrolysis, may occur in the synthesis process,
Coordination polymers (CPs), as an important branch of func-
tional materials, have been widely investigated for their interesting
structures and potential applications in the field of gas adsorption
and separation, sensing and recognition, drug delivery and release,
catalysis and photocatalysis, as well as fluorescent and nonlinear
optical properties [1e8]. Such materials are generally assembled
from organic linkers and metal nodes through coordination bonds
and other weak interactions. As we all known, the construction of
CPs are greatly effected by many factors [9e14]. Among them, there
is no doubt that the design or the rational selection of organic
linkers are the most important [15e17].
especially under hydrothermal or solvothermal conditions [18e22].
Take into consideration of high temperature and pressure, as well
as the catalytic activity of metal ions, the in-situ reactions under
hydrothermal or solvothermal conditions displaying another
perspective to investigate the reaction mechanisms [23,24], for the
coordination reaction between metal ions and generated organic
linkers can frozen the in-situ reactions [25].
Recently, we designed CPs by using the ligand of N,N0-bis(3,5-
dicarboxylatophenyl)pyromelliticdi-imide) (H4L), fortunately or
unfortunately, three CPs, namely, {[Zn(BTC)0.5(bimb)]$4H2O}n (1),
[Cu(BTC)0.5(bimb)]n (2), and {[Cd(AIP)(H2O)]$H2O}n (3), were ob-
tained based on the two hydrolysates (H4BTC and H2AIP, as shown
in Scheme 1) of H4L and 1,3-bis(imidazol-1-ylmethyl)benzene
(bimb). The possible hydrolysis mechanism of H4L was investigated.
And structure analyses reveal that 1 is a 3D (4,4)-c {64.82}{66}2-bbf
net. Complex 2 displays a 2D 4-c {32.62.72}-kgm sheet. While 3
exhibits a 3D (3,6)-c {4.62}2{42.610.83}-rtl net based on binuclear
{Cd2(COO)4} SBUs. Besides, the luminescent sensing of complexes 1
and 3 were investigated.
As the development of CPs, numerous organic linkers have been
designed. It is noteworthy that some unexpected in-situ reactions
* Corresponding author.
** Corresponding author.
E-mail addresses: limingfan@nuc.edu.cn (L. Fan), hutuopingsx@126.com (T. Hu),
xiutangzhang@163.com (X. Zhang).
https://doi.org/10.1016/j.molstruc.2018.05.092
0022-2860/© 2018 Elsevier B.V. All rights reserved.

L. Fan et al. / Journal of Molecular Structure 1171 (2018) 54e61
55
Scheme 1. The possible hydrolysis mechanism of H4L.
Scheme 2. Synthesis routes of complexes 1e3.
2. Experimental
tube, pumped into a near-vacuum, and heated at 130 ꢀC for 3 days,
and then cooled to room temperature. The pink crystals that
formed was collected by filtration with the yield of 2 is 43% (based
on Cu). Anal. (%) calcd. for C19H15CuN4O4: C, 53.46; H, 3.54; N, 13.12.
Found: C, 53.19; H, 3.56; N, 13.09. IR (KBr pellet, cmꢁ1): 3444 (m),
3129 (s), 2366 (m), 1583 (vs), 1526 (m), 1353 (vs), 1250 (m), 1102
(m), 955 (w), 865 (w), 814 (w), 718 (m), 654 (w), 544 (w) (Fig. S1,
see ESI).
2.1. Materials and methods
Chemical reagents were purchased commercially and were used
as received without further purification. Elemental analyses of C, N,
and H were performed on an EA1110 CHNS-0 CE elemental
analyzer. IR (KBr pellet) spectra were recorded on a Nicolet Magna
750FT-IR spectrometer. Thermogravimetric measurements were
carried out in a nitrogen stream using a Netzsch STA449C apparatus
with a heating rate of 10 ꢀC minꢁ1. X-Ray powder diffraction (PXRD)
was carried out on a RIGAKU DMAX2500 apparatus. Fluorescent
data were collected on the Hitachi F-4600 FL Spectrophotometer.
2.2.3. Synthesis of {[Cd(AIP)(H2O)]·H2O}n (3)
A mixture of Cd(NO3)2$4H2O (0.008 mmol), H4L (0.004 mmol),
bimb (0.008 mmol), and DMF/CH3CN/H2O (1 mL, v/v/v ¼ 1/1/2)
were added to a hard glass tube, pumped into a near-vacuum, and
heated at 130 ꢀC for 3 days, and then cooled to room temperature.
The pink crystals that formed was collected by filtration with the
yield of 3 is 37% (based on Cd). Anal. (%) calcd. for C8H9CdNO6: C,
29.33; H, 2.77; N, 4.28. Found: C, 29.38; H, 2.80; N, 4.27. IR (KBr
pellet, cmꢁ1): 3277 (m), 1616 (m), 1558 (vs), 1372 (s), 1314 (s), 1231
(m), 1083 (m), 1025 (m), 968 (m), 782 (s), 730 (s), 654 (m) (Fig. S1,
see ESI).
2.2. Syntheses of complexes 1e3 (Scheme 2)
2.2.1. Synthesis of {[Zn(BTC)0.5(bimb)]·4H2O}n (1)
A mixture of ZnCl2 (0.004 mmol), H4L (0.002 mmol), bimb
(0.004 mmol), and DMF/H2O (1 mL, v/v ¼ 1/1) were added to a hard
glass tube, pumped into a near-vacuum, heated at 130 ꢀC for 3 days,
and then cooled to room temperature. The colorless crystals that
formed was collected by filtration with the yield of 1 is 39% (based
on Zn). Anal. (%) calcd. For C19H23N4O8Zn: C, 45.57; H, 4.63; N, 11.19.
Found: C, 45.39; H, 4.69; N, 11.08. IR (KBr pellet, cmꢁ1): 3437 (s),
3129 (s), 2360 (m), 1616 (vs), 1326 (s), 1359 (vs), 1231 (m), 1096 (m),
1032 (w), 949 (m), 865 (w), 756 (m), 654 (m) (Fig. S1, see ESI).
2.3. X-ray crystallography
Single crystals of 1e3 with appropriate dimensions were chosen
under an optical microscope and quickly coated with high vacuum
grease (Dow Corning Corporation) before being mounted on a glass
fiber for data collection. Intensity data collection was carried out on
a Siemens SMART diffractometer equipped with a CCD detector
2.2.2. Synthesis of [Cu(BTC)0.5(bimb)]n (2)
A mixture of CuCl2$2H2O (0.008 mmol), H4L (0.004 mmol), bimb
(0.008 mmol), DMF/CH3CN/H2O (1 mL, v/v/v ¼ 2/1/3), and one drop
of HNO3 aqueous solution (1.5 mM) were added to a hard glass
using MoK
a
monochromatized radiation (
l
¼ 0.71073 Å). The ab-
sorption correction was based on multiple and symmetry-
equivalent reflections in the data set using the SADABS program.

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L. Fan et al. / Journal of Molecular Structure 1171 (2018) 54e61
The structures were solved by direct methods and refined by full-
matrix least-squares using the SHELXTL package [26]. Anisotropic
thermal parameters were applied to all non-hydrogen atoms. And
all hydrogen atoms attached to C and N atoms were placed
geometrically [27]. Crystallographic data for 1e3 are given in
Table S1. Selected bond lengths and angles for 1e3 are listed in
Table S2.
3. Result and discussion
3.1. Structure descriptions
3.1.1. Crystal structure of {[Zn(BTC)0.5(bimb)]·4H2O}n (1)
Although the structure as well as the luminescence in the solid
state have been reported by Lin and co-workers before [28], we
obtained it through the hydrolysis reaction of N,N0-bis(3,5-
dicarboxylatophenyl)pyromelliticdi-imide) under solvothermal
reaction and further investigated the luminescent sensing here.
Complex 1 crystallizes in the monoclinic system, space group P21/c
and the asymmetric unit contains one ZnII ion, a half of BTC4ꢁ li-
gands, one bimb linker, and four lattice water molecules (Fig. 1).
Each ZnII ion located in a distorted {ZnO2N2} tetrahedral geometry
Fig. 2. The 3D framework of 1 along a axis.
with t4 parameter is 0.89(8) (t4 ¼ [360ꢀ-(
a b a and b are
)]/141ꢀ,
þ
the two largest bond angles in the four-coordinate complexes.)
[29], completed by two carboxyl O atoms from two different BTC4ꢁ
ligands, and two imidazolyl N atoms from two bimb linkers. Be-
sides, the bond lengths of ZneO/N are in the range of 1.993(0)ꢁ
2.008(2) Å.
The H4BTC is completely deprotonated and coordinated with
four ZnII ions by adopting (k1 0)-(k1 0)-(k1 0)-(k1 0)-m4 coor-
-k -k -k -k
dination mode (Mode I, Scheme 3). Four monodentate h1 carboxyl
groups of each BTC4ꢁ ligand connected four ZnII ions, leaving a 2D
[Zn2(BTC)]n sql sheet, with the nearest Zn/Zn distances being
Fig. 3. The simplified binodal (4,4)-connected {64.82}{66}2-bbf topology of 1.
Fig. 1. The coordination environment of Zn(II) ion in 1 (Symmetry codes: A: x, 1/
2ey, ꢁ1/2 þ z; C: 1ex, ꢁ1/2 þ y, ꢁ1/2ez; D: 1ex, 1/2 þ y, ꢁ1/2ez; E: 2ex, ey, ez.).
Scheme 3. The coordination modes of H4BTC/H2AIP in 1 and 2.
Fig. 4. Tiling featured net for the framework of 1.

L. Fan et al. / Journal of Molecular Structure 1171 (2018) 54e61
57
Fig. 8. The coordination environment of Cd(II) in 3 (Symmetry codes: A: 1ex, ey, 1ez;
D: ꢁ1þx, y, z; E: ꢁ1/2 þ x, 1/2ey, 1/2 þ z.).
Fig. 5. The coordination environment of Cu(II) in 2 (Symmetry codes: A: 1/2ex, 1/2ey,
e2ez; B: x, ey, z; C: 1ex, y, e2ez; D: 1ex, ey, e2ez.).
Fig. 9. The 3D network of 3 view along b axis.
6.212(8) Å, and 9.079(3) Å (Fig. S2). Besides, the bimb linkers
bridged the adjacent ZnII ions to form a 1D [Zn(bimb)]n polymeric
chain (Fig. S3), with the bimb separated Zn/Zn distance is
11.705(2) Å. By sharing the central ZnII ions, a 3D framework was
constructed finally (Fig. 2). PLATON software revealed the porosity
of 1 is 3.9% (88.3 out of the 2279.1 Å3 unit cell volume) [30].
Fig. 6. The 2D sheet of 2 view along c axis.
Fig. 10. The simplified binodal (3,6)-connected {4.62}2{42.610.83}-rtl topology of 3.
Fig. 7. The simplified 4-connected {32.62.72}-kgm sheet of 2.

58
L. Fan et al. / Journal of Molecular Structure 1171 (2018) 54e61
To illustrate the structure of 1, the topological analysis approach
through four monodentate (k1 0)-m1 carboxyl groups. BTC4ꢁ li-
-k
is employed [31]. The final structure of 1 can be regard as a binodal
4,4-c net with stoichiometry (4-c)(4-c)2 by denoting both the ZnII
ions and BTC4ꢁ ligands as 4-connected nodes (Fig. 3). And the Point
(Schlafli) symbol for net is {64.82}{66}2 with topological type being
bbf (topos&RCSR.ttd). Further analysis of modular design reveals
that the tiling of 1 is [68] ¼ [6a2.6 b2.6c4] with the transitivity is
2331 (Figs. S4 and 4) [32].
gands connected with CuII ions to form a 2D [Cu2(BTC)]n sheet with
the adjacent Cu/Cu distances being 7.147(2) Å, and 8.498(7) Å
(Fig. S5). At the same times, the bimb linkers bridged with CuII ions,
obtaining an interesting 1D [Cu(bimb)]n chain with bimb separated
Cu/Cu distance is 8.498(7) Å (Fig. S6). Shared with the CuII centers,
the 1D [Cu(bimb)]n chains joined the 2D [Cu2(BTC)]n sheets
together, finally formed a 3D frameworks (Fig. 6). From a topology
view, the CuII ions as well as the BTC4ꢁ ligands both be simplified to
4-connected nodes, giving rise to a 4-connected kgm sheet with
the Point (Schlafli) symbol of {32.62.72} for the final structure of 2
(Fig. 7).
3.1.2. Crystal structure of [Cu(BTC)0.5(bimb)]n (2)
Structural analysis reveals that complex 2 crystallizes in the
monoclinic system, space group C2/m space group. As shown in
Fig. 5, there are one CuII ion, half of BTC4ꢁ ligands, and one bimb
ligand in the asymmetric unit. Each CuII is tetra-coordinated,
completed by two carboxyl O atoms from two BTC4ꢁ ligands and
two imidazolyl N atoms from two different bimb linkers, resulting
in a perfect centrosymmetry {CuO2N2} parallelogram geometry
with t4 ¼ 0. The bond distances of CueO are 2.002(2) Å, and CueN
bond lengths are 1.963(8) Å, respectively.
3.1.3. Crystal structure of {[Cd(AIP)(H2O)]·H2O}n (3)
The crystal structure has been reported before [33], our nov-
elties are the synthetic method of hydrolysis reaction of N,N0-
bis(3,5-dicarboxylatophenyl)pyromelliticdi-imide
under
sol-
vothermal reaction and its luminescent sensing. Structural analysis
reveals that complex 3 crystallizes in the monoclinic system, space
group P21/n space group. As shown in Fig. 8, there are one CdII ion,
one AIP2ꢁ ligand, one coordinated water molecule, and one lattice
water molecule in the asymmetric unit. Each CdII is hepta-
coordinated, completed by six O atoms from three AIP2ꢁ ligands
and one coordinated water molecule, and one N atom from another
AIP2ꢁ ligand, resulting in a distorted {CdO6N} pentagonal bipyr-
amid geometry. The bond distances of CdeO are in the range of
2.228(0)-2.662(3) Å, and CdeN bond length is 2.243(5) Å,
respectively.
In complex 2, the H4BTC adopted similar coordination mode
(Mode I, Scheme 3) like that in complex 1, linked with four CuII ions
Table 1
Comparisons of complexes 1 and 2.
Complex
1
2
t4 of metal ion
M-BTC
M-bimb
Structure
Topology
0.89(8)
0
2D [Zn2(BTC)]n sheet
1D [Zn(bimb)]n chain
3D bbf net
2D [Cu2(BTC)]n sheet
1D [Cu(bimb)]n chain
2D kgm sheet
{32.62.72}
{64.82}{66}2
Fig. 11. The luminescence spectra of complexes 1 (a) and 3 (b) which were dispersed in
Fig. 12. The luminescence intensities of 1 (a) and 3 (b) which were dispersed in the
different solvents.
aqueous solution of different anions.

L. Fan et al. / Journal of Molecular Structure 1171 (2018) 54e61
59
In complex 3, the H2AIP is completely deprotonated and
adopting
k1 1)-(k1 2)- 1N-m4 coordination mode (Mode II,
Scheme 3) to coordinate with CdII ions. It is noteworthy that two
h2 h1 carboxyl groups connected two CdII
ions to form a binuclear {Cd2(COO)4} SBUs with the Cd/Cd dis-
tance is 3.794(4) Å (Fig. S7). Then each AIP2ꢁ ligands linked with
three {Cd2(COO)4} SBUs, finally constructed a 3D framework with
1D channels (Fig. 9). PLATON software revealed the porosity of 3 is
13.2% (126.0 out of the 953.1 Å3 unit cell volume) after removal of
solvents.
Topological analysis reveals that the final structure of 3 can be
regard as a binodal 3,6-c net with stoichiometry with stoichiometry
(3-c)2(6-c) by denoting both the {Cd2(COO)4} SBUs and AIP2ꢁ li-
gands as six-connected, and three-connected nodes, respectively
(Fig. 10). And the Point (Schlafli) symbol for the net is
{4.62}2{42.610.83} with the topological type being rtl
(topos&RCSR.ttd).
sheets (Figs. S2 and S5, Table 1). And the auxiliary ligand of bimb
can be further expanded the 2D layers into 3D networks. While the
H2AIP can provide a triangular pyramid skeleton to link metal ions,
finally expanding into 3D architecture. Compared 1 and 2, we can
found the coordination preferences of metal ions make a huge
change of the final framework, since the ZnII ion tend to form a
tetrahedron coordination geometry with t4 ¼ 0.89(8) in 1, and CuII
ion lies in a planar quadrilateral with t4 ¼ 0.00 in 2, respectively
(Table 1). All in all, the coordination preferences of different metal
ions determine the coordination reactions of H4BTC/H2AIP, and
further ascertain the final structures of obtained CPs.
(
-
k
-
k
k
chelating þ bridging m2
- :
3.3. Powder X-ray diffraction and thermal analysis
To check the phase purity of these complexes, the PXRD patterns
of title complexes were checked at room temperature. As shown in
Fig. S8, the peak positions of the simulated and experimental PXRD
patterns are in agreement with each other, demonstrating the good
phase purity of the complexes. The dissimilarities in intensity may
be due to the preferred orientation of the crystalline powder
samples. The thermal stability experiments were performed on
samples consisting of numerous single crystals under N2 atmo-
sphere with a heating rate of 10 ꢀC minꢁ1, as shown in Fig. S9. The
TGA curve of complex 1 displays steady weight loss in the tem-
perature range of 90e140 ꢀC (found 14.67%), corresponding to the
loss of lattice water molecules (calcd. 14.38%). And then the
framework can be exist stably until the temperature up to 380 ꢀC.
For 2, there is no obviously weight loss before 320 ꢀC, and a rapid
3.2. Structure discussion
As shown in Scheme 1, the H4L ligand hydrolyzed into two kinds
hydrolysates of 1,2,4,5-benzenetetracarboxylic acid (H4BTC), and 5-
aminoisophthalic acid (H2AIP) under solvothermal condition.
Furthermore, the H4BTC and H2AIP reacted with metal salts in the
presence of bimb linkers, finally leaving three CPs. Compared the
above three CPs, we can found H4BTC and H2AIP ligands have
competition effects when coordinating with metal ions. H4BTC
ligand offers a plane to connect metal ions, leaving 2D [M2(BTC)]n
Fig. 13. Effect on the emission spectra of 1 dispersed in aqueous solution upon in-
Fig. 14. Effect on the emission spectra of 3 dispersed in aqueous solution upon in-
cremental addition of (a) CrO24ꢁ and (b) Cr2O27ꢁ anions.
cremental addition of (a) CrO24ꢁ and (b) Cr2O27ꢁ anions.

60
L. Fan et al. / Journal of Molecular Structure 1171 (2018) 54e61
weight loss can be found beyond this temperature, suggesting the
decomposition of architecture. For 3, the first weight loss of 10.67%,
which occurred before 130 ꢀC, corresponds to the release of lattice
and coordinated water molecules (calcd. 11.00%), followed by a long
plateau from 140 to 395 ꢀC. And beyond 395 ꢀC, there exists a rapid
weight loss, suggesting the decomposition of architecture.
1 mg finely ground samples into 2 mL 0.01 M aqueous solutions of
thirteen different anions: KnX (X ¼ Clꢁ, Brꢁ, Iꢁ, NOꢁ3 , SO24ꢁ, CO23ꢁ
,
HCOꢁ3 , PO34ꢁ, HPO42ꢁ, H2PO4ꢁ, SCNꢁ, CrO42ꢁ, and Cr2O27ꢁ) at room
temperature. As can be seen in Figs. 12 and S12, the luminescence
intensities of Xnꢁ@CPs suspensions are heavily dependent on the
species of anions. And the Cr(IV) anions, CrO24ꢁ, and Cr2O27ꢁ, exhibits
extremely significant luminescent quenching effects.
To better understand the luminescence responses of two CPs to
chromate anions, the relationships between the concentrations of
chromate anions and the luminescence intensities were studied
here. As shown in Figs. 13 and 14, with increasing addition of
chromate anions, the intensities of luminescence intensities are
steadily decrease with the quenching rates increasing (Figs. S13 and
S14). In the concentration range of 0e0.4 mM, the I0/I versus the
concentrations of CrO42ꢁ/Cr2O27ꢁ anions can be well-fit to the
nonlinear SterneVolmer curves in exponential equations (in where,
the I0 and I are the luminescence intensities of the emulsions in the
absence and presence of the chromate anions) (Fig. 15 and Table 2).
And in the low concentration, the I0/I versus the concentrations of
chromate anions are fitted to the linear SterneVolmer of I0/I-
1¼Ksv[Cr(IV)]þC (Fig. S15) [38,39]. Besides, the anti-interference
3.4. Luminescent sensing of chromate anions
The solid state luminescent spectra of complexes 1 and 3 were
examined at room temperature, given in Fig. S10. Under the exci-
tation wavelength of 325 nm, the emissions of complexes 1 and 3
exhibit strong blue-fluorescent emission peaks at 428 nm for 1, and
396 nm for 3, respectively. The emissions are neither metal-to-
ligand charge transfer (MLCT) nor ligand-to-metal transfer
(LMCT) for the Zn/CdII ions are difficult to oxidize or reduce due to
their d10 configurations. Thus, they can be assigned to intraligand
(p*/n or p*/p) emission [34,35]. Eight kinds of solvent mole-
cules, including DMA, DMF, DMSO, MeOH, MeCN, EtOH, BuOH, and
H2O, were selected to choose a suitable solvent in the following
detection of anions. As shown in Figs. 11 and S11, after the finely
ground samples of 1 and 3 (1 mg) were dispersed in 2 mL different
solvents, those spectra displaying different luminescent intensities,
the strongest in H2O and the weakest in BuOH for both two CPs.
Different emissions with distinct intensities in those solvents can
be attributed to the weak interactions between the architectures
and the guest solvent molecules [36,37]. Considering the strongest
luminescent intensity in H2O and the daily detection of waste
water, the aqueous solutions were selected in the following tests.
For two CPs, the sensing of anions were performed by adding
Table 2
Related parameters in the sensing of chromate anions in 1 and 3.
Anion
Quenching rate
Exponential equation
Ksv (Mꢁ1
)
1
3
CrO24-
46.19%
77.52%
45.06%
70.06%
I0/I ¼ 0.68e2044[CrO42ꢁ]þ0.32
I0/I ¼ 1.35e3152[Cr2O72ꢁ]-0.34
I0/I ¼ 1.41e1164[CrO42ꢁ]-0.42
I0/I ¼ 1.07e2885[Cr2O72ꢁ]-0.06
1.57 ꢂ 103
5.97 ꢂ 103
1.84 ꢂ 103
4.17 ꢂ 103
Cr2O27ꢁ
CrO24-
Cr2O27ꢁ
Fig. 15. The plots of I0/I versus concentrations of chromate anions in the series aqueous suspension of 1 and 3.

L. Fan et al. / Journal of Molecular Structure 1171 (2018) 54e61
61
abilities of two CPs for sensing chromate anions are displayed in
References
Figs. S16 and S17, indicating both two CPs show good anti-
interference abilities in detecting chromate anions from normal
anions in aqueous solution. To further learn the recyclability of
complexes 1 and 3 as sensor in detecting chromate anions, the
quenching effects were tested for three cycles, and no evidently
reduces being found (Fig. S18). After the tests, the PXRD patterns of
the recycled samples are still well correspond with the simulated
data of those CPs (Fig. S19). This phenomenon shows that com-
plexes 1 and 3 may be good candidates to detect chromate anions.
The possible luminescence quenching mechanism of two CPs for
chromate anions were investigated here. UVevis absorption
spectra of chromate anions in aqueous solution was recorded. As
shown in Fig. S20, chromate anions in aqueous solution both show
two broad absorption bands are 258 and 360 nm for Cr2O27ꢁ and 273
and 372 nm for CrO24ꢁ anion, which cover the absorption bands of
the complex 1 (210e340 nm), complex 3 (210e360 nm), indicating
that there are competitive absorptions of the exciting light between
the chromate anions and CPs. Hence, the luminescence quenching
by chromate anions may be the process involving competitive ab-
sorption on light excitation between the chromate anions and the
CPs as well as energy resonance transfer from the frameworks of
complexes 1 and 3 to chromate anions [40e43].
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Acknowledgements
The work was supported by financial support from the Natural
Science Foundation of China (Grant Nos. 2160806, 21676258),
Natural Science Foundation of Shanxi Province (No.
201601D021053), and Qilu Normal University is also gratefully
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Appendix A. Supplementary data
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.molstruc.2018.05.092.