Construction of functional coordination polymers derived from designed flexible bis(4-carboxybenzyl)amine

Article abstract of DOI:10.1039/c8ce01418c

Four coordination polymers (CPs), [Zn₂(H₂BCA)₂(o-bimb)₂(H₂O)₂]_n (1), {[Pb(H₂BCA)(p-bib)_0.5]·H₂O}_n (2), {[Cd₂(H₂B

Full text of DOI:10.1039/c8ce01418c

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Construction of functional coordination polymers
derived from designed flexible bisIJ4-
carboxybenzyl)amine†
Cite this: DOI: 10.1039/c8ce01418c
Xiutang Zhang, ‡* Hongtai Chen, Bin Li, Guangzeng Liu and Xinzheng Liu
Four coordination polymers (CPs), [Zn
[Cd IJH BCA) IJp-bib) ]·(H O) (3) and {[ZnIJH
designed flexible bisIJ4-carboxybenzyl)amine (H
,4-diylbisIJ1H-imidazole), m-bib 1,3-bisIJ1-imidazoly)benzene, and o-bimb
2
IJH
2
BCA)
BCA)IJm-bib)]·H
BCA) with bisIJimidazole) linkers (p-bib = 1,1′-benzene-
1,2-bisIJimidazol-1-
2
IJo-bimb)
2
IJH
2
O)
2
]
n
(1), {[PbIJH
2 2 n
BCA)IJp-bib)0.5]·H O} (2),
{
2
2
2
2
2
}
3 n
2
2
O}
n
(4), have been derived from the
2
1
=
=
ylmethyl) benzene). X-ray single crystal diffraction analyses reveal that complex 1 is a 3D supramolecular
structure composed of 2D 3-connected hcb layers via hydrogen contacts. Complex 2 exhibits a 3D
4
2
4
6
2
-nodal (4,5)-connected {4 .6 }{4 .6 }-tcs net. Complex 3 shows a novel 2-nodal 3D (4,5,5)-connected
6
3
2
2
2
net with the point symbol {4.6 .8 }
2
{4 .6 .8 }. Complex
4
displays
a
3D 3-fold interpenetrating
3
Received 22nd August 2018,
Accepted 5th December 2018
3-connected {10 } ThSi2 net. Structural comparison reveals that the central ions as well as the auxiliary
2
ligand play critical roles in determining the coordination modes of H BCA and the final structures. In
addition, the luminescence measurements of two zinc-containing compounds (1 and 4) have been
DOI: 10.1039/c8ce01418c
2
−
2 7
discussed and show excellent selectivity and sensitivity in detecting acetone molecules and Cr O /
2−
rsc.li/crystengcomm
CrO
4
anions in aqueous solution.
nescent CPs have received great interest because they can be
employed for the selective and sensitive detection of environ-
mental pollutants.
Introduction
7
–9
Coordination polymers (CPs) as a new type of functional ma-
terials have attracted great interest due to their novel topolog-
ical diversities, special physical or chemical properties, and a
wide range of potential uses. With the improvement of the
level of industrialization and the development of human so-
cial activities, environmental and water pollution have be-
Ligand selection is crucial to the synthesis of CPs, and the
spatial configurations of the carboxylate ligands have a direct
bearing on the structure and the corresponding application
properties of the compounds. Depending on whether the con-
figuration of the ligand can be distorted, they can be divided
into rigid or flexible ones. Compared with rigid ligands, flexi-
ble ligands have stronger deformability, which can adapt to
different coordination environments and induce diverse
1
–3
4
–6
come a major problem.
Among these pollutants, a large
number of small toxic organic molecules and heavy metal
ions have caused a great negative impact on the survival of
human beings. Therefore, the effective and rapid detection of
these pollutants is crucial to environmental safety and land
security. As a new type of potential functional material, CPs
have great applications in the fields of gas adsorption and
separation, catalysis and photocatalysis, molecular sensing
and fluorescence probing, and so on. Among them, the lumi-
1
0
structures such as holes and interpenetrating structures,
while carboxylate ligands are considered to be excellent struc-
tural constructors and mostly used to construct coordination
1
1
polymers due to their versatile coordination modes. BisIJ4-
carboxybenzyl)amine (H BCA) has a unique –C–NH–C– flexi-
2
ble group. The H BCA ligand can rotate freely around a C
2
atom of its own, which is adaptable to more environments in
the process of self-assembly with metal ions.
Inspired by the above-mentioned points and following our
recent research, we have synthesized a flexible ligand, bisIJ4-
carboxybenzyl)amine (H BCA), and used it to react with tran-
2
sition metal ions with bisIJimidazole) linkers as auxiliary
ligands, finally resulting in four CPs with distinct structures
ranging from a 2D 3-connected hcb layer for 1, a 3D (4,5)-
connected tcs net for 2, a 3D novel (4,5,5)-connected net for 3
and 3D 3-fold interpenetrated 3-connected ThSi2 nets for 4.
Advanced Material Institute of Research, College of Chemistry and Chemical
Engineering, Qilu Normal University, Jinan, 250013, China.
E-mail: xiutangzhang@163.com
†
Electronic supplementary information (ESI) available: Additional figures, pow-
der XRD patterns, TG curves, and X-ray crystallographic data. CCDC 1568821 for
, 1568819 for 2, 1568822 for 3, and 1568820 for 4. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c8ce01418c
Current address: Department of Chemistry, College of Science, North Univer-
1
‡
sity of China, Taiyuan 030051, China.
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Luminescence investigations of 1 and 4 indicated that they
are efficient blue emission materials, which show excellent
selectivity and sensitivity in detecting acetone molecules and
2−
2−
Cr O /CrO4 anions in aqueous solution.
2
7
Experimental section
Materials and methods
The raw materials for the synthesis of bisIJ4-carboxybenzyl)-
amine and a series of bisIJimidazole) ligands were purchased
from Jinan Henghua Sci. & Tec. Co. Ltd. and were used with-
out further purification. Elemental analyses were carried out
on a Vario MACRO cube elemental analyzer. TGA was carried
out from 25 to 700 °C on a ZCTA analyzer at a heating rate of
2
Scheme 2 The route for the synthesis of H BCA.
in a 25 mL Teflon-lined stainless steel vessel was put into an
oven at 120 °C for 3 days and then cooled to room tempera-
ture slowly. Colourless block crystals of 1 were obtained with
−
1
1
0 °C min under air atmosphere. X-ray powder diffractions
of the title compounds were measured on a Rigaku D/Max-
500 PC diffractometer with Mo-Kα radiation over the 2θ
a yield of ca. 76% (based on H BCA). Anal. calcd. for
2
2
28 25 5 5
C H N O Zn: C, 58.29; H, 4.37; N, 12.14 (%). Found: C,
range of 5–50° at room temperature. Fluorescence spectra
were recorded on a Hitachi F-4600 FL spectrophotometer at
room temperature.
58.68; H, 4.02; N, 12.75 (%).
Preparation of {[PbIJH
2 2 n
BCA)IJp-bib)0.5]·H O} (2)
A mixture of H BCA (0.17 mmol, 0.050 g), p-bib (0.20 mmol,
Synthesis of N,N′-bisIJ4-carbonylbenzyl)amine (H BCA)
2
2
0
.042 g), PbIJOAC)
2
·3H
2
O (0.20 mmol, 0.065 g), NaOH (0.30
O in
A mixture of (1)–(5) (0.10 mol) (Scheme 2), 20 g NaOH, and
mmol, 0.012 g), 3 mL DMF, 3 mL methanol and 6 mL H
2
2
00 mL H O was sealed in an autoclave and heated to 180 °C
2
a 25 mL Teflon-lined stainless steel vessel was put into an
oven at 120 °C for 3 days and then cooled to room tempera-
ture slowly. Colourless block crystals of 2 were obtained with
a yield of ca. 69% (based on H BCA). Anal. calcd. for
C
for one night. The cooled solution was acidified and filtered.
White powder was obtained with a yield of 50–70%. EI-MS:
−
m/z [M − H] , 284.10 (calcd for C H NO , 285.10). Anal. (%)
1
6
15
4
2
4
calcd. for C16H15NO , C, 67.36; H, 5.30; N, 4.91. Found: C,
7.25; H, 5.18; N, 4.81. The H NMR data of the designed
44 40 6 9 2
H N O Pb : C, 43.63; H, 3.33; N, 6.94 (%). Found: C,
1
6
44.21; H, 3.18; N, 6.84 (%).
H BCA ligand are shown in Fig. S9.†
2
Preparation of {[Cd IJH BCA) IJp-bib) ]·(H O) } (3)
2
2
2
2
2
3 n
Preparation of {[ZnIJH BCA)IJm-bib)]·H O} (1)
2
2
n
The synthesis process of 3 is similar to that of compound 2
except that PbIJOAC) ·3H O (0.20 mmol, 0.065 g) was replaced
A mixture of H
2
BCA (0.17 mmol, 0.050 g), m-bib (0.20 mmol,
2
2
0
.042 g), ZnSO ·7H O (0.20 mmol, 0.057 g), NaOH (0.10
4
2
4 2
by GdSO ·8/3H O (0.20 mmol, 0.051 g). Colourless flake crys-
tals of 3 were obtained with a yield of ca. 45% (based on
2
mmol, 0.0040 g), 3 mL DMF, 3 mL methanol and 6 mL H O
H BCA). C H Cd N O : C, 53.90; H, 4.04; N, 11.22 (%).
2
56 50
2 10 10
Found: C, 53.62; H, 4.31; N, 11.38 (%).
Preparation of [Zn IJH BCA) IJo-bimb) IJH O) ] (4)
2
2
2
2
2
2 n
A mixture of H
2
BCA (0.15 mmol, 0.044 g), o-bimb (0.30
mmol, 0.071 g), ZnSO ·7H O (0.30 mmol, 0.086 g), NaOH
4
2
(
0.20 mmol, 0.080 g), 3 mL ethanol and 6 mL H
mL Teflon-lined stainless steel vessel was put into an oven at
50 °C for 5 days and then cooled to room temperature
slowly. Colourless block crystals of 4 were obtained with a
yield of ca. 69% (based on BCA). Anal. calcd. for
C H N O Zn : C, 59.56; H, 4.83; N, 11.58 (%). Found: C,
2
O in a 25
1
H
2
60
58 10 10
2
58.93; H, 4.96; N, 12.08 (%).
X-ray crystallography
Intensity data collection was carried out on a Siemens
SMART diffractometer equipped with a CCD detector using
Mo-Kα monochromatized radiation (λ = 0.71073 Å) at 296 (2)
2
Scheme 1 The coordination modes of H BCA.
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K. The absorption correction was based on multiple and
symmetry-equivalent reflections in the data set using the
SADABS program. The structures were solved by direct
methods and refined by full-matrix least-squares using the
SHELXTL package. All non-hydrogen atoms were refined
anisotropically. Hydrogen atoms except those on water mole-
cules were generated geometrically with fixed isotropic ther-
mal parameters and included in the structure factor calcula-
tions. Crystallographic data for compounds 1–4 are given in
Table 1. Selected bond lengths and angles for 1–4 are listed
in Table S1.† Further details on the crystal structure investiga-
tions may be obtained from the Cambridge Crystallographic
Data Centre, with the CCDC depository number 1568821 for
the two benzene rings)], leaving a 1D snake-like [ZnIJH BCA)]n
2
chain with the neighbouring ZnIJ1)⋯ZnIJ1) distance being
2
15.69 Å. Meanwhile, two μ -m-bib ligands adopt the cis-
configuration to bridge two neighbouring chains with the di-
hedral angles δ and ε being 36.64° and 66.64° (δ and ε corre-
spond to the dihedral angles between the central benzene
ring with the two terminal imidazole rings), successfully con-
struct a binuclear [Zn IJH BCA) IJ1,3-bib) ] chain, in which the
1
2
2
2
2
2
nearest ZnIJ1)⋯ZnIJ1) distance is 9.62 Å, and further extended
II
to a 2D layer structure by sharing the Zn ions (Fig. 1b).
II
In order to explore the topology of compound 1, each Zn
ion can act as a 3-c node; the structure of 1 can be simplified
3
into a 3-connected layer with the point symbol {6 } and the
1, 1568819 for 2, 1568822 for 3, and 1568820 for 4.
topological type being hcb (uninodal.ttd) (Fig. 1c), while the
2
[ZnIJH BCA)IJ1,3-bib)] units are expanded into a 3D supramo-
lecular structure through hydrogen bonds (C(22)–HIJ22)⋯OIJ1)
and C(16)–HIJ16A)⋯OIJ4)) (Fig. 1d). The free water molecules
lie between layers. Selected hydrogen bond data for com-
pound 1 are shown in Table 3.
Results and discussion
Structural description of {[ZnIJH BCA)IJm-bib)]·H O} (1)
2
2
n
Single-crystal X-ray diffraction analyses reveal that compound
crystallizes in the monoclinic system with the space group
1
II
1 2
P2 /n. The unit contains one Zn ion, one H BCA ligand, one
II
Structural description of {[PbIJH
Structural analysis reveals that compound 2 crystallizes in
the monoclinic system with the space group P2 /n and the
2 2 n
BCA)IJp-bib)0.5]·H O} (2)
m-bib ligand, and one free water molecule (Fig. 1a). The Zn
ion is located in a slightly distorted {ZnO N } trigonal bipyra-
midal geometry, completed by three O atoms from two
3
2
1
II
H BCA ligands [ZnIJ1)–OIJ1) = 1.97(1), ZnIJ1)–OIJ2) = 2.76(1),
2
asymmetric unit consists of one Pb ion, one H BCA ligand,
2
ZnIJ1)–OIJ3) = 1.93(1) Å] and two N atoms from two 1,3-bib
ligands [CoIJ1)–NIJ4) = 2.02(1), ZnIJ1)–NIJ5B) = 2.00(1) Å], with
τ = 0.541 (τ = |γ–β|/60°, in which β and γ are the two largest
half a p-bib linker, and one lattice water molecule. As shown
II
in Fig. 2a, the Pb ion is located in a distorted {PbO
5
N} octa-
hedral coordination environment, completed by five carboxyl
5
5
bond angles in the five-coordinate compound; here, β =
O atoms from three different H BCA ligands [PbIJ1)–OIJ1) =
2
1
3
∠
OIJ2)ZnIJ1)OIJ3) = 153.92°, γ = ∠OIJ3)ZnIJ1)NIJ5A) = 120.49°).
2.60(2) Å, PbIJ1)–OIJ2) = 2.41(2) Å, PbIJ1)–OIJ2B) = 2.87(2) Å,
PbIJ1)–OIJ4) = 2.34(2) Å, and PbIJ1)–OIJ5) = 2.67(2) Å] and one N
atom from a 1,4-bib linker [PbIJ1)–NIJ2) = 2.51(2) Å].
In the assembly process of compound 1, the H BCA is
2
II
completely deprotonated and connected with two Zn ions
which adopted (η )–(η )-μ
1
2
2
coordination modes [Mode I, see
In complex 2, the completely deprotonated H
2
BCA ligand
2
2
1
Scheme 1, with α = 88.23° (α = the dihedral angle between
adopts the coordination mode of (η )–(η : η )-μ (Mode IV,
3
Table 1 Summary of crystal data and structure refinement parameters for compounds 1–4
Compound
1
2
3
4
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C
28
H
25
N
5
O
5
Zn
C
44
H
40
N
6
O
Pb
9 2
C
56
H
50Cd
2
N
O
10 10
C
60 58 10 2
H N O10Zn
576.90
Monoclinic
P2 /n
10.1766(4)
18.0574(8)
15.0263(6)
108.4870
2617.78IJ19)
4
1211.20
Monoclinic
P2 /n
11.7153(5)
7.8003(3)
23.8533IJ10)
96.4710IJ10)
2165.90IJ15)
2
1247.86
Monoclinic
P2 /c
22.0684(9)
17.0982(7)
14.8533(6)
104.6660IJ10)
5422.0(4)
4
1209.9
Monoclinic
C2
19.4892IJ11)
16.7208IJ10)
19.5898IJ16)
119.827
5538.17(6)
4
1
1
1
b (Å)
c (Å)
β (°)
3
V (Å )
Z
D
−3
calcd (Mg m
)
1.463
0.986
1.857
7.825
1.529
0.853
1.451
0.937
−
1
μ (mm
)
θ range (°)
3.7–25.00
34 336
4005/12/376
1192
2.95–24.99
27 210
3812/4/285
1164
2.99–25.00
71 505
9536/7/719
2528
3.18–25.01
28 105
9610/165/721
2512
Reflections collected
Data/restraints/parameters
F (000)
R
R
int
0.0931
0.3666
0.0656
0.1331
1
(wR
2
) (all data)
R
1
= 0.0642,
R
1
= 0.0780,
wR = 0.2051
1.004
R
1
= 0.0690,
wR = 0.1695
1.002
R
1
= 0.1191,
wR = 0.1849
1.066
wR = 0.1188
2
2
2
2
Gof
= Σ‖F
1.002
2
o
2 2
2 2 1/2
R
1
o
c
| − |F ‖/Σ|F
o
|, wR
2
= [ΣwIJF
− F
c o
) ]/ΣwIJF ) ] .
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Fig. 1 (a) The coordination environment of Zn ions in 1 with one free water molecule omitted, (symmetry codes: A: 1 − x, −y, 2 − z; B: 1.5 + x, 0.5
3
−
y, 0.5 + z). (b) The 2D layer of compound 1. (c) The 2D 3-connected hcb layer with the point symbol {6 }. (d) The 3D supramolecular structure by
the hydrogen bonds of compound 1.
Table 2 Structural comparison and discussion of compounds 1–4
Compound
Coord. mode
Coord. environment
{ZnO
Ancillary ligands/role
Dihedral angle (°) of H
2
BCA
Structure and topology
1
2
3
4
Mode (I)
3 2
N }
m-Bib/bridging
p-Bib/bridging
p-Bib/bridging
o-Bimb/bridging
88.23
65.75
65.51
40.25
2D 3-connected hcb layer
Mode (IV)
Mode (II, III)
Mode (I)
{PbO
{CdO
{ZnN
5
N}
3D (4,5)-connected tcs net
3D novel (4,5,5)-connected net
3D 3-fold 3-connected ThSi2 net
4
N
2
}, {CdO
5 2
N }
2 3
O }
II
with α = 65.75°) to link three Pb ions and further extends
into a 2D [PbIJH BCA)] fishbone-like polymeric sheet (Fig. 2c)
described as a 3D 2-nodal 4,5-connected net (Fig. 2d). The
point symbol for this net is {4 .6 }{4 .6 }, with the topological
type being tcs.
4
2
4
6
2
n
with the Pb1⋯Pb1 distances being 17.11 Å, 14.17 Å, and 4.33
Å. At the same time, the trans-p-bib linker acts as a bridge to
link two adjacent Pb ions with the distance of PbIJ1)⋯PbIJ1)
being 14.60(1) Å and the dihedral angles δ and ε being 38.14°
and 38.14°, respectively, successfully connecting
PbIJH BCA)]n sheet into a 3D [PbIJH BCA)IJp-bib)
0.5 n
work. The μ -OIJ2) atom located on the carboxyl group con-
nects two Pb ions, leaving left- and right-handed [–PbIJ1)–
OIJ2)–PbIJ1)–]n helix chains, respectively (Fig. 2b), with
II
Structural description of {[Cd
Structural analysis reveals that compound 3 crystallizes in
the monoclinic system with the space group P2 /c. The asym-
metric unit contains two crystallographically independent
2 2 2 2 2 3 n
IJH BCA) IJp-bib)] ·(H O) } (3)
a
2D
1
[
] frame-
2
2
2
II
II
Cd ions, two H BCA ligands, two p-bib ligands, and three
2
free water molecules. As shown in Fig. 4a, Cd(1) is located in
a distorted {CdO N } octahedral coordination environment,
4
2
∠
PbIJ1)OIJ2)PbIJ1) = 109.96° and ∠OIJ2)PbIJ1)OIJ2) = 131.76°.
These two kinds of 1D chiral helical chains can connect as
the backbones into a 3D structure through the H BCA and
completed by four O atoms (O(5), O(6E), O(7), and O(8)) from
three carboxyl groups on three different H BCA ligands
CdIJ1)–OIJ5) = 2.26(1) Å, CdIJ1)–OIJ6E) = 2.32 (1) Å, MnIJ1)–OIJ7) =
2
2
[
1
,4-bib linkers.
II
2.44(1) Å, and CdIJ1)–OIJ8) = 2.44(1) Å] and two N atoms from
two 1,4-bib linkers [CdIJ1)–NIJ8) = 2.28(1) Å, CdIJ1)–NIJ9) =
From the viewpoint of topology, the Pb ion can act as a
-connected node, while the H BCA and p-bib ligands can be
simplified to a 5-connected node. The whole structure can be
4
2
2.28(1) Å]. The coordination geometry of Cd(2) is a centro-
symmetric {CdO N } pentagonal bipyramid, which was com-
5
2
pleted by five O atoms (O1, O(2), O(3), O(4), and O(4D)) from
three carboxyl groups of three H BCA ligands [CdIJ2)–OIJ1) =
2
Table 3 Selected hydrogen bond data for 1
2.51(1) Å, CdIJ2)–OIJ2) = 2.33(1) Å, CdIJ2)–OIJ3) = 2.38(1) Å,
D–H⋯A
dIJH⋯A)/[Å]
dIJD⋯A)/[Å]
∠(D–H⋯A)/[°]
CdIJ2)–OIJ4) = 2.53(1) Å, CdIJ2)–OIJ4E) = 2.33(1) Å], and two N
atoms from two distinct 1,4-bib ligands [CdIJ2)–NIJ3) = 2.28(1)
Å, CdIJ2)–NIJ5) = 2.29(1) Å].
C22–H22⋯O1
C16–H16A⋯O4
2.72
2.78
3.38
3.54
128
135
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Fig. 2 (a) The coordination environment of Pb ions in 2 with one free water molecule omitted (symmetry codes: A: 1 − x, 1 − y, 1 − z; B: 0.5 − x,
2
−
n
6
0
.5 + y, 0.5 − z; C: 0.5 + x, 0.5 − y, −0.5 + z). (b) The left- and right-handed [PbIJO )]
2 n
helix chains in 2. (c) The 2D [PbIJH BCA)] sheet viewed along
4
2
4
the a axis of 2. (d) The 3D 4,5-connected tcs net with the point symbol {4 .6 }{4 .6 } of 2.
II
Fig. 3 (a) The coordination environment of Cd ions in 3 with three water molecules omitted (symmetry codes: A: 1 − x, −0.5 + y, 1.5 − z; B: −1 +
x, −1 + y, z; C: x, 1 − y, −0.5 − z; D: 1 − x, −y, 1 − z; E: 2 − x, 1 − y, 1 − z). (b) The 2D [Cd
2 2 2 4 2 n
IJμ -H bca)IJμ -H bca)] sheet in 3 viewed along the b axis. (c)
The coordination mode of the 1,4-bib linker in 3 viewed along the c axis. (d) The 3D framework of 3. (e) The novel 3D 4,5-connected net with the
6
3
2
2
2
2
point symbol {4.6 .8 } {4 .6 .8 } of 3.
In compound 3, the trans-p-bib connects Cd(1) and Cd(2)
as a linker, leaving two pairs of double-chains with the same
structure but extending in different directions (Fig. 3b). The
structure of the two single chains which compose the double
chain is slightly different (the distances of CdIJ1)⋯CdIJ2) are
and 12.73° vs. 5.65° and 17.36°), which indicated that the li-
gand makes the whole structure tend to be stable through
the deformation. The completely deprotonated H
exists with two coordination modes: (η )–(η )-μ
2
BCA ligand
2
(Mode II,
2
2
with α = 65.51° and the distance of CdIJ1)⋯CdIJ1) being 18.30
2
1
1
1
1
3.91 Å vs.14.02 Å, and the dihedral angles δ and ε are 21.15°
Å) and (η : η )–(η : η )-μ
4
(Mode III, with α = 83.17°). As
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Fig. 4 (a) The coordination environment of Zn ions in 4 (symmetry codes: A: −1 − x, y, −z; B: 0.5 + y, 1.5 + y, z; C: −1 − x, y, −1 − z). (b) The 1D
3
[
ZnIJH
2
BCA)]
n
polymeric chain viewed along the a axis. (c) The 3D framework of 4. (d) The 3D 3-fold 3-connected {10 } ThSi2 net of 4.
II
shown in Fig. 3b, two H BCA ligands with different coordina-
Zn ions on the two nearest 1D [ZnIJH BCA)] chains to form
2
2
n
tion modes extend in an interlaced direction, leaving a 2D
the 3D [Zn IJH BCA) IJo-bimb) ]
2 2 2 2 n
framework.
[
Cd
2
IJμ
2
-H
2
BCA)IJμ
4
-H
2
BCA)]
n
sheet, and further expanded into
The topology for 4 was analyzed using the TOPOS pro-
gram. The Zn ions can be regarded as a 3-connected node.
II
II
a 3D framework by sharing the Cd ions.
After simplification by using the TOPOS software, the final
whole network can be considered as a novel 3D 2-nodal
Therefore, the whole structure can be represented as a 3D
3-fold interpenetrating 3-connected ThSi2 net with the point
symbol {10 } (Fig. 4d).
3
4
,5-connected net with stoichiometry (4-c)IJ5-c) , by simplify-
2
ing the {Cd1
with the point symbol being {4.6 .8 }
2 8 2 2 8 2
O C } and {Cd2 O C } as two 5-connected nodes,
6
3
2
2
2
2
{4 .6 .8 } (Fig. 3e).
Structural comparison and discussion
From the crystal structures of the four compounds discussed
above, we can see that H BCA ligands present a variety of co-
ordination modes under similar reaction conditions, with the
two deprotonated carboxyl groups coordinating two to four
2
2 2 2 2 2 2 n
Structural description of [Zn IJH BCA) IJo-bimb) IJH O) ] (4)
Crystallographic analysis shows that compound 4 crystallized
in the monoclinic system with the space group C2. There
metal ions. As shown in Scheme 1 and Table 2, the H BCA li-
gands in two zinc-based compounds (1 and 4) are both
2
II
are two Zn ions, two H BCA ligands, two o-bimb linkers,
2
and two lattice water molecules in the asymmetric unit of 4
connected to two central atoms with the same coordination
(
Fig. 4a). Zn(1) is located in a distorted {ZnN O } trigonal
mode (Mode I) and further extend into a 1D [ZnIJH BCA)]n
2
3
2
biyramidal geometry with τ being 0.737, surrounded by three
chain. These two zinc-containing compounds eventually pres-
ent different frame structures mainly attributed to the role of
auxiliary ligands in the assembly process. Both m-bib and
o-bimb ligands connect two adjacent one-dimensional
[ZnIJH BCA)] chains, leaving a structure of a 2D 3-connected
5
O atoms from two different H
.94(2), ZnIJ1)–OIJ5) = 1.99(2), ZnIJ1)–OIJ6) = 2.60(2) Å] and two
N atoms from two different 1,2-bimb linkers [ZnIJ1)–NIJ2) =
.20(2), ZnIJ1)–NIJ5A) = 1.98(2)]. The coordination environment
of Zn(2) is similar to that of Zn1 located in a {ZnN O } trigo-
2
BCA ligands [ZnIJ1)–OIJ1) =
1
1
2
n
2
3
hcb layer and a 3D 3-connected ThSi2 net, respectively. As a
flexible ligand, o-bimb has greater deformation capacity in
space compared with m-bib, which has a more flexible con-
nal biyramidal geometry with the τ5 being 0.717; the bond
length of ZnIJ2)–O/N is in the range of 1.95(2) Å – 2.61(2) Å.
1
4
The completely deprotonated H BCA ligand acts as a
nection to form a high-dimensional structure. For com-
2
II
1
2
linker to connect two Zn ions by adopting a (η )–(η )-μ
pound 2, the H BCA ligand adopts the coordination mode of
2
2
2
2
1
II
mode (Mode I, with α being 40.25°, and the distance of the
nearest Zn⋯Zn being 14.48 Å), successfully constructing a 1D
(η )–(η : η )-μ (Mode IV) to connect three Pb ions and fur-
3
ther extends into a 2D [PbIJH BCA)] sheet, and p-bib further
2
n
[
ZnIJH BCA)] polymeric chain (Fig. 4b). In addition, two
bridges these 2D sheets to form a 3D (4,5)-connected tcs net.
Similar to 2, the p-bib ligand of 3 connects two adjacent
[CdIJH BCA)] layers to form a 3D (4,5,5)-connected net. Inter-
2
n
II
o-bimb linkers bridge two adjacent Zn ions by using trans-
configuration, successfully obtaining a binuclear [Zn IJtrans-o-
2
2
n
bimb) ] SBU, with the o-bimb linker Zn⋯Zn separation dis-
estingly, the H BCA ligands adopt two kinds of coordination
2
2
tance of 5.33 Å and the dihedral angles δ and ε being 89.943°
and 80.89°. Meanwhile, the trans-1,4-bib linkers connect the
modes (Modes II and III) to accommodate two different con-
II
figurations of Cd ions.
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To the best of our knowledge, all of the coordination
modes have never been documented up to now, which also
indicates that the selection of central ions has an important
Sensing of small organic molecules
In view of the excellent fluorescence properties of these two
zinc-containing compounds, we explored the sensing abilities
of compounds 1 and 4; methanol, ethanol, DMF, DMA, aceto-
nitrile, N-butyl alcohol, and acetone were selected for the lumi-
nescence sensing studies. Three milligram samples of 1 and 4
were dispersed in 2 mL diverse solvents with ultrasonication
for 30 min. As shown in Fig. 5 and S4 ,† the intensity is in the
order methanol > DMA > ethanol > DMF > acetonitrile >
N-butyl alcohol > acetone (1) and methanol > DMF > DMA >
ethanol > acetonitrile > N-butyl alcohol > acetone (4). Both 1
and 4 display the strongest luminescence intensity in metha-
nol, while exhibiting the weakest in acetone.
Acetone (Ac) is an important chemical raw material and
organic solvent. Therefore, effective and rapid detection of Ac
is vital to chemical production and scientific research. The
sensing properties of 1 and 4 for Ac were further investigated
by monitoring a series of emissions of 1 and 4 in aqueous so-
lutions versus gradually increased Ac concentration. As shown
in Fig. 6a and S5a,† the fluorescence intensity decreased con-
tinuously upon incremental addition of Ac into a standard
emulsion of 1 and 4 in aqueous solutions. For compound 1,
the quenching rate of the emissions reach as much as
influence on the diversity of the H BCA coordination mode.
2
In addition, the bisIJimidazole) ancillary linkers have a great
influence on the final packing structures by modulating their
conformations and coordination modes.
Powder X-ray diffraction and thermogravimetric analysis
In order to check the phase purity of these compounds, the
PXRD patterns of the title compounds were checked at room
temperature. As shown in Fig. S1,† the peak positions of the
simulated and experimental PXRD patterns are in agreement
with each other, demonstrating the good phase purity of the
compounds. The dissimilarities in intensity may be due to
1
5
the preferred orientation of the crystalline powder samples.
To investigate the thermal stability of these compounds,
thermogravimetric analyses were performed from ambient
temperature to 700 °C, and the TG curves are given in Fig.
S2.† For compound 1, the first weight loss of 3.56% corre-
sponds to the release of lattice water molecules (calcd.
3
°
.44%), and then almost no weight loss is observed until 312
C, at which temperature it starts to lose the 1,3-bib organic
ligand. The final residue is ZnO (found 16.09% and calcd.
5.46%). For 2, the first weight loss in the temperature range
9
5.29% when the concentration of Ac in the suspension solu-
tion is 0.235 mM, and 96.35% for compound 4 when the con-
centration of Ac is 0.260 mM. The I /I versus the Ac concen-
tration plots are shown in the insets of Fig. 6a and S5a† to
further quantify the quenching efficiency, where I and I are
1
0
of 85–130 °C is consistent with the removal of the coordi-
nated water molecules. Then, the packing structure starts to
collapse with the temperature increasing. For 3, the initial
weight loss occurs at 90–120 °C, corresponding to the loss of
coordinated water molecules. Above 309 °C, the second
weight loss corresponds to the loss of the organic ligands.
Compound 4 can stably exist until a temperature of up to 387
0
the fluorescence intensities of the emulsion in the absence
and presence of the analyte, respectively. It is notable that
the I /I versus Ac concentration plots bend upwards instead
0
of being typically linear plots; this may be attributed to the
presence of simultaneous static and dynamic quenching.
Nonlinear Stern–Volmer curves in aqueous systems can be
°C, and then the frameworks decompose gradually, with the
final residue being 25.32% (calcd. 23.15% for CdO).
[Ac]/97.583
0
well fitted to the exponential equations I /I = 4.193e
0
.643
−
3.409 (1) and I /I = 0.052[Ac]
+ 0.999 (4), respectively,
0
4
−1
4
−1
with a Ksv of 3.7 × 10 M (1) and 2.0 × 10 M (4) in the low
concentration range. The limits of detection (LODs) of 1 and
Luminescence properties
The fluorescence spectra of two zinc compounds (1 and 4)
4
were found to be as low as 0.09 and 0.13 μM, respectively,
and the free H BCA, m-bib, and o-bimb ligands were tested
2
which was calculated with the equation LOD = 3δ/S (where δ
in the solid state at room temperature. As can be seen in Fig.
S3,† emissions of the ligands were observed with wavelengths
at 351 nm for m-bib, 342 nm for o-bimb, and 310 nm for the
H BCA ligand, which may be assigned to π–π* transitions of
2
the benzene and imidazole rings. Intense emission bands
were found at 405 and 407 nm for 1 and 4, respectively (λ
=
ex
II
3
25 nm). As the Zn ion is difficult to oxidize or to reduce
1
0
due to its d configuration, the emission bands of 1 and 4
are neither metal-to-ligand charge transfer (MLCT) nor
ligand-to-metal charge transfer (LMCT) but originate from
the intraligand charge transfer because a similar emission
was observed for the free H BCA ligand. The observed blue
2
shift of the maximum emission bonds of the two CPs as com-
pared with that of the free H
2
BCA ligand might be attributed
to the increased degree of π electron overlap of the organic
linkers and the introduction of an auxiliary ligand.
Fig. 5 The luminescence intensities of compound 1 dispersed in
different organic solvents.
1
6
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Fig. 6 (a) The PL spectra of the aqueous suspension of compound 1 upon incremental addition of acetone. Inset: The luminescence intensity (I
0
/I)
versus the acetone concentration. (b) Luminescence intensities of 1 in six different standard solvents or mixed solvents in the presence of acetone.
is the standard deviation of the blank signal and S is the
slope of the linear calibration plots). The observed fluores-
cence quenching may be ascribed to the interactions be-
tween the framework and the acetone molecules, in particu-
lar, the “CO” of acetone and the frameworks of 1 and 4,
since such ligand-based fluorescence can be quenched by
energy transfer between the organic ligands and the acetone
molecules. The different fluorescence sensing performance
of complexes 1 and 4 for acetone can be explained as follows:
First is the structural difference of complexes 1 and 4. The
were ground and dispersed in aqueous solutions containing
12 different Na X with a concentration of [M] = 0.01 M (X =
n
−
−
−
2−
−
2−
−
3−
2−
Br , Cl , I , CO , HCO , C O , SCN , PO , HPO4
,
3
3
2
4
4
−
2−
2−
H
2
PO
4 2 7 4
, Cr O , and CrO ) to form an X@1/4 suspension.
2−
2−
As shown in Fig. 7, the Cr O
and CrO4 anions cause the
2
7
most significant luminescence quenching effects, with the
quenching efficiencies being both more than 99%, showing
high selectivity.
1
7
To obtain a better understanding of the sensing ability of
2−
2−
1 and 4 for the Cr
O
2 7
/CrO
4
anions, a luminescence titra-
H BCA ligand adopted different coordination modes in 1 and
tion experiment of the 1/4-H O suspension was carried out
with the gradual addition of an aqueous Cr O /Cr O solu-
2 7 2 7
2
2
2−
2−
4, and a different auxiliary bisIJimidazole) ligand took part in
the construction of 1 and 4. Second, the weak interactions be-
tween CPs and acetone molecules may lead to the different
orders. Lastly, other factors might be one of the important
causes, including electron-withdrawing ability, electrical
properties, and vapor pressure of the analytes.
tion. As shown in Fig. 8 and S6,† the titration plots revealed
that the emission intensities of compounds 1 and 4 de-
2−
2−
creased with increasing concentrations of the Cr O /CrO4
2
7
42−
2−
anions. The quenching efficiencies of Cr
O
2 7
/CrO
(M) to
compounds 1 and 4 can be quantitatively rationalized by the
1
1.540[M]
In order to further explore the anti-interference ability of
the title compounds for acetone recognition, we studied the
sensing abilities of 1 and 4 to different mixed solutions
containing acetone. Three milligram samples of 1 and 4 were
dispersed in 2 mL of an S/acetone mixed solution in a 1 : 1
ratio (S = methanol, ethanol, acetonitrile, N-butyl alcohol,
DMF, or DMA). As can be seen in Fig. 6b and S5b ,† compared
to six standard emulsions based on different solvents, the
luminescence intensity of composite emulsions doped with
acetone decreased in different degrees. For compound 4, only
the DMF/acetone mixing systems exhibit extremely significant
quenching effects on the luminescence of the title CPs, while
compound 1 shows a stronger sensing ability for all six mixing
systems, and the quenching rates are all more than 90%. The
experimental result indicated that compound 1 has excellent
anti-interference ability in the identification of acetone.
equations I0/I = 5.828e
0.575e
− 5.028 (1) and I0/I =
3
1.707[M]
2−
+ 0.677 (4) for Cr
1.006 (1) and I /I = 17.445[M] + 1.017 (4) for CrO . Obvi-
2
O
7
0
and I /I = 17.945[M] +
2−
0
4
ously, a good linear Stern–Volmer relationship is observed in
2−
1 and 4 for CrO
4
anion sensing, suggesting that they play a
role in the dynamic quenching process for detecting the
Selective detection of anions
Meanwhile, to further explore their ability to detect anions of
Fig. 7 The luminescence intensities of compounds 1 and 4 in aqueous
compounds 1 and 4, as-synthesized samples of 1 or 4 (3 mg)
solution with different anions.
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2
−
2−
the strong UV-vis absorption bands of the Cr O /CrO4
2
7
1
9
aqueous solution in the range of 230–420 nm, while the
other anions' aqueous solutions did not overlap with these
2
−
absorption ranges. The wide absorption bands of Cr O
/
2
7
2−
CrO4 may cover the absorption bands of 1 and 4 upon light
2−
excitation. In addition, the quenching effect of Cr
(
O
2 7
@1/4
in the low concentration) and CrO4 @1/4 can well fit the
S–V equation, indicating that the quenching effect is attrib-
uted to dynamic quenching (collision interaction). Hence,
the luminescence quenching by Cr O /CrO4 anions may
2−
20
2−
2−
2
7
be the process involving the competitive absorption upon
light excitation and the collision interaction between the
2−
2−
Cr O /CrO4 anions and the compounds.
2
7
Conclusions
In summary, based on the designed flexible ligand of bisIJ4-
carboxybenzyl)amine (H BCA), four CPs were obtained, with
2
the structures ranging from a 2D 3-connected hcb layer for 1,
a 3D (4,5)-connected tcs net for 2, a 3D novel (4,5,5)-connected
net for 3 and 3D 3-fold interpenetrated 3-connected ThSi2 nets
for 4. Moreover, luminescence sensing measurements indicate
that compounds 1 and 4 both show highly selective and sensi-
2−
2−
2 7 4
tive sensing ability for acetone molecules and Cr O /CrO
anions through fluorescence quenching in aqueous solution,
indicating that they are promising candidates for practical
applications as chemical sensors.
Fig.
different concentrations of Cr
Luminescence intensity vs. the Cr
8
Luminescence spectra of
1
in an aqueous solution with
2
−
42−
2
O
7
(a) and CrO
42−
(b). Inset:
2
−
2
O
7
/CrO
concentrations plots.
Conflicts of interest
2
−
72−
can
CrO
4
anion, and the quenching efficiency of Cr
2
O
The authors declare no competing financial interest.
also fit well to the S–V curve in a low concentration range,
with a Ksv of 6.6 × 10 M (1) and 5.3 × 10 M (4), respec-
tively. The LODs of CrO
4
−1
4
−1
2−
2−
Acknowledgements
4
and Cr O
2 7
were estimated to be
0
.13 and 0.07 μM for 1, and 0.14 and 0.07 μM for 4, respec-
This work was financially supported by the National Natural
Science Foundation of China (Grant No. 21451001) and the
Key Discipline, Innovation Team and Key Lab. of Qilu Normal
University.
2−
2−
tively. The LODs of CrO
4
and Cr O
2 7
using 1 and 4 were
significantly lower than those observed for other CPs such as
[Zn IJTPOM)IJNH -BDC) ]·4H O} (4.8/3.9 μM, TPOM
tetrakisIJ4-pyridyloxymethylene)methane, NH -BDC = 2-amino-
(10/2 μM, btz = 1,5-bisIJ5-
tetrazolo)-3-oxapentane), [ZnIJttz)H O] (20/2 μM, ttz = 1,2,3-
{
=
2
2
2
2
n
2
1
7
terephthalic acid),
[ZnIJbtz)]
n
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