Luminescent sensing of Fe3+ and K+ by three novel imidazole dicarboxylate-based MOFs

Article abstract of DOI:10.1080/10610278.2016.1198485

In this paper, three luminescent metal–organic frameworks, namely: [Zn(p-IPhHIDC)]_n (1), {[Cd(p-IPhIDC)(H₂O)]·CH₃OH}_n (2) and [Zn(p-TIPhHIDC)]_n (3), bearing two novel substituted imidazole dicarboxyla

Full text of DOI:10.1080/10610278.2016.1198485

Supramolecular Chemistry
ISSN: 1061-0278 (Print) 1029-0478 (Online) Journal homepage: http://www.tandfonline.com/loi/gsch20
Luminescent sensing of Fe3+ and K+ by three novel
imidazole dicarboxylate-based MOFs
Qiuying Huang, Jifeng Wang, Qi Wang & Gang Li
To cite this article: Qiuying Huang, Jifeng Wang, Qi Wang & Gang Li (2016): Luminescent
sensing of Fe3+ and K+ by three novel imidazole dicarboxylate-based MOFs, Supramolecular
Chemistry, DOI: 10.1080/10610278.2016.1198485
To link to this article: http://dx.doi.org/10.1080/10610278.2016.1198485
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Date: 03 October 2016, At: 11:02

Supramolecular chemiStry, 2016
http://dx.doi.org/10.1080/10610278.2016.1198485
Luminescent sensing of Fe3+ and K+ by three novel imidazole dicarboxylate-
based MOFs
Qiuying Huanga, Jifeng Wangb, Qi Wangb and Gang Lib
aDepartment of chemical engineering, henan polytechnic institute, Nanyang, p.r. china; bcollege of chemistry and molecular engineering,
Zhengzhou university, Zhengzhou, p.r. china
ABSTRACT
ARTICLE HISTORY
received 1 may 2016
accepted 1 June 2016
In this paper, three luminescent metal–organic frameworks, namely: [Zn(p-IPhHIDC)]n (1), {[Cd(p-
IPhIDC)(H2O)]·CH3OH}n (2) and [Zn(p-TIPhHIDC)]n (3), bearing two novel substituted imidazole
dicarboxylate ligands, 2-(p-N-imidazol-1-yl)-phenyl-1H-imidazole-4,5dicarboxylic acid (p-IPhH3IDC)
and 2-p-(1H-1,2,4-triazol-1-yl)-phenyl-1H-imidazole-4,5dicarboxylic acid (p-TIPhH3IDC), have been
prepared and characterised through infrared spectra, X-ray powder diffraction, elemental analyses,
thermogravimetric analyses and single-crystal X-ray diffraction. Ignoring the free methanol molecule
and coordinated water in 2, 1–3 are similar structures. Moreover, the luminescent properties of the
MOFs have been explored. It was found that MOFs 1 and 2 show good luminescent sensing of Fe3+
in varying degrees, and 3 of K+.
KEYWORDS
moFs; substituted imidazole
dicarboxylate; crystal
structure; sensing property
Two imidazole dicarboxylate-based ligands, 2-(p-N-imidazol-1-yl)-phenyl-1H-imidazole-
4,5dicarboxylic acid and 2-p-(1H-1,2,4-triazol-1-yl)-phenyl-1H-imidazole-4,5dicarboxylic acid, and
three corresponding luminescent MOFs have been prepared and characterised. The luminescent
properties of the polymers have been explored. It was found that polymers 1 and 2 showed good
uminescent sensing for Fe3+ in varying degrees, and 3 for K+.
1. Introduction
and magnetic materials, ion exchange and molecular rec-
ognition and so on (1–12). However, it is still a challenge to
prepare more intriguing MOFs with various potential appli-
cations from designed multifunctional organic ligands.
Consequently, considerable efforts have been devoted
to design or choose the multifunctional bridging ligands.
In this context, due to the strong coordination ability
and various coordination modes of two carboxylate groups
and a imidazole ring (13–16), imidazole-4,5-dicarboxylic
Over the past three decades, the research community
has witnessed the prominent growth of a special class
of materials, namely: metal–organic frameworks (MOFs),
that have risen to the forefront of solid-state chemistry.
On account of their porosity, large specific surface area,
unsaturated coordination position and diverse struc-
tures etc., MOFs are widely used in many fields, such
as catalysis, gas storage/adsorption, optical, electric
CONTACT Gang li
gangli@zzu.edu.cn
© 2016 informa uK limited, trading as taylor & Francis Group

2
Q. HuaNG eT aL.
in air on a Netzsch STa 409PC differential thermal ana-
lyzer (Germany NeTZSCH Co. Selb, Germany). X-ray pow-
der diffraction (XRD) measurements were recorded on a
Panalytical X’pert PRO X-ray diffractometer (PaNalytical B.V.
Holland). Fluorescence spectra were characterised at room
temperature by a F-4600 fluorescence spectrophotome-
ter (Hitachi High-Technologies Co. Tokyo, Japan) (240 nm/
min). uV–visible absorption spectra were measured on a
agilent 8453 spectrophotometer (agilent Technologies,
uSa). The 1H-NMR spectra were recorded at ambient tem-
perature using a Bruker DPX 400 instrument and were ref-
erenced internally to residual solvent resonances (Bruker
instrument Co., Germany).
Scheme 1. Syntheses of moFs 1–3.
acid (H3IDC) and its derivatives have attracted much atten-
tion. Several H3IDC derivatives bearing aromatic groups at
the 2-position of the imidazole ring and the related MOFs
have been explored by our laboratory (17–22). The studies
show that these substituted phenyl imidazole dicarboxy-
late ligands can build up interesting MOFs. Prompted by
the findings, we continue to probe the substituent effect
of the N-heterocycles on phenyl imidazole dicarboxylate
ligands.
2.2. Preparation of the organic ligands, p-IPhH3IDC
and p-TIPhH3IDC
as shown in Scheme 2, 2, 3-bis(nitrooxy)maleic acid,
4-(1H-imidazol-1-yl)benzaldehyde and 4-(1H-1,2,4-triazol-
1-yl)benzaldehyde were firstly prepared by us, and then
organic ligands, p-IPhH3IDC and p-TIPhH3IDC, were made
according to the literature procedure (26). anal. Calcd. for
p-IPhH3IDC: C, 56.38; H, 3.38; N, 18,79%; Found: C, 56.52; H,
3.26; N, 19.02%. IR (cm−1, KBr): 3484 (m), 3116 (w), 2939 (w),
2704(w), 1934 (m), 1725 (w), 1536 (m), 1419 (s), 1356 (s),
1274 (w), 1124 (s), 1052 (s), 956 (s), 842(s), 771 (w), 734 (s),
699 (s), 649 (s), 622(w), 563 (w). 1H NMR (300 MHz, DMSO,
25°C, TMS, ppm): 9.61 (s, 1H, –NH), 9.01 (d, 2H, –C5H3N2),
8.41 (d, 1H, –C5H3N2), 8.39 (d, 2H, –C6H4), 8.31–8.33 (d,
2H, –C6H4). uV-vis (CH3CN): 635 nm (m), 649 nm (w). anal.
Calcd for p-TIPhH3IDC: C, 52.18; H, 3.04; N, 23.41%; Found:
C, 52.37; H, 3.34; N, 23.75%. IR (cm−1, KBr): 3407 (m), 3115
(w), 2748 (w), 2568(w), 1934 (m), 1724 (m), 1511 (m), 1359
(s), 1278 (s), 1214 (w), 1141 (s), 1039 (s), 967 (w), 842 (s),
796 (s), 771 (s), 736 (s), 696(w), 669 (w). 1H NMR (300 MHz,
DMSO, 25°C, TMS, ppm): 9.45 (s, 1H, –NH), 9.11 (d, 1H, –
C5H3N2), 8.46 (d, 1H, –C5H3N2), 8.38 (d, 2H, –C6H4), 8.30–8.32
(d, 2H, –C6H4).uV-vis (CH3CN): 639 nm (m), 651 nm (w).
In this work, two novel organic ligands, 2-(p-N-imi-
dazol-1-yl)-phenyl-1H-imidazole-4,5dicarboxylic
acid
(p-IPhH3IDC) and 2-p-(1H-1,2,4-triazol-1-yl)-phenyl-1H-im-
idazole-4,5dicarboxylic acid (p-TIPhH3IDC), bearing
N-imidazol-1-yl or 1H-1,2,4-triazol-1-yl rings have been
designed and prepared. Consequently, three related
MOFs, [Zn(p-IPhHIDC)]n (1), {[Cd(p-IPhIDC)(H2O)]·CH3OH}n
(2) and [Zn(p-TIPhHIDC)]n (3), have been constructed and
structurally characterised (Scheme 1). Furthermore, the
thermal and luminescent properties have been also inves-
tigated. To our surprise, in varying degrees, the three MOFs
show a good luminescent sensing of Fe3+ or K+, respec-
tively. although several examples of imidazole dicarbo-
xylate-based complexes as anion or cation sensors have
been previously reported (23–25), MOFs that sense K+ have
yet to be described.
2.3. Preparation of crystalline polymer [Zn(p-
IPhHIDC)]n (1)
2. Experimental section
.
a mixture of Zn(Oac)2 2H2O (21.9 mg, 0.1 mmol), p-IPh-
2.1. Materials and methods
H3IDC (29.8 mg, 0.1 mmol), H2O-CH3CN (4:3, 7 mL) and
hydrochloric acid (0.05 mL, 36–38%) was sealed in a
25-mL Teflon-lined bomb and heated at 150(C for 96 h,
and then allowed to cool to room temperature. The brown
acicular crystals of 1 were collected, washed with distilled
water and dried in air (72% yield based on Zn). anal. Calcd
for C14H8N4O4Zn: C, 46.50; H, 2.23; N, 15.50%; Found: C,
46.32; H, 2.14; N, 15.85%. IR (cm−1, KBr): 3424(m), 3234(w),
3098(m), 2171(s), 1959(w), 1722(s), 1531(w), 1506(w),
1377(s), 1132(w), 1068(s), 856(m), 739(m), 659(m), 572(m).
all chemicals were of reagent grade quality obtained from
commercial sources and used without further purification.
The C, H and N analyses were carried out on a FLaSH
ea 1112 analyzer (Thermo electron Corporation, Madison,
WI, uSa). IR spectra were recorded on a BRuKeRTeNSOR
27 spectrophotometer as KBr pellets in the 400–4000 cm−1
region (GMI, Inc., Ramsey, MN, uSa). Thermogravimetric
(TG) measurements were performed by heating the crys-
talline samples from 20 to 850 °C at a rate of 10°Cmin−1

SuPRaMOLeCuLaR CHeMISTRy
3
Scheme 2. Synthesis pathways of the organic ligands.
2.4. Preparation of crystalline polymer {[Cd(p-
IPhHIDC)(H2O)]·CH3OH}n (2)
2.6. Crystal structure determinations
Suitable single crystals of compounds 1–3 were selected
for single-crystal X-ray diffraction analyses. The intensity
data were measured on a Bruker Smart 1000 diffractom-
eter with a graphite-monochromated MoKα radiation
(λ = 0.71073 Å). Single crystals of 1–3 were selected and
mounted on a glass fibre. all data were collected at room
temperature using the ω − 2θ scan technique and cor-
rected for Lorenz polarisation effects. a correction for sec-
ondary extinction was applied.
The three structures were solved by direct methods
and expanded using the Fourier technique. The non-
hydrogen atoms were refined with anisotropic thermal
parameters. The hydrogen atoms on C were positioned
geometrically and refined using a riding model. The
hydrogen atoms on O were found at reasonable positions
in the differential Fourier map and located there. all the
hydrogen atoms were included in the final refinement.
The final cycle of full-matrix least squares refinement
was based on 2430 observed reflections and 208 varia-
ble parameters for 1, 2870 observed reflections and 246
variable parameters for 2 and 2350 observed reflection
and 208 variable parameters for 3. all calculations were
performed using the SHeLX-97 crystallographic software
package (27). The crystallographic data, and selected
bond lengths and angles are given in Tables 1 and 2,
respectively.
Polymer 2 was prepared in a manner analogous to that
used to prepare 1, only Cd(NO3)2·4H2O (30.8 mg, 0.1 mmol)
.
was used instead of Zn(Oac)2 2H2O and H2SO4 (0.05 mL,
36–38%). The colourless crystals of two were isolated,
washed with distilled water and dried in air (54.5% yield
based on Cd). anal. Calcd. forC15H14N4O6Cd: C, 39.27; H,
3.08; N, 12.22%; Found: C, 39.20; H, 2.71; N, 12.14%. IR
(cm−1, KBr): 3425 (s), 3115 (m), 2170 (s), 1895 (m), 1682 (s),
1529 (m), 1386 (m), 1268 (w), 1061 (m), 847 (m), 749 (s),
732 (s), 511 (m).
2.5. Preparation of crystalline polymer [Zn(p-
TIPhHIDC)]n (3)
.
a mixture of Zn(Oac)2 2H2O (21.9 mg, 0.1 mmol), p-TIPh-
H3IDC (12.0 mg, 0.04 mmol), H2O-CH3CN (4:3, 7 mL) and
hydrochloric acid (0.1 mL, 36–38%) was sealed in a 25-mL
Teflon-lined bomb and heated at 150 °C for 96 h, then
allowed to cool to room temperature. Then, the brown acic-
ular crystals of 3 were collected, washed with distilled water
and dried in air (55% yield based on Zn). anal. Calcd. for
C13H7N5O4Zn: C, 43.06; H, 1.95; N, 19.32%; Found: C, 42.75;
H, 1.78; N, 18.97%. IR (cm−1, KBr): 3442 (m), 3088 (w), 2920
(w), 2850 (s), 1578 (s), 1536 (s), 1469 (s), 1279 (s), 1288 (m),
1140 (m), 977 (w), 864 (m), 748 (m), 673 (w), 560 (w), 526 (w).

4
Q. HuaNG eT aL.
Table 1. crystallographic data for polymers 1–3.
1
2
3
Formula
Fw
crystal system
crystal size/mm
c14h8N4o4Zn
361.63
monoclinic
0.20 × 0.20 × 0.20
P21/c
8.6321(6)
13.0479(9)
12.9456(9)
90
108.5992(11)
90
c15h14N4o6cd
c13h7N5o4Zn
458.70
monoclinic
0.22 × 0.21 × 0.19
P21/n
362.61
monoclinic
0.49 × 0.33 × 0.20
P21/n
Space group
a, Å
8.8099(4)
15.3396(7)
12.5757(6)
90
105.342(5)
90
8.6757(6)
12.6925(8)
12.8642(9)
90
109.097(8)
90
b, Å
c, Å
α, °
β °
γ,°
V, Å3
1381.92(17)
1.738
1638.92(13)
1.859
1338.60(16)
1.799
Dc, mg m−3
Z
4
4
4
μ, mm−1
1.805
1.375
1.865
reflnscollected/unique
Data/restraints/parameters
7135/ 2430 [r(int) = 0.0208]
2430 / 0 /208
0.0994
6306 / 2870 [r(int) = 0.0330]
2870 / 6 / 246
0.0385
5200 / 2350 [r(int) = 0.0292]
2350 / 0 / 208
0.0433
R
Rw
0.2533
1.215
0.693 and −1.354
0.0919
1.012
1.113 and −0.693
0.1179
1.042
0.517 and −0.530
GoF on F2
Δρmax and Δρmin, e Å−3
Table 2. Selected bond distances (Å) and angles (deg) for complexes 1–3.
1
Zn(1)-N(3)#1
Zn(1)-o(4)
Zn(1)-o(2)
Zn(1)-N(2)
2.033(7)
2.062(7)
2.069(6)
2.130(6)
Zn(1)-N(4)#2
N(4)-Zn(1)#3
N(3)-Zn(1)#4
2.158(7)
2.158(7)
2.033(7)
N(3)#1-Zn(1)-o(4)
N(3)#1-Zn(1)-o(2)
o(4)-Zn(1)-o(2)
N(3)#1-Zn(1)-N(2)
o(4)-Zn(1)-N(2)
129.4(3)
o(2)-Zn(1)-N(2)
81.2(2)
91.5(3)
80.3(3)
93.7(3)
172.1(3)
115.8(3)
114.5(3)
96.2(3)
96.1(3)
N(3)#1-Zn(1)-N(4)#2
o(4)-Zn(1)-N(4)#2
o(2)-Zn(1)-N(4)#2
N(2)-Zn(1)-N(4)#2
2
cd(1)-N(2)
cd(1)-N(1)#1
cd(1)-N(4)#2
cd(1)#3-N(1)
cd(1)#2-N(4)
2.248(4)
cd(1)-o(1 W)
cd(1)-o(1)#1
cd(1)-o(4)
2.377(4)
2.399(4)
2.473(4)
2.399(4)
2.257(4)
2.289(4)
2.257(4)
2.289(4)
cd(1)#3-o(1)
N(1)#1-cd(1)-o(1)#1
N(2)-cd(1)-N(1)#1
N(2)-cd(1)-N(4)#2
N(1)#1-cd(1)-N(4)#2
N(2)-cd(1)-o(1 W)
N(1)#1-cd(1)-o(1 W)
N(4)#2-cd(1)-o(1W)
N(2)-cd(1)-o(1)#1
72.35(12)
157.03(15)
100.42(14)
95.13(14)
90.20(16)
108.49(16)
83.09(16)
88.64(13)
N(4)#2-cd(1)-o(1)#1
o(1 W)-cd(1)-o(1)#1
N(2)-cd(1)-o(4)
N(1)#1-cd(1)-o(4)
N(4)#2-cd(1)-o(4)
o(1 W)-cd(1)-o(4)
o(1)#1-cd(1)-o(4)
98.36(15)
178.29(14)
70.82(12)
100.89(13)
155.36(14)
74.16(14)
104.26(14)
3
Zn(1)-o(4)#1
Zn(1)-N(5)#2
Zn(1)-o(1)
Zn(1)-N(1)
2.037(3)
2.071(4)
2.078(3)
2.119(3)
Zn(1)-N(3)#1
N(3)-Zn(1)#3
N(5)-Zn(1)#4
o(4)-Zn(1)#3
2.135(3)
2.135(3)
2.071(4)
2.037(3)
o(4)#1-Zn(1)-N(5)#2
o(4)#1-Zn(1)-o(1)
N(5)#2-Zn(1)-o(1)
o(4)#1-Zn(1)-N(1)
N(5)#2-Zn(1)-N(1)
128.21(13)
114.21(14)
117.10(13)
99.30(11)
95.40(14)
o(1)-Zn(1)-N(1)
80.48(11)
81.11(11)
89.98(13)
92.67(12)
172.69(12)
o(4)#1-Zn(1)-N(3)#1
N(5)#2-Zn(1)-N(3)#1
o(1)-Zn(1)-N(3)#1
N(1)-Zn(1)-N(3)#1
Note. Symmetry codes for 1: #1: –x + 1, y + 1/2, -z + 1/2; #2: x, –y + 1/2, z + 1/2; #3: x, –y + 1/2, z–1/2; #4: –x + 1, y–1/2, –z + 1/2; For 2: #1: x–1/2, –y + 1/2, z–1/2;
#2: –x, –y + 1, –z + 1; #3: x + 1/2, –y + 1/2, z + 1/2; For 3: #1: x–1/2, –y + 1/2, z–1/2; #2: –x + 1/2, y–1/2, –z + ½; #3: x + 1/2, –y + 1/2, z + ½; #4: –x + 1/2, y + 1/2,
–z + 1/2.

SuPRaMOLeCuLaR CHeMISTRy
5
Figure 1. (colour online) (a) coordination environment of Zn2+ atom in 1 (h atoms omitted for clarity). (b) 2D layer of 1. (c) the 3D solid-
state framework of 1 constructed by π...π interaction.
2.7. Luminescence experiments
The 1 (or 2 or 3)/Mn+ (n = 1 or 2 or 3) samples were pre-
pared by introducing 80 mg of 1 (or 2 or 3) crystalline pow-
der into 4.0 mL of different aqueous solutions of M(NO3)x
Luminescent properties of 1 (or 2 or 3)/Mn+ (n = 1 or 2 or 3)
were investigated in the solid state at room temperature.

6
Q. HuaNG eT aL.
(0.01 mol/L) (M = Na+, K+, Mg2+, Ca2+, al3+, Fe3+, Co2+, Ni2+,
or Pb2+, et al.), and treated for 17 h; then, the powder was
isolated and washed with redistilled water, and dried in air
for fluorescence study.
3. Results and discussion
3.1. Crystal structures of crystalline polymers
The crystal structures of polymers 1–3 are similar, ignor-
ing the free methanol molecule and coordinated water in
2. That is to say, they have the same topology structures.
Therefore, we will restrict our description to the polymer 1,
and only mention pertinent points for the polymers 2 and
3, where appropriate.
Polymer 1 crystallises in monoclinic space group P21/c.
The asymmetric unit of 1 comprises one metal centre and
three p-IPhHIDC2− ligands (Figure 1a). The Zn2+ is penta-co-
ordinated with three N and two O atoms forming a twisted
double-tapered hexahedron, in which O2, N2 and O4, N4#2
are from two imidazole dicarboxylate ligands, respectively,
and N3#1 atom is from the imidazole ring at the 4-position
of benzene from another p-IPhHIDC2− ligand. Zn–N bond
lengths are in the range of 2.033(7)–2.033(7) Å. Zn–O dis-
tances vary from 2.062(7) to 2.069(6) Å. The bond angles
around each Zn(II) are in the range of 80.3(3)–172.1(3)°,
which are consistent with the values in literature (28, 29).
each μ3-p-IPhHIDC2− anion connects the adjacent Zn(II)
atoms through N,O-chelating or N’,O’-chelating modes to
form a one-dimensional chain along the c-axis (Figure 1b).
The chains are bridged by the μ3-p-IPhHIDC2− anions and
expanded into a layer structure. Furthermore, these layers
are assembled into a three-dimensional supramolecular
solid-state structure via π...π stacking interactions between
the neighbouring two benzene rings (dihedral angle being
0.000° and distance being 3.2908 Å between the two ben-
zene rings) (Figure 1c).
as shown in Figure 2a, for polymer 2, the central
Cd(II) ion is six-coordinated with three O and three N atoms,
forming a distorted octahedron, in which O1 W is from the
coordinated water, O1#1, N1#1, O4 and N2 atoms are from
two p-IPhHIDC2− ligands, respectively, and N4#2 is from the
imidazole at the 4-position of benzene of another p-IPh-
HIDC2− ligand. as indicated in Figure 2b and c, the structure
of 2 is similar to that of 1. The Cd–N and Cd–O lengths are
in the range of 2.248(4)–2.289(4) Å and 2.377(4)–2.473(4)
Å, respectively, which are in accordance with the values in
previous documents (28). The bond angles around each
Cd2+ ion vary from 70.82(12)° to 157.03(15)°.
Figure 2. (colour online) (a) coordination environment of cd2+
atom in 2 (partial h atoms are omitted for clarity). (b)the 2D sheet
of 2. (c) the 3D solid-state structure of 2 built by π...π interaction.
(B&W for printed version).
from 80.48(11)° to 172.69(12)°, which are all similar to those
reported in the literature (28, 29).
The p-IPhHIDC2− and p-TIPhHIDC2− ligands in 1–3 all
adopt the same coordination mode, μ3-kN, O; kN´, O´; kNʺ
(Scheme 3).
To understand the framework of 3 better, it is neces-
sary to simplify the blinding blocks of compound 3. each
imidazole dicarboxylate ligand connects three cations,
which can be represented by a three-connected unit,
and each cation bridges three imidazole dicarboxylate
ligands and can be represented by the three-connected
unit. Therefore, the whole structure can be simplified as a
(2, 4)-connected net (Figure 3d).
as depicted in Figure 3, the coordination environment
of each Zn2+ ion and the 3D solid-state framework of 3 are
same to those of 1. The Zn–N and Zn–O lengths range from
2.071(4) Å to 2.135(3) Å and from 2.037(3) Å to 2.078(3) Å,
respectively. The bond angles around each Zn2+ ion vary

SuPRaMOLeCuLaR CHeMISTRy
7
Scheme 3. (colour online) coordination modes of the imidazole
dicarboxylate ligands (for p-iphhiDc2− r=c，for p-tiphhiDc2−
r=N).
3.2. XRD Patterns and thermal analyses
To confirm the phase purity of the three polymers, the XRD
patterns were recorded. Most of the peak positions of sim-
ulated and measured patterns are in good agreement with
each other (Figure 4).
The thermogravimetric analyses of the three complexes
were carried out to investigate the thermal stabilities
within the range of 20.0–850 °C (Figure 5). as seen from
the TG curves, polymers 1–3 are stable up to 330 °C. The
whole weight losses are from 332 to 652 °C for 1, from
326 to 639 °C for 2 and from 324 to 681 °C for 3, which
can be attributed to the decomposition of the collapse of
organic ligands.
In conclusion, the thermal data of complexes 1–3 are in
reasonable agreement with the crystal structure analyses.
3.3. Luminescence behaviours and sensing
properties
MOFs have received much attention due to their potential
applications in luminescene sensing for small molecules,
ions and so on (30–33). enlightened by such interesting
luminescent properties of the MOFs, the solid-state fluo-
rescent and sensing properties of 1–3 have been investi-
gated at room temperature.
The luminescence spectra of the free organic ligands,
p-IPhH3IDC and (p-TIPhH3IDC, and polymers were deter-
mined in solid state at room temperature (Figure 6).
Compared with the free ligands, the emission peaks of
the polymers 1–3 occur (blue shift) at varying degrees. as
shown in figure 6a, the free p-IPhH3IDC ligand displays
luminescence, with the emission maximum at 479 nm
by selective excitation at 410 nm which is attributed
to the π*→n transition. Polymers 1 and 2 indicate rela-
tively strong luminescence, with an emission maximum
at 373 nm upon excitation at 275 nm for 1 and with an
emission maximum at 429 nm upon excitation at 356 nm
for 2. They show blue shift (106 nm for 1, 50 nm for 2)
compared with the emission spectrum of p-IPhH3IDC.
The free ligand p-TIPhH3ID exhibits a strong emission at
493 nm when excited at 441 nm. The emission maximum
peak of polymer 3 is at 429 nm excited at 356 nm, which
Figure 3. (colour online) (a) coordination environment of Zn2+
atom in 3 (h atoms omitted for clarity). (b) 2D sheet of 3. (c) the
3D solid-state framework of 3 constructed by π…π interaction.
(d) the (3,3)-connected network of 1–3 by considering the
organic ligand as a three-connected node and the cation as a
three-connected node (For 2, the free methanol molecule and
the coordinated water are omitted). (B&W for printed version).

8
Q. HuaNG eT aL.
Figure 6. (colour online) (a) pl intensity of the ligand p-iphh3iD
and polymers 1–2. (b) pl intensity of the ligand p-tiphh3iD and
polymer 3.
indicates 64-nm blue shift compared with the free ligand
p-TIPhH3ID (Figure 6b).
Since the Zn(II) and Cd(II) ions are difficult to oxidise
or to reduce due to their features of electronic configu-
rations, the emission bands of complexes of 1 and 2 are
neither metal-to-ligand charge transfer (MLCT) nor ligand-
to-metal charge transfer in nature. So the emission of 1
and 2 might be attributed to the ligand-to-ligand charge
transfer, and the blue shift of 1–3 is due to intramolecular
charge transfer (ICT).
Figure 4. (colour online) XrD spectra of polymers 1–3.
The photoluminescence sensing experiments of
polymer+M are determined at room temperature (Figure 7).
It is interesting to find that 1 and 2 show selective recogni-
tion for Fe3+ ion, and polymer 3 shows good sensing for K+.
as shown in Figure 7a, it could be found that the
luminescent intensity of 1 heavily depends on the type
of metal ions: Co2+, Ni2+ and Na+ ions have basically no
effect on its luminescence, while other cations have slight
effects on the luminescent intensity (increasing (Sr2+ and
K+) or decreasing (Cd2+, Mg2+, Ca2+, Pb2+ and al3+) effects).
Impressively, the luminescent intensity is nearly one-third
Figure 5. (colour online) tG analysis profiles of polymers 1–3.

SuPRaMOLeCuLaR CHeMISTRy
9
Figure 8. (colouronline) (a) emissiveresponsespectraof 1 treated
by Fe3+of different molar concentrations. (b) emissive response
spectra of 2 treated by Fe3+ of different molar concentrations. (c)
emissive response spectra of 3 treated by K+ of different molar
concentrations.
Figure 7. (colour online) photoluminescence intensity of
polymers, 1(a), 2(b) and 3(c) treated by different metal salt
solutions.
of 1 after treatment with Fe3+ ion. For polymer 2, the most
metal ions (Cd2+, Mg2+, Ca2+, Pb2+, al3+, Sr2+, K+, Co2+ and
Ni2+) have varying degrees on the luminescent intensity,
but Fe3+ ion has a dramatic quenching effect (Figure 7b). as
indicated in Figure 7c, both Fe3+ and K+ ions have notable
quenching effect. at the same time, there is an approximate
48-nm blue shift of the emission band induced by K+ ion
(λex = 274 nm) (Figure 7c). That is to say, the recognition
effect of 3 for K+ ion is more distinct.
To examine the sensing sensitivity towards Fe3+ or K+
in more detail, the samples of compounds 1–3 treated by
increasing Fe3+ or K+ concentrations (0.1, 1, 10 mmol/L)

10
Q. HuaNG eT aL.
were prepared, and their emission spectra were recorded
(Figure 8). as shown in Figure 8, it can be clearly seen that the
fluorescence intensity gradually decreases with increase in
Fe3+ or K+ contents, which indicates that 1 and 2 are promis-
ing fluorescent probes for detecting Fe3+ cation, and 3 for K+.
To elucidate the possible mechanism for such lumines-
cence behaviours, as well as to identify if the frameworks
of 1–3 collapse after treatment with different metal ions,
the XRD and IR spectra (Figure 9) of the solid-state samples
were carried out. XRD data showed that the as-synthesised
products are in good agreement with the corresponding
simulated ones, indicating the phase purity of the samples.
In addition, the results of XRD and IR spectra indicate no
obvious difference in 1 (or 2 or 3) immersing in different
cation solutions before or after, revealing that the original
framework remains upon treatment. So, the introduction
Figure 9. (colour online) XrD (a) and ir (b) spectra of the polymers treated by different concentrations of metal salt aqueous solution.

SuPRaMOLeCuLaR CHeMISTRy
11
Foundation and advancedTechnology Research Project [Project
number 162300410206].
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Disclosure statement
No potential conflict of interest was reported by the authors.
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