An amino-functionalized three-dimensional cadmium metal–organic framework: Synthesis, characterization and excellent fluorescence sensing of Fe3+

Article abstract of DOI:10.1177/17475198211018981

An amino-functionalized three-dimensional cadmium metal–organic framework, [Cd_1.5(L)(DMF)]·2H₂O (complex 1) L = H₃TTCA-NH₂ = 2′-amino-[1,1′:3′,1″-terphenyl]-4,4″,5′-tricarboxylic acid), is successfully synthesized under solvothermal conditions and structurally characterized. Interestingly, as a transition metal organic framework, the cadmium metal–organic framework exhibits favorable luminescence properties. In addition, the cadmium metal–organic framework reveals excellent selective and sensitive fluorescence sensing for the recognition of Fe³⁺ with high quenching efficiency (K_sv = 3.340 × 10³ M^?1), demonstrating that the cadmium metal–organic framework can be used as a potential sensor for Fe³⁺.

Full text of DOI:10.1177/17475198211018981

1
research-arti
0cle2021 18981CHL0010.1177/17475198211018981Journal of Chemical ResearchYin et al.
Research Paper
Journal of Chemical Research
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1
An amino-functionalized three-dimensional
cadmium metal–organic framework:
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Synthesis, characterization and excellent
3+
fluorescence sensing of Fe
Jifa Yin , Youjie Han, Hongmei Zhu and Ye Tian
Abstract
An amino-functionalized three-dimensional cadmium metal–organic framework, [Cd (L)(DMF)]·2H O (complex
1
.5
2
1
) L = H TTCA-NH = 2′-amino-[1,1′:3′,1″-terphenyl]-4,4″,5′-tricarboxylic acid), is successfully synthesized under
3 2
solvothermal conditions and structurally characterized. Interestingly, as a transition metal organic framework, the
cadmium metal–organic framework exhibits favorable luminescence properties. In addition, the cadmium metal–organic
3
+
framework reveals excellent selective and sensitive fluorescence sensing for the recognition of Fe with high quenching
3
−1
efficiency (K = 3.340 × 10 M ), demonstrating that the cadmium metal–organic framework can be used as a potential
sv
3
+
sensor for Fe .
Keywords
1
D secondary building unit, amino-functionalized, crystal structure, fluorescence sensing, metal organic framework
Date received: 27 February 2021; accepted: 3 May 2021
A Cd-MOF was obtained based on an amino-functionalized ligand and exhibited excellent fluorescence sensing
3
+
performance for Fe .
Introduction
Jinan Motor Vehicle Pollution Prevention and Control Center, Jinan,
Metal organic frameworks (MOFs) constructed from inor- People’s Republic of China
ganic metal centers and bridged organic ligands have
attracted considerable attention in recent years. As a
new porous material different from zeolites and molecular
Corresponding author:
Jifa Yin, Jinan Motor Vehicle Pollution Prevention and Control Center,
Jinan 250014, Shandong Province, People’s Republic of China.
1
–3
sieves, MOFs possess a high specific surface area, a large Email: 12118198@qq.com
Creative Commons Non Commercial CC BY-NC: This article is distributed under the terms of the Creative Commons
Attribution-NonCommercial 4.0 License (https://creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use,
reproduction and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and
Open Access pages (https://us.sagepub.com/en-us/nam/open-access-at-sage).

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Journal of Chemical Research
Table 1. Crystal data and structure refinement of complex 1.
Identification code
Complex 1
CCDC No.
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
A (°)
B (°)
1988988
C H Cd N O
48
38
3
4
14
1232.02
150.00(10)
Triclinic
P-1
10.2760(10)
10.5841(6)
13.2275(5)
104.266(6)
93.267(7)
94.605(6)
1385.38(19)
1
γ/°
3
Volume (Å )
Z
3
ρcalc (mg/mm )
μ (mm )
F(000)
1.477
1.202
610.0
−
1
2
θ range for data collection
3.188–50
9569
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F
4827 (Rint = 0.0695, Rsigma =0.1163)
4827/49/345
0.908
2
Final R indexes (I ⩾ 2σ (I))
Final R indexes (all data)
Largest difference in peak/hole (e Å )
R = 0.0512, wR = 0.1052
1
2
R = 0.0866, wR = 0.1211
1
2
−
3
1.21/−0.77
aperture, structural functional diversity, and unsaturated Results and discussion
4
–7
metal sites. They offer opportunities for applications
such as in gas storage and separation, in catalytic pro-
The amino-functionalized H TTCA-NH was synthesized
3
2
8
–11
according to a literature method, and the solvothermal reac-
tion of H TTCA-NH and Cd(NO ) in DMF-EtOH-H O
cesses, as fluorescent sensors, and in drug delivery.
In
3
2
3 2
2
terms of structural features, the design of functional MOFs
is a prerequisite for many applications, which can be regu-
lated according to adjustable structures and modified
(5/2/1, v/v/v) afforded light yellow, block-shaped crystals
of complex 1.
1
2–14
skeletons.
As is well known, heavy metal ions are harmful to
humans and organisms, and thus finding sensitive and
selective detection methods is an important scientific
Crystal structure
The crystallographic data of complex 1 are shown in Table 1.
Single-crystal X-ray diffraction (SCXRD) analysis reveals that
1
5–17
goal.
At present, the most reported fluorescent MOF
sensors, transition MOFs, and lanthanide MOFs contain complex 1 crystallizes in the triclinic space group P-1. The
important groups such as �SO 3− or pyridyl nitrogen elec- asymmetric structural unit includes one deprotonated ligand
3−
tron–deficient groups inside the pores or cavities as Lewis (TTCA-NH ) , one and a half Cd(II) atoms, and a coordinated
2
basic sites for convenient and fast sensing of metal dimethylformamide (DMF) molecule. The coordination envi-
1
8–22
ions.
ronment of the ligands is shown in Figure 1(a). The Cd(II)
Herein, we have modified and synthesized the amino- atoms take two coordination modes; Cd1 adopts the seven-
modified organic ligand 2′-amino-[1,1′:3′,1″-terphenyl]- coordination mode to coordinate with six oxygen atoms of the
4
,4″,5′-tricarboxylic acid (H TTCA-NH ). Taking into carboxylic acids from four ligands and one µ -oxygen atom
3 2
2
consideration the luminescence performance of transition from an H O molecule. The average Cd1–O distance is 2.577
2
metal MOFs, an amino-functionalized cadmium (Cd)- Å. Cd2 is connected to four oxygen atoms of four ligands and
MOF, [Cd (L)(DMF)]·2H O (complex 1), was synthe- two µ -oxygen atoms from H O molecules. The average Cd2–
1
.5
2
2
2
sized by the solvothermal method. Interestingly, complex O distance is 2.353 Å. Cd1 and Cd2 are connected by ligand
exhibits excellent luminous intensity. As a fluorescent bridging and chelation to form one-dimensional chain second-
sensor, complex 1 exhibits selectivity and sensitivity for ary building units (SBUs) (Figure 1(b)). The SBUs and ligands
1
3
+
Fe in ethanol through fluorescence quenching with a are connected to each other to form a three-dimensional (3D)
3
−1
high quenching efficiency of 3.340 × 10 M . Therefore, framework structure with amino groups extending into the pore
complex 1 is a promising sensor for identifying and detect- channels. (Figure 1(c) and (d)). The distance of the adjacent
3
+
ing Fe .
amino groups in the pore channel is 3.487 Å.

Yin et al.
3
3−
Figure 1. (a) The coordination environment of the ligand (TTCA-NH ) . (b) The one-dimensional chain SBUs. (c, d) The three-
2
dimensional framework structure viewed from the b and c axes.
Characterization of powder diffraction,
thermogravimetry, and surface area
emission at λmax = 455 nm (EXslit = 2.5 nm, EMslit = 1.0
nm), which has a blue shift of 20 nm compared to the ligand
at λmax = 475 nm. Obviously, the fluorescence intensity of
complex 1 is higher than that of the organic ligand
The purity of the synthesized complex was evaluated by
powder X-ray diffraction (PXRD). The PXRD figure shows
that the as-synthesized crystal pattern is consistent with that
simulated from SCXRD data (Figure 2(a)), indicating the
pure phase of complex 1. At the same time, the thermal
stability of complex 1 was tested by thermogravimetry
(
H TTCA-NH ) (Figure 3(a)). Simultaneously, lumines-
3 2
cence in different solvents was measured. As Figure 3(b)
shows, the fluorescence intensities in DMF and ethanol
were relatively high and stable. Considering the green cre-
dentials of ethanol, fluorescence detection studies were
subsequently carried out in this solvent. After adding eight
analysis (TGA) measurements under an N atmosphere in
2
the temperature range of 40 °C–900 °C (Figure 2(b)).
Complex 1 lost a weight of 2.31% at 100 °C, which can be
attributed to the loss of water molecules. Then, complex 1
lost the weight of 19.9% at 240 °C; this part corresponds to
the loss of N,N-DMF from the framework. A relatively sta-
ble platform exists from 240 °C to 400 °C. The framework
of complex 1 finally collapsed at 400 °C, illustrating that
complex 1 has excellent thermal stability. The permanent
+
+
2+
2+
2+
3+
3+
different metal ions (Ag , Li , Ba , Pd , Hg , Cr , Al ,
3
+
−1
Fe ; c = 1 mmol·L ), the relative intensities of fluores-
cence changes are shown in Figure 4(a). Surprisingly, Fe
3
+
significantly quenched the fluorescence intensity of com-
plex 1. The corresponding fluorescence spectra after add-
3
+
ing Fe ions are shown in Figure 4(b). In order to further
3
+
prove the quenching efficiency of complex 1 for Fe , we
calculated the quenching constant (K ) using the Stern–
porosity of complex 1 is confirmed by N adsorption–des-
sv
2
2
3
Volmer (SV) equation: (I /I) = 1 + K [A]. Here, I0/I
orption isotherms at 77 K (see Figure S2 in the Supporting
Information), which show a type IV isotherm with a maxi-
0
sv
represents the initial fluorescence intensity over the lumi-
nescence intensity after addition of the analyte, and [A] is
3
−1
mum uptake of 54.9 cm ·g . The Brunauer–Emmett–Teller
2
−1
the molar concentration of the analyte. The K value of
(
BET) surface area is estimated to be 14.5 m ·g and the
sv
−1
3
3
−1
complex 1 was calculated to be 3.340 × 10 M toward
pore volume is calculated as 0.076 cm ·g .
3
+
Fe , which is comparable to or higher than those of some
other reported MOFs in the literature (see Supplemental
Table S1). The limit of detection (LOD) was calculated to
Fluorescence studies
Transition-metal MOFs have specific luminescence advan- be 0.01 mM according to the equation: LOD = 3s/k. The
3
+
tages; therefore, solid state fluorescence and liquid fluores- quenching fluorescence of complex 1 by Fe can be attrib-
3
+
cence tests were performed using a Hitachi F-7000 uted to the relatively small radius of Fe and the strong
fluorescence spectrophotometer. When the excitation electron attraction of the nitrogen atom in the NH group of
2
wavelength was 330 nm, complex 1 exhibited a clear the ligand.

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Journal of Chemical Research
Figure 2. (a, b) The PXRD and TGA patterns of complex 1.
Figure 3. (a) The solid state fluorescence spectra of complex 1. (b) Fluorescence spectra of complex 1 in different solvents.
Figure 4. (a) The relative fluorescence intensity after adding eight different metal ions relative to complex 1. (b) The fluorescence
3
+
3+
spectra after adding Fe ions (insert: Stern–Volmer plot of I /I versus the Fe concentration in ethanol solution).
0

Yin et al.
5
Scheme 1. Synthesis procedures of the H TTCA-NH ligand.
3
2
-
1
Conclusion
3.94; found: C, 40.42; H, 3.50; N, 3.89. IR (KBr, cm ):
3
2
472 (s), 1660 (s), 1102 (s), 3923(m), 794(m), 731(m),
527 (w), 570(w).
In summary, on the basis of designing the amino functional
group–modified organic ligand (H TTCA-NH ), an amino-
3
2
functionalized 3D Cd-MOF (complex 1) was successfully
synthesized via the solvothermal method. At the same time,
complex 1 was characterized by PXRD, infrared spectrom-
etry (IR), and TGA. Interestingly, it was found by fluores-
cence experiments that complex 1 exhibits favorable
luminescence properties and excellent fluorescence sensing
performance. To our surprise, complex 1 can rapidly detect
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with
respect to the research, authorship, and/or publication of this
article.
Funding
3
+
The author(s) disclosed receipt of the following financial support
for the research, authorship, and/or publication of this article: This
research was funded by Jinan Motor Vehicle Pollution Prevention
and Control Center.
Fe through fluorescence quenching with high quenching
efficiency. The K value of complex 1 reaches up to 3.340
sv
3
−1
×
10 M , demonstrating that complex 1 can be used as a
fluorescent sensor with useful prospects for identifying
metal ions.
ORCID iD
Jifa Yin
https://orcid.org/0000-0002-1181-7548
Experimental section
Supplemental material
Materials and method
Supplemental material for this article is available online.
All chemical reagents were purchased from chemical ven-
dors and were used without further purification. The PXRD
diffractograms were obtained on a PANalytical X-Pert PRO
diffractometer with Cu-Kα radiation. Elemental analyses
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