A new Keggin-type heteropolyoxometalates compound built up by coordinated cadmium

Article abstract of DOI:10.1007/s11696-019-00738-5

A new Keggin-type heteropolyoxometalates compound, {[Cd(DMA)₄]₂(bibp)(SiW₁₂O₄₀)}_n (1), (DMA = N, N-dimethylacetamide, bibp = 4,4′-bis(1-imidazolyl) biphenyl) has been synthesized and characterized by

Full text of DOI:10.1007/s11696-019-00738-5

Chemical Papers
https://doi.org/10.1007/s11696-019-00738-5
ORIGINAL PAPER
A new Keggin‑type heteropolyoxometalates compound built
up by coordinated cadmium
Hang Xiao1 · Xiao‑Yuan Wu2 · Ming‑Xue Yang2 · Lang Lin1 · Shuai Li1 · Xin‑Yuan Chen1 · Xiao‑Yu Jiang1
Received: 4 December 2018 / Accepted: 5 March 2019
© Institute of Chemistry, Slovak Academy of Sciences 2019
Abstract
A new Keggin-type heteropolyoxometalates compound, {[Cd(DMA)4]2(bibp)(SiW12O40)}n (1), (DMA=N, N-dimethylacet-
amide, bibp=4,4′-bis(1-imidazolyl) biphenyl) has been synthesized and characterized by single-crystal X-ray difraction,
IR spectrum, elemental analysis, powder X-ray difraction, thermogravimetric (TG) analysis and electrochemical analysis.
Compound 1 is crystallized in orthorhombic with Pbca space group. The [SiW12O40]4− anions and bibp ligands are linked
by coordinated Cd2+ ions alternately into a zigzag-like chain, and the chains are extended into a three-dimensional (3D)
framework by the C–H···O hydrogen bonds. The cyclic voltammetry analyses show that compound 1 presences of W-centered
reversible redox processes and that 1 has electrocatalytic activities towards the reduction of nitrite.
Keywords Heteropolyoxometalate · Coordinated cadmium · Crystal structure · Hydrogen bonds · Electrochemical behavior
Introduction
ability to accept or to release a specifc number of electrons
reversibly, making POMs used as catalysts in the feld of
electrochemical and electrocatalysis (Wu et al. 2017; Silva
and Oliveira 2018; Hu et al. 2017). The rigid organic ligands
containing N-donors are used in the construction of com-
pounds with new structures to create unique electrochemi-
cal properties (Enferadi-Kerenkan et al. 2018; Proust et al.
2008). In recent years, 4,4′-bis(1-imidazolyl) biphenyl (bibp)
as a rigid organic ligand containing N-donors, is widely used
for the feld of coordination polymers (CPs), metal–organic
frameworks (MOFs) (Meng et al. 2017; Zhang et al. 2013).
However, there are only a few researches focusing on bibp-
based POMs materials.
Polyoxometalates (POMs) have been of interest to research-
ers, due to the excellent performance of POMs in industrial
catalysis, such as rich composition, structural diversity, elec-
tronic versatility and its amphoteric (acidic and oxidative)
(Zhao et al. 2014, 2016; Jiang et al. 2011). POMs are clus-
ters of early transition metal oxyanions and usually classi-
fed into isopolyoxometalates or heteropolyoxometalates, by
whether or not heteroatoms (P, Si, etc.) in the composition.
The structure of a POM can be adjusted at the molecular
level, which can lead to the development of unique electronic
properties. One of the most critical features of POMs is the
Herein, we report a new Keggin-type heteropolyoxo-
metalates compound, {[Cd(DMA)4]2(bibp)(SiW12O40)}n
(1), in which the bibp units and [SiW12O40]4− anions are
linked by coordinated Cd2+ ions alternately into a zigzag-
like chain. The chains are extended into a three-dimensional
(3D) framework by the hydrogen bonds. The electrochemical
characterizations of 1 are explored, and its electrocatalytic
activity towards the reduction of nitrite is characterized by
cyclic voltammetry method.
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11696-019-00738-5) contains
supplementary material, which is available to authorized users.
* Xiao-Yu Jiang
xyjiang@fut.edu.cn
1
College of the Ecology and Environment Engineering,
Fujian University of Technology, Fuzhou 350108, Fujian,
China
2
CAS Key Laboratory of Design and Assembly
of Functional Nanostructures, and Fujian Key Laboratory
of Nanomaterials, Fujian Institute of Research
on the Structure of Matter, Chinese Academy of Sciences,
Fuzhou 350002, Fujian, China
Vol.:(0123456789)
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yellow block-shaped crystals. The crystals were collected
and washed with ethanol. Yield 75% based on Cd. Anal.
Calcd. for 1 (%): C, 14.71; H, 2.01; O, 18.82; N, 4.12. Found
(%): C, 15.54; H, 1.85; O, 18.25; N, 4.87. FT-IR (KBr pel-
let, cm−1): 3126w, 2937w, 1601 m, 1514 m, 1402w, 1309w,
1261w, 1192w, 1124w, 1066 m, 1014 m, 972 s, 920 s, 798 s,
530w.
Experimental
All the starting chemicals and solvents were purchased
commercially from Sinopharm (China) and used without
further purifcation. Pure water was obtained by passing
water through a Merck Millipore Direct-Q5UV water puri-
fcation set (France). The bibp ligand was prepared accord-
ing to literature (Fan and Hanson 2005). The C, H, O and
N elemental analyses were measured on a Vario MICRO
elemental analyzer (Germany). The 1H NMR spectra were
recorded on a Bruker Avance III 400 MHz NMR spec-
trometer. X-ray powder difraction data were recorded on
a Mini Flex II difractometer (China) with a scan speed
of 2° min−1. The FT-IR spectra were recorded on a Ver-
tex 70 FT-IR spectrometer (Germany) using KBr pellets in
the range of 4000–400 cm−1. Thermogravimetric analyses
were carried out on a TGA/DSC1/1100 thermogravimetric
analyzer (Switzerland) under a nitrogen atmosphere from
30 to 1000 °C at a heating rate of 15 °C min−1. The elec-
trochemical set-up was a CHI760C electrochemical work-
station (China). A conventional three-electrode system was
used. The working electrode was a modifed glassy carbon
electrode (GC). A platinum electrode was used as a coun-
ter electrode, and a saturated calomel electrode (SCE) was
used as reference electrode. All potentials were measured
and reported versus the SCE. All voltammetric experiments
were carried out at room temperature.
The crystallographic measurement for 1 was taken on a
Super Nova CCD difractometer equipped with a graphite-
monochromatic Cu Kα radiation (λ=1.54178 Å) at 100 K.
Empirical absorption corrections were applied to the data
using the CrysAlisPro program (Flack and Bernardinelli
2000). The structure was solved by direct methods using
SHELXS-97 and refned with full-matrix least-squares on
F2 using SHELXL-97 program (Sheldrick 2015). All of the
non-hydrogen atoms were refned anisotropically. The crys-
tal data of X-ray structural analyses are given in Table S1,
and the CCDC reference number is 1855374.
Results and discussion
Single-crystal X-ray structural analysis revealed that com-
pound 1 crystallizes in a centrosymmetric Pbca space group.
Compound 1 is composed of bibp units, [SiW12O40]4− ani-
ons, coordinated Cd2+ ions, and DMA molecules (Fig. 1).
The [SiW12O40]4− anion is in well-known Keggin-type
structure, and the central SiO4 tetrahedron is orientationally
disordered where the Si atom is surrounded by eight oxygen
atoms, with each oxygen site half-occupied (Shi et al. 2013;
Kong et al. 2012). The Si–O bonds range from 1.5883 (210)
to 1.7356 (197) Å. W–O bond distances can be divided into
three groups: W–Ot (terminal O) 1.6341 (121)–1.6883 (143),
W–Oa (O in the SiO4 tetrahedron) 2.3116 (197)–2.5054
(217) and W–Ob (bridge O) 1.8480 (127)–2.0985 (218) Å,
respectively. All coordinated W atoms in 1 are WVI accord-
ing to BVS calculations (Brese and O’keefe 1991). The
bibp unit is composed of two benzenes and two imidazoles.
The two benzenes are on a plane and the two imidazoles on
another plane. The angle between the benzene plane and
imidazole plane was 38.8°. The Cd2+ ion has six-coordina-
tion with fve oxygen and one nitrogen atoms, four oxygen
atoms (O (21), O (22), O (23) and O (24)) from DMA mol-
ecule, one (O (1)) from [SiW12O40]4− anion and one nitro-
gen atom (N (1)) from bibp ligand. Cd–O bonds range are
2.2016 (142)–2.3957 (135) Å, and the Cd–N bond is 2.2062
(162) Å.
Synthesis of ligand bibp
A mixture of imidazole (5.76 g, 84 mmol), 4,4′- dibromobi-
phenyl (6.24 g, 20 mmol), CuSO4 (0.064 g, 0.4 mmol) and
K2CO3 (8.78 g, 63 mmol) were heated at 180 °C for 12 h,
under an argon atmosphere, and then it was gradually cooled
to room temperature, washed with water and extracted by
ethanol three times. The product was separated and evapo-
rated to dryness to give a solid crude product, which was
purifed by recrystallization to give a white powder (bibp).
1
Yield: 72%. H NMR (400 MHz, CDCl3): δ 7.28 (2H, s),
7.37 (2H, s), 7.53 (4H, d), 7.74 (4H, d), 7.95 (2H, s).
Synthesis of {[Cd(DMA)4]2(bibp)(SiW12O40)}n (1)
The yellow crystalline compound 1 was prepared via a
solvothermal procedure by heat-sealing all reactants into
a Tefon-lined stainless container, in weighed amounts of
H4[SiW12O40]·xH2O (0.1001 g, 0.035 mmol), bibp (0.0102 g,
0.035 mmol), Cd(NO3)2·4H2O (0.0101 g, 0.035 mmol),
5-aminoisophthalic acid (0.0630 g, 0.035 mmol) and DMA
(5.0 mL). The container was heated at 130 °C for 3 days
and then cooled to room temperature within 1 day to give
[SiW12O40]4− anions and bibp ligands are linked by
Cd2+ ions alternately into a zigzag-like chain elonga-
tion along the a axis (Fig. 2). To be viewed in ab plane,
adjacent chains are connected with the hydrogen bonds C
(5)–H (5) ···O (15) to spread out in the ab plane (Fig. 3a).
Finally, the neighboring planes are balanced to form a 3D
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Fig. 1 Ball/stick view of com-
pound 1 (all hydrogen atoms
were omitted for clarity)
Fig. 2 The zigzag-like chain in compound 1 viewed along the b axis
Fig. 3 Three types of hydrogen bonds in compound 1
supermolecular with hydrogen bonds (C (14)–H (14A) ···O
(12) (Fig. 3b) and C (16)–H (16A)···O (9) (Fig. 3c). The
C (14)–H (14A) ···O (12) and C (16)–H (16A) ···O (9)
involves coordinated DMA molecule and oxygen atoms
of polyoxometalate unit, with the D···A distance from
3.4165(322) Å to 3.4853(286) Å and D–H···A angle from
150.0° to 165.8°. C (5)–H (5) ···O (15) involves coordi-
nated bibp ligand and oxygen atoms of polyoxometalate
unit, of which the hydrogen bonding parameters (Table S2)
(C···O, 3.2357(270) Å, and ∠C–H···O, 154.8°) are in the
acceptance range of C–H···O interaction.
In the IR spectrum of 1 (Fig. S1), the vibrations at
1014, 972, 920, 798 cm−1 are the characteristic bands of
the Keggin-type heteropolyoxometalates, while the vibra-
tions in the region of 3150–1050 cm−1 can be attributed to
the characteristic peaks of the bibp ligands and the DMA
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molecules. In addition, the broad peak at about 3300 cm−1
shows the hydrogen bonding interactions in the compound
1.
the positive direction. The anodic current of peaks (II) is
proportional to the scan rates shown in the insets of Fig. 4,
which suggests that the redox process is surface-control
(Zonoz et al. 2014).
The result of the thermogravimetric analysis (TGA) is
depicted in Fig. S2. A gradual weight loss during heating
from 230 to 600 °C, corresponding to the removal of four
DMF molecules (found 9.85%, calcd 8.53%). Then, dur-
ing heating from 620 to 960 °C, the residual framework
began to decompose, corresponding to the removal of the
other DMF molecules and bibp ligands (found 17.29%,
calcd 15.54%).
Figure 5 shows the cyclic voltammograms of 1 in the
solution of 0.05 mol L−1 H2SO4 (A), and 0.05 mol L−1
H2SO4 + 9.6 × 10−3 mol L−1 NaNO2 (B). Compared with
the solution containing H2SO4, when the solution contains
NaNO2, the peak(II), and peak(III) are cannot be observed
clearly, and a big and broad cathodic peak (IV′) is observed
at − 0.38 V. The peak (IV′) would be assigned as nitrite
reduction (Hao et al. 2012).
The cyclic voltammograms in 0.05 mol L−1 of H2SO4
are shown in Fig. 4. There are three pairs of reversible
redox peaks (I–I′, II–II′, III–III′) in the potential range
from + 0.1 to − 1.0 V, and the mean peak potentials
E1/2 = (Epa + Epc)/2 are − 0.28 V (I–I′), − 0.57 V (II–II′)
and − 0.82 V (III–III′) at scan rate of 50 mV s−1, The
three pairs of reversible redox peaks are typical for the
W-cluster which may be assigned to two one-electron and
one two-electron wave (Teazea et al. 2007; Dong et al.
1995). Cd divalent transition metal cations do not exhibit
electroactive at pH less than 3.
VI
VI
SiW O44−0 + e− ↔ SiWVW O45−0 (SiW12O45−0
)
(1)
(2)
12
11
VI
VI
SiWVW O54−0 + e− ↔ SiWV2 W O460−(SiW12O64−0
)
11
10
SiWV2 W O64−0 + 2e− + 2H+ ↔ H2SiWV4 WV8 IO64−0 (H2SiW12O64−0
VI
)
10
(3)
When the scan rate varied from 25 to 200 mV s−1, the
cathode and anode currents of peak increased, and the
cathodic peak potentials shifted to the negative direction
and the corresponding anodic peak potentials shifted to
Fig. 5 Cyclic voltammograms of
1 in diferent solutions. (A)
0.05 mol L−1 H2SO4. (B) 0.05 mol L−1 H2SO4 +9.6×10−3 mol L−1
NaNO2. The scan rate was 50 mV s−1
Fig. 4 Cyclic voltammograms of compound 1 in 0.05 mol L−1
H2SO4 solution at diferent scan rate (a 25, b 50, c 100, d 150, e
200 mV s−1). The inset shows a plot of the anodic current of peak II
against scan rate
Fig. 6 Cyclic voltammograms of 1 in aqueous solution of 0.05 mol
L−1 H2SO4 +9.6×10−3 mol L−1 NaNO2 at diferent scan rate (a 25,
b 50, c 75, d 100, e 150, f 200 mV s−1). The inset shows a plot of the
anodic peak currents against the square root of the scan rate
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processes and that 1 has electrocatalytic activities towards
the reduction of nitrite.
Acknowledgements This work was supported by the National Natural
Science Foundation of China [Grant numbers 51672271]; the National
Natural Science Foundation of China [Grant numbers 21701172]; the
Key Project of Science and Technology Plan of Fujian Province [Grant
numbers 2014H0007]; and the Fujian University of Technology [Grant
numbers GY-Z12088].
Compliances with ethical standards
Conflict of interest On behalf of all authors, the corresponding author
states that there is no.
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Fig. 7 Cyclic voltammograms (Scan rate 50 mV s−1) of compound
1 in 0.05 mol L−1 H2SO4 +NaNO2 solution, the concentration of
NaNO2: (i) 4.8×10−3 mol L−1. (ii) 7.2×10−3 mol L−1. (iii) 9.6×10−3
mol L−1. (iv) 12.0×10−3 mol L−1. The inset shows the relationship
between cathode current and NO2− concentration
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