Synthesis of two coordination polymer photocatalysts and significant enhancement of their catalytic photodegradation activity by doping with Co2+ Ions

Article abstract of DOI:10.1002/ejic.201500069

The coordination polymers (CPs) [Zn₂(tipm)(1,3-BDC)₂] (1) and [Co₂(tipm)(1,3-BDC)₂]·0.5CH₃CN (2·0.5CH₃CN) were synthesized by the reactions of Zn(NO₃)₂ or Co(NO_3<

Full text of DOI:10.1002/ejic.201500069

FULL PAPER
DOI:10.1002/ejic.201500069
Synthesis of Two Coordination Polymer Photocatalysts
and Significant Enhancement of Their Catalytic
2
+
Photodegradation Activity by Doping with Co Ions
[
a,b]
[a]
[c]
Duan-Xiu Li,
Zhi-Gang Ren,* David J. Young, and Jian-
[
a,b]
Ping Lang*
Keywords: Coordination polymers / Photocatalysis / Zinc / Cobalt / Doping / N ligands / Carboxylate ligands
2
2
3
2
3
The coordination polymers (CPs) [Zn
and [Co (tipm)(1,3-BDC) ]·0.5CH CN (2·0.5CH
synthesized by the reactions of Zn(NO or Co(NO
tetrakis[4-(1-imidazolyl)phenyl]methane (tipm) and benz-
ene-1,3-dicarboxylic acid (1,3-H BDC) under solvothermal
2
(tipm)(1,3-BDC)
CN) were
with
2
] (1)
symbol (4·7 )(6 ·7 ·12)(4·6 ·7 ). Cobalt ions were incorpo-
rated into the Zn-based CP framework 1 during solvothermal
2
2
3
3
3
)
2
3
)
2
crystallization to yield [Zn(2–2x)Co2x(tipm)(1,3-BDC)
(x = 2.4%, b = 0 for 1a, x = 23%, b = 1 for 2a·H O). Doped
CPs 1a and 2a·H O exhibited greater catalytic photodegrad-
2 2
]·bH O
2
2
2
conditions. Compounds 1 and 2 are isostructural and possess
ation of the dye rhodamine B (RhB) than the undoped com-
complicated three-dimensional frameworks with the Schläfli
plexes 1 and 2 and many literature examples.
to control in designed CP syntheses.[8] The rigid ligand
Introduction
3,3Ј,5,5Ј-tetra(1H-imidazol-1-yl)-1,1Ј-biphenyl (L) and the
Photocatalysis is an environmentally friendly method for
auxiliary 1,3,5-tri(4-carboxyphenyl)benzene (H BTB) have
3
[
1,2]
destroying organic dyes and other industrial pollutants.
Suitable coordination polymers (CPs) can exhibit excellent
been combined with ZnSO ·7H O to yield the two-dimen-
4
2
[8e]
sional network [Zn(L)0.5(CO )]·H O. Rigid ligands with
3
2
photocatalytic efficiencies and stabilities.[
3,4]
Photocatalytic
longer branched chains were used in this case to prevent
the formation of chelate compounds.
efficiency can be improved by doping specific transition
metal ions into CP frameworks.[ Liu reported that the
photocatalytic activity of [Zn(cca)(4,4Ј-bipy)]n (cca = 4-
carboxycinnamate dianion, 4,4Ј-bipy = 4,4Ј-bipyridine)
towards the decomposition of rhodamine B (RhB) was en-
5]
In our previous studies, we have constructed CPs with
imidazole ligands as the building blocks and investigated
[
9]
their photocatalytic activity. In this work, we designed
and synthesized the rigid tetraimidazolyl-based ligand tet-
rakis[4-(1-imidazolyl)phenyl]methane (tipm). This four-
connected ligand can be topologically represented as a tet-
rahedral node and has not, to the best of our knowledge,
been used hitherto to construct CPs. This ligand was chosen
because (1) four imidazole N atoms of the tipm ligand can
act as four potential coordination nodes and (2) the four
phenyl groups can lengthen the distance to the quaternary
carbon atom (Ccentre) to meet the requirements of the coor-
dination geometries. We have successfully synthesized the
tipm ligand in high yield through microwave heating. The
solvothermal reactions of tipm and 1,3-benzenedicarboxylic
3
+
3+
3+
2+
2+
hanced by doping with Fe , Cr , Ru , Co or Ni ions
through a simple ion-exchange process.[ This phenome-
5c]
non may be explained by the narrower band gaps (E ) of
g
the doped CPs. Multidentate N-donor ligands, multicarb-
oxylates and their admixtures are powerful building blocks
for the construction of CPs.[ Among the various multiden-
tate N-containing ligands, multipyridyl, multiimidazolyl,
and multipyrazolyl ligands as well as their derivatives are
6]
[
6e–6h,7]
commonly used, particularly bidentate examples.
and tetradentate ligands are harder to prepare and harder
Tri-
[
a] Key Laboratory of Organic Synthesis of Jiangsu Province, Col-
lege of Chemistry, Chemical Engineering and Materials Science,
Soochow University,
acid (1,3-H BDC) with Zn(NO ) or Co(NO ) gave rise to
2
3 2
3 2
the coordination polymers [Zn (tipm)(1,3-BDC) ] (1) and
2
2
Suzhou 215123, P. R. China
[
Co (tipm)(1,3-BDC) ]·0.5CH CN (2·0.5CH CN). Coordi-
2 2 3 3
E-mail: jplang@suda.edu.cn
http://lmdc.suda.edu.cn/index.asp
nation polymers 1 and 2 are isostructural and possess com-
[
[
b] State Key Laboratory of Organometallic Chemistry, Shanghai plicated 3D frameworks with the Schläfli symbol
Institute of Organic Chemistry, Chinese Academy of Sciences,
Shanghai 200032, P. R. China
2
2
3
2
3
(
4·7 )(6 ·7 ·12)(4·6 ·7 ). The doping of different amounts of
2+
c] School of Science, Monash University Malaysia, Jalan Lagoon Co ions into 1 during the solvothermal crystallization
Selatan,
yielded the doped isostructural CPs [Zn(2–2x)Co2x-
4
7500 Bandar Sunway, Selangor Darul Ehsan, Malaysia
(
tipm)(1,3-BDC) ]·bH O (x = 2.4%, b = 0 for 1a, x = 23%,
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201500069.
2 2
b = 1 for 2a·H O). The photocatalytic activities of these
2
Eur. J. Inorg. Chem. 2015, 1981–1988
1981
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FULL PAPER
undoped and doped products were investigated with the de- similar except for the central metal atoms. Thus, only the
gradation of RhB as a model reaction, and the results indi- structure of 1 (Figure 1, Table 1) is described in detail. Each
cated that the doped CPs 1a and 2a exhibited higher photo- Zn atom in 1 is tetrahedrally coordinated by two N atoms
catalytic activities than the undoped 1 and 2 and many lit- from two different tipm ligands and two O atoms from two
erature examples.
different 1,3-BDC ligands. The average Zn–N [2.001(6) Å]
and Zn–O bond lengths [1.961(5) Å] in 1 are shorter than
those
in
[Zn (tib) (HBDC-OH) (BDC-OH)]·2H O
2 2 2 2
[
2.017(2) and 1.972(2) Å, respectively; tib = 1,3,5-tris(1-
Results and Discussion
[
11]
imidazolyl)benzene].
The orientations of the 1,3-BDC
The ligand tipm was synthesized by a microwave-assisted molecules connecting Zn1 and Zn2 are different (Figure 1,
solid-state Ullmann coupling reaction between tetrakis(4- a and b); thus, the coordination sphere of Zn1 differs some-
bromophenyl)methane and imidazole. The traditional solu- what from that of Zn2. The two 1,3-BDC ligands around
tion reaction requires reflux in dimethyl sulfoxide (DMSO) Zn1 are trans with an O1–Zn1–O3A angle of 98.5(2)° and
[
10a]
for 2 d.
The convenient method reported herein is com- connect two neighbouring Zn1 atoms to form a 1D
plete in 90 s and uses less organic solvent. Excess imidazole [Zn (1,3-BDC) ] chain extending along the b axis (Fig-
2
2 n
was used to compensate for the possible sublimation of this ure 1, c). By comparison, the 1,3-BDC molecules bonded
reagent. The ligand tipm is stable in air and soluble in com- to Zn2 are cis with an O5–Zn2–O7C angle of 119.3(3)° and
mon solvents such as MeOH, EtOH, CH Cl , CHCl , N,N- lead to the formation of a cyclic dinuclear [Zn (1,3-BDC) ]
2
2
3
2
2
dimethylformamide (DMF) and DMSO but insoluble in unit (Figure 1, d). The 1D [Zn (1,3-BDC) ] chain connects
2
2 n
1
H O. In the H NMR spectrum of tipm in CDCl at 298 K to adjacent chains through tipm ligands to form a 2D
2
3
(
Figure S1), three singlets at δ = 7.87, 7.29 and 7.21 ppm [Zn (tipm) (1,3-BDC) ] layer (Figure 1, e), which is further
2 2 2
could be assigned to be the proton signals of the imidazole interpenetrated with an adjacent layer along the bc plane
groups, and one singlet at δ = 7.38 ppm was assigned to be (Figure 1, f). An important structural feature of these com-
1
3
the proton signal of the phenyl group. The C NMR spec- plexes is that each of them possesses an array (Figure S5)
trum of tipm in CDCl at 298 K exhibited signals for seven formed from weak edge-to-face π-π stacking interactions.
3
different carbon atoms of the imidazole and phenyl rings at The distances between the imidazole proton and the phenyl
δ = 117.9–144.7 ppm and that of the quaternary carbon ring centroid are ca. 3.2406(4) Å (1), 3.1508(4) Å (2),
atom (Ccentre) at δ = 63.7 ppm (Figure S2). The hydrother- 3.1769(7) Å (1a) and 3.1590(1) Å (2a), and these interac-
mal reactions of Zn(NO ) or Co(NO ) with tipm and 1,3- tions play a significant role in the stabilization of the corre-
3
2
3 2
H BDC (molar ratio 2:1:2) in H O/CH CN (4:1 v/v) at sponding framework. This interpenetrated double 2D layer
2
2
3
1
50 °C for 1 d afforded yellow blocks of 1 (62% yield) or is connected by the aforementioned [Zn (1,3-BDC) ] units
2 2
blue blocks of 2 (54% yield). When zinc(II) and cobalt(II) to form a 3D framework (Figure 1, h). If each Zn1 centre,
II
II
nitrates were added at the Zn /Co /tipm/1,3-H BDC ratios each Zn2 centre and each tipm ligand are regarded as a
2
of 2:2:1:2 and 1:2:1:2, 1a and 2a could be separated with the four-connecting node, a three-connecting node and a four-
Zn/Co ratios of 97.6:2.4 (1a) and 77:23 (2a), respectively. connecting node, respectively, the whole net can be simpli-
Increasing the percentage of Co from 1 to 1a, 2a and 2 fied as a 3D (3,4,4)-connected net. Compounds 1 and 2 are
changed the colours of these compounds from yellow (1) to isostructural and possess complicated 3D frameworks with
2
2
3
2
3
orange (1a), red (2a) and blue (2; Figure S3). Complexes 1, the Schläfli symbol (4·7 )(6 ·7 ·12)(4·6 ·7 ) (Figure 1, i).
, 1a and 2a are stable in air and insoluble in common The solvent-accessible void volumes calculated with PLA-
solvents such as H O, CHCl , CH CN, DMF and DMSO. TON24 are 25.1% for 1, 25.6% for 2, 25.1% for 1a and
2
2
3
3
Their elemental analyses were consistent with their chemi- 24.1% for 2a.
cal formulas. The Zn/Co ratios in 1a and 2a were deter-
The framework stabilities of 1, 2, 1a and 2a were investi-
mined by atomic absorption spectroscopy (AAS) analyses. gated by thermogravimetric analysis (TGA) under an ambi-
The observed powder XRD (PXRD) patterns for each com- ent atmosphere (Figure S6). The first weight losses (1.86%
pound correlated well with the simulated ones generated for 2 and 1.57% for 2a; calculated: 1.95% for 2 and 1.70%
from their single-crystal X-ray diffraction data (Figure S4). for 2a) from 20 to 150 °C correspond to the loss of the
The IR spectra of 1, 2, 1a and 2a exhibited strong absorp- acetonitrile molecules or water solvate. For all samples, the
tion bands in the ranges ν˜ = 1524–1614 and 1313– main weight loss was produced in the temperature range
–
1
1
374 cm , which indicated that they all contain coordi- 350–600 °C and can be attributed to the decomposition of
nated carboxylic groups. The strong peaks at ν˜ ≈ 1068 and the organic linkers. The residual weights (16.03% for 1,
–
1
6
55 cm confirm the existence of imidazolyl groups in 14.76% for 2, 15.02% for 1a and 16.21% for 2a) were calcu-
these complexes. lated, and the residual species were assumed to be ZnO for
The coordination polymers 1, 2·0.5CH CN, 1a and 1 (calcd. 15.60%), CoO for 2 (calcd. 14.25%), ZnO/CoO for
3
2
a·H O crystallize in the monoclinic space group C/2c. The 1a (calcd. 15.60%) and ZnO/Co O for 2a (calcd. 15.44%).
2
2
3
asymmetric units contain two crystallographically unique
The band gap energy (E ) of a photocatalyst is a factor
g
II
[12]
M
ions, one tipm ligand, two 1,3-BDC ligands and in its photocatalytic efficiency. The optical diffuse reflec-
CH CN (2·0.5CH CN) or H O (2a·H O) solvent molecules. tance spectra of crystalline solids 1, 2, 1a and 2a (Figure
3
3
2
2
The 3D supramolecular architectures of 1, 2, 1a and 2a are S7) were recorded at room temperature, and the absorption
Eur. J. Inorg. Chem. 2015, 1981–1988
1982
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Figure 1. (a) View of the coordination environment of the Zn1 centre in 1 with a labeling scheme. (b) View of the coordination environment
of the Zn2 centre in 1 with a labeling scheme. (c) View of the 1D [Zn (1,3-BDC) chain based on the Zn1 centre. (d) View of the cyclic
dinuclear [Zn (1,3-BDC) ] unit based on the Zn2 centre. (e) View of the 2D [Zn (tipm) (1,3-BDC) ] network along the a axis. (f) View
of the 2D [Zn (tipm) (1,3-BDC) ] double layers along the c axis. The tipm ligands in the two interpenetrated layers are plotted with blue
2
2 n
]
2
2
2
2
2
2
2
2
and yellow lines, respectively. (g) View of the 3D net along the c axis. (h) Schematic view of the topological net of 1. The cyan and blue
spheres represent Zn centres and tipm ligands, respectively. The thin and thick red lines represent the single carboxylate bridge in the 1D
[Zn
2 2 n 2 2
(1,3-BDC) ] chain and the double carboxylate bridge in the [Zn (1,3-BDC) ] unit, respectively. Symmetry codes: A: x, –y, z + 1/2;
B: –x + 1, y – 1, –z + 3/2; C: –x + 1/2, –y + 1/2, –z + 2; D: –x + 1/2, –y + 1/2, –z + 1; all H atoms are omitted for clarity.
Eur. J. Inorg. Chem. 2015, 1981–1988
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Table 1. Selected bond lengths [Å] and angles [°] for 1 and 2.[a]
Compound 1
tion spectroscopy. The λmax at 554 nm for RhB (Figure S8)
decreased with the irradiation time and particularly in the
presence of 1, 2, 1a and 2a. RhB decomposed very slowly
without any catalyst under the same conditions (Figure S9).
Zn(1)–N(1)
Zn(1)–O(1)
Zn(2)–N(3)
Zn(2)–O(5)
O(1)–Zn(1)–O(3A) 98.5(2)
O(3A)–Zn(1)–N(1) 103.2(2)
O(3A)–Zn(1)–N(5B) 107.3(2)
1.998(6)
1.991(4)
2.014(6)
1.919(5)
Zn(1)–O (3A)
Zn(1)–N(5B)
Zn(2)–O(7C)
Zn(2)–N(7D)
O(1)–Zn(1)–N(1)
O(1)–Zn(1)–N(5B)
1.996(5)
2.003(6)
1.939(5)
1.987(6)
111.3(2)
103.2(2)
Plots of log(c /c ) versus irradiation time are given in Fig-
t 0
ure 3. When the reaction solutions were mixed with equi-
molar catalyst and irradiated by UV light, each substrate
was almost completely decomposed within 4 h (for 1 at 4 h,
N(1)–Zn(1)–N(5B) 129.2(3)
O(5)–Zn(2)–N(7D) 119.3(3)
95%; for 2 at 3 h, 97 %; for 1a at 2.5 h, 94%; and for 2a at
O(5)–Zn(2)–O(7C)
96.0(3)
O(7)–Zn(2)–N(7D) 119.3(3)
O(5)–Zn(2)–N(3)
N(7D)–Zn(2)–N(3) 106.3(2)
110.2(3)
2 h, 90%). A comparison of the photodegradation param-
eters for reactions catalyzed by 1, 2, 1a, 2a and some known
catalysts is presented in Table 2. The times required for al-
most complete degradation of RhB in the presence of 1a
O(7)–Zn(2)–N(3)
104.7(2)
Compound 2
Co(1)–N(1)
Co(1)–O(1)
Co(2)–N(5)
Co(2)–O(5)
2.015(3)
1.997(3)
2.013(4)
1.938(3)
Co(1)–O(3A)
Co(1)–N(3B)
Co(2)–O(7C)
Co(2)–N(7D)
1.999(3)
2.014(4)
1.954(4)
2.007(3)
107.79(14)
103.25(14)
130.42(16)
and 2a were comparable to those of Fe O @SiO @TiO /
3
4
2
2
[
14a]
graphene oxide (2 h, 92%)
and Ag/Pt@TiO2 (2.5 h,
and significantly shorter than those (9 h)
required with the photocatalysts (3-H pya)[(3-Hpya) Ag]-
[14b]
99%)
O(1)–Co(1)–O(3A) 96.75(13) O(1)–Co(1)–N(3)
O(3A)–Co(1)–N(3) 102.71(14) O(1)–Co(1)–N(1)
O(3A)–Co(1)–N(1) 110.99(13) N(3)–Co(1)–N(1)
O(5)–Co(2)–O(7C) 94.7(2)
O(7)–Co(2)–N(7D) 118.95(18) O(5)–Co(2)–N(5)
O(7)–Co(2)–N(5) 2.029(4) N(7D)–Co(2)–N(5) 105.53(13)
2
2
[
AgAlMo H O ]·3H O [pyrolysis, 3-Hpya = 3-(3-pyridyl)-
6 6 24 2
O(5)–Co (2)–N(7D) 121.58(16) acrylic acid], HNa [(3-pya)(3-Hpya)Ag] [AlMo H O24]·
2 2 6 6
111.99(15) 8H O (pyrolysis) and [(3-Hpya) Ag][(H O) Ag] [Al-
2
2
2
2
2
[14c]
Mo H O ]·2H O (pyrolysis).
The degree of degrada-
6
6
24
2
[
3
a] Symmetry codes for 1: A: x, –y, z + 1/2; B: –x + 1, y – 1, –z + tion after 4 h for reactions catalyzed by [La(HL)(L)(H O) -
2
6
/2; C: –x + 1/2, –y + 1/2, –z + 2; D: –x + 1/2, –y + 1/2, –z + 1;
{
La(H L) (α-PW O H)La(H O) }] ·8H O, [Ce(HL)(L)-
2 0.5 11 39 2 4 2 2
symmetry codes for 2: A: x, –y, z + 1/2; B: –x + 1, y – 1, –z + 3/
2
(
H O) {Ce(H L) (α-PW O H)Ce(H O) }] ·12H O and
2 6 2 0.5 11 39 2 4 2 2
; C: –x + 1/2, –y + 1/2, –z + 2; D: –x + 1/2, –y + 1/2, –z + 1.
[
Pr(HL)(L)(H O) {Pr(H L) (α-PW O H)Pr(H O) }] ·
2 6 2 0.5 11 39 2 4 2
8
H O (H L = 2,5-pyridinedicarboxylic acid) were 60, 56
2 2
[
14d]
and 45%, respectively.
These results indicate that the
(
α/S) data were calculated from the reflectance by using the
doped CPs 1a and 2a are superior photocatalysts than the
undoped CPs 1 and 2 and that all four CPs are comparable
or better than previously reported photocatalysts, for which
comparison is possible. Moreover, 2a could be recovered
[13]
Kubelka–Munk (K–M) function:
(
1 – R)2
α/S =
2
R
α is the absorption, S is the scattering coefficient, and R is from the catalytic system by centrifugation and reused for a
the reflectance at a given energy. The band gap energies fresh photodegradation. This catalyst showed no significant
(
Eonset) obtained by extrapolation of the linear portion of decrease in efficiency even after five cycles (Figure S10).
the absorption edges were estimated to be 2.25 (1), 1.38 (2), The PXRD patterns of the recycled catalyst were almost
1
.80V (1a) and 1.77 eV (2a), which are in the semiconductor identical to those of the freshly made material; therefore,
range (Figure 2).
its original structural framework was retained during the
photocatalytic degradation process (Figure S11). After the
Figure 2. K–M functions versus energy [eV] for 1, 2, 1a and 2a.
The photocatalytic activities of the undoped CPs 1 and
Figure 3. Photocatalytic degradation rate of RhB as a function of
irradiation time in the presence of catalysts 1 (green), 2 (blue), 1a
2
and the doped CPs 1a and 2a were evaluated by measur-
(
yellow) and 2a (pink). A control experiment without any catalyst
ing the degradation of RhB in aqueous solution by absorp- (black) was run under the same conditions.
Eur. J. Inorg. Chem. 2015, 1981–1988
1984
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Table 2. Comparison of the efficiency of the catalytic photodegradation of RhB with different catalysts.
Catalyst
Reaction time [h] Photocatalytic efficiency [%]
Ref.
1
2
4
3
2.5
2
2
2.5
9
9
9
4
4
95
97
94
90
92
99
94
95
90
60
56
45
this work
this work
this work
this work
1
2
a
a
[
14a]
Fe
Ag/Pt@TiO
3-H pya)[(3-Hpya)
HNa [(3-pya)(3-Hpya)Ag]
(3-Hpya) Ag][(H O) Ag]
{La(H
{Ce(H
3
O
4
@SiO
2
@TiO
2
2
/GO
[
14b]
[
[
[
14c]
14c]
14c]
(
2
2
Ag][AgAlMo
[AlMo
[AlMo
6
H
6
O
24]·3H
24]·8H
24]·2H
2
O (pyrolysis)
2
2
6
H
6
O
2
O (pyrolysis)
O (pyrolysis)
[
[
[
[
2
2
2
2
6
H
6
O
2
[
[
[
14d]
14d]
14d]
La(HL)(L)(H
Ce(HL)(L)(H
2
O)
O)
6
2
L)0.5(α-PW11
L)0.5(α-PW11
L)0.5(α-PW11
O
39 H)La(H
39 H)Ce(H
O)
2
O)
O)
}]
4
}]
}]
·8H
2
·8H
2
O
2
6
2
O
O
2
4
2
·12H
2
O
O
Pr(HL)(L)(H
2
O)
6
{Pr(H
2
39 H)Pr(H
2
4
2
2
4
+
photodegradation of RhB, the final solution was filtered same number of holes (h ) are formed in the VB. Then, O
2
–
and extracted with diethyl ether, and the organic phase was or OH adsorbed on the surfaces of the complexes interact
analyzed by LC–MS. No other organic species were ob- with the electrons (e ) of the CB or holes (h ) in the VB,
–
+
served; thus, we assumed that the RhB was converted into respectively, to form hydroxy radicals (·OH). The hydroxy
[
15]
CO and H O.
radicals are highly active and decompose the organic pol-
2
2
To exclude the possibility that soluble metal ions assisted lutants into CO and H O (Scheme S1a). The doped cata-
2
2
the RhB degradation, two control experiments were con- lysts possess a narrower band gap (E ) than the undoped
g
ducted (Figures 4 and S12). In the first, RhB solution was catalysts, which may accelerate this photocatalytic activity
stirred with the catalysts overnight. In the second, the RhB (Scheme S1b).
–
4
solution was readjusted to 3ϫ10 m by the addition of
RhB into the centrifuged solutions after the photocatalytic
degradation. As indicated in Figure 4, the degradation of Conclusions
RhB in the two control experiments was almost identical to
We have demonstrated the formation of the isostructural
coordination polymers 1 and 2 from the reactions of
the rate of the catalyst-free reaction. However, Zn(NO )
3
2
–
4
and Co(NO ) (1ϫ10 m) could gradually degrade RhB
3
2
Zn(NO ) or Co(NO ) with tipm and 1,3-H BDC under
3
2
3 2
2
(ca. 75% after 4 h, Figure S13) under similar conditions.
solvothermal conditions. These coordination polymers have
unique 3D framework with Schläfli symbol
These results indicated that there were no soluble metal ions
in the degradation system and that the catalysts did not
decompose or leach ions during this reaction.
a
(
(
a
2
2
3
2
3
4·7 )(6 ·7 ·12)(4·6 ·7 ). Under the irradiation of UV light
365 nm), compounds 1 and 2 exhibit good catalytic activity
in the photodegradation of RhB. The partial isomorphic
substitution of Zn by Co ions is described, and the resulting
doped CPs 1a and 2a have higher photocatalytic activities
than the undoped catalysts 1 and 2. As a representative ex-
ample, 2a can be recycled and reused at least five times
without the loss of catalytic photodegradation performance.
These results further demonstrate the importance of metal
doping to the tuning of the properties of materials.
Experimental Section
General Methods: Chemicals and reagents were obtained from com-
mercial sources and used as received. Tetrakis(4-bromophenyl)
methane was prepared from tetraphenylmethane by a literature
Figure 4. Degradation of RhB as a function of irradiation time by
method.[ Infrared spectra (KBr disk, 400–4000 cm ) were ob-
tained with a Nicolet iS10 spectrometer. Elemental analyses for C,
H and N were performed with a Carlo–Erba CHNO-S microana-
lyzer. Thermogravimetric analysis (TGA) was performed with a TA
SDT-2960 analyzer (heating rate of 10 °C/min). The PXRD mea-
surements were performed with a PANalytical X’Pert PRO MPD
system (PW3040/60). The solid-state UV/Vis spectra were recorded
with a Shimadzu UV-3150 spectrometer at room temperature in the
range λ = 200–800 nm. The UV/Vis absorption spectra of RhB
10]
–1
1
under UV light. Black: the RhB solution without catalyst; red:
the RhB solution with the catalyst; blue: the filtrate after the RhB
solution was stirred with the catalyst overnight; pink: the RhB solu-
tion that was readjusted to 3ϫ10–4 m by the addition of RhB into
the centrifuged solution after the photocatalytic degradation.
The mechanism for the photocatalytic degradation of or-
ganic molecules by metal catalysts in aqueous solution was
[
4a,4b]
–
reported
to involve the following steps: electrons (e )
of the metal complexes are excited from the valence band aqueous solutions were recorded with a Varian Cary-50 UV/Vis
VB) to the conduction band (CB), and simultaneously, the spectrophotometer.
(
Eur. J. Inorg. Chem. 2015, 1981–1988
1985
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

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FULL PAPER
Tetrakis[4-(1-imidazolyl)phenyl]methane (tipm): A mixture of tet-
rakis(4-bromophenyl)methane (0.636 g, 1 mmol), imidazole
0.68 g, 10 mmol), K CO (0.828 g, 6 mmol) and CuI (0.076 g,
.4 mmol) was finely ground and then heated under microwave ir-
Compound 2a·H
2
O was separated as red block crystals by the same
procedure with Zn(NO
6H O (0.030 g, 0.10 mmol), tipm (0.029 g, 0.05 mmol) and 1,3-
BDC (0.016 g, 0.10 mmol), yield 0.021 g (40% based on tipm).
3 2 2 3 2
) ·6H O (0.015 g, 0.05 mmol), Co(NO ) ·
(
0
2
3
2
H
2
radiation (720 W) for 90 s (Scheme 1). The resultant mixture was
poured into water (10 mL), ethylenediaminetetraacetic acid
The formulas were determined by atomic absorption spectros-
copy (AAS) and elemental analyses. Compound 1a:
(EDTA; 0.117 g, 0.4 mmol) and NH
3
·H
2
O (25–28%, 0.5 mL) were
53 36 8 8
C H N O Zn1.95Co0.05 (1043.33): calcd. C 61.01, H 3.48, N
added, and the mixture was stirred for 5 h. The solid product was
collected by filtration, washed with water and then purified by
recrystallization from MeOH/H O (1:4 v/v) to afford yellow crys-
2
tals, which were dried under vacuum to afford tpim as a light yel-
low powder, yield 0.528 g [90%, based on tetrakis(4-bromophenyl)
10.74; found C 60.32, H 3.65, N 10.01. IR (KBr disk): ν˜ = 3432
(m), 3136 (m), 1612 (s), 1561 (m), 1522 (s), 1367 (s), 1312 (m), 1270
(w), 1126(w), 1068 (s), 966 (m), 827 (m), 750 (s), 728 (m), 655 (m),
–
1
2 53 8 9
561 (w) cm . Compound 2a·H O: C H38Co0.46N O Zn1.54
(1058.69): calcd. C 60.12, H 3.62, N 10.58; found C 59.78, H 3.92,
N 10.29. IR (KBr disk): ν˜ = 3431 (m), 3136 (m), 1612 (s), 1563
(m), 1522 (s), 1368 (s), 1312 (m), 1270 (w), 1125 (m), 1068 (s), 966
methane]. C37
28 8
H N (584.69): calcd. C 76.01, H 4.83, N 19.17;
found C 75.96, H 4.82, N 19.22. IR (KBr disk): ν˜ = 3410 (m), 3111
–
1
(
(
m), 1606 (m), 1517 (s), 1423 (w), 1305 (s), 1245 (w), 1192 (w), 1108 (m), 828(m), 750 (s), 728 (m), 652 (m), 561 (w) cm .
–
1 1
m), 1057 (s), 963 (m), 818 (s), 737 (m), 658 (m), 559 (m) cm . H
, 298 K, TMS): δ = 7.87 (s, 4 H, imidazole
ring), 7.38 (s, 16 H, benzene ring), 7.29 (s, 4 H, imidazole ring),
Crystallographic Data Collection and Refinement: Single crystals of
, 2·0.5CH CN, 1a and 2a·H O suitable for X-ray analysis were
obtained directly from the above preparations. With an enhanced
X-ray source (Mo-K , λ = 0.71073 Å), the data for 1 and 1a were
NMR (300 MHz, CDCl
3
1
3
2
13
7
(
1
.21 (s, 4 H, imidazole ring) ppm (Figure S1). C NMR
75.4 MHz, CDCl , 298 K): δ = 144.7, 135.8, 135.4, 132.1, 130.7,
20.8, 117.9, 63.7 ppm (Figure S2). HRMS (EI): calcd. for
α
3
recorded with a Rigaku Saturn 724 CCD diffractometer, the data
for 2 were recorded with a Bruker D8 QUEST diffractometer, and
the data for 2a were recorded with an Aglient Gemini Atlas dif-
fractometer. Each single crystal was mounted on a glass fibre at
+
37 28 8
C H N [M] 584.2437; found 584.2442 (error: 0.86 ppm).
293 K. The cell parameters were refined with the programs Crys-
talClear (version 1.3, Rigaku Inc.), Bruker-SAINT and CrysAlis-
Pro (version 1.171.36.32, Agilent Technologies), respectively, and
absorption corrections (multiscan) were applied. The reflection
data were also corrected for Lorentz and polarization effects.
The crystal structures were solved by direct methods and refined
2
on F by full-matrix least-squares methods with the SHELXL-2013
program.[ A large amount of spatially delocalized electron den-
sity in the lattice of each compound was found, but acceptable
refinement results could not be obtained for this electron density.
Thus, the water solvent contribution to the scattering factors has
been taken into account with SQUEEZE in the Platon program
suite. All non-hydrogen atoms were refined anisotropically.
16]
Scheme 1. Synthesis of the tipm ligand.
[
Zn
2
(tipm)(1,3-BDC)
.10 mmol), tipm (0.029 g, 0.05 mmol) and 1,3-H
.10 mmol) in CH CN (0.5 mL) and H O (2.0 mL) was sealed in a and constrained to ride on their parent atoms. Selected bond
2 3 2 2
] (1): A mixture of Zn(NO ) ·6H O (0.030 g,
0
0
2
BDC (0.016 g, Hydrogen atoms were placed in geometrically idealized positions
3
2
glass tube and then heated at 150 °C for 24 h. The solution was
cooled to room temperature at the rate of 5 °C/h to produce yellow
block crystals of 1, which were collected by filtration, washed with
water and EtOH, and dried in air, yield 0.032 g (62% based on
lengths and bond angles for 1 and 2 are listed in Table 1. A sum-
mary of key crystallographic data for 1, 2, 1a and 2a is given in
Table 3.
CCDC-1033791 (for 1), -1033792 (for 2·0.5CH
3
CN), -1041854 (for
tipm). C53
36 8 8 2
H N O Zn (1043.64): calcd. C 60.99, H 3.48, N 10.74;
1
a) and -1041844 (for 2a·H O) contain the supplementary crystal-
2
found C 60.12, H 3.59, N 10.12. IR (KBr disk): ν˜ = 3454 (m), 3136
lographic data for this paper. These data can be obtained free of
charge from the Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/datarequest/cif.
(
(
m), 1614 (s), 1563 (m), 1524 (s), 1374 (s), 1313 (m), 1126 (w), 1068
–
1
s), 966 (m), 828 (m), 753 (s), 728 (m), 655 (m), 561 (w) cm .
(tipm)(1,3-BDC) ]·0.5CH CN (2·0.5CH CN): Compound
·0.5CH CN was separated as blue block crystals by a similar
[Co
2
2
3
3
Photocatalytic Activity Study: The photocatalytic activities of the
solid samples 1, 2, 1a and 2a were evaluated for the model degrada-
tion of RhB in aqueous solution. An aqueous solution (50 mL) of
2
3
method to that described above for the preparation of 1 with
Co(NO ·6H O (0.030 g, 0.1 mmol), tipm (0.029 g, 0.05 mmol)
and 1,3-H BDC (0.016 g, 0.10 mmol), yield 0.028 g (54% based on
tipm). C54 (1051.28): calcd. C 61.69, H 3.60, N
1.32; found C 61.01, H 3.79, N 10.97. IR (KBr disk): ν˜ = 3445
3
)
2
2
–
1
–4
RhB with a concentration of 0.14 gL (ca. 3ϫ10 m) was mixed
with the catalyst (10 mg), magnetically stirred in the dark for 2 h
to ensure the equilibrium of adsorption/desorption and then irradi-
ated with a 400W (365 nm) high-pressure mercury lamp. The mix-
ture was stirred continuously with a magnetic stirrer. At regular
time intervals, a 1 mL sample was collected, filtered and diluted to
2
H
2 8.5 8
37.5Co N O
1
(
(
(
m), 3137 (w), 2210 (w), 1608 (s), 1557 (m), 1520 (s), 1372 (s), 1311
m), 1269 (w), 1124 (s), 1145 (w), 1067 (s), 965 (w), 825 (m), 751
–1
m), 725 (m), 655 (m), 560 (w) cm .
]·bH O (x = 2.4%, b = 0 for 1a, x =
O): Compound 1a was separated as orange
10 mL in a volumetric flask. The UV/Vis absorption maxima of
[Zn(2–2x)Co2x(tipm)(1,3-BDC)
2
2
RhB at 554 nm was chosen to monitor the photocatalytic degrada-
tion process.
2
3%, b = 1 for 2a·H
2
block crystals by a similar method to that described for the prepa-
ration of 1 with Zn(NO ·6H O (0.030 g, 0.10 mmol), Co(NO
3
)
2
2
3
)
2
·
Supporting Information (see footnote on the first page of this arti-
1
13
6H
2
O (0.030 g, 0.10 mmol), tipm (0.029 g, 0.05 mmol) and 1,3- cle): H and C NMR spectra of tipm, PXRD patterns, TGA plots
H
2
BDC (0.016 g, 0.10 mmol), yield 0.028 g (55% based on tipm). and photocatalytic spectra of 1, 2, 1a and 2a.
Eur. J. Inorg. Chem. 2015, 1981–1988
1986
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Table 3. Summary of crystal data and structure refinement parameters for 1, 2, 1a and 2a.
1
2·0.5CH
3
CN
1a
2
2a·H O
Chemical formula
Fw
C
53
H
36
N
8
O
8
Zn
2
C
54
H
37.5
N
8.5
O
8
Co
2
C
53
H
36
N
8
O
8
Co0.05Zn1.95
53 38 8 9
C H N O Zn1.54Co0.46
1058.69
1043.64
1051.28
1043.33
Crystal system
Space group
monoclinic
C2/c
monoclinic
C2/c
monoclinic
C2/c
monoclinic
C2/c
Crystal size /mm
0.30ϫ0.30ϫ0.20
41.021(8)
14.365(3)
20.259(4)
108.59(3)
11315(4)
8
0.25ϫ0.20ϫ0.10
40.575(5)
14.3747(16)
20.156(3)
108.058(3)
11177(2)
8
0.40ϫ0.40ϫ0.30
40.999(8)
14.353(3)
20.257(4)
108.79(3)
11285(4)
8
0.40ϫ0.30ϫ0.30
40.6544(13)
14.3377(5)
20.2429(5)
108.733(3)
11174.3(6)
8
a /Å
b /Å
c /Å
β /°
V /Å3
Z
D
calcd. /gcm–3
1.225
1.249
1.228
1.259
F(000)
μ (Mo-K
4272
0.903
4312
0.651
4271
0.899
4341
0.856
) /mm–1
α
Total reflections
44732
9936
7046
640
120694
10269
8865
31068
12821
6960
640
40156
14693
8599
662
Unique reflections
Observed reflections [IϾ2σ(I)]
Parameters
668
R
R
int
a]
0.0726
0.0628
0.1561
1.065
0.0172
0.0561
0.1705
1.031
0.1107
0.0800
0.2134
0.993
0.0771
0.0619
0.1969
1.010
[
[
b]
wR
GOF
Residual peaks /eÅ–3
[
c]
0.807, –0.309
2.073, –0.510
0.766, –0.308
1.554, –0.914
o o c o o c
a] R = Σ||F | – |F ||/Σ|F –F
|. [b] wR = [Σw(F 2 2)2/Σw(F 2)2]1/2. [c] GOF = {Σw[(F 2–F 2)2]/(n – p)}1/2, n = number of reflections, and p =
[
o
c
total number of parameters refined.
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The authors thank the National Natural Science Foundation of
China (NSFC) (grant numbers 21171124, 21271134 and 21373142)
and the State Key Laboratory of Organometallic Chemistry of
Shanghai Institute of Organic Chemistry (grant number
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Received: January 22, 2015
Published Online: March 9, 2015
Eur. J. Inorg. Chem. 2015, 1981–1988
1988
© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim