Polycarboxylate-directed various Co(II) complexes based on a "v"-like bis-pyridyl-bis-amide derivative: Construction, electrochemical and photocatalytic properties

Article abstract of DOI:10.1039/c5ce01239b

A series of new Co(ii) complexes based on a new semi-rigid "V"-like bis-pyridyl-bis-amide derivative, namely, [Co(3-bpha)₂(2,3-HPDC)₂] (1), [Co(3-bpha)(3-NPH)(H₂O)₂]·2H₂O (2), [Co(3-bpha)(1,3-BDC)]·4H₂O (3), [Co(3-bpha)(HIP)]·3H₂O (4), [Co(3-bpha)(MIP)(H₂O)]·H₂O (5), and [Co₃(3-bpha)₂(1,3,5-BTC)₂(H₂O)₄]·2H₂O (6) (3-bpha = N,N′-bis(pyridin-3-yl)-5-hydroxybenzene-1,3-dicarboxamide, 2,3-H₂PDC = 2,3-pyridinedicarboxylic acid, 3-H₂NPH = 3-nitrophthalic acid, 1,3-H₂BDC = 1,3-benzenedicarboxylic acid, H₂HIP = 5-hydroxyisophthalic acid, H₂MIP = 5-methylisophthalic acid, 1,3,5-H₃BTC = 1,3,5-benzenetricarboxylic acid), have been hydrothermally synthesized by tuning aromatic polycarboxylate co-ligands and characterized by single-crystal X-ray diffraction, IR spectra, powder XRD and TG analysis. Complex 1 is a discrete zero-dimensional (0D) structure in which the 3-bpha ligands and the 2,3-HPDC anions act as the terminal groups simultaneously to coordinate with the Co^II ions. Complex 2 is a 1D meso-helical chain in which the 3-bpha ligands show a μ₂-bridging mode and the 3-NPH anions act as the terminal groups. In complexes 3 and 4, pairs of 3-bpha ligands integrate with two Co^II ions to generate 28-membered Co₂(3-bpha)₂ rings, which connect with the 1D [Co-1,3-BDC]_n or [Co-HIP]_n chains to create the 2D networks. In complex 5, the Co^II ions are linked to 3-bpha ligands, resulting in a single-strand [Co-3-bpha]_n helix chain, which is further connected to the MIP anions to form a 2D network. Complex 6 shows a 3D framework with (3,3,4)-connected (8³)₄(8⁴·10²) topology, which contains [Co-(1,3,5-BTC)]_n 2D grid-like sheets and 1D [Co-3-bpha]_n helical chains. Finally, the 0D discrete architecture in 1, 1D chain in 2, and 2D networks in 4 and 5 are extended to 3D supramolecular frameworks through hydrogen-bonding interactions. The effect of polycarboxylate auxiliary ligands with different substitute groups and different carboxyl positions and number on the assembly and structures of the target complexes were discussed. Moreover, the thermal stabilities, electrochemical properties and photocatalytic activities of complexes 1-6 were investigated.

Full text of DOI:10.1039/c5ce01239b

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Polycarboxylate-directed various CoIJII) complexes
based on a “V”-like bis-pyridyl-bis-amide
derivative: construction, electrochemical and
photocatalytic properties†
Cite this: DOI: 10.1039/c5ce01239b
Xiu-Li Wang,* Xiao-Ting Sha, Guo-Cheng Liu, Nai-Li Chen and Yuan Tian
A series of new CoIJII) complexes based on a new semi-rigid “V”-like bis-pyridyl-bis-amide derivative,
namely, ijCoIJ3-bpha)
2
IJ2,3-HPDC)
3), ijCoIJ3-bpha)IJHIP)]·3H O (4), ijCoIJ3-bpha)IJMIP)IJH
2H O (6) (3-bpha = N,N′-bisIJpyridin-3-yl)-5-hydroxybenzene-1,3-dicarboxamide, 2,3-H
NPH = 3-nitrophthalic acid, 1,3-H BDC = 1,3-benzenedicarboxylic acid,
HIP = 5-hydroxyisophthalic acid, H MIP = 5-methylisophthalic acid, 1,3,5-H BTC = 1,3,5-benzenetri-
2
] (1), ijCoIJ3-bpha)IJ3-NPH)IJH
2
O)
2
]·2H
2
O (2), ijCoIJ3-bpha)IJ1,3-BDC)]·4H
IJ3-bpha) IJ1,3,5-BTC) IJH O)
PDC = 2,3-
2
O
(
2
2
O)]·H O (5), and ijCo
2
3
2
2
2
4
]
·
2
2
pyridinedicarboxylic acid, 3-H
2
2
H
2
2
3
carboxylic acid), have been hydrothermally synthesized by tuning aromatic polycarboxylate co-ligands and
characterized by single-crystal X-ray diffraction, IR spectra, powder XRD and TG analysis. Complex 1 is a
discrete zero-dimensional (0D) structure in which the 3-bpha ligands and the 2,3-HPDC anions act as the
II
terminal groups simultaneously to coordinate with the Co ions. Complex 2 is a 1D meso-helical chain in
which the 3-bpha ligands show a μ
2
-bridging mode and the 3-NPH anions act as the terminal groups. In
II
complexes 3 and 4, pairs of 3-bpha ligands integrate with two Co ions to generate 28-membered Co
2
IJ3-
chains to create the 2D networks. In
complex 5, the Co ions are linked to 3-bpha ligands, resulting in a single-strand ijCo-3-bpha] helix chain,
which is further connected to the MIP anions to form a 2D network. Complex 6 shows a 3D framework
2 n n
bpha) rings, which connect with the 1D ijCo-1,3-BDC] or [Co-HIP]
II
n
3
4
2
4 n
with (3,3,4)-connected IJ8 ) IJ8 ·10 ) topology, which contains ijCo-IJ1,3,5-BTC)] 2D grid-like sheets and 1D
Received 26th June 2015,
Accepted 12th August 2015
ijCo-3-bpha]n helical chains. Finally, the 0D discrete architecture in 1, 1D chain in 2, and 2D networks in 4
and 5 are extended to 3D supramolecular frameworks through hydrogen-bonding interactions. The effect
of polycarboxylate auxiliary ligands with different substitute groups and different carboxyl positions and
number on the assembly and structures of the target complexes were discussed. Moreover, the thermal
stabilities, electrochemical properties and photocatalytic activities of complexes 1–6 were investigated.
DOI: 10.1039/c5ce01239b
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ions, the reaction time, temperature, pH, solvent system and
so on. Among these factors, the organic ligands as the struc-
Introduction
2
The rational design and construction of novel metal–organic
coordination polymers (MOCPs) is currently attracting consid-
erable attention not only because of their fascinating topolog-
ical structures but also their potential applications in the
fields of catalysis, luminescence, gas adsorption, nonlinear
optics and magnetic materials. It is well known that several
factors have effects on the formation of the final structures,
such as organic ligands, geometric requirement of the metal
ture connectors play the most important role in the whole
framework of MOCPs. Therefore, significant interest has
3
arisen in the structural tuning of coordination polymers
through the rational design and selection of organic ligands
containing an N/O donor. Among various N/O donor ligands,
bis-pyridyl-bis-amide ligands and their derivatives, a type of
excellent organic ligands with the unique potential to provide
two types of hydrogen-bonding sites, the –NH moieties acting
as electron acceptors and the –CO groups acting as electron
1
4
donors, are now receiving extensive attention.
Department of Chemistry, Bohai University, Liaoning Province Silicon Materials
Engineering Technology Research Centre, Jinzhou, 121000, PR China.
E-mail: wangxiuli@bhu.edu.cn; Fax: +86 416 3400158; Tel: +86 416 3400158
On the other hand, organic polycarboxylates as
multidentate O-donor ligands are excellent building blocks
with versatile coordination modes for constructing metal–
organic frameworks with interesting structures and proper-
†
Electronic supplementary information (ESI) available: IR, TG, PXRD and
additional figures. CCDC 1404928–1404933. For ESI and crystallographic data in
5
CIF or other electronic format see DOI: 10.1039/c5ce01239b
ties. Therefore, the combination of pyridyl-amide-based
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ligands and polycarboxylate ligands can be regarded as an
effective strategy to prepare attractive metal–organic coordi-
nation frameworks with different dimensionalities, which
and 40 mA with Cu-Kα (λ = 1.5406 Å) radiation. Electro-
chemical measurements were carried out on a CHI 440
electrochemical workstation. A conventional three-electrode
system was used at room temperature. The title complexes'
chemically bulk-modified carbon paste electrodes (CPEs)
were used as the working electrodes. A saturated calomel
electrode (SCE) and a platinum wire were used as the refer-
ence and auxiliary electrodes, respectively. UV-vis absorption
spectra were obtained using an SP-1901 UV-vis
spectrophotometer.
6
attracted great interest from researchers. We also devoted
our efforts to the synthesis of carboxylate-assisted pyridyl-
acylamide-based coordination polymers with diverse struc-
7
tures and functions. However, reports on the combination of
semi-rigid bis-pyridyl-bis-amide derivatives and organic poly-
carboxylates with different substitute groups and carboxyl
8
groups are still limited. Thus, in this work we designed a
semi-rigid “V”-shaped N,N′-bisIJpyridin-3-yl)-5-hydroxybenzene-
1
,3-dicarboxamide (3-bpha) as the main ligand to construct
Preparation of complexes 1–6
target complexes, which has not been used in the construc-
tion of complexes according to the CCDC database. In order
to explore the effect of substitute groups as well as the car-
boxyl position and number of polycarboxylates on the struc-
tures of target complexes, six types of aromatic poly-
carboxylates, namely, 2,3-pyridinedicarboxylic acid IJ2,3-
H PDC), 3-nitrophthalic acid IJ3-H NPH), 1,3-benzenedi-
Synthesis of ijCoIJ3-bpha) IJ2,3-HPDC) ] (1).
A
mixture
2
2
containing CoCl ·6H O (0.048 g, 0.2 mmol), 3-bpha (0.033 g,
2 2
0.10 mmol), 2,3-H PDC (0.034 g, 0.20 mmol), NaOH (0.016 g,
2
0.40 mmol) and H O (12 mL) was placed in a 25 mL Teflon-
2
lined autoclave and heated to 120 °C for 4 days under autoge-
nous pressure. Then it was allowed to cool to room tempera-
ture, and yellow block crystals of 1 suitable for X-ray diffrac-
tion were isolated in about 16% yield (based on Co). IR (KBr,
2
2
carboxylic acid IJ1,3-H
2
BDC), 5-hydroxyisophthalic acid
(
2 2
H HIP), 5-methylisophthalic acid (H MIP) and 1,3,5-
−
1
benzenetricarboxylic acid IJ1,3,5-H BTC) were selected as the
cm ): 3275w, 3140w, 3076w, 2358w, 1656s, 1583s, 1543s,
1425s, 1354s, 1278m, 1230s, 1101s, 1056w, 981m, 885s, 810s,
746m, 719s, 667s, 599m, 561m, 516m.
3
co-ligands to combine with the “V”-shaped pyridyl-formam-
ide derivative 3-bpha for constructing the target complexes.
The different groups and carboxyl groups for these ligands
may be favorable to generating novel architectures.
Synthesis of ijCoIJ3-bpha)IJ3-NPH)IJH O) ]·2H O (2). Complex
2 was prepared in the same way as 1 except that 3-H NPH
(0.042 g, 0.20 mmol) was used instead of 2,3-H PDC. Pink
2
2
2
2
2
II
The Co ions are the most commonly reported metals and
show excellent electrochemical properties when coordinated
to multidentate ligands. In addition, photocatalysts have
crystals of 2 suitable for X-ray diffraction were isolated in
about 40% yield (based on Co). IR (KBr, cm ): 3344w, 2362w,
9
−1
attracted much attention because of their potential applica-
tions in purifying waste water by thoroughly decomposing
organic pollutants. Some transition metal complexes have
been proved to be efficient photocatalysts on the degradation
1668m, 1589s, 1552s, 1489m, 1463m, 1428s, 1396s, 1342s,
1282w, 1222m, 1134w, 1055m, 1001m, 927m, 893m, 815s,
700s, 642m.
2
Synthesis of ijCoIJ3-bpha)IJ1,3-BDC)]·4H O (3). The synthetic
7
a,10
II
of organic dyes.
However, reports on Co -based CP
procedure for 3 was the same as for 1 except that 1,3-H BDC
2
photocatalysts are still very limited.
(0.033 g, 0.20 mmol) was used instead of 2,3-H PDC. Purple
2
II
Herein six new Co complexes, namely, ijCoIJ3-bpha)
2
IJ2,3-
crystals of 3 were obtained in a yield of about 20% based on
−
1
HPDC) ] (1), ijCoIJ3-bpha)IJ3-NPH)IJH O) ]·2H O (2), ijCoIJ3-bpha)-
Co. IR (KBr, cm ): 3429w, 3282w, 3066w, 2360w, 1654m,
1618s, 1550s, 1485s, 1392s, 1334m, 1292s, 1219s, 1112w,
1055w, 999w, 920w, 815m, 752s, 721m, 669w, 601w.
2
2
2
2
IJ1,3-BDC)]·4H
2
O (3), ijCoIJ3-bpha)IJHIP)]·3H
2
O (4), ijCoIJ3-bpha)-
4
IJH O) ]
IJMIP)IJH
2
O)]·H
2
O (5), and ijCo IJ3-bpha) IJ1,3,5-BTC)
3
2
2
2
·
2H O (6), were obtained under hydrothermal conditions. The
Synthesis of ijCoIJ3-bpha)IJHIP)]·3H O (4). Synthesis of 4
2
2
effect of polycarboxylate auxiliary ligands on the assembly
was similar to that of 1 except that H HIP (0.036 g, 0.20
2
and structures of the title complexes is discussed. In addi-
tion, the photocatalytic activities and electrochemical proper-
ties of complexes 1–6 were investigated.
mmol) was used instead of 2,3-H
2
PDC. Purple block crystals
of 4 were obtained in a 32% yield based on Co. IR (KBr,
−
1
cm ): 3344w, 3072w, 2362w, 1660s, 1577s, 1537s, 1421s,
1
7
344m, 1276m, 1240m, 1109m, 1053w, 981m, 883s, 786s,
31s, 698s, 646w, 594w.
Experimental section
Materials and methods
Synthesis of ijCoIJ3-bpha)IJMIP)IJH O)]·H O (5). The syn-
2
2
thetic procedure for 5 was similar to that of 1 except that
Materials and characterization. All chemicals were of
H MIP (0.036 g, 0.20 mmol) was used instead of 2,3-H PDC.
2
2
reagent grade and used without further purification. Ligand
Light pink crystals of 5 suitable for X-ray diffraction were iso-
lated in about 35% yield (based on Co). IR (KBr, cm ):
1
1
−1
3
-bpha was synthesized according to the literature method.
FT-IR spectra (KBr pellets) were taken on a Varian-640
spectrometer. Thermogravimetric analyses (TGAs) were
recorded on a Pyris Diamond TG instrument. Powder X-ray
diffraction (PXRD) investigations were carried out with an
Ultima IV diffractometer with a D/teX Ultra system at 40 kV
3421w, 2362w, 1676w, 1610m, 1544s, 1483s, 1427s, 1375s,
1338s, 1288m, 1232m, 1112w, 1053w, 999w, 810s, 775s, 702s,
597w.
Synthesis of ijCo IJ3-bpha) IJ1,3,5-BTC) IJH O) ]·2H O (6).
3
2
2
2
4
2
The preparation of complex 6 was the same as for 1, except
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that 1,3,5-H BTC (0.042 g, 0.2 mmol) was used instead of 2,3-
specific atoms and refined isotropically with fixed thermal
factors. O4W of complex 2 was restricted by the ‘isor’ com-
mand, and the distances between H3WB and H8A in complex
4 and N3 and H3B in complex 6 were restricted by the ‘dfix’
command. In addition, the unit cell of complex 6 includes a
large region of disordered solvent water molecules, which
could not be modeled as discrete atomic sites. Thus, the
SQUEEZE program was used to further estimate the num-
ber of solvent water molecules in the crystal structure. When
the electron density and TGA were taken into account, two
water molecules were determined. The crystal data and struc-
ture refinement results for complexes 1–6 are summarized in
Table 1. Selected bond distances and bond angles are listed
in Tables S1–S6.† Crystallographic data for the structures
reported in this paper have been deposited at the Cambridge
Crystallographic Data Center with CCDC numbers 1404928–
3
H PDC and a different amount of NaOH (0.024 g, 0.60
2
mmol). Purple crystals of 6 were obtained in a yield of about
−
1
2
1
7
2% based on Co. IR (KBr, cm ): 3246w, 2360w, 1670m,
633s, 1583s, 1427s, 1371s, 1280m, 1236w, 1101w, 885w,
96m, 732s, 700m, 669w, 536w.
1
4
Preparation of complexes 1–6 bulk-modified CPEs
Complex 1 bulk-modified carbon paste electrode (1-CPE) was
fabricated as follows: 0.10 g of graphite powder and 0.010 g
of complex 1 were mixed and ground together with an agate
mortar and pestle to achieve an even mixture, and then 0.05
mL of Nujol was added with stirring. The homogenized mix-
ture was packed into a glass tube with 3 mm inner diameter
to a length of 8 mm, and the tube surface was wiped with
weighing paper. Electrical contact was established with a cop-
1404933.
1
2
per wire. The same procedure was used for the preparation
of bare CPE and 2–6-CPEs.
Results and discussion
X-ray crystallography
Description of crystal structures
Diffraction data for complexes 1–6 were collected on a Bruker
SMART APEX II diffractometer equipped with a CCD area
2 2
ijCoIJ3-bpha) IJ2,3-HPDC) ] (1). Single-crystal X-ray diffrac-
detector and graphite monochromated Mo-K
α
radiation (λ =
tion analysis reveals that complex 1 crystallizes in the triclinic
space group P ¯1 . The crystal structure of complex 1 contains a
0
.71073 A°) by using the φ–ω scan technique at 296(2) K. The
II
structures were solved by direct methods using the program
Co cation, two 3-bpha ligands and two 2,3-HPDC anions. As
2
II
SHELXS and refined anisotropically on F by the full matrix
shown in Fig. 1a, each Co ion with a {CoN
4 2
O } octahedral
least-squares technique using the SHELXL crystallographic
coordination geometry is six-coordinated by four pyridyl
nitrogen atoms from two 3-bpha ligands and two 2,3-HPDC
anions, respectively ijCoIJ1)–NIJ1) = CoIJ1)–NIJ1)#1 = 2.164(13) Å,
CoIJ1)–NIJ5) = CoIJ1)–NIJ5)#1 = 2.116(13) Å], and two oxygen
1
3
software package. For the title complexes, all non-hydrogen
atoms were refined anisotropically; the hydrogen atoms of
the organic ligands were generated theoretically onto the
Table 1 Crystallographic data for complexes 1–6
Complex
1
2
3
4
5
6
Formula
Formula wt
Crystal system
Space group
T (K)
a (Å)
b (Å)
c (Å)
α (°)
C
50
H
36CoN10O
14
C
26
H
25CoN
O
5 13
C
26
H
26CoN
O
4 11
C
26
H
24CoN
O
4 11
C
27
H
23CoN
4
O
9
C
54 3 8 24
H46Co N O
1059.82
Triclinic
P¯1
674.44
629.44
Triclinic
P¯1
627.42
Triclinic
P¯1
606.42
Monoclinic
P2IJ1)/c
1367.78
Orthorhombic
Pbcn
296(2)
12.6867(7)
27.5595IJ15)
15.8184(8)
90
90
90
5530.7(5)
4
1.643
Monoclinic
P2IJ1)/n
296(2)
7.2427(4)
25.0077IJ14)
15.4019(8)
90
99.4770IJ10)
90
2751.6(3)
4
296(2)
296(2)
296(2)
296(2)
8.6580(6)
10.2661(7)
13.9044(9)
76.2120IJ10)
72.9620IJ10)
72.0970IJ10)
1109.39IJ13)
1
10.0924(6)
11.0595(7)
13.9619(8)
66.8310IJ10)
83.4210IJ10)
71.2790IJ10)
1356.78IJ14)
2
10.0129IJ19)
10.724(2)
13.961(3)
73.385(3)
73.609(4)
64.888(3)
1278.2(4)
2
9.9555(6)
16.4810IJ10)
16.1393IJ10)
90
100.6730IJ10)
90
2602.3(3)
4
1.548
β (°)
γ (°)
V (Å )
3
Z
D
−3
calc (g cm
)
1.586
0.474
545
1.628
0.704
1388
1.541
0.702
650
1.630
0.745
646
−
1
μ (mm
FIJ000)
)
0.723
1248
0.985
2796
θmax (°)
28.30
28.01
28.36
28.31
24.95
25.00
R
R
wR
GOF
Δρmax (e Å
int
a
0.0114
0.0342
0.1007
1.000
0.566
−0.518
0.0314
0.0559
0.1631
1.000
2.312
−1.560
0.0205
0.0413
0.1084
1.000
0.513
−0.402
0.0313
0.0685
0.2136
1.000
2.681
−0.852
0.0315
0.0384
0.1046
1.000
0.439
−0.465
0.0765
0.0783
0.1676
1.001
0.741
−0.674
1
[I > 2σIJI)]
(all data)
b
2
−
3
)
−3
Δρmin (e Å
)
P
P
P
P
a
b
2
o
2 2
2 2 1/2
R
1
=
‖F
o
| − |F
c
‖/ |F
o
|
wR
2
=
ijwIJF
− F
c
) ]/ ijwIJF
o
) ]
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II
Fig. 1 (a) The coordination environment of the Co ion in complex 1
(
#1 −x + 1, −y + 1, −z). (b) 1D supramolecular chain of 1 extended by
hydrogen-bonding interactions. The hydrogen atoms are omitted for
clarity.
atoms of two carboxyl groups from two 2,3-HPDC anions ijCo-
IJ1)–OIJ1) = CoIJ1)–OIJ1)#1 = 2.088(11) Å].
In complex 1, both 3-bpha and 2,3-HPDC ligands show
one type of coordination mode. Two 3-bpha and two
II
Fig. 2 (a) Coordination environment of the Co ion in 2 (#1 x − 1/2, −y
1/2, z + 1/2). (b) The 1D meso-helical chain of 2. (c) The 2D supramo-
+
lecular network extended by hydrogen-bonding interactions. The
hydrogen atoms are omitted for clarity.
2
,3-HPDC ligands act as terminal groups coordinating with
II
2 2
Co ion to form a 0D complex ijCoIJ3-bpha) IJ2,3-HPDC) ].
These discrete complexes are connected together by the
hydrogen-bonding interactions between the oxygen atoms of
2
,3-HPDC anions and the nitrogen atoms of 3-bpha ligands
2.072(2) to 2.132(2) Å, forming a distorted octahedral geom-
ijOIJ4)–HIJ4A)⋯NIJ4), O⋯N = 2.596(1) Å] to form a 1D supramo-
lecular chain (Fig. 1b). The adjacent 1D chains are linked
together by the hydrogen-bonding interactions between the
nitrogen atoms of 3-bpha ligands and the oxygen atoms of
2 4 .
etry {CoN O }
In complex 2, each 3-bpha as a bidentate ligand with a μ -
bridging mode connects the adjacent Co ions to form a 1D
2
II
ijCo-3-bpha]
n
meso-helical chain, in which the Co⋯Co separa-
2
,3-HPDC anions ijNIJ2)–HIJ2B)⋯OIJ3), N⋯O = 2.864(2) Å] to
tion is 12.618 Å (Fig. 2b). In addition, two carboxyl groups of
0
1
construct a 2D supramolecular net (Fig. S1a†). The final 3D
supramolecular framework of complex 1 is generated also
through the hydrogen-bonding interactions between the car-
bon atoms of 2,3-HPDC anions and oxygen atoms from
1
each 3-NPH anion show a μ -η :η monodentate coordination
II
mode and coordinate with one Co ion as terminal groups.
The adjacent 1D chains are extended into a 2D supramolecu-
lar network by the hydrogen-bonding interactions between
the oxygen atoms from 3-bpha ligands and 3-NPH anions
ijOIJ8)–HIJ8B)⋯OIJ2), O⋯O = 2.692(1) Å] (Fig. 2c). The final 3D
supramolecular framework of complex 2 is formed also
through the hydrogen-bonding interactions between the oxy-
gen atoms from lattice water molecules and 3-bpha ligands,
respectively ijOIJ2W)–HIJ2WB)⋯OIJ3), O⋯O = 2.670(7) Å] (Fig.
S2†). In our previous studies, we have used 3-NPH anions as
the secondary ligand combining with flexible bis-pyridyl-bis-
amide ligands to construct complexes, such as ijCuIJ3-dpyh)IJ3-
3
-bpha ligands ijCIJ23)–HIJ23A)⋯OIJ6), C⋯O = 3.246(6) Å] (Fig.
S1b†). Generally speaking, semi-rigid bis-pyridyl-bis-amide
ligands and other polycarboxylate mixed ligands exhibit
bridging coordination modes, such as ijZnIJbppdca)IJBDC)]
8
b
15
·H O and ijCdIJMEDPQ)IJ2,3-PDC)] . , while in complex 1,
2
n
3
-bpha and 2,3-HPDC anions act as the terminal groups
simultaneously, which is rarely reported to the best of our
knowledge.
ijCoIJ3-bpha)IJ3-NPH)IJH
2
O)
2
]·2H
2
O
(2). X-ray diffraction
analysis reveals that complex 2 crystallizes in the mono-
clinic space group P2IJ1)/n. Complex 2 consists of one Co
NPH)IJH
2 2 2 2
O) ], ijNiIJ3-dpyh)IJ3-NPH)IJH O) ] and ijCoIJ3-dpyh)IJ3-
II
16
NPH)IJH O) ]. In those complexes, 3-NPH exhibits bridging
2
2
ion, one 3-bpha ligand, one 3-NPH anion, two coordinated
water molecules and two lattice water molecules. As shown
in Fig. 2a, each Co ion is six-coordinated by two pyridyl
coordination mode. In complex 2, 3-NPH anions act as the
terminal groups, which is different from the above
complexes.
II
nitrogen atoms from two individual 3-bpha ligands ijCoIJ1)–
NIJ1) = 2.165(3) Å, CoIJ1)–NIJ4)#1 = 2.197(3)], two oxygen
atoms from two carboxyl groups of one 3-NPH anion and
two coordinated water molecules with Co–O distances from
ijCoIJ3-bpha)IJ1,3-BDC)]·4H
2
O (3) and ijCoIJ3-bpha)IJHIP)]
·3H O (4). Structural analyses indicate that the final networks
2
of complexes 3 and 4 are very similar, as shown in Fig. 3 and
S3,† so complex 3 is taken as a representative example for
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molecules. As depicted in Fig. 3a, the coordination environ-
II
ment around the Co ion is composed of two nitrogen atoms
from two 3-bpha ligands ijCoIJ1)–NIJ1) = 2.152(19) Å, CoIJ1)–
NIJ4)#3 = 2.185(19) Å] and four oxygen atoms of three carboxyl
groups from three 1,3-BDC anions with Co–O distances from
2.005(15) to 2.418(15) Å, showing a distorted octahedral
geometry {CoN O }.
2
4
In complex 3, two 3-bpha ligands in the anti-configuration
II
integrate with two Co ions to generate a 28-membered
Co IJ3-bpha) ring. The carboxyl groups of 1,3-BDC possess
2
2
two different coordination modes: bidentate bridging coordi-
nation mode and chelate coordination mode. It is noted that
all the carboxylic oxygen atoms from the 1,3-BDC carboxylate
II
coordinate with the Co ions, forming an infinite 1D ijCo-1,3-
n
BDC] ladder-like double chain. The adjacent 1D chains are
linked by the 28-membered Co IJ3-bpha) loops to form an
2
2
intricate 2D network (Fig. 3b). In order to simplify the struc-
II
ture of complex 3, each Co , 1,3-BDC anion and 3-bpha
ligand can be defined as 5-, 3- and 2-connected nodes,
respectively. Thus, the 2D structure of complex 3 can be
2
3
4
described as a (2,3,5)-connected network with IJ4 ·6)IJ4 ·6·8
2
·
10 )IJ4) topology (Fig. 3c). There are no appropriate hydrogen-
bonding interactions in 3, while in 4, the 2D networks are
extended to a 3D supramolecular framework through the
hydrogen-bonding interactions between the oxygen atoms of
3-bpha ligands and oxygen atoms from the carboxyl group of
HIP anions and lattice water molecules, respectively ijOIJ5)–H-
IJ5B)⋯OIJ1W), O⋯O = 2.786(8) Å, OIJ1W)–HIJ1WB)⋯OIJ2), O⋯O
=
2.810(7) Å] (Fig. S3†).
ijCoIJ3-bpha)IJMIP)IJH
2
2
O)]·H O (5). Single-crystal X-ray dif-
fraction analysis reveals that complex 5 crystallizes in the
monoclinic space group P2IJ1)/c. In the coordination environ-
II
ment of 5, there is one crystallographically independent Co
center, one 3-bpha ligand, one MIP anion, one coordinated
II
water molecule and one lattice water molecule. The Co cen-
ter is six-coordinated by two pyridyl N atoms from two 3-bpha
ligands ijCoIJ1)–NIJ1) = 2.093(2) Å, CoIJ1)–NIJ4)#2 = 2.124(2) Å]
and four O atoms from two MIP anions and one coordinated
water molecule, respectively [Co–O = 2.019IJ18)–2.161IJ2) Å],
which adopts an octahedral {CoN O } coordination geometry
2
4
(
Fig. 4a).
In complex 5, the μ
2
-bridging 3-bpha ligands connect the
adjacent Co ions to result in a single-strand helix chain ijCo-
-bpha]
II
3
n
with the Co⋯Co separation of 13.57 Å (Fig. 4b). The
two carboxyl groups of MIP anions adopt chelate and mono-
dentate coordination modes, respectively, to link the adjacent
II
Co ions, forming an infinite 1D [Co-MIP]
n
linear chain. The
II
Fig. 3 (a) Coordination environment of the Co ion in 3 (#1 −x, −y + 1,
two types of 1D chains IJ[Co-3-bpha]
n
and [Co-MIP] ) are alter-
n
−
z + 2; #2 −x + 1, −y + 1, −z + 2). (b) The 2D network of 3. (c) The 2D
topology with IJ4 ·6)IJ4 ·6·8 ·10 )IJ4). The hydrogen atoms are omitted
2 3 4 2
natively connected with each other, constructing a 2D puck-
ered (4,4) network (Fig. 4c). In addition, the adjacent 2D
layers are interconnected by hydrogen-bonding interactions
between the nitrogen atoms of 3-bpha ligands and the oxygen
atoms from MIP anions ijNIJ3)–HIJ3B)⋯OIJ4), N⋯O = 3.073(9)
Å] to generate the final 3D supramolecular framework (Fig.
S4†). Generally speaking, the “V”-shaped bis-pyridyl-bis-amide
ligands tend to integrate with metal ions into ring-like
for clarity.
detailed structural description. Single-crystal X-ray diffraction
analysis reveals that 3 crystallizes in the triclinic system with
space group P ¯1 . Complex 3 consists of one Co ion, one
-bpha ligand, one 1,3-BDC anion and four lattice water
II
3
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II
Fig. 4 (a) Coordination environment of the Co ion in 5 (#1 x − 1, y, z).
(
b) View of the 1D ijCo-3-bpha]
n
helical chain. (c) The 2D network of 5.
(
d) Simplification of the 2D structure to a 4-connected network. The
hydrogen atoms are omitted for clarity.
II
Fig. 5 (a) Coordination environment of the Co ion in 6 (#1 −x + 3/2,
−
y + 1/2, z + 1/2; #2 x + 1/2, −y + 3/2, −z; #3 −x + 3/2, −y + 3/2, z − 1/
2
; #4 −x + 2, y, −z − 1/2). (b) View of the 2D network. (c) View of the 1D
structures, such as complexes 3 and 4 in this work and ZnIJL)-
3 4
ijCo-3-bpha]
·
n
helical chain. (d) View of the 3D topology with IJ8 )
4
IJ8
6
d
IJbdc)·IJH
-bpha ligands connect Co ions to generate single-strand
helix chains, which is rarely reported to our knowledge.
ijCo IJ3-bpha) IJ1,3,5-BTC) IJH O) ]·2H (6). Single-crystal
2
O)0.5 in the literature, while in complex 5, the
2
10 ). The hydrogen atoms are omitted for clarity.
II
3
3
2
2
2
4
2
O
and two coordinated water molecules, respectively [Co2–O =
2.086IJ6)–2.206IJ6) Å].
In complex 6, the carboxyl groups from the 1,3,5-BTC
anion exhibit two coordination modes: monodentate and
chelate coordination modes. Two carboxyl groups of the
1,3,5-BTC anion with monodentate mode linked the Co ions
to generate a 2D sheet (Fig. 5b). The 3-bpha ligands adopt a
-bridging mode connecting adjacent Co ions to form a
X-ray diffraction analysis reveals that 6 crystallizes in the
orthorhombic system with space group Pbcn. The unit con-
II
sists of three Co ions, two 3-bpha ligands, two 1,3,5-BTC
anions, four coordinated water molecules and two lattice
water molecules. There are two crystallographically indepen-
II
II
dent Co centers. As shown in Fig. 5a, the Co1 center exhibits
II
a {CoO
4
} tetrahedral coordination geometry with four oxygen
μ
2
atoms from four 1,3,5-BTC anions [Co1–O = 2.013IJ5)–2.020IJ5)
Å]. The Co2 ion shows a distorted octahedral coordination
geometry, being coordinated by two pyridyl N atoms from
two 3-bpha ligands ijCoIJ2)–NIJ1) = 2.128(7) Å, CoIJ2)–NIJ4)#5 =
single-strand helix chain ijCo-3-bpha] (Fig. 5c). The 2D sheets
n
and the 1D helix chains are further linked by the chelating
carboxyl groups of 1,3,5-BTC anions to form the final 3D
framework (Fig. S5†). In order to better understand the whole
structure, the Co1/Co2 ions can be considered as 4-/3-connected
2
.105(7) Å] and four oxygen atoms from one 1,3,5-BTC anion
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II
nodes, the 1,3,5-BTC anions can be regarded as 3-connectors
and the 3-bpha ligands can be viewed as linkers. Thus, the
structure of 6 can be simplified as a trinodal (3, 3, 4)-connected
coordination mode to coordinate with Co ions as terminal
groups. The oxygen atoms of the –CO groups from 3-bpha
also turn the same orientation; the nitrogen–nitrogen (N1 to
N4) distance of the 3-bpha ligand and the corresponding
dihedral angles are 10.527(5) Å, 26.10° and 9.91°, respec-
3
4
2
topology with the Schläfli symbol IJ8 ) IJ8 ·10 ) (Fig. 5d).
4
17
Sun et al. have reported a 2D network ijCo IJL) IJBTC) ]·4H O
3
2
2
2
[L = 3,3′,5,5′-tetraIJ1H-imidazol-1-yl)-1,1′-biphenyl] based on
2
tively. When 1,3-H BDC and HIP were used in 3 and 4,
the same metal and aromatic carboxylate ligand IJ1,3,5-BTC)
with complex 6, in which the Co -L 2D network is further
respectively, we obtained two similar structures. The 3-bpha
ligands and dicarboxylates (1,3-BDC for 3 and HIP for 4) in
complexes 3 and 4 display the same coordination modes. The
II
linked by BTC anions, resulting in the formation of the
final 2D structure. In 6, the BTC anions link the 2D sheets
and the 1D helix chains to form a 3D framework. Thus,
the N-donor ligands show a significant effect on the final
structures.
3-bpha ligands, acting as bidentate ligands with μ -bridging
2
II
mode, integrate with Co ions to generate 28-membered
2 2 2 2
Co IJ3-bpha) rings. These Co IJ3-bpha) loops connect adja-
cent 1D ijCo-1,3-BDC] chains in 3 and [Co-HIP] in 4 to form
n
n
the intricate 2D networks. The oxygen atoms of the –CO
groups from 3-bpha in 3 and 4 are both in the opposite orien-
tation. In complex 3, the distance between the nitrogen
atoms (N1 and N4) of the terminal pyridyl groups and the
dihedral angles between the two pyridyl rings and the ben-
zene ring are 11.876(5) Å, 43.12° and 55.35°, respectively,
while in complex 4, the relative distance and the dihedral
angles are 10.926(5) Å, 17.94° and 18.41°, respectively. When
a similar dicarboxylate MIP was selected in complex 5,
although the coordination mode of 3-bpha ligand is the same
Effect of the polycarboxylate anions on the structures of the
title complexes
In this work, by tuning the polycarboxylate co-ligands with
different carboxyl position and number as well as substitute
groups under the same conditions, we obtained six new
metal–organic complexes with different architectures. When
a short pyridyl-containing dicarboxylate 2,3-H PDC was used
2
in complex 1, the 3-bpha ligand and the 2,3-HPDC anion only
act as the terminal groups simultaneously with μ
1
-coordina-
as that in complexes 3 and 4, the μ
2
-bridging 3-bpha ligands
from 5 connect the adjacent Co ions to result in a single-
strand helix chain ijCo-3-bpha] , which is different from those
in 3 and 4. The adjacent ijCo-3-bpha] chains are connected
II
II
tion mode (Scheme 1) to coordinate with the Co ion,
resulting in the 0D complex 1. The two oxygen atoms of –
CO groups from the 3-bpha ligand are in the same orienta-
tion; the N⋯N (N1 and N4) distance of the terminal pyridyl
group is 13.772(5) Å and the dihedral angles between the two
pyridyl rings and the benzene ring are 7.14° and 10.10°.
n
n
by MIP anions to construct a 2D puckered (4,4) network. The
oxygen atoms of the –CO groups from 3-bpha in 5 turn the
same orientation; the nitrogen–nitrogen (N1 to N4) distance
of the 3-bpha ligand and the corresponding dihedral angles
are 12.812(5) Å, 15.42° and 7.59°, respectively. In complexes
When another nitro-containing dicarboxylate 3-H NPH was
2
used instead of 2,3-H PDC in complex 2, the 3-bpha ligand
2
II
II
exhibits a μ
2
-bridging mode connecting the adjacent Co ions
1–5, all the Co ions adopt a six-coordinated mode with an
to form a 1D ijCo-3-bpha]n meso-helical chain, and two car-
octahedral coordination arrangement. When a tricarboxylate
1,3,5-BTC was used in complex 6, the Co ions exhibited
0
1
II
boxyl groups of each 3-NPH anion show a μ -η :η monodentate
1
six-coordinated and four-coordinated modes. The two car-
boxyl groups from the 1,3,5-BTC anion with monodentate
II
mode link the Co ions to generate a 2D sheet. The third car-
boxyl group of the 1,3,5-BTC anion with a chelating coordina-
tion mode linked the single-strand helix ijCo-3-bpha] chains
n
to form the final 3D framework. The oxygen atoms of the –
CO groups turn the same direction. The N1⋯N4 distance
of the 3-bpha ligand and the corresponding dihedral angles
are 11.964(5) Å, 57.96° and 67.40°, respectively. The success-
ful assembly of complexes 1–6 with different structures from
0D to 3D can be attributed to the effects of the poly-
carboxylate anions (Scheme 2). Therefore, we can conclude
that the substitute groups, the position of the carboxyl
groups and the carboxyl number of the polycarboxylates play
significant roles in the construction and various architectures
of the title complexes.
PXRD measurement and thermogravimetric analysis (TGA)
II
In order to confirm the phase purity of the bulk materials for
the title complexes, powder X-ray diffraction (PXRD)
Scheme 1 Coordination modes of Co ions, the 3-bpha ligand and
polycarboxylates in complexes 1–6.
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behaviors of the 1–6-CPEs are similar except for some slight
potential shifts (Fig. S9† and Fig. 6). Thus, 2-CPE is taken as
an example to describe their cyclic voltammograms. As shown
in Fig. 6, it can be seen clearly that a redox couple was
observed in the potential range of +600 to −100 mV for 2-CPE
at different scan rates, which could be attributed to the redox
III
II 19
of Co /Co , and the mean peak potential E = (Epa + E )/2
1
/2
pc
−1
is 264 mV (100 mV s ). When the scan rates are varied from
0 to 300 mV s , the peak potentials gradually change: the
−1
2
cathodic peak potentials shifted toward the negative direction
and the corresponding anodic peak potentials shifted to the
positive direction with increasing scan rates. In addition, the
peak currents are proportional to the square root of the scan
−1
rates up to 300 mV s (inset of Fig. 6), which shows that the
redox process of the 2-CPE is diffusion-controlled.
Scheme 2 Schematic view of the effect of polycarboxylates on the
structures of complexes 1–6.
Photocatalytic properties
Photocatalysts have attracted much attention because of their
potential applications in purifying water by thoroughly
decomposing organic pollutants. Herein, the photocatalytic
experiments were performed. As shown in Fig. S7,† the mea-
sured powder XRD patterns are in good agreement with the
simulated ones, implying the phase purities of the samples.
The difference in reflection intensities between the simulated
and the experimental patterns may be attributed to the differ-
2
0
activities of complexes 1–6 were investigated with the photo-
2
1
degradation of methylene blue (MB). The photocatalytic
reactions were performed through a typical process: 150 mg
of complex 1 or 2, 3, 4, 5, 6 was mixed together with 90 mL
1
8
ent orientations of the crystals in powder samples.
−
1
To estimate the stability of the coordination architectures,
the thermal behaviors of the title complexes were studied by
of an aqueous solution of MB (10 mg·L ) under stirring in
the dark for 30 min to ensure the equilibrium of the working
solution. Then the solution was exposed to UV irradiation
from an Hg lamp (125 W) and kept under continuous stirring
during irradiations. Samples of 5 mL were taken every 30
min for analysis.
−
1
TGA under N atmosphere with a heating rate of 10 °C min
2
in the temperature range from room temperature to 800 °C
(Fig. S8†).
The TG curves show that complex 1 displays only one
weight loss step and complexes 2–6 exhibit two separate
weight loss steps. In complex 1, the weight loss is about
The absorption peaks of MB obviously decrease under UV
irradiation in the presence of the title complexes, as shown
in Fig. 7 and S10.† The concentration of MB gradually
9
1.74% (calc. 92.92%) from 260 °C to 480 °C, corresponding
to the decomposition of organic ligands, leading to the for-
mation of CoO as the residue. The first weight loss stages are
observed from 80 °C to 140 °C for 2, 70 °C to 100 °C for 3,
105 °C to 150 °C for 4, 100 °C to 140 °C for 5, and 140 °C to
260 °C for 6, giving the weight loss of about 9.12% for 2,
13.11% for 3, 7.53% for 4, 4.21% for 5, and 8.32% for 6, indi-
cating the loss of the lattice water molecules and/or coordi-
nated water molecules (calcd. 10.68% for 2, 11.44% for 3,
8
.61% for 4, 5.83% for 5, 7.90% for 6). The second weight
loss starting at 190 °C up to 400 °C for 2, 340 °C up to 470 °C
for 3, 360 °C up to 510 °C for 4, 350 °C up to 560 °C for 5,
and 390 °C up to 550 °C for 6 may be due to the decomposi-
tion of 3-bpha and aromatic polycarboxylate ligands. The
remaining weights are 10.09% for 2, 8.93% for 3, 10.12% for
4, 11.23% for 5, and 15.97 for 6, which can be assigned to
CoO (calc. 11.12% for 2,11.92% for 3, 11.95% for 4,12.35%
for 5, 16.45% for 6).
Fig. 6 Cyclic voltammograms of the 2-CPE in 0.01 M H
Na SO aqueous solution at different scan rates (from inner to outer:
0, 40, 60, 80, 100, 140, 180, 220, 260, 300 mV s ). The inset shows
the plots of the anodic and cathodic peak currents against the square
root of the scan rates.
2 4
SO + 0.5 M
Electrochemical behaviors of 1–6-CPEs
2
4
−
1
2
The redox properties of 1–6 were investigated in 0.01 M
H SO + 0.5 M Na SO aqueous solution. The electrochemical
2
4
2
4
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orbital (HOMO) contributed by the oxygen and/or nitrogen
2p bonding orbital (valence band) to the lowest unoccupied
molecular orbital (LUMO) contributed by an empty metal
orbital (conduction band). The HOMO strongly demands one
electron to return to its stable state. Thus, one electron was
captured from the water molecule, which was oxygenated into
the ·OH radical. The ·OH active species could decompose MB
2
3
effectively to complete the photocatalytic process.
Conclusion
II
We have successfully synthesized six new Co complexes
from the mixed ligands of N,N′-bisIJpyridin-3-yl)-5-hydroxy-
benzene-1,3-dicarboxamide and six different aromatic poly-
carboxylates under hydrothermal conditions. Complexes 1–6
show from 0D to 3D (0D for 1, 1D for 2, 2D for 3, 4 and 5,
and 3D for 6) architectures. The polycarboxylates with differ-
ent substitute groups, position of carboxyl groups and car-
boxyl number play important roles in the assembly and struc-
tures of the final complexes. Moreover, complexes 1–6
display electrochemical properties and photocatalytic activi-
ties, demonstrating their possible potential applications in
the catalysis and electrochemical fields.
Fig.
7 Absorption spectra of the MB solution during the
decomposition reaction under UV irradiation in the presence of
complex 1.
Acknowledgements
This work was financially supported by the National Natural
Science Foundation of China (no. 21171025, 21471021,
21401010) and the Program of Innovative Research Team in
University of Liaoning Province (LT2012020).
Notes and references
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Fig.
8 Photocatalytic decomposition of MB solution under UV
irradiation with the use of the title complexes, no catalyst under the
same conditions and complex 1 in the dark.
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