Structural diversity and catalytic properties of five Co2(COO)4 cluster-based coordination polymers modified with R-isophthalic acid (R = H, NO2, CH3, OH and :tBu)

Article abstract of DOI:10.1039/c7ce01100h

The self-assembly of 5-substituted isophthalic acid (R-H₂BDC, R = H, -NO₂, -CH₃, -OH and -^tBu), Co^II ions and 2,4,6-tris(4-pyridyl)-1,3,5-triazine (TPT) under solvothermal conditions yielded five Co-based coordination polymers (CPs): {[Co(BDC)(TPT)]·0.5(H₂O)}_n (CP1), {[Co(NO₂-BDC)(TPT)]·H₂O}_n (CP2), {[Co(CH₃-BDC)(TPT)]·0.5H₂O}_n (CP3), {[Co(HO-BDC)(TPT)]·0.5H₂O}_n (CP4), and {[Co(^tBu-BDC)(TPT)_2/3]·(CH₃CH₂OH)(H₂O)}_n (CP5) (H₂BDC = isophthalic acid, NO₂-BDC = 5-nitroisophthalic acid, CH₃-BDC = 5-methylisophthalic acid, OH-BDC = 5-hydroxyisophthalic acid and ^tBu-BDC = 5-tert-butylisophthalic acid). All compounds comprise Co₂(COO)₄ binuclear units, which are connected via a combination of R-H₂BDC and TPT ligands. In CP1, the binuclear Co₂(COO)₄ units are bridged into 1D chains extending along the [1 1 0] and [-1 1 0] directions, which are further interlinked by TPT ligands into a 3D network with CdS net topology. CP2, CP3 and CP4 are iso-structural and all exhibit 3D frameworks with pcu (α-Po) topology. In CP5, the Co₂(COO)₄ units are firstly linked into a 3D NbO net via^tBu-BDC ligands, which are further accommodated by size-matching trigonal TPT ligands into a novel (3,8)-connected 3D net. Catalytic measurements show that CP2 and CP3 are good catalysts for the Knoevenagel condensation reaction of benzaldehyde with ethyl cyanoacetate, exhibiting conversions of 91.3% and 96.6% in 120 min, respectively, compared with the other present compounds. In addition, CP2 and CP5 exhibit highly efficient catalytic properties for the selective epoxidation of styrene.

Full text of DOI:10.1039/c7ce01100h

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HIGHLIGHT
Tiddo J. Mooibroek, Antonio Frontera et al.
Towards design strategies for anion–π interactions in crystal engineering
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H
Structural Diversity and Catalytic Properties of Five Co (COO) Cluster
2
4
Based Coordination Polymers Modified by Rꢀisophthalic acid (R=H,
t
NO , CH , OH and Bu)
2
3
,
a
a
a
a
,a
JianꢀYong Zhang* , JunꢀXia Shi , PengꢀHui Cui , ZiꢀJian Yao , and Wei Deng*
t
The selfꢀassembly of 5ꢀsubstituted isophthalic acid (RꢀH BDC, R=H, ꢀNO , ꢀCH , ꢀOH and ꢀ Bu),
2
2
3
II
Co ions and 2,4,6ꢀtris(4ꢀpyridyl)ꢀ1,3,5ꢀtriazine (TPT) under solvothermal conditions yield five
Coꢀbased coordination polymers (CPs): {[Co(BDC)(TPT)]·0.5(H O)}n (CP1), {[Co(NO2ꢀ
2
BDC)(TPT)]·H O}
(CP2),
{[Co(CH ꢀBDC)(TPT)]·0.5H O}
(CP3),
{[Co(HOꢀ
2
n
3
2
n
t
BDC)(TPT)]·0.5H O} (CP4), and {[Co( BuꢀBDC)(TPT) ]·(CH CH OH)(H O)} (CP5) (H BDC
2
n
2/3
3
2
2
n
2
=
isophthalic acid, NO ꢀBDC = 5ꢀnitroisophthalic acid, CH ꢀBDC = 5ꢀmethylisophthalic acid, OHꢀ
2 3
t
BDC = 5ꢀhydroxyisophthalic acid and BuꢀBDC = 5ꢀtertꢀbutylisophthalic acid). All compounds are
constructed from the Co (COO) binuclear unit, and connected by the mixed RꢀH BDC and TPT
2
4
2
ligands. In CP1, the binuclear Co (COO) units are bridged into 1D chains extended along [1 1 0]
2
4
and [ꢀ1 1 0] directions, which are further interlinked by TPT ligands into threeꢀdimensional
network with CdS net topology. CP2, CP3 and CP4 are isoꢀstructural and all exhibit threeꢀ
dimensional frameworks with pcu (αꢀPo) topology. In CP5, the Co (COO) units are firstly linked
2
4
t
into threeꢀdimensional NbO net by BuꢀBDC ligands, which are further accommodated by the sizeꢀ
matching trigonal TPT ligands into novel (3,8)ꢀconnected threeꢀdimensional net. The catalytic
measurements show that CP2 and CP3 are good catalysts for Knoevenagel condensation reaction
of benzaldehyde with ethyl cyanoacetate and give 91.3%, and 96.6% conversions in 120 min,
respectively, compared with the other present compounds. In addition, CP2 and CP5 exhibit
highly efficient catalytic properties for the selectivity to the epoxidation of styrene.
substituents on organic linkers can result in the variation of
1
2
Introduction
the final CPs. Therefore, utilizing similar or isomeric
ligands to construct MOFs is considered to be an effective
way to investigate the influence of organic ligands on the
Coordination polymers (CPs), also known as metalꢀorganic
frameworks (MOFs), are regarded as the new generation of
porous materials, which are built from metal ions or clusters
13
structure. Simple isophthalic acid and its 5ꢀsubstituted
derivatives have been fruitfully utilized as bridging ligands
for the generation of CPs due to their strong and versatile
1
as building units and adjustable organic ligands. As an
emerging research field, the design and synthesis of new CPs
are of contemporary interest within the last decade not only
because of their interesting topologies but also their potential
applications in gas separation and storage, chemical sensors,
luminescence, heterogeneous catalysis, electrical energy
storage and magnetism. Among of them, CPs as catalysts,
especially selective and recyclable heterogeneous catalysts,
have been widely investigated.
traditional catalysts, CPs are superior catalysts due to their
inorganicꢀorganic hybrid composition and polymeric nature.
In addition, the CPs based catalysts can be easily prepared via
selfꢀassembly or postꢀsynthetic modification. Thus their
coordination modes of the carboxylate groups in binding
14,15
metal ions.
The R substitutions on 5ꢀposition with
different electronic properties and shapes may also influence
the coordination modes of the related carboxylate groups and
CPs with different topological structures may be obtained by
2
ꢀ9
15
simply tuning the substitutions on the dicarboxylate ligands.
On the other hand, it is well known that the mixedꢀligands
strategy has been proved to be a useful method for the
construction of new CPs due to their ability to incorporate the
virtues of different functional groups and to easily form
controlled structures by changing one of the ligands. The
multiꢀpyridyl ligands have been triumphantly used in
combination with polycarboxylate ligands to create new CPs
7
,10
In comparison with other
16
7
utilization as catalysts has become a hot topic nowadays.
Generally speaking practical applications of CPs directly
depend on their structural features. To obtain novel structures,
many efforts have been devoted to modifying the building
blocks and controlling the assembled motifs via judicious
selection of organic bridging ligands, although the selfꢀ
assembly of CPs is always influenced by many variable
factors, such as the pH value, reaction temperature and
solvent, coordination modes of metal ions and organic
17
with versatile topologies and properties. Among them, the
rigid trigonal multipyridyl ligand 2,4,6ꢀtris(4ꢀpyridyl)ꢀ1,3,5ꢀ
triazine ligand (TPT, C3 symmetry) is of special interest in
recent years and has been used to construct a number of
highly symmetrical polynuclear complexes with unusual
properties. In our previous work, we have shown the
systematic research of mixedꢀligand CPs by modifying
18
19,20
connection modes and sizeꢀmatching auxiliary ligands.
1
1
ligands. Among these factors, the organic bridging linkers
play a key role and the structural changes of the ligand, such
as geometry, the relative orientation of the donor, even the
Following the above consideration, we presented the synthesis
of a series of Coꢀbased CPs by using different combinations
of isophthalic acids based linkers having different
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DOI: 10.1039/C7CE01100H
◦
◦
substitutions at 5ꢀposition (RꢀH BDC, R = H, ꢀNO , ꢀCH , ꢀ
then raised to 280 C at 30 C/min and held for 5 min. Inlet and
2
2
3
t
◦
OH and ꢀ Bu) along with the trigonal TPT ligands including
singleꢀcrystal structures and catalytic properties. These
compounds, comprised from the Co (COO) binuclear unit,
detector temperatures were 280 C. The analysis was carried
out directly after withdrawing to avoid any additional
conversion. All the samples were all characterized by FTꢀIR
(Fig. S1), TG analyses (Fig.S2) and the phase purity and
stabilities of bulk samples were also confirmed by PXRD
analysis (Fig. S3).
2
4
are formulated as {[Co(BDC)(TPT)]·0.5(H O)} (CP1),
2
n
{
[Co(NO ꢀBDC)(TPT)]·H O}
(CP2),
(CP3),
(CP4),
{[Co(CH3ꢀ
2
2
n
BDC)(TPT)]·0.5H O}
BDC)(TPT)]·0.5H O}
{[Co(HOꢀ
2
n
n
t
and
{[Co( Buꢀ
2
Synthesis
BDC)(TPT)2/3]·(CH CH OH)(H O)} (CP5), where H BDC =
3
2
2
n
2
isophthalic acid, NO ꢀH BDC = 5ꢀnitroisophthalic acid, CH ꢀ
2
2
3
H BDC
=
5ꢀmethylisophthalic acid, OHꢀH BDC
=
5ꢀ
2
2
t
hydroxyisophthalic acid and
BuꢀH BDC
=
5ꢀtertꢀ
2
butylisophthalic acid. Interestingly, only two pyridyl nitrogen
II
atoms in TPT ligand coordinated to Co center in CPs 1 ꢀ 4,
thus the left uncoordinated nitrogen atoms may be good Lewis
basic sites for the catalysis reaction. Preliminary
investigations into the catalytic properties for Knoevenagel
condensation reaction of benzaldehyde with ethyl
cyanoacetate and selective epoxidation of styrene are also
described.
Scheme 2. The synthesis scheme for compounds 1 ꢀ 5.
{[Co(1,3ꢀBDC)(TPT)]·0.5(H O)} (CP1). Co(NO3)2 (0.05
2
n
mmol, 0.015 g), 1,3ꢀH BDC (0.05 mmol, 0.008 g), and TPT
2
(
0.05 mmol, 0.016 g) were mixed in DMF (N,N'ꢀ
dimethylformamide) /EtOH/H O (4/4/2 mL). The mixture was
2
stirred vigorously for 30 min at room temperature and then
o
was heated in a 10 mL Teflonꢀlined autoclave at 100 C for 3
days. After cooling to room temperature, pink prismꢀshaped
crystals of CP1 were obtained with only one phase. Yield,
0
.0124g, (83% based on Co(NO ) ). Elemental analysis calc.
3 2
for C H N O Co (M =544.39): C, 57.36; H, 3.15; N, 15.44.
2
6
17
6
4.5
ꢀ
1
Found: C, 57.04; H, 2.96; N, 15.27%. IR (KBr, cm ): 3279br,
Scheme. 1. Schematic present of TPT and auxiliary 5ꢀsubstituted
isophthalic acid used in this paper.
3
1
1
043m, 1638s, 1599m, 1578m, 1515vs, 1449m, 1431m,
404m, 1374vs, 1315m, 1268m, 1159w, 1129m, 1067m,
053m, 1034m, 991m, 924w, 852w, 798vs, 764s, 721s, 640vs.
Experimental
{[Co(NO ꢀBDC)(TPT)]·H O} (CP2). Co(NO ) (0.05 mmol,
2 2 n 3 2
0
.015 g), NO ꢀH BDC (0.05 mmol, 0.011 g), and TPT (0.05
2 2
Materials. The 5ꢀsubstituted isophthalic acid (RꢀH BDC,
2
t
mmol, 0.016 g) were mixed in IPA (isopropanol)/H O (4/2
mL), and the mixture was heated at 130 C for 3 days. After
cooling to room temperature slowly, orange rodꢀshaped
crystals of CP2 were collected. Yield, 0.0066g, (44% based
on Co(NO ) ). Elemental analysis calc. for C H N O Co (M
R=H, ꢀNO , ꢀCH , ꢀOH and ꢀ Bu), cobalt nitrate hexahydrate,
2
2
3
t
o
tertꢀbutyl hydroperoxide ( BuOOH), acetonitrile (MeCN),
styrene and other chemical reagents were obtained from
commercial sources and used without further purification
unless stated otherwise. The TPT ligand was synthesized
2
1
3
2
26 17
7
7
following a modified reported procedure.
=
598.39): C, 52.19; H, 2.86; N, 16.39. Found: C, 52.33; H,
ꢀ
1
Physical measurements. The FTꢀIR spectra were recorded in
2.96; N, 16.26%. IR (KBr, cm ): 3281br, 3077w, 1628vs,
1576s, 1518vs, 1455m, 1432m, 1373vs, 1348vs, 1312s,
1213m, 1160w, 1106w, 1077m, 1062m, 1016m, 933w, 870w,
806vs, 788s, 738s, 727s, 712s, 669m, 654m, 647m.
ꢀ
1
the range 500 ꢀ 4000 cm using KBr pellets on a Nicolet
NEXUS 670 spectrophotometer. Elemental analysis (EA) was
carried out on an Elementar Vario El III elemental analyzer.
TG analyses (TGA) were carried out on a Mettler Toledo
TGA/SDTA851 instrument under flowing air at a heating rate
{[Co(CH
similar to that of CP2 was followed to prepare CP3, except
the 1,3ꢀH BDC (0.05 mmol, 0.008 g) and the solvent were
replaced by CH ꢀH BDC (0.05 mmol, 0.009 g) and
O/CH CN (acetonitrile) (4/4 mL) mixture, respectively.
ꢀBDC)(TPT)]·0.5H
O}
(CP3).
A
procedure
3
2
n
◦
−1
of 5 C min . The powder Xꢀray diffraction (PXRD) was
recorded on a Rigaku D/Maxꢀ2500 diffractometer at 35 kV,
2
3
2
2
5 mA for a Cu Kα radiation (λ = 1.5418Å) over the 2ɵ range
H
2
3
o
of 5 ꢀ 40 at room temperature. Simulation of the PXRD
spectra was carried out by the singleꢀcrystal data and
diffractionꢀcrystal module of the Mercury (Hg) program
The mixture was stirred at room temperature for 30 min and
then heated at 130 C for 3 days in 10 mL Teflonꢀlined
autoclave. After cooling to room temperature slowly, orange
o
available
free
of
charge
via
the
Internet
at
rodꢀshaped crystals of CP3 were collected. Yield, 0.0083g,
http://www.iucr.org. The catalytic products were analyzed by
Gas chromatographyꢀMass spectrometer (SHIMADZUꢀ
QP2010. The temperature program for GCꢀMS analysis was
(56% based on Co(NO
) ). Elemental analysis calc. for
3 2
C H N O
27 17 6
4.5Co (M =556.40): C, 58.28; H, 3.08; N, 15.10.
ꢀ
1
Found: C, 58.14; H, 2.96; N, 14.98 %. IR (KBr, cm ): 3067m,
2909w, 1625m, 1589m, 1577m, 1553m, 1518vs, 1427s,
◦
set as follows: the temperature was held at 40 C for 1 min,
2
| Journal Name, [year], [vol], 00–00
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DOI: 10.1039/C7CE01100H
1
1
{
375vs, 1314m, 1249w, 1214w, 1162w, 1112m, 1063s,
017w, 935w, 896w, 869m, 804vs, 777vs, 717s, 651m.
Crystal structure analysis
Diffraction intensity data were collected on a Bruker SMART
APEX II diffractometer equipped with a CCD area detector
and graphiteꢀmonochromated Mo Kα radiation (λ = 0.71073
Å) for CP1, CP4, CP5 and Cu Kα radiation (λ = 1.54178 Å)
for CP2, CP3. Empirical absorption corrections were applied
using the SADABS program. The structures were solved the
direct methods and refined on F by fullꢀmatrix leastꢀsquares
technique using the SHELXꢀ2014 program package. All
[Co(HOꢀBDC)(TPT)]·0.5H O} (CP4). A mixture of HOꢀ
2
n
H BDC (0.05 mmol, 0.009 g), Co(NO ) (0.05 mmol, 0.015
g), and TPT (0.05 mmol, 0.016 g) in IPAꢀH OꢀEG (ethyl
glycol) (2/2/2 mL) mixed solvent, which was stirred
vigorously for 30 min at room temperature and then was
heated at 130 C for 3 days. After cooling to room temperature
2
3 2
2
22
o
2
slowly, orange diamondꢀshaped crystals of CP4 were
collected. Yield, 0.0103g, (69% based on Co(NO ) ).
23
3
2
nonꢀhydrogen atoms in the structures were refined with
anisotropic displacement parameters, and all the hydrogen
atoms attached to C atoms were placed in calculated positions
and refined isotropically using the riding model. The
hydrogen atoms of lattice water molecule in CP1, CP2, CP3
and ethanol solvent molecule in CP5 were located from the
difference maps and included in the refinements with
restraints on OꢀH distances. The hydrogen atoms of lattice
water molecules in CP4 and CP5 could not be located from
the difference maps. The details of the relevant
crystallographic data collection and refinement parameters for
the five compounds are summarized in Table 1 and selected
bond lengths and angles are listed in Table S1.
Crystallographic data (without structural factors) for the
structures reported in this paper have been deposited
with the Cambridge Crystallographic Data Centre
with reference number CCDC 1531424ꢀ1531428 for
CPs 1− 5, which can be obtained free of charge via
www.ccdc.cam.ac.uk/dataꢀrequest/cif.
Elemental analysis calc. for C H N O5.5Co (M =560.38): C,
2
6
17
6
5
%
5.73; H, 3.06; N, 15.00. Found: C, 55.84; H, 3.12; N, 15.14
IR (KBr, cm ): 3066w, 1628s, 1596s, 1575s, 1544m,
ꢀ
1
1
1
7
519vs, 1428m, 1373vs, 1313m, 1270m, 1212m, 1160w,
124w, 1110w, 1060m, 975m, 888w, 871w, 804vs, 783s,
18m, 670m, 654m, 646m.
t
t
{
[Co( BuꢀBDC)(TPT) ]·(CH CH OH)(H O)} (CP5). Buꢀ
2/3 3 2 2 n
H BDC (0.05 mmol, 0.011 g), Co(NO ) (0.05 mmol, 0.015
2
3 2
g), and TPT (0.05 mmol, 0.016 g) were dissolved in mixed
DMF /EtOH solvent (3/3 mL). The mixture was stirred
vigorously for 30 min at room temperature and then heated at
o
9
0
C for 3 days in 10 mL Teflonꢀlined autoclave. After
cooling to room temperature slowly, red cubicꢀshaped crystals
of CP5 were collected. Yield, 0.0095g, (63% based on
Co(NO ) ). Elemental analysis calc. for C H N O Co (M
3
2
26 27
4
6
=
550.45): C, 56.73; H, 4.94; N, 10.18. Found: C, 56.94; H,
ꢀ
1
4
1
1
8
.66; N, 9.99 %. IR (KBr, cm ): 3409w, 2964m, 1616s,
576s, 1575s, 1547s, 1517vs, 1438m, 1374vs, 1312s, 1272m,
213m, 1163w, 1114w, 1091w, 1059s, 1017m, 911w, 869w,
22w, 806vs, 781s, 752m, 723s, 654m, 669m, 652s.
Table 1. Crystallographic data and refinement parameters for CPs 1ꢀ5.
CP1 CP2 CP3 CP4
1531425 1531424 1531426 1531427
Compound
CCDC number
CP5
1531428
Formula
C
26
H
17
N
6
O4.5Co
C
26
H
17
N
7
7
O Co
C
27
H
17
N
6
O4.5Co
C
26
H
17
N
6
O5.5Co
26 27 4 6
C H N O Co
Formula weight
544.39
598.40
556.40
560.39
550.44
Crystal system
Space group
Monoclinic
C2/c
Monoclinic
Monoclinic
C2/c
Monoclinic
C2/c
Trigonal
Rꢀ3
C2/c
a, Å
b, Å
c, Å
α, º
β, º
γ, º
Z
15.3687(18)
12.8671(16)
24.517(3)
90
98.481(2)
90
28.6922(14)
13.6439(6)
14.4273(7)
90
112.028(5)
90
24.1447(5)
13.0986(3)
16.0330(4)
90
97.903
90
24.418(3)
13.0005(15)
15.5741(18)
90
99.9820(10)
90
26.7166(8)
26.7166(8)
21.7748(13)
90
90
120
8
8
8
8
18
3
V, Å
ɵ range ( )
4795.2(10)
1.68ꢀ27.90
5235.6(4)
3.32ꢀ66.58
5022.5(2)
3.70ꢀ70.38
4869.2(10)
1.69ꢀ26.00
13460.1(10)
1.28ꢀ26.00
o
Crystal size / mm
0.08x0.11x0.29 0.14x0.16x0.18 0.10x0.15x0.22 0.11x0.15x0.19 0.16x0.20x0.24
ꢀ
3
D
c, g cm
1.508
0.765
1.518
5.667
1.472
5.773
1.529
0.758
1.222
0.615
ꢀ
1
µ, mm
Reflections collected
Unique reflections
17957
5707
9153
4562
9745
4726
17753
4780
24975
5881
R
int
0.0388
1.034
0.0271
1.058
0.0334
1.056
0.0734
0.972
0.0463
1.170
2
GOF on F
R
R
1
,wR
,wR
2
[I>2σ(I)]
0.0376, 0.0915
0.0638, 0.1135
0.569, ꢀ0.255
0.0409, 0.1081
0.0549, 0.1230
0.590, ꢀ0.370
0.0535, 0.1378
0.0714, 0.1480
0.727,ꢀ0.382
0.0614, 0.1424
0.1115, 0.1778
0.794, ꢀ0.465
0.0491, 0.1457
0.0760, 0.1732
0.921, ꢀ0.579
1
2
(all data)
ꢀ
3
ꢀρmax, ꢀρmin, e Å
Results and discussion
Crystal Structures
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DOI: 10.1039/C7CE01100H
ions with µꢀ1,3ꢀCOO bidentate fashion at the other end. As
demonstrated in Fig. 1c, the 1D chains propagate along two
directions: [1
1 0] and [ꢀ1 1 0], which are almost
perpendicular to each other, and just due to this arrangement
fashion, the TPT ligands can linked these 1D [Co(BDC)]n
chains to produce the final 3D framework. In order to
understand the whole structure, we can simplify the intricate
structure as nodeꢀand connecting nets. Each binuclear
Co (COO) unit connected four neighbouring ones through
2
4
2
ꢀ
four BDC and four TPT ligands, and thus can be considered
2
ꢀ
as 4ꢀconnected node, and the BDC and TPT ligands can be
viewed as linker. Therefore, the whole structure can be
5
reduced as a 4ꢀconnected CdS net with point symbol 6 ·8
2
5
(
Fig.2) . Generally, TPT shows exoꢀtridentate coordinate
II
Fig. 1 (a) The local coordination environments of Co ion, H
2
BDC and
mode in coordination polymers. In CP1, the TPT ligand acts
as Vꢀshaped ditopic ligand to coordinated two Co ions
TPT ligand in CP1, hydrogen atoms and water molecule were omitted for
II
2ꢀ
II
clarity; (b) View of the 1D chain composed of BDC and Co ions; (c)
View of the 3D network, highlighting the chains extended along two
directions (green and red colour).
through two pyridyl groups to form oneꢀdimensional zigzag
chains with the three pyridyl rings and triazine plane almost
being coꢀplane (Table 2). The leaving uncoordinated pyridyl
group, as an unbound arm, can serve as the active base site for
the catalysis reactions.
The singleꢀcrystal diffraction analysis revealed that CP1
crystallized in the monoclinic space group C2/c and the
II
2ꢀ
asymmetric unit contains one Co ion, one BDC anion, one
TPT ligand and a H O solvent molecule. As shown in Fig. 1,
2
II
the Co ion adopts the sixꢀcoordinative [N O ] environment,
2
4
completed by a chelating carboxylate group (O3B and O4B),
two carboxylate oxygen atoms (O1 and O2A) from two other
BDC ligands, and two pyridyl nitrogen atoms (N1 and N2C)
from two TPT ligands in trans positions. The CoꢀO bond
lengths are in the range of 2.025(2) ꢀ 2.229(2) Å, the CoꢀN
bond lengths are 2.157(2) / 2.161(2) Å, which are all well
2
4
matched to those found in other reported similar CPs. Due to
the chelating coordination mode of one carboxylate group,
which has a small bite angle [O3BꢀCo1ꢀO4B = 60.49(4)°] and
dissymmetric CoꢀO bonds [2.1192) and 2.2262) Å], the
II
2ꢀ
Fig. 3 (a) The local coordination environments of Co ion, NO
2
ꢀBDC
and TPT ligand in CP2; Hydrogen atoms and lattice water molecule were
omitted for clarity (b) View of the 2D sheet constructed from NO
2
ꢀBDC
II
and Co ions.
II
coordination geometry of Co center is highly distorted from
the octahedral.
When the reaction was carried out with NO ꢀH BDC as
2
2
dicarboxyloate ligand, in which the ꢀNO2 substituent on 5ꢀ
position may impose strong electronꢀwithdrawing effect on
the assembling processes and structures, although it was not
involved in coordination. Under similar reaction conditions,
we isolated single crystals of CP2. According to the Xꢀray
diffraction analysis, CP2 crystallized in the same monoclinic
space group C2/c and exhibited 3D framework. In the
asymmetric unit, there are one NO ꢀBDC anion, one TPT
2
II
ligand and one H O solvent. As shown in Fig. 3a, the Co ion
2
assumes [N O ] fiveꢀcoordinated trigonal bipyramidal
2
3
geometry. The equatorial positions are defined by three
carboxylate oxygen atoms (O1, O2A and O3B) from three
different NO ꢀBDC ligands with CoꢀO bond lengths being in
2
the narrow rang of 1.963(3)ꢀ2.005(2) Å, whereas the axial
positions are occupied by two nitrogen atoms (N1 and N2C)
from two TPT ligands with CoꢀN bond lengths being 2.180(2)
Å and 2.164(2) Å, respectively, which is evidently longer than
the equatorial ones. The other selected bond lengths and bond
angles are listed in Table S1.
Fig. 2 View of CdS topology net in CP1.
II
Two symmetry equivalent Co ions are double connected
by two µꢀ1,3ꢀcarboxylate groups to give a centrosymmetric
binuclear Co (COO) unit with Co…Co distance of 4.159(1)
2
4
Å, which are further bridged by the benzoate backbones of
H BDC ligand to form 1D ladder like [Co(BDC)] chain. In
2
n
2
ꢀ
II
the 1D chain, each BDC ligand connects three Co ions,
II
II
chelating a Co ion at one end and binding another two Co
| Journal Name, [year], [vol], 00–00
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DOI: 10.1039/C7CE01100H
nitrogen atoms from two TPT ligands (Fig.5), and the
coordination geometry is similar to that of CP1. The CoꢀO/N
bond lengths are in the range of 1.999(2)ꢀ2.315(3) Å for CP3
and 2.002(3)ꢀ2.177(4) Å for CP4.
II
Two equivalent Co ions are also bridged by two
carboxylate groups leading to the binuclear Co (COO) motif
2
4
with Co…Co distance of 4.112(3) Å for 3 and 4.048(1) Å for
CP4, which are further linked by the phenyl backbones into
2
D Co(RꢀBDC) (R= ꢀCH for CP3 and ꢀOH for CP4) sheet
n 3
(
sql net). These 2D sheets are similar to that of CP2, except
2
ꢀ
Fig. 4 (a) View of the 3D “pillared” framework consisted of the 2D
the coordination linkage of RꢀBDC ligands and they are also
further “pillared” by the TPT ligands in the interꢀsheets into
[
Co(NO
2
ꢀBDC)]
n
sheet and TPT pillars in CP2; (b) the pcu topology
network.
3
D frameworks. Due to the similarities to CP2, the reduced
II
Two equivalent Co ions are bridged by two µꢀ1,3ꢀ
carboxylate groups to give a centrosymmetric binuclear
Co (COO) unit with Co…Co distance of 3.936(1) Å, which
topology nets for CP3 and CP4 were also 6ꢀconnected pcu net
(
αꢀPo) with the binuclear Co (COO) motif as 6ꢀconnected
2 4
25
2
4
node (Fig. S4 in ESI).
smaller than that of CP1. Each binuclear Co (COO) unit join
2
4
four neighbouring ones by four benzoate backbones of NO ꢀ
2
2
ꢀ
BDC into a 2D gridꢀlike Co(NO ꢀBDC) sheet (sql net),
2
n
paralleling to the crystallographic bc plane (Fig.3b). In the 2D
2
ꢀ
II
sheet, each NO ꢀBDC links three Co ions through a µꢀ1,3ꢀ
2
COO bidentate and a monodentate carboxylate. Neighbouring
2
D sheets are further “pillared” by TPT ligands into 3D
II
frameworks through the connections to Co ions. From the
topological point of view, if the NO ꢀBDC and TPT ligands
2
ꢀ
2
can be viewed as linker, each binuclear Co (COO) unit can be
2
4
viewed as a node, which is connected six neighbouring units
2
ꢀ
by four NO ꢀBDC and four TPT ligands. Therefore, the
2
whole structure can be viewed as a 6ꢀconnected net with pcu
1
2
3
25
topology (αꢀPo) and the symbol point is 4 ·6 (Fig.4). As
described in above compounds, there is also only two pyridyl
nitrogen atoms (N1 and N2) in TPT ligand are coordinated to
II
Co ions, and the uncoordinated nitrogen atom (N3) are
towards to the cavities.
II
t
2ꢀ
Fig. 6 The local coordination environments of Co ion, BuꢀBDC and
TPT ligand in CP5. Hydrogen atoms and solvent molecules were omitted
for clarity.
Encouraged by the results above, another substituent group
ꢀ
C(CH3)3 with larger steric hindrance and electronꢀdonating
effect was considered, and when the reaction was done with
t
BuꢀH BDC as the dicarboxylic acid, we separated CP5. Xꢀray
2
structure determination revealed that it crystallized in trigonal
crystal system with the Rꢀ3 space group and exhibited 3D
frameworks based on binuclear Co (COO) unit. In CP5, the
2
4
2ꢀ
t
asymmetric unit consists of one BuꢀBDC anion, 2/3 TPT
Fig. 5 The similar coordination environments of Co , RꢀBDC2ꢀ and TPT
ligands in CPs 3 (a) and 4 (b).
II
ligand, one ethanol and H O solvent molecules. The selected
2
bond distances and angles are listed in Table S1. As shown in
II
Substitution of NO ꢀH BDC using the similar derivatives of
Fig. 6, the Co ion adopts a sixꢀcoordinated [N O ] distorted
2
2
2
4
CH ꢀH BDC and OHꢀH BDC ligands with electronꢀdonating
groups respectively, we separated CP3 and CP4, which are
isomorphous and isoꢀstructural with CP2 differing only with
octahedral coordination geometry, defined by a carboxylate
group (O1 and O2), two oxygen atoms from two different
carboxylate groups (O3A and O4B) in the equatorial plane,
two nitrogen atoms from two TPT ligands (N1 and N2) in the
3
2
2
respect to the –R functional groups on 5ꢀposition of H BDC
2
II
(
R= ꢀNO for CP2, ꢀCH for CP3 and ꢀOH for CP4) and both
axial positions. The coordination geometry of Co is highly
2
3
compounds crystallize in the monoclinic space group C2/c.
Therefore, we depict the structure of crystal 3 as example
herein. Some relevant structural parameters are listed in Table
distorted from octahedral due to the asymmetric chelating
mode, as evidenced by the large different CoꢀO bond lengths
[2.089(2) Å vs. 2.310(3) Å]. As presented in compounds
II
II
S1. Different from that in CP2, the Co ion adopts [N O ] sixꢀ
reported above, two equivalent Co ions are also linked by
2
4
coordinated distorted pyramidal geometry, completed by four
two carboxylate groups, giving rise to a centrosymmetric
binuclear Co (COO) motif with Co…Co distance of 4.215 (1)
oxygen atoms from three CH ꢀBDC/OHꢀBDC ligands and two
3
2
4
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DOI: 10.1039/C7CE01100H
Å.
Fig. 8 View of the 3D framework in CP5, showing the derivation of the
newly (3,8)ꢀconnected network.
Table 2. The relevant structural parameters for the five compounds
.
Fig. 7 View of the binuclear and TPT connectors, serving as 8ꢀ and 3ꢀ
connected nodes in CP5, respectively.
Compounds
CoꢀObridging 2.031(2),
CP1
CP2
1.980(3),
2.005(3)
1.963(3)
CP3
1.999(3)
CP4
CP5
2.002(4), 2.015(2),
2.004(3) 2.035(2)
(Å)
2.025(2)
Different from the reported compounds above, in CP5, each
CoꢀOchelating 2.229(2),
2.106(3), 2.053(4), 2.089(2),
2.315(3) 2.492(5) 2.310(3)
2.175(3), 2.162(4), 2.152(3),
2.176(3)
4.111(1)
t
a
binuclear Co (COO) units were bridged by four BuꢀBDC
(Å)
CoꢀN (Å) 2.157(3),
.161(2)
Co…Co (Å) 4.159(1)
Dihedral
2.118(2)
2
4
2.164(4),
2.180(4)
3.936(5)
ligands in three directions and extended into a 3D framework.
Taking the binuclear Co (COO) motif as 4ꢀconnected node,
2
2.177(4) 2.184(3)
4.048(1) 4.215(1)
2
4
the resulting 3D framework can be considered as a single
10.90(13), 10.09(17), 9.76(28), 13.50(30),27.29(25),
angels ( ) 18.52(21) 11.96(16) 27.89(25) 39.98(38) 8.99(36)
4
2
o b
nodal fourꢀconnected (4ꢀc) net with the point symbol of (6 ·8 )
2
6
Dihedral
3.85(11),
angels ( ) 9.68(09),
.90(12)
3.55(12),
3.52(12),
3.91(23)
4.93(18), 1.81(23), 12.20(05),
9.48(17), 7.81(21), 16.87(07)
which is collected in RCSR as the NbO topology. As in
other reported NbO net, there are 1D hexagonalꢀshaped
o
c
0
5.18(28)
2.38(35)
t
channels down the c axis, and the Bu groups protrude toward
d
Mode
synꢀskew, synꢀsyn,
chelating
synꢀsyn,
synꢀsyn, synꢀskew,
the centres of the channels with the radii of about 6.05 Å (the
shortest distances between the cavity centres and any
framework atoms), which offers a good opportunity for the
monodentate chelating chelating chelating
a
b
For CP2, one carboxylic group is monodentate carboxylate the dihedral
c
angle between the carboxyl group and conjoint phenyl ring; the dihedral
d
angle between three pyridyl rings and the corresponding triazine plane;
the coordination mode of carboxylate group of RꢀBDC ligand.
1
2b
accommodation of sizeꢀmatching trigonal TPT ligands.
II
Meanwhile, the TPT ligands bonded to the Co centres via its
three outer pyridyl donors into 2D honeycomb network,
paralleling to the ab plane, which further filled in the 1D
channels of the NbO net above. Due to the blocking of
coordinated large TPT ligands, no evident channels are
observed from the structural analysis, which is consistent with
Investigation of the catalytic activity towards Knoevenagel
condensation and Selective Epoxidation
the N sorption curves at 77K, although the total accessible
2
volume of CP5 with removal of the guest solvent molecules is
Scheme 3 Knoevenagel condensation reaction of benzaldehyde and ethyl
cyanoacetate.
3
4
778.3 Å , comprising 35.5% of the crystal volume
3
27
(
13460.1(10) Å ) calculated by PLATON software.
As
Knoevenagel condensation reaction of a carbonyl group
with the methylene group activated by two electron
withdrawing groups is an important CꢀC bond coupling
reaction and has been continually employed in the producing
of pharmaceutical products and fine chemicals. In addition,
it is also a typical model reaction to analyse the activity of a
variety of base catalysts. Very recently, some porous CPs
containing potential coordinatively unsaturated metal sites
shown in Fig.7, in the final 3D framework, owing to the
coordination of TPT ligands, each Co (COO) unit connects
2
4
four binuclear units and two pairs of TPT ligands, serving as
ꢀconnected node. Topologically, the overall 3D structure of
CP5 can be therefore simplified into a binodal unprecedented
8
2
8
1
2
10
6
3
(
3,8)ꢀconnected net with the point symbol of (4 ·6 ·8 ) (4 )
3 4
with TPT as threeꢀconnected node, according to the TOPOS
2
6
calculations (Fig.8). Differently from the TPT ligands in the
four compounds reported above, three pyridyl nitrogen atoms
(
CUSs) or base groups (such as ꢀNH or ꢀNH) as efficient
2
II
catalyst have been used for Knoevenagel condensation
of TPT all coordinated to Co centres and give the biggest
2
9
reaction to synthesize various malononitrile derivatives.
dihedral angles between the pyrigyl ring and conjoint triazine
o
o
According to the crystal structural analysis, it was found that
only two pyridyl nitrogen atoms in TPT ligand coordinated to
plane (12.20(05) and 16.87(07) , Table 2).
II
Co centres in CPs 1 ꢀ 4, and the left uncoordinated nitrogen
6
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DOI: 10.1039/C7CE01100H
atoms protrude towards the cavities, which serve as good
Lewis basic sites and will facilitate the heterogeneous
3
0
Knoevenagel condensation reaction. Here, the condensation
reaction of benzaldehyde and ethyl cyanoacetate was
performed as test reaction to evaluated the catalytic activities
of these reported five compounds. The typical procedure was
as follows: 0.05 mmol activated CPs 1ꢀ4 and 0.075 mmol
CP5 (corresponding to 0.05 mmol uncoordinated pyridyl
groups in CPs 1ꢀ4) were added to a solution of benzaldehyde
(
5 mmol), ethyl cyanoacetate (10 mmol) and nꢀdodecane (5
mmol as internal standerd) in ethanol (8 mL). The reaction
mixture was stirred vigorously and refluxed in oil bath under
nitrogen atmosphere. During the process, small aliquots of the
supernatant were withdrawn at different time intervals to
monitor the reaction conversion by GCꢀMS. The time
dependence of benzaldehyde conversions are illustrated in
Fig. S5 and selected data are given in Fig.9. In all cases, the
reactions of benzaldehyde and ethyl cyanoacetate in the
presence of CPs 1ꢀ5 yielded only the ethyl(E)ꢀαꢀ
cyanocinnamate product and thus the selectivity for ethyl(E)ꢀ
αꢀcyanocinnamate is 100%. It was interesting to observe that
CP2 and CP3 showed good catalytic activities for the
condensation reaction, and gave ethyl(E)ꢀαꢀcyanocinnamate
as the only the condensation adduct with about 91.3% and
Fig. 9 Knoevenagel condensation reaction of benzaldehyde and ethyl
cyanoacetate catalyzed by different catalysts. Conditions: benzaldehyde
(5 mmol), ethyl cyanoacetate (10 mmol), solvent: ethanol (8 mL), 60 C
o
for 2h, catalyst: 0.05 mmol CPs 1ꢀ4.
Scheme 4 The oxidation of styrene catalyzed by CPs 1ꢀ5.
The selective oxidation of alkenes, catalyzed by both
homogeneous and heterogeneous catalysts, is also important
reaction not only for fundamental study but also for fine
9
4
4
6.6% conversions after 120 min (TOF value was 45.6 and
8.3h , respectively). For CP1 and CP4, only 69.5% and
8.4% yield were obtained, which were somewhat lower than
ꢀ
1
31
chemical products in the industry. Herein, the heterogeneous
catalytic activity of the five Coꢀbased CPs was carried out
t
CP2 and CP3. For comparison, the blank experiment without
any catalysts led to only 12% conversion after 120 min under
the same conditions, which ensured that CP2 and CP3 were
indeed responsible for the high catalytic activities. We also
evaluated the catalytic activity of CP5. The results show that
there is no markedly improved catalytic efficiency (17.1%
conversion in 120 min) for CP5, which is consistent with its
structural characteristic: all pyridyl nitrogen atoms of TPT
using tertꢀbutyl hydroperoxide ( BuOOH) or H O as oxidants
2
2
and styrene as model substrate in MeCN solvent. In a typical
reaction: the 50 mL flask containing the activated CPs 1ꢀ5
was charged with a given amount of styrene (10 mmol),
t
BuOOH or H O (20 mmol) and pyrene (15µL as an internal
2
2
standard) in MeCN (12 mL). The reaction mixture was stirred
o
with a stir bar and kept at 70 C for 20 h in oil bath under
static nitrogen atmosphere. Aliquots of the supernatant were
withdrawn at different time intervals and immediately
monitored by GCꢀMS.
The results obtained for the catalytic reactions in the presence
of different catalyst are summarized in Table 3. The blank
reaction in the absence of any catalyst gave a conversion of
only 15%. For comparison, the introducing CPs 1ꢀ5 can lead
to significant increase in the conversion (entries 1ꢀ6),
indicating that CPs 1ꢀ5 are active in catalyzing the
epoxidation of styrene. Notably, ours results suggest that the
II
ligand join to the Co centers, and there is no open basic site
for catalysis reactions, although the three triazine nitrogen
atoms may also contribute the catalytic activity. To check the
heterogeneities of CP3 in the condensation reaction, a control
filtration experiments was carried out (Fig.S6). After the
reaction mixture proceeded for 30 min (45% conversion),
removal of the catalyst of CP3 via filtration led to the
complete shut down of the reaction, which suggested the
catalytic reaction of CP3 was heterogeneous in nature. The
high catalytic activity of CP2 and CP3 was maintained after
four cycles. The IR and PXRD patterns show similar curves
with the asꢀsynthesized samples, but with some slight
decreases of peaks intensities after the catalysis process,
indicating remaining of the crystalline and frameworks (Fig.
S3 and S7).
CP2 containing NO ꢀBDC as bridging ligand is more active
2
(96% conversion after 20h) than the other CPs, which was
compared with the previously reported Coꢀbased CPs as
3
2,33
heterogeneous catalysts,
although all compounds contain
the similar binuclear Co (COO)4 unit. A higher conversion
2
(75%) was observed using Co(NO ) salt as homogenous
3
2
II
catalyst, indicating the Co centres as active site in the
epoxidation reaction. When H O was used as the oxidant, CP2
2
2
and CP5 achieved relatively low styrene conversion (13% and
%, respectively), which maybe due to the rapid decomposition
of H O into O in the initial stage. The recycling studies were
2
2
2
2
also performed using the CP2 and CP5. After four cycles,
there is ca.10% reduction of the conversion compared with the
fresh synthesized samples, which maybe caused by the loss of
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DOI: 10.1039/C7CE01100H
the catalysts during the filtration and partly decrease of the
crystallinities during the reaction process (Fig S3).
interlinked by TPT ligands into 3D network with CdS net
topology. CP2, CP3 and CP4 are isomorphous and all exhibit 3D
frameworks with pcu (αꢀPo) topology based on the Co (COO)
As shown in Table 3, the oxidation of styrene under yielded
three products: styrene oxide (A), benzaldehyde (B),
phenylacetaldehyde (C). In all cases, the phenylacetaldehyde is a
minor product (less than 8%). With CP1, CP3 and CP4 as
catalysts, the selectivity for benzaldehyde (higher than 60%) is
always higher than that for styrenen oxide, while CP2 and CP5
favor styrene oxide (66% and 76%, respectively), but
benzaldehyde was the dominant product using H O as oxidant
2
4
binuclear unit. In CP5, the Co (COO) units are firstly linked into
2
4
t
threeꢀdimensional NbO net by BuꢀBDC ligands, which are
further accommodated by the sizeꢀmatching trigonal TPT ligands
into novel (3,8)ꢀconnected net. The catalytic measurements show
that CP2 and CP3 are good catalysts for Knoevenagel
condensation reaction of benzaldehyde with ethyl cyanoacetate
and give 91.3%, and 96.6% conversions in 120 min, respectively,
compared with the other present compounds. Furthermore, CPs
1ꢀ5 have also been investigated as heterogeneous catalysts for
2
2
for CP2 and CP5 (entries 10, 11), which have also been
1
0b
observed in previous literatures. Recently, J. Boonmak have
II
t
also reported one Co ꢀbased CPs that can catalyze the
epoxidation of styrene with BuOOH as oxidant in acetonitrile.
epoxidation of styrene with high conversion (86%) and
The results suggest that CP2 and CP5 exhibit high conversion
relatively low selectivity (25%) compared with CP2 and CP5
and selectivity to the epoxidation of styrene.
(entry 12).
Table 3. Catalytic data for the selective epoxidation of styrene over CPs
Acknowledgement
a
1
ꢀ5
We are thankful the financial supported from Science and
Technology Development of Shanghai (14ZR1447900), the
starting up foundation from Shanghai Institute of Technology
(YJ2015ꢀ32).
Entry
Catalyst
Oxidant Time (h) Conv Selectivity Ref.
c
(%)
b
(
%)
15
40
96
68
65
63
75
88
53
13
2
A
9
B
C
t
t
t
t
t
t
t
t
t
1
2
3
4
5
6
7
8
9
No catalyst
CP1
BuOOH
BuOOH
BuOOH
BuOOH
BuOOH
BuOOH
BuOOH
BuOOH
BuOOH
20
20
20
20
20
20
24
20
20
24
24
20
24
24
6
91 0 Herein
33 66 1 Herein
66 28 6 Herein
31 67 2 Herein
34 61 4 Herein
76 17 7 Herein
45 51 4 Herein
68 25 7 Herein
77 19 4 Herein
15 85 0 Herein
22 78 0 Herein
CP2
CP3
CP4
CP5
References
a
School of Chemical and Environmental Engineering, Shanghai Institute
of Technology, Shanghai 201418, China. Eꢀmail: jianyong1106@163.com,
wdeng@sit.edu.cn.
Co(NO
3
)
2
d
CP2
CP5
d
1
(a) S. R. Batten, S. M. Neville, D. R. Turner, Coordination Polymers
Design, Analysis and Application; The Royal Society of Chemistry:
London, 2009; pp 273ꢀ372; (b) H. Furukawa, K. E. Cordova, M.
O’Keeffe, O. M. Yaghi, Science, 2013, 341, 1230444; (c) S. R.
Batten, N. R. Champness, X.ꢀM. Chen, J. GarciaꢀMartinez, S.
Kitagawa, L. Öhrström, M. O’Keeffe, M. P. Suh, J. Reedijk.
CrystEngCom, 2012, 14, 3001.
1
1
1
1
1
0
1
2
3
4
5
CP2
H
H
2
O
O
2
CP5
2
2
2
t
[Co(L )(bpa)]
n
BuOOH
86
75
68
25
63 37
57
ꢀ
ꢀ
0
ꢀ
33a
33b
33b
33c
1
[Co(L )(bpe)]
n
H
H
2
O
O
2
1
[Co(L )(bpee)]
n
2
2
ꢀ
1
Co
6
ꢀCp
O
2
94.2 76.8 ꢀt
ꢀ
a
Condition: styrene (10 mmol); catalyst (0.2 mmol%); BuOOH or
(20 mmol); acetonitrile (12 mL) and pyrene (15µL, as an
2
3
D. Farrusseng, (Ed.), MetalꢀOrganic Frameworks: Applications from
Catalysis to Gas Storage, WileyꢀVCH, Weinheim, 2011.
2 2
H O
o
internal standard); 70 C for 20h. Aꢀstyrene oxide, Bꢀbenzaldehyde,
Cꢀphenylacetaldehyde. Determined by GCꢀMS. Epoxide yield /
b
c
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d
conversion%. the fourth cycle.
Some Coꢀbased CPs has been used as selfꢀsupported catalysts
for the epoxidation of alkenes with good activity in recent
literatures. However, only very few octahedral Coꢀbased CPs
as heterogeous catalysts have been reported. Based on the
inꢀdeep study of our experimental results and relevant
literatures, we found that the possible mechanism for the
epoxidation reaction may be a radical epoxidation, involving the
formation of a Co(III)ꢀperoxy adduct, the release of BuOO•
radical species, and the regenerates of Co(II) CPs, which are
similar to that for the reported Co(II) catalyst.
4
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In summary, by regulation the substituted functional groups on
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TPT as auxiliary ligands, and all compounds are constructed from
the Co (COO) binuclear unit, connected by the mixed 5ꢀ
2
4
substituted isophthalic acid and TPT ligands. In CP1, the
binuclear Co (COO) units are bridged into 1D chains extended
2
4
along two directions ([1 1 0] and [ꢀ1 1 0]), which are further
8
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