Cobalt-based 3D metal-organic frameworks: Useful candidates for olefin epoxidation at ambient temperature by H2O2

Article abstract of DOI:10.1002/ejic.201300560

Two new 3D metal-organic frameworks (MOF), [Co(H₂-DHBDA)(bpe)] _n (1) and [Co(H₂-DHBDA)(bpee)]_n (2) [H ₂-DHBDA = 2,5-dihydroxy-1,4-benzenediacetate, bpe = 1,2-bis(4-pyridyl)ethylene, bpee = 1,2-bis(4-pyridyl)ethane], were synthesized hydrothermally. Both compounds have a similar 3D structure. The secondary building unit is a Co₂ dimer with a Co···Co distance of 4.02 A. The hydroxy groups remain free on the surface of the compounds, and they participate in the intramolecular hydrogen bonding. A detailed structural analysis revealed that the structure is a 7-c uninodal net with the Schlaefli symbol 3³.4¹³.5⁴.6 and the vertex symbol [3.3.3.4.4.4.4.4.4.4.4.4.4.4.4.*.*.*. *.*.*]. The compound is catalytically active towards epoxidation reactions in heterogeneous medium with H₂O₂ as an oxidant. They catalyze the epoxidation of almost all types of olefinic substrates with good efficiency. After the reaction, the catalysts can be recovered quite easily, and they can be used for further reactions without any loss of activity for several cycles. Two cobalt-based metal-organic frameworks were synthesized and characterized by single-crystal X-ray diffraction analysis. Both compounds show an interesting 7-c net structure and are catalytically active towards epoxidation reactions, and they can be recycled up to five times without loss of activity. Copyright

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DOI:10.1002/ejic.201300560
Cobalt-Based 3D Metal–Organic Frameworks: Useful
Candidates for Olefin Epoxidation at Ambient
Temperature by H2O2
Rupam Sen,*[a] Debraj Saha,[b] Dasarath Mal,[a] Paula Brandão,[a]
and Zhi Lin*[a]
Keywords: Heterogeneous catalysis / Cobalt / Epoxidation / Hydrothermal synthesis / Structure elucidation
Two new 3D metal–organic frameworks (MOF), [Co(H2-
DHBDA)(bpe)]n (1) and [Co(H2-DHBDA)(bpee)]n (2) [H2-
DHBDA = 2,5-dihydroxy-1,4-benzenediacetate, bpe = 1,2-
structural analysis revealed that the structure is a 7-c unin-
odal net with the Schläfli symbol 33.413.54.6 and the vertex
symbol [3.3.3.4.4.4.4.4.4.4.4.4.4.4.4.*.*.*.*.*.*]. The com-
pound is catalytically active towards epoxidation reactions in
heterogeneous medium with H2O2 as an oxidant. They cata-
lyze the epoxidation of almost all types of olefinic substrates
with good efficiency. After the reaction, the catalysts can be
recovered quite easily, and they can be used for further reac-
tions without any loss of activity for several cycles.
bis(4-pyridyl)ethylene, bpee
=
1,2-bis(4-pyridyl)ethane],
were synthesized hydrothermally. Both compounds have a
similar 3D structure. The secondary building unit is a Co2
dimer with a Co···Co distance of 4.02 Å. The hydroxy groups
remain free on the surface of the compounds, and they par-
ticipate in the intramolecular hydrogen bonding. A detailed
tential applications in fields ranging from catalysis to gas
adsorption. It is well reported that bifunctional dicarboxyl-
ates can bridge various metal ions, affording a lot of highly
porous and catalytically active frameworks.[6] The group of
Yaghi has developed a family of compounds based on a
structural arrangement, in which the pore size may be tuned
over a wide range. By using longer or shorter organic mole-
cules of similar geometry, Yaghi et al. have now prepared
16 variations of the MOF-5 structure with pores varying in
diameter from 3.8 to 28.8 Å.[7] By tuning the porous chan-
nel, one can rationalize adsorption and catalytic properties
within the pores of the materials.
Among the recent developments in the application of
MOF materials as catalysts, the epoxidation of alkenes is
one of the basic reactions in the industry, because epoxides
are the key intermediate for the syntheses of several valu-
able organic products.[8] By using stoichiometric amounts
of peroxy acids we can successfully isolate epoxy olefinic
products, which are widely used in the industrial synthesis
of fine chemicals.[9] Hydrogen peroxide is the most attract-
ive green oxidant, as it is environmentally benign and also
quite cheap, and it affords water as the only waste product,
which also simplifies the isolation of the desired prod-
uct.[10,11] To date, a few truly heterogeneous and recyclable
MOF-based catalysts have been established in the literature
for H2O2-based alkene epoxidation, and the exploration of
such catalysts is still a challenge for many chemists. The
heterogeneous catalytic process, which eliminates the sepa-
ration problem and reduces the generation of waste prod-
ucts is of prime importance.[12] In this regard, the hetero-
Introduction
There has been a rapid development in the synthesis and
application of metal–organic frameworks (MOF) during
the last decade. A lot of effort has been invested to ration-
ally design MOF materials in the fields of gas adsorption
and storage, catalysis, and magnetic materials.[1–3] Among
the different connecting ligands, aliphatic and aromatic car-
boxylic acids (mono-, di-, tri-, etc.) proved to be the most
demanding candidates, and their use led to a large class of
desired MOFs. Notably, carboxylates have versatile bridg-
ing modes; they can act as monodentate or bidentate li-
gands, or they can have an even higher denticity.[4,5] Because
of their different coordination modes of syn–syn, syn–anti,
and anti–anti they are capable of tuning the effective mag-
netic moment and also the surface properties of the MOFs.
Moreover, the bridging carboxylate ligands can be function-
alized and also post-modified quite easily. Framework ma-
terials with carboxylates have a wide range of structural
properties (from rigid to flexible). One can tune their struc-
ture by introducing an appropriate ligand according to the
desired properties. It is worth mentioning that MOFs with
large pores are of wide interest because of their many po-
[a] Department of Chemistry, CICECO, University of Aveiro,
3810-193 Aveiro, Portugal
E-mail: rupamsen1@yahoo.com
zlin@ua.pt
Homepage: http://www.ciceco.ua.pt/
[b] Department of Chemistry, Jadavpur University,
Kolkata 700032, Kolkata, India
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300560.
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geneous catalytic process is superior over the homogeneous main difference between the structures of 1 and 2 is the
process because of the easy recovery and the solution sta- middle C–C bond length of the bridging amine ligand
bility. Several approaches have been made to heterogenize (1.33 Å and 1.53 Å for 1 and 2, respectively). To further
homogeneous systems in various catalytic reactions includ- understand the structure of 1, a topological analysis was
ing the oxidation of C–H bonds or epoxidation reactions. performed by reducing the multidimensional structure to
Besides the traditional strategy of using polymer-supported a simple node-and-linker net. The topological analysis by
homogeneous complexes,[13] other new efforts, such as en- TOPOS[20] revealed that the structure is a 7-c uninodal net
capsulating molecular complexes in zeolites,[14] using poly- with the Schläfli symbol 33.413.54.6 and the vertex symbol
oxometalate(POM)–phosphonate cluster compounds,[15] [3.3.3.4.4.4.4.4.4.4.4.4.4.4.4.*.*.*.*.*.*].
The
hydroxy
mineral-based materials,[16] nanoparticle-based catalyst,[17] groups remain free on the surface of the compounds, and
etc., and most remarkably, building up porphyrin-based they participate in intramolecular hydrogen bonding
metal-encapsulated MOFs, have recently been intro- {O(11)–H(11)·· O(16) [-x + 1, –y + 2, –z + 1], O(12)–H(12)
duced.[18] More convincingly, in contrast to these systems, ·· O(1) and O(12)–H(12)·· O(15) [x-1/2, –y + 3/2, z-1/2]
the direct use of MOFs as the catalyts is of wide interest. (Table S2)}.
Recently a few MOFs have been developed, which are cata-
lytically active. Herein, in continuation of our work, we in-
troduce a new 3D carboxylate MOF, which can be used as
a heterogeneous catalyst for olefin epoxidation reactions. In
the present work, we used a new dihydroxy dicarboxylate,
2,5-Dihydroxy-1,4-benzenediacetic acid (H2-DHBDA), to
construct the 3D MOFs. In the literature there are very lim-
ited results reported for this dicarboxylate ligand. Cheng et
al. constructed a 1D compound with Zn and 2,2Ј-bipyr-
idine,[19a] and in another study Zhang et al. reported a 1D
coordination compound containing Cd and phenanthrolin
as the blocking amine.[19b] In this paper, we report two new
MOFs, [Co(H2-DHBDA)(bpe)]n (1) and [Co(H2-
DHBDA)(bpee)]n (2) [bpe = 1,2-bis(4-pyridyl)ethylene, bpee
= 1,2-bis(4-pyridyl)ethane], which are well stable in the re-
action medium and capable of catalyzing epoxidation reac-
Figure 1. Polyhedral representation of compound 1 with the carb-
oxylate ligands.
tions with H2O2 as the oxidant. Remarkably, they can be
used for several cycles with good selectivity and without
any loss of activity.
Results and Discussion
X-ray Structure of Compounds 1 and 2
Both compounds crystallized in the space group P21/n
with Z = 4. ORTEP diagrams of compounds 1 and 2 with
an atom numbering scheme are shown in Figures S1 and
S2. A summary of bond lengths and angles is presented in
Table S1. Because both compounds have a similar structure,
only compound 1 is discussed here in detail. The asymmet-
ric unit of compound 1 contains one independent cobalt(II)
center in a distorted octahedral coordination environment.
The basal plane is formed by the two chelating oxygen
atoms (O15 and O16) and two bridging O atoms from three
carboxylato groups (O1 and O2). The axial positions are
occupied by two nitrogen atoms (N17 and N28) from two
bridging co-ligands. The secondary building unit is a Co2
diad. The two Co centres are linked by two bridging biden-
tate carboxylate groups (Co···O1–C3–O2···Co) to form a
Figure 2. Polyhedral 3D representation of compound 1 with the
bridging amine ligands.
Thermogravimetric Analysis
Thermogravimetric (TG) analyses between room tem-
Co2 paddlewheel unit with a Co···Co separation of 4.02 Å perature and 800 °C show the high thermal stability of com-
(Figure 1). These carboxylate groups bridge the metal ions pounds 1 and 2. Upon increasing the temperature, there
to form 2D layers through the crystallographic ab plane was no mass loss up to 200 °C for both compounds. Com-
(Figure 1), which are further connected by the bridging pound 1 is somewhat more thermally stable (up to 295 °C)
amines to ultimately form a 3D network (Figure 2). The than the compound 2. Whereas compound 2 starts to de-
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grade at approximately 215 °C and spontaneously loses Table 1. Epoxidation of olefins catalyzed by compounds 1 in aceto-
nitrile.[a]
mass until complete decomposition at 610 °C, compound 1
starts to lose mass at approximately 295 °C, and its decom-
position completes at 600 °C (Figure S3). These results
clearly indicate that the compounds are highly stable and
can be used for catalytic reactions at higher temperatures.
Catalytic Epoxidation Reactions
Olefin epoxidation reactions catalyzed by various MOFs
and molecular complexes have been reported in the litera-
[21]
ture with H2O2
or TBHP[22] as oxidants, but there are
limited studies, where the materials used as catalysts show
true heterogeneity. Many approaches have been made in the
literature to develope heterogeneous MOF catalysts. A new
cobalt-based carboxylate framework has recently been in-
troduced for different olefin epoxidations.[22d] In other stud-
ies, Volkmer and co-workers described the epoxidation of
cyclohexene by using pyrazolate MOFs.[22a–22c] In further
studies, a metalloporphyrin-encapsulated zeolite-like 3D
MOF has been used for the heterogeneous oxidation of cy-
clohexane.[23] In our previous attempt, we reported layered
metal carboxylates and lanthanide-based MOFs, which
show good activity in epoxidation reactions of olefins under
heterogeneous conditions.[24,25] In contrast to these systems,
in this study we introduce a new 3D MOF, which is active
towards epoxidation. The catalytic activity of 1 can be sum-
marized on the basis of the results shown in Table 1. Be-
cause the structures of 1 and 2 are very similar, all the reac-
tions were performed by using compound 1, and to confirm
the catalytic activity of compound 2, we tested it with two
substrates under the same reaction conditions used for 1.
Compound 1 catalyzes the epoxidation of almost all kinds
of alkenes: terminal linear, cyclic, styrene, substituted styr-
ene, stilbene, and also limonene (conversion plot derived
[a] Reaction conditions: olefin (10 mmol); catalyst (2 mg); 1.5 mL
of 30% H2O2 (14.4 mmol, 1.5 equiv.); solvent (10 mL); temperature
40 °C. The products of the catalytic reactions were collected at dif-
ferent time intervals and were identified and quantified by using a
Varian CP-3800 gas chromatograph equipped with an FID detector
and a packed column. The results of the catalytic reactions are
given here after 24 h of reaction. [b] Turnover frequency (TOF):
mole converted per mol of active site per hour. [c] 2-Cyclohexen-1-
ol. [d] Benzaldehyde. [e] 4-Methylbenzaldehyde. [f] Limonene oxide.
[g] Unidentified product.
Although terminal alkenes need higher activation ener-
from the GC data is shown in the Supporting Information gies, we got fair conversions of 88 and 71% for 1-hexene
S4–S11). As examples of cyclic olefins, cyclohexene and cy- and 1-octene, respectively, with oxide as the sole product,
clooctene were used. Cyclohexene was successfully con- which clearly demonstrates the good efficiency of the cata-
verted up to 82% with an epoxide selectivity of 36% at lyst. To study conjugated olefins, styrene and 4-methylstyr-
40 °C. For the cyclohexene oxidation, it is quite a challenge ene were used. The substrates were converted with 75 and
to increase the oxide yield. Hwang et al. recently used a 80% efficiency, respectively, and the product selectivity re-
carboxylate MOF (Ni–dihydroxyphthalate) for the oxi- mained around 63 and 48%, respectively, with benzalde-
dation of cyclohexene, and a maximum conversion of hyde as the usual corresponding by-product. Generally, in
39.7% was achieved at 60 °C, but the TOF remained within the epoxidation of styrene catalyzed by transition metal im-
the range of 11.8.[26] Kholdeeve et al. achieved a good selec- mobilized on zeolites or supported molecular catalysts, ep-
tivity of 80% with a conversion of 84% at 50 °C by using oxide yields of higher than 40% are hardly found in earlier
a polyoxometalate/MIL-101 composite material.[27] In an- studies.[25] Recently, we succeeded in improving the yield of
other study, Janiak and co-workers introduced a series of styrene epoxide to up to 72% by using a layered transition
Mn-based dicarboxylate frameworks, with which they got metal carboxylate MOF.[24] In another recent attempt,
good epoxide yields of 64% at 60 °C.[28] We also achieved Kholdeeva et al. highlighted a good example of using a
quite a good epoxide selectivity for the oxidation of cyclo- MIL-101/POM composite, with which they successfully in-
octene. Cyclooctene was successfully converted with 100% creased the epoxide selectivity to up to 73%, but the conver-
epoxide selectivity and a maximum conversion of 86%. Jan- sion remained low (30%).[27] Compound 1 exhibited a good
iak et al. reported a highest selectivity of 75% by using efficiency for the trans-stilbene oxidation. After 24 h, we got
the Mn–MOFs as catalysts.[28] Kholdeeva and co-workers 63% of conversion with 100% of product selectivity, which
recently presented another example of the cyclooctene oxi- is quite remarkable with respect to the recently reported
dation by using a MIL-101/polyoxometalate based catalyst, results. Janiak el al recently used Mn–carboxylate MOFs
achieving 99% selectivity and a conversion of 76%.[27]
for trans-stilbene oxidation, but their selectivity did not ex-
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ceed 7%.[28] In contrast to these systems, Kholdeeva et al. mum polarity of the solvent, which is needed for a higher
successfully achieved a good epoxide selectivity of 69%, but conversion of the substrates. To monitor the temperature
the conversion again remained around 35%.[27] A different effect, we tuned the reaction temperature from 30–60 °C for
substrate, limonene, was also subjected to oxidation reac- the epoxidation of cyclooctene and 1-hexene, a good yield
tion; the conversion was good (78%) with a product selec- with good product selectivity was obtained at a moderate
tivity of 81% and along with some unidentified products. temperature of 40 °C. At higher temperatures the conver-
A comparison of the catalytic performances on the basis of sion decreases, as H2O2 starts to degrade at higher tempera-
different Co-based catalysts has been accumulated in tures, which clearly demonstrates the vital influence of the
Table 2. The overall reaction study shows that this new temperature on the reaction course (Figure 4).
compound is a good candidate for catalyzing the epoxid-
ation of olefins in a heterogeneous medium at moderate
temperatures, and no induction period was observed in any
of the catalytic reactions. On the other hand, Compound 2
was also employed for the oxidation of cyclooctene and
styrene. This framework also shows similar reactivity for
these oxidation. With cyclooctene, after 24 h, it achieved up
to 78% of conversion with 100% epoxide selectivity, and
with styrene, it produced 57% epoxide with a conversion of
68%.
Table 2. Epoxidation of olefins catalyzed by a variety of Co-based
catalysts.[a]
Catalyst
Conversion Yield of product [%] TOF Ref.
[wt..-%] Epoxide Others
Cyclohexene
Figure 3. Catalytic efficacy of 1 in different solvents. Reaction con-
ditions were the same as given in the footnote of Table 1.
[29d]
[22a]
[Co(BPB)]·3DMF 62
MFU-1
Compound 1
17
34
36
83
66
64
3.66
–
79
27.5
82
t.w.
Styrene
[22d]
[29a]
[Co(Hoba)2]
Co(cyclam)-
SBA-15
96
40
96
66
4
–
–
Compound 1
75
63
37
–
73
t.w.
trans-Stilbene
[22d]
[Co(Hoba)2]
Compound 1
86
63
100
100
–
52
t.w.
[a] Reaction conditions were the same as given in the footnote of
Table 1; t.w.: this work.
To observe the nature of the catalyst and to optimize the
reaction conditions, we carried out some control experi-
ments, varying different reaction parameters. At first we
studied the oxidation reaction of cyclooctene without the
MOF catalyst at the same reaction conditions, but after
Figure 4. Catalytic efficacy of 1 at different temperatures. Reaction
conditions were the same as given in the footnote of Table 1.
Thus, the overall reaction study shows that this com-
24 h we did not get any conversion of the substrate. We pound is active and efficient besides the results published
also studied the reaction under homogeneous conditions by in recent studies.[25–28] To find out the surface nature of the
using Co(NO3)2 as the catalyst, but we only got a very poor MOFs, we carried out nitrogen adsorption studies, but
conversion of 5%, which proves the activity of the present there was no measurable pore volume found in the MOFs,
catalyst. We examined the epoxidation of 1-hexene and cy- which clearly indicates that there is no appreciable void
clooctene in six different solvents to find the optimal sol- space to accommodate any guest molecule within the pore.
vent. The best conversion and selectivity were found in ace- Therefore, we assume that the catalysis reaction takes place
tonitrile. This can be explained as follows: the optimum po- at the surface of the compounds and not in the pores. To
larity of the acetonitrile might be alleviating by allowing understand the pathway of the reaction, it can be assumed
both the oxidant and the substrate in the same solution that for the H2O2 catalyzed epoxidation the general reaction
phase to carry out the epoxidation reaction smoothly. proceeds through the CoIII–peroxido intermediate by a con-
The
conversion
decreased
in
the
order certed oxygen atom transfer to the double bond to yield
CH3CNϾCH3COCH3 ϾCHCl3 ϾCH2Cl2 ϾEtOHϾMeOH the epoxide. The proposed mechanism for the oxidation of
(Figure 3). This study evidences the necessity of the opti- alkene with H2O2 is illustrated in Scheme 1. The reversible
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redox cycle from CoII to CoIII to CoIV and back to CoII, catalyst convincingly demonstrates that the structural integ-
which involves the formation of a peroxo species and an rity of the complex 1 remained unaffected after the epoxid-
oxygen atom transfer, is the key factor for these catalytic ation reactions (Figures S12 and S13). Notably, the reco-
oxidations.[29a] Similar mechanisms via metal–peroxido in- vered catalyst can be reused in further epoxidation reactions
termediates have been proposed in earlier studies.[29a–29c]
without any considerable loss of activity (Figure 5).
Figure 5. Catalytic activity of 1 in different catalytic cycles. Reac-
tion conditions were the same as given in the footnote of Table 1.
Conclusions
In summary, two new 3D frameworks were prepared and
characterized by X-ray diffraction analyses. Both com-
pounds have similar interesting 3D structures. The com-
pounds are capable of catalyzing the epoxidation reaction
in heterogeneous medium with H2O2 as the oxidant. The
compound is equally active with all types of olefinic sys-
tems. The frameworks behaved as heterogeneous catalysts,
can be easily recovered after reaction by filtration and
washing, and can subsequently be used without significant
catalyst deactivation due to either leaching of active species
or degradation of the structure. This study affords a new
outlook for the design of new MOF oxidation catalysts.
Scheme 1. Proposed mechanism for the epoxidation reaction cata-
lyzed by compound 1.
Separation, Catalyst Reuse, and Heterogeneity Test
The main advantages of the use of heterogeneous cata-
lysts are the easy recovery of the catalyst from the reaction
mixtures and its reuse. To test the leaching of the solid cata-
lyst during reaction, the liquid phase of the reaction mix-
ture was collected by filtration at the reaction temperature
after 30% of the epoxidation reaction was completed, and
the residual activity of the supernatant solution after sepa-
ration of the catalysts was studied. Now, the organic phase
of a first run was separated from the catalyst, and the com-
position of the reaction mixture was determined by gas
chromatography. This homogeneous reaction mixture was
treated as a standard catalytic experiment. After 6 h of
maintaining the reaction conditions, the composition was
re-determined, and no progress of the reaction was ob-
Experimental Section
Materials and Physical Measurements: Cobalt nitrate hexahydrate,
2,5-dihydroxy-1,4-benzenediacetic acid, 1,2-bis(4-pyridyl)ethane,
1,2-bis(4-pyridyl)ethylene, 1-hexene, 1-octene, cyclohexene, cyclo-
octene, styrene, 4-methylstyrene, trans-stilbene, and limonene were
purchased from Aldrich and were used as received. 30% H2O2 was
purchased from Merck India and used as received. FTIR spectra
served, which confirms the absence of active species in the of samples suspended in KBr pellets were measured with a Unican
Mattson Mod 7000 spectrophotometer equipped with a DTGS CsI
detector. Thermogravimetric analyses (TGA) were carried out by
using a Shimadzu TGA 50 with a heating rate of 5 °Cmin–1 under
a continuous stream of nitrogen with a flow rate of 20 cm3 min–1.
Elemental analyses (CHN) were performed by using a Perkin–El-
mer 240 elemental analyzer. The products of the catalytic reactions
were identified and quantified with a Varian CP-3800 Gas Chroma-
tograph by using a packed column. The powder X-ray diffraction
(PXRD) patterns of the samples were recorded with a Scintag
XDS-2000 diffractometer using Cu-Kα radiation. N2 sorption mea-
solution. These experiments clearly demonstrate that metal
is not leached from the solid catalyst during epoxidation
reactions. To check the stability of the catalysts, we charac-
terized the solids after the reactions were over. After the
catalytic reactions, the solid catalyst was recovered by cen-
trifugation, washed several times with fresh acetonitrile,
and dried in air in an oven. The recovered catalyst was then
subjected to PXRD (powder X-ray diffraction) and IR
spectroscopic analyses. A comparison of PXRD patterns
and IR spectra of the pristine complex and the recovered surements were performed with an Autosorb iQ (Quantachorme
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Inc., USA) gas sorption system at 77 K. Prior to sorption experi-
ments, samples were degassed at the desired temperature (80 °C)
for approximately 3–4 h under vacuum (10–3 Torr).
Table 3. Summary of crystal data and refinement parameters for
compounds 1 and 2.
1
2
Synthesis and Preliminary Characterization of the Compounds
Formula
Mw
C22H18N2O6Co
465.31
C22H20N2O6Co
467.33
Synthesis of the Compounds [Co(H2-DHBDA)(bpe)]n (1) and
[Co(H2-DHBDA)(bpee)]n (2): Both the compounds were synthe-
sized by using a hydrothermal method. Compounds 1 and 2 were
obtained as dark-red needle crystals in a teflon-lined acid-digestion
bomb, after it was kept at 160 °C for 3 d, which was followed by
slow cooling to room temperature. For the digestion, Co(NO3)2
hydrate, 2,5-dihydroxybenzene-1,4-diacetic acid, and 1,2-bpe (for 1)
or 1,2-bpee (for 2) were mixed in a 1:1:1 ratio. The obtained crystals
were washed with ethanol and dried at ambient temperature. For
catalysis, the phase purity of compound 1 was checked by PXRD
(Figure S12). The nitrogen sorption study for compound 1 (Fig-
ure S14) indicates that the framework is not porous in nature.
Yields of 1 and 2 were in the range of approximately 60 and 55%,
respectively, on the basis of the carboxylic acid. [Co(H2-
DHBDA)(bpe)]n (1): calcd. C 56.73, H 3.86, N 6.01; found C 55.94,
a [Å]
b [Å]
c [Å]
β [°]
Crystal system
Volume [Å3]
Z
10.5127(3)
14.4115(5)
13.5983(4)
104.979(2)
monoclinic
1990.19(11)
4
10.2433(5)
14.7641(9)
13.4621(8)
102.984(3)
monoclinic
1983.86(19)
4
Space group
ρcalc [gcm–3]
F(000)
P21/n
1.553
956
0.906
0.0402, 0.0871
1.026
3627
P21/n
1.565
964
0.909
0.0322, 0.0773
1.024
3978
μ(Mo-Kα) [cm–1]
R1, wR2
Goodness-of-fit (S)
Unique reflections
Observed reflections
[IϾ2σ(I)]
4960
4938
H 3.19, N 5.88. Selected IR peaks for 1 (KBr disk): ν = 1618, 1584
˜
Largest diff. peak
0.429, –0.330
0.367, –0.350
–
–
[υas(CO2 )], 1432 [υs(CO2 )], 1329, 1286 [υs(C–O)], and 2900–3200
[br. s, υ(O–H)] cm–1. [Co(H2-DHBDA)(bpee)]n (2): calcd. C 56.49,
H 4.27, N 5.99; found C 55.89, H 4.10, N 6.23. Selected IR peaks
and hole [e– Å–3]
–
–
for 2 (KBr disk): ν = 1608, 1567 [υ (CO )], 1425 [υ (CO )], 1323,
˜
as
2
s
2
Acknowledgments
1292 [υs(C–O)], and 2930–3200 [br. s, υ(O–H)] cm–1.
R. S. thanks the Fundação para a Ciência e a Tecnologia (FCT)
for a postdoctoral fellowship (SFRH/BPD/71798/2010). This work
was also financially supported by the Programa Operacional Ciên-
cia e Inovação 2010 (POCI2010), the Fundo Social Europeu (FSE)
and the Fundo Europeu de Desenvolvimento Regional (FEDER).
X-ray Crystallography: X-ray diffraction data for 1 and 2 were col-
lected with a Bruker SMART APEX CCD X-ray diffractometer by
using graphite-monochromated Mo-Kα radiation (λ = 0.71073 Å).
The determination of integrated intensities and the cell refinement
were performed with the SAINT[30] software package by using a
narrow-frame integration algorithm. An empirical absorption cor-
rection (SADABS)[31] was applied. All the structures were solved
by direct methods and refined by using full-matrix least-squares
techniques against F2 with anisotropic displacement parameters for
non-hydrogen atoms with the programs SHELXS97 and
SHELXL97.[32] The hydrogen atoms of the C–H bonds were placed
at geometrical positions and refined with Uiso = 1.2Ueq of the atom,
to which they are attached, whereas the hydrogen atoms bonded to
hydroxide oxygen atoms were obtained from the last final difference
Fourier maps and refined isotropically. In the final difference Fou-
rier maps there were no remarkable peaks except the ghost peaks
surrounding the metal centres in both the compounds. A summary
of the crystal data and relevant refinement parameters for com-
pounds 1 and 2 are given in Table 3.
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I30560
/KAP1
Date: 22-08-13 10:21:52
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FULL PAPER
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Received: April 29, 2013
Published Online: ᭿
Eur. J. Inorg. Chem. 0000, 0–0
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Job/Unit: I30560
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Date: 22-08-13 10:21:52
Pages: 8
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FULL PAPER
Metal–Organic Frameworks
R. Sen,* D. Saha, D. Mal, P. Brandão,
Z. Lin* ............................................. 1–9
Two cobalt-based metal–organic frame-
works were synthesized and characterized
by single-crystal X-ray diffraction analysis.
Both compounds show an interesting 7-c
net structure and are catalytically active
towards epoxidation reactions, and they
can be recycled up to five times without
loss of activity.
Cobalt-Based 3D Metal–Organic Frame-
works: Useful Candidates for Olefin Epox-
idation at Ambient Temperature by H2O2
Keywords: Heterogeneous catalysis / Co-
balt / Epoxidation / Hydrothermal syn-
thesis / Structure elucidation
Eur. J. Inorg. Chem. 0000, 0–0
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim