Two-fold interpenetrating btc based cobaltous coordination polymer: A promising catalyst for solvent free oxidation of 1-hexene

Article abstract of DOI:10.1016/j.jssc.2017.08.034

This work describes the synthesis of a new 2-D coordination polymer (CP), [Co₃(btc)₂(dmp)₈]_n (btc = 1,3,5-benzenetricarboxylate and dmp = 3,5-dimethylpyrazole) and its catalytic activity towards the oxidation reaction of 1-hexene to form oxygenated compounds under solvent free condition. Structural analysis reveals that Co(II) cations in this polymeric compound are linked by btc^3- anions with alternate tetrahedral/octahedral coordination forming a two-fold interpenetrated 3-connected hcb underlying net. Electronic spectrum of the cobaltous polymer has been calculated using TDDFT/B3LYP method for making the appropriate assignments of electronic transitions. Catalytic results show good conversions of the starting material to oxygenated products with high selectivities for 1,2-epoxyhexane and 1-hexanal.

Full text of DOI:10.1016/j.jssc.2017.08.034

Author’s Accepted Manuscript
Two-fold interpenetrating btc based cobaltous
coordination polymer: a promising catalyst for
solvent free oxidation of 1-hexene
Sanchay J. Bora, Rima Paul, Mithun Nandi, Pradip
K. Bhattacharyya
www.elsevier.com/locate/yjssc
PII:
S0022-4596(17)30341-9
http://dx.doi.org/10.1016/j.jssc.2017.08.034
YJSSC19924
DOI:
Reference:
To appear in:
Journal of Solid State Chemistry
Received date: 9 July 2017
Revised date: 11 August 2017
Accepted date: 24 August 2017
Cite this article as: Sanchay J. Bora, Rima Paul, Mithun Nandi and Pradip K.
Bhattacharyya, Two-fold interpenetrating btc based cobaltous coordination
polymer: a promising catalyst for solvent free oxidation of 1-hexene, Journal of
Solid State Chemistry, http://dx.doi.org/10.1016/j.jssc.2017.08.034
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Two-fold interpenetrating btc based cobaltous coordination polymer:
a promising catalyst for solvent free oxidation of 1-hexene
Sanchay J. Bora*a, Rima Paul,a Mithun Nandib and Pradip K. Bhattacharyyac
aDepartment of Chemistry, Pandu College, Guwahati-781012, Assam, India
bDepartment of Chemistry, Gauhati University, Guwahati-781014, Assam, India
cDepartment of Chemistry, Arya Vidyapeeth College, Guwhati-781016, Assam, India
Tel: +91-361-2570450, E-mail:sanchay.bora@gmail.com
Abstract
This work describes the synthesis of a new 2-D coordination polymer (CP), [Co3(btc)2(dmp)8]n
(btc = 1,3,5-benzenetricarboxylate and dmp = 3,5-dimethylpyrazole) and its catalytic activity
towards the oxidation reaction of 1-hexene to form oxygenated compounds under solvent free
condition. Structural analysis reveals that Co(II) cations in this polymeric compound are linked
by btc3- anions with alternate tetrahedral/octahedral coordination forming a two-fold
interpenetrated 3-connected hcb underlying net. Electronic spectrum of the cobaltous polymer
has been calculated using TDDFT/B3LYP method for making the appropriate assignments of
electronic transitions. Catalytic results show good conversions of the starting material to
oxygenated products with high selectivities for 1,2-epoxyhexane and 1-hexanal.
Graphical Abstract
A new btc based 2-D coordination polymer of Co(II) has been synthesised solvothermally.
Structural analysis reveals the presence of interpenetrating 3-coordinated hcb underlying nets in
the crystal structure of the CP. This polymer is also found to be an excellent candidate towards
the conversion of 1-hexene to various oxygenated products with high selectivity under solvent
free condition.

Keywords: 2-D Coordination polymer, Solvothermal synthesis, Topological analysis, hcb net,
Heterogeneous catalysis, TD-DFT
1. Introduction
Recent advances in the fast growing field of functional coordination polymers (CPs) have led to
numerous developments and is widely practiced area of research across the globe. Specifically,
the chemistry of CPs have provided a range of low-cost porous crystalline materials assembled
from molecular building blocks that exhibit high stability, tunable properties and porosity. Such
inorganic materials with inner cavities are known to bind many organic molecules in the hollow
spaces and often exhibit unique catalytic properties for a number of organic reactions [1-8].
Well-known among this class of materials are frameworks involving the polycarboxylate ligands
that bridge the metal nodes giving rise to robust network topologies. During the past years,

several two- and three-dimensional coordination polymers have been synthesised using transition
metals with carboxylates and N-heterocycles [9-14]. In this context, the highly symmetrical
1,3,5-tricarboxylate (btc) ligand posses interesting features that are beneficial for the
construction of versatile coordination architectures [15-17]. The multicarboxylate groups on the
molecule which, when linked with metal containing units, yield a variety of polymeric and
supramolecular aggregates of metal-carboxylates. For example, the porous btc based
coordination polymer HKUST-1 is a well-studied coordination solid that possesses framework
Cu(II) cations and has widely been used as a catalyst for cyanosilylation of aldehydes/ketones;
hydrosilylation of ketones, oxidation of benzene, toluene, hydroquinone etc. [18]. Aerobic
oxidations of a series of styrenes to give benzaldehyde, styrene oxide and derivatives have been
reported recently using Fe(BTC) polymers under different reaction conditions [19]. It is
noteworthy that metal ions present in these coordination complexes also play an important role in
the oxidation of various organic compounds. Literature reports reveal that a large number of
aromatic compounds can be effectively oxidized with Co(II)/Co(III) complexes under
considerably mild conditions [20-24]. In particular, cobalt complexes with oxygenated ligands
are known as active catalysts in oxidation and epoxidation reactions of hydrocarbons.
Although selective oxidation of alkenes is viewed as an important organic transformation
reaction in chemical industries [25-26], it is very difficult to accomplish it while observing the
perspective of green chemistry [27]. Traditional catalytic procedures involved in the oxidation of
alkenes produce a great deal of environmentally undesirable wastes. As such, it justifies the
investigation of new environment friendly catalysts, which can be used for such oxidation
reactions. Alkene oxidation has, thus become an exciting issue in the field of heterogeneous
catalysis. The key aspects of heterogeneous oxidation reactions using porous coordination

polymers (PCPs) or MOFs have been reviewed recently by Dhakshinamoorthy et al [28]. Several
reports have been made on selective epoxidation of olefins using various transition metal
complexes [29-32].
Taking these points into account, we have been able to construct a new 2-D
coordination polymer by combining btc and dmp with Co2+ ions. Presently, we
demonstrate the use of as-synthesised CP as a catalyst in the oxidation of 1-hexene. Since
there is no need to use any additional solvents for the oxidation, our results also appear to
be significant from the green chemistry point of view.
2. Experimental
All reagents and solvents used in this work were obtained from commercial sources and used
without purification. Trisodium benzenetricarboxylate was prepared by evaporating a NaOH-
neutralized aqueous solution of trimesic acid.
CHN analysis was performed using a Perkin-Elmer 2400 Series II CHNS/O Analyzer.
The FT-IR spectrum was recorded using a Perkin-Elmer RX1 spectrophotometer in the mid-IR
region (4000 to 400 cm-1) for KBr pellets. The UV-vis-NIR (240-2600 nm) diffuse-reflectance
spectra were obtained using a Hitachi U-4100 spectrophotometer equipped with an integrating
sphere. BaSO4 powder was used as reference (100% reflectance). Absorption data were
calculated from the reflectance data using the Kubelka-Munk function (a/S = (1-R)2/2R where a
is the absorption coefficient, R the reflectance and S the scattering coefficient).
Thermogravimetric studies were carried out under a flow of N2 gas using a Mettler Toledo
TGA/DSC1 STARe system at a heating rate of 10° C min-1.
2.1. Synthesis and properties of [Co3(btc)2(dmp)8]n (1)

An aqueous mixturte (25mL) of cobalt nitrate hexahydrate Co(NO3)2.6H2O (0.291 g,1mmol), btc
(Na3C9H3O6) (0.276g, 1mmol) and dmp (C5H8N2) (0.096 g, 1mmol) was placed in a stainless
steel autoclave, which was sealed and placed in a programmable oven. The mixture was heated
at 120°C at 5°C min-1 for 24 hrs followed by further cooling at room temperature. The resulting
violet crystals were filtered, washed with water and then dried in a vacuum desiccator over fused
CaCl2. Yield: 0.31 g (68%). Anal. calcd. for C58H70N16O12Co3: C, 51.30%; H, 5.19%; N,
16.52%; Co, 13.02%. Found: C, 51.22%; H, 5.15%; N, 16.49%; Co, 13.01%. IR spectral data
(KBr disc, cm-1): 3204(w), 3142(w), 3035(w), 2929(w), 2868(w), 1890(w), 1613(s), 1549(s),
1492(m), 1431(s), 1360(s), 1284(m), 1181(m), 1098(m), 1045(s), 939(w), 813(w), 771(m),
715(s), 626(w), 553(m) [s, strong; m, medium; w, weak; br, broad; sh, shoulder]. This non-
hygroscopic solid product is insoluble in water and common organic solvents and it retains its
composition and crystallinity over long periods of time under ambient conditions.
2.2 Computational Details
The ground state geometrical minima of the species are obtained at B3LYP/6-31G(d)
level of theory which are confirmed by the absence of any imaginary frequency.
Observed electronic transitions in the absorption spectra are assigned by using TD-DFT
calculations (on the optimized geometries) using TD method (N = 150 states) at the same
level of theory [33]. The calculations are carried out using Gaussian 09 [34].
2.3 Catalysis
Catalytic oxidation of 1-hexene was carried out with 70 % tert-butyl hydroperoxide (TBHP) in a
25 mL reaction flask equipped with a water condenser. Various parameters such as the molar
ratio, temperature, amount of catalyst and reaction time were optimized maintaining the total
volume of reactants at 5 mL for each run. The catalyst was preheated at 383 K for 3 hr before

every use. The progress of the reaction was monitored by withdrawing the reaction mixture after
definite intervals of time and analyzing by gas chromatography (Bruker 430 GC) fitted with
WCOT fused silica 30 m  0.32 mm column and FID detector. The identities of the products
were confirmed by comparing with the authentic sample.
2.4 X-ray Crystallographic Procedures
Single-crystal X-ray diffraction measurements of 1 was performed on a Bruker SMART CCD
Diffractometer (Mo Kα radiation, λ = 0.710 73 Å) [35]. The crystal structure was solved by
direct methods (SHELXS) and refined by full-matrix least squares technique (SHELXL) with
SHELX-97 [36] using the WinGX [37] platform. The hydrogen atoms in compound 1 were
refined isotropically after placing them at calculated positions using a riding model of
refinement. Crystallographic and structure refinement details are listed in Table 1. The structural
diagrams were drawn using Diamond [38].
Powder X-ray diffraction pattern in the 3-80 2-range was recorded on a Philips X’Pert
PRO instrument using Cu-K radiation (1.5418 Å) at a scan rate of 0.5 sec (0.5 2per step at
40 KV/30 mA. The calculated diffraction patterns assuming Bragg-Brentano geometry were
obtained from results of single crystal structure analyses using PowderCell [39].
3. Results and Discussion
3.1 Crystal Structure of [Co3(btc)2(dmp)8]n
Single crystal X-ray Diffraction analysis shows that the principal building units of
[Co3(btc)2(dmp)8]n are the tetrahedral and octahedral Co(II) centers bridged by the tris-
monodentate btc3- ligands [Fig. 1] Each btc3- anion bridges two neighbouring Co(dmp)2 units
forming a tetrahedral geometry around the Co(II) ion that extends along the crystallographic b-

axis. The btc anions are further connected to Co(dmp)4 units forming an octahedral coordination
of the metal ion in an another direction giving rise to a 2D network structure.
Figure 1 An ellipsoid presentation of [Co3(btc)2(dmp)8]n with anisotropic atoms drawn as
50% probability; only non-hydrogen atoms for the asymmetric unit are labelled.
Table 1 Crystal and structure refinement data for [Co3(btc)2(dmp)8]n (1)
[Co3(btc)2(dmp)8]n
C29H35N8O6Co1.50
680.05
Details
Empirical formula
Formula weight
Temperature/ K
296(2)
Wavelength
Crystal system, space group
0.71073Å
Triclinic, Pī
9.243(2)
a/Å
b/Å
c/Å
°
18.985(5)
19.661(5)
77.58(1)
76.45(1)
89.89(1)
°
°
Volume/Å3
3271.2(15)
4, 1.381
0.822
Z, Calculated density/ gcm-3
Absorption coefficient/ mm-1

F(000)
1414
Crystal size/ mm
0.27 × 0.23 × 0.11
1.10 to 30.09
Index ranges
-12≤h≤12, -26≤k≤26, -27≤l≤27
60001 / 18732 [R(int) = 0.0948]
Full-matrix least-squares on F2
18732 / 0 / 822
Reflections collected/ unique
Refinement method
Data / restraints / parameters
Goodness-of-fit* on F2
Final R indices† [I>2 (I)] R1/ wR2
R indices† (all data) R1/ wR2
Shift / esd max
0.948
0.0471 / 0.1166
0.1351 / 0.1404
0.001
Largest diff. peak and hole /e.Å-3
0.616 and -0.912
†wR2 = {

[ w(Fo –Fc2)2 ] /

[ w(Fo ) ] }1/2; R1 =

| |Fo| – |Fc| | /

|Fo *GooF = S = {

[w(Fo - Fc2)2]
2
2 2
2
/ (n-p)2}1/2
The two atoms, Co(1) and Co(3), coordinate two oxygens (of btc3-) and two nitrogens (of
dmp) in corners of tetrahedron [Fig. 2a] . CoO/N bond distances for these two Co2+ centers are
found within the range of 1.939(2)Å2.025(2)Å, which are comparable to those reported for
similar tetrahedral Co(II) coordination spheres [40-43]. The observed bond angles involving
CoN2O2 coordination around Co(1) and Co(3) centers are ranging from 105.61(9)°–113.27(10)°
and 105.35(9)°–113.38(9)° respectively, indicating the distorted nature of tetrahedral geometries.
Other two atoms, Co(2) and Co(4), have an octahedral coordination: two oxygen (of btc3-) atoms
in axial (trans) positions and four nitrogen (of dmp) in equatorial positions [Fig. 2b]. The
corresponding CoO (trans) bond lengths are 2.141(2) Å and 2.140 (2)Å for Co(2) and Co(4)
centers respectively, which are little shorter than the equatorial CoN bond lengths ranging from
2.171(2) to 2.204(2)Å. These coordination bond lengths indicate that Co2+ ions adopt distorted
octahedral geometry and are in good agreement with the other reported complexes of CoN4O2
coordination [44-46]. Each btc-ligand is connected to three Co2+ cations, and each Co2+ cation
coordinates two btc3- anions. Additionally, terminal dmp ligands are coordinated to Co2+ cations.
It is worth noticing that the polymers in the crystal structure of 1 are assembled into 3-D

supramolecular structure via hydrogen bonds and CH interactions. In fact, the resulting
network architecture is reinforced by 14 different (Table S2 in ESI) intermolecular N/CH…O
bonds between btc and dmp ligands. According to graph set approach [47], the hydrogen bonded
2
1
1
2
network is found to consist of supramolecular rings of notation R1 (3), R1 (6), R1 (7), R2 (6),
3
R3 (9) etc. as shown [Fig. S1, ESI]. Further, it is observed that the aromatic rings of the two dmp
molecules attached with the tetrahedral Co2+ centers make an interplanar angle of ~70.5°. It is
very likely that this alignment is an outcome of C−H∙∙∙ interactions between the methyl (−CH3)
groups and the pyrazole aromatic rings [Fig. S2, ESI]. The observed C∙∙∙centroid distances
associated with tetrahedral Co(1) and Co(3) centers are 3.742Å and 3.744Å respectively and the
corresponding C−H∙∙∙centroid angles are found to be 171.07° and 109.25° respectively.
Figure 2
a) Tetrahedral coordination environment of the Co(1) and b) octahedral
coordination of Co(2).
Topological analysis shows that the structure consists of two-fold interpenetrating 2-
periodic coordination networks of undulated shape [Fig. S3 in ESI]. Each network is built up of
tri-dentate bridging btc3- anions coordinated to Co2+ ions. It is important to note that only btc-
ligands and Co(II) cations in the crystal structure of 1 participate in formation of the polymeric
structure. The overall topological motif is classified by ToposPro [48] as 3-coordinated hcb net

(Shubnikov hexagonal plane net/(63) [Fig. 3a-b]. Each ring of the net is catenated by two rings of
the other net, forming catenating ladder-like chains in the [010] direction. Extended ring net of
such catenation belongs to the topological type of 2-periodic sphere packing net 36which is
similar to that described by Batten et al. [49] for the structure of [Ag(tcm)] (tcm =
-
tricyanomethanide, C(CN)3 ).
Figure 3 a) 2-Periodic hexagonal network formed by coordination of btc3- anions to Co2+
cations b) Mode of interpenetration of two hcb underlying nets in the structure of 1.

3.2 Powder X-ray diffraction behaviour
All the observed peaks in the experimental powder pattern are seen in the powder pattern
calculated on the basis of structural results obtained from single-crystal X-ray data. A
comparison of experimental and calculated PXRD patterns is shown in Fig. S4 [ESI]. The close
similarities observed between the PXRD patterns suggest the purity of crystalline bulk sample of
the compound and correctness of the structure described by us. Powder XRD data with hkl
indices i.e. indexing for the prominent lines are obtained by comparing the experimental and
calculated pattern.
3.3 UV-vis spectroscopy
Since the present Co-CP consists of both tetrahedral and octahedral cobalt(II)
coordination, we found it interesting to calculate the ground as well as excited state electronic
structures of the molecule. Density functional theory (DFT) [50-52] has all through been an
efficient tool for providing an accurate ground state electronic structure of a molecule, while its
time dependent extension, TD-DFT [53-54], treats the electronically excited-states. As such,
attempts have been made to have an insight into the nature of electronic transitions involved in
the absorption spectrum of the metal complex by employing DFT and TD-DFT calculations. The
solid state UV-visible spectra obtained at room temperature for a powdered sample of 1 is

presented in Fig. S5 [ESI]. The observed electronic spectral measurements are in good
agreement with the calculated values and are used to assign the stereochemistries of cobalt(II)
ion in 1 based on the positions and the number of d-d transitions involved. The visible bands due
4
to [4A2  T1(P)] transitions in tetrahedral Co(II) complexes generally appear as multiple
absorption in the range 550−700 nm [55-56] whereas absorption bands of octahedral Co(II)
complexes are observed in the visible region near 500 nm having lower intensities. The
appearance of absorption bands in the expected positions of the calculated electronic spectrum
confirms the subsistence of tetrahedral and octahedral coordination around the Co(II) centers.
The peaks appeared due to the transition from deeper MOs (for example, the peak at 511 nm) are
because of octahedral Co, whereas peaks (for example, the peak at 578 nm) that are associated
with the tetrahedral Co are due to higher MOs. Shapes of few MOs involved in the transition of
the complex are depicted in Fig. 4.

Figure 4 Shapes of MOs (both in tetrahedral and octahedral ligand environment) involved in the
electronic transitions of the complex 1.
3.4 Thermogravimetric analysis
Thermogravimetric (TG) analysis of 1 shows that [Fig. S6 in ESI] the first step of
decomposition involves the release of three dmp molecules with a weight loss of ca. 20.96%
(calculated value is 21.2%) in the temperature range 110°C – 240°C. In the subsequent steps,
release of organic matters took place in an unidentified manner and the final product was
identified as Co3O4. While the gaseous products have not been experimentally identified by us,
the observed PXRD pattern confirms the identity of the residue [Fig. S7 in ESI]. This pathway is

however tentative because it has been proposed only on the basis of observed weight losses. All
these however are speculative possibilities only.
3.5 Catalytic activity of 1 for oxidation of 1-hexene
Catalytic activity of as-prepared Co-CP was investigated for oxidation of 1-hexene using
TBHP as oxidant in a solvent free condition. Several reports are found in the literature that
shows satisfactory results of 1-hexene oxidation using a wide variety of catalysts/oxidants (57-
64). However, to best of our knowledge, no reports have been made so far representing solvent
free oxidation of 1-hexene in presence of MOF catalysts with excellent selectivity. Most of these
reactions are ended up with epoxide formation along with the other products.
In the present work, oxygenated products obtained during this organic transformation
reaction are 1,2-epoxyhexane (P1), 1-hexanal (P2) and a little amount of hexanoic acid (P3)
(scheme 1). The blank reaction provided only 5% conversion of 1-hexene even after 6 hrs of
reaction time. Different reaction parameters that could influence the conversion and selectivity in
the present oxidation reaction have also been investigated.
Scheme 1
Conversion of 1-hexene to oxygenated products in presence of catalyst 1.
3.5.1 Effect of temperature

Effect of temperature in the oxidation of 1-hexene was assayed using catalyst 1. The
reaction was carried out in a range of temperatures from 323 to 373 K. The results obtained are
presented in Fig. 5. The amount of the oxygenated products formed during oxidation, varies
interestingly with increase in the reaction temperature. Rise in reaction temperature is
accompanied by an increase in the percentage conversion. The 1-hexene conversion reached a
value of 91% at a temperature of 373 K. The selectivity to 1-hexanal increases from 18% to 73%
as the temperature rises from 323 to 373 K and that of epoxide decreases from 81% to 17%.
From this, it is clear that the conversion of epoxide to aldehyde occurs at higher temperature. It
has also been observed that with increase in the reaction time from 0.5 h to 4 h there is an
increase in the conversion with decrease in the selectivity of epoxide under all temperatures.
Figure 5
Effect of temperature on the conversion and selectivity over catalyst 1. S-P1, S-
P2, S-P3 are respective selectivities of product P1, P2 and P3. Time = 4 h, catalyst amount = 30
mg, 1-hexene : TBHP = 1:2.
3.5.2 Effect of catalyst amount
As stated earlier, the present oxidation of 1-hexene was not observed (only 5%
conversion) in the absence of the catalyst Co-CP demonstrating that TBHP alone is unable to
oxidize the substrate effectively. The influence of catalyst amount in the oxidation of 1-hexene

was studied by varying the amount of the catalyst (Fig. 6). A gradual increase in the conversion
was observed with increase in the quantity of catalyst from 10–40 mg. It was observed that with
10 mg of catalyst, only 57% of 1-hexene was converted and this has increased to 88% on
increasing the catalyst amount to 30 mg. Consequently, the selectivity of the epoxide also
decreased from 82% to 67%. However, further increase in the catalyst amount to 40 mg leads to
a negligible increase in the conversion with substantial decrease in the selectivity of the epoxide
and simultaneous increase in the selectivity of 1-hexanal. The excess active sites with the
increase in catalyst amount may easily absorb the so formed epoxide which may undergo
isomerization to 1-hexanal and a small amount of 2-hexanone. Hence, 30 mg may be considered
as the ample amount of the catalyst from both conversion and selectivity point of view for the
present reaction.
Figure 6
Effect of catalyst amount on conversion and selectivity. Time = 4 h, 1-
hexene:TBHP = 1:2, T = 363 K.
3.5.3 Effect of molar ratio
The substrate to oxidant molar ratio (i.e. 1-hexene: TBHP) has also an important role in
this oxidative reaction. Activity of Co-CP catalyst in the oxidation of 1-hexene has been

investigated by means of four different molar ratios (1:1, 1:2, 1:3 and 2:1) of substrate to oxidant
at 363K for 4 hr and the results are presented in Fig. 7. It is clearly seen that the conversion of 1-
hexene increased considerably with increase in the amount of oxidant. When the substrate to
oxidant molar ratio was taken as 1:1, a conversion of 72% was obtained. However, when the
molar concentration of the oxidant was increased (1:2), a conversion of 88% was achieved.
Thereafter, increasing the oxidant amount shows no considerable enhancement in the conversion
of 1-hexene. The selectivity of the products also appeared to be affected by the variation in the
molar ratio. Selectivity of the epoxide decreases from 84% to 67% with the increase in the molar
ratio from 1:1 to 1:2. Further increase in the oxidant amount (molar ratio1:3) lowers the
selectivity of the epoxide to 34%. However, with 2:1 molar ratio the conversion was found to be
very low. Therefore, we can conclude that 1:2 is the optimum substrate:oxidant molar ratio for
this epoxidation reaction.
Figure 7
Effect of molar ratio on conversion and selectivity. Time = 4 h, catalyst amount =
0.1g, T = 363 K.
3.5.4 Kinetics Study

Based upon the experimental data obtained for the oxidation reaction, kinectic study was
carried out under the optimized conditions at different temperatures. The kinetic experiment was
carried out to determine the overall order and rate constant (k) of the reaction. The ln (1-
conversion) vs time plots were obtained using normalized data, which were found to be linear
with a satisfactory R2 (>0.9) value. The slopes of these linear plots at different temperatures
represent first order rate constants (k). The rate constant obtained for the oxidation of 1-hexene
under heterogeneous condition at different temperatures over a definite interval of time are
summarized in Fig. 8a and Table 2. The activation energy for the reaction under the optimised
reaction condition was determined using the Arrhenius equation (Fig. 8b) and found to be 9.04
Kcal mol-1. This value is found to be relatively lower than 10.62 Kcal mol-1 as reported by
Katkar et.al for oxidation of 1-hexene utilizing cis-MoO2 Schiff base complex [65].
(a)
(b)
Figure 8
a) First-order plot for the oxidation of 1-hexene at different temperatures (i) 323
K (ii) 343 K (iii) 363 K and (iv) 373 K. 1-hexene : TBHP = 1 : 2, 30 mg catalyst. b) Arrhenius
plot for the oxidation of 1-hexene.
Table 2 Rate constants at different temperatures for the oxidation of 1-hexene.
Temperature (K)
323
k (min-1)
2.4×10-3
R2
(i)
0.97

2.6×10-3
6.8×10-3
7.8×10-3
0.98
0.99
0.99
(ii)
343
363
373
(iii)
(iv)
4
Conclusion
A new two-fold interpenetrating coordination polymer of composition
[Co3(btc)2(dmp)8]n have been prepared by employing btc3- as a bridging spacer. The 2-D
polymeric chain consists of alternate tetrahedral and octahedral ligand coordination
around the Co(II) ions. The overall topological motif of this coordination solid can be
described as 3-connected hcb underlying net. TD-DFT calculation on the electronic states
of the polymer indicates the presence of both tetrahedral and octahedral ligand
environment around the Co(II) centres. The CP has been tested as a catalyst for oxidation
of 1-hexene to give oxygenated products under solvent free condition. The results showed
evidence that the Co-CP successfully catalyzes the epoxidation of 1-hexene with
selectivities for 1,2-epoxyhexane and 1-hexanal. Activation energy for this reaction under
the optimised reaction condition was found to be 9.04 Kcal mol-1. The observations of
such catalytic behavior with no significant amount of catalyst decomposition during the
course of the reactions prove the heterogeneous nature of catalyst.
Acknowledgements
Financial support from Department of Science and Technology, India
(FASTTRACK Grant No. SB/FT/CS-047/2013) is gratefully acknowledged. The authors
also thank Department of Instrumentation and USIC, Gauhati University, Guwahati for
providing us with the X-ray diffraction data.

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