The functionality of the hybrid systems driven by molecular dimension of the guest copper Schiff-base complexes entrapped in Zeolite-Y

Article abstract of DOI:10.1002/aoc.4765

On encapsulation inside the supercage of zeolite-Y planar Cu (II)–Schiff base complexes show the modified structural, optical and functional properties. The electronic effect of the different substituent groups present in the catalyst plays the decisive r

Full text of DOI:10.1002/aoc.4765

Received: 19 September 2018
DOI: 10.1002/aoc.4765
Revised: 12 November 2018
Accepted: 20 November 2018
F U L L P A P E R
The functionality of the hybrid systems driven by molecular
dimension of the guest copper Schiff‐base complexes
entrapped in Zeolite‐Y
Susheela Kumari | Archana Choudhary | Saumi Ray
Birla Institute of Technology and Science,
On encapsulation inside the supercage of zeolite‐Y planar Cu (II)–Schiff base
Pilani, Rajasthan 333031, India
complexes show the modified structural, optical and functional properties.
Correspondence
Saumi Ray, Department of Chemistry,
The electronic effect of the different substituent groups present in the catalyst
plays the decisive role towards their reactivity in the homogeneous phase but
after the encapsulation in zeolite Y, reactivity is mainly governed by the molec-
ular dimensions of the guest complexes rather than the electronic factor of the
substituent groups attached on them. These systems are well characterized
with the help of different characterization tools like XRD analysis, SEM ‐
EDX, AAS, FTIR, XPS, DSC, TGA, BET and UV–Visible spectroscopy and
the comparative optical and catalytic studies have provided a rational explana-
tion of enhanced reactivity of zeolite encapsulated metal complexes for various
oxidation reactions compared to their corresponding solution states.
Birla Institute of Technology and Science,
Pilani, Rajasthan 333031 India.
Email: saumi@pilani.bits‐pilani.ac.in
KEYWORDS
catalysis, copper Schiff‐base complexes, encapsulation, styrene oxidation, zeolite‐Y
1 | INTRODUCTION
transition metal complexes in the microporous,[3–6] meso-
porous materials[7] and MOFs,[8,9] homogeneous catalyst
Transformation of hydrocarbons into their oxy‐
functionalized derivatives are the important chemical
processes for the industrial and academic purpose.
Transition metal complexes are usually efficient catalysts
for the oxidation of various organic compounds in mild
reaction conditions; however, these homogeneous cata-
lysts always have some drawbacks in the catalytic process
like their instability, difficulty in the separation, and lack
of reusability.[1,2]
The state‐of‐the‐art of the catalytic science prefers
such type of catalysts, which can overcome the limita-
tions of the homogeneous catalytic processes without
the loss of reactivity. In this direction heterogenization
of the homogeneous catalyst is a convenient approach
to couple the reactivity of the complex with the stability,
specific environment and ease of separation provided by
host materials. Impregnation and encapsulation of
tagged with ionic liquids,[10,11] alumina‐supported metal
complexes[12] and phase transfer catalyst[13] are some
interesting examples of heterogeneous systems, which
have been successfully employed in the various oxidation
reactions by using H2O2, TBHP, and molecular O2 as
oxidants.[14,15] Zeolites, the microporous aluminosilicate
materials are the competent hosts for the encapsulation
of transition metal complexes having the molecular
dimension comparable with the diameter cavities of the
host zeolites.[5,16] These contemporary classes of catalysts
comprise the catalyst molecule encapsulated within the
well‐structured architecture of the host, with a large sur-
face area. This is undoubtedly a unique way of site isola-
tion of the desired catalyst. These systems have shown a
structural and functional analogy with cytochrome
P450,[17] and are well explored as the proficient catalysts
for the selective oxidative transformation of olefinic C‐H
Appl Organometal Chem. 2019;e4765.
wileyonlinelibrary.com/journal/aoc
© 2019 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.4765

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KUMARI ET AL.
bonds to its oxy‐derivatives. P. Ratanasmy et al. have
reported that both copper salen and 5‐chloro copper salen
complexes, when encapsulated in zeolite Y suffer from
structural distortion and also are recognized as efficient
catalysts for the oxidation of p‐xylene and phenol. The
authors also emphasize upon the fact that the presence
of electron withdrawing group on the phenyl rings
immensely improves the TOF, h−1 of the oxidation
reaction.[2]
dimers and stepped confirmation and 5‐OCH3‐Cu‐salen
complex, which has an electron‐donating ‐OCH3 substitu-
ent maintains more planarity around the metal center
proximity and forms weak dimer whereas an electron
withdrawing chloro‐substituted complex (5‐chloro‐Cu‐
salen) is essentially a monomer in solid state and have
distorted square‐planar geometry around CuN2O2 prox-
imity.[25] It is interesting to know the diverse effects of
molecular association e.g., steric and electronic effects
and ligand architecture on the reactivity of the catalyst
in the homogeneous and heterogeneous states.
Few more reports are available in the literature,
which also recognize the distorted geometry of the guest
complex under space constraint imposed by the zeolite
framework is the primary reason for enhanced reactivity
of the encapsulated complex. Maurya M. R. et al. have
studied catalytic activities of different metal complexes
encapsulated in zeolite Y for oxidation of different hydro-
carbons such as styrene, cyclohexane, cyclohexene, and
methyl phenyl sulfide, where authors have evidently
shown that encapsulated complexes are much more reac-
tive for oxidative transformation than the corresponding
free state complex.[3,14,18,19] Some other reports on the
encapsulated metal phthalocyanine and Tris(2,2′
bipyridine) iron complexes for the oxidation reaction for
phenols, styrene, and methyl styrene also confirm that
the free state complex especially Tris(2,2bipyridine) iron
complex is definitely not so efficient catalyst like its
encapsulated analogue in identical reaction condi-
tions.[20] Recently, R. Ananthakrishnan and coworkers
have reported the synthesis of [Ru (bpy)3]Cl2 complex
on a mesoporous silica SBA‐15 support and its applica-
tion for degradation of chlorophenol under visible light
in an aqueous medium.[21] In another report, an encapsu-
lated chiral nickel Schiff base complexes inside the cavity
of zeolite Y has been recognized as an excellent catalyst
for asymmetric Henry reaction.[22] In another compara-
tive study of different metal picolinato complexes in zeo-
lite Y, R. C. Deka et al. have observed that the copper and
cobalt complexes are more reactive catalysts compared to
the its corresponding nickel complexes for the selective
oxidation of phenol by using H2O2 as the oxidant.[6] It is
quite clear that the encapsulated complexes in zeolite Y
are competent catalysts for oxidation of hydrocarbons,
and most of the studies have suggested that enhanced
activity of the encapsulated complex is definitely a conse-
quence of the distorted geometry of the complex under
space constraint inside the rigid cavity.[23,24] Already the
diverse effects of different substituents on the structure
and functionality of the copper Schiff‐base complexes
are discussed thoroughly.[25] Bhadbhade et al. have
explored the effect of substituents (H, ‐OCH3 and ‐Cl on
Cu‐salen, 5‐OCH3‐Cu‐salen, and 5‐chloro‐Cu‐salen) on
various aspects like molecular association, conformation,
and electronic structure. Cu‐salen complex forms strong
In the present study, we choose the complexes with
different substitution (H, OH, Br and ‐ OCH3 on the 5th
position of the phenyl rings) on the phenyl rings of Schiff
base salen and salophen ligands. These complexes of two
different series copper salen and copper salophen are abbre-
viated as CuS1, CuS2, CuS3 and CuS4 and CuSp1, CuSp2,
CuSp3 and CuSp4 respectively. In a particular series, com-
plexes (say, from CuS1 to CuS4) vary on the basis of their
increasing order of the molecular dimensions and these
are encapsulated inside nearly spherical supercage of zeo-
lite Y via flexible ligand synthesis method (given in
scheme 1). These systems are well characterized with the
help of powdered XRD, AAS, SEM‐EDS, IR, XPS, DSC,
TGA, BET and UV–Visible spectroscopy. We employ the
systems as catalysts for the styrene oxidation reaction.
The encapsulation and catalysis of different copper
complexes in the voids of zeolite Y are extensively stud-
ied;[26] however, the systematic approach to study the
structural changes of the complexes upon encapsulation
are still on demand. Our selection of the copper Schiff‐base
complexes largely depends upon the end‐to‐end distance
of the complex so that the host supercage of 12.47 Å diam-
eter imposes the steric constraints on the guest complex.
Under such condition, the geometry adopted by the com-
plex are studied thoroughly. Detailed studies of modified
reactivity towards styrene oxidation evolving from struc-
tural distortion as a function of the end‐to‐end distance
of the complex is the prime objective of our research.
Comparative structural and catalytic studies of these
coupled systems have been carried out in detail to com-
prehend the geometry of the complex after encapsulation
as well as to identify the origin of the modified function-
ality of the systems. Research on the link between
enhanced selective catalysis and adopted geometry of
the guest complex is relatively rare in the literature and
our research attempts to address this question. Compara-
tive studies reveal quite a fascinating correlation existing
between the catalytic activities and modified structure
experienced by the complexes under encapsulation which
leaves a lot of scopes to further modify the activity of the
catalysts and to have a better insight of these heteroge-
neous systems.

KUMARI ET AL.
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SCHEME 1 Synthesis of copper Schiff‐bases complexes derived from ethylene diamine (or 1, 2 diamino benzene) and salicyaldehyde (or
its derivetives)
2 | EXPERIMENTAL SECTION
2.1 | Materials and preparation
2.3 | Synthesis of Cu‐exchanged zeolite Y
and encapsulated of Cu (II) Schiff‐base
complex[2,27]
Pure zeolite‐Y was purchased from sigma – Aldrich,
Delhi, India. salicylaldehyde and its derivatives, phenyl
diamine, ethylene diamine are purchased from alfa aecer
and copper acetate and solvents (ethanol, acetone, meth-
anol and diethyl ether) were purchased from S.D. fine,
Delhi, India.
Pure Na‐zeolite Y (Na58Al58Si136O388•yH2O) was dis-
persed in 0.01 M copper acetate solution and stirred at
room temperature for 24 hr to obtain the desired loading
level of copper metal ions in the zeolite. The slurry was
filtered, washed repeatedly with deionized water and des-
iccated for 12 hr at 150 °C. Synthesis of copper (II) Schiff
base complex was carried out via ‘flexible ligand’
approach’ (given in scheme 2). The Cu‐exchanged zeolite
and excess amount of ligands were heated together under
solvent‐free condition at (200–250)°C as the melting
points of different ligands vary approximately from 160–
230 °C, with constant stirring for 24 hr. To synthesize
the complex inside the supercage of zeolite Y, diffusion
of melted ligand through zeolite pore is mandatory. On
heating, the color of the solid reaction mass was changed
from pale yellow to reddish‐brown. The solid reaction
mixture was recovered and further subjected to Soxhlet
extraction with the different solvents maintaining the
order, like as acetone, methanol, and finally diethyl ether.
The product was dried in a muffle furnace for (10–12) h at
150 °C. The recovered product was further treated with
0.01 M NaCl solution for 12 hr to remove the unreacted
Cu2+ ions, followed by filtration and continuous washing
until the filtrate is free from the chloride ion.
2.2 | Preparation of ligand and
complexes[2,23]
The salen and the salophen ligand was synthesized as fol-
lows. Two mole of salicylaldehyde (or its derivatives) was
dissolved in ethanol and refluxed for (10–15) minutes.
One mole of ethylene‐diamine (or phenylene diamine)
was added into it in order to synthesize salen (or
salophen) ligands. The reaction mixture was refluxed for
(30–120) minutes at (60–70)°C and then ice cooled for
1 hr. A bright yellow solid flakes were obtained as prod-
uct which was thoroughly washed with ethanol and then
dried in air (given in scheme 1).
For the synthesis of free state salen and salophen
complexes, the ligands (S1, S2, S3, and S4) and (Sp1,
Sp2, Sp3, and Sp4) were dissolved in ethanol and refluxed
under N2 atmosphere. An equi molar ratio of copper
acetate solution was added drop‐wise into the reaction
mixture and further refluxed for the (30–240) minutes
for the synthesis of different complexes. The reaction
mass was recovered, filtered and washed with ethanol
and diethyl ether and then further air dried at room
temperature (given in scheme 1).
2.4 | Catalytic oxidation reaction
To investigate the catalytic activity of the encapsulated
complexes, styrene oxidation transformation catalyzed
by copper Schiff‐base complexes in free and encapsulated

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KUMARI ET AL.
SCHEME 2 Schematic representation of encapsulation of metal complex in the supercage of zeolite via ‘flexible ligand method’ to prepare
‘ship‐in‐a‐bottle’ complex
states were explored by using H2O2 as an oxidant in the
aerobic condition. The optimum conditions for epoxida-
tion reaction were as follows: (Styrene: 1.56 g, 15 mmol),
(H2O2: 3.40 g, 30 mmol), acetonitrile 15 ml, temperature
80 °C, and catalyst (0.05 g for encapsulated complexes
and 0.0045 g for neat complexes). After the reaction was
finished, the products were identified and quantified with
the help of Gas Chromatography by using the internal
standard method.
3.2 | Catalytic study
Catalytic activities of the metal complexes in their free
and encapsulated states are explored by studying the
oxidation reaction of styrene and then compared.
Styrene can be oxidized into the different organic
compounds as benzaldehyde, styrene oxide, benzoic acid,
phenylacetaldehyde and phenylethane‐1, 2‐diol; some of
these products of the reaction are previously
reported.[3,14] Calibration curve of styrene, benzaldehyde
and styrene oxide are shown in supporting information
(Figure S2 A‐C). Reaction conditions are optimized with
respect to the CuS1 complex in the encapsulated state as
the representative catalyst by varying different reaction
parameters like temperature, the time duration of reac-
tion and amount of catalysts to attain maximum effi-
ciency. To standardize the reaction condition, styrene
(1.56 g, 15 mmol) and 30% H2O2 (3.40 g, 30 mmol) are
mixed with 15 ml acetonitrile and catalysts of different
amounts (0.015 g, 0.030 g and 0.05 g) are added at various
temperatures 40 °C, 80 °C and 120 °C for variable reac-
tion durations (2 hr, 5 hr and 8 hr). Initially, the amount
of catalysts is optimized for encapsulated CuS1 in zeolite
Y as it has shown the improved reactivity when employed
in two different sets of reaction with 0.030 g and 0.050 g.
The conversion of styrene is found to be the least when
0.015 g of the catalyst is used (catalytic data are presented
in supporting information, Table S1‐S3, and Figure S3).
We have considered 0.050 g as an optimized amount of
the catalysts for above reaction conditions because no
substantial improvement in the % conversion of styrene
is observed while taking 0.070 g of the catalysts. A further
3 | RESULTS AND DISCUSSIONS
3.1 | Elemental analysis
Parent zeolite has Si/Al ratio of 2.34 and its unit cell
formula of the host material is Na58Al58Si136O388 yH2O.
The Si/Al ratio of host framework remains unaffected
even after the complete synthesis of the metal complex
inside it which essentially signifies the lack of
dealumination during the whole process of ion
exchange and encapsulation (EDX data are given in
supporting information Figure S1).[28] The concentration
of metals in different samples are determined by atomic
absorption spectroscopy and it is found that the metal
content in the encapsulated Cu complexes is always less
than that present in the Cu‐ exchanged zeolite Y (AAS
data given in Table 1). The observation essentially
indicates the complex formation inside the host cavity
with slight leaching of some of the metal ions during
the process of encapsulation.

KUMARI ET AL.
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TABLE 1 Amount of Cu‐atom (mmol) for all catalysts
[a]
S. No
Catalyst
Cu‐atom in catalyst (mmol)a
S. No
Catalyst
% weight of Cub
Cu‐atom in catalyst (mmol)
1
Zeolite‐Y
CuS1
‐
2
Cu‐Y
0.81
0.62
0.59
0.37
0.39
0.67
0.52
0.39
0.34
0.00637
0.00487
0.00464
0.00291
0.00306
0.00527
0.00409
0.00306
0.00267
3
0.01360
0.01240
0.00922
0.01154
0.01190
0.01090
0.00840
0.01020
4
CuS1‐Y
CuS2‐Y
CuS3‐Y
CuS4‐Y
CuSp1‐Y
CuSp2‐Y
CuSp3‐Y
CuSp4‐Y
5
CuS2
6
7
CuS3
8
9
CuS4
10
12
14
16
18
11
13
15
17
CuSp1
CuSp2
CuSp3
CuSp4
ammol of Cu atom calculated in 0.0045 g for neat complexes and 0.05 g for encapsulated complexes and Cu‐Y).
b% weight of Cu obtained from AAS.
increase in the amount of catalyst causes a drop in % con-
version since it lowers the probably of adsorption of two
different reactant molecules on the same catalytic site
hence reduces the effective interaction between reactant
molecules.[3]
and CuS4) and copper salophen complexes (CuSp1,
CuSp2, CuSp3, and CuSp4) are employed as catalysts in
free as well as encapsulated states (catalytic data pre-
sented in Table 2). These catalysts are more selective for
benzaldehyde formation in both states while the other
products like styrene oxide are formed as a minor product
along with negligibly small amounts of benzoic acid and
phenylacetaldehyde as shown in Table 2. The higher yield
of benzaldehyde might be associated with the formation
of hydroperoxylstyrene intermediate by the nucleophilic
attack of H2O2, which is further cleaved to produce benz-
aldehyde. Another route of formation of benzaldehyde is
further oxidation of styrene oxide, one of the products of
the styrene oxidation. The formation of benzoic acid is
the result of further oxidation of benzaldehyde and
phenylacetaldehyde is the isomerized product of styrene
oxide.[29]
Turn over number (TON) calculated from the cata-
lytic data have repeatedly shown a clear‐cut reactivity
trend; free state salen and salophen complexes follow
the reactivity order as CuS3 > CuS1 > CuS2 > CuS4
and CuSp1 > CuSp3 > CuSp2 > CuSp4 respectively
however upon encapsulation within zeolite Y, scenario
changes. It is CuS4 > CuS3 > CuS1 > CuS2 for the
encapsulated salen complexes, whereas the encapsulated
salophen complexes demonstrate the order as
CuSp4 > CuSp3 > CuSp2 > CuSp1.The catalytic activity
is certainly governed by the electronic factor or electron
density on the metal when the complexes are in their free
states. Complexes with different substituent groups
render electron density of the metal differently, and
consequently, the outcome of catalysis varies, however,
after encapsulation, the steric constraint imposed by the
zeolite framework upon the guest complex contributes
significantly to the catalytic activity. On encapsulation,
the complexes with larger molecular dimension possibly
For the oxidation reaction, styrene (1.56 g, 15 mmol),
30% H2O2 (3.40 g, 30 mmol) in 15 ml acetonitrile and
0.050 g catalyst have been kept for different time dura-
tions e.g., 2 hr, 5 hr and 8 hr. Since there is no significant
improvement observed in the % conversion of styrene
after 8 hr and this is chosen as the adequate time for
the reaction. With these optimized conditions, the styrene
oxidation reaction is studied at three different tempera-
tures 40 °C, 80 °C and 120 °C, and conversion of styrene
is quantified as 5%, 47% and 58% for the encapsulated
CuS1 complex at 40 °C, 80 °C and 120 °C, respectively.
Therefore, 80 °C temperature is found to be the
appropriate/optimum temperature for the reaction. How-
ever, for the free state complexes, quite a low amount of
0.0045 g has been employed as a catalyst in each of the
cases because within this amount, the neat complexes
have active metal centers much higher in number as
compared to their analogous encapsulated state com-
plexes. Comparative studies (shown in Table 1) clearly
indicate that 0.0045 g free state complex still contains 2–
4 times higher the amount of Cu active centers than that
present in 0.05 g of the corresponding encapsulated com-
plex. Within the optimum range of the amount of cata-
lyst, more the number of active metal sites more is the
% conversion of styrene. Therefore, to study catalysis
driven by the geometry of the metal complex, the ratio-
nale is to reduce the catalytic data in terms of the turn-
over number (TON) rather than the % conversion so
that difference in concentrations of active metal centers
in both the states could be nullified. With these suitable
conditions, copper salen complexes (CuS1, CuS2, CuS3,

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KUMARI ET AL.
TABLE 2 Conversion of styrene after 8 hr reaction time with H2O2 as oxidant
Selectivity
Selectivity
S. No
Samples
% Conversion
TON
Benz.
SO
S. No
Samples
% Conversion
TON
Benz.
SO
1
Zeolite‐Y
CuS1
3
86
56
76
50
74
59
50
12
‐
73.97
81.83
89.79
87.80
90.47
89.47
89.62
95.45
93.41
26.02
18.16
10.20
12.19
9.52
2
4
Cu‐Y
20
47
23
54
64
50
57
62
63
455.2
1435.3
711.2
90.90
96.35
99.30
91.64
96.87
93.15
91.05
97.56
95.17
9.09
3.64
0.69
8.35
3.12
6.84
8.94
2.43
4.82
3
941.1
677.4
1236.4
649.9
937.8
807.3
892.8
187.2
CuS1‐Y
CuS2‐Y
CuS3‐Y
CuS4‐Y
CuSp1‐Y
CuSp2‐Y
CuSp3‐Y
CuSp4‐Y
5
CuS2
6
7
CuS3
8
2793.8
3137.2
1423.1
2078.2
3042.4
3543
9
CuS4
10
12
14
16
18
11
13
15
17
CuSp1
CuSp2
CuSp3
CuSp4
10.52
10.37
4.54
6.59
Reaction conditions: Reaction conditions (Styrene: 1.56 g, 15 mmol), (H2O2: 3.40 g, 30 mmol), acetonitrile 15 ml, temperature 80 °C, catalyst (0.05 g for encap-
sulated complexes and 0.0045 g for neat complexes),TON (turn over number): mole of substrate converted per mole of metal center (encapsulated complexes),
Benz.: Benzaldehyde, SO: Styrene oxide.
undergo more distortion imposed by the supercage,
3.3 | X‐ray diffraction and scanning
finally leading to the alteration of the overall reactivity
order. Hence, the final structure adopted by the encapsu-
lated complex is the major decisive factor for improved
catalysis. Therefore, to understand to verify the mecha-
nism of a catalytic reaction and the appropriate structural
involvement of the catalyst, encapsulation could be a
technically potent process. Detailed structural analysis
of the complex especially after encapsulation inside
zeolite is expected to provide the insight of the catalytic
process hence, leads to the route of the tunable catalysis.
The CuS4‐Y catalyst is found to be efficient enough for
this oxidation reaction up to six cycles with a marginal
loss in its catalytic activity as in form of percentage
conversion from 64% to 63.3% (Shown in Figure 1).
electron microscopy analysis
To investigate the order of retention of zeolite crystal-
linity, surface morphology, and integrity of host zeolite
Y, XRD patterns of parent zeolite Y, Cu‐zeolite Y and
zeolite with encapsulated copper Schiff‐base complexes
are recorded. (XRD pattern are given in Figure 2)
Essentially similar patterns of all the samples indicate
the preservation of the integrity of the host framework
during the process of encapsulation. On comparison of
the XRD patterns of encapsulated complexes with the
pure and copper exchanged zeolite‐Y, an evident
distinction in the XRD patterns of the encapsulated
complexes has been observed. Alteration of relative
intensities of peaks at the 2θ = 10° and 12° are noticed
after encapsulation. For parent zeolite and Cu‐
exchanged zeolite the relation I220 > I311 exist, but for
zeolite, with encapsulated complexes, the relation is just
reverse; I311 > I220. The observed modification in these
intensities after the encapsulation previously has been
recognized and empirically associated with the fact that
a large complex is indeed present within the zeolite‐Y
supercage.[30] Scanning electron microscopy also sup-
ports the fact that the complex formation is primarily
taking place inside the host cavities. From the SEM
images (SEM micrographs given in Figure 3a‐3c before
Soxhlet extraction for CuS4‐Y with different resolution;
Figure 3d‐3f for CuS4‐Y and Figure 3g‐3i for CuSp4‐Y
after Soxhlet extraction and Figure S4 in supporting
information for CuS1‐Y and CuSp1‐Y), it is observed
that before Soxhlet extraction, there are some detectable
surface species probably due to the formation of the
complex at the surface or un‐reacted ligands, however,
FIGURE 1 Recyclability of the CuS4‐Ycatalyst for styrene
oxidation reaction

KUMARI ET AL.
7 of 16
FIGURE 2 (i) Powder XRD patterns of (a) pure zeolite‐Y (b) Cu‐ exchanged zeolite‐Y, (c) CuS1‐Y, (d) CuS2‐Y, (e) CuS3‐Y and (f) CuS4‐Y.
(ii) Powder XRD patterns of (a) pure zeolite‐Y, (b) Cu ‐ exchanged zeolite‐Y, (c) CuSp1‐Y, (d) CuSp2‐Y, (e) CuSp3‐Y and (f) CuSp4‐Y
FIGURE 3 SEM images before Soxhlet extraction (a‐c) CuS4‐Y with different resolution, and after Soxhlet extraction (d‐f) CuS4‐Yand (g‐i)
CuSp4‐Y
are disappeared after Soxhlet extraction.[28,31] making
zeolite particle boundaries more clearly visible. The
3.4 | IR spectroscopic study
IR spectral data of ligands, (given in supporting informa-
tion Figure S5 and Table S5) pure zeolite Y and all copper
Schiff‐base complexes in free and encapsulated states are
given in Figure 4 and Table S4. Pure zeolite Y has shown
strong IR peak at 1018 cm−1, which is mainly attributed
clarity in the observation of boundaries of host lattice
in SEM micrographs and the persistent color of Soxhlet
extracted final product are certainly logical indications
of successful encapsulation of the complex inside the
cavities of zeolite Y.

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KUMARI ET AL.
FIGURE 4 (i) FTIR spectra of free state salen complexes (a) CuS1, (b) CuS2, (c) CuS3 and (d) CuS4. (ii) FTIR spectra of free state salophen
complexes (a) CuSp1, (b) CuSp2, (c) CuSp3 and (d) CuSp4. (iii) FTIR spectra of encapsulated copper salen complexes (a) pure zeolite Y, (b)
CuS1‐Y, (c) CuS2‐Y, (d) CuS3‐Y and (e) CuS4‐Y. (iv) FTIR spectra of encapsulated copper salophen complexes (a) pure zeolite Y, (b) CuSp1‐Y,
(c) CuSp2‐Y, (d) CuSp3‐Y and (e) CuSp4‐Y
to the presence of asymmetric stretching vibrations of (Si/
Al)O4 units of the framework. Other some prominent
peaks are present at 560, 717, 786, 1643 and 3500 cm−1
position, which are mainly assigned to (Si/Al)O4 bending
mode, double ring, symmetric stretching vibrations, other
two IR bands at 1643 and 3500 cm−1 positions are attrib-
uted to lattice water molecules and surface hydroxylic
group.[6,31] These IR bands are remaining unaffected even
after encapsulation processes. All the encapsulated com-
plexes have exhibited the bands without any significant
alternation in the peak positions, evidently revealing the
fact that the host framework doesn't get modified during
the complex formation inside the supercage. The suitable
IR region for the characterization of encapsulated Schiff‐
base complex is 1200–1600 cm−1, because in this region
host lattice remains silent and observed IR peaks with
smaller shifts are mainly due to the presence of guest
complex within the framework having different environ-
ment from its free state. Studies in this region of 1200–
1600 cm−1 become beneficial as some of the significant
IR bands of the Schiff base complexes like C=N, C=C,
C‐O stretching and C‐H deformation have emerged in
this particular region, which are unaffected by host lat-
tice. Comparative IR data indicates the complex forma-
tion in neat as well as in encapsulated state. Ligand (S1)
has shown IR peaks at 1636 cm−1 and 1273 cm−1 which
are assigned as C=N and C‐O stretching, These IR bands
are shifted towards lower wave numbers and appeared at
1634 cm−1 and 1194 cm−1 under complexation. In the
encapsulated complexes these bands appear at compara-
tive positions to free state complex and the higher shifts
in νC‐H deformation frequencies have already been
attributed to the presence of complex inside the zeolite
cavity.[32] The observed FTIR spectral data (Table S4)
suggest the formation of copper Schiff‐base complexes
in the free and encapsulated states inside the zeolite Y
supercage.
3.5 | X‐ray photoelectron spectroscopy
(XPS)
The existence of the guest metal complex in zeolite Y is
also confirmed with the help of XPS study, which is an
indirect technique to investigate the location of the metal
complex in the host framework. The XPS survey spectra
(given in supporting information Figure S6) and binding
energy data of CuS1, CuS1‐Y, and CuSp1‐Y are presented
in Table 3. It is observed that the elements/metal ions (C,
N, O, Si, Al, and Cu2+) are present in their respective sur-
face chemical states in these complexes. The low concen-
tration of metal contents in the encapsulated complexes
makes the XPS signal for metal weak, which is actually
in accordance with the concentration‐dependent studies
like IR, UV–Vis spectroscopy. The appearance of Cu(2p)
peaks in XPS spectrum confirms the presence of copper

KUMARI ET AL.
9 of 16
TABLE 3 Binding energy (eV) of free and encapsulated complexes
Binding energy (eV)
S. No
Samples
Si (2p)
Al (2p)
C (1 s)
N (1 s)
O (1 s)
Cu2+ (2p)
Δ2p
1
2
3
CuS1
‐
‐
283.35, 285.03
283.90, 285.76
284.13, 285.41
397.68, 399.61
397.65, 400.11
399.18 401.65
531.26, 533.74
530.80, 533.08
530.66, 532.88
932.80, 952.72
934.13, 954.06
934.17, 954.13
19.92
19.93
19.96
CuS1 ‐Y
CuSp1‐Y
103.46
103.56
75.21
75.23
and is assigned to the Cu 2p3/2 and Cu 2p1/2 confirms the
+2 oxidation state of Cu and square planar geometry of
the complexes in the free and encapsulated states. Cu
2p3/2 and Cu 2p1/2 XPS signals have appeared at the bind-
ing energies of 932.80 eV and 952.72 eV respectively for
the CuS1 complex whereas for the encapsulated com-
plexes (CuS1‐Y and CuSp1‐Y) these peaks are slightly
shifted towards the higher binding energies and have
appeared at 934.13, 954.06 and 934.17, 954.13 eV respec-
tively.[6,33] (XPS spectra presented in Figure 5) Such
observed higher shifts in the binding energies upon
encapsulation could be the result of lowering of electron
density on the metal center because of the weakening in
the delocalization of electrons due to alteration in the
square planar proximity of the encapsulated complexes.[6]
However, XPS signals for other atoms are more or less
unshifted. C (1 s) signals in the free state CuS1 complex
appear at 283.35 and 285.03 eV, which corresponds to
the sp2 and sp3 carbon atoms respectively.[33] N (1 s)
peaks for the complex are observed at binding energies
397.68 eV (M‐N) and 399.61 eV (C=N) whereas O (1 s)
peaks appear at the binding energies of 531.26 eV (M‐O)
and 533.74 eV (C‐O).[23,33] These XPS peaks are observed
at almost identical binding energies for the encapsulated
complexes. For CuS1‐Y‐complex, the C(1 s) XPS signals
are observed at 283.90, 285.76 eV and attributed to sp2,
sp3 carbon atom whereas signals at 397.65, 400.11 eV
and 530.80, 533.08 eV are attributed to (M‐N, C=N) and
(M‐O, C‐O) form of the respective elements. The equiva-
lent XPS signals for CuSp1–Y complex are also observed
at their corresponding binding energies; for the C (1 s),
signals have appeared at 284.13, 285.41 eV, whereas
N(1 s) and O (1 s) signals are observed at 399.18,
401.65 eV and 530.66, 532.88 eV respectively. Further-
more, both the encapsulated complexes have shown
zeolitic Na(1 s), Al(2p) and Si(2p) XPS signals at their
respective positions[6,23,33] (XPS spectra are presented in
supporting information Figure S7‐S9). Comparative XPS
binding energy data of both free and encapsulated com-
plexes, as well as higher shifts in binding energy for the
Cu 2p3/2 and Cu 2p1/2 peaks in both encapsulated com-
plexes, essentially signify the encapsulation of metal com-
plexes inside the zeolite Y.
3.6 | DSC study
DSC curves recorded at a temperature range from 25 to
500 °C (heating rate: 10 °C/min and sample weight is
taken: 3 mg) for zeolite‐Y, CuS1 and CuS1‐Y are shown in
Figure 6. The neat copper complex CuS1 decomposes exo-
thermically at a temperature range from 318 °C to
500 °C.[34] DSC curve of encapsulated copper complex
CuS1‐Y has shown a broad endothermic peak in between
30 to 300 °C which corresponds to the removal of water
molecules adsorbed on zeolite surface.[35] Further heating
leads to the appearance of two exothermic peaks in
between 340 °C to 500 °C. Comparative studies with zeo-
lite and neat complex indicate that these two peaks
appeared for CuS1‐Y are due to the decomposition of
the encapsulated complex, as pure zeolite does not show
any exothermic peak in that temperature range. The
peaks are shifted towards higher temperatures compared
to that of the neat complex signifying that the
FIGURE 5 High resolution XPS spectra for the Cu 2p3/2 signal (a) CuS1, (b) CuS1‐Y and (c) CuSp1‐ Y

10 of 16
KUMARI ET AL.
FIGURE 6 DSC curves of zeolite‐Y, CuS1 and CuS1‐Y
TABLE 4 Thermogravimetric analysis data of free and encapsu-
lated complexes
encapsulated metal complex is thermally more stable
than the neat complex. A very small heat flow supports
quite a low concentration of guest complex inside the
supercage of zeolite‐Y.
S.No. Samples Temperature range (°C) Weight loss (%)
1
2
Zeolite Y 50–300
24.0
CuS1
318–370
371–560
48.5
12.5
3.7 | TGA analysis
3
4
5
6
7
CuS1‐Y
CuS4
50–300
340–660
11.6
16.5
The TGA curves of pure zeolite Y, neat and encapsulated
complexes are obtained in a nitrogen atmosphere and are
shown in Figure 7 (TGA data given in Table 4). Accord-
ing to the TGA curve, weight loss for the neat copper
complex CuS1 occurred in two steps. The first weight loss
takes place in the temperature range (318–370)°C and in
the second step, weight loss starts immediately after the
first step in the range (371–560)°C suggesting decomposi-
tion of the chelating salen ligand.[22] For pure zeolite Y,
weight loss (24%) is obtained in the one‐step temperature
range of (50–300)°C due to the loss of water molecules.[36]
Unlike pure zeolite Y, the encapsulated copper complex
CuS1‐Y shows two‐step weight losses. The first step
weight loss occurs in the range of (50–300)°C correspond-
ing to desorption of physically adsorbed water molecules
from the zeolite framework with a mass loss of 11.6%.
The second step involves the weight loss occurring after
315–350
351–700
30.9
46.1
CuS4‐Y
CuSp4
CuSp4‐Y
50–300
340–750
5.5
39.8
308–360
361–575
13.0
64.8
50–300
320–580
11.3
31.1
340 °C with a mass loss of 16.5% which definitely corre-
sponds to the loss of organic moieties from the zeolite
cages.[36]
3.8 | BET surface area analysis
The BET surface area analysis has been performed to find
out the surface area and pore volume of pure zeolite Y
and encapsulated complexes. The comparative N2
adsorption–desorption isotherms for zeolite Y and two
of such encapsulated complexes (CuS4 and CuSp4 in zeo-
lite) using BJH method are shown in Figure 8 along with
the data of surface area and micropore volume, given in
Table 5. The pattern of nitrogen sorption isotherms for
all the catalysts are found to be nearly identical
(Figure 8), indicating that the zeolite framework is not
affected during the encapsulation process. All the cata-
lysts have shown type I adsorption–desorption isotherms,
which is a characteristic of the microporous material.[37]
The lowering of BET surface areas and pore volumes of
FIGURE 7 TGA curves of CuS1, CuS4, CuSp4, zeolite‐Y, CuS1‐Y,
CuS4‐Y and CuSp4‐Y

KUMARI ET AL.
11 of 16
whereas in the range of (300–384) nm are mainly
assigned as n‐π* transitions. The electronic transitions,
which are mainly originated from the metal d orbitals,
are identified in the comparative lower energy region of
the spectrum. Bands appeared in the range of (404–471)
nm and (502–607) nm are attributed to charge transfer
and d‐d transitions respectively. UV–Visible data of free
CuS1 complex have shown good concurrence with the
reported data in the literature[38] and also provided the
information about the complex formation in the free
state. After the encapsulation in zeolite Y, complexes
have shown a similar prototype of electronic spectra,
indicating that the complexes are indeed present in the
host lattice. Comparative studies of the electronic spectra
of the complexes in free and their encapsulated states,
make it quite clear that the intra‐ligand transitions
(π‐π* and n‐π*) are relatively unaffected under the encap-
sulation; however, transitions which are mainly insti-
gated from the metal center are primarily altered in
terms of peak positions as well as intensities for all guest
complexes. It is quite interesting to perceive a regular
blue shift and intensification of the d‐d transitions in
the encapsulated copper ‐ Schiff‐base complexes. Such
behavior already has been observed in the zeolite Y
encapsulated complexes.[23,28,32] Observed modified elec-
tronic behavior in the d‐d region is certainly an effect of
different geometry of the co‐ordination sphere, which
the guest complex has adopted under the space restric-
tions of host supercage. Theoretical studies have also
revealed the fact that changes in the bond angles, bond
lengths, and HOMO‐LUMO gaps can be introduced in
the guest complex by the process of encapsulation in zeo-
lites.[28,31] In the present study, the copper complexes
have chosen on the basis of their molecular dimensions
(i.e., end to end distances) of the complexes, which follow
the order as CuS1 < CuS2 < CuS3 < CuS4 and
CuSp1 < CuSp2 < CuSp3 < CuSp4 for the salen and
salophen copper complexes respectively. The complex
with larger molecular dimensions experiences the more
steric impulsion and obviously, it adopts more distorted
geometry to accommodate itself into the framework cav-
ity. There are some interesting reports, which have
explored the correlation between the geometry of the
metal complexes and different factors and their conse-
quence. It is previously studied that effect of the substitu-
ent groups (‐Cl and –OCH3) on the geometry of copper
Schiff‐base complexes is so prominent.[2,39] Another
report has revealed that the replacement of the atoms in
the N2O2 square planar proximity by N2OS and N2S2
leads the distortion in the geometry of that complex and
its effect can be seen in the optical behavior of that com-
plex.[40] Sankar et al. have suggested that the different
substituent groups can cause the push‐pull effect on the
FIGURE 8 BET isotherms for pure zeolite‐Y and zeolite
encapsulated complexes: (a) pure zeolite Y, (b) CuS4‐Y and (c)
CuSp4‐Y
TABLE 5 BET surface area and pore volume of pure zeolite Y,
encapsulated complexes CuS4‐Y and CuSp4‐Y
BET surface
area (m2/g)
Pore volume
(cm3/g)
S.No.
Sample
1
2
3
Pure zeolite Y
CuS4‐Y
535
430
420
0.3456
0.2735
0.2611
CuSp4‐Y
both the zeolite samples with encapsulated copper com-
plexes compared to that of pure zeolite Y clearly suggest
the presence of metal complex within the supercage of
zeolite Y rather than on the external surface.[19,22] The
decreases in the surface area and pore volume of the cat-
alyst largely depend upon the loading level of metal in
zeolites along with the molecular dimension and geome-
try of the complex encapsulated inside the zeolite
supercage.
3.9 | UV–visible study
To confirm the complex formation inside the cavity of
zeolite and to study the co‐ordination environment
around the metal center, electronic spectroscopy is
always being informative. The relative UV–Visible spec-
troscopic studies in the solid state of all the copper
Schiff‐base complexes presented in Figure 9 and Table 6
and solution UV–Visible spectra for CuS1 and CuSp3
are presented in supporting information Figure S10,
thereby provide the significant evidence about the com-
plex formation in both states. Absorption bands in the
range of (230–250) nm are recognized as π‐π* transitions,

12 of 16
KUMARI ET AL.
FIGURE 9 (i) Solid state UV‐Vis spectra of free satate copper salen complex (a) CuS1, (b) CuS2, (c) CuS3 and (d) CuS4. (ii) The solid state
UV‐Vis spectra of free state copper salophen complex (a) CuSp1, (b) CuSp2, (c) CuSp3 and (d) CuSp4. (iii) The solid state UV‐Vis spectra of
encapsulated copper salen complexes in zeolite Y (a) CuS1‐Y, (b) CuS2‐Y, (c) CuS3‐Y and (d) CuS4‐Y. (iv) The solid state UV‐Vis spectra of
encapsulated copper salophen complexes in zeolite Y, (a) CuSp1‐Y, (b) CuSp2‐Y, (c) CuSp3‐Y and (d) CuSp 4‐Y
TABLE 6 Solid state UV–Visible spectroscopic data of complexes in free and encapsulated state
S.No
Samples
π—π* transitions
n—π* transitions
CT transitions
d‐d transitions
1
CuS1
232
234
248
252
238
232
232
241
246
249
251
253
249
247
253
251
364
362
397
395
367
360
391
387
306
300
347
343
336
338
321
315
404
417
447
471
406
419
435
418
419
423
479
394
445
471
484
382
592
533
584
514
609
528
592
495
607
588
668
567
502
610
646
503
2
CuS1‐Y
CuS2
3
4
CuS2‐Y
CuS3
5
6
CuS3‐Y
CuS4
7
8
CuS4‐Y
CuSp1
CuSp1‐Y
CuSp2
CuSp2‐Y
CuSp3
CuSp3‐Y
CuSp4
CuSp4‐Y
9
10
11
12
13
14
15
16

KUMARI ET AL.
13 of 16
porphyrin complexes which is actually associated with
the change in the energy gaps in the d‐d orbitals.[41] In
the present study we have observed a nice correlation
between the observed blue shift in d‐d bands and the
molecular dimensions of the copper Schiff base com-
plexes. On encapsulation, the complexes with largest
molecular dimension in both the series (CuS4 and
CuSp4) are expected to adopt the most distorted geome-
tries, which are actually depicted as maximum blue
shifted d‐d bands in the electronic spectrum, whereas
CuS1 and CuSp1 complexes have shown minimum
blue shifts. The degree of blue shift in d‐d bands is
just in accordance to the increasing order of the
molecular dimensions of complexes and the order is
support the generation of more electropositive metal cen-
ter in encapsulated complexes. Encapsulation, therefore,
appears to be an effective alternative approach to gener-
ate more electron deficient metal center in guest complex
inside the rigid zeolite host.[2] Lower the electron density
on the metal center, more receptive the metal center is for
the nucleophilic attack. However, the depletion of
electron density can also be achieved by an addition of
electron withdrawing group (‐Cl).[43] It has been also
discussed that an electron withdrawing (‐Cl) substituent
makes the complex essentially monomer in solid state
with distorted square‐planar geometry around the metal.
The report states that distorted chloro ‐ copper salen com-
plex provides the admixing of the ground state dxy orbital
2
CuS1
<
CuS2
<
CuS3
<
CuS4
and
with dz orbital and thereby enhances the stability of
CuSp1 < CuSp2 < CuSp3 < CuSp4 for the salen and
salophen complexes respectively. This behavior of com-
plexes is quite reasonable and can be well‐correlated with
the extent of distortion and molecular dimensions of the
guest complex and their consequence in the optical
spectra.
electron‐rich axial ligand complex suggesting that elec-
tron withdrawing group on the phenyl rings makes the
metal complex significantly non‐planar. However, an
electron donating group (‐OCH3) on the same position
maintains the planarity of the complex. Planar conju-
gated system makes the metal center rich with electron
density so that it acts as a less efficient receptive center
for the nucleophilic attacks. Recently, it is observed
experimentally as well as theoretically that the nickel
(II) Schiff‐base complexes with different molecular
dimensions adopt distorted geometry under encapsula-
tion in zeolite Y. Largest complex experiences more dis-
tortion and shows the most enhanced catalytic activity
for styrene oxidation after the encapsulation. Interest-
ingly, this complex is least reactive for the same catalytic
process in its free state.[23] In the present study, the
parallel behavior of zeolite Y encapsulated copper salen
complexes is observed for the oxidation of styrene in pres-
ence of H2O2. Detailed catalytic studies for the series of
salen complexes have indicated that the CuS3 complex
is the most reactive for the styrene oxidation in a free
state. Electron withdrawing ‐Br group in CuS3 makes
the complex distorted even in its free state. As a conse-
quence, the complex is more reactive towards the
nucleophillic attack stabilizing the electron‐rich axial
ligand (nucleophile) in the transition state (proposed
mechanism for styrene oxidation is presented in
supporting information Figure S11). In the other series,
CuSp3 complex shows slightly lesser reactivity than
expected, the reason could be the low solubility of the
complex in the reaction medium. Encapsulation of CuS3
and CuSp3 complexes inside the supercage further
enhances the degree of distortion and makes the metal,
even more, electron deficient and consequently more
reactive. The performance of the catalysts is well under-
stood, as the main decisive factors like an electronic fac-
tor of electron withdrawing groups and space constraint
imposed by zeolite Y under encapsulation are additive
3.10 | Structural and functional
correlations
It is quite interesting to note that the reactivity in terms of
turn over number (TON) of encapsulated complexes is
substantially higher compared to the corresponding free
state complexes. These observations signify that encapsu-
lation within the supercage of zeolite has converted the
metal complexes significantly reactive and hence, to
achieve the same extent of activity, required active cata-
lytic sites are much lesser in quantity. This makes the
zeolite‐encapsulated complexes as attractive heteroge-
neous catalysts for various organic oxidative transforma-
tions.[29,31] The modified reactivity of the encapsulated
complexes is mostly a consequence of the distorted geom-
etry of the complexes they adopt, under encapsulation in
zeolite Y. Copper Schiff‐base complexes are generally effi-
cient catalysts in solution as well as heterogeneous phases
in comparisons to their corresponding nickel analogues.
Crystal study of these complexes evidently indicates that
copper metal is out of the square CuN2O2 proximity and
shows distorted square planar geometry, whereas nickel
Schiff base complexes are slightly less distorted retaining
its nearly square planar geometry.[42] These complexes
when encapsulated in zeolite Y, are further distorted
due to space constraint imposed by rigid host zeolite
supercage. As a consequence, depletion in the electron
density on the metal center takes place. Comparative
shifts towards the higher value of binding energy in XPS
signals for the zeolite‐encapsulated complexes also

14 of 16
KUMARI ET AL.
to each other and working in synergistic fashion here.
Free state CuS2, CuSp2, CuS4, and CuSp4 complexes
are not as much reactive, since they may exist in the
dimeric form in their solution states,[39] or because of
the less receptive copper metal center for the
nucleophillic attack of H2O2 since all these complexes
have electron donating groups attached on the phenyl
rings. However, these complexes when encapsulated in
zeolite Y, have shown very exciting catalytic behavior.
Among all, the most striking observation is with CuS4
and CuSp4 complexes as when encapsulated they have
shown remarkable enhancement in reactivity for the
above‐mentioned reaction. On encapsulation, TON of
CuS4 catalyst increases from 650 to 3137 and that of
CuSp4 enhances even remarkably from 187 to 3543.
Hence the competence of these heterogeneous systems
is mainly driven by the electron deficiency of the
metals administered by the steric factor, which actually
opposes the original electronic factor of substituent
groups (‐OCH3). The electron deficient character of the
metals via steric constraint imposed by the topology of
zeolite supercage dominates and enhances the reactivity
as the addition of two ‐OCH3 groups on phenyl rings
makes the complex largest in the series and hence more
distorted inside the rigid host cavity of zeolite Y. Conse-
quently, the metal center becomes more electropositive,
showing extraordinarily higher catalytic activities. CuS2
and CuSp2 complexes having electron donating substitu-
ent groups (‐OH) and with moderate molecular dimen-
sions when encapsulated, are not so efficient catalysts as
CuS4, and CuSp4 complexes in their encapsulated states.
For CuS2, inherent electronic factor and electronic factor
is driven by steric constraints oppose each other and
eventually their contributions become comparable as
indicated by TON (shown in Table 2) after encapsulation
in zeolite Y. However, being larger than CuS2, encapsu-
lated CuSp2 complex shows enhancement of catalytic
activity as steric constraints obscure the inherent electron
effect. Overall catalytic data have illustrated the reactivity
of free state copper Schiff‐base complexes driven by only
the electronic factor and therefore the trend of reactivity
follows the order as CuS3 > CuS1 > CuS2 > CuS4 for
salen and CuSp1 > CuSp3 > CuSp2 > CuSp4 for salophen
complexes. After encapsulation of complexes in the zeo-
lite Y, the reactivity order is mainly driven by molecular
dimensions and extent of distortion of the guest com-
plexes. The catalytic reactivity order in the encapsulated
state for the salen complexes therefore becomes
CuS4 > CuS3 > CuS1 > CuS2, whereas the salophen
complexes; larger is the blue shift, more will be the cata-
lytic activity. A further interesting observation, while
comparing the catalytic activities of salen with that of
salophen complexes in both states, is the reactivity of cop-
per salen and salophen complexes are approximately
comparable, however, that is not the case for encapsu-
lated analogues. Only CuS1 and CuSp1 complexes show
comparable reactivity however other substituted copper
salophen complexes are definitely better catalysts than
the corresponding salen complexes. Larger is the molecu-
lar dimensions of a complex, more is the reactivity after
the encapsulation in the zeolite Y towards the styrene
oxidation reaction.
4 | CONCLUSION
Zeolite framework certainly provides a route to design the
heterogeneous catalyst with customized reactivity by the
encapsulation process. Rigid walls of framework impose
space restraint on the guest complex forcing the guest
complex to adopt distorted structure. Such alteration in
the structure of the complex plays a crucial role for the
modified reactivity of the system. The observed blue shift
in a d‐d band in electronic spectra signifies the alterna-
tion in the metal d orbitals energy levels, which is cer-
tainly an effect of the altered coordination sphere
around the metal center. This adaptation of nearly planar
geometry finally leads to the non‐planar geometry and as
a consequence, metal center becomes more electroposi-
tive. Non‐planar geometry impedes the conjugation
around the metal center. XPS studies also support the
enhanced electropositive character of the metal in the
encapsulated complexes as the Cu2p/3 (II) XPS signal for
the encapsulated complexes shifts towards higher binding
energy. More electropositive character of the metal cen-
ter, more susceptible it will be for the nucleophilic attack
of H2O2. It is quite obvious that the larger molecular
dimension leads more deformation in the geometry of
the complex and as a consequence, more active metal
center is created in the encapsulated state of the complex.
Comparative catalytic studies of these hybrid systems pro-
vide a fascinating correlation between modified structural
aspects and modified functionality of complexes, and
therefore it can be concluded, as the degree of distortion
in the structure of the encapsulated complex is the key
point for the remarkable modified catalytic activity of
the systems.
complexes
demonstrate
the
following
order:
ACKNOWLEDGEMENTS
CuSp4 > CuSp3 > CuSp2 > CuSp1. The experimentally
observed blue shift of d‐d transition in electronic spectra
also support above catalytic order of the encapsulated
The authors acknowledge the DST, New Delhi, for the
financial support (DST Project no. SR/FT/CS‐038/2010)

KUMARI ET AL.
15 of 16
Bazarganipour, Catal. Commun. 2006, 7, 336. f) M. Salavati‐
Niasari, E. Zamani, M. R. Ganjali, P. Norouzi, J. Mol. Catal.
A: Chem. 2007, 261, 196.
and for the instrumental facility funded by DST‐FIST,
Department of Chemistry and Department of Physics,
BITS, Pilani, for the XPS measurement, and MNIT Jaipur.
[16] a) F. Bedioui, Coord. Chem. Rev. 1995, 144, 39. b) S.‐N.
Masoud, Chem. Lett. 2005, 34, 1444. c) M. Salavati‐Niasari,
Inorg. Chem. Commun. 2005, 8, 174. d) S.‐N. Masoud,
Chem. Lett. 2005, 34, 244. e) M. Salavati‐Niasari, Inorg.
Chem. Commun. 2004, 7, 963. f) M. Salavati‐Niasari, Poly-
hedron 2009, 28, 2321.
ORCID
Saumi Ray https://orcid.org/0000-0002-6893-9634
REFERENCES
[17] R. F. Parton, I. F. J. Vankelecom, M. J. A. Casselman, C. P.
Bezoukhanova, J. B. Uytterhoeven, P. A. Jacobs, Nature 1994,
370, 541.
[1] a) N. Y. Chen, W. E. Garwood, J. Catal. 1978, 52, 453. b) J. R.
Anderson, K. Foger, T. Mole, R. A. Rajadhyaksha, J. V.
Sanders, J. Catal. 1979, 58, 114.
[18] a) M. R. Maurya, A. K. Chandrakar, S. Chand, J. Mol. Catal. A
Chem. 2007, 270, 225. b) B. Neelam, N. Fehmida, B. Alok, B.
Sudha, A. Amir, Eur. J. Med. Chem. 2000, 35, 481. c) M.
Maurya, S. Titinchi, S. Chand, I. Mishra, J. Mol. Catal. A Chem.
2002, 180, 201. d) M. R. Maurya, S. J. Titinchi, S. Chand, J. Mol.
Catal. A Chem. 2003, 201, 119.
[2] S. Deshpande, D. Srinivas, P. Ratnasamy, J. Catal. 1999, 188, 261.
[3] M. R. Maurya, A. K. Chandrakar, S. Chand, J. Mol. Catal. A
Chem. 2007, 274, 192.
[4] a) C. Jin, W. Fan, Y. Jia, B. Fan, J. Ma, R. Li, J. Mol. Catal. A
Chem. 2006, 249, 23. b) E. R. Shilpa, V. Gayathri, J. Environ.
Chem. Eng. 2016, 4, 4194. c) M. Salavati‐Niasari, J. Mol. Catal.
A Chem. 2005, 229, 159. d) M. Salavati‐Niasari, A. Sobhani,
J. Mol. Catal. A Chem. 2008, 285, 58. e) M. Salavati‐Niasari,
J. Mol. Catal. A Chem. 2008, 283, 120. f) M. Salavati‐Niasari,
F. Davar, Inorg. Chem. Commun. 2006, 9, 263.
[19] D. R. Godhani, H. D. Nakum, D. K. Parmar, J. P. Mehta, N. C.
Desai, J. Mol. Catal. A Chem. 2017, 426, 223.
[20] a) M. Martis, K. Mori, H. Yamashita, Dalton Trans. 2014, 43,
1132. b) S. Seelan, A. K. Sinha, Appl. Catal., A 2003, 238, 201.
[21] S. Bhar, R. Ananthakrishnan, Photochem. Photobiol. Sci. 2017,
16, 1290.
[5] K. J. Balkus, A. G. Gabrielov, in Inclusion Chemistry with
Zeolites: Nanoscale Materials by Design, (Eds: N. Herron, D.
R. Corbin), Springer Netherlands, Dordrecht 1995 159.
[22] M. Sharma, B. Das, G. V. Karunakar, L. Satyanarayana, K. K.
Bania, J. Phys. Chem. C 2016, 120, 13563.
[6] K. K. Bania, R. C. Deka, J. Phys. Chem. C 2013, 117, 11663.
[23] A. Choudhary, B. Das, S. Ray, Dalton Trans. 2016, 45, 18967.
[7] a) J. Zhu, Z. Kónya, V. F. Puntes, I. Kiricsi, C. X. Miao, J. W.
Ager, A. P. Alivisatos, G. A. Somorjai, Langmuir 2003, 19,
4396. b) D. E. De Vos, M. Dams, B. F. Sels, P. A. Jacobs, Chem.
Rev. 2002, 102, 3615.
[24] M. Salavati‐Niasari, Z. Salimi, M. Bazarganipour, F. Davar,
Inorg. Chim. Acta 2009, 362, 3715.
[25] M. M. Bhadbhade, D. Srinivas, Inorg. Chem. 1993, 32, 6122.
[8] a) C.‐Y. Sun, X.‐L. Wang, X. Zhang, C. Qin, P. Li, Z.‐M. Su, D.‐
X. Zhu, G.‐G. Shan, K.‐Z. Shao, H. Wu, J. Li, Nat. Commun.
2013, 4, 2717. b) P. Ling, J. Lei, L. Zhang, H. Ju, Anal. Chem.
2015, 87, 3957.
[26] a) K. O. Xavier, J. Chacko, K. K. Mohammed Yusuff, Appl.
Catal. A Gen. 2004, 258, 251. b) S. Sharma, S. Sinha, S. Chand,
Ind. Eng. Chem. Res. 2012, 51, 8806. c) C. R. Jacob, S. P. Varkey,
P. Ratnasamy, Appl. Catal. A Gen. 1998, 168, 353. d) G.
Ramanjaneya Reddy, S. Balasubramanian, K. Chennakesavulu,
J. Mater. Chem. A 2014, 2, 15598. e) G. R. Reddy, S.
Balasubramanian, K. Chennakesavulu, J. Mater. Chem. A
2014, 2, 19102. f) M. R. Maurya, A. K. Chandrakar, S.
Chand, J. Mol. Catal. A Chem. 2007, 263, 227. g) M. R.
Maurya, A. K. Chandrakar, S. Chand, J. Mol. Catal. A:
Chem. 2007, 274, 192.
[9] D. T. Genna, A. G. Wong‐Foy, A. J. Matzger, M. S. Sanford,
J. Am. Chem. Soc. 2013, 135, 10586.
[10] a) Q. Yao, Y. Zhang, Angew. Chem. Int. Ed. Engl. 2003, 42, 3395.
b) I. J. B. Lin, C. S. Vasam, J. Organomet. Chem. 2005, 690, 3498.
[11] M. Benjamin, D. Manoj, K. Thenmozhi, P. R. Bhagat, D.
Saravanakumar, S. Senthilkumar, Biosens. Bioelectron. 2017,
91, 380.
[27] J. Deka, L. Satyanarayana, G. V. Karunakar, P. K.
[12] M. Salavati‐Niasari, P. Salemi, F. Davar, J. Mol. Catal. A Chem.
2005, 238, 215.
Bhattacharyya, K. K. Bania, Dalton Trans. 2015, 44, 20949.
[28] A. Choudhary, B. Das, S. Ray, Dalton Trans. 2015, 44, 3753.
[13] a) M. Cinouini, S. Colonna, H. Molinari, F. Montanari, P.
Tundo, J. Chem. Soc. Chem. Commun. 1976, 394. b) X. Zuwei,
Z. Ning, S. Yu, L. Kunlan, Science 2001, 292, 1139.
[29] M. R. Maurya, B. Singh, P. Adão, F. Avecilla, J. Costa Pessoa,
Eur. J. Inorg. Chem. 2007, 2007, 5720.
[14] M. R. Maurya, A. K. Chandrakar, S. Chand, J. Mol. Catal. A
Chem. 2007, 263, 227.
[30] W. H. Quayle, G. Peeters, G. L. De Roy, E. F. Vansant, J. H.
Lunsford, Inorg. Chem. 1982, 21, 2226.
[15] a) C. Bowers, P. K. Dutta, J. Catal. 1990, 122, 271. b) A. A.
Valente, J. Vital, in Studies in Surface Science and Catalysis,
Vol. 108, (Eds: H. U. Blaser, A. Baiker, R. Prins), Elsevier
1997 461. c) M. Salavati‐Niasari, Microporous Mesoporous
Mater. 2006, 95, 248. d) M. Salavati‐Niasari, Inorg. Chem.
Commun. 2006, 9, 628. e) M. Salavati‐Niasari, M.
[31] K. K. Bania, D. Bharali, B. Viswanathan, R. C. Deka, Inorg.
Chem. 2012, 51, 1657.
[32] R. Ganesan, B. Viswanathan, J. Phys. Chem. B 2004, 108, 7102.
[33] G.
Ramanjaneya
Reddy,
S.
Balasubramanian,
K.
Chennakesavulu, J. Mater. Chem. A 2014, 2, 15598.

16 of 16
KUMARI ET AL.
[34] a) Y. Yang, H. Ding, S. Hao, Y. Zhang, Q. Kan, Appl.
Organomet. Chem. 2011, 25, 262. b) B. Cristóvão, J. Kłak, B.
Miroslaw, J. Coord. Chem. 2014, 67, 2728. c) É. T. G.
Cavalheiro, F. C. D. Lemos, J. Z. Schpector, E. R. Dockal,
Thermochim. Acta 2001, 370, 129.
[42] A. Boettcher, H. Elias, E. G. Jaeger, H. Langfelderova, M.
Mazur, L. Mueller, H. Paulus, P. Pelikan, M. Rudolph, M.
Valko, Inorg. Chem. 1993, 32, 4131.
[43] M. M. Bhadbhade, D. Srinivas, Inorg. Chem. 1993, 32, 6122.
[35] L. Wu, A. Navrotsky, Phys. Chem. Chem. Phys. 2016, 18,
SUPPORTING INFORMATION
10116.
Additional supporting information may be found online
in the Supporting Information section at the end of the
article.
[36] S. L. Hailu, B. U. Nair, M. Redi‐Abshiro, I. Diaz, R.
Aravindhan, M. Tessema, Chin. J. Catal. 2016, 37, 135.
[37] B. Kumar Kundu, V. Chhabra, N. Malviya, R. Ganguly, G. S.
Mishra, S. Mukhopadhyay, Microporous Mesoporous Mater.
2018, 271, 100.
[38] S. Koner, Chem. Commun. 1998, 593.
How to cite this article: Kumari S, Choudhary
A, Ray S. The functionality of the hybrid systems
driven by molecular dimension of the guest copper
Schiff‐base complexes entrapped in Zeolite‐Y. Appl
Organometal Chem. 2019;e4765. https://doi.org/
10.1002/aoc.4765
[39] M. M. Bhadbhade, D. Srinivas, Inorg. Chem. 1993, 32,
6122.
[40] L. Gomes, E. Pereira, B. de Castro, J. Chem. Soc. Dalton Trans.
2000, 1373.
[41] N. Grover, M. Sankar, Y. Song, K. M. Kadish, Inorg. Chem.
2016, 55, 584.