A nitrate bridged one-dimensional copper(II) coordination polymer with a tridentate (NNO) Schiff base: synthesis, X-ray structure and catalytic efficacy

Article abstract of DOI:10.1007/s11243-020-00415-7

A one-dimensional Cu(II) coordination polymer of [Cu(L)(μ-ONO₂)]_n (1) (HL = 4-methoxy-2-[1-(methylaminoethylimino)methyl]-phenol) with bidentate bridging nitrate has been isolated and characterized by X-ray diffraction analysis and spectroscopic studies. Single crystal?X-ray analysis revealed that each copper(II) center in the asymmetric unit of complex 1 adopts a distorted square pyramidal geometry with a CuN₂O₃ chromophore ligated through a tridentate Schiff base (L) with (NNO) donor sets and two O atoms of bridging nitrate ion. The adjacent copper atoms are connected by bridging nitrate (μ-ONO₂) in bidentate fashion affording a 1D coordination polymeric chain structure along the?crystallographic b-axis. In the polymeric framework, the Cu…Cu separation is 4.3749(4) ?. The catalytic efficacy of complex 1 was studied in a series of solvents for the epoxidation of cyclooctene using tert-butyl-hydroperoxide (TBHP) as an efficient oxidant under mild conditions. The catalytic reaction mixture was analyzed by gas chromatography and the data indicated that the yield of the epoxidation?reaction and its selectivity is maximum in acetonitrile medium.

Full text of DOI:10.1007/s11243-020-00415-7

Transition Metal Chemistry
https://doi.org/10.1007/s11243-020-00415-7
A nitrate bridged one‑dimensional copper(II) coordination polymer
with a tridentate (NNO) Schif base: synthesis, X‑ray structure
and catalytic efcacy
Habibar Chowdhury1 · Rajesh Bera2 · Corrado Rizzoli3 · Chandan Adhikary4
Received: 25 May 2020 / Accepted: 18 July 2020
© Springer Nature Switzerland AG 2020
Abstract
A one-dimensional Cu(II) coordination polymer of [Cu(L)(μ-ONO2)]n (1) (HL=4-methoxy-2-[1-(methylaminoethylimino)
methyl]-phenol) with bidentate bridging nitrate has been isolated and characterized by X-ray difraction analysis and spec-
troscopic studies. Single crystal X-ray analysis revealed that each copper(II) center in the asymmetric unit of complex 1
adopts a distorted square pyramidal geometry with a CuN2O3 chromophore ligated through a tridentate Schif base (L) with
(NNO) donor sets and two O atoms of bridging nitrate ion. The adjacent copper atoms are connected by bridging nitrate
(μ-ONO2) in bidentate fashion afording a 1D coordination polymeric chain structure along the crystallographic b-axis. In
the polymeric framework, the Cu…Cu separation is 4.3749(4) Å. The catalytic efcacy of complex 1 was studied in a series
of solvents for the epoxidation of cyclooctene using tert-butyl-hydroperoxide (TBHP) as an efcient oxidant under mild
conditions. The catalytic reaction mixture was analyzed by gas chromatography and the data indicated that the yield of the
epoxidation reaction and its selectivity is maximum in acetonitrile medium.
Introduction
Coordination polymers (CPs) [1] and metal–organic frame-
works (MOFs) [2] through strong metal–ligand covalent
bonds [3] and multiple weak non-covalent forces [4] have
attracted great attention of many research groups in the iso-
lation of diferent advanced functional materials [5–9]. Sin-
gle-pot synthesis [10] is an efcient synthetic approach using
judiciously chosen metal ions, organic ligands and bridging
units in pre-assigned molar ratios to isolate such target mate-
rials. Cu(II), a 3d9 ion, afords [11] a variety of geometries
that may lead to signifcant diferences in overall molecular
and crystalline architectures and thereby produce diferent
biological and catalytic activities [12]. The copper ion also
fnds signifcant use in bioinorganic chemistry [13]. A group
of mono-negative NNO donor tridentate Schif base ligands
derived from the mono-condensation of diamines with car-
bonyl compounds (salicylaldehyde, o-hydroxyacetophenone,
acetylacetone or benzoylacetone), readily react with transi-
tion metal ions and auxiliary ligands to form mono- and
polynuclear complexes with varied functionalities and versa-
tile applications. Depending on the relative position, number
and nature of the donor atoms of a Schif base, the ligand
approves a favourable control over the stereochemistry of the
metallic centers in homo- and heteropolynuclear compounds
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11243-020-00415-7) contains
supplementary material, which is available to authorized users.
* Chandan Adhikary
cadhikary123@gmail.com
Habibar Chowdhury
habibar_hs@yahoo.co.in
Rajesh Bera
berarajesh2010@gmail.com
Corrado Rizzoli
corrado.rizzoli@unipr.it
1
Department of Chemistry, Kabi Nazrul College, Murarai,
Birbhum, West Bengal 731 219, India
2
Department of Chemistry, Dinabandhu Andrews College,
Kolkata, West Bengal 700084, India
3
Departimento di Scienze Chimiche, della Vita e della
Sostenibilità Ambientale, Parco Area delle Scienze 17/A,
43124 Parma, Italy
4
Department of Chemistry, Institute of Education (P.G.)
for Women, Chandernagore, Hooghly, West Bengal 712138,
India
Vol.:(0123456789)
1 3

Transition Metal Chemistry
Fig. 1 Diferent coordination
motifs of the nitrate ion
tert-BuOOH (70% aq.) were purchased from Aldrich and
used as received. All other chemicals and solvents were AR
grade. The solvents used were distilled and dried before
use. The synthetic reactions and work-up were done in
the open air. Microanalysis (CHN) was performed using
a Perkin Elmer 240 elemental analyzer. IR spectra were
recorded with a Bruker Alpha T 200140 FT-IR spectrometer.
Absorption spectra were studied with a Shimadzu UV2100
UV–Vis recording spectrophotometer. GC analysis was
carried out with an Agilent Technologies 6890 N network
GC system equipped with a fused silica capillary column
(30 m×0.32 mm) and a FID detector.
Fig. 2 Framework of tridentate (NNO) Schif base ligand (HL)
[14]. All these opportunities make Schif bases privileged
ligands in the attempt to synthesize metal complexes having
relevance to bioinorganic chemistry, catalysis, encapsula-
tion, transport and separation processes [14]. Schif base
copper complexes can now be extensively used as active
catalysts in several oxidation reactions, both in homogene-
ous [15–18] and heterogeneous condition [19, 20]. Nitrate
Synthesis of Schif base (HL)
5-Methoxysalicyladedehyde (0.15 g, 1 mmol) was refuxed
(10 h) with N-methylethylenediamine (0.07 g, 1 mmol)
in dehydrated alcohol (20 ml) with a little modifcation
[22]. After 10 h the reaction solution was evaporated
under reduced pressure to yield a gummy mass, which was
dried and stored in vacuo over CaCl2 for subsequent use
(Scheme 1). Yield 0.28 g (80% based on amine). Elemen-
tal Anal. Calcd for C11H16N2O2 (HL): C, 63.4; H, 7.7; N,
13.5%. Found: C, 63.8; H, 8.2; N, 13.5%. FTIR (cm−1):
ν(C=N), 1632; ν(N–H), 3120.
−
ion (NO3 ) [21] acts as monodentate, bidentate bridging
and bidentate chelating ligand (Fig. 1) for the construction
of supramolecular architectures. In the framework of our
research eforts constituting a part of our continuing study
on metal complexes of tridentate Schif base ligands based
on substituted ethylenediamines, we have chosen a triden-
tate Schif base (HL) (Fig. 2) to isolate a neutral coordina-
tion polymer, [Cu(L)(μ-ONO2]n (1) (HL=4-methoxy-2-[1-
(methylaminoethylimino)methyl]-phenol). The structure
of complex 1 has been determined by X-ray difraction
measurements and the catalytic efcacy of 1 for the epoxi-
dation of cyclooctene, employing tert-butyl-hydroperoxide
(TBHP) as an efcient oxidant in diferent solvent media, is
also reported.
Synthesis of [Cu(L)(μ‑ONO2)]n (1)
A solution of HL (0.21 g, 1 mmol) in MeOH (5 ml) was added
dropwise to a solution of Cu(II) nitrate hexahydrate (0.29 g,
1 mmol) in the same solvent (10 ml). The fnal deep blue solu-
tion was fltered and the supernatant liquid was kept undis-
turbed in open air for slow evaporation. After 5 days, a blue
crystalline product of 1 was isolated by fltration, washed with
dehydrated alcohol and dried in vacuo over silica gel. Yield
0.44 g (70% based on ligand). Anal. Calcd for C11H15N3O5Cu
(1): C 39.7; H 4.5; N 12.6%. Found: C 40.2; H 4.1; N 13.0%.
FTIR (KBr/cm−1): νs(NO3) 1735, 1794. UV–Vis in DMF
[λmax, nm (εmax/dm3mol−1 cm−1)]: 266, 296 (1.20×104), 387
(1.15×104), 607 (2.30×102); ΛM (DMF/ohm−1 cm2 mol−1):
Experimental
Materials and method
High purity 5-Methoxysalicyladehyde (E. Merck, India),
N-methyl ethanediamine (Aldrich, USA) and Cu(II) nitrate
hexahydrate (E. Merck, India) were purchased from their
respective concerns and used as received. Cyclooctene and
Scheme 1 Synthetic route for
OH
MeOH
Reflux
OH
H
N
Schif base HL
H
N
+ H2N
N
CH3
CHO
H3CO
H3CO
C
H
CH3
Schiff base (HL)
1 3

Transition Metal Chemistry
Table 1 Crystallographic data and structure refnement parameters
for 1
6. μef. (B.M.)=1.78. ESR (solid state): g║=2.042; g┴=2.013,
gav =2.022; G=4.753.
Crystal parameters
1
X‑ray crystallographic analysis
Empirical formula
Formula weight
C11H15N3O5Cu
332.80
A single crystal of 1 suitable for X-ray analysis was selected
from those obtained by slow evaporation of a methanol solu-
tion at room temperature. Difraction data were collected on
a Bruker SMART 1000 CCD difractometer using graphite
monochromated Mo-Kα radiation (λ=0.71073 Å) and were
used to measure cell dimensions and difraction intensities.
Data were collected using the ω–θ scan technique in the range
to a maximum 2.7°<θ<25.5°. For data collection, data reduc-
tion and cell refnement. the program SAINT-Plus [23] was
used. The structure was solved by direct methods using SIR97
[24] and refned with version 2018/3 of SHELXL [25] using
Least Squares minimisation. The model was refned. The
amine H atoms were located on a diference Fourier map and
refned freely. C-bound H atoms were positioned geometrically
and refned using a riding model, with C–H=0.96–0.97 Å and
with Uiso=1.2 Ueq(C) or 1.5 Ueq(C) for methyl H atoms.
The fnal positional and thermal parameters are available as
supplementary material. A summary of the crystallographic
data and structure determination parameters for complex 1 is
set in Table 1. Crystallographic data for the structural analysis
has been deposited with the Cambridge Crystallographic Data
Centre (CCDC No. 2000429 for 1). A copy of this information
can be obtained free of charge from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (fax:+44-1223-336-
033; e-mail: deposit@ccdc.cam.ac.uk or www: https://www.
ccdc.cam.ac.uk).
Crystal system
Monoclinic
P 21/n
12.8738 (10)
7.8553 (6)
13.0713 (10)
90
93.6188 (12)
90
1319.23 18)
0.71073
1.672
Space group
A (Å)
b(Å)
c (Å)
α0
β°
γ0
V (Å3)
λ (Å)
ρcalcd (g cm−3
)
Z
4
T (K)
294(2)
1.676
684
0.17×0.09×0.08
2.15 to 25.25
μ (mm−1
F(000)
)
Crystal size (mm3)
θ ranges (°)
Index ranges
−14≤h≤15
−9≤k≤9
−15≤l≤15
Refections collected
Independent refections
Tmax and Tmin
8498
2401
0.878 and 0.812
2401/1/187
0.025
Data/restraints/parameters
R (int)
Goodness-of-ft on F2
Final R indices [I>2σ(I)]
R indices (all data)
Largest peak and hole (eÅ−3
1.066
R=0.0275 and wR=0.0734
R=0.0307 and wR=0.0756
0.333 and −0.186
Catalytic reactions
)
The catalytic reactions were carried out in a glass batch
reactor, according to the following procedure. Substrate
(10 mmol), solvent (8 ml) and catalyst (0.005 mmol) were
frst mixed in a round-bottom fask. The mixture was then
equilibrated to 65 °C in an oil bath. After addition of tert-
BuOOH (20 mmol), the mixture was stirred continuously for
24 h. The products of the oxidation reactions were collected
at diferent time intervals and were identifed and quantifed
by a VARIAN CP-3800 gas chromatograph equipped with
an FID detector. A CP-Sil 8 CB capillary column was used
for analysis of the products.
2 2
Weighting scheme: R=Σ||Fo|−|Fc||/Σ|Fo|, wR=[Σw(Fo2 −Fc ) /
2 2 1/2
2
Σw(Fo ) ]
,
calcd w=1/[σ2(Fo )+(0.0422P)2 +0.5323P] where
2
P=(Fo2 +2Fc )/3
HL = 4-methoxy-2-[1-(methylaminoethylimino)methyl]-
phenol) has been isolated using a one-pot reaction of a 1:1
molar ratio of Cu(NO3)2·6H2O and a Schif base (HL) in
methanol at room temperature. The typical synthesis is sum-
marized in Eq. (1):
(
)
[
(
)]
n
MeOH
Cu NO3 ⋅6H2O + HL ⟶ Cu(L) ꢀ − ONO2
[298 K]
(1)
2
Results and discussion
Complex 1 was characterized by microanalytical (C, H
and N), spectroscopic and other physico-chemical results.
The microanalytical data are in good agreement with the
formulation of the complex. The air stable moisture insensi-
tive compound is stable over a long period of time in powder
and crystalline states and is soluble in MeOH, EtOH, MeCN,
Synthesis and physical measurements
A
nitrate bridged 1D chain Cu(II) coor-
d i n a t i o n p o ly m er, [ C u ( L ) (μ - O NO2) ]n ( 1 )
1 3

Transition Metal Chemistry
Fig. 3 An ORTEP diagram of the asymmetric unit of [Cu(L)
(μ-ONO2)]n (1) with displacement ellipsoids drawn at the 50% prob-
ability level
Fig. 5 Partial and complete crystal packing views of 1 showing a pol-
ymeric chain extending along b axis
Table 2 Selected bond distances (Å) and bond angles (°) for 1
Bond distances
Cu1–N1
Cu1–N2
Cu1–O1
Cu1–O3
Cu1–O4
1.9384 (17)
2.0386 (19)
1.9026 (15)
2.0531 (15)
2.5817 (16)
Cu1–O4_a
Cu1_b–O4
O3–N3
O4–N3
O5–N3
2.4319 (16)
2.4319 (16)
1.276 (2)
1.242 (2)
1.215 (2)
Bond angles
N1–Cu1–N2
N1–Cu1–O1
N1–Cu1–O3
N1–Cu1–O4
N1–Cu1–O4_a
N2–Cu1–O1
N2–Cu1–O3
N2–Cu1–O4
84.54 (7)
94.14 (7)
172.11 (7)
119.12 (6)
107.44 (7)
176.19 (7)
91.99 (7)
92.04 (7)
N2–Cu1–O4_a
O1–Cu1–O3
O1–Cu1–O4
O1–Cu1–O4_a
O3–Cu1–O4
O3–Cu1–O4_a
O4–Cu1–O4_a
Cu1–O4–Cu1_b
86.94 (7)
89.76 (6)
91.72 (6)
90.05 (7)
53.81 (6)
79.37 (6)
133.12 (6)
121.50 (7)
Fig. 4 Perspective view of molecular unit of 1
DMF and DMSO, but is insoluble in water. In DMF solution,
the complex 1 is a non-electrolyte as refected from the low
conductivity value (6 Ω−1cm2mol−1).
Symmetry code: (a) 1/2−x, −1/2+y, 1/2−z; (b) 1/2−x, 1/2+y,
1/2−z
Crystal structure of [Cu(L)(μ‑ONO2)]n (1)
Single crystal X-ray difraction study of [Cu(L)(μ-ONO2)]n
(1) was made to defne the coordination sphere. An ORTEP
diagram of asymmetric units, molecular unit and packing
view of 1D polymeric chain structure of 1 are depicted in
Figs. 3, 4 and 5, respectively. Selected bond distances and
angles relevant to the coordination spheres are presented in
Table 2. X-ray structural analysis reveals that each Cu(II)
center in the asymmetric unit of 1 adopts a distorted square
pyramidal geometry (τ=0.07) with a CuN2O3chromophore
[26] coordinated by two N atoms (N1, N2) and one O atom
(O1) of the tridentate Schif base ligand (L) and two O
atoms (O3, O4) of the bridging nitrate (Fig. 3). A consid-
erable deviation from ideal square pyramidal geometry is
seen, which is presumably due to the smaller bite angles
produced by ligand [N1–Cu1–N2 84.54(7)°] and nitrate
[O3–Cu1–O4_a 79.37(6)°]. The coordination sites of the
basal plane are occupied by two N atoms (N1, N2) and one
O atom of the Schif base (L) and two O atoms (O3, O4)
of bridging nitrate acting as a bidentate ligand. The bond
distance of Cu1–N1(amine) [1.9384(17)Å] is smaller than
Cu1–N2(imine) [2.0386(19) Å]. The three Cu–O bond lengths
are diferent, where Cu1–O1(ligand) [1.9026(15) Å] is small-
est than the other two Cu1–O3(nitrate) [2.0531(15) Å] and
Cu1–O4(nitrate) [2.5817(16) Å] (Table 2). The Cu(II) center
deviates 0.0314(2) Å from the N1/N2/O1/O3 mean plane.
The apical position is occupied by O atom [Cu1–O4_a:
2.4319(16) Å; symmetry code: a=½−x,−½+y, ½−z] of
the other bridging nitrate (Fig. 6). Complex 1 is an example
of a coordination polymer containing a bidentate bridging
nitrate. The adjacent copper atoms are connected by a biden-
tate bridging nitrate with μ-ONO2 bridging mode afording a
1D polymeric chain structure (Fig. 5). The Cu1–O4–Cu1_b
1 3

Transition Metal Chemistry
(symmetry code: b=½−x,−½+y, ½−z) bridging angle is
121.49(6)°. In the polymeric framework, the Cu…Cu sepa-
ration is 4.3749(4) Å.
good yield with high selectivity in diferent solvents when cat-
alyzed by complex 1. The results of the catalytic epoxidation
of cyclooctene are given in Table 3. As evident from Table 3,
complex 1 exhibits the highest conversion of 88% with 86%
epoxide selectivity. A graphical representation of the rela-
tive efcacy of complex 1 as catalyst for the epoxidation of
cyclooctene in diferent solvents has been given in Fig. S1.
In general, the catalytic efciency in diferent solvents fol-
lowed the order: acetonitrile>chloroform>dichlorometh-
ane>methanol. The optimum polarity of acetonitrile that is
suitable to dissolve both tert-BuOOH and cyclooctene might
be facilitating the highest catalytic activity. We studied the
reactions by varying the temperature from room temperature
to 75 °C in acetonitrile to determine the optimum temperature.
It was found that the maximum conversion occurred at 65 °C
(Fig. S2). The results of control experiments in the epoxi-
dation of cyclooctene with tert-BuOOH at 65 °C are pre-
sented in Table 4. Control experiments without using cata-
lyst failed to produce the desired product. The conversion of
cyclooctene was only 4% in the absence of the catalyst. The
Cu(NO3)2 salt, however, achieved a conversion of 66%, but
selectivity was lower (53%). The results of reported epoxi-
dation reactions of cyclooctene using tert-BuOOH as oxi-
dant over Cu(II) Schif base complexes under homogene-
ous conditions are collated in Table 5 [15–18]. We have
earlier studied the oxidation reactions of a variety of olefns
over Cu(II) Schiff base complexes, [Cu(L1)(H2O)](ClO4)
FT‑IR and electronic spectra of 1
In the FT-IR spectrum, complex 1 exhibits a band at
1794 cm−l with a shoulder at 1735 cm−l due to the bidentate
bridging nitrate [21]. Also, the bands of weak intensity at
3062, 2945 and 2840 cm−1 are assigned to the C–H stretch-
ing vibrations of aromatic rings, methylene and methoxy
groups, respectively [27]. In the UV–Vis spectrum, a weak
low-intensity absorption band at 600 nm is assignable to d–d
transition, consistent with the square pyramidal (sp) geome-
try of the Cu(II) centers [28]. The absorption band observed
at 380 nm may be attributed to the ligand -to -Cu(II) charge
transfer transition (LMCT) [29]. Additionally, two strong
absorption bands in the region 265 and 295 nm may be
assigned to ligand-based transitions.
Magnetic study and EPR spectroscopy of 1
Room-temperature solid-phase magnetic susceptibility
measurement shows that compound (1) has a magnetic
moment of 1.78 BM, which is close to the expected spin-
only value. The powder EPR spectrum of complex 1 in
the solid state is depicted in Fig. 6. The principal g values
have been determined by conventional methods of EPR spec-
troscopy [30]. The g║ and g┴ values of the complex were
calculated to be 2.18 and 2.08 with gav =2.022; G=4.753.
This is a typical axial spectrum in which the copper(II) ion
possesses either a square planar or fve-coordinate geometry.
The X-ray crystal structure shows that the complex indeed
displays a square-pyramidal coordination geometry.
Table 3 Homogeneous oxidation of cyclooctene catalyzed by the
complex [Cu(L)(μ-ONO2)]n (1) at 65 °C in diferent solvents
Solvents
Reaction time Conversion
Yield of products
(Hr)
(wt%)
Epoxide
Others
CH3CN
CH2Cl2
CHCl3
24
24
24
24
88
64
58
55
86
59
53
44
2a
5a
Catalytic activities
5a
CH3OH
11a
The catalytic activity of [Cu(L)(μ-ONO2)]n (1) was studied in
the epoxidation of cyclooctene with tert-BuOOH as an oxi-
dant. Cyclooctene was converted to cyclooctene epoxide in
Reaction conditions: Cyclooctene (10 mmol); catalysts (0.005 mmol);
tert-BuOOH (20 mmol); acetonitrile (8 mL). a2-Cyclooctene-1-ol
Fig. 6 Powder EPR spectrum of
the complex 1
1 3

Transition Metal Chemistry
Table 4 Control experiments in epoxidation of cyclooctene with tert-
(conversion 86%, selectivity 81%) with tert-BuOOH as oxi-
dant [16]. Rayati et al. reported the oxidation of cyclooctene
with tert-BuOOH in the presence of electron-rich salen-type
Schif base copper(II) complexes, where the highest conver-
sion was 70% after 8 hr in acetonitrile media and epoxide
selectivity was 100% [17] (Table 5). Abbasi et al. studied the
epoxidation of cyclooctene using a series of mononuclear and
dinuclear salen-type copper(II) Schif base complexes, where
the highest conversion goes to 85%, but epoxide selectivity
maximum was 67%. Along with the epoxide, the allylic oxi-
dation product cyclooct-2-enol, and cyclooct-2-enone were
also obtained [18]. However, in our present study, the conver-
sion of cyclooctene by complex 1 displayed marked improve-
ment with good selectivity. Cu(II) Schif base catalysts under
heterogeneous conditions have been used for epoxidation of
olefns with tert-BuOOH in the recent past. Sakthivel et al.
have reported the oxidation of cyclooctene with tert-BuOOH
over a tetrahydro-salen Cu(II) complex grafted on iodosilane
modifed surfaces of MCM-41 and MCM-48, but the conver-
sion was only 53–54% with 78–85% selectivity. However, in
homogeneous condition, there was a reported 73.7% con-
version and 73% selectivity [31]. Jana et al. have obtained
92% conversion of cyclooctene with 92% epoxide selectivity
using a Cu(II) Schif-base anchored MCM-41 catalyst [20].
Zarnegaryan et al. have reported that the efective conversion
of cyclooctene (conversion 88%, selectivity 100%) by Cu(II)
Schif base complex immobilized on graphene nanosheets
using tert-BuOOH in acetonitrile media, although the highest
conversion (99%) occurred in dichloromethane media [32].
Banaei et al. studied the epoxidation of cyclooctene by zeolite-
Y encapsulated Cu(II) complexes with 16- and 17-membered
diazadioxa macrocyclic Schif bases nanocomposite materials,
where conversion goes to a highest value of 84% (selectiv-
ity up to 82%) with the formation of three by-products [33].
However, in the case of complex 1, allylic C–H oxidation was
2–11% in diferent solvents. The reaction profle of the epoxi-
dation of cyclooctene with diferent solvents is shown in Fig.
S3. The complex contains fve-coordinated coordinatively
unsaturated Cu-center; thus, the complex has been used for the
Lewis acidic catalysis reaction under homogeneous conditions.
The Cu(II) binds the peroxo-group on treatment with peroxides
[34] to form the pre-catalyst containing LxCu–OOH (where
L=ligand), which are capable of transferring the oxo-function-
ality to the organic substrates to produce the oxidized products
[35]. We assume that a similar kind of mechanism is operative
in our case. The probable mechanism for catalytic cycle is
depicted in Scheme 2. X-ray crystal structure analysis shows
the presence of fve-coordinated Cu(II) in [Cu(L)(μ-ONO2]n
(1). So, the coordination environment around Cu(II) is easily
accessible for an external ligand. As a result, tert-BuOOH has
enough space to bind copper in the intermediate stages of the
catalytic cycle.
BuOOH at 65 °C
Run
Catalyst
Conversion
(wt%)
% Yield
of epox-
ide
1
2
3
No catalyst
Cu(NO3)2
[Cu(L)(μ-ONO2)]n
4
66
88
4
35
86
Reaction condition: Cyclooctene (10 mmol), Catalyst (0.005 mmol),
tert-BuOOH (20 mmol), CH3CN (8 ml)
Table 5 Comparison of catalytic efcacy of the complex [Cu(L)
(μ-ONO2)]n (1) with other reported copper(II) catalysts for the epoxi-
dation of cyclooctene with tert-BuOOH in CH3CN media
Complexes
Conversion (%)
Reference
[Cu(L1)(H2O)](ClO4)
[Cu(L2)]
75
75
76
86
70a
70a
69
92
88
84
88
[15]
[15]
[15]
[16]
[17]
[17]
[18]
[20]
[Cu(L3)]
[CuL(μ -1,1-N3)]n
][Cu{salnptn(3-OMe)2}]
[Cu(hnaphnptn)]
(CuLn, n=1–4)
Cu-MCM-41
CuII(Schif base)Cl2@GO-CPb
Cu-L’-Y
[32]
[33]
This study
[Cu(L)(μ-ONO2)]n
HL1 = 1-(N-ortho-hydroxy-acetophenimine)-2-methyl-pyridine,
H2L2 =N,N’-(2-
hydroxy-propane-1,3-diyl)-bis-salicylideneimine,
H2L3 = N,N’-(2,2-dimethyl-propane-1,3-diyl)-bis-salicylideneimine,
H2{salnptn(3-OMe)2}=Schif-base derived by thecondensationof2,2′
-dimethylpropandiamineand2-hydroxy-3-methoxybenzaldehyde,
H2{hnaphnptn} = Schiff-basederivedbythecondensationof2,2′-
dimethylpropandiamine
and
2-hydroxy-1-naphthaldehyde,
Schif-base derived from the condensation of meso-1,2-diphe-
nyl-1,2-ethylenediamine with various salicylaldehyde derivatives
(x-salicylaldehyde for H2Ln, x=H (n=1), 5-Br (n=2), 5-Br-3-NO2
(n=3) and 2′-hydroxyacetophenone (n=4).Cu(II) (Schif base)Cl2@
GO-CP=Cu(II) Schif base complex immobilized on Graphene
oxide. L’=3,4,11,12-dibenzo-1,14-diaza-5,10-dioxa cyclohexade-
cane-1,13-diene.aFor 8 h, bFor5hr
(HL1 =1-(N-ortho-hydroxy-acetophenimine)-2-methylpyri-
dine), [Cu(L2)] (HL2 =N,N’-(2-hydroxy-propane-1,3-diyl)-
bis-salicylideneimine),[Cu(L3)](HL3 =N,N’-(2,2-dimethyl-
propane-1,3-diyl)-bis-salicylideneimine), which exhibit high
catalytic activity with tert-BuOOH in diferent solvent media,
where cyclooctene has been converted to its epoxide (con-
version 76–75%, selectivity 63–56%) in acetonitrile media
[15]. We have also demonstrated the epoxidation of cyclooc-
tene using a single end-on azido bridged 1D chain Schif-
base copper(II) complex [CuL(µ1,1-N3]n(HL=1-(N-ortho-
hydroxyacetophenimine)-2-(N-ethyl)aminoethane) as catalyst,
where the highest conversion occurs also in acetonitrile
1 3

Transition Metal Chemistry
Scheme 2 Probable mechanism
of catalytic cycle for olefnic
epoxidation catalyzed by
complex 1
3. Neidig ML, Clark DL, Martin RL (2013) Coord Chem Rev
257:394
Conclusion
4. Reedijk J (2013) Chem Soc Rev 42:1776
In summary, a neutral nitrate bridged coordination polymer 1
of Cu(II) containing a tridentate Schif base has been isolated
and characterized by single crystal X-ray difraction. Structural
analysis revealed that each Cu(II) center features a distorted
square pyramidal geometry bearing a CuN2O3 chromophore
in 1. The adjacent copper atoms are connected by a bidentate
μ-NO3 bridge to form a one-dimensional coordination poly-
meric structure. Complex 1 displayed moderate catalytic ef-
cacy in homogeneous cyclooctene epoxidation. The catalytic
reaction also revealed the highest selectivity in acetonitrile
medium.
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Pi-interactions in crystal engineering: frontiers in crystal engi-
neering, 1st edn. Wiley, Chichester, UK
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NR (2004) Inorg Chim Acta 357:4208
Acknowledgements The work was financially supported by the
Department of Science and Technology, Government of India, by a
grant (SR/S1/IC-13/2010) (to CA).
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Compliance with ethical standards
15. Adhikary C, Bera R, Dutta B, Jana S, Bocelli G, Cantoni A,
Chaudhuri S, Koner S (2008) Polyhedron 27:1556
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Polyhedron 29:2166
Conflict of interest No potential confict of interest was reported by
the authors.
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(2010) Inorg Chem Commun 13:203
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