Synthesis, structural and magnetic characterizations of a dinuclear copper(II) complex with an (N,S,O) donor ligand: Catecholase and phenoxazinone synthase activities

Article abstract of DOI:10.1016/j.ica.2018.02.004

A new dinuclear Cu(II) complex (1) was synthesized and crystallographically characterized. Each of the Cu(II) centres has penta coordination and been found to adopt square pyramidal geometry. Variable temperature magnetic measurements showed that there is weak ferromagnetic interaction between the Cu(II) centres in 1. 1 shows catecholase as well as phenoxazinone synthase activities in different solvents. The turn over numbers for the catecholase activity were 4.02 × 10³ h^?1 (MeOH) and 9.57 × 10³ h^?1 (MeCN), and that of phenoxazinone synthase activity were 1.065 × 10³ h^?1 (MeOH), 2.13 × 10² h^?1 (MeCN) and 2.844 × 10³ h^?1 (DCM).

Full text of DOI:10.1016/j.ica.2018.02.004

Accepted Manuscript
Research paper
Synthesis, structural and magnetic characterizations of a dinuclear copper(II)
complex with an (N,S,O) donor ligand: catecholase and phenoxazinone synthase
activities
Ayon Kanti Ghosh, Anzar Ali, Yogesh Singh, Chandra Shekhar Purohit,
Rajarshi Ghosh
PII:
S0020-1693(17)31838-8
https://doi.org/10.1016/j.ica.2018.02.004
ICA 18113
DOI:
Reference:
Inorganica Chimica Acta
To appear in:
Received Date:
Revised Date:
Accepted Date:
2 December 2017
31 January 2018
1 February 2018
Please cite this article as: A.K. Ghosh, A. Ali, Y. Singh, C.S. Purohit, R. Ghosh, Synthesis, structural and magnetic
characterizations of a dinuclear copper(II) complex with an (N,S,O) donor ligand: catecholase and phenoxazinone
synthase activities, Inorganica Chimica Acta (2018), doi: https://doi.org/10.1016/j.ica.2018.02.004
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1
Synthesis, structural and magnetic characterizations of a dinuclear copper(II)
complex with an (N,S,O) donor ligand: catecholase and phenoxazinone synthase
activities
Ayon Kanti Ghosha, Anzar Alib, Yogesh Singhb, Chandra Shekhar Purohitc, Rajarshi Ghosha,*
aDepartment of Chemistry, The University of Burdwan, Burdwan 713 104, India
bDepartment of Physical Sciences, Indian Institute of Science Education & Research, Mohali,
Sector 81, S. A. S. Nagar, Knowledge City, Manauli PO, Mohali, 140 306, India
cSchool of Chemical Sciences, National Institute of Science Education & Research,
Bhubaneswar, Orissa, 751 005,India
Abstract
A new dinuclear Cu(II) complex (1) was synthesized and crystallographically
characterized. Each of the Cu(II) centres has penta coordination and been found to adopt square
pyramidal geometry. Variable temperature magnetic measurements showed that there is weak
ferromagnetic interaction between the Cu(II) centres in 1. 1 shows catecholase as well as
phenoxazinone synthase activities in different solvents. The turn over numbers for the
catecholase activity were 4.02 × 103 h-1 (MeOH) and 9.57 × 103 h-1 (MeCN), and that of
phenoxazinone synthase activity were 1.065 × 103 h-1 (MeOH), 2.13 × 102 h-1 (MeCN) and
2.844 × 103 h-1 (DCM).
Keyword: Copper, Schiff base, catecholase activity, phenoxazinone synthase activity
__________

2
*Corresponding author, E. mail: rghosh@chem.buruniv.ac.in
1. Introduction
Copper containing proteins are well known redox catalysts in different biological processes.
These copper proteins are classified as type-1, type-2 and type-3 based on their spectroscopic
features [1a]. Catechol oxidase is a type 3 copper protein and is found in plants. Catalysis of
catechol-quinone oxidation reactions by catechol oxidase in presence of aerial oxygen is known
as catecholase activity [1]. The resulting quinones auto-polymerize to give brown pigments
which are responsible to defend the damages caused by pathogens and insects to plants. As soon
as the active site structure of catechol oxidase appeared in literature [3] as an
antiferromagnetically coupled dinuclearcopper(II), a number of groups around the world started
to report [4-6] different Cu(II) and other transition metal complexes as structural and/or
functional model for catecholase activity (Scheme 1). Phenoxazinone synthase [1b, 2], which is
an another multicopper enzyme, is naturally produced by Streptomyces antibioticus. The active
site structure of phenoxazinone synthase as hexameric copper complex appeared in literature in
2006 [8]. This is responsible for six electron oxidative coupling of two molecules of an o-
aminophenol (OAPH) to form the phenoxazinone chromophore (Scheme 2) [2, 9, 10]. Metal
complexes of different (N,N), (N,O) and (N,S) donor ligands, which exhibit catecholase and
phenoxazinone synthase activities, are there in literature [4-7, 9, 10]. Use of different donor
groups in the ligand backbone, which ligates to the metal with different strengths, helps to attack
substrates by opening their donor site(s) with different extents leading to increased or decreased
catalytic rates. In this endevour, we have synthesized a new (N,S,O) donor organic ligand having
mixed soft-hard donor sites and its ferromagnetically coupled dichloro bridged dinuclear Cu(II)
II
complex.
The
metal
complex
[Cu2 L2Cl2]
(1)
[HL
=
2-((E)-(2-

3
(benzylthio)ethylimino)methyl)phenol] is X-ray crystallographically and magnetically
characterized. It mimics the activities of catechol oxidase as well as phenoxazinone synthase in
different solvents. The mechanistic pathway for these activities are tried to be enumerated. Here
to note, in spite of our best effort, we have not found any metal system complexed with (N,S,O)
donor ligand.
Scheme 1. Catecholase activity
Scheme 2. Phenoxazinone synthase activity
2. Experimental
2.1.Materials
High purity benzylmercaptan, 2-chloroethylamine, salicylaldehyde and Copper(II)
chloride dehydrate were purchased from Sigma Adrich, India. Ethanol and methanol were used
as reagent grade solvents. 3,5-di-tert-butylcatechol was purchased from Sigma Aldrich, India and
2-aminophenol was purchased from Loba Chemie.
2.2. Physical measurement

4
Elemental analyses (carbon, hydrogen and nitrogen) were performed on Perkin-Elmer
2400 CHNS/O elemental analyzer. UV-VIS and IR spectra (KBr discs, 4000-300 cm-1) were
recorded using a Shimadzu UV-VIS 1800 spectrophotometer and Perkin-Elmer FT-IR model
RX1 spectrometer, respectively.
2.3. Synthesis of HL
The synthesis of ligand HL is depicted in Scheme 3. Sodium ethoxide was prepared in
situ by addition of pinch of metallic sodium in dry ethanol. Benzyl mercaptan (8 mmol, 0.99 g)
was added to sodium ethoxide solution by stirring. Then 2-chloroethylamine (8 mmol, 0.63 g)
was added slowly to the reaction mixture and stirred for about 1 hour. The precipitation of
sodium chloride confirms the formation of the 2-(benzylthio)ethanamine (Scheme 3). This
product was characterized by1H NMR (δ (ppm): 1.75 (t, J = 7.6 Hz, 2H), 2.81 (t, J = 6.8 Hz, 2H),
3.14 (t, J = 6.8 Hz, 2H), 3.60 (s, 2H), 7.25-7.33 (m, 5H)). (Fig. S1; Supporting information) and
high resolution mass spectrometry (m/z= 168.0927) (Fig. S2; Supporting information). Sodium
chloride was separated by filtration. Addition of salicylaldehyde (8 mmol, 0.97 g) to this solution
of 2-(benzylthio)ethanamine with six hour reflux gives the ligand HL. Yield: (based on
salicylaldehyde) 1.56 g (72%). Anal. calc. for C16H17NOS (HL): C, 70.81; H, 6.31; N, 5.16;
Found: C, 70.79; H, 6.33; N, 5.18 and high resolution mass spectrometry (m/z = 296.0271)
Selected IR bands (cm-1): 698, 756, 1028, 1278, 1452, 1492, 1629. UV-Vis (λ, nm): 254 (ɛ =
2863 M-1cm-1), 313 (ɛ = 945 M-1cm-1), 389 (ɛ = 300 M-1cm-1).
Scheme 3

5
2.4. Synthesis of compound 1
Compound 1 was prepared by drop-wise addition of copper(II) chloride dihydrate (0.370 g, 1
mmol) solution in ethanol (15ml) into a stirring ethanolic solution of HL(0.271g, 1 mmol). The
yellowish ligand solution was turned green after addition of copper(II) salt. Then the reaction
mixture was filtered and kept in air for slow evaporation. After about 60 days, the greenish
coloured shiny square shaped crystals of X-ray quality of 1 was collected, washed with hexane
and dried in vacuo over silica gel indicator.
Yield: (based on metal salt) 0.554 g (75%). Anal. calc. for C32H32N2O2S2Cl2Cu2 (1): C, 52.03; H,
4.34; N, 3.79; Found: C, 52.01; H, 4.29; N, 3.82. Selected IR bands (cm-1): 1620, 1028. UV-Vis
(λ, nm): 238(ɛ = 34180 M-1cm-1), 271 (ɛ = 21900 M-1cm-1), 323 (ɛ = 9020 M-1cm-1), 371 (ɛ =
6140 M-1cm-1), 644 (ɛ = 360 M-1cm-1).
2.5. X-ray diffraction study
Single crystals of 1 were collected and selected for single crystal X-ray diffraction. Single
crystal X-ray diffraction data were collected on collected on a Bruker AXS KAPPA APEX II
diffractometer using Mo-Kα radiation (λ = 0.71073 Å) at 293(2) K. Systematically absent
reflections led to the identification of space groups P121/n1 for 1. Of the 16850 total reflections
for the complex, 4882 with [I >2r(I)] were used for structure solutions. The structures were
solved by direct methods, and the structure solution and refinement were based on |F2|. All non-
hydrogen atoms were refined with anisotropic displacement parameters whereas hydrogen atoms
were placed in calculated positions when possible and given isotropic U values 1.2 times that of
the atom to which they are bonded. The final differences Fourier map showed the maximum and
minimum peak heights at 0.463 and -0.6590 eÅ-3 for 1 with no chemical significance. All

6
calculations were carried out using SHELXL-97 [11] and ORTEP-32 [12]. The crystal data and
data collection parameters are listed in Table 1.
3. Results and discussion
3.1. Synthesis and formulation
The ligand was synthesized in two steps. In the first step, the thiol group of
benzylmercaptan was deprotonated using sodium ethoxide which was generated in situ.
Nucleophilic attack at 2-chloro carbon in 2-chloroethylamine was done by that deprotonated
benzyl mercaptan (Scheme 3). The resulting 2-(benzylthio)ethanamine was characterized by
proton NMR spectroscopy and mass spectrometry. The signals for the amine protons of 2-
(benzylthio)ethanamine appeared at  1.75 (t, J = 7.6 Hz, 2H). The two triplet signals for four
protons of the two methyl groups were found at  2.81 (t, J = 6.8 Hz, 2H) for one methylene
group  to amine group and  3.14 (t, J = 6.8 Hz, 2H) for another methylene group α to the NH2
group. The signal appeared at  3.60 (s, 2H) due to the methylene group which is α to the C-S
bond. The signals of the five aromatic protons were appeared at the range between δ 7.25 ppm to
δ 7.33 ppm (m, 5H). The molecular ion peak of 2-(benzylthio)ethanamine in HRMS appeared at
m/z = 168.09 which is the molecular weight of the compound. This 2-(benzylthio)ethanamine
was condensed with salicyaldehyde to get the ligand HL. The HRMS of sodium aggregate of HL
appears at m/z = 296.02 (Fig. S3; Supporting information), and IR and UV-Vis spectroscopic
data were collected to characterize this. Ethanolic mixture of copper(II) chloride dihydrate and
HL resulted the dinuclear complex 1. X-ray crystallographic characterization of 1 was done to
know exact coordination sphere. IR spectrum of 1 shows sharp peaks among which peaks at
1028 and 1620 cm-1 were identified as Cu-O stretch in the complex and imine stretch of the

7
corresponding ligand [13]. Electronic spectrum of 1 was measured in methanol. It displays a d-d
transition band at 644 nm and a OH- Cu(II) charge transfer band at 323 nm and 371 nm [14].
3.2. X-ray structure
The ORTEP of the complex is given in Fig. 1. The Molecular unit contains dichloro
bridged dinuclearcopper(II) centres. Each of the copper(II) centres is five coordinated.
Calculation of τ = 0.24 [15] suggests that the metal centre is in square pyramidal geometry. From
consideration of bond angle and bond distance data O(1) (phenolic oxygen), N(1) (imine
nitrogen) and S(1) (thio ether sulfur) from the ligand network and Cl(1) (one of the bridging
chlorides) are in the square plane. The bond distance range in the basal plane is 1.8920(18) to
2.815 Å. The another chloro bridge Cl(1') having larger bond distance than the other four are in
the axial position.
3.3. Magnetism
Magnetic susceptibility χ versus temperature T measurements were performed on powder
samples in an applied magnetic field of H = 1 T, using the VSM option of a Quantum Design
PPMS.
The χ(T) vs T data are shown in Fig. 2. To extract the nature and magnitude of magnetic
interactions in the system we have first analyzed the χ(T) data using the Curie-Weiss model for
which the susceptibility in the paramagnetic state is given by the expression χ = χ0 + C/(T – θ),
where χ0 is the temperature independent contribution, C is the Curie constant which depends on
the effective magnetic moment, and θ is the Weiss temperature, the sign and magnitude of which
will give the nature of the magnetic exchange interactions. For small χ0, this will lead to 1/χ(T)
being linear. The 1/χ(T) vs T data above T = 150 K are shown in the inset (I) of the figure. It can

8
be seen that at high temperatures, the behavior is linear as expected. These data were fit to the
above Curie-Weiss expression. The parameters obtained from the fit are χ0 = -9.17(3) × 10-5
cm3/Cu mol, C = 0.382(3) cm3/Cu mol K, and θ = 17.1(9) K. From C, the effective moment µeff
can be estimated using the expression C = NAµ2eff/3kBT, where NA is the Avogadro’s number
and kB is the Boltzmann constant. This gives µeff = 1.75(2) µB which is close to the value
expected for S = ½ magnetic moments is µeff = 1.73 µB assuming a g-factor of g = 2. This fit is
shown as the red curve through the data in inset I of Fig. 2.
Let us now turn to the nature of the magnetic exchange interactions between these S = ½
Cu(II) moments. The value θ = 17.1 K indicate moderate ferromagnetic coupling between the
Cu(II) ions. Evidence for this can also be seen in the χT data which is shown in inset II of the
Fig. 2. χT, which is roughly the effective moment, is weakly T-dependent for higher
temperatures but increases dramatically as the temperature is lowered towards T = θ. Normally,
the system would undergo long-ranged ferromagnetic transition at this temperature. However,
our system is built up of Cu-Cu dimers which are isolated from each other and are expected to be
interacting very weakly with each other.
We have thus tried fitting our χT data using a model of non-interacting S = ½ dimers.
The magnetic susceptibility χ(T) for a collection of non-interacting S = ½ dimers with intra-
dimer coupling J1 can be written as
.
Assuming that the interactions between dimers acts as a mean-field, the susceptibility of
interacting dimers can then be written as

9
Where λ is the exchange coupling which can be given in terms of the inter-dimer
exchange J2 as λ = J2/3C, where C is the Curie constant for a S = ½. In addition to the
contribution from dimers, there could be other core and paramagnetic impurity contributions.
The experimental χ(T) data were therefore fit by the expression
,
Where, χ0 is a T independent of temperature Cimp is the Curie constant of impurity spins,
and θimp is the Weiss temperature giving interactions between these impurity spins. The fit,
shown in Fig.1 as the red curve through the data in the main panel and in inset (II) gave the
values χ0 = -6.4(7) × 10-5 cm3/Cu mol, Cimp = 0.0013(3) cm3/Cu mol K, θimp = -0.24(1) K, J1 =
16.8 (1) K and J2 = -0.50(5) K. The error factor came out to be R = 2.07 × 10-5. The small values
of Cimp and θimp indicate that paramagnetic impurities, if present, are in small numbers and are
almost non-interacting. The value J1 = 16.8 K shows the presence of ferromagnetic interactions
within Cu-Cu dimers and the small value of J2 = -0.5 K suggests very weak antiferromagnetic
interactions between dimers.
3.4. Catecholase activity of 1:spectrophotometric study
In order to study the catecholase activity, 3,5-ditertiarybutylcatechol (3,5-DTBC) was
chosen as a substrate. It can easily be oxidized to the corresponding quinone 3,5-
ditertiarybutylquinone (3,5-DTBQ) which is very stable because the low quinine catechole
reduction potential. Before proceeding the detail kinetic experiment we have done simple
repetitive UV-VIS scan for 6 hours by adding the mixture of the catalyst (1 × 10-4
M
concentration) and 100 equivalent amount of the substrate 3,5-DTBC in methanol and
acetonitrile solvents (Figs. 3 and 4). 3,5-DTBC shows a single band at 282 nm (inset to Fig. 3).
Characteristic peaks of 3,5-DTBQ, which is an oxidation product of 3,5-DTBC by aerial oxygen

10
in presence of 1, appears at 398 nm in methanol and 401 nm in acetonitrile are very close or
same to the reported value of 401 nm [16]. The quinone was separated and purified by column
chromatography and the product was isolated with high yield (70%). The quinine is chracterised
by melting point measurements with the value 110˚C [17].
In order to find out the reaction rate between 3,5-DTBC and 1, the reaction kinetics was
studied and observed that the time dependent change in absorbance was at a wavelength of 398
nm in methanol and 401 in acetonitrile. Gradually the colour of the solution was turned deep
brown that indicates that the gradual conversion of 3,5-DTBC to 3,5-DTBQ. In methanol the
difference in absorbance ΔA at 398 nm was plotted against time to calculate the initial rate for
that particular catalyst to substrate concentration ratio (Fig.5). A first-order catalytic reaction was
observed, with initial rate 5.08 × 10-3 min-1. But in acetonitrile the same was done at 401 nm, the
reaction was also of first order (Fig. 6) with initial rate 3.25 × 10-5 min-1.
3.4.1. Enzyme kinetics study
Enzymatic kinetic experiments were performed UV-Vis spectrophotometrically
thermostated at 25°C with the complex, and the substrate 3,5-DTBC in MeOH. 0.04 ml of each
complex solution, with a constant concentration of 1 × 10-4 M, was added to 2 ml of 3,5-DTBC
of a particular concentration (varying its concentration from 1 × 10-3 M to 1 × 10-2 M) to achieve
the ultimate concentration of the complex as 1 × 10-4 M. The conversion of 3,-5-DTBC to 3,5-
DTBQ was monitored with time at a wavelength of 398 nm for solutions in MeOH and 401 nm
in acetonitrile. The rate for each concentration of the substrate was determined by the initial rate
method.

11
The rate versus concentration of substrate data were analyzed on the basis of Michaelis-
Menten approach of enzyme kinetics to get the Lineweaver-Burk (double reciprocal) plot as well
as the values of the various kinetic parameters Vmax (maximum velocity), KM (Michaleis-Menten
constant) and Kcat (Turn over number). The observed rate vs. [substrate] plot along with
Lineweaver-Burk plot in methanol and acetonitrile solutions are given respectively in Figs. 7 and
8. The turnover numbers (Kcat) are calculated as 4.02 × 103 h-1 in methanol and 9.57 × 103 h-1 in
acetonitrile.
3.4.2. Mechanism of catecholase activity
The catalytic process takes place in two steps. The first step is the slowest and is
considered as the rate determining step. In this step 1:1 adduct of copper complex and catechol
may form. The mechanistic pathway of catecholase activity was explained by mass spectral
analysis of a 1:100 mixture of 1 and 3,5-DTBC. 1 was dissociated much readily and formed a
mononuclear unit which is characterized by HRMS peak at 369.54 (Fig. S4(a); Supporting
information). ESI MS spectrum of 1 is also given with m/z 369.97 (Fig. S4(b); Supporting
information). In HRMS, m/z value at 554.66 indicates the formation of the adduct of 1 and 3,5-
DTBC (Fig. S5; Supporting information).The sodium aggregate of 3,5-DTBQ was detected by
HRMS peak at 244.78 (Fig. S6; Supporting information). The catalytic cycle (Scheme 3) of the
catecholase activity was proposed and the probable molecular units in the cycle were
characterized by HRMS (Fig. S7(a-c), Supporting information). In this process molecular oxygen
oxidized 3,5-DTBC to the corresponding quinone, 3,5-DTBQ and reduced itself to hydrogen
peroxide. The liberated H2O2was identified and characterized spectrophotometrically (S1;
Supporting information) [18].

12
3.5. Phenoxazinone synthase activity of 1: spectrophotometric study
The phenoxazinone synthase activity has been studied by using the substrate,o-
aminophenol (OAPH). In presence of molecular oxygen, the oxidation of OAPH to the
corresponding 2-aminophenoxazinone-3-one was catalyzed by the compound 1. The spectral
band of OAPH appears at 232 nm and 286 nm in methanol (inset to Fig. 9), 233 nm and 292nm
in acetonitrile (inset to Fig. S8, Supporting information) and 238 nm and 288 nm in
dichloromethane (DCM) (inset to Fig. S9, Supporting information). The solution of 1 in various
solvents like, methanol, acetonitrile and dichloromethane are treated into 100 equivalent of
OAPH and the repetitive UV-Vis scan was recorded. One representative scan is given in Fig.9
(other scans in MeCN and DCM are given in Fig. S8 and S9; Supporting information). The
colourless solution of OAPH becomes deep brown due to the formation of APX. The
characteristic peak of APX grows smoothly at ~420 nm in MeOH, MeCN and DCM (419, 423
and 416 nm, respectively) [10d]. The identification of APX was also done by HRMS at m/z
value 213.80 (Fig. S10; Supporting information). The time dependent change of absorbance for
the catalytic reaction was done at a wavelength 420 nm for 30 min in the above solvents to
monitor the reaction kinetics and find out the initial rate between OAPH and 1. The difference in
absorbance at 420 nm is plotted against time in minute in different solvents. One representative
plot (in MeOH) is given in Fig. 10 (plots in MeCN and DCM are given in Figs. S11 and S12;
Supporting information).From the slope the initial rate for the particular catalyst and substrate is
obtained. The initial rates are 5.43 × 10-3, 6.14 × 10-4, 1.53 × 10-3 min-1 in MeOH, MeCN and
DCM, respectively.
3.5.1. Enzyme kinetic study

13
Enzymatic kinetic experiments were performed UV-Vis spectrophotometrically
thermostated at 25°C with the complex, and the substrate OAPH in MeOH, MeCN and DCM.
0.04 ml of each complex solution, with a constant concentration of 1 × 10-4 M, was added to 2
ml of OAPH of a particular concentration (varying its concentration from 1 × 10-3 M to 1 × 10-2
M) to achieve the ultimate concentration of the complex as 1 × 10-4M. The conversion of OAPH
to APX was monitored with time at a wavelength of 420 nm for solutions in different solvents.
The rate for each concentration of the substrate was determined by the initial rate method.
The rate versus concentration of substrate data were analyzed on the basis of Michaelis-
Menten approach of enzymatic kinetics to get the Lineweaver-Burk (double reciprocal) plot as
well as the values of the various kinetic parameters Vmax, KM and Kcat in MeOH, MeCN and
DCM. Plot in MeOH is given in Fig. 11. The other plots (in MeCN and DCM) are available in
Figs. S13 and S14; Supporting information). The turnover numbers (Kcat) are 1.065 × 103 h-1 in
MeOH, 2.13 × 102 h-1 in MeCN and 2.844 × 103 h-1 in DCM.
3.5.2. Mechanism of phenoxazinone synthase activity
To predict the mechanistic pathway of phenoxazinone synthase activity of 1, it is found
that initially OAPH forms an adduct with 1 which is identified by mass spectrometry at m/z =
847.30 (OAPH-1) (Fig. S15; Supporting information). This adduct generates 2-
amoinophenoxazine-3-one through some intermediate reaction with molecular oxygen. Reduced
molecular oxygen in the form of H2O2 was detected spectrophotometrically (S1; Supporting
information) [18].
4. Conclusion

14
We have synthesized and X-ray crystallographically characterized
a
new
antiferromagnetically coupled dinuclear copper(II) complex 1. 1 was found to catalyze separately
the aerial oxidation of 3,5-ditertiarybutyl catechol to its corresponding quione and o-
aminophenol to phenoxazinone chromophore. The turn over number for the catecholase activity
by 1 in methanol and acetonitrile solvent was better than that of the other reported dinuclear
copper complexes [4, 5(a), 5(b), 6(a)]. Similarly the turn over number in phenoxazinone synthase
activity by 1 in different solvents is appreciable, sometimes better than few reported ones [2(a),
9(a), 9(b)]. Henece compound 1 we reported may be regarded as a good addition to the
catecholase mimic dinuclear copper(II) complex.
5. Supplementary data
CCDC 1572023 contains the supplementary crystallographic data for 1. This data can be
obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44)
1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
Acknowledgement
RG is thankful to Department of Science & Technology, Government of West Bengal
[No. 781(Sanc.)/ST/P/S&T/4G-4/2013 dated 04-12-2014], India for financial assistance. AKG
thanks CSIR, New Delhi for his fellowship. Different infrastructural facilities at our university
provided by PURSE programme, DST, Govt of India is gratefully acknowledged.

15
Table 1  Crystal data and structure refinement parameter of compound 1
Emperical formula
Formula weight
T (K)
C32 H32N2O2S2Cl2Cu2
738.74
293(2)
Wavelenght (Å)
Crystal system
Space group
0.71073
Monoclinic
P121/n1
Unit cell dimensions
a (Å)
12.556(5)
7.677(5)
16.653(5)
90
b (Å)
c (Å)
α (˚)
β (˚)
93.037(5)
90
γ (˚)
V(Å3)
1603.0(13)
4
Z
Dcalc(mg m-3)
1.535
Absorption coefficient(mm-1)
1.656
F(000)
760
Crystal size (mm3)
Theta range for data collection (˚)
Index ranges
0.42 0.31 × 0.24
1.98-30.58
-17 ≤ h ≤ 17, -10 ≤ k ≤10, -23 ≤ l ≤23
16850
Reflections collected
Independent reflections
Completeness of theta
Absorption correction
Tmax and Tmin
4882 [Rint= 0.0289]
99.4 % [θ=30.58]
Multi-scan
0.7461 and 0.5134
Full matrix
Refinement method
Data/restrains/parameters
Goodness-of fit (GOF) F2
4882/0/190
1.032

16
Final R index [l >2σ(l)]
R1= 0.0407 and wR2=0.1110
R1= 0.0659 and wR2=0.1423
0.463, -0.659
R index (all data)
Largest difference between peak and hole (e Å-3)
Table 2  Bond lengths (Å) and bond angles (˚) of 1
Bond lengths
Cu(1)-O(1)
1.8920(18)
1.953(2)
Cu(1)-Cl(1)
Cu(1)-Cl(1')
2.2860(9)
2.815
Cu(1)-N(1)
Cu(1)-S(1)
2.3569(10)
Bond angles
O(1)-Cu(1)-N(1)
93.21(9)
93.21(9)
92.78(6)
O(1)-Cu(1)-N(1)
O(1)-Cu(1)-Cl(1)
N(1)-Cu(1)- Cl(1)
O(1)-Cu(1)-S(1)
N(1)-Cu(1)-S(1)
Cl(1)-Cu(1)-S(1)
O(1)-Cu(1)-Cl(1) 92.78(6)
N(1)-Cu(1)-Cl(1) 173.15(7)
173.15(7)
158.84(7)
85.71(7)
89.90(3)
O(1)-Cu(1)-S(1)
N(1)-Cu(1)-S(1)
158.84(7)
85.71(7)
Cl(1)-Cu(1)-S(1) 89.90(3)

17
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19
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20
Fig. 1  ORTEP of 1 with 30% ellipsoid probability
0.30
0.60
0.55
0.50
0.45
0.40
0.35
(II)
0.25
0.20
0.15
0.10
0.05
0.00
0
50 100 150 200 250 300
900
800
700
600
500
400
300
T (K)
(I)
140 160 180 200 220 240 260 280 300
T (K)
0
50
100
150
T (K)
200
250
300
Fig. 2  Plot of χ(T) vs T of complex 1 [inset I: 1/χvs T and inset II: χTvs T]

21
Fig. 3  Change in spectral pattern of complex 1 after reaction with 3,5-DTBC, observing the
reaction for 6 h in methanol [inset: spectrum of pure 3,5-DTBC in methanol]
Fig. 4  Change in spectral pattern of complex 1 after reaction with 3,5-DTBC, observing the
reaction for 6 h in acetonitrile [inset: spectrum of pure 3,5-DTBC in acetonitrile]

22
Fig. 5  A plot of the difference in absorbance (ΔA) vs time to evaluate the rate of catalysis of
3,5-DTBC by 1 in MeOH
Fig. 6  A plot of the difference in absorbance (ΔA) vs time to evaluate the rate of catalysis of
3,5-DTBC by 1 in MeCN

23
Fig. 7  Plot of rate vs. [substrate] (3,5-DTBC) in presence of 1 in MeOH [inset: Lineweaver-
Burk plot]
Fig. 8  Plot of rate vs. [substrate] (3,5-DTBC) in presence of 1 in MeCN [inset: Lineweaver-
Burk plot]

24
Scheme 3  Catalytic cycle for catecholase activity by 1

25
Fig. 9  Change in spectral pattern of complex 1 after reaction with OAPH, observing the
reaction for 6 h in methanol [inset: spectrum of pure OAPH in methanol]
Fig. 10 A plot of the difference in absorbance (ΔA) vs time to evaluate the rate of catalysis of
OAPH by 1 in methanol

26
Fig. 11  Plot of rate vs. [substrate] (OAPH) in presence of 1 in MeOH [inset: Lineweaver-Burk
plot]

27
A weakly ferromagnetically coupled dinuclear Cu(II) complex with square pyramidal
geometry at each metal centre was synthesized and crystallographically characterized. The
compound was found to had catecholase and phenoxazinone synthase-like activities in different
solvents with appreciable turn over number.

28
Highlight
 Dinuclear Cu(II) complexes
 Schiff base
 Catecholase activity
 Phenoxazinone synthase activity