Synthesis and characterization of three hetero-dinuclear complexes with CuO2M cores (M?=?Na, Hg): Exploration of their phenoxazinone synthase mimicking activity

Article abstract of DOI:10.1016/j.poly.2018.04.018

Three new hetero-dinuclear complexes, [CuL¹Na(NCS)]·0.5H₂O (1), [CuL¹Na(OClO₃)]·0.25H₂O (2) and [CuL²HgCl₂] (3) {where H₂L¹ = N,N′-bis(3-ethoxysalicylidene)

Full text of DOI:10.1016/j.poly.2018.04.018

Accepted Manuscript
Synthesis and characterization of three hetero-dinuclear complexes with
CuO2M cores (M= Na, Hg): Exploration of their phenoxazinone synthase mim-
icking activity
Sourav Roy, Michael G.B. Drew, Shouvik Chattopadhyay
PII:
S0277-5387(18)30186-4
https://doi.org/10.1016/j.poly.2018.04.018
POLY 13120
DOI:
Reference:
Polyhedron
To appear in:
Received Date:
Accepted Date:
22 February 2018
12 April 2018
Please cite this article as: S. Roy, M.G.B. Drew, S. Chattopadhyay, Synthesis and characterization of three hetero-
dinuclear complexes with CuO2M cores (M= Na, Hg): Exploration of their phenoxazinone synthase mimicking
activity, Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.04.018
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Synthesis and characterization of three hetero-dinuclear
complexes with CuO2M cores (M= Na, Hg): Exploration of their
phenoxazinone synthase mimicking activity
Sourav Roy,a Michael G. B. Drew,b Shouvik Chattopadhyay*a
a Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata - 700032, India.
Tel: +9133-2457-2941; E-mail: shouvik.chem@gmail.com
b School of Chemistry, The University of Reading, P.O. Box 224, Whiteknights, Reading RG6 6AD,
United Kingdom, E-mail: m.g.b.drew@reading.ac.uk
Abstract
Three
[CuL1Na(OClO3)]·0.25H2O (2) and [CuL2HgCl2] (3) {where H2L1 = N,N'-bis(3-ethoxysalicylidene)-
H2L2
N,N'-bis(3-methoxysalicylidene)-2,2-
new
hetero-dinuclear
complexes,
[CuL1Na(NCS)]·0.5H2O
(1),
2,2-dimethylpropane-1,3-diamine
and
=
dimethylpropane-1,3-diamine] are N2O4 donor compartmental Schiff bases} have been
synthesized and characterized. The phenoxazinone synthase mimicking activity of each complex
in acetonitrile has been investigated with the model substrate o-aminophenol.
Keywords: Hetero-dinuclear complex; Schiff Base Ligand; Phenoxazinone synthase mimicking
activity.

1. Introduction
Compartmental Schiff bases represent fascinating ligand systems that are very effective
in preparing multimetallic complexes with s, p and d-block metals [1]. There has been
enormous interest in the synthesis and characterization of these heteronuclear metal
complexes for their applications in magnetism, catalysis, biological modelling experiments,
molecular architectures etc [2]. They can also be used for developing molecular systems
capable of mimicking naturally occurring molecules responsible for the selective transport of
ions [3]. On the other hand, diverse ranges of supramolecular architectures of such complexes
are reported in the literature which in turn display a range of interesting functionalities
including catalysis and host-guest chemistry [4]. These complexes may also be used as
biomimetic catalysts, as they can mimic natural metalloproteins [5]. Some of these
metalloproteins utilize their active sites for the activation, storage, and transport of aerial
dioxygen molecules in enzymatic pathways: e.g., catechol oxidase (COx), phenoxazinone
synthase (PHS) etc [6].
Multinuclear complexes are important due to their potential applications in catalysis [7-
8]. The presence of different metal ions in one cluster may drastically change catalytic activity
as a result of multimetallic cooperative activities [9]. Positive cooperativity occurs when the
affinity for binding of a substrate with multiple binding sites to a metal is increased upon
fixation to another metal. Each metal centre may be specifically responsible for elementary
steps/transformations contributing to the overall transformation under investigation. One may
thus envisage that the sharing of electrons between the metals forming the bi- or multimetallic

system will be at the origin of the specific reactivity observed [10]. A few multinuclear
complexes have also been used to mimic phenoxazinone synthase, a multicopper oxidase
enzyme [11-13].
In the present work, two N2O4 donor compartmental Schiff bases, N,N'-bis(3-
ethoxysalicylidene)-2,2-dimethylpropane-1,3-diamine
(H2L1)
and
N,N'-bis(3-
methoxysalicylidene)-2,2-dimethylpropane-1,3-diamine (H2L2) (Scheme 1) have been prepared
and used to synthesize three new heteronuclear complexes with CuO2M cores, where M = Na
for complexes 1, 2 and M = Hg for complex 3. Single crystal X-ray diffraction analyses have
confirmed their structures. All three complexes have the potential to mimic phenoxazinone
synthase activity.
Scheme 1: Schematic representation of H2L1 and H2L2.
2. Experimental Section
All other materials were commercially available, reagent grade and used as purchased
from Sigma-Aldrich without further purification.

Caution!!! Although no problems were encountered in this work, copper(II) complexes
containing organic ligands in the presence of perchlorates are potentially explosive. Only a
small amount of the material should be prepared and it should be handled with care.
2.1 Preparation
2.1.1 Preparation of H2L1 [N,N'-bis(3-ethoxysalicylidene)-2,2-dimethylpropane-1,3-diamine] and
H2L2 [N,N'-bis(3-methoxysalicylidene)-2,2-dimethylpropane-1,3-diamine]
A methanol solution (10 mL) of 3-ethoxysalicylaldehyde (332 mg, 2 mmol) and 2,2-
dimethyl-1,3-diaminopropane (0.13 mL, 1 mmol) was refluxed for ca. 1 h to form H2L1. H2L1 was
prepared in a similar method except that 3-methoxysalicylaldehyde (300 mg, 2 mmol) was used
instead of 3-ethoxysalicylaldehyde. The ligands were not isolated and used directly for the
synthesis of complexes [H2L1 for complexes 1 and 2; H2L2 for complex 3]. The ligands are
presented in scheme 1.
2.1.2 Preparation of complexes
2.1.2.1 Preparation of [CuL1Na(NCS)]·0.5H2O (1)
A methanol (10 mL) solution of copper(II) acetate monohydrate (200 mg, 1 mmol) was
added to the methanol solution (20 mL) of H2L1 and the resulting solution was stirred for 15
min. A methanol (10 mL) solution of sodium thiocyanate (81 mg, 1 mmol) was then added to it.
The stirring was continued for about 2 h. Crystalline form of complex 1 started to appear after
three days. Single crystals, suitable for X-ray diffraction, were obtained after seven days on slow
evaporation of the solution in open atmosphere.

Yield: 825 mg (75%); based on copper(II). Anal. Calc. for C48H58Cu2N6Na2O9S2 (FW =
1100.20): C, 51.56; H, 5.41; N, 7.52; Found: C, 51.7; H, 5.2; N, 7.6%. ESI-MS (positive ion mode,
Acetonitrile) m/z: 482.10 [100%, Cu(L1)Na]+. FT-IR (KBr, cm-1): 1612 (C=N); 2070 (NCS); 3448 (O-
27
H); 2954 (C-H). UV-VIS [λmax(nm)] [εmax(Lmol-1cm-1)] (acetonitrile): 220 (3.3104); 6 (1.9104);
348 (8.9103); 605 (4.1102).
2.1.2.2 Preparation of [CuL1Na(OClO3)]0.25H2O (2)
It was prepared in a similar method as that of complex 1 except that copper(II)
perchlorate hexahydrate (370 mg, 1 mmol) and sodium azide (66 mg, 1 mmol) was used instead
of copper(II) acetate monohydrate and sodium thiocyanate, respectively. Single crystals,
suitable for X-ray diffraction, were obtained after seven days on slow evaporation of the
solution in open atmosphere.
Yield: 407 mg (70%); based on copper(II). Anal. Calc. for C23H28.5ClCuN2NaO8.25 (FW =
586.96): C, 47.06; H, 4.89; N, 4.77; Found: C, 47.3; H, 4.7; N, 4.9%. ESI-MS (positive ion mode,
Acetonitrile) m/z: 482.11 [100%, Cu(L1)Na]+. FT-IR (KBr, cm-1): 1612 (C=N); 1100 (Cl-O); 2950 (C-
H). UV-VIS [λmax(nm)] [εmax(Lmol-1cm-1)] (Acetonitrile): 225 (2.9104); 280 (2.2104); 352
(1.1103); 598 (1.3102).
2.1.2.3 Preparation of [CuL2HgCl2] (3)
A methanol (10 mL) solution of copper(II) chloride dihydrate (170 mg, 1 mmol) was
added to the methanol solution (20 mL) of H2L2 and the resulting solution was stirred for 15
min. A methanol (10 mL) solution of mercury(II) acetate (348 mg, 1 mmol) was then added to it.

The stirring was continued for about 2 h. Single crystals, suitable for X-ray diffraction, were
obtained after one week on slow evaporation of the solution in open atmosphere.
Yield: 506 mg, 72%. Anal. Calc. for C21H24Cl2CuHgN2O4 (FW = 703.46): C, 35.85; H, 3.44;
N, 3.98. Found: C, 35.9; H, 3.2; N, 4.1%. ESI-MS (positive ion mode, Acetonitrile) m/z: 454.04
[100%, Cu(L2)Na]+, 432.06 [Cu(L2)H]+. FT-IR (KBr, cm-1): 1613 (C=N); 745 (M-Cl); 2925 (C-H). UV-
VIS [λmax(nm)] [εmax(Lmol-1cm-1)] (acetonitrile): 227 (3.8104); 273 (2.8104); 368 (8.1103); 602
(2.1102).
2.2 Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen) were performed using a Perkin
Elmer 240C elemental analyzer. IR spectra in KBr (4500-500 cm-1) were recorded with a Perkin
Elmer Spectrum Two spectrophotometer. Electronic spectra in acetonitrile were recorded on a
Perkin Elmer Lambda 35 UV-visible spectrophotometer. Powder X-ray diffraction was
performed on a Bruker D8 instrument with Cu K (λ = 1.5406 Å) radiation. In this process, the
complexes were ground with a mortar and pestle to prepare fine powders which were then
dispersed with alcohol onto a zero background holder (ZBH). The alcohol was then allowed to
evaporate to provide a nice, even coating of powder adhered to the sample holder. Thermo-
gravimetric Analysis (TGA) was performed in a PerkinElmer Diamond (TG/DTA) instrument using
Pyris software. Mass spectra were recorded on an XEVO G2QTof spectrometer (Waters) with an
electrospray ionization source.

2.3 X-ray crystallography
Suitable single crystals of complexes 1 and 3 were picked, mounted on a glass fibre and
diffraction intensities were measured with an Oxford Diffraction XCalibur diffractometer
equipped with Mo Kα radiation (λ =0.71073 Å, 50 kV, 40 mA) at an ambient temperature (150
K). Data collection and reduction were performed with the Crysalis software [14]. On the other
hand, a suitable single crystal of complex 2 was used for data collection using a ‘Bruker SMART
APEX II’ diffractometer equipped with graphite-monochromated Mo Kα radiation (λ = 0.71073
Å) at 150 K. The structures of all three complexes were solved by direct methods. For all
complexes, non-hydrogen atoms were refined anisotropically. Hydrogen atoms attached with
oxygen atoms were located by difference Fourier maps and refined with distance constraints.
All other hydrogen atoms were placed in their geometrically idealized positions and constrained
to ride on their parent atoms. Absorption corrections for complexes 1 and 3 were carried out
using ABSPACK [15] and for complex 2 using SADABS [16]. The structures were refined by full-
matrix least squares on F2, using the SHELXL-2016/6 package [17].
3. Results and Discussion
3.1 Synthesis
2,2-dimethyl-1,3-diaminopropane was refluxed separately, with 3-ethoxysalicylaldehyde
and 3-methoxysalicylaldehyde, in 1:2 ratio to form two N2O4 donor compartmental Schiff base
ligands, H2L1 and H2L2, following the literature method [18]. The Schiff base ligand (H2L1) on
reaction with copper(II) acetate monohydrate (200 mg, 1 mmol) followed by the addition of
sodium thiocyanate (81 mg, 1 mmol) in methanol formed complex 1. The same Schiff base

(H2L1) on reaction with copper(II) perchlorate hexahydrate (370 mg, 1 mmol) followed by the
addition of sodium azide (66 mg, 1 mmol) in methanol produced complex 2. Schiff base (H2L2)
on reaction with copper(II) chloride dihydrate followed by the addition of mercury(II) acetate
tetrahydrate in methanol produced complex 3. Formation of all complexes is shown in Scheme
1.
Scheme 1: Preparation of ligands and complexes.

3.2 Structure description
3.2.1 [CuL1Na(NCS)]·0.5H2O (1) and [CuL1Na(OClO3)]·0.25H2O (2)
Single crystal X-ray diffraction analyses reveal that complex 1 crystallizes in triclinic
space group P , whereas complex 2 crystallizes in monoclinic space group I2/a. Details of
crystallographic data and refinement details are given in Table 1. Important bond lengths and
bond angles are gathered in Tables S1 and S2 [Supplementary Information (SI)] respectively.
Table 1: Crystal data and refinement details of complexes 1-3.
Complex
1
2
3
Formula
C48H58Cu2N6Na2O9S2
C23H28.5ClCuN2NaO8.25 C21H24Cl2CuHgN2O4
Formula Weight
Temperature(K)
Crystal system
Space group
a (Å)
1100.20
150
586.96
150
703.46
150
Triclinic
P
Monoclinic
I2/a
Monoclinic
P21/c
8.7492(6)
10.6600(9)
13.8973(8)
109.628(6)
96.568(5)
94.050(6)
1
16.4292(6)
15.1691(7)
21.0946(10)
(90)
12.5433(6)
11.6488(5)
16.3580(8)
(90)
b (Å)
c (Å)
α (°)
β (°)
106.246(3)
(90)
105.367(5)
(90)
γ (°)
Z
8
4
Volume (Å3)
dcalc (g cm-3)
μ (mm-1)
1204.56(16)
1.517
5047.2(4)
1.545
2304.69(19)
2.027
1.051
1.040
7.838

F (000)
572
8541
2428
16953
1356
14634
Total Reflections
Unique Reflections
Observed data [I > 2 σ (I)]
6726
4756
6505
5306
3660
4315
No. of parameters
R (int)
326
331
284
0.036
0.036
0.061
R1, wR2 (all data)
R1, wR2 [I > 2 σ (I)]
0.0721, 0.1324
0.0541, 0.1186
0.0716, 0.1798
0.0546, 0.1609
0.1358, 0.2162
0.0889, 0.1958
Molecular structures of complexes 1 and 2 are built from isolated hetero-dinuclear
molecules of [CuL1Na(NCS)] and [CuL1Na(OClO3)] respectively. Both complexes contain lattice
water molecules with occupancies of 0.5, that in complex 2 situated on a two-fold axis. In
complex 2, the perchlorate ion is disordered with the four oxygen atoms taking two
orientations which were refined with occupation parameters, x and 1-x where x refining to
0.59(1). Perspective views of complexes 1 and 2 are depicted in Figures 1 and 2, respectively.
H2L1 is a N2O4 donor compartmental Schiff base having inner N2O2 and outer O4 compartments
with copper(II) occupying the inner N2O2 compartment and sodium occupying the outer O4
compartment. In both complexes, copper(II) centres are tetracoordinated whereas sodium
centres are pentacoordinated. The copper(II) centres, Cu(1), in both complexes have square
planar geometry in which two imine nitrogen atoms, N(19) and N(23), and two phenoxo oxygen
atoms, O(11) and O(31), of the deprotonated di-Schiff base, are coordinated around the
copper(II) centres. The sum of different angles around copper(II) centre is 359.93° for complex 1
and 360.08° for complex 2, indicating slight distortion from perfect square planar geometry.

The trans angles [O(11)-Cu(1)-N(23)] and [O(31)-Cu(1)-N(19)] are found to be 169.1(1)°,
172.6(1)° for complex 1 and 169.4(1)°, 172.1(1)° for complex 2 respectively.
The geometry around the sodium atoms is best considered as a pentagonal pyramid
with one equatorial site missing. The sodium atoms are bonded to four donor atoms from the
Schiff base in the equatorial plane, e.g. two phenoxo oxygen atoms [O(11) and O(31)] and two
ethoxy oxygen atoms [O(13) and O(32)]. The axial site is occupied by a nitrogen atom, N(1),
from a terminal thiocyanate in complex 1 and in complex 2 by a perchlorate oxygen disordered
between two sites, labelled O(41A) and O(41B).
The deviations of the four coordinating atoms, O(11), O(31), O(32) and O(13), in the
basal plane from the mean plane passing through them are 0.087(1), -0.045(1) -0.086(1),
0.045(1) Å respectively for complex 1 and 0.038(2), -0.036(2), 0.019(1), -0.019(1) Å respectively
for complex 2. The deviation of Na(1) from the equatorial plane is 0.384(2) Å in complex 1 and
0.262(3) Å in complex 2. The distances between copper(II) and sodium centres are 3.380(1) Å in
complex 1 and 3.371(2) Å in complex 2. It is noteworthy that the two equatorial planes
coordinated to the copper and sodium atoms are approximately coplanar, intersecting at angles
of 2.67(17) and 2.69(18)o in complexes 1 and 2 respectively. The saturated six-membered
chelate rings, [Cu(1)-N(19)-C(20)-C(21)-C(22)-N(23)], have envelope conformations with
puckering parameters: q = 0.574(3) Å; θ = 58.3(3)°;  = 188.4(3)° for complex 1 and q = 0.589(5)
Å; θ = 61.4(4);  = 179.7(5) for complex 2 [19].

Fig. 1: ORTEP view of complex 1 with ellipsoids at 50% probability. Lattice water molecule has
been omitted for clarity.

Fig. 2: ORTEP view of complex 2 with ellipsoids at 50% probability. Lattice water molecule has
been omitted for clarity. Only the major fraction of the disordered oxygen atom of perchlorate
has been shown.
3.2.2 [CuL2HgCl2] (3)
The X-ray crystal structure determination revealed that the complex crystallizes in the
monoclinic space group P21/c. A perspective view of the complex is shown in Fig. 3. Important
bond lengths and bond angles are gathered in Tables S3 and S4 [Supplementary Information
(SI)] respectively.
The molecular structure is built from isolated hetero-dinuclear molecules of [CuL2HgCl2].
H2L2 is a N2O4 donor compartmental Schiff base with copper(II) occupying the inner N2O2 cavity
and mercury(II) occupying the outer O4 cavity. The copper(II) centre, [Cu(1)] has square planner
geometry, where two imine nitrogen atoms, N(19) and N(23), and two phenoxo oxygen atoms,
O(11) and O(31), of the deprotonated di-Schiff base, are coordinated with the copper(II) centre.
The sum of different angles around copper(II) centre is 364.8° indicating distorted square planar
geometry. The trans angles [O(11)-Cu(1)-N(23)] and [O(31)-Cu(1)-N(19)] are found to be
160.6(4)° and 163.6(4)° respectively.
The mercury(II) atom is six-coordinate with a geometry best described as distorted
hexagonal bipyramidal with two adjacent equatorial sites missing. In the equatorial plane there
are two phenoxo oxygen atoms, O(11) and O(31) and two ethoxy oxygen atoms O(131) and
O(291), of the compartmental Schiff base coordinate with the mercury(II) centre. The O(131)-

Hg(1)-O(291) angle in the equatorial plane, adjacent to the two vacant sites, is 178.7(3)o
validating that the structure cannot be an octahedron.
The axial coordination sites are occupied by two chlorine atoms, Cl(1) and Cl(2). The
bridging angles between the metals, Cu(1)-O(11)-Hg(1) and Cu(1)-O(31)-Hg(1) are 107.1(4)° and
108.3(3)° respectively. The dihedral angle is 2.61° indicating the Cu(1)O(11)O(31)Hg(1) core is
almost planar. The distance between the metal centres [Cu(1) and Hg(1)] is 3.652(1) Å.
The deviation of all the coordinating atoms, O(11), O(31), O(131) and O(291), in the
basal plane from the mean plane passing through them are -0.098(9), 0.097(8), 0.047(3) and -
0.047(3) Å respectively. The deviation of Hg(1) is -0.031(7) Å. The saturated six membered
chelate ring [Cu(1)-N(19)-C(20)-C(21)-C(22)-N(23)] has an envelope conformation with
puckering parameters q = 0.598(13) Å; θ = 119.2(11);  = 351.6(14) [19].
Fig. 3: ORTEP view of complex 3 with ellipsoids at 50% probability.

3.3 IR and electronic spectra
In the IR spectra of complexes 1-3, distinct bands due to the azomethine (C=N) groups
within the range of 1610-1615 cm-1 are routinely noticed [20]. A strong band at 2072 cm-1
indicates the presence of terminal thiocyanate in complex 1 [21]. Sharp peak around 1100 cm-1
indicates the presence of a coordinated perchlorate in complex 2 [22]. Peak around 745 cm-1
indicates the presence of metal coordinated chlorine atom in complex 3 [23]. Bands around
2935 cm-1 are observed due to alkyl C-H bond stretching in all complexes [24].
In the UV spectra, square planar copper(II) usually shows three transitions; viz.
2
2
2A1g2B1g, B2g2B1g, and Eg2B1g [25]. Electronic spectra of complexes 1-3 in acetonitrile
display absorption bands ~600 nm. This band may be assigned to two superimposed transitions
2
2B2g2B1g, and Eg2B1g [26]. A strong ligand to metal charge transfer transition ~350 nm is
observed which is characteristic of transition metal complexes with Schiff base ligands. Bands
~225 nm and ~280 nm may be assigned as π* n and π* π transitions respectively [27].
3.4 X-ray diffraction of powdered samples
The experimental PXRD patterns of the bulk products are in good agreement with the
simulated XRD patterns from single crystal X-ray diffraction results, indicating consistency of
the bulk sample. The simulated patterns of the complexes are calculated from the single crystal
structural data (Cif) using the CCDC Mercury software.
3.5 Thermo-gravimetric analysis
The thermal behaviour of all complexes is studied in a dynamic nitrogen atmosphere (20
mL min-1) at a heating rate of 10°C min min-1 using thermo-gravimetric (TG) technique. The

thermo-gravimetric plots for complexes 1-3 are given in Figures 4, S17 and S18 [Supplementary
Information (SI)] respectively. Complex 1 is stable up to ~50°C. An elimination of a water
molecule from complex 1 in the temperature range 50-100°C occurs. The second weight loss for
complex 1 occurs in the temperature range 275-450°C, where a weight loss of ~29.1% is
observed (calc. 29.5%). This corresponds to the loss of two metals and thiocyanate anion which
converts complex 1 in to H2L1. An elimination of water molecule from complex 2 in the
temperature range 70-100°C happens. The second weight loss for complex 2 occurs in the
temperature range 295-360°C, where a weight loss of ~31.3% is observed (calc. 31.9%). This
corresponds to the loss of two metals and perchlorate anion which converts complex 2 in to
H2L1. Complex 3 is stable up to ~240°C. The first weight loss for complex 3 occurs in the
temperature range 250-350°C where a weight loss of ~38.3% is observed (calc. 38.5%). This
corresponds to the loss of the mercury and two chloride molecule which converts complex 3 in
to copper-ligand complex. The second weight loss for complex 3 occurs in the temperature
range 260-470°C whereas the same of ~14.1% is observed (calc. 14.4%). This corresponds to the
loss of copper which converts complex 3 in to H2L2. Endothermic peaks in the DSC plots have
also been found indicating total combustion of the complexes and are found to be matching
with major weight loss in TGA.

Fig. 4: TGA plot of complex 1.
3.6 Phenoxazinone synthase like activity
To check the ability of the complexes to oxidize o-aminophenol to 2-aminophenoxazine-
3-one (phenoxazinone synthase mimicking activity), 10-1 M acetonitrile solution of o-
aminophenol are mixed separately with 10-5 M solution of all three complexes, and the spectra
are recorded for 2 h and 30 min at room temperature. It is found that all complexes show
phenoxazinone synthase mimicking activity. The time dependent spectral profiles of complexes
1-3 are shown in Figures 5, S19 and S20 [Supplementary Information (SI)] respectively. The
gradual increase of peak (characteristic of the phenoxazinone absorption) intensity at ~410 nm
implies the catalytic conversation of o-aminophenol to 2-aminophenoxazine-3-one under
aerobic conditions. The spectral growth (corresponding to the formation of phenoxazinone) is
negligible for bare metal {copper(II), sodium and mercury(II)} salts compared to the spectral

growth for the complexes and hence it may be concluded that the complexes act as better
catalysts compared to the bare salts of these metals.
Fig. 5: The spectral profile showing the growth of 2-aminophenoxazine-3-one at ~410 nm upon
addition of 10-1 M o-aminophenol to a solution containing complex 1 (10−5 M) in CH3CN.
3.7 Kinetic parameters and rationalization of the Kcat values
The above mechanism is based upon the well-known Michaelis–Menten equation:
V =
Where, V = initial rate; [S] = concentration of the substrates; KM = (k2 + k3)/k1, Michaelis–
Menten constant for the metal complex and Vmax = maximum initial rate attained for a
particular concentration of the metal complex in the presence of a large excess of the

substrate. One of the most widely used transformation of the above equation, is the well-
known Lineweaver-Burk Equation as follows:
The Lineweaver-Burk plot is used to analyse different parameters, viz. Vmax (Maximum
reaction velocity), KM (Michaelis constant), and Kcat (Turnover number). Table 2 contains all
these kinetic parameters of complexes 1-3 for phenoxazinone synthase like activity. The initial
rate is determined from the slope of the absorbance vs time plot. In all cases, first order
dependence is observed at low substrate concentrations, whereas saturation kinetics was
found at higher substrate concentrations. The initial rate versus substrate concentration plot
and Lineweaver-Burk plot for complex 1 are shown in Fig. 6.
Fig. 6: Initial rate versus substrate concentration plot for the oxidation of o-aminophenol
catalyzed by complex 1 in CH3CN (left). Representative Lineweaver-Burk plot for the oxidation
of o-aminophenol catalyzed by complex 1 in CH3CN (right).

The catalytic activity depends on the interaction between substrate and catalyst. More
facile interaction leads to higher Kcat values (Table 6). The formal oxidation state of copper and
sodium in both complexes is +2 and +1 respectively, which facilitate the approach of a
negatively charged substrate to the metal centre. Due to this reason both complexes exhibit
catalytic property.
Table 2: Kinetic parameters of complexes 1-3 for phenoxazinone synthase mimicking activity at
250 C in acetonitrile medium.
Complex
Vmax (M min-1)
2.23x10-3
KM(M)
Kcat (min-1)
222.9
1
2
3
1.79 x10-2
5.58 x10-2
10.6 x10-2
3.10x10-3
310.1
4.97x10-3
497.4
Literature survey shows that several hetero-dinuclear copper(II)/sodium and
copper(II)/mercury(II) complexes using similar kind of ligands have been reported by several
groups [28]. All such complexes are gathered in Table 3. However, catalytic activities of these
complexes have not been investigated. Complexes 1-3 are eventually the first examples of
hetero-dinuclear copper(II)/sodium and copper(II)/mercury(II) complexes showing
phenoxazinone synthase mimicking activity.

Table 3: X-ray characterized copper(II)/sodium and copper(II)/mercury(II) complexes reported
in literature.
CCDC
FOFLIX
Complex
Kcat (min-1)
Not explored
Not explored
Not explored
Not explored
Not explored
Not explored
Not explored
Not explored
Not explored
Not explored
Not explored
Not explored
Not explored
Not explored
Not explored
Not explored
222.9
Ref
[28a]
[28b]
[28b]
[28c]
[CuL1Na(ClO4)(CH3OH)]
[CuL2Na(NO3)(CH3OH)]
[CuL1Na(NO3)(CH3OH)]
[CuL3Na(NO3)(CH3OH)]
[Cu(HL4)Na(NO3)(CH3OH)]
[CuL5Na(ClO4)(CH3CN)]
[CuL1Na(NO3)(H2O)]
CIKPAP
XEDBIR02
XEDBIR01
VEYLAO
KESYOY
QEHGUH
QEHGOB
QEHHAO
HAXFUJ
HAMSOF
HAMSUL
HAMTAS
HAMTEW
KEZYOF
WENXIY
-
[28d]
[28e]
[28f]
[CuL1Na(N3)(CH3OH)]
[28f]
[CuL1Na(NCS)(H2O)]
[28f]
[CuL1Na(CH3COO)(H2O)]·2H2O
[CuL6Na(NO3)(H2O)]·2CH3CN
[CuL6NaN3(CH3OH)]·CH3OH
[CuL6Na(ClO4)(CH3CN)]·0.5CH3CN
[CuL6Na(BF4)(CH3OH)]·H2O
[Cu(HL4)HgCl2]
[28g]
[28h]
[28h]
[28h]
[28h]
[28d]
[28i]
[(CuL7CH3)HgCl2]
[CuL1Na(NCS)]·0.5H2O
[CuL1Na(OClO3)]·0.25H2O
This work
This work
-
310.1

-
[CuL2HgCl2]
497.4
This work
where, H2L1
=
N,N’-bis(3-methoxysalicylidene)propane-1,3-diamine; H2L2
H2L3
=
N,N’-bis(3-
N,N’-bis(3-
methoxysalicylidene)-2-methylpropane-1,2-diamine;
=
methoxysalicylidene)ethane-1,2-diamine; H3L4 = N,N’-bis(3-methoxysalicylidene)-2-hydroxy-
propane-1,3-diamine; H2L5 = N,N’-bis(3-methoxysalicylidene)phenylene-1,2-diamine; H2L6 =
N,N’-bis(3-ethoxysalicylidene)phenylene-1,2-diamine;
H2L7
=
N,N’-bis(α-
methylsalicylidene)propane-1,3-diamine.
4. Concluding Remarks
In summary, synthesis and X-ray characterization of three hetero-dinuclear complexes
with CuO2M core (M=Na, Hg) are described in this paper. Single crystal X-ray diffraction has
confirmed their structures. All complexes are found to show catalytic property towards the
oxidation of o-aminophenol. The catalytic efficiency of all complexes has been assessed
following conventional Michaelis-Menten enzyme kinetics.
Acknowledgments
Crystallographic data for complex 2 were collected at the DST-FIST, India, funded by Single
Crystal Diffractometer Facility at the Department of Chemistry, Jadavpur University. We also
thank the EPSRC (U.K) and the University of Reading for funds for the diffractometer which was
used to collect data for complexes 1 and 3. S. R. thanks the UGC for funding.
Appendix A. Supplementary data

CCDC 1823123-1823125 contain the supplementary crystallographic data for 1, 2 and 3
respectively.
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Synthesis and characterization of three hetero-dinuclear
complexes with CuO2M cores (M= Na, Hg): Exploration of their
phenoxazinone synthase mimicking activity
Sourav Roy, Michael G. B. Drew, and Shouvik Chattopadhyay
Synthesis and characterization of three hetero-dinuclear
complexes with CuO2M cores (M= Na, Hg): Exploration of their
phenoxazinone synthase mimicking activity
Sourav Roy, Michael G. B. Drew, and Shouvik Chattopadhyay

Phenoxazinone synthase mimicking activities have been investigated in hetero-dinuclear
copper(II)/sodium and copper(II)/mercury(II) complexes with N2O4 donor compartmental Schiff
bases.