Synthesis and structural characterization of three manganese(III) complexes with N2O2 donor tetradentate Schiff base ligands: Exploration of their catalase mimicking activity

Article abstract of DOI:10.1016/j.ica.2019.05.003

Three manganese(III) complexes, [Mn(L¹)(N₃)(H₂O)]·CH₃OH·H₂O (1), [Mn(L²)(N₃)(H₂O)] (2) and [Mn(L³)(H₂O)₂]ClO₄ (3) {where H<

Full text of DOI:10.1016/j.ica.2019.05.003

Accepted Manuscript
Research paper
Synthesis and structural characterization of three manganese(III) complexes
with N O donor tetradentate Schiff base ligands: Exploration of their catalase
2
2
mimicking activity
Ipsita Mondal, Kousik Ghosh, Shouvik Chattopadhyay
PII:
S0020-1693(18)31695-5
https://doi.org/10.1016/j.ica.2019.05.003
ICA 18904
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
3 November 2018
3 April 2019
2 May 2019
Please cite this article as: I. Mondal, K. Ghosh, S. Chattopadhyay, Synthesis and structural characterization of three
manganese(III) complexes with N O donor tetradentate Schiff base ligands: Exploration of their catalase mimicking
2
2
activity, Inorganica Chimica Acta (2019), doi: https://doi.org/10.1016/j.ica.2019.05.003
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Synthesis and structural characterization of three manganese(III)
complexes with N O donor tetradentate Schiff base ligands:
2
2
Exploration of their catalase mimicking activity
Ipsita Mondal, Kousik Ghosh, Shouvik Chattopadhyay*
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700 032, India
e-mail: shouvik.chem@gmail.com Tel. +91-33- 2457-2941
Abstract:
1
Three
manganese(III)
complexes,
[Mn(L )(N )(H O)]·CH OH·H O
(1),
3
2
3
2
Mn(L )(N )(H O)] (2) and [Mn(L )(H O) ]ClO (3) {where H2L1
2
3
=
N,N'-bis(3-
[
3
2
2
2
4
2
methoxysalicylidene)1,2-ethanediamine, H L = N,N'-bis(3-methoxysalicylidene)1,2-diamino-1-
2
3
propene and H L = N,N'-bis(3-methoxysalicylidene)1,2-propanediamine} have been synthesized
2
and characterized. Single crystal x-ray diffraction analysis confirmed their structures. Weak
noncovalent interactions generate extended supra-molecular assemblies in all three complexes.
Catalase mimicking activities (catalytic decomposition of hydrogen peroxide into oxygen and
water) of the complexes have been investigated. Complex 3 catalyzes the decomposition of
hydrogen peroxide most effectively. The higher catalase mimicking efficiency of complex 3 has
been related to its structure.
Keywords: Manganese(III); Crystal structure; Catalase mimicking activity.
1

1
. Introduction
Manganese(III) complexes have attracted a lot of attention because of their interesting
magnetic properties (with four unpaired electrons in high spin and two unpaired electrons in low
spin complexes) and structural diversities [1-5]. SOD (superoxide dismutase) and catalase are
two important enzymes that help to defend the cell structure against various reactive oxygen
species, e.g. hydrogen peroxide, hydrogen superoxide etc (capable of damaging different cellular
components), produced naturally during oxygen metabolism [10-12]. If not destructed, these
reactive oxygen species can cause oxidative stress leading to a number of human diseases [13-
1
5]. SOD destroys hydrogen superoxide reducing it into hydrogen peroxide [16,17]. Catalase is
responsible for the catalytic decomposition of hydrogen peroxide by means of its
disproportionation reaction into nontoxic dioxygen and water [18-20]. Many manganese(III)
complexes have also been used to mimic several enzymes, e. g. superoxide dismutase, catalase
etc [6-9]. Signorella et al. reported a manganese(III) complex that can exhibit both superoxide
dismutase and catalase-like activity [21]. Two manganese(II) complexes were also synthesised
by the same group and both of these complexes show superoxide dismutase and catalase-like
activity [22]. Britovsek et al. synthesized a bio-inspired manganese(II) complex with a linear
pentadentate ligand framework containing soft sulfur donors and an alternating NSNSN binding
motif which can displays excellent dual catalase/SOD-like antioxidant activity [23]. Párkányi et
al. have reported a manganese(II) complex exhibiting similar type activity [24]. Synthesis,
structural characterization and catalase-like activity of a number of manganese(II) complexes
were reported by Devereux et al. [25]. A novel single site manganese(II) complex was
successfully synthesized and tested in the aqueous disproportionation of hydrogen peroxide by
Barszcz et al. [26]. Li et al. synthesized two new manganese(II) complexes which can
2

decompose hydrogen peroxide catalytically, and possess the combined functions of SOD and
catalase in basic or weakly basic solutions [27].
With the specific aim to mimic catalase enzyme, we have synthesized and characterized
three octahedral manganese complexes, each having [MnLXY] core, where H L is tetradentate
2
Schiff base ligand occupying the equatorial positions; X and Y are monodentate ligands occupy
the axial positions, as expected from considering the structures of similar Mn(III) complexes
[9,28]. These monodentate ligands could be substituted by hydrogen peroxide to initiate catalase
4
activity of the complexes (Manganese(III) is d and labile). This special characteristic feature
makes them good catalysts towards decomposition of hydrogen peroxide into dioxygen and
water.
2
. Experimental Section
2
.1. Materials
All starting materials were available from commercial suppliers and were used without
further purification. Sodium azide was purchased from Merck, India. All other chemicals and
solvents were purchased from Sigma–Aldrich. The reactions and all manipulations of the
samples were carried out under aerobic conditions.
Caution!!! Although no problem was encountered during this work, perchlorate salts
containing organic ligands and azide are potentially explosive. Only a minute quantity of the
materials should be prepared and they must be handled with care.
2
.2. Preparations
3

.2.1. Preparation of [Mn(L )(N )(H O)]·CH OH·H O (1) [H2L1
1
=
N,N'-bis(3-
2
3
2
3
2
methoxysalicylidene)-1,2-ethanediamine]
1
The Schiff base ligand, H L , was synthesized by refluxing ethane-1,2-diamine (0.10 mL,
2
~1 mmol) with 3-methoxysalicylaldehyde (0.304 g, ~2 mmol) in methanol (20 mL) for ca. 1 h.
The ligand was not isolated and a methanol solution (10 mL) of manganese(II) perchlorate
hexahydrate (370 mg, ~1 mmol) was then directly added to the methanolic solution of ligand
under stirring condition. An aqueous methanol solution of sodium azide (0.065 g, ~1 mmol) was
then added to it and stirring was continued for further ca. 2 h. The resulting solution was then
filtered and kept for slow evaporation in open atmosphere. Dark brown coloured block shape
single crystals, suitable for X-ray diffraction, were obtained after few days which were collected
through filtration and then dried in aerobic condition.
Yield: 372 mg (~76 %); based on manganese(III). Anal. Calc. for C H MnN O (FW =
1
9
24
5
7
-
1
4
1
89.37): C, 46.63; H, 4.94; N, 14.31 %. Found: C, 46.3; H, 5.0; N, 14.6 %. FT-IR (KBr, cm ):
599, 1616, (υC=N); 2035 (υ ); 2833-2970 (υC-H); 3420 (υO-H). UV-Vis, max (nm), [εmax (L mol-1
N3
-1
4
4
3
2
cm )] (DMF), 272 (3.73 x 10 ), 327 (1.73 x 10 ), 426 (1.11 x 10 ), 501(3.75 x 10 ). Magnetic
moment = 4.96μB.
2
2
2
.2.2. Preparation of [Mn(L )(N )(H O)] (2) [H L = N,N'-bis(3-methoxysalicylidene)-1,2-
3 2 2
diamino-1-propene]
In the preparation of complex 2, propane-1,2-diamine (0.12 mL, ~1 mmol) was used
instead of ethane-1,2-diamine. All other reagents were identical to that used in the preparation of
complex 1. Diffraction quality single crystals were obtained after a few days on slow evaporation
of dark brown methanol solution of the complex in open atmosphere.
4

Yield: 326 mg (~72 %); based on manganese(III). Anal. Calc. for C H MnN O (FW =
1
9
20
5
5
-
1
4
1
53.34): C, 50.34; H, 4.45; N, 15.45 %. Found: C, 50.5; H, 4.3; N, 15.6 %. FT-IR (KBr, cm ):
-1
-1
600, 1619 (υC=N); 2828-2955 (υC-H); 3435 (υO-H). UV-Vis, max (nm), [εmax (L mol cm )]
4
3
3
2
(
DMF), 272 (3.98 × 10 ), 328 (5.26 × 10 ), 428 (1.94 × 10 ), 508 (4.88 x 10 ). Magnetic moment
=
4.98μB.
3
3
2
.2.3. Preparation of [Mn(L )(H O) ]ClO (3) [H L = N,N'-bis(3-methoxysalicylidene)-
2 2 4 2
1
,2-propanediamine]
A methanol solution of propane-1,2-diamine (0.12 mL, ~1 mmol)
and 3-
methoxysalicylaldehyde (0.304 g, ~2 mmol) was refluxed for ca. 1 h to prepare the tetradentate
3
Schiff base ligand H L . A methanol (10 ml) solution of manganese(II) perchlorate hexahydrate
2
3
(
370 mg, ~1 mmol) was directly added into the methanol solution of the ligand H L with
2
constant stirring. The stirring was continued for an additional ca. 2 h to get dark a dark brown
resulting solution. Deep brown blocked shaped single crystals of the complex, suitable for X-ray
diffraction, were obtained after a few days by slow evaporation of resulting solution in open
atmosphere.
Yield: 394 mg (~74 %); based on manganese(III). Anal. Calc. for C H MnN O Cl
1
9
24
2
10
(
FW = 530.79): C, 42.99; H, 4.56; N, 5.28 %. Found: C, 42.8; H, 4.4; N, 5.4 %. FT-IR (KBr, cm-
1)
: 1601, 1616 (υC=N); 2840-2965 (υC-H); 3430 (υO-H). UV-Vis, max (nm), [εmax (L mol cm )]
-1
-1
4
3
3
2
(
DMF), 270 (3.68 × 10 ), 329 (4.04 × 10 ), 422 (1.71 × 10 ), 500 (2.81 x 10 ). Magnetic moment
=
5.02μB
2
.3. Physical measurements
5

Elemental analyses (carbon, hydrogen and nitrogen) were performed on a Perkin-Elmer
-1
2
40C elemental analyzer. Infrared spectra in KBr (4500–400 cm ) were recorded using a
PerkinElmer Spectrum Two FTIR spectrophotometer. Electronic spectra (800–200 nm) were
recorded on a SHIMADZU UV-1700(E) Pharma Spec UV-Vis spectrophotometer. The magnetic
susceptibility measurements were performed with a magnetic susceptibility balance, made by
Sherwood Scientific, Cambridge, UK at room temperature (300 K). The corrected magnetic
susceptibility,  , was calculated using the relation:  meas –  . Diamagnetic susceptibilities,
m
m =
D
D were calculated using Pascal’s constants [29]. Effective magnetic moments were calculated
1
/2
using the formula, eff = 2.828(χ T) , where χ was the corrected molar susceptibility. The
m
m
instrument was calibrated using metallic nickel. Powder X-ray diffraction was performed on a
Bruker D8 instrument with Cu-K radiation (λ = 1.5418 Å) generated at 40 kV and 40 mA. The
α
powder XRD spectrum was recorded in a 2θ range of 5–50° using a 1D Lynxeye detector under
ambient conditions.
2
.4. Crystal data collection and refinement details
Suitable single crystals of all three complexes were used for data collection using a
‘Bruker D8 QUEST area detector’ diffractometer equipped with graphite-monochromated Mo-
K radiation (λ = 0.71073 Å) at 273 K. Molecular structures were solved by direct method and
α
2
refined by full-matrix least squares on F using the SHELX-2014/7 package [30]. Non hydrogen
atoms were refined with anisotropic thermal parameters. Hydrogen atoms, attached to oxygen,
were located by difference Fourier maps and were kept at fixed positions. All other hydrogen
atoms were placed in their geometrically idealized positions and constrained to ride on those
atoms to which they were attached. Multi-scan empirical absorption corrections were applied to
the data using the program SADABS [31]. In the unit cell of complex 1, a highly disordered
6

water molecule was present which could not be modeled as discrete atomic sites. We employed
PLATON/SQUEEZE to calculate the diffraction contribution of the solvent molecules and
thereby were able to produce a set of solvent-free diffraction intensities. Details about the
SQUEEZE procedure are given in the CIF file. A summary of crystallographic data and
refinement details of all three complexes are given in Table S1 (Supplementary information).
Selected bond lengths and bond angles are listed in Tables 1 and 2, respectively.
2
.5. Hirshfeld surface analysis
Hirshfeld surfaces [32-34] and the associated two-dimensional (2D) fingerprint plots [35-
7] were calculated using Crystal Explorer, [38] with bond lengths to hydrogen atoms set to
3
standard values [39]. The details can be found in many of our previous papers [40-43].
2
.6. Catalase-like activity studies
Volumetric measurements of evolved dioxygen during the reactions of the
3
manganese(III) complexes with H O were carried out as mentioned hereafter: a 50 cm three-
2
2
-3
3
necked round-bottom flask containing a solution of the complexes (10 M) in DMF (10 cm )
was placed in a water bath at 25°C. One of the necks was connected to a burette and the others
were stoppered by a rubber septum. While the solution was stirring, hydrogen peroxide (30%
v/v) was injected into it through the rubber septum using a microsyringe. Volumes of evolved
dioxygen were measured for 5 min time intervals volumetrically.
3
. Results and discussion
3
.1. Synthesis
7

1
3
Schiff base ligands, H L and H L , were synthesized by the 1:1 condensation of 3-
2
2
methoxysalicyldehyde with ethane-1,2-diamine and propane-1,2-diamine respectively in
2
methanol following the literature method [44,45]. On the other hand, H L was formed through
2
3
oxidation of ligand, H L in reaction environment. The ligands were not isolated and were used
2
directly for the preparation of manganese(III) complexes.
Addition of the methanol solution of manganese(II) perchlorate hexahydrate in the
1
methanol solution of the Schiff base, H L followed by the addition of sodium azide produced a
2
1
dark brown coloured complex, [Mn(L )(N )(H O)]·CH OH·H O (1). Similarly, reaction of the
3
2
3
2
methanol solution of manganese(II) perchlorate hexahydrate with methanol solution of Schiff
3
base, H L followed by the addition of sodium azide produced another dark brown coloured
2
2
complex [Mn(L )(N )(H O)] (2). It is very interesting to note that during the reaction 1,2-
3
2
3
diaminopropane moiety of H L is oxidized to 1,2-diamino-1-propene (1,2-pn) in reaction
2
2
environment and due to this oxidative dehydrogenation a new Schiff base ligand, H L is formed.
2
Oxidative dehydrogenation of diamine ligands coordinated to several transition metals is
reported in the literature [46,47]. On the other hand, a methanol solution of manganese(II)
3
perchlorate hexahydrate was made to react with methanolic solution of Schiff base, H L under
2
3
stirring condition to prepare mononuclear complex, [Mn(L )(H O) ]ClO (3). Synthetic route to
2
2
4
all three complexes are shown in Scheme 1. Manganese(II) was converted into manganese(III)
by aerial oxidation, as was observed in many previous cases [9,28].
8

Scheme 1: Synthetic route to the complexes.
3
3
.2. Description of the structures
1
.2.1. [Mn(L )(N )(H O)]·CH OH·H O (1)
3
2
3
2
The structure determination reveals that complex 1 consists of a discrete mononuclear
1
unit [Mn(L )(N )(H O)]. A lattice methanol molecule is also present in the asymmetric unit.
3
2
Perspective view of the complex is given in Figure 1. A lattice water molecule was present
which is squeezed in order to minimize the void space in the crystal structure. It crystallizes in
monoclinic space group P2 /c. The manganese(III) centre, Mn(1), has a six-coordinate pseudo-
1
octahedral geometry in which two imine nitrogen atoms [N(1) and N(2)] and two phenoxo
1
2-
oxygen atoms [O(1) and O(2)] of the deprotonated di-Schiff base ligand {(L ) } constitute the
equatorial plane. The remaining two coordination sites of manganese(III) centre is occupied by
one azide nitrogen atom [N(3)] and one water oxygen atom [O(5)] to constitute its axial plane.
9

The axial Mn–O(5) and Mn–N(3) distances [ 2.367(6) and 2.244(6) Å, respectively] are much
longer than the basal Mn–O(1), Mn–O(2), Mn–N(1) and Mn–N(2) distances [1.873(5), 1.873(5),
1
.980(7) and 1.979(7) Å, respectively] (see Table 1), which fall within the range observed for
structurally characterized manganese(III) complexes [48-55]. The elongation of axial bonds
indicates clear evidence of Jahn–Teller distortion, as expected for high-spin manganese(III)
complexes [28]. The distortion from the perfect octahedral geometry can be easily observed from
its coordinate bond angles, which deviate from the ideal values of 90° (for cis angles) or 180°
(for trans angles). Mn(III)-Nimine and Mn(III)-Ophenoxo bond lengths in the complex are
comparable to previously reported similar type manganese(III)-Schiff base complexes [48-55].
The saturated five membered chelate ring, Cg(1) [Mn(1)–N(1)–C(9)–C(10)–N(2)] in this
complex shows half chair conformation with puckering parameters [56] Q = 0.319(10) Å and ϕ
=
91.2(11)°. The terminal azide is quasi-linear with the N-N-N angle being 178.6(10)°, as
observed in similar complexes [40,42].
1
0

Figure 1: Perspective view of complex 1 with selective atom numbering scheme. Lattice
methanol molecule has been omitted for clarity.
2
3
.2.2. [Mn(L )(N )(H O)] (2)
3
2
The X-ray crystal structure determination reveals that complex 2 crystallizes in the
monoclinic space group, P2 /c. Perspective view of the complex along with selective atom-
1
numbering scheme is shown in Figures 2. The manganese(III) center is in a six-coordinate
distorted octahedral environment, being bonded to two imine nitrogen atoms, N(1) and N(2), and
2
-
two phenoxo oxygen atoms, O(1) and O(2), of a deprotonated Schiff base ligand, (L ) . The
remaining two axial coordination sites of manganese(III) centre is occupied by one azide
nitrogen atom, N(3) and one water oxygen atom, O(5) to complete its octahedral geometry. The
coordination geometry around the metal centre is highly distorted from ideal octahedral
geometry as suggested by the coordinate bond angles. The axial Mn–O(5) and Mn–N(3) bond
lengths are much longer than the equatorial Mn–O(1), Mn–O(2), Mn–N(1) and Mn–N(2) bond
lengths (see Table 1), which clearly indicates Jahn–Teller distortion, as expected for high-spin
manganese(III) complexes [28]. The terminal azide is quasi-linear as observed in previously
reported similar type complexes with the N-N-N angle being 178.2(13)° [40,42].
The most exciting observation is the oxidation of Schiff base ligand during the reaction
procedure. The 1,2-diaminopropane moiety is oxidized to 1,2-diamino-1-propene (1,2-pn) via
oxidative dehydrogenation reaction, which is probably catalyzed by manganese(III). The metal
coordinated amine (or diamine) is oxidized by aerial oxygen to form α-imine (or α-di-imine)
[47]. In our case, 1,2-diaminopropane moiety of the Schiff base ligand, coordinated to
manganese(III) is oxidized by aerial oxygen to an α-imine. The methyl group probably restricts
1
1

the formation of an α-di-imine. This α-imine may easily then be rearranged to form the 1,2-
diamino-1-propene. The C-C bond lengths of complexes 1, 2 and 3 (oxidized part of salen-type
ligands) are 1.484(13), 1.30(2) and 1.381(19), respectively. In case of complex 2, much shorter
C-C bond length confirms oxidation of Schiff base ligand.
Figure 2: Perspective view of complex 2 with selective atom numbering scheme.
3
3
.2.2. [Mn(L )(H O) ]ClO (3)
2
2
4
Single crystal X-ray structure determination analysis reveals that the asymmetric unit of
2
+
the complex consists of a mononuclear cation [Mn(L )(H O) ] together with a non-coordinating
2
2
perchlorate anion. The complex crystallizes in the monoclinic space group P2 /c. A perspective
1
view of the complex with selective atom-numbering scheme is shown in Figure 3. The central
manganese(III) center, Mn(1), is again in a six-coordinate octahedral environment, being bonded
to two imines nitrogen atoms, N(1) and N(2) and two phenoxo oxygen atoms, O(1) and O(2),
3
−
from a deprotonated Schiff base ligand (L ) . Other vacant sites are coordinated by two water
1
2

oxygen atoms, O(5) and O(6), to complete its distorted octahedral geometry. The longer values
of axial bonds compared to equatorial bonds (see Table 1) are indicative of tetragonal
elongations as a result of the Jahn–Teller distortion, expected for high-spin manganese(III)
4
complexes with d configuration [9,28]. The saturated five membered ring, [Mn(1)–N(1)–C(9)–
C(10)–N(2)], has an half chair conformation, with puckering parameters Q = 0.219(14) Å, ɸ =
1
00(2)° [56].
Figure 3: Perspective view of complex 3 with selective atom numbering scheme. Non-
coordinated perchlorate anion has been omitted for clarity.
3
.3 Hirshfeld surface analysis
Hirshfeld surfaces of all three complexes mapped over dnorm, shape index and curvedness
Figure 11). The surfaces are shown as transparent to allow visualization of the molecular moiety
(
around which they are calculated. The dominant interactions between N···H/H···C for all
complexes can be seen in the Hirshfeld surfaces as red spots on the dnorm surface in Figure 11.
1
3

Additional visible spots in the Hirshfeld surfaces correspond to mainly C···H/H···C and H···H
contacts. The tiny extent of area and light color on the Hirshfeld surfaces signify weaker and
long range interactions other than hydrogen bonds. Moreover, the two dimensional fingerprint
plots (Figure 12) illustrate the difference between the intermolecular interaction patterns and the
relative contributions (in percentage) for the major intermolecular interactions associated with
the complex. In two dimensional fingerprint plots (Figure 12) intermolecular interactions appear
as distinct spikes. Complementary regions are visible in the fingerprint plots where one molecule
acts as a donor (d > d ) and the other as an acceptor (d < d ).
e
i
e
i
Figure 11: Hirshfeld surfaces mapped with dnorm (left-side), shape index (middle) and
curvedness (right-side).
1
4

Figure 12: Fingerprint plot: Resolved into H···H, C···H/H···C, O···H/H···O and N···H/H···N
contact contributed to the total Hirshfeld Surface area of complex 1 (left), complex 2 (middle)
and complex 3 (right).
3
.4. Spectral Analysis
Infrared spectra provide enough information to identify the way of bonding of the ligands
to the metal centres. The most characteristic vibrations are selected by comparing the IR spectra
of all complexes. In the IR spectra of all complexes, distinct bands as a result of the azomethine
-1
(
C=N) groups around 1616 cm are customarily noticed [57]. The appearances of strong bands
-1
around 2032 cm indicate the presence of the monodentate azide coligands in complexes 1 and
2
, respectively [40,42]. Broad bands centered at around 3420 cm-1 due to O–H stretching
vibrations are observed in IR spectra of all complexes [58-60]. Bands in the range of 2970–2830
1
5

cm-1 due to alkyl C–H bond stretching vibrations are usually noticed in IR spectra of all
complexes [61].
The electronic spectra of the complexes are quite comparable to each other in DMF
medium at room temperature. Intense absorption bands in the high energy region of 270 nm are
assigned as intra-ligand * transitions involving the aromatic rings. Absorption bands around
3
25 nm are due to n* transitions within the ligands. Strong absorption bands around 425 nm
may be attributed to the ligand to metal charge transfer (LMCT) transitions [62]. Absorption
bands with shoulders around 500 nm region are due to spin allowed d–d transitions [63,64].
Molar extinction coefficient value of d-d transition is very high may be due to the fact that
LMCT band partly overlaps the d-d transition.
Formulations of all complexes as manganese(III) complexes are further supported by the
room temperature solid state magnetic moment values in the region 4.96-5.02. These values are
휇퐵 expected for discrete, high-spin (S = 2), magnetically non-coupled manganese(III) complexes
having four unpaired electrons [28,65].
3
.5. Catalytic decomposition of hydrogen peroxide (Catalase mimicking activity) study
The catalytic activity of all three complexes towards decomposition of hydrogen peroxide
has been investigated in DMF medium at 25°C temperature. In the beginning, solutions of the
manganese(III) complexes were dark brown coloured but after addition of 30% (v/v) hydrogen
peroxide they became fade yellow coloured or colorless and instantaneous evolution of a gas was
observed for all three complexes. It can be easily understood that the evolved gas is oxygen and
it comes from the catalytic decomposition of hydrogen peroxide solution. Volumetric
measurements of this evolved oxygen confirmed that all three complexes are very much capable
1
6

of catalytic decomposition of hydrogen peroxide into water and oxygen but the degree of
decomposition is different i.e. complex 3 is the most efficient in hydrogen peroxide
decomposition followed by other two complexes. Complexes 1 and 2 have comparable
efficiency. To analyze the catalytic activity four set of experiments were carried out for each
complexes with different initial amount of hydrogen peroxide (10, 20, 30, 40, 50 mL 30% v/v),
and a constant catalyst concentration. The measurement of the volume of evolved oxygen
indicates that for constant catalyst concentration the rate of decomposition increases with
increase in the initial amount of hydrogen peroxide. The volume of oxygen evolved at different
initial amount of 30% v/v hydrogen peroxide for most efficient complex i.e. complex 3 is shown
in Figure 13. A blank experiment in presence of 30 mL hydrogen peroxide (30% v/v) has also
been performed (Figure 13). From Figure 13, it can be clearly understood that at constant
catalyst concentration, decomposition of H O exhibits rate saturation kinetics. The efficiency of
2
2
complex 3 at different initial amount of 30% v/v hydrogen peroxide is shown in the turnover
number (TON) versus time plot in Figure 14. TON is defined as the number of moles of oxygen
evolved per mole of the catalyst. Since two molecules of H O on decomposition liberates one
2
2
molecule of oxygen, if V and V denote the volumes of oxygen given out at any time t and at
t
inf
the completion of reaction, then (V -V ) is proportional to the amount of undecomposed H O at
inf
t
2
2
time t. Now, rate constant of the reaction can be calculated from the equation: Rate constant, k =
.303/t log{V /(V -V )}, provided it follows first order kinetics. Substitution of experimental
2
t
inf
t
data (Table 3) revealed constancy in the value of rate constant (k), confirming first order
kinetics. In some previously published reports, similar type tentative catalytic cycles have been
proposed [9,66]. A plausible mechanistic pathway for the decomposition of hydrogen peroxide is
also shown in Scheme 2. It is clear from the catalytic cycle that during the catalytic cycle,
1
7

manganese(III) is oxidised to manganese(IV) by replacing one axially coordinated ligand (water
or azide) simultaneously H O is reduced to H O. Subsequently, molecular oxygen is generated
2
2
2
when the catalyst regenerates to its original form. Figure 15 shows the comparison between turn
over numbers of complexes 1, 2 and 3. Complex 3 seems to be the most efficient catalyst as it
contains two labile solvent molecules at the axial positions of its octahedral geometry. A few
mononuclear manganese(III) complexes showing catalase mimicking activity already exist in
literature. Some of these previously reported complexes exhibiting catalase mimicking activity
are gathered in Table 4.
-3
Figure 13: Time dependence of oxygen evolution upon reaction of complex 3 (10 M) with
different initial amount of hydrogen peroxide at 25 °C. A blank experiment in presence of 30 mL
H O has also been included.
2
2
1
8

Figure 14: Turnover number {[Evolved oxygen]/[Catalyst]) vs time for complex 3 in the
different initial amount of hydrogen peroxide at 25 °C.
Figure 15: Comparison between turn over numbers of complexes 1, 2 and 3 when 50 mL 30%
(
v/v) H O is used in each case.
2 2
1
9

Scheme 2: Plausible mechanistic pathway for the catalytic decomposition of hydrogen peroxide
into water and oxygen.
In order to verify whether these complexes is capable of maintaining its structural
integrity after H O decomposition process, IR spectrum of complex 3 was recorded before and
2
2
after decomposition reaction. The IR spectrum of complex 3 after decomposition reaction is in
excellent agreement with the IR spectrum of pure complex, confirming the structural integrity of
the complex after catalytic decomposition of H O . Alternatively, we can say that the complex is
2
2
chemically intact during the decomposition reaction. Figure 16 illustrates IR spectrum of
complex 3 before and after the H O decomposition reaction.
2
2
2
0

Figure 16: IR spectrum of complex 3 before (blue) and after (red) the H O decomposition
2
2
reaction.
4
. Conclusion
In the present work, three manganese(III) complexes derived from N O donor
2
2
tetradentate Schiff base ligands were synthesized and the structures of these complexes were
confirmed by single crystal X-ray diffraction technique. The solid state structures of these
complexes showed the involvement of the organic ligands in several weak supramolecular
interactions involving the alkoxy arms and the aromatic rings. All complexes were found to be
active towards catalytic decomposition of hydrogen peroxide. Probable catalytic cycle showing
the catalytic decomposition of hydrogen peroxide was also projected. During the course of
hydrogen peroxide decomposition, hydrogen peroxide molecule has to coordinate the
manganese(III) center by replacing the axially coordinated ligands. Since water is a neutral
2
1

molecule, it could easily be replaced by hydrogen peroxide. Alternatively, the replacement of
azide coligand is probably somewhat difficult, as it is anionic in nature. The decomposition of
hydrogen peroxide is, therefore, catalyzed more efficiently by complex 3 than other two
complexes.
Acknowledgement
I.M. thanks the CSIR, India, for awarding a Junior Research Fellowship. K. G. expresses
his gratitude to UGC, India, for awarding a Senior Research Fellowship.
Appendix A. Supplementary data
CCDC 1871955-1871957 contain the supplementary crystallographic data of complexes
1
, 2 and 3, respectively. These 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. The complete description on supramolecular interactions of all three
complexes is given in Supplementary Information part.
References
[1] Q. Yue, X. Liu, W. -X. Guo, E. -Q. Gao, CrystEngComm 20 (2018) 4258-4267.
[2] X. Dong, Y. Yao, Y. Li, Q. Wang, Y. Gou, J. Mol. Struct. 1149 (2017) 744-749.
[3] M. Pait, M. Shatruk, D. Ray, Dalton Trans. 44 (2015) 11741-11754.
2
2

[4] S. Ganguly, P. Kar, M. Chakraborty, A. Ghosh, New J. Chem. 42 (2018) 9517-9529.
[5] G. E. Kostakis, A. M. Ako, A. K. Powell, Chem. Soc. Rev. 39 (2010) 2238-2271.
[6] M. Maneiro, M. R. Bermejo, A. Sousa, M. Fondo, A. M. Gonzalez, A. Sousa-Pedrares, C. A.
McAuliffe, Polyhedron 19 (2000) 47-54.
[7] M. Á. Vázquez-Fernández, M. R. Bermejo, M. I. Fernández-García, G. González-Riopedre,
M. J. Rodríguez-Doutón, M. Maneiro, J. Inorg. Biochem. 105 (2011) 1538-1547.
[8] P. Kar, M. G. B. Drew, A. Ghosh, Inorg. Chim. Acta 405 (2013) 349-355.
[9] N. Sarkar, P. K. Bhaumik, S. Chattopadhyay, Polyhedron 115 (2016) 37-46.
[10] R. Than, A. Schrodt, L. Westerheide, R. van Eldik, B. Krebs, Eur. J. Inorg. Chem. (1999)
1
537-1543.
[11] G.C. Dismukes, in: J. Reedijk, Bioinorganic catalysis (Ed.), Marcel Dekker, New York,
1
993, p. 317.
[
12] E. Birben, U. M. Sahiner, C. Sackesen, S. Erzurum, O. Kalayci, World Allergy Organ J. 5
2012) 9-19.
(
[13] L. A. Pham-Huy, H. He, C. Pham-Huy, Int. J. Biomed. Sci. 4 (2008) 89-96.
[14] D. Giustarini, I. Dalle-Donne, D. Tsikas, R. Rossi, Crit. Rev. Clin. Lab. Sci. 46 (2009) 241-
2
81.
[15] V. Kumar, A. A. Khan, A. Tripathi, P. K. Dixit, U. K. Bajaj, The Journal of
Phytopharmacology 4 (2015) 126-132.
2
3

[16] V. Gómez, M.Corbella, Eur. J. Inorg. Chem. (2012) 3147-3155.
[
17] C. Palopoli, N. Bruzzo, C. Hureau, S. Ladeira, D. Murgida, S. Signorella, Inorg. Chem. 50
2011) 8973-8983.
(
[18] M. Grau, F. Rigodanza, A. J. P. White, A. Sorarú, M. Carraro, M. Bonchio, G. J. P.
Britovsek, Chem. Commun. 50 (2014) 4607-4609.
[
[
[
19] B. Dede, I. Ozmen, F. Karipcin, Polyhedron 28 (2009) 3967-3974.
20] B. Dede, F. Karipcin, M Cengiz, J. Hazard. Mater. 163 (2009) 1148-1156.
21] G. N. Ledesma, H. Eury, E. Anxolabéhère-Mallart, C. Hureau, S. R. Signorella, J. Inorg.
Biochem. 146 (2015) 69-76.
[
22] D. Moreno, V. Daier, C. Palopoli, J.-P. Tuchagues, S. Signorella, J. Inorg. Biochem. 104
2010) 496-502.
(
[23] M. Grau, F. Rigodanza, A.J.P. White, A. Soraru, M. Carraro, M. Bonchio, G. J. P.
Britovsek, Chem. Commun. 50 (2014) 4607-4609.
[24] J. Kaizer, T. Csay, P. Kovari, G. Speier, L. Parkanyi, J. Mol. Catal. A Chem. 280 (2008)
2
03-209.
[25] M. Devereux, M. McCann, V. Leon, V. McKee, R.J. Ball, Polyhedron 21 (2002) 1063-
1
071.
[26] M. Zienkiewicz, J. Szlachetko, C. Lothschütz, M. Hodorowicz, A. Jabłońska-Wawrzycka, J.
Sá, B. Barszcz, Dalton Trans. 42 (2013) 7761-7767.
2
4

[
27] Q.X. Li, Q.-H. Luo, Y.Z. Li, Z.Q. Pan,M.C. Shen, Eur. J. Inorg. Chem. (2004) 4447-4456.
28] N. Sarkar, M. G. B. Drew, K. Harms, A. Bauzá, A. Frontera, S Chattopadhyay,
[
CrystEngComm 20, (2018) 1077-1086.
[
29] O. Kahn, Molecular magnetism, VCH, New York, 1993.
30] G.M. Sheldrick, Acta Crystallogr. Sect. A 64 (2008) 112-122.
[
[31] G.M. Sheldrick, SADABS, Software for Empirical Absorption Correction, University of
Göttingen, Institute fur AnorganischeChemiederUniversitat, Gottingen, Germany, 1999-2003.
[
[
[
32] M. A. Spackman, D. Jayatilaka, CrystEngComm 11 (2009) 19-32.
33] F. L. Hirshfeld, Theor. Chim. Acta 44 (1977) 129-138.
34] H. F. Clausen, M. S. Chevallier, M. A. Spackman, B. B. Iversen, New J. Chem. 34 (2010)
1
93-199.
35] A. L. Rohl, M. Moret, W. Kaminsky, K. Claborn, J. J. McKinnon, B. Kahr, Cryst. Growth
Des. 8 (2008) 4517-4525.
36] A. Parkin, G. Barr, W. Dong, C. J. Gilmore, D. Jayatilaka, J. J. McKinnon, M. A.
Spackman, C. C. Wilson, CrystEngComm 9 (2007) 648-652.
[
[
[37] M. A. Spackman, J. J. McKinnon, CrystEngComm 4 (2002) 378-392.
[38] S. K. Wolff, D. J. Grimwood, J. J. McKinnon, D Jayatilaka, M. A. Spackman, Crystal
Explorer
http://hirshfeldsurfacenet.blogspot.com/.
39] F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen, R. J. Taylor, J. Chem.
Soc., Perkin Trans. 2 (1987) S1-S19.
2.0;
University
of
Western
Australia:
Perth,
Australia,
2007.
[
2
5

[40] K. Ghosh, S. Roy, A. Ghosh, A. Banerjee, A. Bauzá, A. Frontera, S. Chattopadhyay,
Polyhedron 112 (2016) 6-17.
[
[
[
41] T. Basak, K. Ghosh, S. Chattopadhyay, Polyhedron 146 (2018) 81-92.
42] K. Ghosh, K Harms, S Chattopadhyay, Polyhedron 123 (2017) 162-175.
43] S. Jana, K. Harms, A. Bauzá, A. Frontera, S. Chattopadhyay, Cryst. Growth Des. 15 (2015)
2
57-267.
[44] L. K. Das, R. M. Kadam, A. Bauzá, A. Frontera, A. Ghosh, Inorg. Chem. 51 (2012) 12407-
1
2418.
[45] K. Ghosh, K. Harms, A. Bauzá, A. Frontera, S. Chattopadhyay, Dalton Trans. 47 (2018)
3
31-347.
[
[
[
46] F. R. Keene, Coord. Chem. Rev. 187 (1999) 121-149.
47] S. Jana, S. Chattopadhyay, J. Coord. Chem. 66 (2013) 3906-3914.
48] M. Á. Vázquez-Fernández, M. I. Fernández-García, A. M. González-Noya, M. Maneiro, M.
R. Bermejo, M. J. Rodríguez-Doutón, Polyhedron 31 (2012) 379-385.
[49] G. Assey, R. J. Butcher, Y. Gultneh, Acta Cryst. E66 (2010) m851-m852.
[50] C. -H. Li, K. -L. Huang, J. -M. Dou, Y.-N. Chi, Y. -Q. Xu, L. Shen, D. -Q. Wang, C. -W.
Hu, Cryst. Growth Des. 8 (2008) 3141-3143.
[51] C. -G. Zhang, G. -H. Tian, Z. -F. Ma, D. -Y. Yan, Transition Met. Chem. 25 (2000) 270-
2
73.
2
6

[52] A. Gutiérrez, M. F. Perpiñán, A. E. Sánchez, M. C. Torralba, V. González, Inorg. Chim.
Acta 453 (2016) 169-178.
[53] H. Kara, Anal. Sci. 24 (2008) 263-284.
[54] S. Nastase, F. Tuna, C. Maxim, C. A. Muryn, N. Avarvari, R. E. P. Winpenny, M. Andruh,
Cryst. Growth Des. 7 (2007) 1825-1831.
[55] M. R. Bermejo, M. I. Fernández, E. Gómez-Fórneas, A. González-Noya, M. Maneiro, R.
Pedrido, M. J. Rodríguez, Eur. J. Inorg. Chem. (2007) 3789-3797.
[56] D. Cremer, J. A. Pople, J. Am. Chem. Soc. 97 (1975) 1354-1358.
[57] K. Nakamoto, Infrared Spectra of Inorganic and Coordination Compounds, Fourth ed.,
Wiley, New York, 1986.
[
[
[
58] M. Das, S. Chattopadhyay, Polyhedron 50 (2013) 443-451.
59] A. Bhattacharyya, K. Harms, S. Chattopadhyay, Inorg. Chem. Commun. 48 (2014) 12-17.
60] J.-B. Brubach, A. Mermet, A. Filabozzi, A. Gerschel, P. Roy, J. Chem. Phys. 122 (2005)
1
84509.
[
[
[
[
61] K. Ghosh, K. Harms, S. Chattopadhyay, ChemistrySelect 2 (2017) 8207-8220.
62] A. Saha, P. Majumdar, S. Goswami, J. Chem. Soc. Dalton Trans. (2000) 1703-1708.
63] A. Bartyzel, A.A. Kaczor, J. Coord. Chem. 68 (2015) 3701-3717.
64] P. Bhowmik, H.P. Nayek, M. Corbella, N´ . Aliaga-Alcalde, S. Chattopadhyay, Dalton
Trans. 40 (2011) 7916-7926.
2
7

[65] B. J. Kennedy, K. S. Murray, Inorg. Chem. 24 (1985) 1552-1557.
[66] S. R. Doctrow, K. Huffman, C. B. Marcus, G. Tocco, E. Malfroy, C. A. Adinolfi, H. Kruk,
K. Baker, N. Lazarowych, J. Mascarenhas, B. Malfroy, J. Med. Chem. 45 (2002) 4549-4558.
[67] Y. Noritake, N. Umezawa, N. Kato, T. Higuchi, Inorg. Chem. 52 (2013) 3653-3662.
[
68] V. Daier, D. Moreno, C. Duhayon, J.-P. Tuchagues, S. Signorella, Eur. J. Inorg. Chem.
2010) 965-974.
(
Table 1: Selected Bond lengths (Å) of the complexes 1, 2 and 3.
1
2
3
Mn(1)-O(1)
Mn(1)-O(2)
Mn(1)-O(5)
Mn(1)-O(6)
Mn(1)-N(1)
Mn(1)-N(2)
Mn(1)-N(3)
1.873(5)
1.873(5)
2.367(6)
-
1.913(6)
1.895(6)
2.364(7)
-
1.867(6)
1.865(5)
2.221(5)
2.373(8)
1.968(7)
1.986(8)
-
1.980(7)
1.979(7)
2.244(6)
1.987(9)
2.004(9)
2.191(10)
2
8

Table 2: Selected bond angles (°) of the complexes 1, 2 and 3.
1
2
3
O(1)-Mn(1)-O(2)
O(1)-Mn(1)-O(5)
O(1)-Mn(1)-O(6)
O(1)-Mn(1)-N(1)
O(1)-Mn(1)-N(2)
O(1)-Mn(1)-N(3)
O(2)-Mn(1)-O(5)
O(2)-Mn(1)-O(6)
O(2)-Mn(1)-N(1)
O(2)-Mn(1)-N(2)
O(2)-Mn(1)-N(3)
O(5)-Mn(1)-N(1)
O(5)-Mn(1)-N(2)
O(5)-Mn(1)-N(3)
N(1)-Mn(1)-N(2)
N(1)-Mn(1)-N(3)
N(2)-Mn(1)-N(3)
O(5)-Mn(1)-O(6)
O(6)-Mn(1)-N(1)
O(6)-Mn(1)-N(2)
93.0(2)
89.3(2)
-
92.2(2)
88.2(3)
-
92.9(2)
93.1(2)
91.8(3)
91.8(3)
174.7(3)
-
91.8(2)
173.4(3)
93.4(2)
92.9(2)
-
92.5(3)
171.1(3)
95.3(3)
89.2(3)
-
91.4(2)
90.8(3)
175.0(3)
92.2(3)
-
174.6(3)
91.6(3)
94.2(2)
84.6(3)
85.7(3)
172.2(3)
83.4(3)
88.0(3)
91.0(3)
-
171.7(3)
91.6(3)
98.2(3)
84.1(3)
83.7(3)
171.7(4)
82.8(4)
88.2(4)
92.3(4)
-
90.2(3)
88.6(3)
-
83.1(3)
-
-
174.5(3)
87.2(4)
86.3(3)
-
-
-
-
2
9