Bio-mimetic of catecholase and phosphatase activity by a tetra-iron(III) cluster

Article abstract of DOI:10.1016/j.poly.2019.114156

An oxido- and acetato-bridged tetranuclear iron(III) cluster, [Fe₄^III(μ-O)₂(μ-OAc)₆(phen)₂(H₂O)₂](NO₃)₂·(H₂O)₃ (1), [OAc = acetate; ph

Full text of DOI:10.1016/j.poly.2019.114156

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Bio-mimetic of Catecholase and Phosphatase Activity by a Tetra-iron(III) Clus-
ter
Chanchal Kumar Pal, Shreya Mahato, Hare Ram Yadav, Madhusudan Shit,
Angshuman Roy Choudhury, Bhaskar Biswas
PII:
S0277-5387(19)30593-5
DOI:
https://doi.org/10.1016/j.poly.2019.114156
POLY 114156
Reference:
To appear in:
Polyhedron
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Accepted Date:
10 July 2019
13 September 2019
15 September 2019
Please cite this article as: C. Kumar Pal, S. Mahato, H. Ram Yadav, M. Shit, A. Roy Choudhury, B. Biswas, Bio-
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Bio-mimetic of Catecholase and Phosphatase Activity by a Tetra-iron(III)
Cluster
a
a
b
c
Chanchal Kumar Pal, Shreya Mahato, Hare Ram Yadav, Madhusudan Shit,
b
a,*
Angshuman Roy Choudhury, Bhaskar Biswas
aDepartment of Chemistry, University of North Bengal, Darjeeling-734013, India
bDepartment of Chemical Sciences, Indian Institute of Science Education and Research,
Mohali, Sector 81, Knowledge City, S. A. S. Nagar, Manauli PO, Mohali, Punjab 140306,
India
cDepartment of Chemistry, Dinabandhu Andrews College, Kolkata 700084, India
Abstract
III
An oxido- and acetato-bridged tetranuclear iron(III) cluster, [Fe (µ-O) (µ-
4
2
OAc) (phen) (H O) ](NO ) (H O) (1), [OAc = acetate; phen = 1,10-phenanthroline] has
6
2
2
2
3 2·
2
3
been prepared in the crystalline phase. X-ray structural analysis of the compound reveals that
all the Fe(III) centres in 1 adopt an octahedral coordination geometry and the tetra-iron(III)
core exists in an unusual asymmetric conformation. Bond valence sum (BVS) calculations
recommend the existence of all iron ions in the +3 oxidation state in the crystalline phase. The
tetra-iron(III) cluster elegantly catalyzes the oxidation of 3,5-di-tert-butylcatechol (DTBC),
2
-1
viz. catecholase-like activity, with a good turnover number, k = 9.28  10 h in acetonitrile
cat
medium. Spectrophotometric titration shows the existence of two distinct isosbestic points,
which unanimously proves the rarely observed enzyme-substrate binding phenomenon in
solution. Electrochemical analysis recommends the production of Fe(II)-semiquinone species
in the course of the catalytic oxidation of DTBC. Furthermore, the same iron(III) cluster
displays phosphoester cleavage activity towards the disodium salt of p-nitrophenylphosphate
-4
-1
(
PNPP) in aqueous-methanol medium with rate of 7.20  10 m . ESI-MS measurements of
the tetra-iron(III) complex in the presence of PNPP indicate the formation of an
organophosphorus intermediate in solution and solvent aqua molecules probably make a
nucleophilic attack on the phosphorus centre, favouring the generation of the
organophosphorus intermediate.
Keywords: Iron; X-ray structure; Electrochemistry; Catecholase activity; Phosphatase study

2
*
Corresponding author. E-mail: bhaskarbiswas@nbu.ac.in / icbbiswas@gmail.com
1
. Introduction
In nature, emergent biological processes often utilize 3d metal-based coordination
compounds as functional sites for facilitating highly selective bio-chemical reactions [1-5].
Due to this, paramount interest has been shown by synthetic coordination chemists to design
and synthesize bio-inspired catalysts in the pursuit of selective bond activation and organic
transformations [6-16]. Nowadays, coordination compounds comprising of earth abundant
transition metal ions in combination with different (N,N) and (N,O) donor ligands have
received significant attention for their potential applications in biological and material science
[17-24]. Iron is one of the most prevalent metal ions among the transition metal ions in living
systems. The design of new catalytic systems based on abundant and inexpensive metal ions,
particularly iron, for fundamental chemical transformations under environmentally benign
conditions is an important paradigm in chemical synthesis [25-29]. In recent times, iron-based
coordination compounds with varied nuclearities have shown unprecedented catalytic activity
for different catalytic transformations of organic substrates [19,30-33]. Indeed, it has been
demonstrated that the proper design of iron complexes by judiciously choosing ligands can aid
in the development of novel catalysts [34-41].
Iron clusters bring additional importance for advances in the avenue of magnetism for
metallo-clusters. Hence, considerable attention has been paid to synthetic approaches which
may produce polymetallic coordination cores with promising magnetic properties [19,28,29].
A literature survey indicates the impact as well as the importance of the magnetic properties
corresponding to the design and preparation of such tetra-iron(III) clusters. Previously, A.K.
Boudalis et al, M.W. Wemple et al and J.K. McCusker et al [42-44] synthesized a similar type
of tetra-iron(III) cluster, keeping azides as terminal ions to the iron centres. Recently, we also
prepared a similar tetra-iron(III) cluster with bipyridine ligands and different counter anions
[19]. However, catalytic performance, in relation to bio-mimics, by tetra-iron(III) clusters is
limited. Based on the invaluable contribution of iron centric coordination compounds ranging
from heme proteins to iron-sulfur clusters and redox-enzymes in the living world and focusing
on industrial importance, we have designed and structurally characterised an oxido-acetato-

3
bridged tetra-iron(III)-phenanthroline cluster. Spectrophotometric titration shows the presence
of two distinct isosbestic points in the course of the catalytic oxidation of DTBC and this
remarkable phenomenon unanimously confirms the binding of the enzyme with the substrate
in solution. Electrochemical analysis consolidates the production of Fe(II)-semiquinone
species in the DTBC oxidation. This tetra-iron(III) cluster catalyzes the production of quinone
2
-1
species with a good turnover number, kcat = 9.28  10 h . This iron(III) cluster also effectively
catalyses the cleavage of phosphoester linkages in PNPP and the rate of phosphatase activity
-4
-1
is found to be as high as 7.20  10 m . Experimental observations and ESI-MS analysis
suggest that solvent aqua molecules make a nucleophilic attack on the phosphorus centre and
the course of the catalysis proceeds through the formation of an organophosphorus
intermediate in solution.
2
. Experimental section
2
.1. Preparation of the tetra-iron(III) cluster
(a) Chemicals, solvents and starting materials
High purity 1,10-phenanthroline (Lancaster, UK), iron(III) chloride hexahydrate (E.
Merck, India), ceric ammonium nitrate (E. Merck, India) were purchased from commercial
sources and used as received. All the other reagents and solvents were used of analytical grade
(A.R. grade).
(b) Synthesis of the tetra-iron(III) cluster
An aqueous-acetic acid (40/60; v/v) solution (10 ml) of 1,10-phenanthroline (0.360 g, 2.0
mmol) was added to an aqueous solution of hydrated FeCl (0.271 g, 1.0 mmol, 20 ml),
3
followed by a solution of sodium acetate (0.164 g, 2.0 mmol). The reaction mixture was
stirred slowly for 30 min, then solid ceric ammonium nitrate (CAN) (0.550 g, 1.0 mmol) was
added and the resulting solution was stirred slowly for another 30 minutes. After that, the
brown coloured solution obtained was filtered. The filtrate was kept in air for slow
evaporation. After 12-15 days, a brown coloured compound (1) in the form of single crystals
separated out. The tetra-iron compound was washed with hexane and dried in vacuo over

4
silica gel. Yield of the tetra-iron compound: 0.207 g (76.4% based on the metal salt)
-1
Spectroscopic results for C H N O Fe (1); IR (KBr pellet, cm ): 3379 (v ), 1592 (vC=N),
3
6
44
6
25
4
OH
-4
1
498, 1471(vM(µ-OAc)), 1384(v(-NO3)); UV-Vis (1×10 M, λmax, nm, MeCN): 249, 299, 353, 521.
.2. Physical measurements
2
The infrared spectrum (KBr) was recorded with a FTIR-8400S SHIMADZU
–
1
1
spectrophotometer in the range 4000–400 cm with a KBr pellet. The H NMR spectrum was
obtained on a Bruker Advance 300 MHz spectrometer at 25 °C. Ground state absorption and
all spectrophotometric analysis were recorded with
a
JASCO V-730 UV-Vis
spectrophotometer. The electrospray ionization (ESI) mass spectrum was recorded using a Q-
tof-micro quadruple mass spectrometer. The pH value of the solutions was measured using a
Labman pH meter at room temperature.
2
.3. X-ray diffraction analysis
Single crystal X-ray diffraction data of the oxido-acetato-bridged tetra-iron(III) complex
was collected using a Rigaku XtaLABmini diffractometer equipped with a Mercury CCD
detector. The data were collected with graphite monochromated Mo-Kα radiation (λ =
0
.71073 Å) at 100.0(2) K, using  scans. The data were reduced using Crystal Clear suite 2.0.
2
[
45] and the space group determination was done using Olex . The structure was resolved by
the direct method and refined by full-matrix least-squares procedures using the SHELXL-
2
2
014/7 software package, using the OLEX suite [46,47].
2
.4. Catecholase activity of the tetra-iron(III) cluster
−
4
To examine the catechol oxidation activity of the iron(III) cluster, a 10 M solution of the
tetra-iron compound in acetonitrile (ACN) medium was treated with 100 equiv. of 3,5-di-tert-
butylcatechol (DTBC) at room temperature under an aerobic atmosphere. Absorbance vs.
wavelength (wavelength scans) of these solutions were recorded at regular time intervals of 5
min in the wavelength interval 300–800 nm [48,49]. It may be noted that a control experiment

5
in the absence of this tetranuclear iron(III) catalyst was also performed, which showed very
little development of the quinone species up to 6h in acetonitrile medium and thus can be
ignored. Kinetic experiments were further performed spectrophotometrically with the iron(III)
cluster and DTBC in ACN at 25 °C. A 0.04 ml solution of the tetra-iron(III) cluster, with a
constant concentration of 1 × 10-4 M, was added to 2 ml of DTBC of a particular
-3
-2
concentration (varying its concentration from 1 × 10 M to 1 × 10 M) to achieve an ultimate
-4
concentration of the tetra-iron(III) cluster of 1×10 M. The conversion of DTBC to DTBQ
quinone band maxima) was monitored with time at a wavelength of 400 nm (time scan) in
(
ACN medium. The initial rate method [48,49] was applied to determine the rate constant
value for each concentration of the substrate and each experiment was repeated thrice.
2
.6. Electrochemical measurements
A BASi Epsilon−EC electro-analytical instrument was used for the cyclic voltammetric
experiment in CH CN solutions containing 0.2 M tetrabutylammonium hexafluorophosphate
3
as the supporting electrolyte. A BASi platinum working electrode, platinum auxiliary
electrode and Ag/AgCl reference electrode were used for the measurements. The cyclic
voltagrams were recorded for the tetra-iron(III) complex in the absence and presence of
DTBC under molecular oxygen and molecular nitrogen atmospheres.
2
.7. Phosphatase activity of the tetra-iron(III) cluster (1)
The disodium salt of 4-nitrophenylphosphate (PNPP) was used as a standard substrate to
study the hydrolytic cleavage of the phosphoesterase linkage of PNPP in aqueous methanolic
medium following a reported procedure [50,51]. An initial screening of the hydrolytic
tendency of the tetra-iron(III) cluster was performed until 2% formation of 4-nitrophenolate
was reached, and then its kinetic data were collected. The hydrolysis rate of PNPP in the
presence of the iron(III) cluster was measured by the initial rate method, keeping the
incremental band intensity in the absorption fixed at 412 nm for the release of the 4-
nitrophenolate ion in aqueous H O-CH OH at 25 °C. For the wavelength scan, the spectrum
2
3
-4
-3
was recorded on addition of the 1 × 10 M tetra-iron(III) complex solution to the 1 × 10 M

6
PNPP solution for 4 hours. A blank experiment with PNPP in the absence of the tetra-iron(III)
complex under identical reaction conditions does not show any phosphatase activity.
Kinetics experiments for the phosphoester cleavage study were carried out by
monitoring the growth of the 4-nitrophenolate species at 412 nm as a function of time under
the condition of excess substrate in the presence of the tetra-iron(III) complex, keeping the
other parameters constant. The kinetic experiment was performed with a 1 × 10-4
concentration of the tetra-iron(III) cluster and PNPP (varying the concentration from 1 × 10-3
M
-2
M to 1 × 10 M) in H O-CH OH, using a UV-Vis spectrophotometer. The visible absorption
2
3
increase was recorded for a total period of 4 hours at 12 min intervals. All measurements were
performed in triplicate.
3
. Results and discussion
3
.1. Synthesis and formulation of the tetra-iron(III) cluster (1)
The iron(III)-phenanthroline cluster was prepared by addition of 1,10-phenanthroline to
hydrated ferric chloride, followed by a solution of sodium acetate and solid ceric ammonium
nitrate (CAN) in aqueous-acetic acid solution. A control experiment was also carried out with
the absence of CAN, under similar experimental conditions. It was observed that for the
successful synthesis of this iron(III) cluster, the addition of CAN is a mandatory step. CAN
helps to maintain the oxidation state of the iron ion, which facilitates the cluster formation of
the iron ions by receiving molecular oxygen from the air and acetate ions in the presence of
phenanthroline ligands in solution. CAN further supplies nitrate ions to stabilize the cationic
tetra-iron(III) cluster in the crystalline state. The structural formulation of the iron(III) cluster
is principally confirmed by X-ray diffraction analysis, along with different conventional
spectroscopic methods.
3
.2. Description of the crystal structure
Single crystal X-ray structural analysis reveals that the iron(III) cluster crystallizes in the
monoclinic crystal system, with the C2/c space group. Each of the iron(III) centres in this
2
-
cluster adopts an octahedral coordination geometry. Furthermore, two oxido-linkages (µ -O ;
3

7
O1, O2) in association with six end-to-end type symmetric acetato bridges remain the driving
force in assembling the four Fe(III) ions in close vicinity and producing a dicubane geometry.
The phenanthroline ligand, a bidentate end-capper, in combination with aqua molecules help
to saturate the coordination number of the iron(III) centres in this cluster. The cationic charges
of the iron(III) centres are compensated by two units of nitrate ions, while three aqua
molecules are also observed as water of crystallization. The ORTEP diagram of this tetra-
iron(III) cluster is shown in Figure 1. The crystallographic refinement parameters, bond
distance and bond angle data are tabulated in Tables 1 and S1 respectively.
The Fe–O–Fe linkages exhibit high non-linearity and display angles ranging from 84.25
to 134.40°. The Fe–μ -O distances [1.831(3) to 1.954(3) Å] show some similarity as well as
3
dissimilarity with previously reported iron complexes [8,30]. The association of the non-linear
bridges with strong Fe–μ-O bonding has a great impact on the production of inter-metallic
(Fe…Fe) spacings from 3.251 to 3.483 Å. The C–N and C–C bond lengths in the
phenanthroline ligands are found in a similar range to the literature values [8,18,23,26].
A comparison of the structural aspects is drawn between the crystal structures of the
III
previously reported tetra-iron(III) cluster [Fe (µ-O) (µ-OAc) (N ) (phen) ].3MeCN and our
4
2
6
3 2
2
III
tetra-iron(IIII) cluster, [Fe (µ-O) (µ-OAc) (phen) (H O) ](NO ) (H O) (Table S2). From a
4
2
6
2
2
2
3 2·
2
3
crystallographic point of view, the molecular weights, cell dimensions (a, b, c, α, β, γ), volume
and space group symmetry are entirely different. The relative torsion angles are different in
both cases. The cationic charges of the iron centres in the reported structure are internally
compensated by oxides, carboxylates and azide ions. Our tetra-iron(III) structure has similar
types of oxides and carboxylates as bridging units, however two counter anionic nitrate ions
are also present to satisfy the cationic charges of the iron(III) ions. The reported structure has
no counter anions, which makes it a non-electrolyte, whilst our structure is a 1:2 type
electrolyte. Both the tetra-iron(III) clusters crystallize in the monoclinic system, but the space
groups are found to be different, as P2 /n and C2/c (Table S2). The structural core, [Fe (µ -
1
4
3
2
+
O) (µ -OAc) ] , for both the structures remain the same while the bridging linkages (oxido
2
3
6

8
and acetate bridges) are disposed in a slightly different arrangement in space. The solvents of
crystallization are also different in the two structures.
8
+
Previously, it was observed by crystallography that [Fe (µ -O) ] core species may exist with
4
3
2
either bent (butterfly) or planar dispositions of the tetra-iron core of A and B conformations
(
Scheme 1). Another type of asymmetric conformation of type C, a hybrid of types A and B
Scheme 1), for such a tetrametallic core may also be possible. For this case, both the
(
structures exhibit a type C conformation, which had been previously only been observed in
limited examples (Table S2) [19,52,53].
M
M
M
M
O
O
O
O
O
M
M
M
M
M
M
M
O
M
TypeA
TypeB
TypeC
8
+
Scheme 1. Different conformations of the [Fe (µ -O) ] core
4
3
2
3
.3. Bond Valence Sum (BVS) calculations
Bond Valence Sum (BVS) [54] is a highly useful theoretical method to quantify the
oxidation level of metal ions in cluster/normal compounds in solids by employing bond
distance values determined from X-ray crystallography. We have applied this method to
identify the oxidation level for the iron ions in our iron cluster. All the iron ions present in the
iron(III) cluster are found to be at the +3 oxidation level. The details of the calculations for
finding out the oxidation states of the iron ions are presented in Table S3.
3
.4. Catalytic oxidation of DTBC with mechanistic implications
The catecholase activity of this tetra-iron(III) cluster has been investigated with a model
substrate, 3,5-di-tert-butylcatechol in acetonitrile (ACN) medium. DTBC contains two bulky
t-butyl groups in the aromatic ring. The low quinone-catechol reduction potential makes
DTBC a model substrate which undergoes easy oxidation to the corresponding o-quinone,
DTBQ (Scheme 2). DTBQ is a stable compound and exhibits a maximum absorption in the
wavelength range from 380 to 420 nm [14,18,22,23,48,49].
O
O
OH
OH
Catalyst, O2

9
Scheme 2. Catalytic oxidation of DTBC to DTBQ in acetonitrile medium
The tetra-iron(III) cluster displays spectral bands at 249, 299, 353 and 521 nm in the
electronic spectrum in acetonitrile medium. The high energy electronic bands at 249 and 299
nm correspond to π-π* or n-π* electronic transitions of phenanthroline origin. The low energy
-1
-1
broad optical bands at 353 and 521 nm (ɛmax = 1373 and 1227 M cm respectively) are
2
˗
assignable to O →iron(III) charge transfers (LMCT). Previous scientific studies authenticate
2
-
the characteristic electronic transitions for O →iron(III) species as ligand to metal charge
transfer (LMCT) transitions in oxido-acetato bridged iron(III) complexes, which are located in
-1
-1
the range 350-520 nm with ɛmax values of 930-1450 M cm [55-59].
The standard substrate, DTBC, displays an absorbance maximum at 284 nm in solution.
Upon addition of the tetra-iron(IIII) cluster to DTBC, two new optical bands at 400 and 695
nm are developed with incremental absorbance (Fig. 2) and concomitantly a spectral band at
5
21 nm with a decrease in absorbance value is also observed during the spectrophotometric
time scan. The growth of optical band at 400 nm is a definite signature for the generation of
o-quinone species, while the decrement of the electronic band at 521 nm recommends the
possibility of depletion of metal bound semiquinone species in solution [60-62]. Moreover,
the gradual development of a broad band at 695 nm is indicative of a LMCT for the iron-
catecholate adduct in solution [63-65]. Renowned scientist groups across the globe have
explicitly proved the existence of dicatechoate adducts, metal bound quinone and ortho-
quinone species in the solution phase [60-65].
Very significantly, two isosbestic points are observed at 469 and 550 nm during the
course of the catalytic oxidation of DTBC (Fig. 2). The presence of isosbestic points, which
are considered as reactive intermediates (ES1 and ES2), are rarely observed phenomenon in
catechol oxidation studies. A few years back, we observed the existence of two isosbestic
points in examining catecholase activity by a mono-iron(II) complex [18]. In a real sense,

1
0
limited examples are available where isosbestic points are observed during the course of
catechol oxidation by iron complexes [8,18]. This experimental observation explicitly proves
the catalytic transformation of DTBC to DTBQ under aerobic atmosphere and recommends
the formation of DTBQ through enzyme-substrate binding. The produced DTBQ in solution
was isolated by column chromatographic purification with hexane-ethyl acetate as the eluant
1
1
mixture. The quinone was identified by H NMR spectroscopy (Fig. S1). H NMR (CDCl ,
3
4
1
00 MHz)  , ppm: 1.17 (s, 9H), 1.22 (s, 9H), 6.14 (d, J = 2.4 Hz, 1H), 6.87 (d, J = 2.4 Hz,
H
H).
The development of the quinone band was monitored at 400 nm as a function of time
and illustrates saturation kinetics where the Michaelis−Menten model seems to be very
suitable (Fig. S2). We considered the mechanism to involve the formation of a catalyst–
substrate complex (CS), which subsequently breaks down in a second step to form the free
catalyst (C) and the product (P), as shown below.
k1
k2
k3
k4
C + S
CS
C+P
The above mechanism leads to the well known Michaelis–Menten equation:
Vmax [S]
V =
K + [S]
M
where V is the reaction velocity (the reaction rate), Km is the Michaelis–Menten
constant, Vmax is the maximum reaction velocity and [S] is the substrate concentration.
The Michaelis–Menten equation can be transformed into different form, namely the
Lineweaver–Burk Equation (Double reciprocal plot; Fig. S2), which is one of the most widely
used equations, employing the reciprocal of both sides of the above equation and leading to
the equation as follows:
KM
1
V
1
1
.
=
+
Vmax [S]
Vmax
The kinetic parameters for the catechol oxidation by the tetra-iron(III) cluster are presented in

1
1
Table 2. The turn over number (TON) was also determined to evaluate the catalytic efficacy
for transformation of a maximum number of substrate molecules to product per catalyst per
2
-1
time unit. The turnover number (k ) for the tetra-iron(III) cluster is k = 9.2810 h in
cat
cat
ACN.
3
.5. Electrochemical behavior of the Fe(III) complex in the presence of DTBC
Electrochemical analysis was employed to find out the mechanistic perspectives of the
catechol oxidation studies by this iron(III) cluster in anhydrous acetonitrile medium. The
iron(III) cluster undergoes two successive one-electron quasi-reversible diffusion controlled
reductions, showing two peaks at -1.36 and -1.52 V vs. Ag/AgCl, saturated KCl (Fig. 3, Table
3
). Chronocoulometry studies at a constant potential confirm that only one electron is
involved in each reduction [66]. In this tetra-iron(III) cluster, two types of iron(III) centres are
present where two Fe(III) ions are coordinated by a phenanthroline chelator (FeO N
4
2
environment) and the other two iron centres have oxido, acetato bridges and coordinated aqua
molecules in their primary zone of coordination (FeO environment). Thus, the two Fe(III)
6
ions with the phenanthroline coordination in the tetra-iron(III) cluster are reduced to Fe(II)
ions, thereby two waves are developed. The quasi-reversible nature of the reduction may be
assigned to the greater stabilization of the Fe(II) ion in the presence of the phenanthroline
ligand. The cyclic voltammogram of the tetra-iron(III) cluster in the presence of DTBC (Fig.3,
Table 3) under molecular oxygen exhibits two reduction peaks at +0.153 and -0.314 V, along
with three irreversible reduction peaks at -1.22, -1.35 and -1.510 V (Fig. 3, Table 3). The
reduction peaks developed at -1.35 and -1.51 V are assignable to the reduction of the Fe1 and
Fe2 centres in 1, although a small peak at -1.22 V probably indicates the reduction of
molecular oxygen to peroxide. Other important peaks appearing at +0.153 V (quasi-
reversible) and -0.314 V (irreversible) focus on the production of semiquinone and quinone
species in the reaction mixture. Previous investigations on the electrochemical nature of
several quinones in organic polar media recommend that the peaks at +0.153 and -0.314 V
appear solely for the development of semiquinone and quinone in the course of the catalysis
[67, 68]. The electro-chemical behavior of the tetra-iron(III) cluster in the presence of DTBC
under molecular N was also examined to reveal the oxidizing nature of the cluster. Four
2

1
2
reversible peaks at -1.35, -1.7, -0.123 and -0.393 V (Fig. S3) are observed for the reaction
mixture under the N environment. The first two peaks with, potentials of -1.35 and -1.7 V,
2
are assignable to the reduction of two iron centres in the cluster, however the peaks at -0.123
and -0.393 V authenticate the conversion of semiquinone to quinine and catechol to
semiquinone, respectively (Fig. S3, Table 3). These observations indicate that this iron(III)
cluster can also behave as an oxidizer for the conversion of catechol to quinone in the absence
of a molecular oxygen atmosphere. A literature survey also reflects that the tetra-iron(III)
cluster shows a good catalytic efficacy towards the oxidative conversion of DTBC to DTBQ
[1,2,17,18].
3
.6. Phosphatase activity of the tetra-iron(III) cluster (1) and its mechanistic inferences
-4
-3
Upon addition of a 10 M aq. methanolic solution of the tetra-iron(III) cluster to a 10 M
PNPP solution, a new band with incremental absorbance at 412 nm is developed (Fig. 4). The
rise of the optical band at max = 412 nm may correspond to the evolution of the 4-
nitrophenolate ion in solution during the course of the phosphatase activity [17,51,69]. The
changes observed in the spectral features are displayed in Fig. 4.
The kinetic parameters are determined by employing the initial slope method. The initial
-1
-4
-5
first order rate constant, V (min ) = 7.20×10 (Error = 1.89×10 ) is determined directly from
a plot of the log[A /(A - A )] values versus time (Fig. 5) in this catalytic cleavage of PNPP.


t
2
The nature of the plot maintains good linearity with R = 0.989. Control experiments were
also performed to validate the non-catalytic role of phenanthroline, and experiments under
similar reaction conditions are found to be non-responsive towards phosphoesterase activity of
PNPP. A literature survey on the rate of catalytic phosphatase activity of iron complexes was
made to compare the level of activity of this tetra-iron(III) cluster with previously reported
compounds (Table 4) [69-71].
The previous scientific observations helped us to unveil the mechanistic route for this
phosphoesterase activity. Different modes of activation, namely Lewis acid activation, leaving
group activation and metal-nucleophilic attack, including experimental observations, provide
sufficient sources of information to propose a reasonable catalytic cycle of phosphoester

1
3
cleavage (Scheme 1) by this tetra-iron(III) cluster [72-75]. The presence of coordinated aqua
molecules at the metal centres may also play a pivotal role in the phosphoester cleavage
activity [76-78].
Scheme 1. Plausible catalytic cycle for phosphoester cleavage by the iron cluster
For this tetra-iron(III) cluster, at the primary stage, PNPP binds with the oxido-acetato-tetra-
+
iron(III) core. The existence of an iron cluster-PNPP adduct ([C H Fe NO P] ) is evidenced
1
8
23
4
19
by the presence of a peak at 811.0634 m/z (Calcd. m/z 811.0121). The in situ development of
organophosphorus intermediates is further confirmed by the appearance of the isotopic
distribution pattern of the signal at m/z 827.0327 (Calcd. m/z 827.7221) and m/z 844.1074
(Calcd. m/z 844.4124) (Fig. S4). Important peaks at m/z 827.0327 (Calcd. m/z 827.7221) and

1
4
m/z 844.1074 (Calcd. m/z 844.4124) represent the existence of reactive intermediates as
+
+
molecular species, [C H Fe NO P] and [C H Fe NO P] respectively. The presence of
1
8
23
4
20
18 24
4
21
such peaks in the ESI mass spectrum provides sufficient evidence for the nucleophilic attack
by aqua molecules to the P atom of PNPP, which actually facilitates hydrolytic cleavage of
PNPP. High spin iron(III) ions always exhibit super acidic behaviour and this property assists
in the generation of the hydroxide ion, which probably remains the driving force. This
phenomenon leads to the construction of an organophosphorus intermediate developed by the
nucleophilic substitution reaction and simultaneous eviction of the 4-nitrophenolate ion.
Finally, it gradually breaks down into the active form of the tetra-iron(IIII) cluster and
phosphoric acid.
4
. Conclusion
In this present work, we report the synthesis and structural characterization of an oxido-
III
acetato-bridged tetra-iron(III) cluster, [Fe (µ-O) (µ-OAc) (phen) (H O) ](NO ) (H O) (1).
4
2
6
2
2
2
3 2
2
3
Analysis of its X-ray structure reveals that the tetra-iron(III)-oxido core remains in a unusual
asymmetric conformation, which will definitely enrich the molecular library of such a rare
class of compounds. This iron(III) compound may be accessed as a precursor for facile
incorporation of other monodentate ligands to iron(III) centres with the aim of achieving
higher nuclearity iron clusters having good magnetic properties. The tetra-iron(III) cluster
catalytically oxidizes DTBC to DTBQ in acetonitrile medium with a high turnover number,
2
-1
kcat = 9.28  10 h . Spectroscopic detection of two distinct isosbestic points at 469 and 550
nm in the course of DTBC oxidation recommends the formation of reactive intermediates, ES1
and ES , which are very limited in scientific studies on the catecholase activity of iron(III)
2
complexes. The iron(III) centres in the iron cluster in the presence of DTBC form Fe(II)-
semiquinone and ortho-quinone species in solution, and this phenomenon is justified through
electrochemical analysis of the iron cluster in the presence of DTBC under aerobic conditions.
The rate of hydrolytic decomposition of the phosphoester linkage in the disodium salt of p-
nitrophenylphosphate (PNPP) in aqueous-methanol medium is found to be as high as 7.20 
-4
-1
1
0 m . ESI-MS measurements of the iron(III) cluster in the presence of PNPP proves that

1
5
aqua molecules undergo a nucleophilic attack on the phosphorus centre, proceeding through
an organo-phosphorus intermediate at one of the iron(III) centres to produce the 4-
nitrophenolate ion. Bio-inspired catalysis by tetra-iron(III) clusters is very limited in the
literature and these mimicking activities of the tetra-iron(III) cluster may be helpful in
advancing investigations of this type to a good extent.
5
. Supplementary data
Crystallographic data are available free of charge from The Director, CCDC, 12 Union
Road, Cambridge, CB2 1EZ, UK (fax: +44-1223-336033; E-mail: deposit@ccdc.cam.ac.uk or
www: http://www.ccdc.cam.ac.uk) upon request, quoting the deposition number CCDC
1
939346 for the tetra-iron(III) complex.
Acknowledgements
BB thanks the Science and Engineering Research Board (SERB) for financial support under
the FAST TRACK scheme, YOUNG SCIENTIST (No. CS-088/2013 dtd 21-5-2014). ARC
thanks the X-ray facility of the Department of Chemical Sciences, IISER Mohali for single
crystal X-ray diffraction data collection. This work is dedicated to Dr. Indranil Kar, Principal,
Surendranath College, Kolkata 700009 who remains a constant source of inspiration to me.
References
[1] Biomimetic Oxidations Catalyzed by Transition Metal Complexes, B. Meunier (Ed.),
Imperial College Press, London, 2000.
[2] A.-F. Miller, FEBS Lett., 586 (2012) 585-595
[3] Cytochrome P-450. Structure, Mechanism and Biochemistry, 2nd ed.; J.T.
Groves, Y.Z. Han, P.R. Ortiz de Montellano, Eds. Plenum Press: New York, (1995) 3-48.
[
[
[
[
4] W. Nam, Acc. Chem. Res. 40 (2007) 465.
5] M. Costas, M.P. Mehn, M.P. Jensen, L. Que, Chem. Rev., 104 (2004) 939-986.
6] J.P. Layfield, S. Hammes-Schiffer, Chem. Rev., 114 (2014) 3466-3494
7] J.J.A. Cotruvo, J. Stubbe, Metallomics, 4 (2012) 1020-1036.

1
6
[
8] D. Dey, A. De, H.R. Yadav, P.S. Guin, A.R. Choudhury, N. Kole, B. Biswas,
ChemistrySelect 01 (2016) 1910-1916.
9] B. Das, A. Al-Hunaiti, M. Haukka, S. Demeshko, S. Meyer, A.A. Shteinman, F. Meyer, T.
Repo, E. Nordlander, Eur. J. Inorg. Chem., 21 (2015) 3590-3601.
[
[
[
(
[
10] H.G. Jang, D.D. Cox, L. Que Jr, J. Am. Chem. Soc., 113 (1991) 9200-9204.
11] M. Merkel, M. Pascaly, B. Krebs, J. Astner, S. P. Foxon, S. Schindler, Inorg. Chem., 44
2005) 7582-7589.
12] I. Ghosh, S. Banerjee, S. Paul, T. Corona, T.K. Paine, Angew. Chem. Int. Ed., (2019)
1
0.1002/anie.201906978.
[
13] M. Bordeaux, A. Galarneau, J. Drone, Angew. Chem. Int. Ed., 51 (2012) 10712-10723.
14] D. Dey, G. Kaur, A. Ranjani, L. Gyathri, P. Chakraborty, J. Adhikary, J. Pasan, D.
[
Dhanasekaran, A.R. Choudhury, M.A. Akbarsha, N. Kole, B. Biswas, Eur. J. Inorg. Chem.,
(2014) 3350-3358.
[15] P.C.A. Bruijnincx, M. Lutz, A.L. Spek, W.R. Hagen, B.M. Weckhuysen, G. van Koten,
R.J.M.K. Gebbink, J. Am. Chem. Soc., 129 (2007) 2275-2286.
16] M.P. Valley, C.K. Brown, D.L. Burk, M.W. Vetting, D.H. Ohlendorf, J.D. Lipscomb,
Biochemistry, 44 (2005) 11024-11039
[
[
(
[
(
[
17] M. Garai, D. Dey, H.R. Yadav, A.R. Choudhury, N. Kole, B. Biswas, Polyhedron, 129
2017) 114-122.
18] A. De, M. Garai, H.R. Yadav, A.R. Choudhury, B. Biswas, Appl. Organomet. Chem., 31
2017) e3551.
19] D. Dey, M. Garai, S. Arar, A. Almherat, A. Al-Hunaiti, H.R. Yadav, M. Maji, A.R.
Choudhury, B. Biswas, J. Mol. Struct., 1180 (2019) 220-226.
20] A. De, D. Dey, C.K. Pal, S. Paul, B. Biswas, J. Mol. Struct., 1195 (2019) 293-301.
21] R. Mayilmurugan, M. Sankaralingam, E. Suresh. Palaniandavar, Dalton Trans., 39
2010) 9610-9625.
22] S. Pal, B. Chowdhury, M. Patra, M. Maji, B. Biswas, Spectrochim. Acta Part A: Mol.
[
[
(
[
Biomol. Spect., 144 (2015) 148-154.
23] D. Dey, S. Das, H.R. Yadav, A. Ranjani, L. Gyathri, S. Roy, P.S. Guin, D. Dhanasekaran,
A.R. Choudhury, M.A. Akbarsha, B. Biswas, Polyhedron, 106 (2016) 106-114.
[

1
7
[
24] A. Al-hunaiti, M. Räisänen, T. Repo, Chem. Commun., 52 (2016) 2043-2046.
25] R. Rahaman, B. Chakraborty, T.K. Paine, Angew. Chem. Int. Ed., 55 (2016) 13838-
3842.
26] B. Biswas, A. Al-Hunaiti, M. T. Räisänen, S. Ansalone, M. Leskelä, T. Repo, Y.-T.
[
1
[
Chen, H.-L. Tsai, A.D. Naik, A.P. Railliet, Y. Garcia, R. Ghosh, N. Kole, Eur. J. Inorg.
Chem., (2012) 4479-4485.
[27] B. Biswas, M. Mitra, J. Adhikary, G.R. Krishna, P.P. Bag, C.M. Reddy, N. Aliaga-
Alcalde, T. Chattopadhyay, D. Das R. Ghosh, Polyhedron, 53 (2013) 264-268.
[28] W.H. Armstrong, S.J. Lippard, Inorg. Chem., 24 (1985) 981-982.
[29] K.T.V. Rao, P.S.N. Rao, P. Nagaraju, P.S. Sai Prasad, N. Lingaiah, J. Mol. Catal. A
Chem., 303 (2009) 84-89.
[
30] Y. Hitomi, Y. Iwamoto, A. Kashida, M. Kodera, Chem. Commun., 51 (2015) 8702.
31] A.W. Nichols, S. Chatterjee, M. Sabat, C. W. Machan, Inorg. Chem., 57 (2018) 2111-
[
2
121.
32] E. Balaraman, A. Nandakumar, G. Jaiswalab, M. K. Sahoo, Catal. Sci. Technol., 7 (2017)
177.
[
3
[
[
[
[
(
[
33] A. Taheri, L.A. Berben, Inorg. Chem., 55 (2016) 378-385
34] J.R. Khusnutdinova, D. Milstein, Angew. Chem., Int. Ed., 54 (2015) 12236-12273.
35] O.R. Luca, R.H. Crabtree, Chem. Soc. Rev., 42 (2013) 1440-1459.
36] M. Bourrez, F. Molton, S. Chardon-Noblat, A. Deronzier, Angew. Chem., 2011, 123
42), 10077-10080.
37] K.T. Ngo, M. McKinnon, B. Mahanti, R. Narayanan, D.C. Grills, M.Z. Ertem, J.
Rochford, J. Am. Chem. Soc., 139 (2017) 2604-2618.
[
(
[
38] B. Biswas, P. Raghavaiah, N. Aliaga-Alcalde, J.-D. Chen, R. Ghosh, Polyhedron, 29
2010) 2716-2721
39] B. Biswas, A. Pal, G.R. Krishna, C.M. Reddy, F. Tuna, R. Ghosh, Polyhedron, 30 (2011)
2
032-2037
40] D. Dey, A. De, S. Pal, P. Mitra, A. Ranjani, L. Gayathri, S. Chandraleka, D.
Dhanasekaran, M. A. Akbarsha, N. Kole, B. Biswas, Indian J. Chem., Sect. A, 54A (2015)
70-178.
[
1

1
8
[
41] D. Dey, A. Basu Roy, C.-Y. Shen, H.-L. Tsai, A. Ranjani, L. Gayathri, S. Chandraleka,
D. Dhanasekaran, M.A. Akbarsha, N. Kole, B. Biswas, J. Chem. Sci, 127 (2015) 649-661.
42] A.K. Boudalis, V. Tangoulis, C.P. Raptopoulou, A. Terzis, J.-P. Tuchagues, S.P.
Perlepes, Inorg. Chim. Acta, 357 (2004) 1345-1354.
43] M.W. Wemple, D.A.K. Coggin, J.B. Vincent, J.K. McCusker, W.E. Streib, J.C. Huffman,
D.N. Hendrickson, G. Christou, J. Chem. Soc., Dalton Trans., (1998) 719-725.
44] J.K. McCusker, J.B. Vincent, E.A. Schmitt, M.L. Mino, K. Shin, D.A.K. Coggin, P.M.
Hagen, J.C. Huffman, G. Christou, D.N. Hendrickson. J. Am. Chem. Soc., 113 (1991) 3012-
021.
45] G.M. Sheldrick, SHELXT - Integrated space-group and crystal-structure determination
Acta Cryst. A71 (2015) 3-8.
46] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, J. Appl.
Cryst., 42 (2009) 339.
[
[
[
3
[
[
[47] L.J. Farrugia. J. Appl. Cryst., 45 (2012) 849.
[48] S. Das, A. Sahu, M. Joshi, S. Paul, M. Shit, A. Roy Choudhury, B. Biswas,
ChemistrySelect, 3 (2018) 10774-10781.
[
(
[
49] M. Garai, D. Dey, H.R. Yadav, A.R. Choudhury, M. Maji, B. Biswas, ChemistrySelect, 2
2017) 11040-11047
50] M. Garai, A. Das, M. Joshi, S. Paul, M. Shit, A.R. Choudhury, B. Biswas, Polyhedron,
1
56 (2018) 223-230.
[
(
[
51] M. Garai, D. Dey, M. Maji, H.R. Yadav, A.R. Choudhury, B. Biswas, J. Chem. Sci., 129
2017) 1513-1520.
52] B. Biswas, M. Mitra, A. Pal, A. Basu, S. Rajalakshmi, P. Mitra, N. Aliaga-Alcalde, G.S.
Kumar, B.U. Nair, R. Ghosh, Indian J. Chem., 52A (2013) 1576-1583.
[
[
[
[
[
53] Y.P. Tian, C.Y. Duan, X.X. Xu, X.Z. You, Acta Crystallogr. C, 51 (1995) 2309-2312.
54] H.H. Thorp, Inorg. Chem., 31 (1992) 1585-1588.
55] M. Kodera, H. Shimakoshi, K. Kano, Chem. Commun., (1996) 1737.
56] K. Visvaganesan, E. Suresh, M. Palaniandavar, Dalton Trans., (2009) 3814.
57] W.H. Armstrong, A. Spool, G.C. Papaefthymiou, R.B. Frankel, S.J. Lippard, J. Am.
Chem. Soc., 106 (1984) 3653.

1
9
[58] P. Gomez-Romero, N. Casan-Pastor, A. Ben-Hussein, G.B. Jameson, J. Am. Chem. Soc.,
1
10 (1988) 1988.
[59] M. Sankaralingam, M. Palaniandavar, Polyhedron, 67 (2014) 171-180
[60] L. Que, Jr., Iron Carriers and Iron Proteins, T.M. Loehr, ed.VCH: New York, (1989) 467-
5
24.
[
(
[
[
[
61] E.L. Spence, M. Kawamukai, J. Sanvoisin, H. Braven, T.D.H. Bugg, J. Bacteriol. 178
1996) 5249.
62] S. Chatterjee, D. Sheet, T.K. Paine, Chem. Commun., 49 (2013) 10251-20253.
63] T. Kurahashi, K. Oda, M. Sugimoto, T. Ogura, H. Fujii, Inorg. Chem. 45 (2006) 7709.
64] M. Balamurugan, P. Vadivelu, M. Palaniandavar, Dalton Trans., 43 (2014) 14653-
1
4668.
[
[
[
[
[
65] M.J. Sever, J.J. Wilker, Dalton Trans., (2004) 1061-1072.
66] T. Shiga, H. Miyamoto, G.N. Newton, H. Oshio, Dalton Trans., 47 (2018) 13402-13407.
67] P.S. Guin, S. Das, P.C. Mandal, Int. J. Electrochem., (2011) Article ID 816202.
68] S. Roy, P.S. Guin, J. Electrochem. Soc., 162 (2015) 124 -131.
69] N. Dutta, S. Haldar, G. Vijaykumar, S. Paul, A.P. Chattopadhyay, L. Carrella, M. Bera,
Inorg. Chem., 57 (2018) 10802-10820.
[
(
[
[
70] A. Kantacha, R. Buchholz, S.J. Smith, G. Schenk, L.R. Gahan, J. Biol. Inorg. Chem., 16
2011) 25-32.
71] C. Pathak, M.K. Gangwar, P. Ghosh, Polyhedron, 145 (2018) 88-100.
72] (a) P. Hendry, A.M. Sargeson, Inorg. Chem., 29 (1990) 92-7; (b) P. Hendry, A.M.
Sargeson, Aust. J. Chem., 39 (1986) 1177.
[73] S. Benkovic, L. Dunikoski, J. Am. Chem. Soc., 93 ( 1971) 1526.
[74] Y. Murakami, J. Sunamoto, Bull. Chem. Soc. Japan, 44 (1971) 1827.
[75] T. Fife, M. Pujari, J. Am. Chem. Soc., 110 (1988) 7790-7797.
[76] F. Mancin, P. Scrimina, P. Tecilla, Chem. Commun., 48 (2012) 5545-5559.
[77] N.H. Williams, B. Takasaki, M. Wall, J. Chin, Acc. Chem. Res., 32 (1999) 485-493.
[78] Y. Ren, J. Lu, B. Cai, D. Shi, H. Jiang, J. Chen, D. Zheng, B. Liu, Dalton Trans., 40
(2011) 1372-1381.

2
0
Table 1 Crystallographic data and structure refinement parameters for the tetra-iron(III)
cluster
Parameters
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
1
C H N O Fe
4
3
6
44
6
25
1184.17
100
Monoclinic
C2/c
27.9634(14)
12.7441(6)
27.6727(13)
b (Å)
c (Å)
α, , γ (º)
Volume (Å3)
Z
90, 104.878(5), 90
9531.1(8)
8
–
3
ρ (g cm )
1.651
–
1
μ (mm )
1.287
F (000)
4848
θ ranges (º)
2.7-32.9
0.086
Rint
Number of unique reflections
Total number of reflections
Final R indices
16607
57573
0.0984, 0.2993
5.17, -1.53
-3
Largest peak and hole (e Å )

2
1
Table 2. Kinetic parameters for the oxidation of DTBC catalyzed by the tetra-iron(III) cluster
-
1
-1
Complex
1
Vmax (M s )
K (M)
k ( h )
Ref
m
cat
1.469  10-5
2.10  10-4
9.28  102
Present
-1
-7
-5
Std. Error: Vmax (M s ) = 5.35  10 ; K (M) = 1.55  10
m
Table 3. Electrochemical data of the tetra-iron(III) complex in ACN
Compound
Ep,c (CV)(V)
Redox processes
Tetra-iron(III) cluster (1)
Fe
Fe
1
(III)→Fe
(III)→Fe
1
(II)
(II)
-
-
-
-
-
-
1.36
1.52
1.22
2
2
2
-
O
2 2
→ O
Fe
Fe
1
2
(III)→Fe
(III)→Fe
1
2
(II)
(II)
1.35 (-1.35 in N )*
2
Tetra-iron(III) cluster (1)
1.51 (-1.7 in N )*
2
in the presence of DTBC
DTBSQ→DTBQ
semiquinone to quinone)
DTBC→DTBSQ
Cat to Semiquinone)
0.314 (-0.123 in N )*
2
(
H
2
+
0.153 (-0.393 in N )*
2
(
*
CV value in parenthesis indicates the potential value obtained under an N environment
2
Table 4. Kinetic parameters for the hydrolysis of the phosphoester linkage in PNPP catalyzed
by the tetra-iron(III) cluster in aqueous methanol
-
1
-1
Complex
Vmax (M s )
6.54  10-7
6.83  10-9
K (M)
k (S )
Ref
Present
26
m
cat
8.30  10-5
6.44  10-3
1
[
[
[
(
Fe (cpdp) (phth) (OH) ]
4.80  10-3
2.73  10-5
4
2
2
2
Fe (cpdp) (terephth) (OH) ]
.66  10-9
4.08  10-3
1.06  10-5
4
2
2
2
2
26
Fe (HPBA) (μ-OAc) (μ-O)-
1.6  10-3
4
2
2
-
-
27
2
+
μ-OH)(OH ) ]
2
2

2
2
III
+
2.94  10-3
{
[(Fe (μ-OAc))]L}
-
-
28
2
-1
-8
-6
Std. Error: Vmax (M s ) = 5.036  10 ; K (M) = 3.634  10
m
Fig
1. X-
ray

2
3
structure of the cationic tetra-iron(III) cluster (1) with 30% ellipsoid probability. H atoms are
removed for clarity
-4
Fig 2. Rise of the DTBQ band at 400 nm upon addition of 1 (10 M) to 100 equivalents of
DTBC in acetonitrile. The spectra were recorded after every 5 min.

2
4
Fig 3. Left: Cyclic voltammogram of the tetra-iron(III) cluster in anhydrous acetonitrile
media; Right: Cyclic voltammogram of the mixture of the tetra-iron(III) cluster and DTBC
under a molecular oxygen atmosphere in anhydrous acetonitrile media.
Fig 4. Increase of the 4-nitrophenolate band at 412 nm after addition of the tetra-iron(III)
cluster to 100 equivalents of PNPP in aq. methanolic solution. (The spectra were recorded
after every 12 min). Inset: Time vs Absorbance plot at the defined wavelength

2
5
Fig 5. Initial rate determination for phosphoester cleavage activity by the tetra-iron(III) cluster
towards PNPP using a plot of time vs log[A /(A -A )] for the same solution


t
Bio-mimetic of Catecholase and Phosphatase Activity by a Tetra-iron(III)
Cluster
a
a
b
c
Chanchal Kumar Pal, Shreya Mahato, Hare Ram Yadav, Madhusudan Shit,
b
a,*
Angshuman Roy Choudhury, Bhaskar Biswas
aDepartment of Chemistry, University of North Bengal, Darjeeling-734013, India
bDepartment of Chemical Sciences, Indian Institute of Science Education and Research,
Mohali, Sector 81, Knowledge City, S. A. S. Nagar, Manauli PO, Mohali, Punjab 140306,
India
cDepartment of Chemistry, Dinabandhu Andrews College, Kolkata 700084, India
III
This paper highlights the catalytic aspects of a tetra-iron(III) cluster, [Fe (µ-O) (µ-
4
2
OAc) (phen) (H O) ](NO ) (H O) [phen = 1,10-phenanthroline], towards catechol oxidation
6
2
2
2
3 2·
2
3
and phosphoesterase activity, showing significant catalytic efficacy.

2
6

2
7