Catecholase activity of a structurally characterized dinuclear iron(III) complex [FeIII2(L)2] [H3L = N,N′-bis(3-methoxysalicylaldimine)-1,3-diaminopropan-2-ol]

Article abstract of DOI:10.1016/j.poly.2013.08.064

A dinuclear Fe(III) complex, [Fe^III₂(L)₂] (1) [H₃L = N,N′-bis(3-methoxysalicylaldimine)-1,3- diaminopropan-2-ol], has been synthesized and characterized using microanalysis, spectroscopy and X-ray crystallography. Structural analysis reveals a pentadentate chelation behaviour of the trianionic ligand H₃L, having a distorted octahedral coordination environment around each iron(III) center with an FeN₂O₄ chromophore. Variable-temperature magnetic susceptibility measurements of 1 indicate an antiferromagnetic interaction between the two iron(III) centers, coupled with J = -28.5. 1 behaves as an effective catalyst towards the oxidation of 3,5-di-tert-butylcatechol in different solvents, viz. methanol, dichloromethane and acetonitrile, to its corresponding quinone derivative in aerial oxygen. The reaction follows Michaelis-Menten enzymatic reaction kinetics with turnover numbers (K _cat) 7.51 × 10², 1.69 × 10³ and 1.23 × 10³ h^-1 in methanol, dichloromethane and acetonitrile, respectively.

Full text of DOI:10.1016/j.poly.2013.08.064

Polyhedron 67 (2014) 19–26
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Catecholase activity of a structurally characterized dinuclear iron(III)
complex [FeIII (L)2] [H3L = N,N0-bis(3-methoxysalicylaldimine)-1,
2
3-diaminopropan-2-ol]
Merry Mitra a, Ashis Kumar Maji a, Barindra Kumar Ghosh a, Pallepogu Raghavaiah b, Joan Ribas c,
,
⇑
Rajarshi Ghosh a,
⇑
a Department of Chemistry, The University of Burdwan, Burdwan 713 104, India
b School of Chemistry, University of Hyderabad, Hyderabad 500 046, India
c Departament de Química Inorgànica, Universitat de Barcelona, Diagonal, 645, 08028 Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
A dinuclear Fe(III) complex, [FeIII2(L)2] (1) [H3L = N,N0-bis(3-methoxysalicylaldimine)-1,3-diaminopro-
pan-2-ol], has been synthesized and characterized using microanalysis, spectroscopy and X-ray crystal-
lography. Structural analysis reveals a pentadentate chelation behaviour of the trianionic ligand H3L,
having a distorted octahedral coordination environment around each iron(III) center with an FeN2O4
chromophore. Variable-temperature magnetic susceptibility measurements of 1 indicate an antiferro-
magnetic interaction between the two iron(III) centers, coupled with J = ꢀ28.5. 1 behaves as an effective
catalyst towards the oxidation of 3,5-di-tert-butylcatechol in different solvents, viz. methanol, dichloro-
methane and acetonitrile, to its corresponding quinone derivative in aerial oxygen. The reaction follows
Michaelis-Menten enzymatic reaction kinetics with turnover numbers (Kcat) 7.51 ꢁ 102, 1.69 ꢁ 103 and
1.23 ꢁ 103 hꢀ1 in methanol, dichloromethane and acetonitrile, respectively.
Article history:
Received 23 June 2013
Accepted 14 August 2013
Available online 7 September 2013
Keywords:
Iron(III)
Schiff base
Crystal structure
Magnetism
Biocatalytic activity
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
continuation to our recent report [5e] on catecholase activity, here
we present the synthesis and structural characterization of a dinu-
Catechol oxidase, found in bacteria, fungi and plants, belongs to
the class of type 3 copper proteins that catalyze the oxidation of a
wide range of o-diphenols (catechols) to the corresponding o-qui-
nones, coupled with 2e/2H+ reduction of O2 to H2O, in a process
known as catecholase activity [1–10]. The crystal structure of the
met form of the enzyme was determined in 1998, revealing that
the active center consists of a hydroxo-bridged dicopper(II) center
in which each copper(II) center is coordinated to three histidine
nitrogens and adopts a trigonal pyramidal environment with one
nitrogen in the apical site [11]. Such a structural finding has
prompted extensive investigation on model compounds to under-
stand the structure-property relationship at the molecular level
[1–10]. Indeed, several dicopper(II) complexes derived from nitro-
gen-containing dinucleating ligands have been mainly employed
for this purpose [1–4]. Several monocopper(II) complexes are also
known to exhibit catecholase activity [5]. Recently, the catecholase
activity of complexes of other metal ions, like Mn(III) [5e,6], Fe(III)
[7], Co(II/III) [8], Ni(II) [9] and Zn(II) [10] has been explored. In a
clear Fe(III) complex, [FeIII2(L)2] (1) [12], with an (N,O) donor trian-
ionic Schiff base ligand which catalyzes a catechol derivative to its
corresponding quinone in methanol (MeOH), dichloromethane
(DCM) and acetonitrile (MeCN) in the open air. An investigation
of the Michaelis–Menten kinetics and calculation of the turnover
numbers are calculated in each case.
2. Experimental
2.1. Materials
High purity o-vanillin (Aldrich, UK), 1,3-diaminopropan-2-ol
(Aldrich, UK), iron(III) nitrate nonahydrate (Aldrich, UK), benzoic
acid (E. Merck, India), sodium bicarbonate (E. Merck, India), 3,
5-di-tert-butylcatechol (Aldrich, UK) and all other solvents were
purchased from the respective concerns and used as received. Sol-
vents were dried according to standard procedures and distilled
prior to use.
The ligand H3L was prepared using a reported procedure [13].
O-vanillin (0.3043 g, 2 mmol) was heated under reflux with
1,3-diaminopropan-2-ol (0.0955 g, 1 mmol) in 30 ml dehydrated
ethanol. After 2 h, the reaction solution was evaporated under
⇑
Corresponding authors. Tel.: +91 342 2533913x424; fax: +91 342 2530452 (R.
Ghosh).
E-mail addresses: joan.ribas@qi.ub.es (J. Ribas), rajarshi_chem@yahoo.co.in
(R. Ghosh).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.08.064

20
M. Mitra et al. / Polyhedron 67 (2014) 19–26
Table 1
reduced pressure to yield a yellow coloured solid, which was dried
under vacuum and stored over CaCl2 for subsequent use.
For the catecholase activity study, a 1 ꢁ 10ꢀ4 mol dmꢀ3 solution
of 1 (0.0009 g) was treated with 1 ꢁ 10ꢀ2 mol dmꢀ3 (100 equiva-
lents) of 3,5-DTBC (0.0222 g) under aerobic conditions.
Crystal data and structure refinement parameters for 1.
Empirical formula
Formula weight
T (K)
C42H44N6O10Fe2
904.53
293(2)
0.71073
monoclinic
P21/c
k (Å)
Crystal system
Space group
Unit cell dimensions
a (Å)
2.2. Physical measurements
11.3773(9)
Elemental analyses (carbon, hydrogen and nitrogen) were per-
formed on a Perkin-Elmer 2400 CHNS/O elemental analyzer. UV–
Vis and IR spectra (KBr discs, 4000–300 cmꢀ1) were recorded using
a Shimadzu UV–Vis 2450 spectrophotometer and Perkin-Elmer FT-
IR model RX1 spectrometer, respectively. The 1H NMR spectral data
were collected in CDCl3 on a Bruker 400 MHz spectrometer. Mag-
netic measurements were carried out in the ‘‘Servei de Magnet-
oquímica (Universitat de Barcelona)’’ on polycrystalline samples
(30 mg) with a Quantum Design SQUID MPMS-XL magnetometer
working in the 2–300 K range. The magnetic field was 0.1 T. The
diamagnetic corrections were evaluated from Pascal’s constants.
b (Å)
c (Å)
15.1816(10)
23.6480(17)
90.00
97.156(7)
90.00
4052.8(5)
4
1.482
0.783
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢀ1
F(000)
)
1880
Crystal size (mm3)
h (°)
0.42 ꢁ 0.32 ꢁ 0.18
2.6945–29.0539
ꢀ13 6 h 6 13,
ꢀ18 6 k 6 16,
ꢀ17 6 l 6 28
15376
7137 [Rint = 0.0587]
99.9 % (h = 26.37°)
multi-scan
0.8719 and 0.7345
full-matrix least-squares on F2
7137/0/547
0.970
R1 = 0.0566, wR2 = 0.0864
R1 = 0.1240, wR2 = 0.1109
0.573, ꢀ0.436
Index ranges
2.3. Preparation of 1
Reflections collected
Independent reflections
Completeness to theta
Absorption correction
Tmax and Tmin
Compound 1 was prepared by the dropwise addition of a solu-
tion of H3L (0.0224 g, 0.125 mmol) in acetonitrile (15 ml) into a
stirring solution of the precursor [Fe3O(RCOO)6(H2O)3](NO3)
[R = Ph] [14] (0.0641 g, 0.125 mmol) in a methanol-acetonitrile
mixture (15 ml). The resulting red-brown coloured solution was
kept in the open air for slow evaporation. After 2–3 days, deep
brown crystals of 1 were collected, washed with hexane and dried
in vacuo over silica gel indicator.
Refinement method
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [l > 2
r(l)]
R indices (all data)
Largest difference in peak and hole(e Åꢀ3
)
Yield: (based on metal salt) 0.0758 g (89.42%). Anal. Calc. for
C
42H44N6O10Fe2 (1): C, 55.77; H, 4.90; N, 9.29. Found: C, 55.93;
H, 4.73; N, 9.16%. Selected IR bands (KBr pellet, cmꢀ1): 3433 (s),
1630 (s), 1600 (s), 1548 (s). UV–Vis (k, nm, MeOH): 499, 330,
271, 226.
relatively intense peaks around 1590-1600 cmꢀ1 due to the C@N
stretching frequency appear in the complex.
3.2. X-ray structure
2.4. X-ray diffraction study
In order to define the coordination spheres conclusively, a
single crystal X-ray diffraction study of 1 was made. The ORTEP dia-
gram along with atom numbering scheme of 1 is shown in Fig. 1.
Selected interatomic bond lengths and bond angles are given in
Table 2. Structural analysis reveals that compound 1 is a cen-
tro-symmetric binuclear entity where the two iron(III) centers
are bridged by two alkoxo O atoms (O1 and O2) of L. The coordi-
nation geometry around each iron(III) center is best described as
distorted octahedral. The two phenolic O (O7 and O9 for Fe1, and
O3 and O5 for Fe2) atoms and two bridging alkoxo O (O1 and O2)
atoms from the two ligand moieties define the equatorial plane
around each metal(III) center. The two imine N (N2 and N3 for
Fe1, and N1 and N4 for Fe2) atoms from each ligand framework
bind to the metal(III) center via the elongated axial direction,
with Fe1–N2 and Fe1–N3, and Fe2–N1 and Fe2–N4 bond dis-
tances of 2.119(3) and 2.135(3), and 2.140(3) and 2.127(3) Å,
respectively. These bonds are considerably longer than those
found in the equatorial plane [Fe1–O1 2.024(3) Å; Fe1–O2
2.011(3) Å; Fe1–O7 1.927(3) Å; Fe1–O9 1.919(3) Å, and Fe2–O1
2.032(3) Å; Fe2–O2 2.054(3) Å; Fe2–O3 1.917(3) Å; Fe2–O5
1.930(3) Å], which presumably is due to the different type of
coordination mode of ligands. The geometric distortion of each
octahedron at the metal(III) center can be characterized by the
asymmetric parameter D [17]. The positive D value [18]1 indicates
axial elongation at each metal center.
A single crystal of 1 suitable for X-ray crystallographic analysis
was selected following examination under a microscope. Diffrac-
tion data were collected at 293(2) K on a Bruker SMART APEX II
CCD diffractometer using Mo-Ka radiation (k = 0.71073 Å) and
the P21/c space group was identified. The crystal data and refine-
ment details are listed in Table 1. The structure was solved by di-
rect methods, and the structure solution and refinement were
based on |F|2. The final differences Fourier map showed maximum
and minimum peak heights at 0.573 and ꢀ0.436 e Åꢀ3 with no
chemical significance. All calculations were carried out using SHEL-
XL-97 [15] and were refined using SHELSL-97 [15]. All the figures have
been generated using ORTEP-32 [16].
3. Results and discussion
3.1. Synthesis and formulation
The self-assembly of [Fe3O(PhCOO)6(H2O)3](NO3) and the
ligand H3L in methanol-acetonitrile afforded the hexacoordinated
dinuclear complex 1. The complex was characterized by microan-
alytical (C, H and N), spectroscopic and other physicochemical re-
sults. The microanalytical data are in good conformity with the
formulation of 1. The moisture insensitive complex is stable over
long periods of time in powdery and crystalline states, and is solu-
ble in methanol, ethanol, acetonitrile, dimethyl formamide and di-
methyl sulfoxide, but is insoluble in water. In the IR spectra,
1
D = dz – (dx + dy)/2, D = + 0.1735 for Fe1, + 0.2170 for Fe2.

M. Mitra et al. / Polyhedron 67 (2014) 19–26
21
Fig. 1. ORTEP of [Fe2(L)2] (1) with the atom numbering scheme and 20% probability ellipsoids for all non-hydrogen atoms.
Table 2
Bond lengths [Å] and angles [°] for 1.
5
4
3
2
1
0
Bond distances
Fe(1)–O(1)
Fe(1)–O(2)
Fe(1)–O(7)
Fe(1)–O(9)
Fe(1)–N(2)
Fe(1)–N(3)
2.024(3)
2.011(3)
1.927(3)
1.919(3)
2.119(3)
2.135(3)
Fe(2)–O(1)
Fe(2)–O(2)
Fe(2)–O(3)
Fe(2)–O(5)
Fe(2)–N(1)
Fe(2)–N(4)
2.032(3)
2.054(3)
1.917(3)
1.930(3)
2.140(3)
2.127(3)
Bond angles
χ
O(2)–Fe(1)–O(1)
O(7)–Fe(1)–O(1)
O(7)–Fe(1)–O(2)
O(9)–Fe(1)–O(1)
O(9)–Fe(1)–O(2)
O(9)–Fe(1)–O(7)
O(1)–Fe(1)–N(2)
O(1)–Fe(1)–N(3)
O(2)–Fe(1)–N(2)
O(2)–Fe(1)–N(3)
O(7)–Fe(1)–N(2)
O(7)–Fe(1)–N(3)
O(9)–Fe(1)–N(2)
O(9)–Fe(1)–N(3)
N(2)–Fe(1)–N(3)
Fe(1)–O(1)–Fe(2)
73.76(10)
155.50(12)
96.10(12)
94.33(12)
153.59(12)
103.18(13)
77.21(12)
107.09(11)
107.99(12)
77.50(13)
85.21(13)
91.86(12)
91.62(13)
83.94(14)
174.00(14)
106.94(11)
O(1)–Fe(2)–O(2)
O(3)–Fe(2)–O(1)
O(3)–Fe(2)–O(2)
O(3)–Fe(2)–O(5)
O(5)–Fe(2)–O(1)
O(5)–Fe(2)–O(2)
O(1)–Fe(2)–N(1)
O(1)–Fe(2)–N(4)
O(2)–Fe(2)–N(1)
O(2)–Fe(2)–N(4)
O(3)–Fe(2)–N(1)
O(3)–Fe(2)–N(4)
O(5)–Fe(2)–N(1)
O(5)–Fe(2)–N(4)
N(4)–Fe(2)–N(1)
Fe(1)–O(2)–Fe(2)
72.67(10)
93.81(11)
140.17(12)
116.89(13)
140.66(11)
94.50(12)
76.21(13)
126.25(12)
125.27(11)
76.43(12)
84.96(12)
82.93(12)
82.33(13)
83.84(12)
155.05(14)
106.62(11)
0
50
100 150 200 250 300
T / K
Fig. 2. Plots of
text).
v
MT vs. T for 1. The solid line represents the best fit calculation (see
3.5
3.0
2.5
2.0
1.5
1.0
0.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
3.3. Magnetic properties
300
400
500
(nm )
600
700
λ
Taking into consideration the dinuclear nature of 1, the mag-
netic data were analysed for two iron(III) ions. A plot of MT versus
T is shown in Fig. 2.
MT at 300 K is 5.0 cm3 molꢀ1 K, which is much
lower than the typical value for two isolated Fe(III) ions (d5,
v
v
g = 2.00; v
MT = 8.8 cm3 molꢀ1 K), then a rapid decrease in the value
is seen and it limits to ꢂ0 cm3 molꢀ1 K at 2 K. This feature is indic-
ative of antiferromagnetic coupling between the iron(III) ions.
For this dinuclear iron(III) system (S = 5/2), the experimental
susceptibility data can be fitted using the formula given by Fisher
for a model with classical spin [19]. The best fit parameters are:
0.0
200
300
400
500
600
λ
(nm)
J = ꢀ28.52 cmꢀ1, g = 2.00 (fixed),
q(mononuclear impurities) =
Fig. 3. Change in spectral pattern of complex 1 after reaction with 3,5-DTBC,
observing the reaction for 6 h in methanol; inset: spectrum of pure 3,5-DTBC in
methanol.
0.035 and R = 0.56 ꢁ 10-5. The R factor is the agreement factor de-
fined as Ri[(
v
mT)obs ꢀ (
v v
MT)calc]2/Ri[( MT)obs]2.

22
M. Mitra et al. / Polyhedron 67 (2014) 19–26
Fig. 4. Colour change during conversion of 3,5-DTBC to 3,5-DTBQ on addition of complex 1.
For alkoxido iron(III) dimers, Gatteschi and co-workers estab-
lished the dependence of the magnetic properties on geometrical
and electronic parameters [20], and from the linear correlation be-
tween J and the Fe–O–Fe (h) angle it was found that with an in-
crease in h larger J values are obtained. The best-fit straight line
through the experimental points is J = 1.48 h – 135. In complex 1,
the h values are 106.9 and 106.6°, so the expected J value will be
close to ꢀ23 cmꢀ1. The experimental J value of ꢀ28.5 cmꢀ1 is in
good conformity with the formula used. The deviation of the
experimental J value from the theoretical one in 1 may be attrib-
uted primarily to the strong distortions of the octahedron around
each Fe(III) centre. Secondly, the linear fit derived by Gatteschi
and co-workers [20] was only for a series of b-diketonate-alkoxido
diiron(III) compounds.
3.4. Catecholase activity of 1: spectrophotometric study
In order to study the catecholase activity of complex 1, 3,
5-DTBC with two bulky t-butyl substituents on the ring and a
low quinone-catechol reduction potential has been chosen as the
test substrate. This makes it easily oxidized to the corresponding
o-quinone, 3,5-DTBQ, which is highly stable and shows a maxi-
mum absorption at 401 nm in methanol [6c]. A solution of 1 was
treated with 100 equivalents of 3,5-DTBC under aerobic conditions.
Fig. 5. A plot of the difference in absorbance (
rate of the catalysis by 1 in methanol.
DA) vs. time to evaluate the initial
Fig. 6. Change in the spectral pattern of complex 1 in dicholoromethane after reaction with 3,5-DTBC, observing the reaction for 4 h; inset: spectrum of the resulting solution
after 24 h.

M. Mitra et al. / Polyhedron 67 (2014) 19–26
23
0.018
0.016
0.014
0.012
0.010
0.008
0.006
0.004
0.002
0.000
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Time (min)
Fig. 7. A plot of the difference in absorbance (
D
A) vs. time to evaluate the initial rate of the catalysis by 1 in dichloromethane.
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0.8
0.6
0.4
0.2
0.0
300
400
λ (nm)
500
60
200
300
400
500
600
700
800
λ (nm)
Fig. 8. Change in the spectral pattern of complex 1 in acetonitrile after reaction with 3,5-DTBC, observing the reaction for 6 h; inset: spectrum of the resulting solution after
24 h.
The repetitive UV-Vis spectral scan was recorded in pure methanol
(Fig. 3). Spectral bands at 499, 330, 271 and 226 nm appear in the
electronic spectrum of complex 1, whereas 3,5-DTBC shows a sin-
gle band at 282 nm. After addition of 3,5-DTBC, the time dependent
spectral scan shows a very smooth increase of a quinone band at
ꢂ401 nm, as reported by Krebs et al [21], concomitant with a
decrease in the characteristic ꢂ282 nm band for 3,5-DTBC, which
indicates the formation of the respective quinone derivative,
3,5-DTBQ, which was purified by column chromatography. The
product was isolated in high yield (96.4%) by slow evaporation of
the eluant and was identified by 1H NMR spectroscopy (Fig. S1;
Supplementary file). 1H NMR (CDCl3, 400 MHz) dH: 1.16 (s, 9H),
1.20 (s, 9H), 6.15 (d, J = 2.4 Hz, 1H), 6.86 (d, J = 2.4 Hz, 1H).
In order to find out the comparative reaction rate between
3,5-DTBC and 1, the reaction kinetics between 1 and 3,5-DTBC
were studied by observing the time dependent change in absor-
bance at a wavelength of 401 nm, which is characteristic of
3,5-DTBQ in methanol. The colour of the solution gradually
turned deep brown (Fig. 4), indicative of a gradual conversion
of 3,5-DTBC to 3,5-DTBQ. The difference in absorbance
DA at
401 nm was plotted against time to obtain the initial rate for that
particular catalyst to substrate concentration ratio (Fig. 5). A

24
M. Mitra et al. / Polyhedron 67 (2014) 19–26
0.014
0.012
0.010
0.008
0.006
0.004
0.002
0.000
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
Time (min)
Fig. 9. A plot of the difference in absorbance (
D
A) vs. time to evaluate the initial rate of the catalysis by 1 in acetonitrile.
0.000020
0.000015
0.000010
0.000005
0.000000
70000
65000
60000
55000
50000
0
200
400
600
800
1000
1/[Substrate]
0.000
0.002
0.004
0.006
0.008
0.010
[Substrate] (M)
Fig. 10. Plot of rate vs. [substrate] in the presence of 1 in MeOH; inset: Lineweaver–Burk plot.
Table 3
absorption at 401 nm (Fig. 8), similar to that in methanol. The 3,5-
DTBQ obtained in each medium was purified by column chroma-
tography with yields of 64.30% in dichloromethane and 60.56% in
acetonitrile. This was characterized by determining its melting
point (ꢂ110 °C), which agreed well with that reported in the liter-
ature [22]. The reaction kinetics were studied by observing the
time dependent change in absorbance at wavelengths of 386 and
401 nm respectively for catalysis in dichloromethane and in aceto-
Kinetic parameters for the oxidation of 3,5-DTBC catalyzed by 1.
Solvent Vmax Std. error KM (M) Std. error
Kcat (hꢀ1
)
(M sꢀ1
)
MeOH
DCM
MeCN
2.08 ꢁ 10ꢀ5 1.45 ꢁ 10ꢀ6 4.38 ꢁ 10ꢀ4 7.01 ꢁ 10ꢀ5 7.51 ꢁ 102
4.71 ꢁ 10ꢀ5 5.59 ꢁ 10ꢀ6 9.04 ꢁ 10ꢀ4 5.65 ꢁ 10ꢀ5 1.69 ꢁ 103
3.42 ꢁ 10ꢀ5 3.68 ꢁ 10ꢀ6 8.70 ꢁ 10ꢀ4 2.25 ꢁ 10ꢀ5 1.23 ꢁ 103
nitrile. The differences in absorbance,
DA, at these particular wave-
first-order catalytic reaction is observed, with an initial rate of
lengths were plotted against time to obtain the intial rate of the
reaction. A first-order catalytic reaction is observed in both the
solvents, where the initial rates are found to be 4.70 ꢁ 10ꢀ3 minꢀ1
(Fig. 7) and 3.56 ꢁ 10ꢀ3 minꢀ1 (Fig. 9), respectively in DCM and
MeCN.
4.78 ꢁ 10ꢀ3 minꢀ1
.
The catecholase activity of complex 1 was similarly studied in
DCM and MeCN media. In DCM 3,5-DTBQ shows a maximum
absorption at 386 nm (Fig. 6), while in MeCN it shows a maximum

M. Mitra et al. / Polyhedron 67 (2014) 19–26
25
3.5. Enzyme kinetics study
References
[1] (a) M. Merkel, N. Möller, M. Piacenza, S. Grimme, A. Rompel, B. Krebs,
Chemistry–A European Journal 11 (2005) 1201;
Kinetic experiments were performed spectrophotometrically
with complex 1 and the substrate 3,5-DTBC in methanol, dichloro-
methane and acetonitrile, thermostated at 20 °C. 0.04 ml of the
complex solution, with a constant concentration of 1 ꢁ 10ꢀ4 M,
was added to 2 ml of 3,5-DTBC at a particular concentration (vary-
ing its concentration from 1 ꢁ 10ꢀ3 M to 1 ꢁ 10ꢀ2 M) to achieve
the ultimate concentration of the complex as 1 ꢁ 10ꢀ4 M. The con-
version of 3,-5-DTBC to 3,5-DTBQ was monitored with time at a
wavelength of 401 nm for solutions in MeOH and MeCN, and
386 nm for solutions in DCM. The rate for each concentration of
the substrate was determined by the initial rate method.
(b) J. Reim, B. Krebs, Journal of the Chemical Society, Dalton Transactions
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4. Conclusion
We have synthesized and structurally characterized a dinuclear
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that the catalytic reaction follows a first order reaction pathway
with rates about 10 times higher in MeOH and DCM than MeCN.
The turnover numbers of 1 in different solvents are much greater
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This indicates that 1 is a good and effective catalyst towards the
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Acknowledgements
RG acknowledges financial support from the Department of
Science & Technology, New Delhi, India (F. No. SR/FT/CS-83/2010
dt. 11-02-2011). We sincerely thank Dr. K.C. Bhowmick, Depart-
ment of Chemistry, Visva Bharati, Shantiniketan 731 235, India
for NMR spectroscopic studies. Valuable discussion regarding
Michaelis–Menten kinetics with Dr. D. Das, Department of Chemis-
try, University of Calcutta, Kolkata 700 009, India is gratefully
acknowledged. MM acknowledges The University of Burdwan,
Burdwan for her research fellowship. JR acknowledges the financial
support from the Spanish Government (Grant CTQ2009/07264/
BQU).
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CCDC 945632 contains the supplementary crystallographic data
for compound 1. These data can be obtained free of charge via
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bridge CB2 1EZ, UK; fax: +44 1223-336-033; or e-mail: depos-
it@ccdc.cam.ac.uk. Supplementary data associated with this
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