pH dependent catecholase activity of Fe(II) complexes of type [Fe(L)]X2 [L = N-(phenyl-pyridin-2-yl-methylene)-ethane-1,2-diamine; X = ClO4? (1), PF6? (2)]: Role of counter anion on turnover number

Article abstract of DOI:10.1016/j.ica.2020.119933

Two mononuclear Fe(II) complexes having same ligand framework, coordination geometry but different counter anions [Fe(L)]X₂ [L = N-(phenyl-pyridin-2-yl-methylene)-ethane-1,2-diamine; X = ClO₄^? (1), PF₆^?

Full text of DOI:10.1016/j.ica.2020.119933

InorganicaChimicaActa513(2020)119933
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Research paper
pH dependent catecholase activity of Fe(II) complexes of type [Fe(L)]X2
−
[L = N-(phenyl-pyridin-2-yl-methylene)-ethane-1,2-diamine; X = ClO4
(1), PF6 (2)]: Role of counter anion on turnover number
−
Arnab Chatterjeea, Gurpreet Kaurb, Mayank Joshib, Angshuman Roy Choudhuryb,
Rajarshi Ghosh⁎,a
a Department of Chemistry, The University of Burdwan, Burdwan 713 104, India
b Department of Chemical Sciences, Indian Institute of Science, Education and Research Mohali, Manauli 140 306 India
A R T I C L E I N F O
A B S T R A C T
Keywords:
Fe complexes
Catecholase activity
pH dependence
Counter anion effect
Two mononuclear Fe(II) complexes having same ligand framework, coordination geometry but different counter
−
−
anions [Fe(L)]X2 [L = N-(phenyl-pyridin-2-yl-methylene)-ethane-1,2-diamine; X = ClO4 (1), PF6 (2)] have
been synthesized and crystallographically characterized. Both the complexes catalyzed catechol-quinone oxi-
dation pH dependently. In the pH range 8.3–8.5 the suitable activity of both the complexes were found. Counter
anions in the complexes played a significant role in controlling the turn over numbers of the catalytic reactions.
In acetonitrile (MeCN), the turn over number for 1 was 4.99 h−1 and for 2, it was 42.75 h−1
.
1. Introduction
the structure of the catalyst molecule and therefore, the activity [6]. To
the best of our knowledge, its effect on mononuclear complexes is yet to
be explored. In an endeavour to study the same, we synthesized two
mononuclear isostructural Fe(II) complexes with same ligand structure,
differing in counter anions, which showed satisfactory catecholase-like
activity in the pH range 8.3–8.5. The effect of counter anions on turn-
over number of the complexes is also investigated.
The use of molecular oxygen to readily oxidise various organic
substrates is restricted mainly due to its low kinetic reactivity which is
attributed to its triplet character that makes the reaction with singlet
organic species a spin forbidden process [1]. Transition metal com-
plexes, having multiple spin and oxidation state, overcomes the pro-
blem associated with the spin barrier, thereby readily facilitating in-
teraction of dioxygen with organic species. Various research groups all
over the world are utilizing this property of transition metal as di-
oxygen activators. Functional models of various kinds of enzyme no-
tably catechol oxidase [2], phenoxazinone synthase [3], proto-
catechuate-3,4-dioxygenase [4], etc are being successfully mimicked all
over the globe. Our research group is also focussed on designing various
transition metal complexes and using them as catalysts to mimic var-
ious types of oxidation based catalytic activities like catecholase, phe-
noxazinone synthase etc. The active site of catechol oxidase consists of
two hydroxo bridged antiferromagnetically coupled dinuclear Cu(II)
centres which are 2.9 Å apart in which each copper centre is co-
ordinated with histidine unit of protein chain [5]. Many dinuclear as
well as mononuclear metal complexes along with Cu(II) are found to be
showing catecholase-like activity [2]. Catecholase activity often de-
pends on pH of the solution. Effect of pH is studied with dinuclear Cu
(II) complexes in which change in pH of the reaction mixture modifies
2. Experimental section
2.1. Materials
2-Benzoylpyridine and ethylene diamine were purchased from
Sigma Aldrich and used as received. Iron(II) acetate was purchased
from Aldrich. Sodium perchlorate and potassium hexafluorophosphate
were purchased from Sigma-Aldrich. The solvents used during crystal-
lization and kinetic experiment studies were of HPLC grade and used
without further purification.
2.2. Physical measurements
Single crystal X-ray analysis of the complexes 1 and 2 were carried
out on a Rigaku XtaLAB mini diffractometer using Mo-Kα radiation
(λ = 0.71075 Å). Diffraction data for both 1 and 2 were collected at
⁎ Corresponding author.
E-mail address: rghosh@chem.buruniv.ac.in (R. Ghosh).
https://doi.org/10.1016/j.ica.2020.119933
Received 18 February 2020; Received in revised form 10 April 2020; Accepted 29 July 2020
Availableonline31July2020
0020-1693/©2020ElsevierB.V.Allrightsreserved.

A. Chatterjee, et al.
InorganicaChimicaActa513(2020)119933
298 K and was identified with P‾1 space group. Data collection, unit
cell refinement, data reduction and absorption correction (multi-scan)
for the data sets were done using CrysAlis PRO [7]. The crystal struc-
tures were solved by using Olex2 [8] packages using SHELXS 2014/7
[9] and the structures were refined using SHELXL2014/7 [10]. All the
figures have been generated using ORTEP-32 [11]. IR (KBr discs,
4000–500 cm−1) spectra were recorded on Shimadzu IR Prestige
spectrophotometer and UV–Vis analysis were done on Shimadzu
UV–Vis 2450 spectrophotometer. The 1H NMR spectral data were col-
lected using CDCl3 as solvent on a 500 MHz Bruker spectrophotometer.
Mass spectral data were collected on Waters Micromass spectrometer.
pH measurements were done on Systronics Digital pH meter 335. Ele-
mental analyses were performed on a Thermo Scientific Flash 2000
elemental analyzer.
M M
−1mm−1), 610 (ε = 3.483 × 103 −1mm−1) (Fig. S4; ESI). C H N
Analysis: Calcd.: C28H30Cl2FeN6O8 (1): C, 47.68%; H, 4.29%; N,
11.92%. Found, C, 47.61%; H, 4.23%; N, 11.99%.
2.5. Synthesis of 2
Complex 2 was prepared in a similar manner as 1, except that in this
case sodium perchlorate was replaced by potassium hexafluoropho-
sphate. The metal ion, ligand and the salt were taken in the ratio
(1:2:2). The resulting blue solution was stirred for about 1 h. The so-
lution was filtered, covered and kept for crystallization. Bluish crystals
were obtained after 3 days which were collected and air dried.
Yield (Based on metal salt): 0.183 g (46%), Selected IR bands (KBr
pellet, cm−1): 3300, 1660, 835 (Fig. S5; ESI); UV–Vis in MeCN (λ nm):
260 (ε = 3.48 × 104 M−1mm−1) (Fig. S6; ESI); C H N Analysis: Calcd.:
C
28H30F12FeN6P2 (2): C, 42.23%; H, 3.80%; N, 10.55%. Found, C,
2.3. Synthesis of ligand
42.18%; H, 3.76%; N, 10.58%.
10.9 mmol (2.0 g) of 2-benzoylpyridine was dissolved in nearly
90 ml of ethanol taken in a 250 ml round bottomed flask. To this
5.45 mmol (0.33 g) of ethylene diamine, dissolved in 40 ml of ethanol
was added drop wise. The resulting reaction mixture was refluxed for
7 h. The ligand obtained (L′) was characterized using IR and NMR
spectroscopic measurements. During the reaction conditions with metal
ions, one of the imine bonds in the ligand got hydrolysed to form N-
(phenyl-pyridin-2-yl-methylene)-ethane-1,2-diamine (L). As the hy-
drolysis of the ligand was in situ, the spectral characterization of the
hydrolysed ligand could not be carried out, although the indirect proof
of hydrolysis was obtained by SC-XRD measurements of 1 and 2. A
schemetic representation of these facts is provided in Scheme 1.
Yield (based on 2-benzoylpyridine): 0.247 g (58.0%), Selected IR
bands of L′ (KBr pellet, cm−1): 1670, 3050 (Fig. S1; ESI); 1H NMR
spectroscopy of L′ (Fig. S2; ESI). 1H NMR (CDCl3, 500 MHz): δH
(ppm) = 7.47–8.73 (m, 18H), 3.78 (t, 2H), 3.85 (t, 2H); C H N Analysis:
Calcd.: C28H30Cl2FeN6O8 (1): C, 79.97%; H, 5.68%; N, 14.35%. Found,
C, 79.69%; H, 5.50%; N, 14.42%.
2.6. X-ray diffraction study
Single crystal X-ray diffraction data for both the complexes 1 and 2
were recorded on a Rigaku XtaLAB mini diffractometer using Mo-Kα
radiation (λ = 0.71075 Å). Diffraction data for both 1 and 2 were
collected at 298 K and both have been found to crystallize in the cen-
¯
trosymmetric P1 space group. Out of 35,533 and 42,298 total reflec-
tions, 8166 and 7050 with I > 2σ(I) were used for structure solutions
for 1 and 2, respectively. The direct methods were used for structure
solution, and the structure solution and refinement were based on |F2|.
The maximum and minimum peak heights were 0.947 and −0.559 for
1 whereas for 2 the values came out to be 1.401 and −0.550 eÅ−3. The
crystal data and refinement details are listed in Table 1.
3. Results and discussion
3.1. Synthesis and formulation
2.4. Synthesis of 1
2:1 condensation of 2-benzoylpyridine and ethylene diamine in
ethanolic solution resulted in the formation of the ligand L′. IR spec-
troscopic characterization on the ligand indicated the presence of imine
bond at around 1670 cm−1 [12] (Fig. S1, ESI). 1HNMR characterization
of the ligand (Fig. S2, ESI) was done which showed the presence of the
aromatic protons (eighteen numbers) in the range δ = 7.47–8.73, while
the four aliphatic protons appeared at δ = 3.78 and 3.85. Compound 1
was prepared by the reaction of iron(II) acetate with L′ in methanol
followed by addition of sodium perchlorate in appropriate molar ratio
of (1:2:2). Good crystals of diffractable quality were obtained after a
period of about 5 days. Interestingly, on structure solution, it was
0.5 mmol (0.087 g) of Fe(OAc)2 was dissolved in 20 ml of methanol
taken in a beaker. To this 1.0 mmol (0.39 g) of the ligand (L′) was added
followed by addition of 1.0 mmol (0.122 g) of NaClO4. The resulting
blue solution was stirred for about 1 h. Solution was filtered, covered
and kept for crystallization. Blue single crystals of diffractable quality
were obtained after 6 days which were collected and air dried.
Yield (Based on metal salt): 0.168 g (48%), Selected IR bands (KBr
pellet, cm−1): 3300, 1600, 1090, 615 (Fig. S3; ESI); UV–Vis in MeCN (λ
nm): 260 (ε = 4.37 × 104
M
−1mm−1), 355 (ε = 2.44 × 103
Scheme 1. Synthesis of the ligand and metal complexes.
2

A. Chatterjee, et al.
InorganicaChimicaActa513(2020)119933
Table 1
Crystal data and structure refinement parameters.
Parameters
1
2
Formula
Mol. Wt.
C28H30Cl2FeN6O8
705.33
C28H30F12FeN6P2
796.37
Crystal System
Triclinic
Triclinic
Space Group
Temperature (K)
298
298
Wavelength
0.71073
0.71073
a/Å
b/Å
11.4312(2)
12.5054(2)
12.8166(2)
67.053(2)
78.555(1)
69.178(2)
1573.16(5)
2
11.8627(2)
12.6978(2)
12.9813(3)
66.204(2)
75.134(2)
70.645(2)
1670.85(6)
2
c/Å
α/o
β/o
γ/o
V/Å3
Z
Dc/g cm−3
1.489
0.707
728.0
1.583
0.645
808.0
μ/mm−1
F(000)
R(int)
0.023
0.039
Total reflections
unique reflections
I > 2σ(I)
Completeness to theta
Absorption correction
θmax and θmin
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indexes [l > 2σ(I)]
35,533
9872
8166
0.952
multi-scan
31.96° and 3.08°
11108/0/406
1.048
R1 = 0.0594,
wR2 = 0.1758
R1 = 0.0791
wR2 = 0.1995
0.947 and −0.559
42,298
8230
7050
0.998
multi-scan
26.98° and 2.87°
9761/0/450
1.052
R1 = 0.0660,
wR2 = 0.1846
R1 = 0.0883,
wR2 = 0.2215
1.401 and −0.550
Fig. 1. ORTEP of 1 with 40% ellipsoid probability of non-hydrogen atoms.
R indexes (all data)
Largest difference in peak and
hole (e_Å3)
R = Σ|Fo| − |Fc||/Σ|Fo, wR = [Σw(Fo − Fc2)2/Σw(Fo2)2]1/2, calcd w = 1/
2
2
[σ2(Fo2) + (0.1311P)2 + 9.1582P]; where P = (Fo + 2Fc2)/3.
observed that one of the two imine bonds was hydrolysed during the
reaction conditions. To check the reproducibility, the reaction was once
again performed under similar conditions to obtain single crystals.
Those crystals were mounted on an X-ray diffractometer and similar cell
parameters were obtained as that of the previous. The crystals of 1 were
used for spectroscopic measurements. In IR spectrum the imine stretch
appeared at lower value (1600 cm−1) (Fig. S3, ESI) than the free ligand
(1670 cm−1) (Fig. S1, ESI) which indicated the coordination of the
imine nitrogen to the metal centre. Peaks at 615 and 1090 cm−1 were
due to the perchlorate anions which satisfies the primary valencies.
UV–Vis spectrum of 1 was recorded in acetonitrile solution (Fig. S4,
ESI). Solution of 1 showed absorbance at 260 nm, 355 nm and 610 nm.
The final band may be of d-d absorption origin. Compound 2 was
prepared by the reaction of iron(II) acetate with L′ in ethanol followed
by addition of potassium hexaflurophosphate in appropriate molar ratio
of 1:2:2. The resulting solution was stirred for about 2.5 h, filtered and
kept in open air. Single crystals of diffractable quality appeared after a
period of about 7 days. Here also, on structure solution, the hydrolysis
of one imine bond was observed, as observed in case of 1. The re-
producibility of this reaction was also confirmed satisfactorily in a si-
milar manner as discussed for 1. Compound 2 was subjected to various
spectroscopic measurements. In IR spectrum, the imine stretch ap-
peared at lower value (1660 cm−1) (Fig. S5, ESI) which indicated the
coordination of the imine nitrogen to the metal centre. The peaks at
835 cm−1 was due to the hexafluorophosphate anion. UV–Vis spectrum
of 2 was recorded in acetonitrile solution with lower concentration than
1 in which only a peak at 260 nm (because of ligand origin) was ob-
tained (Fig. S6, ESI). No d-d band appeared may be because of lower
concentration of 2.
Fig. 2. ORTEP of 2 with 40% ellipsoid probability of non-hydrogen atoms.
3.2. X-ray structures
The ORTEP plots of 1 and 2 are given in Figs. 1 and 2. Each of the
¯
compounds crystallized in triclinic crystal system with P1 space group
(Table 1). Bond angle bond distance parameters (Table 2) reveal that
each of the metal centres in each of 1 and 2 adopts distorted octahedral
geometry. Both the compounds are isostructural in nature, except that
the primary valency in 1 is satisfied by perchlorate anions whereas for 2
it is satisfied by the hexafluorophosphate anions. The mutual disposi-
tions of the donor sites of the coordinated ligands in 1 and 2 are same.
In each case the pyridine and primary amine nitrogens (for 1, N4 and
N6; for 2, N1 and N3) occupy the axial trans positions whereas the a
pyridine nitrogen, two imine nitrogens and one amine nitrogen (for 1,
N1, N2, N5, N3; for 2 N4, N2, N5, N6) lie in the equatorial plane.
3.3. Catecholase activity
Investigation of catecholase like activity of 1 and 2 were done using
acetonitrile (MeCN) as solvent. Our complexes were unable to show any
catecholase like activity under normal conditions in which the pH of the
solutions in MeCN were 5.05 (for 1) and 5.21 (for 2), respectively. But
on increasing and maintaining the pH of the solution in the range of
8.3–8.4 using triethyl amine, each of our complexes showed satisfactory
3

A. Chatterjee, et al.
InorganicaChimicaActa513(2020)119933
Table 2
Bond angle and distance parameters.
Connecting atoms
Bond angle (°)
Connecting atoms
Bond angle (°)
Bond angle (°) parameters for 1
N(1)-Fe(1)-N6
90.53(8)
N(5)-Fe(1)-N(6)
N(5)-Fe(1)-N(2)
N(5)-Fe(1)-N(3)
N(2)-Fe(1)-N(1)
N(2)-Fe(1)-N(4)
N(2)-Fe(1)-N(6)
N(2)-Fe(1)-N(3)
83.41(7)
178.95(7)
97.38(7)
80.87(7)
98.90(7)
96.66(8)
83.66(7)
N(1)-Fe(1)-N(3)
N(4)-Fe(1)-N(1)
N(4)-Fe(1)-N(6)
N(4)-Fe(1)-N(3)
N(6)-Fe(1)-N(3)
N(5)-Fe(1)-N(1)
N(5)-Fe(1)-N(4)
164.51(7)
91.57(7)
164.44(8)
91.73(8)
90.34(9)
98.08(7)
81.03(7)
Bond angle (°) parameters for 2
N(1)-Fe(1)-N(4)
N(1)-Fe(1)-N(6)
N(1)-Fe(1)-N(3)
N(2)-Fe(1)-N(1)
N(2)-Fe(1)-N(4)
N(2)-Fe(1)-N(5)
N(2)-Fe(1)-N(6)
N(2)-Fe(1)-N(3)
93.0(1)
90.9(1)
163.9(1)
80.71(9)
99.31(9)
179.8(1)
96.5(1)
83.2(1)
N(4)-Fe(1)-N(6)
N(4)-Fe(1)-N(3)
N(5)-Fe(1)-N(1)
N(5)-Fe(1)-N(4)
N(5)-Fe(1)-N(6)
N(5)-Fe(1)-N(3)
N(3)-Fe(1)-N(6)
164.2(1)
90.1(1)
99.22(9)
80.88(9)
83.3(1)
96.8(1)
90.3(1)
Fig. 4. Change in spectral pattern of 2 after reaction with 3,5-DTBC at pH 8.42
observing the reaction for 90 min in MeCN.
Bond distance parameters (Å) for 1
Fe(1)-N(1)
Fe(1)- N(4)
Fe(1)-N(6)
1.963(2)
1.963(2)
2.020(2)
Fe(1)-N(5)
Fe(1)-N(2)
Fe(1)-N(3)
1.895(2)
1.898(2)
2.020(2)
DTBQ was isolated column chromatographically using 10% mixture of
ethyl acetate and hexane as eluent. The isolated o-quinone was iden-
tified by comparing its melting point to that reported in literature [14].
Bond distances (Å) parameters for 2
Fe(1)-N(1)
Fe(1)- N(4)
Fe(1)-N(6)
1.965(2)
1.967(2)
2.023(2)
Fe(1)-N(5)
Fe(1)-N(2)
Fe(1)-N(3)
1.895(2)
1.895(2)
2.018(3)
3.4. Enzyme kinetic study
1, after pH adjustment, was subjected to kinetic experiments spec-
trophotometrically with the substrate 3,5-DTBC using MeCN as solvent.
The reaction setup was thermostated at 25 °C. 0.04 ml of 1 × 10−4 (M)
solution of the complex was added to 2 ml of 3,5-DTBC of a particular
concentration (concentration variation was 1 × 10−3 (M) to 1 × 10−2
(M)) to achieve a final concentration of the complex as 10−4 (M).
Conversion of 3,5-DTBC to 3,5-DTBQ was monitored spectro-
photometrically at a wavelength of 401 nm in MeCN. The data of rate
versus concentration of the substrate were analyzed on the basis of
Michealis-Menten approach to get the Lineweaver-Burk plot (Fig. 5).
From the later plot various kinetic parameters like Vmax, KM, Kcat were
obtained. The kinetic parameters are listed under Table 3. The turnover
number (Kcat) in MeCN is found to be 4.99 h−1. Similar experiment was
set up with 2 using MeCN as solvent. The data of rate versus con-
centration of the substrate were analyzed on the basis of Michaelis-
Fig. 3. Change in spectral pattern of 1 after reaction with 3,5-DTBC at pH 8.31
observing the reaction for 90 min in MeCN.
activities. The substrate 3,5-di-tert-butylcatechol (3,5-DTBC), having
two bulky t-butyl substituent on the ring, resulting in lower quinone-
catechol reduction potential, was chosen for catecholase activity study.
The oxidised stable product o-quinone shows a maximum absorption at
~401 nm in methanol [13]. 3,5-DTBC shows a single band at around
282 nm. Treating 100 equivalents of 3,5-DTBC with 1 in MeCN, under
aerobic conditions, the repetitive UV–Vis spectrum was recorded.
Transformation of colourless solution to deep brown with respect to
time indicated the conversion of 3,5-DTBC to 3,5-di-tert-butyl-o-qui-
none (3,5-DTBQ) which was further corroborated by the continuous
increase in quinone band at 401 nm in MeCN (Fig. 3). Similar results
were obtained on treating 2 with 100 equivalents of 3,5-DTBC under
aerobic conditions in MeCN (Fig. 4). For each of the compounds, the
same reaction was done by scaling up the reactants and the desired 3,5-
Fig. 5. Plot of rate versus [substrate] (3,5-DTBC) in presence of 1 in MeCN
(Inset: Lineweaver-Burk plot).
4

A. Chatterjee, et al.
InorganicaChimicaActa513(2020)119933
Table 3
Kinetic parameters.
reported. Both the compounds are catalyzing catechol-quinone oxida-
tion at alkaline pH. pH dependent catecholase activity (catechol-qui-
none oxidation) is rare [6]. To the best of our knowledge, this is the first
report of mononuclear metal complexes responding catecholase activity
pH dependently. Moreover, interestingly, the turn over number of the
reaction catalysed by 2 is greater than 1. A correlation of the volume of
the counter anions with the turn over number is drawn. From mass
spectrometric measurement, it appeared that higher volume of the ca-
tionic intermediate in the reaction catalysed by 2 is well stabilised by
the higher volume of the counter anion, i.e., hexafluorophosphate. This
leads to the higher turn over number.
Compound
Solvent
Vmax (M s−1
)
Std. error
Kcat (h−1
)
Std. error
1
2
Acetonitrile
Acetonitrile
1.39E−07
1.18E−06
2.96E−09
1.73E−08
4.99
42.75
5.68E−01
1.2E−01
pH Depend.
Declaration of Competing Interest
The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influ-
ence the work reported in this paper.
Acknowledgements
AC is thankful to DST PURSE Phase II, Govt. of India for his fel-
lowship. AC and RG are also thankful to USIC, Burdwan University for
single crystal X-ray diffraction facility. Generous help by Dr Rajib K
Goswami, IACS, Kolkata by measuring a number of mass spectra is
gratefully acknowledged.
Fig. 6. Plot of rate versus [substrate] (3,5-DTBC) in presence of 2 in MeCN
(Inset: Lineweaver-Burk plot).
Appendix A. Supplementary data
Supplementary data to this article can be found online at https://
doi.org/10.1016/j.ica.2020.119933.
Menten approach (Fig. 6). Various kinetic parameters were evaluated
which are listed under Table 3. The turnover number for 2 in acet-
onitrile was found to be 42.75 h−1, which was approximately 8.5 times
higher than 1. Mass spectrometric data (Fig. S7, ESI) obtained after the
initial dissociation of 1 in MeCN indicated the reduction of the per-
chlorate counter anion to chloride [15] and the resulting adduct with
3,5-DTBC (as appears from Fig. S8, ESI) contains a pair of oppositely
charged ions (the positively charged adduct and the chloride as its
counter anion) which differ significantly in their sizes. Such is not the
case with the adduct formed by the association of 2 with 3,5-DTBC (Fig.
S10, ESI) in which the large cationic part is stabilised significantly by
the larger (than the chloride) hexafluorophosphate anions compared to
the small sized chloride anions in 1. Thus the adduct of 2 with 3,5-
DTBC is better stabilised which is related to its higher probability of
formation, and consequently a higher turnover number was obtained.
References
[1] V. Ullrich, Angew. Chem. Int. Ed. 11 (8) (1972) 701–712.
[2] (a) A. Das, S. Goswami, R. Sen, A. Ghosh, Inorg. Chem. 58 (2019) 5787–5798;
(b) P. Zerón, M. Westphal, P. Comba, M.F. Álamo, A.C. Stueckl, C.L. Cervantes,
V.M.U. Saldíver, L. Gasque, Eur. J. Inorg. 1 (2017) 56–62;
(c) M. Mondal, S. Ghosh, S. Maity, S. Giri, A. Ghosh, Inorg. Chem. Front. 7 (2020)
247–259;
(d) T. Chakraborty, S. Mukherjee, S. Dasgupta, B. Biswas, D. Das, Dalton Trans. 48
(2019) 2772–2784.
[3] (a) A. Zaman, S. Khan, B. Dutta, S.M. Yakout, S.S. Ibrahim, M.H. Mir, J. Coord,
Chem. 72 (14) (2019) 2362–2375;
(b) W.P. Sohtun, S. Muthuramalingam, M. Velusamy, R. Mayilmurugan, Inorg.
Chem. Commun. 110 (2019) 107608;
(c) S.Y. Shaban, A.E.-M.M. Ramadan, M.M. Ibrahim, F.I. Elshami, R.V. Eldik, Inorg.
Chim. Acta 486 (2019) 608–616.
[4] (a) T.R. Lakshman, S. Chatterjee, B. Chakraborty, T.K. Paine, Dalton Trans. 45
(2016) 8835–8844;
(b) E. Safaei, S. Heidari, A. Wojtczak, P. Cotic, A. Kozakiewicz, J. Mol. Struct. 1106
(2016) 30–36.
3.5. Probable intermediates
[5] (a) C. Gerdemann, C. Eicken, B. Krebs, Acc. Chem. Res. 35 (2002) 183–191;
(b) I.A. Koval, P. Gamez, C. Belle, K. Selmeczi, J. Reedijk, Chem. Soc. Rev. 35
(2006) 814–840.
[6] (a) C. Belle, C. Beguin, I.G. Luneau, S. Hamman, C. Philouze, J.L. Pierre,
F. Thomas, S. Torelli, Inorg. Chem. 41 (2002) 479–491;
(b) L. Gasque, V.M.U. Saldívar, I. Membrillo, J. Olguín, E. Mijangos, S. Bernès,
I. González, J. Inorg. Biochem. 102 (2008) 1227–1235;
The probable intermediates through which our synthesized com-
plexes converted 3,5-DTBC to 3,5-DTBQ were tried to be understood
using mass spectrometric measurements. All the experiments were
performed with MS grade acetonitrile. Dissolution of 1 resulted in a
structure in which the perchlorate anion was reduced to chloride anion
(Fig. S7, ESI). Probable adduct of 1 with 3,5-DTBC is tried to be trapped
(Fig. S8, ESI). Dissolution of 2 in MeCN resulted in a structure presented
in Fig. S9, ESI. The adduct of 2 with 3,5-DTBC is presented in Fig. S10,
ESI. In case of 1, coordination of 3,5-DTBC to the metal centre is fa-
cilitated by removal of one ligand moiety from the complex (Fig. S8,
ESI) whereas in case of 2, 3,5-DTBC coordinates to the metal centre in
which both the ligands were ligated to the metal centre (Fig. S10, ESI).
(c) A. Neves, L.M. Rossi, A.J. Bortoluzzi, B. Szpoganicz, C. Wiezbicki, E. Schwingel,
Inorg. Chem. 41 (2002) 1788–1794;
(d) A. Banerjee, S. Sarkar, D. Chopra, E. Colacio, K.K. Rajak, Inorg. Chem. 47
(2008) 4023–4031.
[7] Rigaku Oxford Diffraction (2015). CrysAlis PRO.Rigaku Oxford Diffraction,
Yarnton, England.
[8] O.V. Dolomanov, L.J. Bourhis, R.J. Gildea, J.A.K. Howard, H. Puschmann, J. Appl.
Crystallogr. 42 (2009) 339–341.
[9] G.M. Sheldrick, Acta Crystallogr., Sect. A 64 (2008) 112–122.
[10] G.M. Sheldrick, Acta Crystallogr., Sect. A 71 (2015) 3–8.
[11] L.J. Farrugia, ORTEP-32 for Windows, University of Glasgow, Scotl, 1998.
[12] K. Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds, part B: Applications in Coordination, Organometallic, and
Bioinorganic Chemistry, John Wiley & Sons Inc, New Jersey, 2009.
[13] (a) K.S. Banu, T. Chattopadhyay, A. Banerjee, S. Bhattacharya, E. Suresh,
M. Nethaji, E. Zangrando, D. Das, Inorg. Chem. 47 (2008) 7083;
(b) S. Majumder, S. Sarkar, S. Sasmal, E. Carolina Sãnudo, S.S. Mohanta, Inorg.
4. Conclusion
Synthesis and crystal structure of two mononuclear Fe(II) co-
ordination complexes 1 and 2 having same ligand framework as well as
coordination geometry differing only in counter anions have been
5

A. Chatterjee, et al.
InorganicaChimicaActa513(2020)119933
[15] (a) C.L. Ford, Y.J. Park, E.M. Matson, Z. Gordon, A.R. Fout, Science 354 (6313)
(2016) 741–743;
Chem. 50 (2011) 7540;
(c) A. Banerjee, S. Sarkar, D. Chopra, E. Colacio, K.K. Rajak, Inorg. Chem. 47
(2008) 4023;
(b) J. Cao, D. Elliott, W.-X. Zhang, J. Nanopart. Res. 7 (2005) 499–506;
(c) M. Majumder, J.K. Bera, Indian J. Chem. 50A (2011) 409–413.
(d) A. Banerjee, R. Singh, E. Colacio, K.K. Rajak, Eur. J. Inorg. Chem. (2009) 277.
[14] S. Tsuruya, S.-I. Yanai, M. Masai, Inorg. Chem. 25 (1986) 141.
6