A three-dimensional manganese(II) coordination polymer: synthesis, structure and catecholase activity

Article abstract of DOI:10.1080/00958972.2020.1740213

A manganese-based coordination polymer, [Mn₂L₂(μ-MeOH)₂]_n (H₂L = 2-hydroxy-1-naphthaldehyde isonicotinoylhydrazone) was obtained by self-assembly of 2-hydroxy-1-naphthaldehyde isonicotinoylhydrazone and manganese(II) acetate. The coordination polymer was characterized by IR, EPR and UV–Vis spectroscopy. The single-crystal X-ray diffraction study reveals that the dibasic tridentate ligand (L^2?) is bound via ONO donor sites to manganese(II). Two such [ML] fragments are connected by μ₂-bridged methanol (MeOH) to form a di-manganese species. The sixth site of each of the manganese is occupied by the pyridyl N atom of the isonicotinoyl group. This arrangement gives a polynuclear complex of the formula [Mn₂L₂(μ-MeOH)₂]_n. The coordination geometry of manganese is distorted octahedral. The X-band electron paramagnetic resonance (EPR) measurement of the complex at 77 K shows a six-line spectrum and a signal at the half field, with g = 4.88. The half-field signal indicates the dimeric nature of the complex in the solution state. The cyclic voltammetric measurement of the complex shows a reversible Mn^III/Mn^II redox couple. The complex catalyzes the conversion of 3,5-di-tert-butyl catechol to the corresponding o-quinone with a catalytic turnover rate of (k_cat) 27.22 h^?1.

Full text of DOI:10.1080/00958972.2020.1740213

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: https://www.tandfonline.com/loi/gcoo20
A three-dimensional manganese(II) coordination
polymer: synthesis, structure and catecholase
activity
Prama Bhattacherjee, Partha Mitra, Prasenjit Sarkar & Rohith P. John
To cite this article: Prama Bhattacherjee, Partha Mitra, Prasenjit Sarkar & Rohith P. John (2020):
A three-dimensional manganese(II) coordination polymer: synthesis, structure and catecholase
activity, Journal of Coordination Chemistry, DOI: 10.1080/00958972.2020.1740213
To link to this article: https://doi.org/10.1080/00958972.2020.1740213
View supplementary material
Published online: 23 Mar 2020.
Submit your article to this journal
Article views: 2
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
https://www.tandfonline.com/action/journalInformation?journalCode=gcoo20

JOURNAL OF COORDINATION CHEMISTRY
https://doi.org/10.1080/00958972.2020.1740213
A three-dimensional manganese(II) coordination polymer:
synthesis, structure and catecholase activity
a
b
c
a
Prama Bhattacherjee , Partha Mitra , Prasenjit Sarkar and Rohith P. John
a
Department of Chemistry, Indian Institute of Technology (ISM), Dhanbad, Jharkhand, India;
b
Department of Central Scientific Service, Indian Association for Cultivation of Science, Kolkata, India;
Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati, Assam, India
c
ABSTRACT
ARTICLE HISTORY
A manganese-based coordination polymer, [Mn
2 2
L
(m-MeOH)
2
]
n
Received 2 October 2019
Accepted 18 February 2020
(
H L ¼ 2-hydroxy-1-naphthaldehyde isonicotinoylhydrazone) was
2
obtained by self-assembly of 2-hydroxy-1-naphthaldehyde isonico-
tinoylhydrazone and manganese(II) acetate. The coordination
polymer was characterized by IR, EPR and UV–Vis spectroscopy.
The single-crystal X-ray diffraction study reveals that the dibasic
KEYWORDS
Coordination polymer; EPR
spectra; manganese;
catecholase activity; cyclic
voltammetry
2ꢀ
tridentate ligand (L
) is bound via ONO donor sites to
manganese(II). Two such [ML] fragments are connected by m
2
-
bridged methanol (MeOH) to form a di-manganese species. The
sixth site of each of the manganese is occupied by the pyridyl N
atom of the isonicotinoyl group. This arrangement gives a poly-
nuclear complex of the formula [Mn L (m-MeOH) ] . The coordin-
2
2
2 n
ation geometry of manganese is distorted octahedral. The X-band
electron paramagnetic resonance (EPR) measurement of the com-
plex at 77 K shows a six-line spectrum and a signal at the half
field, with g ¼ 4.88. The half-field signal indicates the dimeric
nature of the complex in the solution state. The cyclic voltammet-
III
II
ric measurement of the complex shows a reversible Mn /Mn
redox couple. The complex catalyzes the conversion of 3,5-di-tert-
butyl catechol to the corresponding o-quinone with a catalytic
ꢀ
1
turnover rate of (kcat) 27.22 h
.
CONTACT Rohith P. John
ISM), Dhanbad, Jharkhand, 826004, India
Supplemental data for this article is available online at https://doi.org/10.1080/00958972.2020.1740213.
ß 2020 Informa UK Limited, trading as Taylor & Francis Group
rohithjohn@iitism.ac.in
Department of Chemistry, Indian Institute of Technology
(

2
P. BHATTACHERJEE ET AL.
1. Introduction
Manganese is a metal which can readily shuttle between oxidation states þ2 and þ3.
This behavior is widely utilized in redox metalloenzymes, such as catalase, ribonucleo-
tide reductase, superoxide dismutase and dioxygenase [1]. Manganese enzymes have
various types of active sites having different nuclearity, including the tetranuclear
manganese clusters that exist at the reactive site of photosynthetic water oxidation
[2]. This has led researchers to develop manganese complexes of different nuclearity
not only to develop better and efficient catalysts, but also in the design of single-mol-
ecule magnets [3]. Several multinuclear manganese complexes with diverse structures
such as rings [4], clusters and coordination polymers have been studied, owing to
their structural diversity [5], magnetism [6], sensing [7] and catalysis [8]. The choice of
manganese in many such synthetic models is due to the fact that it is a redox-active
metal ion, has flexible coordination geometry and therefore offers plenty of choice for
structural modulation [9–11]. Dinuclear manganese complexes are widely utilized for
various catalytic conversions, such as epoxidation, hydroxylation, and hydrosilylation/
hydrogermylation [12–15]. Polynuclear manganese complexes also show interesting
magnetic anisotropy properties [16]. In addition, various multinuclear manganese com-
plexes are also shown to catalyze conversions such as oxygen transfer reactions and
water oxidation [17, 18].
In recent years many of the manganese complexes were shown to catalyze super-
oxide-dismutase-like activity and catecholase activity [19, 20]. The two major metal-
loenzymes, catechol dioxygenase and catechol oxidase, catalyze the conversion of cat-
echol to their respective products [21, 22]. Catechol oxidase is generally found in
some plants, algae and fungi and catalyzes the oxidation of o-diphenols to the corre-
sponding o-quinones in the presence of molecular oxygen which gets reduced to

JOURNAL OF COORDINATION CHEMISTRY
3
water. The conversion of catechols into o-quinones is important as the latter is used in
many antiseptic formulations. Although catechol oxidase has a dicopper active site
structure, several transition metal complexes with manganese [23], iron [24] and cobalt
[25] have been reported to show catecholase activity. Among manganese complexes
that display catecholase activity, several have a dinuclear core with alkoxy/phenolate/
oxido/methanol bridges [26]. Various strategies are used to generate a dinuclear Mn-
Mn core in a polymeric matrix. However, simple strategies such as housing a dinuclear
core in a matrix of a coordination polymer that offers voids for the diffusion of the
substrate can be very effective. Herein we report a manganese coordination polymer
that offers dinuclear Mn … Mn core bridged methanol molecules obtained by the pro-
cess of self-assembly.
2. Experimental
2.1. General remarks
All reactions were performed under aerobic conditions. Solvents used for the synthesis
were purchased from RANKEM of analytical grade and used after purifying by standard
methods. Isonicotinichydrazide and 2-hydroxy-1-naphthaldehyde were purchased from
TCI Chemicals and manganese(II) acetate tetrahydrate was purchased from Merck India
and were used without purification.
A Perkin Elmer Spectrum-II FT-IR spectrometer was used for infrared spectral meas-
urements. UV–visible spectrum were recorded in N,N-dimethyl formamide (DMF) on a
Shimadzu UV-2450 spectrometer. Elemental analyses were performed on a Vario Micro
cube for C, H, N, S Analyser by Elemental Analyser System GMBH. ESI-Mass spectra
were recorded on a VARIAN 410 Prostar Binary LC with 500 MS IT PDA in positive
mode at SAIF, Punjab University, Chandigarh. The XPS measurement was carried out
on a VG Scientific ESCALAB 250 instrument. The cyclic voltammogram was recorded in
a CHI1140C electrochemical analyzer equipped with a platinum wire counter electrode,
a calomel reference electrode and a glassy carbon disk working electrode. The working
electrode was polished before each voltammogram with a 1 lm diamond paste, soni-
cated in ethyl alcohol, washed with the same solvent, and dried in air. The electro-
chemical studies were carried out with sample concentrations of 0.5 mM, 0.75 mM and
1
mM in dry DMF (ACROS) using 0.1 M tetrabutylammonium perchlorate (TBAP) as a
supporting electrolyte. Nitrogen was purged into the solution for 15 minutes before
the start of the experiment. The temperature was maintained with a Julabo circulation
ꢁ
bath at 25 C. The EPR spectrum was recorded at 77 K in DMF on a JEOL ESR
Spectrometer at 9.5mW microwave frequency with a fieldset of 330 mT and 200 mT
field sweep. EASYSPIN 5.0.16 was used for EPR simulations [27].
2
.2. Synthesis of ligand (H L)
2
The ligand (E)-N’-((2-hydroxynaphthalen-1-yl)methylene)isonicotinohydrazide (H L,
2
Scheme 1) was synthesized by condensation of isonicotinichydrazide and 2-hydroxy-1-
naphthaldehyde as reported elsewhere [28]. Isoicotinichydrazide (500 mg, 3.64 mmol)
and 2-hydroxynaphthaldehyde (627 mg, 3.64 mmol) were taken in 35 mL ethanol

4
P. BHATTACHERJEE ET AL.
Scheme 1. Schematic diagram of H2L.
solution and refluxed for 4 h. Upon completion of the reaction, a yellow precipitate
was obtained, which was filtered off, washed with ethanol solution and dried under
1
ꢁ
vacuum. 375 mg (75%). H-NMR (DMSO d ), 25 C, 400 MHz): (ppm) 12.51 (s, 1H, OH ),
6
a
1
2.40 (s, 1H, NH ), 9.47 (s, 1H, N ¼ C-H ), 8.83 (d, 2H, CH ), 8.31 (d, 1H, CH ) 7.91 (d, 1H,
b
c
d
e
CH ), 7.94 (d, 1H, CH ), 7.88 (d, 2H, CH ), 7.61 (t, 1H, CH ), 7.41 (t, 1H, CH ), 7.24 (d, 1H,
f
g
h
i
j
ꢀ
1
CH ), FT-IR (KBr, cm ): H L, 3226s (-NH), 3029 m (aromatic –CH), 1680s (>C ¼ O),
k
2
1
660 m (>C ¼ N), 1286 (>C-O), 1186 m (-C-N). Elemental analysis, Anal. Calcd
(C H N O ): C 70.09, H 4.50, N 14.42, found: C 70.05, H 4.60, N 14.44. ESI-MS: (m/z)
1
7 13 3 2
þ
2
92.30 [M þ H] .
2
.3. Synthesis of fpoly[bis(m-((E)-N’-((2-hydroxynaphthalen-1-yl)methylene)
4 1 1 2 3 2
isonicotinohydrazido-j O :N :O :N )bis(m-methanol-j O:O)dimanganese(II)]g (1)
A methanolic solution (4 mL) of Mn(OAc) ꢂ4H O (12 mg, 0.05 mmol) and a DMF solu-
2
2
tion (2 mL) of H L (15 mg, 0.05 mmol) were prepared [29, 30]. The methanolic solution
2
of manganese acetate tetrahydrate was carefully layered over the DMF solution of the
ligand. Brown crystals were obtained after 30 days. 8.5 mg (70%). They were used for
ꢀ
1
further characterization. FT-IR (KBr, cm ): Complex 1 3029 (aromatic –CH), 1667
2
1
(
(
>C ¼ O), 1614 (>C ¼ N ), 1596 (>C ¼ N ), 1332 (C-N), 1194 (C-O), 535 (Mn-O), 493
ꢃ
ꢃ
Mn-N). UV–Vis for 1 (DMF, k , nm): p-p (314–327 nm), n-p (337–400 nm). Elemental
analysis: Anal. calcd f[MnL(m-MeOH)] g ꢂ2n(H O): C 54.83, H 4.35, N 10.66%, found: C
max
2
n
2
5
5.05, H 4.50, N 10.52%.
2.4. X-ray crystallography
The data of 1 were collected at 150 K in a Bruker SMART APEX II CCD detector and
graphite-monochromatic Mo Ka radiation (k ¼ 0.71073) at low temperature. The struc-
2
ture was solved by direct methods using SHELXT [31] and refined on F by full-matrix
least-squares methods using SHELXL [32]. Non-hydrogen atoms were refined aniso-
tropically. H-atoms were allowed to ride on their respective atoms with U values ꢀ1.2
ij
for aromatic CH groups. The SQUEEZE routine [33] in PLATON was used to remove the
electron density distributed in voids. The hydrogen atom attached to the oxygen of

JOURNAL OF COORDINATION CHEMISTRY
5
coordinated methanol molecules could not be identified from difference fourier. The
SQUEEZE routine was able to recover 364 electrons per unit cell, equivalent to one
methanol and 0.5 water molecule per asymmetric unit as disordered solvent accom-
modated in the solvent-accessible void. The final R (all data) values converged to
R1 ¼ 0.0456 and wR2 ¼ 0.0834.
3. Results and discussion
3.1. Synthesis and general spectroscopic characterization
The ligand (H L) (E)-N’-((2-hydroxynaphthalen-1-yl)methylene)isonicotinohydrazide was
2
synthesized by condensation of isonicotinichydrazide with 2-hydroxy-1-naphthalde-
hyde as per the reported literature [28]. The mass spectrum of the ligand is consistent
with the expected molecular mass of the compound (Figure S1, Supporting
1
Information). The H NMR spectrum of the ligand shows a sharp peak at 12.51 and
1
7
2.40 ppm for OH and NH protons, respectively, and the peaks in the range 9.47 to
.22 ppm can be assigned to aromatic protons (Figure S2, Supporting Information).
ꢀ
1
The IR spectrum of H L displays a broad band at 3436 cm which is due to the asym-
metric stretching of the naphthol –OH group, while the band at 3226 cm is due to
the hydrazinic -NH stretching (Figure S3, Supporting Information). In 1, the broad
band at 3428 cm may be due to the presence of hydrogen-bonded water molecules
trapped in the lattice. The ligand displays a strong band at 1680 cm corresponding
2
ꢀ
1
ꢀ
1
ꢀ
1
to > C¼O is stretching, which disappeared in 1, owing to the enolisation. The band at
ꢀ
1
1
660 cm corresponding to the > C¼N- stretching frequency in the ligand is shifted
ꢀ1
to 1596 cm in 1, indicating coordination of azomethine nitrogen atom. The band at
ꢀ
1
1
614 cm may arise from the newly formed > C¼N- bond. The UV-visible spectrum of
the ligand shows bands at 326 nm and 363 nm and a shoulder at 374 nm. These bands
can be assigned to the n-p
ꢃ transition in the ligand backbone and the azomethine
group. A series of three bands observed at 439 nm, 466 nm and 496 nm are character-
ꢃ
istic of the p-p transitions of the naphthyl group [34]. The nature and position of the
latter set of bands depend on strong intramolecular hydrogen bonding between the
hydroxyl group of the naphthyl group and the azomethine nitrogen [35]. The UV-vis-
ible spectrum of the complex (Figure S4, Supporting Information) show bands at
ꢃ
3
4
38 nm and 352 nm corresponding to n-p transitions, while the bands at 430 nm,
60 nm and 478 nm may result from the coordinated azomethine group and modifica-
tion of the energy of the naphthyl backbone upon coordination [12]. The XPS spec-
trum of 1 shows (Figure S5, Supporting Information) peaks at 642.3 and 654.8 eV
which correspond to the binding energies of the spin-orbit splitting components of
Mn 2p3/2 and 2p1/2, respectively, in the þ2 oxidation state of the metal. The value of
Mn 2p3/2 is slightly shifted to higher binding energy due to the bonding of the metal
with higher electronegativity atoms [36, 37].
3.2. X-ray diffraction studies
The molecular structure of 1 with the atom numbering scheme is shown in Figure 1.
Crystallographic refinement parameters are provided in Table 1. Important bond

6
P. BHATTACHERJEE ET AL.
Figure 1. A plot of the repeating unit of 1 drawn with 50% probability ellipsoid.
Table 1. Crystal data and structure refinement for 1.
Empirical formula
36 2 6 6
C H30Mn N O
Formula weight
Temperature/K
Wavelength/Å
Crystal system
Space group
752.54
150(2)
0.71073
Tetragonal
1
I 4 /a
ꢁ
Unit cell dimensions
a ¼ 29.1685(13) Å, a ¼ b ¼ c ¼ 90
b ¼ 29.1685(13) Å
c ¼ 8.8458(5) Å
7526.0(8)
3
Volume/Å
Z
8
3
Density/Mg/m
Absorption coefficient/mm
1.328
0.721
ꢀ
1
F(000)
Crystal size/ mm
Theta range for data collection/
Index ranges
Reflections collected
Independent reflections
3088
3
0.200 ꢄ 0.160 ꢄ 0.120
ꢁ
ꢁ
1.396 to 25.436
ꢀ35ꢅh ꢅ 35, ꢀ35ꢅk ꢅ 35, ꢀ10ꢅl ꢅ 10
36361
3484 [R(int) ¼ 0.0684]
Completeness to theta ¼ 25.242
100.0%
Absorption correction
Semi-empirical from equivalents
0.916 and 0.868
Full-matrix least-squares on F
Max. and min. transmission
Refinement method
2
Data/restraints/parameters
Goodness-of-fit on F
3484/0/227
1.066
2
Final R indices [I > 2sigma(I)]
R indices (all data)
Largest diff. peak and hole
R1 ¼ 0.0325, wR2 ¼ 0.0795
R1 ¼ 0.0456, wR2 ¼ 0.0834
0.521 and ꢀ0.343 e.Åꢀ
3

JOURNAL OF COORDINATION CHEMISTRY
7
ꢁ
Table 2. Selected bond lengths (Å) and angles ( ) for 1.
Bond lengths (Å)
Mn(1)-O(3)
Mn(1)-O(1)
Mn(1)-O(2)
1.8994(15)
1.9159(14)
1.9199(14)
Mn(1)-N(1)
1.9671(18)
2.2428(14)
2.3662(18)
a
Mn(1)-O(3)
b
Mn(1)-N(3)
ꢁ
Bond angles ( )
b
b
b
b
O(3)-Mn(1)-O(1)
O(3)-Mn(1)-O(2)
O(1)-Mn(1)-O(2)
O(3)-Mn(1)-N(1)
O(1)-Mn(1)-N(1)
O(2)-Mn(1)-N(1)a
O(3)-Mn(1)-O(3)a
O(1)-Mn(1)-O(3)a
O(2)-Mn(1)-O(3)
97.73(6)
93.72(6)
168.48(6)
173.08(7)
89.00(7)
79.59(6)
81.48(6)
88.21(6)
94.72(6)
97.21(6)
92.50(6)
O(1)-Mn(1)-N(3)
O(2)-Mn(1)-N(3)
86.82(6)
91.48(6)
89.46(7)
171.62(6)
44.82(4)
93.38(5)
95.61(5)
133.53(5)
36.66(4)
137.01(5)
N(1)-Mn(1)-N(3)
a
O(3) -Mn(1)N(3)
O(3)-Mn(1)-Mn(1)
O(1)-Mn(1)-Mn(1)
O(2)-Mn(1)-Mn(1)
a
a
a
a
N(1)-Mn(1)-Mn(1)
a
a
a
O(3) -Mn(1)-Mn(1)
N(3) -Mn(1)-Mn(1)
a
b
N(1)-Mn(1)-O(3)
O(3)-Mn(1)-N(3)
b
a
b
Symmetry transformations used to generate equivalent atoms: ꢀx þ 1/2, ꢀy þ 1/2, ꢀz þ 1/2, ꢀx þ 3/4, y ꢀ 1/4,
z ꢀ 1/4.
lengths and angles are listed in Table 2. A thermal ellipsoidal plot of the [Mn L (l-
2
2
MeOH) ] repeating unit of 1 is shown in Figure 1.
2
The crystal structure determination of 1, [Mn L (l-MeOH) ] , reveals that the doubly
2
2
2 n
2-
deprotonated ligand (L ) binds with ONO donor atoms viz, phenolate oxygen atom
O1), one imine nitrogen atom (N1) and one oxygen atom (O2). The metal ion is fur-
(
ther coordinated by two methanol molecules in a m -bridging mode. The sixth coord-
2
ination site of Mn(II) is bound by the pyridine nitrogen atom (N3) of another ligand
unit (Figure S6, Supporting Information). The equatorial bond lengths Mn–O1, Mn–O2,
Mn-O3 and Mn-N1 are 1.9159(14), 1.9199(14), 1.8994(15) and 1.9671(18) Å, respectively.
a
b
However, the axial bond lengths Mn-O3 (a ¼ x þ 1/2, ꢀy þ 1/2, ꢀz þ 1/2) and Mn-N3
(
b ¼ y ꢀ 1/4, ꢀx þ 3/4, z ꢀ 1/4) are 2.2428(14) and 2.3662(18) Å, respectively, indicating
axial elongation. The bond lengths are consistent with Mn-O bond lengths of low-spin
manganese(II) complexes reported elsewhere (Table S1, see Supporting Information)
[
38]. The values of distorted octahedral geometry of this Mn complex are satisfied by
ꢁ
a
the bond angles (O3-Mn1-O1 ¼ 97.73(6) , O1-Mn1-O3 (a ¼ x þ 1/2, ꢀy þ 1/2, ꢀz þ 1/2)
ꢁ
ꢁ
a
¼
88.21(6) , O3-Mn1-N1 ¼ 173.08(7) , N1-Mn1-O3 (a ¼ x þ 1/2, ꢀy þ 1/2, ꢀz þ 1/2) ¼
ꢁ
9
7.21(6) . The distortion can also be gauged from the angle variance (r ) and quad-
oct
ꢁ
2
ratic elongation parameter (koct) whose values, 31.95( ) and 1.024, respectively, indi-
cate moderate distortion. The pyridyl ring is twisted compared to the rest of the
ꢁ
metal-ligand moiety with the dihedral angle 14.77 in the asymmetric unit of the
coordination polymer. The bridging of the methanol molecules leads to formation of
the Mn O dimanganese center with a Mn … Mn distance of 3.146 Å. The Mn-O-Mn
2
2
ꢁ
angle measures 98.52 , which falls within the range reported for other dinuclear com-
plexes having low-spin Mn(II) at the core [26d–f]. The dimanganese [Mn L (m-MeOH) ]
2
2
2
units are connected to other similar units via the pyridyl N3 atom of the isonicotinoyl
group. Each Mn O unit acts as a node and leads to a puckered 4-connected closed
2
2
loop; each such closed loop is further connected to each other via an N3 atom of a pyridyl
group of the isonicotinic moiety. These inter-loop connectivity leads to a square-like cavity
propagating along the c-direction in a helical fashion. Strong p-p stacking interactions and

8
P. BHATTACHERJEE ET AL.
Figure 2. A diagram showing the clustering of the naphthyl groups in 1.
favorable C-H … p interactions appear to stabilize the coordination polymer (Table S2 and
Figure S7, see Supporting Information). These interactions favor a clustering of naphthyl
groups along the channels formed by 4-connected closed loops, while the helical channels
appear to hold solvent molecules along the 4-fold screw axis (Figure 2). The program
3
PLATON finds a solvent-accessible void corresponding to 422 (Å) , and an unresolved elec-
tron density of 91 electrons, which can be roughly estimated to the presence of four
methanol and two water molecules in each of the 4-fold helical channel. Partial network
connectivity of this coordination polymer is shown in Figure 3.
3.3. Epr study of 1
The solid-state EPR spectrum of the sample at room temperature gives a broad signal
with giso ¼ 2.023, indicating the presence of a weakly coupled manganese(II) dinuclear
center (Figure S8, Supporting Information) [39]. To understand the integrity of 1 in
solution, the X-band EPR spectrum was measured at 77 K in DMF (Figure 4). The EPR
spectrum is anisotropic, giving a well resolved six-line signal. The EPR simulation with
I ¼ 5/2 gives a best-fit with the parameters g ¼ 2.005, g ¼ 2.010, g ¼ 2.0015 and
x
y
z
g
¼ 2.005. This anisotropy is known to arise due to the presence of distortion in the
iso
molecular geometry from the perfect octahedral symmetry [40]. The appearance of six
lines indicates the coupling of the electronic spin of Mn(II), to the nuclear spin of

JOURNAL OF COORDINATION CHEMISTRY
9
Figure 3. A simplified network connectivity of 1.
Figure 4. The X-band EPR spectrum of 1 recorded at 77 K in DMF. Experimental (black) and simu-
lated (red). Inset: half-field signal of 1.
5
5
Mn (I ¼ 5/2) and that the contribution from axial zero-field splitting parameter (D) is
ꢀ
4
ꢀ1
marginal. The hyperfine coupling constants A ¼ 75, A ¼ 36, A ¼ 95 (ꢄ10 cm
)
x
y
z
indicate that the electronic delocalization is not equivalent in the bonds formed by

1
0
P. BHATTACHERJEE ET AL.
ꢀ
1
Figure 5. Cyclic voltammogram of 1 (0.75 Mm) with scan rate 100 mVs in DMF. (The resting
potential is indicated by 1 mark).
manganese(II) [41]. The weak signal observed at half-field with g value 4.88 can be
inferred as arising from the methanol-bridged dinuclear Mn … Mn core.
3.4. Electrochemical study of 1
Cyclic voltammetry is widely used to study the redox properties of transition metal com-
plexes. Therefore, the redox properties of 1 were investigated using cyclic voltammetry.
The complex dissolves appreciably only in DMF and has limited solubility in acetonitrile
and methanol. Hence, the cyclic voltammogram of 1 at a concentration of 0.75 mM was
n
recorded in dry DMF containing 0.1 M [( Bu) N]ClO as supporting electrolyte in a three-
4
4
electrode system containing glassy carbon electrode as a working electrode, a platinum
wire as counter electrode and calomel electrode as a reference electrode. In order to have
an idea about the oxidation state of the manganese present, the resting potential of the
complex was obtained. The value of ꢀ0.09 V indicates that the manganese metal ion is in
þ2 oxidation state. A cyclic voltammetric potential sweep was performed in the potential
ꢀ
1
range þ0.5 V to ꢀ0.6 V vs. SCE at 100 mV s to minimize the interference, owing to lig-
and based redox processes which occurs beyond this range (Figure 5). Cyclic voltammetric
ꢀ
1
scan of 1 at different scan rates of 50, 100, 150 and 200 mVs were performed within
the same potential range (Figure S9, Supporting Information) to check the redox property
of the manganese complex. The experiment was performed with anodic scan first, fol-
lowed by cathodic scan. The solution of 1 in DMF displays a quasi-reversible one-electron
II
II
II
III
redox process at E1/2 ¼ ꢀ0.03 V corresponding to the Mn -Mn /Mn -Mn redox couple
II
III
III
III
and another one at E1/2 ¼ þ0.4 V originating from the Mn -Mn /Mn -Mn redox couple.
II
III
The anodic scan gives a peak for the Mn /Mn redox couple at E ¼ ꢀ0.0046 V and the
pa
cathodic scan gives a peak at E ¼ ꢀ0.07 V with a peak to peak separation of (DE ¼
pc
p
III
III
Epa ꢀ E ) 65 mV for Mn /Mn redox couple at E ¼ þ0.43 V and the cathodic scan gives
pc
pa
a peak at E ¼ þ0.37 V with a peak to peak separation of (DE ¼ E ꢀ E ) 100 mV. The
pc
p
pa
pc
peak current ratio, I /I ¼ 0.71, 0.83 and E ¼ ꢀ0.03 and þ0.4 V vs. SCE, respectively,
pa pc
1/2

JOURNAL OF COORDINATION CHEMISTRY
11
Figure 6. (a) Increase in absorption intensity with time after addition of 100 equivalent of 3,5-
DTBCH to a solution containing complex in 1 in DMF; (b) Initial rates vs [substrate] for the oxida-
2
tion reaction by 1 as a catalyst in DMF. Lineweaver–Burk plot is given as inset.
II
II
II
III
II
III
III
III
corresponds to the metal centered Mn -Mn /Mn -Mn and Mn -Mn /Mn /Mn redox
processes. In order to identify whether the cortical oxidation is in fact catalyzed by 1, a
potential sweep of 1 (0.75 mM) was performed in the presence of catechol (15 equivalent)
in the potential range ꢀ0.8 V to þ1.7 V under nitrogen atmosphere. The voltammogram
displayed an anodic peak at þ0.93 V corresponding to catechol oxidation, which is found
to appear at the same potential in the absence of 1. However, in the presence of oxygen
a potential scan in the same potential window displayed an increase in catalytic current
beyond þ1.6 V. This indicates that 1 catalyzes catechol oxidation in the presence of oxy-
gen only (Figure S10, Supporting Information).
3.5. Catecholase activity of 1
In most of the studies involving catechol oxidase activity, 3,5-di-tert-butylcatechol (3,5-
DTBCH ) is used as a model substrate due to ease of oxidation of substrate to its cor-
2
responding quinone, 3,5-di-tert-butylquinone (3,5-DTBQ). No further oxidation is
observed due to the bulkier groups present in the substrate [42]. The oxidized sub-
strate 3,5-DTBQ also shows a characteristic strong absorption at ca. 400 nm which
helps monitor the progress of the catalytic reaction. In order to study the catecholase
ꢀ
4
activity of the manganese complex, a 0.25 ꢄ 10 M solution of complex in DMF was
prepared and was treated with 100 fold of 3,5-DTBCH in the same solvent (Figure 6a).
2
The progress in the oxidation of the substrate under aerobic conditions was moni-
tored by recording UV–visible spectra of the reaction mixture every 5 minutes up to a
total time of 60 min after mixing. A gradual increase in the intensity of the spectra is
an indication of the formation of more 3,5-DTBQ, which can be due to the catechol
oxidase activity of the manganese complex. A control experiment performed in exactly
the same conditions, without the manganese complex as the catalyst, show no change
in the absorption intensity at 400 nm, indicating the absence of conversion of 3,5-
DTBC into 3,5-DTBQ.
The kinetic study of the catalysis was monitored by performing a set of time-scans
ꢁ
at the band maximum of the product (quinone) at a fixed temperature of 25 C. The

1
2
P. BHATTACHERJEE ET AL.
Table 3. Comparison of catecholase activity by various compounds.
ꢀ1
ꢀ1
Catalyst
V
max (Ms
)
K
M
(M)
k
cat (h
)
Ref.
(1.89 ± 0.04)ꢄ10ꢀ
7
(2.89 ± 0.26)ꢄ10
ꢀ4
ꢀ4
27.22
17.2
25.4
17.0
44
This work
[23]
[23]
[23]
[45]
[45]
[45]
[45]
[44]
Complex 1
III
a
ꢀ7
ꢀ7
ꢀ7
[
[
[
[
[
[
[
[
[
[
Mn L(OAc)(H
2
O)]
O)]ꢂDMF
a
(1.19 ± 5.57)ꢄ10
(7.73 ± 1.5)ꢄ10
ꢀ4
III
a
Mn L(N
3
)(H
2
(1.76 ± 0.6.414)ꢄ10
(10.2 ± 1.4)ꢄ10
ꢀ4
III
Mn L(NCS)(H
2
O)]
)(N-C
)(N-C
)(H-HPTB)](ClO
)(H-HPTB)](ClO
indH)(H O) (CH CN)](ClO
(H O)(ClO )](ClO
(pyz) (C CH
(1.18 ± 6.31)ꢄ10
(6.22 ± 1.5)ꢄ10
b
Mn
Mn
Mn
Mn
2
2
2
2
(O
(O
(O
2
2
2
2
CCH
CC
CCH
CC
3
H
3
H
H
2 5
-HPTB)](ClO
4
)
4
2
)
–
–
–
–
–
–
–
–
b
2
6
5
2
H
5
-HPTB)](ClO
24
8
8
b
4
)
4
2
)
b
(O
6
5
2
’
c
ꢀ7
ꢀ3
Mn(6 Me
2
2
2
3
4
)
2
23 ꢄ 10
12.7 ꢄ 10
48.8
126.9
2547
II
d
ꢀ4
ꢀ5
ꢀ4
Mn (bpy)
2
2
4
4
)
(63.6 ± 6.48)ꢄ10
(36 ± 1.04)ꢄ10
ꢀ4
[46]
[43]
III
II
e
Mn
2
Mn
4
O
2
2
6
H
5
2
COO)10
]
n
(7.076 ± 16.2)ꢄ10
(1.745 ± 0.32)ꢄ10
a
L ¼ N,N’-ethylenebis(3-ethoxysalicylaldimine), solvent DMF.
b
c
0
0
HPTB ¼ N,N,N ,N -tetrakis(2-benzimidazolylmethyl)-2-hydroxo-1,3-diaminopropane, solvent MeOH.
’
6
Me
2
indH ¼ 6’-methyl-2-pyridylimino)isoindoline, solvent DMF.
bpy ¼ bipyridine, solvent MeOH.
pyz ¼ pyrazine, solvent CH CN.
d
e
3
ꢀ
4
concentration of the complex was kept constant at 0.25 ꢄ 10 M, and the concentra-
ꢀ
3
ꢀ2
tion of the 3,5-DTBCH varied from 0.25 ꢄ 10 M to 0.25 ꢄ 10 M. The initial rate
2
method was used for determining the rate constant for the catalyst, complex 1. At
lower concentrations of the substrate, first-order kinetics were observed, indicating
substrate-catalyst binding in the initial stage of the catalytic reaction [43]. The rate
constant vs. substrate concentration was measured on the basis of the
Michaelis–Menten equation to get the Lineweaver–Burk plot and the parameters Vmax
,
KM and Kcat (Figure 6b). A comparison of the catecholase activity of the manganese
complex with other similar manganese-based catalysts reported in DMF is presented
in Table 3. It can be observed that for a mononuclear manganese(II) complex, reported
elsewhere, the Kcat value appears to be higher in DMF medium [23, 44]. For
manganese(II) dinuclear complexes in methanol medium reported elsewhere [45], the
turnover number is found to be lower than for 1 we have reported here. For a 1 D
Mn(II) coordination polymer in methanolic medium the Kcat value is higher than those
reported for mononuclear complexes [46], but is lower than the one observed in an
II
III
Mn /Mn hexanuclear cluster [43]. It can be observed from the mass spectral data
Figure S11, Supporting Information) that the complex breaks down to a dinuclear
(
species, which may be responsible for catecholase activity in solution. From the above
observations, it can be concluded that the lower activity displayed by 1 may be due
to the electron deficient nature of the ligand used.
The aerobic catechol oxidation reaction is generally assumed to involve the release
of H O during the catalytic cycle. Therefore, to identify the presence of H O during
2
2
2 2
catechol oxidation, the starch-iodide test was performed. For this test, a starch-potas-
sium iodide mixture was added to the mixture of 1 and 3,5-DTBCH . If H O is
2
2 2
released during the catechol oxidation reaction, the hydrogen peroxide is expected to
react with the potassium iodide releasing I . The molecular iodine released forms an
2
inclusion complex with starch, giving a blue color. In our experiment, the blue color-
ation was observed during the starch-iodide test, indicating the release of H O . Based
2
2
on the above observation, a plausible mechanism of the catechol oxidation reaction
by the manganese complex is suggested as given in Scheme 2. The catalytic cycle is
initiated by the loss of the proton from the bridging methanol which then abstracts a

JOURNAL OF COORDINATION CHEMISTRY
13
Scheme 2. A plausible mechanism for catechol oxidation under aerobic condition catalyzed by 1.
proton from a hydroxyl group of the catechol, leading to the formation of methanol
which remains coordinated to Mn . The dioxygen then attacks the coordinatively
1
unsaturated Mn . The coordinated peroxide radical ion then abstracts the second
2
phenolic hydrogen atom from the catecholate species. This leaves behind a phenolate
radical ion which quickly rearranges to the DTBQ radical. The DTBQ radical is then
quickly converted to free 3,5-DTBQ; the odd electron is likely to get transferred to the
Mn(III) of the dinuclear Mn core by tunnelling via the Mn(III)-peroxide bond. This is
2
followed by the release of H O by the abstraction of a proton from coordinated
2
2
methanol on Mn , regenerating the catalytic Mn core.
1
2
4. Conclusion
II
A new manganese coordination polymer, [Mn (L) (MeOH) ] , was synthesized from a
2
2
2 n
tetradentate ligand H L by a self-assembly process. The two manganese(II) metal ions
2
are connected by two methanol molecules in a m -bridging mode. The dinuclear
2
assembly is further linked via the pyridyl nitrogen atoms to form a three-dimensional
coordination polymer. The network formed has 4-connected closed loops linked by 4-
fold helical connectivity. The compound displays moderate catecholase like activity in
aerobic condition with concomitant release of H O .
2
2

1
4
P. BHATTACHERJEE ET AL.
Acknowledgements
The authors, PB and RJ, thank the Department of CSS, IACS Kolkata for facilitating X-ray single
crystal data collection and PB thanks IIT(ISM) Dhanbad for financial support, National Taiwan
University for XPS. The authors also acknowledge Dr. S.K. Padhi for cyclic voltammetry measure-
ments and fruitful discussions.
Disclosure statement
No potential conflict of interest was reported by the author(s).
ORCID
Rohith P. John
http://orcid.org/0000-0003-3175-027X
References
[1] A. Sigel, H. Sigel. Manganese and Its Role in Biological Processes. Metal Ions in Biological
Systems, Vol. 37, Marcel Dekker, New York (2000).
[
2] (a) K.D. Karlin, J. Tyekl ꢀa r (Eds.), Bioinorganic Chemistry of Copper, Chapman & Hall, New
York (1993);(b) G.C. Dismukes. Chem. Rev., 96, 2909 (1996);(c) M.M. Najafpour, S. Heidari,
S.E. Balaghi, M. Hoły nꢀ ska, M.H. Sadr, B. Soltani, M. Khatamian, A.W. Larkum, S.I.
Allakhverdiev. Biochim. Biophys. Acta, 1858, 156 (2017).
[3] (a) T.N. Nguyen, M. Shiddiq, T. Ghosh, K.A. Abboud, S. Hill, G. Christou. J. Am. Chem. Soc.,
1
37, 7160 (2015);(b) T.A. Jenkins, M. Garnero, S.A. Corrales, E.R. Williams, A.M. Mowson, A.
Ozarowski, W. Wernsdorfer, G. Christou, C. Lampropoulos. Inorg. Chem., 56, 14755 (2017).
4] (a) W. Liu, K. Lee, M. Park, R.P. John, D. Moon, Y. Zou, X. Liu, H.-C. Ri, G.H. Kim, M.S. Lah.
Inorg. Chem., 47, 8807 (2008);(b) R.P. John, M. Park, D. Moon, K. Lee, S. Hong, Y. Zou, C.S.
Hong, M.S. Lah. J. Am. Chem. Soc., 129, 14142 (2007);(c) R.P. John, K. Lee, B.J. Kim, B.J.
[
Suh, H. Rhee, M.S. Lah. Inorg. Chem., 44, 7109 (2005).
[
5] L. Radovanovi ꢀc , J. Rogan, D. Poleti, M.V. Rodi ꢀc , N. Begovi ꢀc . Inorg. Chim. Acta, 445, 46
(2016).
[
[
6] S.K. Dey, M. Hazra, L.K. Thompson, A. Patra. Inorg. Chim. Acta, 443, 224 (2016).
7] L.E. Kreno, K. Leong, O.K. Farha, M. Allendorf, R.P. Van Duyne, J.T. Hupp. Chem. Rev., 112,
1
105 (2012).
8] A.H. Chughtai, N. Ahmad, H.A. Younus, A. Laypkov, F. Verpoort. Chem. Soc. Rev., 44, 6804
2015).
9] T.K. Maji, S. Sain, G. Mostafa, T.H. Lu, J. Ribas, M. Monfort, N.R. Chaudhuri. Inorg. Chem.,
2, 709 (2003).
[
[
(
4
[
[
10] J.L. Manson, A.M. Arif, J.S. Miller. Chem. Commun., 1479 (1999).
11] (a) H.J. Chen, Z.W. Mao, S. Gao, X.M. Chen. Chem. Commun., 2320 (2001). (b) E.R.H. Wang,
Q. Gao, M.C. Hong, S. Gao, J.H. Luo, Z.Z. Lin, L. Han, R. Cao. Inorg. Chem., 42, 5486 (2003).
12] H. Hosseini-Monfared, S. Alavi, P. Mayer. Inorg. Chim. Acta, 419, 89 (2014).
13] P. Kar, A. Ghosh. Inorg. Chim. Acta, 395, 67 (2013).
[
[
[
14] J.W. de Boer, W.R. Browne, J. Brinksma, P.L. Alsters, R. Hage, B.L. Feringa. Inorg. Chem., 46,
6353(2007).
[
[
15] H. Liang, Y.-X. Ji, R.-H. Wang, Z.-H. Zhang, B. Zhang. Org. Lett., 21, 2750 (2019).
16] (a) M.K. Singh, G. Rajaraman. Inorg. Chem., 58, 3175 (2019);(b) K.R. Vignesh, S.K. Langley,
C.J. Gartshore, B. Moubaraki, K.S. Murray, G. Rajaraman. Inorg. Chem., 56, 1932 (2017).
17] C. Choe, Z. Lv, Y. Wu, Z. Chen, T. Sun, H. Wang, G. Li, G. Yin. J. Mol. Catal., 438, 230
[
(2017).

JOURNAL OF COORDINATION CHEMISTRY
15
[
[
[
18] (a) J.-W. Wang, D.-C. Zhong, T.-B. Lu. Coord. Chem. Rev., 377, 225 (2018);(b) G. Maayan, N.
Gluz, G. Christou. Nat. Catal., 1, 48 (2018).
19] G.N. Ledesma, H. Eury, E. Anxolab ꢀe h ꢁe re-Mallart, C. Hureau, S.R. Signorella. J. Inorg.
Biochem., 146, 69 (2015).
20] (a) D. Mondal, M.C. Majee. Inorg. Chim. Acta, 465, 70 (2017);(b) A. Panja, N. Ch. Jana, S.
Adak, K. Pramanik. Inorg. Chim. Acta, 459, 113 (2017).
[
[
[
[
21] P. Halder, S. Paria, T.K. Paine. Chem. Eur. J., 18, 11778 (2012).
22] S. Paria, P. Halder, T.K. Paine. Angew. Chem. Int. Ed., 51, 6195 (2012).
23] P. Chakraborty, S. Majumder, A. Jana, S. Mohanta. Inorg. Chim. Acta, 410, 65 (2014).
24] T.P. Camargo, F.F. Maia, C. Chaves, B. de Souza, A.J. Bortoluzzi, N. Castilho, T. Bortolotto,
H. Terenzi, E.E. Castellano, W. Haase, Z. Tomkowicz, R.A. Peralta, A. Neves. J. Inorg.
Biochem., 146, 77 (2015).
[
[
25] S. Majumder, S. Mondal, P. Lemoine, S. Mohanta. Dalton Trans., 42, 4561 (2013).
26] (a) C.-I. Yang, Z.-Z. Zhang, S.-B. Lin. Coord. Chem. Rev., 289, 289 (2015);(b) M. Mitra, A.K.
Maji, B.K. Ghosh, G. Kaur, A.R. Choudhury, C.-H. Lin, J. Ribas, R. Ghosh. Polyhedron, 61, 15
(2013);(c) Y. Gultneh, T.B. Yisgedu, Y.T. Tesema, R.J. Butcher. Inorg. Chem., 42, 1857 (2003);
(d) X. Tang, J. Hua, H. Li, K. Jiang, L. Sun, Y. Ma, R. Yuan. Inorg. Chim. Acta, 441, 126
(2016);(e) D.J. Fanna, Y. Zhang, L. Li, I. Karatchevtseva, N.D. Shepherd, A. Azim, J.R. Price,
J. Aldrich-Wright, J.K. Reynolds, F. Li. Inorg. Chem. Front., 3, 286 (2016);(f) C.-G. Yan, M.-J.
Zhu, J. Sun, W.-L. Liu, Y.-C. Shi. J. Coord. Chem., 60, 1083 (2007);(g) Y. Yang, L. Zhang, L.
Liu, G. Liu, J. Guo, D. Jia. Struct. Chem., 18, 909 (2007).
[
[
[
[
[
27] S. Stoll, A. Schweiger. J. Magn. Reson., 178, 42 (2006).
28] D.R. Richardson, P.V. Bernhardt. J. Biol. Inorg. Chem., 4, 266 (1999).
29] N.S. Biradar, R.H. Raythatha, V.B. Mahale. Curr. Sci., 45, 124 (1976).
30] A. Ahmed, M. Dalia, H. Fatmaa. Aust. J. Basic Appl. Sci., 9, 42 (2015).
31] (a) G.M. Sheldrick, SHELXT-2014/7, Program of Crystal Structure Solution, University of
G o€ ttingen, G o€ ttingen, Germany (2014);(b) G.M. Sheldrick. Acta Crystallogr., Sect. A, 71, 3
(2015).
[32] (a) G.M. Sheldrick, SHELXL-2014/7, Program for the Solution of Crystal Structures, University
of G o€ ttingen, G o€ ttingen, Germany (2014);(b) G.M. Sheldrick. Acta Crystallogr., Sect. C, 71, 3
(2015).
[
[
[
33] A.L. Spek. Acta Crystallogr. C Struct. Chem., 71, 9 (2015).
34] A.A. Gahr. Spectrochim. Acta Part A, 46, 1751 (1990).
35] S.P. Sovilj, V.M. Vasi ꢀc , D.L. Stoji ꢀc , B. Stoj ꢂc eva-Radovanovi ꢀc , L.T. Petkovska. Spectrosc. Lett.,
3
1, 1107 (1998).
36] C. Zhan, J. Lu, A.J. Kropf, T. Wu, A.N. Jansen, Y.-K. Sun, X. Qiu, K. Amine. Nat. Commun., 4,
437 (2013).
37] D. Asakura, Y. Nanba, M. Okubo, Y. Mizuno, H. Niwa, M. Oshima, H. Zhou, K. Okada, Y.
Harada. J. Phys. Chem. Lett., 5, 4008 (2014).
38] (a) A. Saha, P. Majumdar, S. Goswami. J. Chem. Soc., Dalton Trans., 1703 (2000);(b) P. Basu,
A. Chakravorty. Inorg. Chem., 31, 4980 (1992);(c) S. Ganguly, S. Karmakar, C.K. Pal, A.
Chakravorty. Inorg. Chem., 38, 5984 (1999).
[
[
[
2
[39] A. Ray, C. Rizzoli, G. Pilet, C. Desplanches, E. Garribba, E. Rentschler, S. Mitra. Eur. J. Inorg.
Chem., 2009, 2915 (2009).
[40] P. Sarkar, A. Tiwari, A. Sarmah, S. Bhandary, R.K. Roy, C. Mukherjee. Chem. Commun., 52,
10613 (2016).
[
[
[
[
41] T.H. Bennur, D. Srinivas, P. Ratnasamy. Microporous Mesoporous Mater., 48, 111 (2001).
42] J. Mukherjee, R. Mukherjee. Inorg. Chim. Acta, 337, 429 (2002).
43] P. Kar, R. Haldar, C.J. G oꢀ mez-Garc ꢀı a, A. Ghosh. Inorg. Chem., 51, 4265 (2012).
44] J. Kaizer, G. Bar ꢀa th, R. Csonka, G. Speier, L. Korecz, A. Rockenbauer, L. P ꢀa rk ꢀa nyi. J. Inorg.
Biochem., 102, 773 (2008).
[
[
45] A.M. Magherusan, D.N. Nelis, B. Twamley, A.R. McDonald. Dalton Trans., 47, 15555 (2018).
46] S. Ganguly, P. Kar, M. Chakraborty, A. Ghosh. New J. Chem., 42, 9517(2018).