Two new manganese(III) complexes with salicylaldimine Schiff bases: Synthesis, structure, self-assembly and phenoxazinone synthase mimicking activity

Article abstract of DOI:10.1016/j.ica.2016.11.009

Two new mononuclear manganese(III) complexes, [Mn(L¹)₂]ClO₄(1) and [Mn(L²)(NCS)(H₂O)]·DMSO (2), where HL¹?=?3-(N,N-dimethylamino)propyliminomethyl-6-ethoxyphenol, H₂L²

Full text of DOI:10.1016/j.ica.2016.11.009

Accepted Manuscript
Research paper
Two new manganese(III) complexes with salicylaldimine Schiff bases: Synthe-
sis, structure, self-assembly and phenoxazinone synthase mimicking activity
Nandita Sarkar, Mithun Das, Shouvik Chattopadhyay
PII:
S0020-1693(16)30875-1
http://dx.doi.org/10.1016/j.ica.2016.11.009
ICA 17349
DOI:
Reference:
Inorganica Chimica Acta
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25 October 2016
11 November 2016
Please cite this article as: N. Sarkar, M. Das, S. Chattopadhyay, Two new manganese(III) complexes with
salicylaldimine Schiff bases: Synthesis, structure, self-assembly and phenoxazinone synthase mimicking activity,
Inorganica Chimica Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.2016.11.009
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Two new manganese(III) complexes with salicylaldimine
Schiff bases: Synthesis, structure, self-assembly and
phenoxazinone synthase mimicking activity
Nandita Sarkar, Mithun Das, Shouvik Chattopadhyay*
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata - 700032, India.
Tel: +91-33-24572941; e-mail: shouvik.chem@gmail.com
Abstract
Two new mononuclear manganese(III) complexes, [Mn(L1)2]ClO4 (1) and
[Mn(L2)(NCS)(H2O)]·DMSO (2), where HL1 = 3-(N,N-dimethylamino)propyliminomethyl-6-
ethoxyphenol, H2L2 = N,N'-bis(3-ethoxysalicylidene)ethane-1,2-diamine have been prepared and
characterized by elemental analysis, IR, UV–Vis spectroscopy and single crystal X-ray
diffraction studies. Manganese(III) in each complex assumes distorted octahedral geometry.
Supramolecular interactions in these complexes were explored. Both complexes show
phenoxazinone synthase activity but presence of a solvent molecule in the coordination site of
complex 2 makes it more efficient catalyst than complex 1. Therefore these complexes may be
used as functional models for copper(II) containing enzyme, phenoxazinone synthase.
Keywords: Manganese(III), Schiff base, X-Ray structure; Supramolecular interactions,
Phenoxazinone synthase mimicking activity.
1

1. Introduction
Coordination chemistry of manganese with a diverse range of ligands has long been investigated
as an area of considerable interest in inorganic biochemistry [1-4]. Manganese containing redox
enzymes are omnipresent in nature and perform a number of vital functions [5-7]. A large
number of Schiff base complexes of manganese(III) possess suitable biometric properties that
can mimic the structural features of the active site in metalloenzymes, redox and non-redox
proteins [8-9]. Many such complexes are also shown to have interesting catalytic [10-11] and
magnetic properties [12-14]. There has been enhanced interest in the synthesis and
characterization of such complexes for their biological importance [15-18], especially mimicking
the oxygen-evolving compound (OEC) of photosystem II (PSII) [19-20]. They have also been
reported for water oxidation to generate dioxygen [21-22] and have been used to artificially
model PSII [23]. They have also been used to mimic several oxidase enzymes (which catalyze a
kinetically unfavorable reaction of triplet molecular dioxygen to water in various biochemical
pathways) [24-27]. It is very useful and promising area of research to develop more efficient,
bio-inspired and environment friendly catalysts for in vitro oxidation reactions. One of such
enzymes is phenoxazinone synthase, a multicopper oxidase enzyme, found naturally in the
bacterium, Streptomyces antibioticus, which catalyzes the oxidative condensation of ortho
aminophenol derivatives into phenoxazinone chromophore [28-30]. The latter is used clinically
for the treatment of Wilm's tumor, gestational choriocarcinoma, and other tumors in which
phenoxazinone chromophore is recognized to inhibit DNA-dependent RNA synthesis by
intercalation to DNA [31-32].
Studies on the oxidation of o-aminophenol to phenoxazinone by molecular dioxygen in
presence of some mono- and di-nuclear first row transition metal complexes as catalysts have
2

been reported by several groups [33-36]. The essential condition for a complex to have
phenoxazinone synthase activity is the presence of labile sites on the metal centers. In the present
work, we have prepared two manganese(III) Schiff base complexes with two different Schiff
base ligands (one tridentate and one tetradentate). Both complexes have been characterized by
spectral and elemental analysis. Single crystal X-ray diffraction analysis was used to confirm the
structures of both complexes. Phenoxazinone synthase mimicking activities of both the
complexes have been studied. The complex of the tetradentate Schiff base was found to be more
active toward phenoxazinone synthase mimicking activity.
2. Experimental Section
All chemicals were of reagent grade and used as purchased from Sigma-Aldrich without
further purification.
Caution!!! Although no problems were encountered in this work, metal complexes
containing organic ligands in the presence of perchlorates are potentially explosive. Only a small
amount of the material should be prepared and it should be handled with care.
2.1. Preparations
2.1.1. Preparation of the ligand, 3-(N,N-dimethylamino)propyliminomethyl-6-ethoxyphenol
(HL1)
The tridentate Schiff base ligand, HL1 was prepared by refluxing 3-ethoxysalicylaldehyde
(166 mg, 1 mmol) with N,N-dimethylpropane-1,3-diamine (0.13 ml, 1 mmol) in methanol (5
mL) for ca. 1 h. The solvent was evaporated under reduced pressure and the residue of the ligand
was dissolved in acetonitrile. Solid ligand was obtained after 3 days and was used for the
preparation of the complex 1.
2.1. 2. Preparation of the ligand, N,N'-bis(3-ethoxysalicylidene)ethane-1,2-diamine (H2L2)
3

The tetradentate Schiff base ligand, H2L2 was prepared by refluxing 3-
ethoxysalicylaldehyde (332 mg, 2 mmol) and ethane-1,2-diamine (0.1 ml, 1 mmol) in methanol
(5 mL) for ca. 1 h. The solid ligand was isolated and dissolved in acetonitrile. Crystals of the
ligand were obtained one week which were used for the preparation of the complex 2.
2.1.3. Preparation of [Mn(L1)2]ClO4 (1)
A methanol solution of HL1 and the methanol solution (5 mL) of manganese(II)
perchlorate hexahydrate (185 mg, 0.5 mmol) was added to the resulting mixture was refluxed for
ca. 1 h to give a brown solution. It was cooled and kept for slow evaporation in open atmosphere.
Single crystals suitable for X-ray diffraction were obtained after three days.
Yield: 118 mg (42%). Anal. Calc. for C28H42MnN4O8Cl(FW = 663.05): C, 60.75; H,
7.65; N, 10.12%. Found: C, 60.6; H, 7.5; N, 10.3%. ESI-MS (positive ion mode, CH3CN) m/z:
553.47 (100%, [Mn(L1)2]+). IR (KBr, cm-1): 1119 (νClO4), 1609 (νC=N). UV-Vis, λmax (nm) [εmax(L
mol-1 cm-1)] (DMSO): 500 (0.83×102), 292 (1.9×103), 270 (2.1×103). Magnetic moment =
5.13ꢀꢁꢂ.
2.1.4. Preparation of [Mn(L2)(NCS)(H2O)]·DMSO (2)
A methanol solution (5 mL) of manganese(II) perchlorate hexahydrate (370 mg, 1 mmol)
was added to the methanol solution of H2L2 (1 mmol) and the resulting mixture was refluxed for
ca. 1 h to give a deep brown solution. A methanol solution (5 mL) of sodium thiocyanate (80 mg,
1 mmol) was added in it and refluxed further for 1 h. DMSO was added in the mixture as
solvent. It was kept for slow evaporation in open atmosphere. Single crystals suitable for X-ray
diffraction were obtained after one week.
Yield: 462 mg (82%). Anal. Calc. for C23H30MnN3O6S2 (FW = 563.56): C, 49.02; H,
5.37; N, 7.46%. Found: C, 49.0; H, 5.2; N, 7.6%. ESI-MS (positive ion mode, CH3CN) m/z:
4

467.11 (100%, [Na(2-aminophenoxazine-3-one)(H2O)]+), 409.12 (100%, [Mn(L2)]+). IR (KBr,
cm-1):1619 (νC=N), 2063 (νSCN), 3437 (νOH), UV-Vis, λmax (nm) [εmax (L mol-1 cm-1)]
(DMSO): 412 (4.58×102), 324 (1.17×103), 268 (1.55×103). Magnetic moment = 5.14ꢁꢂ.
2.2. Physical measurements
Elemental analyses (carbon, hydrogen and nitrogen) were performed using a PerkinElmer
240C elemental analyzer. IR spectra in KBr (4500-500 cm-1) were recorded with a PerkinElmer
Spectrum Two spectrophotometer. Electronic spectra (800-200 nm) were recorded on a
PerkinElmer Lambda 35 UV-visible spectrophotometer. The magnetic susceptibility
measurement was done with an EG & PAR vibrating sample magnetometer (model 155) at room
temperature and diamagnetic corrections were performed using Pascal’s constants [37]. Powder
X-ray diffraction was performed on a Bruker D8 instrument with Cu Kα radiation (λ = 1.548 Å)
generated at 40 kV and 40 mA. The powder XRD spectrum was recorded in a 2θ range of 5–50°
using 1D Lynxeye detector at ambient conditions. Electro-spray ionization mass spectra were
recorded with Waters QTOF Micro YA263.
2.3. X-ray crystallography
Suitable single crystals of both complexes were used for data collection using a ‘Bruker
SMART APEX II’ diffractometer equipped with graphite-monochromated Mo Kα radiation (λ=
0.71073 Å) at 150 K. The molecular structures were solved by direct method and refined by full-
matrix least squares on F2 using the SHELX-97 package [38-39]. Non hydrogen atoms were
refined with anisotropic thermal parameters. Hydrogen atoms attached with oxygen atom of
coordinated water molecule of complex 2 were located by difference Fourier maps and were kept
at fixed positions. Other hydrogen atoms were placed in their geometrically idealised positions
and constrained to ride on the atoms to which they were attached. Multi-scan empirical
5

absorption corrections were applied to the data using the program SADABS [40].
Crystallographic data and refinement details of complexes are given in Table 1. Selected bond
lengths and bond angles are listed in Tables 2 and 3 respectively.
2.4. Hirshfeld surface Analysis
Molecular Hirshfeld surfaces [41-43] and the associated 2D-fingerprint [44-46] plots
were calculated using Crystal Explorer [47] which accepted a structure input file in CIF format.
Bond lengths to hydrogen atoms were set to standard values. For each point on the Hirshfeld
isosurface, two distances de, the distance from the point to the nearest nucleus external to the
surface and di, the distance to the nearest nucleus internal to the surface, were defined. The
normalized contact distance (dnorm) based on de and di was given by
Where rivdw and revdw were the van der Waals radii of the atoms. The value of dnorm was negative
or positive depending on intermolecular contacts, being shorter or longer than the van der Waals
separations. The parameter dnorm displayed a surface with a red-white-blue colour scheme, where
bright red spots highlighted shorter contacts, white areas represented contacts around the van der
Waals separation, and blue regions were devoid of close contacts. For a given crystal structure
and set of spherical atomic electron densities, the Hirshfeld surface was unique [48] and it was
this property that suggested the possibility of gaining additional insight into the intermolecular
interaction of molecular crystals. The 2D-fingerprint plot provides decomposition of Hirshfeld
surfaces into contribution of different intermolecular interactions present in crystal structure. 2D-
fingerprint plots of each Hirshfeld surface are shown as plots of di against de.
2.6. Catalytic oxidation of 2-aminophenol
6

10-5 M solutions of the complexes in acetonitrile were treated with a 10-3 M solution of o-
aminophenol under aerobic conditions at 25°C. The reaction was followed
spectrophotometrically by monitoring the increase in the absorbance maxima at ~433 nm. 10-5 M
solutions of the complexes were mixed with at least 10 equivalents of substrate to maintain
pseudo-first order conditions to determine the dependence of rate on the substrate concentration
and various kinetic parameters. The rate of a reaction was derived from the initial rate method.
Scheme 1: Synthesis of complexes 1 and 2.
3. Results and discussion
3.1. Synthesis
Two Schiff base ligands HL1 and H2L2, were synthesized by condensation of 3-
ethoxysalicylaldehyde with N,N-dimethylpropane-1,3-diamine and ethane-1,2-diamine,
respectively, following the literature method [49-50]. The IR and UV-Vis data of both ligands
7

are reported in literature [50-51]. The Schiff base ligand, HL1, was made to react with
manganese(II) perchlorate hexahydrate in methanol to prepare the mononuclear manganese(III)
complex, [Mn(L1)2]ClO4 (1). Complex 2 ([Mn(L2)(NCS)(H2O)]·DMSO), on the other hand, was
synthesized by reacting H2L2 with the methanol solution of manganese(II) perchlorate
hexahydrate in presence of pseudohalide thiocyanate. The formation of complexes 1 and 2 is
shown in Scheme 1. In these two complexes manganese(II) get oxidized by the oxygen in the
atmosphere to manganese(III) under the reaction conditions.
It is interesting to note here that the ligand H2L2 was used by a different group to prepare
a very similar manganese(III) complex, [Mn(L2)(SCN)(H2O)].[Mn(L2)(H2O)2]ClO4·CH3CN [51].
The method of preparation of this complex is different from that of complex 2. Many other
manganese(III) complexes, similar to complex 2, were also reported by various groups [52-53].
3.2. Structure descriptions
3.2.1. [Mn(L1)2]ClO4 (1)
ꢃ
Complex 1 crystallizes in the triclinic space group P1. The X-ray structure determination
reveals that in complex 1 there are two independent subunits (A and B). A perspective view of
subunit A along with the selective atom numbering scheme is shown in Figure 1a. The
perspective view and description of the structure of subunit B with selective atom numbering
scheme is given in the Supplementary information.
The molecular structure of subunit A consists of a discrete mononuclear unit
[Mn(L1)2]ClO4. Manganese(III) center is in a six-coordinate octahedral environment, being
bonded to two amine nitrogen atoms, N(1) and N(1)', two imine nitrogen atoms, N(2) and N(2)'
and two phenoxo oxygen atoms, O(2) and O(2)' (Symmetry transformation: ' = -x,-1-y,2-z), from
-
two deprotonated Schiff base ligands (L1) , which occupy facial positions (fac isomer). The six
8

membered ring, [Mn(1)–N(1)–C(17)–C(18)–C(19)–N(2)], has an intermediate conformation
between chair and half chair, with puckering parameters q = 0.753(4) Å, θ = 163.6(4)°, φ =
166.5(12)° [54-55]. The N(1)–Mn(1)–N(2) angle is 80.17(12)°. The Mn(1)–Nimine distance
{2.026(3) Å} is shorter than the Mn(1)–Namine distance {2.420(3) Å}.
The hydrogen atom, H(15b), attached with C(15), is involved in C–H···π interaction with
a symmetry related (1-x,-1-y,2-z) phenyl ring [C(21)-C(22)-C(23)-C(24)-C(25)-C(28)] to form a
supramolecular chain (Figures 1b and 1c). Details of geometric features of C–H···π interactions
are given in Table 4.
3.2.2. [Mn(L2)(NCS)(H2O)]·DMSO (2)
ꢃ
Complex 2 crystallizes in the triclinic space group P1. The asymmetric unit
consists of mononuclear [Mn(L2)(NCS)(H2O)] unit and a solvent DMSO molecule. A
perspective view of the complex with the selective atom numbering scheme is shown in Figure 2.
Manganese(III) is coordinated by two imine nitrogen atoms, N(1) and N(2), and two phenolate
oxygen atoms, O(1) and O(2), of the deprotonated tetradentate Schiff base ligand (L2)2-. Oxygen
atom, O(3), of water molecule and nitrogen atom, N(3), of thiocyanate coordinate
manganese(III) centre to complete a distorted octahedral geometry. The saturated five membered
ring, [Mn(1)–N(1)–C(10)–C(11)–N(2)], twisted on C(10) and C(11) with puckering parameters q
= 0.353(8) Å, φ = 263.0(8)° [54-55]. Coordinated water ligands of two symmetry related (i = 2-
x,2-y,1-z) mononuclear manganese(III) species, are connected through intermolecular hydrogen
bonding interactions. The hydrogen atom, H(3A), attached with oxygen atom, O(3), form
bifurcated hydrogen bonds with symmetry related (2-x,2-y,1-z) oxygen atoms, O(1)i and O(4)i.
Similarly hydrogen atom, H(3B), attached with oxygen atom, O(3), form bifurcated hydrogen
bonds with symmetry related (2-x,2-y,1-z) oxygen atoms, O(2)i and O(5)i. Similar type of
9

hydrogen bonding is shown by hydrogen atoms H(3A)i and H(3B)i. Due to hydrogen bonding a
well isolated supramolecular dimer has been created (Figure 2). Details of hydrogen bonding are
given in Table 5.
The hydrogen atom, H(23A), attached with C(23), is involved in C–H···π interaction
with a symmetry related (2-x,2-y,2-z) phenyl ring [C(13)-C(14)-C(15)-C(16)-C(17)-C(18)] to
form a supramolecular dimer as shown in Figure 3a. Details of geometric features of C–H···π
interactions are given in Table 4.
The π···π stacking interaction occurs between the phenyl ring [C(3)-C(4)-C(5)-C(6)-
C(7)-C(8)] and the symmetry related (2-x,2-y,1-z) phenyl ring [C(13)-C(14)-C(15)-C(16)-C(17)-
C(18)] of neighbor molecule (Figure 3b). Details of geometric features of π···π stacking
interactions are given in Table 6.
3.3. IR, electronic spectra and magnetic property
In the IR spectra of both complexes, distinct bands due to the azomethine (C=N) group
within 1608–1619 cm-1 region are customarily noticed [56]. Strong band at 1119 cm-1 of 1
indicates the presence of perchlorate ion [57]. Complex 2 shows a strong and sharp band at 2063
cm-1 due to presence of nitrogen bonded thiocyanate group [58].
The electronic absorption spectra of two complexes were recorded in DMSO. Absorption
bands at 268-270 nm region are assigned to ligand to metal charge transfer (LMCT) bands from
the phenolate oxygen pπ→dπ* of metal orbital. Bands at 292-324 nm region is due to n→π*
transitions of (C=N). Appearance of absorption bands within the ranges of 412-501 nm is due to
spin allowed d–d transition band. [59-61].
10

The room temperature magnetic susceptibility measurements show that both complexes
have magnetic moments close to 5.1ꢀꢁꢂ. This value is expected for discrete, high-spin (S = 2),
magnetically non-coupled manganese(III) complexes having four unpaired electrons [62-63].
3.4. Powder X-ray diffraction
The experimental PXRD patterns of the bulk products are in good agreement with the
simulated XRD patterns from single crystal X-ray diffraction results, indicating consistency of
the bulk samples (Figures S2a and S2b). The simulated patterns of the complexes were
calculated from the single crystal structural data (Cif files) using the CCDC Mercury software.
3.5. Hirshfeld Surface analysis
The Hirshfeld surface analysis is a powerful method for gaining information about
different intermolecular interactions, and to identify and quantify these interactions. Hirshfeld
surfaces of two complexes, mapped over a 3D dnorm (range of -0.1 to 1.5 Å), shape index and
curvedness, are illustrated in Figure 4. The surfaces are shown as transparent to allow
visualization of the molecular moiety around which they are calculated. The intermolecular
interactions listed in Table 4 are summarized effectively in the spots with the large circular
depressions (deep red) visible on the dnorm surfaces indicative of hydrogen bonding contacts and
other weak contacts. There are several bright red areas on dnorm of both complexes related to C–
H···π interactions. 2D fingerprint plots of Hirshfeld surface for complexes and relative
contributions of different interactions overlapping in the full fingerprint plots are shown in
Figures 5 and 6, respectively. Complementary regions are visible in the fingerprint plots where
one molecule acts as donor (de< di) and the other as an acceptor (de> di). The fingerprint plots
can be decomposed to highlight particular atoms pair close contacts. For both complexes, the
H···H interactions have the highest contribution (67.3% in 1 and 47.9% in 2) of the total
11

Hirshfeld surface. Despite the high share of this interaction, its role in the stabilization of
structure is quite small in magnitude because this interaction is between the same species [64].
C···H/H···C close contacts, attributed to C–H···π interactions, comprise 12.5% and 15.5% of the
total surface for each molecule in 1 and 2, respectively. The high proportion of C···H/H···C
interactions and its appearing as bright red spots on dnorm surface of both complexes is indicating
the importance of this interaction in structures of 1 and 2. The proportion of O···H/H···O
interactions comprise 25.5% and 17.6% of the Hirshfeld surfaces for complexes 1 and 2
respectively. Similarly the proportion of N···H/H···N interactions comprise 3.4% for complex 2.
The figure of 2D fingerprint plot of N···H/H···N interactions is given in Supplementary
information (Figure S3). Complex 1 does not show any proportion of N···H/H···N interactions.
3.6. Phenoxazinone synthase like activity
To check the ability of the complexes to oxidize o-aminophenol to 2-aminophenoxazine-
3-one (Phenoxazinone synthase mimicking activity), 10-3 M acetonitrile solution of o-
aminophenol were mixed separately with 10-5 M solution of each complex, and the spectra were
recorded for 2 h and 5 min at room temperature. It was found that both complexes are showing
phenoxazinone synthase mimicking activity. The time dependent spectral profiles of 1 and 2 are
shown in Figures 7 and 8. The gradual increase of peak (characteristic of the phenoxazinone
absorption) intensity at ~433 nm implies the catalytic conversation of o-aminophenol to 2-
aminophenoxazine-3-one in aerobic conditions. A blank experiment without catalyst under
identical conditions does not show significant growth of the band at ~433 nm.
To understand the extent of the catalytic efficiency, 10-5 M solutions of the complexes
were treated with substrate (o-aminophenol) under pseudo-first order conditions. Time scan at
the λmax of 2-aminophenoxazine-3-one was carried out for a period of 125 min. The initial rate
12

was determined from the slope of the absorbance versus time plot. Rate saturation kinetics of
both complexes is clearly indicated by initial rate of the reaction versus concentration of the
substrate plot. This observation indicates that an intermediate complex substrate adduct is
formed at a pre-equilibrium stage and that the irreversible substrate oxidation is the rate
determining step of the catalytic cycle. This type of saturation rate dependency on the
concentration of the substrate may be treated with the Michaelis-Menten model. This may also,
upon linearization, give a double reciprocal Lineweaver-Burk plot which is used to analyze
different parameters, viz. Vmax (Maximum reaction velocity), KM (Michaelis constant), and Kcat
(Turnover number). The initial rate versus substrate concentration plot and Lineweaver-Burk plot
for complexes 1 and 2 are shown in Figures 9 and 10, respectively. All kinetic parameters of
both complexes are given in Table 7.
3.7. ESI-MS study
The electrospray ionization mass spectra (ESI-MS positive) are useful to know the nature
of possible complex-substrate adduct. The ESI-MS positive spectra of both complexes are
recorded in acetonitrile solution and the results are shown in Figures S4 and S5.
In the mass spectrum of 1, the peak at m/z = 553.47 may be assigned to [Mn(L1)2]+.
Complex 2 exhibits peak at m/z = 409.12 corresponding to the presence of monopositive
[Mn(L2)]+. In the mass spectra of complex 2 with o-aminophenol, peak at m/z =467.11 may be
assigned as [Na(2-aminophenoxazine-3-one)2(H2O)]+ and indicates the formation of
phenoxazinone from 2-aminophenol. The mass spectrum of the mixture of complex 2 with o-
aminophenol is shows in Figure 11. Based on the above results a probable mechanism for
oxidation of O-aminophenol has been proposed (Scheme 2).
13

Scheme 2: Probable mechanistic pathway for the formation of phenoxazinone.
4. Conclusion
Two new octahedral manganese(III) complexes with a Schiff base ligand have been
prepared and characterized. X-ray crystal structure determination confirmed the structures of the
complexes. In complex 1 Schiff base act as a tridentate ligand and form bis complex, whereas, in
complex 2, the dianionic tetradentate Schiff base and pseudohalide ligand occupy five
coordinating sites and the remaining site is coordinated by water molecule. Both complexes are
found to show phenoxazinone synthase mimicking activity but complex 2 is found to be more
active. During the course of catalytic cycle, o-aminophenol has to coordinate the manganese(III)
center by replacing any one coordinated ligand. Since water is a neutral molecule (and not at all
bulky), it could be easily replaced by o-aminophenol and makes complex 2 more efficient
catalyst than 1.
14

Acknowledgments
N.S. thanks the UGC, India, for awarding a Junior Research Fellowship. Crystallographic
data were collected at the DST-FIST, India, funded by Single Crystal Diffractometer Facility at
the Department of Chemistry, Jadavpur University.
Appendix A. Supplementary data
CCDC 1461265 and 1461266 contain the supplementary crystallographic data for
complexes 1 and 2 respectively. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk
15

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20

Table 1: Crystal data and refinement details of complexes 1 and 2
1
2
C23H30MnN3O6S2
563.56
C28H42MnN4O4ClO4
653.05
Formula
Formula Weight
Temperature (K)
Crystal System
Space group
a (Å)
150
150
Triclinic
Triclinic
ꢃ
P1
ꢃ
P1
8.7492(6)
10.4830(7)
19.3978(13)
75.538(4)
89.356(4)
69.253(4)
1605.2(2)
2
11.1318(7)
11.9760(4)
11.9946(4)
114.502(1)
107.042(2)
95.745(2)
1345.26(1)
2
b (Å)
c (Å)
α (˚)
β (˚)
γ (˚)
V(Å3)
Z
dcal (g cm-3
1.391
1.351
)
µ (mm-1)
0.687
0.546
688
F(000)
588
22534
Total reflection
Unique Reflections
20178
6199
5025
4481
Observed data[I>2σ(I)]
R(int)
4258
0.027
0.035
0.0825, 0.1808
0.0594, 0.1648
R1, wR2 (all data)
0.0841, 0.2428
0.0753, 0.2301
R1, wR2 [I>2σ(I)]
21

Table 2: Selected bond lengths (Å) around manganese (III) for complexes 1 (subunit A) and 2
1
2
_
Mn(1)-O(1)
Mn(1)-O(2)
Mn(1)-O(3)
Mn(1)-O(4)
Mn(1)-N(1)
Mn(1)-N(2)
Mn(1)-N(3)
1.880(4)
1.881(4)
2.336(3)
_
1.862(2)
_
_
2.420(3)
2.026(3)
_
1.978(5)
1.975(5)
2.246(4)
22

Table 3: Selected bond angles ( ° ) for complexes 1 (subunit A) and 2
1
2
_
O(1)-Mn(1)-O(2)
O(1)-Mn(1)-O(3)
O(1)-Mn(1)-N(1)
O(1)-Mn(1)-N(2)
O(1)-Mn(1)-N(3)
O(2)-Mn(1)-O(3)
O(2)-Mn(1)-N(1)
O(2)-Mn(1)-N(1)a
O(2)-Mn(1)-N(2)
O(2)-Mn(1)-N(2)a
O(2)-Mn(1)-N(3)
O(3)-Mn(1)-N(1)
O(3)-Mn(1)-N(2)
O(3)-Mn(1)-N(3)
N(1)-Mn(1)-N(2)
N(1)-Mn(1)-N(2)a
N(1)-Mn(1)-N(3)
N(2)-Mn(1)-N(3)
93.76(16)
90.66(14)
91.77(18)
172.56(17)
96.52(16)
90.04(14)
172.91(19)
_
_
_
_
_
_
90.96(12)
89.05(12)
89.15(12)
91.83(18)
_
90.86(12)
_
92.58(16)
85.46(16)
84.43(16)
172.18(16)
82.3(2)
_
_
_
80.17(12)
99.83(12)
_
_
_
91.20(18)
88.12(18)
Symmetry transformations: a = -x,-1-y,2-z of subunit A of 1.
23

Table 4: Geometric features (distances in Å and angles in °) of the C–H···π interactions obtained
for complexes 1 and 2.
X–H···Cg (Ring)
C(15)-H(15b)···Cg(5)c
C(23)-H(23A)···Cg(5)d
H···Cg (Å) X–H···Cg (°)
X···Cg (Å)
3.753(5)
2.83
2.89
162
143
1
2
3.697(12)
Symmetry transformations: c = 1-x,-1-y,2-z; d = 2-x,2-y,2-z
Cg(5) = Centre of gravity of the ring [C(21)-C(22)-C(23)-C(24)-C(25)-C(28)] for 1 and Cg(5) =
Centre of gravity of the ring [C(13)-C(14)-C(15)-C(16)-C(17)-C(18)] for 2.
Table 5: Hydrogen bond distances (Å) and angles (°) for 2.
D–H···A
D-H
0.85
0.85
0.84
0.84
H···A
2.34
2.21
2.21
2.31
D···A
2.34
2.24
2.21
2.31
∠D-H···A
131
O(3)-H(3A)···O(1)e
O(3)-H(3A)···O(4)e
O(3)-H(3B)···O(2)e
O(3)-H(3B)···O(5)e
160
141
149
Symmetry transformation: e = 2-x,2-y,2-z D = donor; H = hydrogen; A = acceptor.
24

Table 6: Geometric features (distances in Å and angles in °) of the π···π stacking interactions
obtained for 2.
Cg(Ring I)···Cg(Ring J)
Cg(4)···Cg(5)f
Cg···Cg(Å)
3.653(3)
α (°)
Cg(I)···Perp (Å)
-3.369(2)
Cg(J)···Perp (Å)
-3.388(2)
2.2(3)
Symmetry transformation: f = 2-x,2-y,1-z.
α = Dihedral angle between ring I and ring J. Cg(I)···Perp = Perpendicular distance of Cg(I) on
ring J. Cg(J)···Perp = Perpendicular distance of Cg(J) on ring I. Cg(4) = Centre of gravity of the
ring [C(3)-C(4)-C(5)-C(6)-C(7)-C(8)] and Cg(5) = Centre of gravity of the ring [C(13)-C(14)-
C(15)-C(16)-C(17)-C(18)] for 2.
Table 7: Kinetic parameters of Phenoxazinone synthase like activity at 25°C in CH3CN.
Complex
Vmax (M min-1 )
1.064 x10-5
KM (M)
2.2 x 10-3
6.8x 10-3
Kcat (h-1)
60
1
2
5.135 x 10-5
308.13
25

Figure 1: (a) Perspective view of 1 with selective atom numbering scheme. Symmetry
transformation a =-x,-1-y,2-z. (b) Highlighted C–H···π interactions and (c) 1D array of 1 via C–
H···π interactions. Selected atoms have been omitted for clarity.
26

Figure 2: Perspective view of 2 with the supramolecular dimeric structure which generated
through intermolecular hydrogen bonding interactions. Symmetry transformation i = 2-x,2-y,2-z.
Only the relevant atoms are labeled. Ethyl groups attached to oxygen atoms have been omitted
for clarity.
27

Figure 3: Supramolecular dimer in 2, (a) generated through C–H···π interactions and (b)
generated through π···π interactions. Selected atoms have been omitted for clarity.
28

Figure 4: Hirshfeld surfaces mapped with dnorm (top), shape index (middle) and curvedness
(bottom). dnorm displayed a surface with a red-white-blue colour scheme, where bright red spots
highlighted shorter contacts, white areas represented contacts around the van der Waals
separation, and blue regions were devoid of close contacts.
29