Cooperative influence of pseudohalides and ligand backbone of Schiff-bases on nuclearity and stereochemistry of cobalt(iii) complexes: Experimental and theoretical investigation

Article abstract of DOI:10.1039/c7dt03040a

Four cobalt(iii) complexes, [Co(HL¹)(NCS)₂(EtOH)] (1), [Co₂(L¹)₂(N₃)₂] (2) and [Co(HL²)(NCS)₂(EtOH)] (3), [Co(HL²)(N₃)₂] (4) were synthesized from two Schiff-base ligands namely, (E)-2-((2-(2-hydroxyethylamino)ethylimino)methyl)phenol (H₂L¹) and (E)-2-((3-(2-hydroxyethylamino)propylimino)methyl)phenol (H₂L²), respectively. All the four complexes have been thoroughly characterised by using various physicochemical studies such as UV-Vis, FT-IR, ESI-MS, EPR and single crystal X-ray diffraction. Depending on flexibility of the ligand backbone subtle structural differences are observed in the synthesized complexes. In complex 1 the two thiocyanate ligands are trans to each other whereas in complex 3 they are cis to each other with addition of one additional methylene (-CH₂-) group to the ligand system. Complex 2 is dinuclear while complex 4 is mononuclear in the presence of the azide co-anionic ligand. Theoretical studies are carried out in order to rationalize the structural differences observed in the complexes. Catecholase like activity of all the four complexes were performed in N,N-dimethylformamide (DMF) using 3,5-di-tert-butylcatechol (3,5-DTBC) as a model substrate. Complex 2 was found to exhibit the highest activity. Mechanistic investigation of the catecholase like activity revealed the formation of the imine radical during catalytic reactions of complexes 2 and 4 which are further corroborated by the EPR study.

Full text of DOI:10.1039/c7dt03040a

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Cooperative Influence of Pseudohalides and Ligand Backbone of Schiff-bases on
Nuclearity and Stereochemistry of Cobalt(III) Complexes: Experimental and
Theoretical Investigation
Arnab Mandal, a Sanchari Dasgupta, a Sumi Ganguly, a Antonio Bauzá, b Antonio Frontera,*, b
and Debasis Das*, a
a Department of Chemistry, University of Calcutta, 92, A. P. C. Road, Kolkata – 700009,
India.
b
Departament de Química, Universitat de les Illes Balears, Crta. de Valldemossa km 7.5,
07122, Palma (Baleares), Spain
Abstract:
Four cobalt(III) complexes, [Co(HL1)(NCS)2(EtOH)] (1), [Co2(L1)2(N3)2] (2) and
[Co(HL2)(NCS)2(EtOH)] (3), [Co(HL2)(N3)2] (4) were synthesized from two Schiffꢀbase
ligands namely, (E)ꢀ2ꢀ((2ꢀ(2ꢀhydroxyethylamino)ethylimino)methyl)phenol (H2L1) and (E)ꢀ
2ꢀ((3ꢀ(2ꢀhydroxyethylamino)propylimino)methyl)phenol (H2L2), respectively. All the four
complexes have been throughly characterised by using various physicochemical studies such
as UVꢀVis, FTꢀIR, ESIꢀMS, EPR and Single crystal Xꢀray diffraction. Depending on
flexibility of the ligand backbone subtle structural differences are observed in the synthesized
complexes. In complex 1 the two thiocyanate ligand are trans to each other whereas in
complex 3 it is cis to each other with addition of one extra methylene(ꢀCH2ꢀ) group in the
ligand system. Complex 2 is dinuclear while complex 4 is mononuclear in presence of azide
coꢀanionic ligand. Theoretical studies are carried out in order to rationalize the structural
differences observed in the complexes. Catecholase like activity of all the four complexes
were performed in N,Nꢀdimethylformamide (DMF) using 3, 5 ꢀdiꢀtertꢀbutylcatechol (3, 5ꢀ
DTBC) as model substrate. Complex 2 was found to exhibit the highest activity. Mechanistic
investigation of catecholase like activity revealed the formation of imine radical during
catalytic reactions of complex 2 and 4 which are further corroborated by the EPR study.
Introduction:
In the past few decades, cobalt(II/III) complexes of Schiffꢀbase ligands having different
nuclearity draw an immense attention because of their potential application in the field of
catalysis for the oxidation of organic functionalities, bioꢀmimicking models of several
1

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metalloenzymes such as cyanocobalamin, supramolecular chemistry, magnetochemistry etc.1ꢀ
9
Nuclearity of the complexes plays a vital role especially when they are used as
biomimicking models and nuclearity of complexes in turn depends on several factors such as
nature of the ligand and coligands, solvent, nature of the metal etc. As far as nature of ligand
is concerned the crucial contributing factors are backbone flexibilty, denticity, steric and
electronic factors of the chelate ring, cavity size (for cyclic ligands) etc.10ꢀ15 Anionic coꢀ
ligands having ability to coordinate in more than one way, e.g. SCNꢀ, N3 etc., may impart
ꢀ
additional interesting features in nuclearity as well as in stereochemistry of the resulting
complexes.16 In this present work two Schiffꢀbase ligands i.e., (E)ꢀ2ꢀ((2ꢀ(2ꢀ
hydroxyethylamino)ethylimino)methyl)phenol
(H2L1)
and
(E)ꢀ2ꢀ((3ꢀ(2ꢀhydroxyꢀ
ethylamino)propylimino)methyl)phenol (H2L2) were purposefully designed to investigate the
role of ligand backbone owing to one methylene –CH2– group difference in collaboration
ꢀ
with two pseudohalides SCNꢀ and N3 towards the structural variations and stereochemistry of
cobalt(III) complexes (Scheme 1) and to explore the catecholase like activity of the resulting
CoIII
complexes,
namely
[Co(HL1)(NCS)2(EtOH)]
(1),
[Co2(L1)2(N3)2]
(2),
[Co(HL2)(NCS)2(EtOH)] (3), [Co(HL2)(N3)2] (4). Here it is noteworthy that since the
discovery of the crystal structure of the met form of catechol oxidase enzyme, a Typeꢀ3
copper protein responsible for catalysing the oxidation of catechol to quinone,17 considerable
research activities have been done in order to mimic the active site structure and to rationalize
the fuction of the metalloenzyme.18ꢀ26 Over the last decade our group have also reported
several metal complexes as model sytem for catechol oxidase enzyme.27ꢀ36 Nevertheless,
there have been systematic efforts from various other groups to understand the role of non
copper complexes as mimics for catechol oxidase. In this context it has to be mentioned here
that reports where cobalt complexes have been studied as a model system for catechol
oxidase are sancty. However, there is almost no report where mechanistic pathways of
catecholase activity of such cobalt containig systems have been portrayed. Considering the
fact that cobalt(II/III) system could be a good alternative of CuII system for catecholase like
activity, in this report we have used cobalt(III) complexes as model system for
catecholase23,37 and predicted the possible pathways of the catalysis. A structure property
correlation have also been established to get better insight into the mechanistic details of the
catalysis. In order to understand the origin of the genesis of different nuclearity or structural
variation in coordination complexes with particular metal and ligand system theoretical
investigation becomes an obvious choice to the chemists. Here also we have performed
2

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extensive DFT calculations to rationalize the observed structural variation in our synthesized
complexes.
Scheme 1. Synthetic route of complexes 1ꢀ4.
Results and discussion
Synthesis of metal complexes
Complexes 1 and 2 were prepared by adding cobalt(II) perchlorate hexahydrate to the Schiffꢀ
base formed in situ in ethanolic medium via condensation between salicylaldehyde and 2ꢀ[(2ꢀ
Aminoethyl)amino]ethanol followed by addition of sodium thiocyanate and sodium azide,
respectively. Complexes 3 and 4 were synthesized in similar manner with only change of the
amine,
i.e
2ꢀ[(3ꢀaminopropyl)amino]ethanol
was
used
instead
of
2ꢀ[(2ꢀ
Aminoethyl)amino]ethanol. Brown coloured crystals suitable for Xꢀray diffraction were
obtained in all the cases.
FT-IR spectral study of the complexes:
All four complexes were initially characterized by the FTꢀIR spectra. For all the four
complexes a sharp band in the region of 1622ꢀ1641 cmꢀ1 is observed as a signature of C=N
stretching. The four spectra consist of a band at 1444ꢀ1448 cmꢀ1 region due to benzene
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skeletal vibration. For complex 1 a sharp peak at 2092 cmꢀ1 is observed due to presence of
thiocyanate anion whereas for complex 3 a doubly splitted band at 2133 and 2078 cmꢀ1 is
assigned to thiocyanate anion, thus suggesting that thiocyanate ion may present in transꢀ
orientation for complex 1 and in cisꢀorientation for complex 3 (Fig.1). This is further
confirmed by XꢀRay crystal structure analysis (vide infra). The peaks at 2021 cmꢀ1 is
observed in the spectra of complex 2 and 4 which is characteristics of azide anion. (Fig. S1ꢀ
S2). 38
(a)
(b)
Fig. 1 FTꢀIR spectra of (a) complex1 and (b) complex 3.
UV-Vis spectral study of the complexes:
The electronic spectra of these compounds were recorded in DMF medium. The complexes
show a broad absorption band at 379, 388, 390, 390 nm for complex 1ꢀ4 respectively. This
band arises due to ligandꢀtoꢀmetal charge transfer transitions for all four complexes.
(Fig.S3).39
Crystal Structure description:
Complex 1 [Co(HL1)(NCS)2(EtOH)]: Crystal structure analysis revealed that complex 1
crystallizes in the monoclinic P21/c space group. The asymmetric unit contains one symmetry
independent of HL1 ligand, one CoIII centre, two coordinated isothiocyanate anion and one
lattice occluded ethanol molecule. As illustrated in Fig.2, the central CoIII has been chelated
by the ligand HL1 by two oxygen atoms coming from phenoxo and hydroxo moiety and two
nitrogen atoms coming from imine and amine moiety. The distorted octahedral coordination
4

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sphere of the metal ion has been completed by two isothiocyanate anions coordinating at the
axial positions. Relevant bond distances and bond angles are summarized in Table S1 (in SI).
The distortion in the equatorial bond angles is presumably due to the difference in the
strength of chelation in oxygen and nitrogen atoms of HL1. In the crystal structure two
independent mononuclear units form dimer in head to tail fashion through hydrogen bonding
interactions involving the lattice occluded ethanol molecule.
Fig. 2 Crystal structure illustration of complex 1: (a) ORTEP diagram with 30% probability
of ellipsoids; (b) coordination geometry of the central CoIII ion; (c) hydrogen bonded dimer of
1 involving the lattice occluded ethanol molecule.
Complex 2 [Co2(L1)2(N3)2]: Complex 2 is a dinuclear species with a crystallographic
inversion centre present between two CoIII atoms. This compound crystallizes in the
monoclinic P21/n space group and the asymmetric unit is composed of one symmetry
independent L1 ligand, one CoIII ion and one coordinated azide moiety. The coordination
geometry of the central CoIII ion in 2 is quite analogues with that of the complex 1. As shown
in Fig. 3, the central metal ion adopts an octahedral geometry in which ligand L1 binds with
the metal centre equatorially in similar chelating fashion as observed in 1. One of the apical
positions is occupied by coordinated azide moiety and the other site is occupied by a bridging
oxygen atom coming from another symmetry related L1 ligand. It is worth mentioning here
that the flexibility of the ligand backbone plays a crucial role in such oxo bridging in 2 which
appears to be responsible for its dinuclear structure. The Co…Co distance in the dinuclear
motif is 2.994(3) Å and the Co…O…Co bond angle is 99.21˚ (the other relevant bond
distance and bond angles are given in table S1 in SI). The crystal structure is further
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stabilized by CꢀH…π interactions involving the the hydrogen atoms belonging to the alkyl
moiety and the phenyl ring of the ligand [C–H…centroid 3.418(5) Å)].
Fig. 3 Crystal structure illustration of complex 2: (a) ORTEP diagram with 30% probability
of ellipsoids; (b) coordination geometry of the central CoIII ion.
Complex 3 [Co(HL2)(NCS)2(EtOH)]: This complex crystallizes in the centrosymmetric
2
ꢀ
triclinic P1 space group where the asymmetric unit contains one symmetry independent HL
ligand, one CoIII centre, two coordinated isothiocyanate anion and one lattice occluded
ethanol molecule. The central metal ion assumes an octahedral geometry as observed in
previous two cases. The equatorial sites are coordinated by two oxygen atoms (phenoxo and
hydroxo) and one nitrogen atom (imine) coming from the ligand and one coordinated
isothiocyanate anion (Fig. 4). Selected bond lengths are bond angles are summarized in Table
S2. Surprisingly one of the axial sites has been coordinated by amine nitrogen atom of HL2
and at the other site there is another coordinated isothiocyanate anion. Such a change in the
binding mode of HL2 could be attributable to the increased flexibility which occurs due to the
presence of an excess methylene moiety at the ligand backbone. Further structural analysis
reveals that the complex forms 1D chain running along crystallographic a axis involving the
hydroxo oxygen and lattice occluded ethanol molecule.
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Fig. 4 Crystal structure illustration of complex 3: (a) ORTEP diagram with 30% probability
of ellipsoids; (b) coordination geometry of the central CoIII ion; (c) hydrogen bonded
2
ꢀ
Complex 4 [Co(HL )(N3)2]: This complex crystallizes in the triclinic P1 space group with
one symmetry independent HL2 ligand, one CoIII metal ion and two coordinated azide groups
in the asymmetric unit. As depicted in Fig. 5, the metal ion has been coordinated by the HL2
with two oxygen atoms (phenoxo and hydroxo) and two nitrogen atoms (imine and amine) at
the equatorial positions. The rest two sites are occupied by the coordinated azide groups. The
relevant bond lengths and bond angles are summarized in table S2 in SI. Unlike complex 2,
herein we have observed the formation of mononuclear species. However, each
monocnuclear unit forms dimer in head to tail fashion through intermolecular hydrogen
bonding involving.
Fig. 5 Crystal structure illustration of complex 4: (a) ORTEP diagram with 30% probability
of ellipsoids; (b) coordination geometry of the central CoIII ion; (c) hydrogen bonded dimer of
4.
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Table 1 Crystallographic data and refinement parameters for complexes 1-4.
1
2
3
4
CCDC Number
1566997
1566998
1566999
1567000
C16H22CoN4O3S2 C16H22CoN4O3S2
Empirical formula C15H19CoN4O3S2 C22H28Co2N10O4
Formula weight 426.39 614.02
441.43
364.27
0.32×0.25×0.16 0.27×0.18×0.07
0.20×0.15×0.07
0.34×0.22×0.13
Crystal size/mm
Crystal system
Space group
a/Å
Monoclinic
P21/n
Monoclinic
P21/n
Triclinic
Triclinic
ꢀ
1
ꢀ
1
P
P
10.088(3)
12.859(3)
14.791(4)
90
9.090(7)
6.708(5)
21.311(16)
90
8.3859(8)
11.4440(11)
11.5557(12)
65.724(3)
84.537(3)
78.011(3)
988.81(17)
1.483
8.345(4)
9.546(5)
10.597(5)
71.366(7)
67.949(7)
67.949(7)
738.5(6)
1.638
b/Å
c/Å
α
/°
β/°
/°
94.505(3)
90
97.470(7)
90
γ
Volume/Å3
Density
Z
1912.9(9)
1.481
1288.4(17)
1.582
4
2
2
2
F(000)
880.0
631.2
458.0
376.0
µMoKα/mmꢀ1
0.202
0.202
0.202
0.202
Mo Kα radiation λ=0.71073Å
λ=0.71073Å
296(2)
λ=0.71073Å
296(2)
λ=0.71073Å
296(2)
Temperature/K
296(2)
0.0923
0.0628
0.0299
0.0544
Rint
ꢀ12/12,ꢀ15/15,
ꢀ16/18
ꢀ11/10,ꢀ8/8,ꢀ25/25 ꢀ8/10,ꢀ13/13,ꢀ
14/14
ꢀ10/10,ꢀ11/11,ꢀ
13/13
Range of h,k,l
θmin/max/
°
2.025/25.813
2.339/ 25.627
1.933/25.986
2.195/ 26.033
Reflections
13248/3626/2607 7156 / 2400 / 1470 12248/3832/3122 5570 / 2780 /1471
collected/unique/
observed [I>2σ(I)]
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Data/restraints/
parameters
Goodness of fit
on F2
3626/0/230
1.080
2400/1/159
1.295
3832 /3/239
2780/3/211
1.038
0.956
Final
R1=0.0490
wR2=0.1214
R1=0.0708
wR2=0.1357
R1= 0.1150
wR2= 0.3295
R1= 0.1647
wR2= 0.3673
R1= 0.0411
wR2= 0.1022
R1= 0.0527
wR2= 0.1092
R1= 0.0538
wR2= 0.0891
R1= 0.1066
wR2= 0.1134
Rindices[I>2σ(I)]
Rindices(all data)
DFT studies of the complexes
Four new Schiff base complexes have been synthesized and Xꢀray characterized, two of them
using H2L1 (1 and 2) another two using H2L2 (3 and 4). Curiously, the reaction of the H2L1
ligand with Co(ClO4)2 in the presence of NaSCN yields a mononuclar compound (1) and,
conversely yields a dinuclear one in the presence of NaN3 (2, see Fig. 6). However, when the
latter reaction is made using the H2L2 ligand that presents one extra methylene –CH2–between
the amino groups, the obtained complex is mononuclear (4) instead of dinuclear. Finally, the
relative arrangement of the SCNꢀ ligands is trans in mononuclear complex 1 and cis in
mononuclear complex 3.
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Fig. 6 DFTꢀoptimized structures of the experimentally observed complexes 1–4. and some
hypothetical complexes varying either the nuclearity of the cis/trans arrangement of the
pseudohalide ligands
In this DFT study we wish to rationalize the differences in structures by means of theoretical
calculations. To do so, we have optimized the experimentally obtained structures and also the
hypothetical cis structure in 1 (denoted as 1c), the hypothetical mononuclear structure in 2
(denoted as 2m), the hypothetical trans structure in 3 (denoted as 3t), the hypothetical
dinuclear structure in 4 (denoted as 4d) and finally the hypothetical cis structure in 4 (denoted
as 4c). The geometries of all compounds are shown in Fig. 6.
Rationalization of the cis/trans isomerism in complexes 1 and 3
As aforementioned, the addition of a methylene group at the Schiffꢀbase ligand provokes a
change in the coordination of pseudohalide ligands in 1 and 3 (using the same reaction
conditions). In order to evaluate energetically the stability of the different complexes, we
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have fully optimized the geometries of complexes 1 and 3 starting from the crystallographic
coordinates (see Fig. 7). Moreover, we have also optimized two hypothetical complexes,
denoted as 1c and 3t where the cis arrangement of the SCNꢀ coligands is used in the
optimization of 1c and the trans in the optimization of 3t. In complex 1, the isomer observed
experimentally is more stable (13.8 kcal mol−1 in the gas phase and 8.9 kcal mol−1 in
solution) thus explains the formation of complex 1 with trans arrangement of NCSꢀ ligands.
In the case of compound 3, both isomers (3 and 3t) are basically isoenergetic in solution
(difference 0.7 kcal mol−1) and the 3t is more stable in the gas phase (4.2 kcal mol−1).
Therefore, the observation of complex 3 in the solid state is likely due to packing forces,
which can easily compensate the 0.7 kcal/mol difference between both isomers, as further
explained below.
A likely explanation for the small cis/trans energy difference observed in 3/3t compared to
1c/1 is that the number of methylene groups is smaller in 1. That is, in compound 1 a fiveꢀ
membered chelate ring is formed with less ability to adapt itself to the geometric
requirements of a cis conformation. In compound 3, the sixꢀmembered chelate ring easily
adopts a chair conformation (see Fig. 7) in both isomers, thus explaining the small cis/trans
energetic difference.
Fig. 7 BP86/def2ꢀTZVP optimized complexes and isomerisation energies of complexes 1 and
3. H atoms are omitted for clarity.
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Rationalization of the nuclearity in complexes 2 and 4
Using the same strategy described above for the cis/trans complexes, we have fully optimized
the geometries of the complexes, 2 and 4 starting from the crystallographic coordinates (see
Fig. 8). Moreover, we have also optimized two hypothetical complexes, denoted as 2m and 4d
where a mononuclear and dinuclear systems are used, respectively (see Fig. 8). We have
evaluated the transformation of mononuclear complexes to dinuclear using the equations
shown in Fig. 8. For both compounds 2 and 4, the formation of the mononuclear complex is
more favorable than the dinuclear one, which is in good agreement with the experimental
observation for complex 4 but in disagreement with the observed for compound 2. It should
be mentioned that in the transformation of the mononuclear complex into the dinuclear one
the Hꢀatoms of the hydroxyl groups are lost. This strongly affects the Hꢀbonding ability of the
complexes are their packing in the solid state, which is further analyzed below.
Fig. 8 BP86/def2ꢀTZVP optimized complexes and energies of mononuclearꢀdinuclear
transformations in complexes 2 and 4. H atoms are omitted for clarity.
Rationalization of the cis/trans isomerism in complexes 3 and 4
As aforementioned, in the case of compound 3, both isomers (3 and 3t) are basically
isoenergetic in solution (difference 0.7 kcal mol−1) that is within the accuracy of the
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theoretical method. However, for complex 4 we have found (see Fig. 9) that the trans isomer
observed experimentally is 3.2 kcal mol−1 more stable than the hypothetical cis isomer, thus
explaining the formation of the trans isomer. The difference is reduced to 1.2 kcal mol−1 in
the gas phase.
Fig. 9 BP86/def2ꢀTZVP optimized complexes and isomerisation energies of complex 4. H
atoms are omitted for clarity
Analysis of the solid state crystal structures 1–4.
Selected supramolecular assemblies observed in the solid state Xꢀray structure of compounds
1, 3 and 4 are shown in Fig. 10. It can be observed the presence of coꢀcrystallized solvent
molecules (EtOH) in compounds 1 and 3 that form Hꢀbonding interactions with the Coꢀ
coordinated hydroxyl group (Fig. 10a,b). In addition, both complexes form N–H···SCN
interactions that govern the formation of 1D chains. On the contrary, Compound 4 (azide
instead of SCN) does not exhibit solvent molecules in the solid state and, consequently, it
forms selfꢀassembled Hꢀbonded dimers instead of 1D chains (Fig. 10c).
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Fig.10 Partial view of the Xꢀray solid state structures of compounds 1, 3 and 4. Distances in
Å.
As aforementioned, the cis/trans energy difference in case of compound 3 is in disagreement
with the experimental results. That is, the trans is more stable energetically than the cisand,
conversely, the latter is obtained. We have evaluated energetically the Hꢀbonding interactions
observed in the solid state of complex 1 (trans arrangement) and 3 (cis arrangement), the
results are gathered in Fig.11. The Hꢀbonding interaction between the EtOH and the
complexes is energetically similar in both complexes (around 2 kcal mol−1). The main
difference is the binding energy corresponding to the N–H···SCN Hꢀbond that is
considerably larger in the cis complex (ꢁE3 = –9.2 kcal mol−1) compared to the trans (ꢁE2 =
–4.0kcal mol−1). This difference (5.2 kcal mol−1) compensates the cis/trans energy difference
in compound 3 (4.2 kcal/mol in the gas phase, see Fig 7 bottom), thus explaining the
formation of the cis isomer. However, it is not able to compensate the cis/trans energy
difference in compound 1 (13.8kcal mol−1 in the gas phase, see Fig 7 top), also explaining the
formation of the trans isomer in 1.
Fig. 11 Interaction energies of several dimers of compounds 1 and3. Distances in Å.
Finally, in the case of mononuclear compound 4, the absence of EtOH molecules facilitates
the formation of the selfꢀassembled dimers, which can be only formed in the trans
arrangement because in the cis the Hꢀbonding donor and acceptor groups are not in the
adequate orientation to interact via selfꢀassembly. The energy of the selfꢀassembled dimer is
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ꢁE1 = –9.2 kcal mol−1 (see Fig. 10c) that compensates the dimerization energy (–4.6 kcal/mol
in the gas phase) and explaining the formation of the mononuclear complex. It should be
mentioned that the hydroxyl Hꢀatom is lost in the formation of the dimer, and consequently,
there is not a possibility for form Hꢀbonding interactions (as donor) in the dimer.
ESI-MS study of the complexes
ESIꢀMS study of all the complexes were performed in acetonitrile solvent. Complexes 1, 3
and 4 are present as mononuclear species. For complex 1 base peak is observed at m/z
=265.0484 amu (calcd. 265.0383 amu) which is consistent with molecular formula
+
C11H14CoN2O2 and the base peak for complex 3 and 4 appeared at m/z = 279.0685 amu and
+
279.0719 amu (calcd. 279.0577 amu) corroborate to molecular formula C12H16CoN2O2 .
Complex 2 converted to mononuclear species in solution phase as is evidenced from
observed base peak at m/z = 265.0250 amu (calcd. 265.0387 amu) which is consistent with
+
the molecular formula C11H14CoN2O2 . In solution phase dinuclear complex is also present
with a relative abundance of 40% as is supported with the peak at m/z = 529.0703 amu (calcd.
530.0775 amu).(Fig. S4ꢀS7)
Catecholase like activity
The catecholase like activity of complexes 1-4 were carried out in N,Nꢀdimethylformamide
(DMF) medium using 3,5ꢀDTBC as model substrate and the course of the reaction was
monitored by time dependent UVꢀVis spectroscopy. In case of all the four complexes a peak
~ 400 nm increases (Fig. 12 and S8) and thus it may be inferred that all the four complexes
are active towards the oxidation of 3,5ꢀDTBC. Kinetic study shows that complex 2 exhibits
the highest activity (Table 2) which is likely to be due to the following reasons. Complex 2
contains dinuclear cobalt(III) centre in its active site and the distance between the two cobalt
centres is 2.987Å which is almost comparable to the CuꢀCu centre in native enzyme and that
very structural features is supposed to enhance substrateꢀmetal centers interaction to exhibit
higher catalytic activity. Additionally, complex 2 undergoes dissociation into two
mononuclear species as is supported by ESIꢀMS study and thus one mole of complex 2
contains more active species in compare with one mole of any mononuclear complex studied
here.
Now it is important to detect either H2O or H2O2 which one is generated due to reduction of
diꢀoxygen during oxidation of 3,5ꢀDTBC. There occurs oxidation of Iꢀ to I2 followed by
ꢀ
formation of I3 as was detected in UVꢀVis spectra of the reaction mixture of 3,5ꢀDTBC,
15

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ꢀ
complex and KI. The characteristics bands of I3 were observed at 354 nm and 356 nm for all
four complexes. From the spectroscopic data it is evident that H2O2 is generated as a result of
diꢀoxygen reduction (Fig. S9).
(a)
(b)
Fig. 12 Oxidation of 3,5ꢀDTBC by (a) complex 2 and (b) complex 4 observed in UVꢀVis
spectroscopy with time.
Kinetics study
In order to have an insight about their relative ability towards oxidation of catechol kinetics
study was carried out for all four complexes. The kcat value calculated from the Lineweaver
Burk plot suggested that the catalytic efficiency of complex 2 (29.3 hꢀ1) is the highest among
all four complexes. All the kinetic parameters are given in Table 2. The Lineweaver Burk
plot and plots for enzymatic kinetic for complex 2 and 4 are depicted in Fig. 13 and that of
complex 1 and 3 is depicted in Fig. S10. The kcat values of some previously reported
transition metal Schiffꢀbase complexes are listed in Table 3.22, 23, 36, 40ꢀ44After comparison the
kcat values of the newly synthesized complexes (1-4) and previously reported complexes it
can be said that among the four complexes, complex 2 is moderately efficient catalyst.
Table 2 Kinetic parameters for the activity of complexes 1-4 using 3,5ꢀDTBC as substrate
Complex
Vmax in Ms-1
Km in M
kcat in h-1
R2
SD
5.81×10ꢀ9
8.1×10ꢀ7
5.45×10ꢀ3
3.33×10ꢀ3
0.209
29.3
0.9639
0.9060
0.8023
2.1055
[Co(L1)(NCS)2](1)
[Co2(L1)2(N3)2] (2)
2.10×10ꢀ8
6.6×10ꢀ4
0.756
0.9239
0.5115
[Co(L2)(NCS)2] (3)
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1.11×10ꢀ7
8.17×10ꢀ4
4.00
0.9305
0.5699
[Co(L2)(N3)2] (4)
(a)
(b)
Fig. 13 Dependence of rate of reaction on substrate concentration (inset Lineweaver Burk
plot) for (a) complex 2 and (b) complex 4
Table 3 kcat values of some previously reported Schiffꢀbase complexes
Catalyst
Solvent
kcat(hꢀ1) Ref.year
(1)cisꢀ[CoIII CoII (L)2(MeOH)2(N3)2(ꢂ1,1ꢀN3)2]
ACN
ACN
142
222015
222015
232014
362013
362013
362013
402014
412013
412013
412013
412013
422005
422005
422005
432013
432013
442017
2
(2)transꢀ[CoIII CoII(L)2(H2O)2(N3)2(ꢂ1,1ꢀN3)2]
85
2
(3)[(CoIII (H2L)2(OAc)2)]
9:1 ACN, DMF
MeOH
79.75
447
2
(4)[CoII (HL1)(H2O)2(OAc)2]2+
2
(5)[CoII (L2)(H2O)2(OAc)2]+
MeOH
45.9
2
(6)[CoII (L3)(H2O)2(OAc)2]+
MeOH
42.9
2
(7)[CoII CoIII (HL)2(H2L)2(OAc)2]
9:1 ACN, MeOH
DMF
72.2
3
2
(8)[CoIIICoII(HL1)2(H2O)(EtOH)]+
29700
24300
21400
20100
(9)[CoIIICoII (H2L2)2(L2)Cl2]
MeOH
2
(10)[CoIIICoII(HL1)2(H2O)(EtOH)]+
MeOH
(11)[CoIIICoII (H2L2)2(L2)Cl2]
DMF
2
(12)[CoII (EGTB)(Cl)2]+ pH 8.0
Methanol TrisꢀHCL buffer 7.02
Methanol TrisꢀHCL buffer 1.14
Methanol TrisꢀHCL buffer 0.9
2
(13)[CoII (EGTB)(Cl)2]+ pH 7.6
2
(14)[CoII (EGTB)(Cl)2]+ pH 7.3
2
(15) [NiL1(H2O)3]I2·H2O
(16) [NiL1(H2O)3]Br2·H2O
(17) [Cu2(L1) 2(dca) 2]
MeOH
MeOH
DMF
92.6
82.8
44.5
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(18) [Cu4(L2)4(MeOH)2(ClO4)2]
(1) N,N’ꢀbis(salicylidene)ꢀ1,3ꢀpropanediamine,
hydroxybenzylideneamino)ꢀ2ꢀ(hydroxymethyl)ꢀpropaneꢀ1,3ꢀdiol,
DMF
(3)
120.3
H4L=2ꢀ(3,5ꢀDiꢀtertꢀbutylꢀ2ꢀ
(4)HL1=4ꢀmethylꢀ2,6ꢀ
442017
bis((E)ꢀ((2ꢀ(piperazinꢀ1ꢀyl)ethyl)imino)methyl)phenol, (5)L2= 4ꢀmethylꢀ2,6ꢀbis((E)ꢀ((2ꢀ
(pyridinꢀ2ꢀyl)ethyl)imino)methyl)phenol, 4ꢀmethylꢀ2,6ꢀbis((E)ꢀ((2ꢀ(piperidinꢀ1ꢀ
(6)L3=
yl)ethyl)imino)methyl)phenol, (7)H4L= 2ꢀ(3,5ꢀDiꢀtertꢀbutylꢀ2ꢀhydroxybenzylideneamino)ꢀ2ꢀ
(hydroxymethyl)propaneꢀ1,3ꢀdiol,
(8)H3L1=3ꢀ[(2ꢀHydroxyꢀbenzylidene)ꢀamino]ꢀpropaneꢀ
1,2ꢀdiol,(9) H3L2=3ꢀ[(2ꢀHydroxyꢀ3ꢀmethoxyꢀbenzylidene)ꢀamino]ꢀpropaneꢀ1,2ꢀdiol, (12)
EGTB =N,N,N ,N ꢀtetrakis(2’ꢀbenzimidazolylmethyl)ꢀ1,4ꢀdiethylene amino glycol ether, (15)
HL1 = 2ꢀ[(2ꢀpiperazinꢀ1ꢀylethylimino)methyl]phenol, (17) HL1=4ꢀBromoꢀ2ꢀ[(2ꢀhydroxyꢀ1,1ꢀ
′
′
dimethylꢀethylimino)ꢀmethyl]ꢀphenol,
ethylamino)ꢀmethyl]ꢀphenol.
(18) HL2=4ꢀBromoꢀ2ꢀ[(2ꢀhydroxyꢀ1,1ꢀdimethylꢀ
EPR Study:
To explain the plausible mechanism of catalysis XꢀBand EPR study was carried out at 77 K
in DMF medium. All the four cobalt(III) complexes are EPR silent since it contains six d
electrons in octahedral arrangement. A sharp signal at g
≅ 2 was appeared just after addition
of 3,5ꢀDTBC to complex solution in 1:10 molar ratio (Fig. 14). This signal is characteristics
for organic radical. Since all the complexes are derived from Schiff base ligand, radical is
likely to be generated by the reduction of imine bond as reported earlier eliminating the
possibility of phenoxyl radical and benzyne anion radical.34,35,43 The experimental evidence
thereby suggests that our cobalt(III) complexes most probably catalyse oxidation of catechol
via radical pathway.
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Fig. 14 EPR Spectra of (a) Complex 2 and Complex 2 in presence of 3,5ꢀDTBC and (b)
Complex 4 and Complex 4 in presence of 3,5ꢀDTBC.
Experimental Section
Physical Methods and Materials
Elemental analyses (carbon, nitrogen and hydrogen) have been performed using a
Perkin−Elmer 240C elemental analyzer. FTꢀIR spectra have been recorded on KBr pellet
(400−4000 cm−1) with a Perkin−Elmer RXI FTIR spectrophotometer. Electronic spectra and
kinetic studies (200−900 nm) have been measured at room temperature on a Shimadzu UVꢀ
3101PC using dry DMF as solvent. Electrospray mass spectra have been recorded on a
WATERS Xevo G2ꢀS Q Tof mass spectrometer using HRMS grade acetonitrile as solvent.
Highꢀpurity 2ꢀ[(2ꢀAminoethyl)amino]ethanol, 2ꢀ[(3ꢀaminopropyl)amino]ethanol and
Salicylaldehyde were purchased from commercial sources (Sigma Aldrich) and used as
received. Solvents are dried according to standard procedures and distilled prior to use. All
other chemicals used are of AR grade.
Caution! Perchlorate salts and metal azide complexes are very explosive. Reactions should
be performed carefully.
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Syntheses of Complexes:
Synthesis of [Co(HL1)(NCS)2] (1): To a ethanolic solution (10 ml) of salicylaldehyde (0.122
g, 1 mmol) 2ꢀ[(2ꢀaminoethyl)amino]ethanol (0.104g, 1 mmol) was added and it was refluxed
for 30 minutes to prepare the Schiffꢀ base ligand. Ethanolic solution of cobalt(II) perchlorate
hexahydrate (0.365g,1mmol) was added in situ to ligand and was stirred slowly for 2h. Then
sodium thiocyanate (0.162g, 2 mmol) solution in water: ethanol (1:3 v/v) was added drop
wise to the mixture and was stirred for further 20 min. The dark brown solution was filtered
and was kept in CaCl2 desiccator. Dark brown crystals suitable for Xꢀray data collection were
obtained from filtrate after a week (yield: 0.266g, 70 %). IR (KBr): ν (C=N) 1641 cm−1; ν (Cꢀ
N) 1541 cm−1; ν (skeletal vibration) 1447cm−1; ν(SCN) 2092 cm−1(Fig.S1.); UV/Vis (DMF):
λmax(ε) = 385 nm (3723 L mol−1 cm−1), 476 nm (649 L mol−1 cm−1 ), 597 nm (197 L mol−1
cm−1 ); (Fig. S2.) ;elemental analysis calcd (%) for C13H14N4O2S2Co1: C 40.94, H 3.70, N
14.69, found: C 40.63, H 3.63, N 14.49.
Synthesis of [Co2(L1)2(N3)2](2): Complex 2 was prepared by adopting the same procedure
followed in case of complex 1, only at the end sodium azide (0.130g, 2 mmol) solution in
water: ethanol (1:3 v/v) was added drop wise in place of sodium thiocyanate. The dark
brown solution was filtered and was kept in CaCl2 desiccator. Dark brown crystals for Xꢀray
data collection were obtained from filtrate after a week (yield: 0.454g, 74 %). IR (KBr):
ν(C=N) 1632 cm−1; ν(CꢀN) 1599 cm−1; ν(skeletal vibration) 1444 cm−1; ν(N3) 2020
cm−1(Fig.S1.); UV/Vis (DMF): λmax(ε) = 372 nm (7659 L mol−1 cm−1), 495 nm (1853 L mol−1
cm−1 ) (Fig. S2.) ; elemental analysis calcd (%) for C22H28N10O4Co2: C 43.01, H 4.59, N
22.80, found: C 42.63, H 4.43, N 22.49
Synthesis of [Co(HL2)(NCS)2](3): To a ethanolic solution(10ml) of salicylaldehyde (0.122g,
1 mmol) 2ꢀ[(3ꢀaminopropyl)amino]ethanol (0.104g, 1 mmol) was added and it was refluxed
for 30 minutes to prepare the Schiffꢀ base ligand. Ethanolic solution of cobalt(II) perchlorate
hexahydrate (0.365g,1mmol) was added in situ to ligand and was stirred slowly for 2h. Then
sodium thiocyanate (0.162g,2 mmol) solution in water: ethanol (1:3 v/v) was added drop
wise to the mixture and was stirred for further 20 min. Then sodium thiocyanate (0.162g, 2
mmol) solution in water: ethanol (1:3 v/v) was added drop wise to the mixture and was stirred
for further 20 min. The dark brown solution was filtered and was kept in CaCl2 desiccator.
Dark brown crystals for Xꢀray data collection were obtained from filtrate after a week (yield:
0.304g, 77 %). IR (KBr): ν(C=N) 1622 cm−1;ν(CꢀN) 1540 cm−1; ν(skeletal vibration) 1448
cm−1; ν(SCN) 2078,2133 cm−1(Fig.S1.); UV/Vis (DMF): λmax(ε) = 377 nm (5255 L mol−1
20

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cm−1), 466 nm (840 L mol−1 cm−1 ), 648 nm (214 L mol−1 cm−1 )(Fig. S2.) ;elemental analysis
calcd (%) for C14H17N4O2S2Co1: C 42.42, H 4.32, N 14.13, found: C 42.21, H 4.11, N 14.01.
Synthesis of [Co(HL2)(N3)2](4): Complex 4 was prepared by adopting the same procedure
followed in case of complex 3, only at the end sodium azide (0.130g,2 mmol) solution in
water: ethanol (1:3 v/v) was added drop wise in place of sodium thiocyanate. The dark brown
solution was filtered and was kept in CaCl2 desiccator. Dark brown crystals for Xꢀray data
collection were obtained from filtrate after a week (yield: 0.258g, 71 %). IR (KBr): ν(C=N)
1632 cm−1; ν(CꢀN) 1597 cm−1; ν(skeletal vibration) 1446 cm−1; ν(N3) 2021 cm−1(Fig.S1.);
UV/Vis (DMF): λmax(ε) = 366 nm (6170 L mol−1 cm−1), 509 nm (589 L mol−1 cm−1 ), 635 nm
(156 L mol−1 cm−1 ) (Fig. S2.) ;elemental analysis calcd (%) for C12H17N8O2Co1: C 39.56, H
4.67, N 30.77, found: C 40.03, H 4.43, N 31.19.
X-ray Crystallography:
Singleꢀcrystal Xꢀray di
ff
raction data were collected using Mo Kα (λ = 0.7107 Å) radiation on
ractometer equipped with a CCD area detector. Data collection, data
a BRUKER APEX II di
ff
reduction, and structure solution refinement were carried out using BRUKER APEX II. All
the structures were solved by direct methods and refined using XL (2016). In all the cases,
the non hydrogen atoms are treated anisotropically except for disordered atoms. Whenever
possible, the hydrogen atoms were located on a difference Fourier map and refined. In other
cases, the hydrogen atoms were geometrically fixed. In case of complex 2 the disordered
atoms (C8, C9) are refined by constraints using the PART command, with a total occupancy
of 1. Furthermore, the hydrogen atoms are also fixed at the disordered carbon atoms.
Crystallographic data are summarized in table 1 in the manuscript. CIF files for the structures
reported in this paper have been deposited with the Cambridge Crystallographic Data Centre
(CCDC). CCDCꢀ1566997ꢀ1567000 contains the supplementary crystallographic data for the
paper. Copies of the data can be obtained, free of charge on application to the CCDC, 12
Union Road, Cambridge, CB2 1EZ UK [Fax: 44 (1233) 336 033 eꢀmail:
deposit@ccdc.cam.ac.uk].
Catecholase Like Activity and Kinetics Study of Complexes.
The catecholase like activity of these two complexes were monitored by treating 1
complex solution with 1
10ꢀ2 (M) 3,5ꢀdiꢀtertꢀbutylcatechol (3,5ꢀDTBC) solution under
×
10ꢀ4 (M)
×
aerobic condition at 25 °C. The time dependent wavelength scan was performed in
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acetonitrile medium to understand the potential of two complexes as catalyst towards
oxidation of 3,5ꢀDTBC.
The kinetic study of the oxidation of 3, 5ꢀDTBC by two complexes was performed by initial
rate method at 25 °C. Solutions of substrates of concentration ranging from 0.001 to 0.05 (M)
were prepared from a 1
concentration of the substrate was monitored by UVꢀVis spectroscopy at the respective
wavelength by maintaining the catalyst concentration 1
10ꢀ4(M) for each set. The complexes
×
10ꢀ2 (M) substrate solution. The dependence of the initial rate on the
×
showed saturation kinetics, and a treatment based on the MichaelisꢀMenten model was
applied. The binding constant (KM), maximum velocity (Vmax), and rate constant for
dissociation of the substrates (i.e., turn over number, kcat) were calculated for the complexes
1
using the Lineweaver−Burk graph of versus ꢁ1ꢂ, with the equation (2),
V
S
1
KM
1
1
ꢁ ꢂ
S
=ꢃ
ꢄ×
+
(2)
V
Vmax
Vmax
Detection of Hydrogen Peroxide in the Catalytic Reaction.
To detect the formation of hydrogen peroxide during the catalytic cycle reaction mixtures
were prepared as in kinetic experiments. After 1 hour of reaction equal volume of water was
added and 3,5ꢀDTBQ formed was extracted with dichloromethane. pH of the aqueous layer
was fixed to 2 with H2SO4. 1 mL of a 10% solution of KI and three drops of 3% solution of
ammonium molybdate were added. In the presence of hydrogen peroxide occurs the reaction
H2O2 + 2Iꢀ + 2H+→ 2H2O + I2, and with an excess of iodide ions, the triiodide ion is formed
ꢀ
according to the reaction I2(aq) + Iꢀ= I3 .The reaction rate is slow but increases with
increasing concentrations of acid, and the addition of an ammonium molybdate solution
ꢀ
renders the reaction almost instantaneous. The formation of I3 could be monitored
ꢀ
spectrophotometrically due to the development of the characteristic I3 band (λmax=353 nm, ε
=26000 L mol−1 cm−1).
Theoretical methods.
The calculations have been performed by means of the TURBOMOLE 7.0 software 45 at the
BP86/def2ꢀTZVP level of theory. The geometries have been fully optimized to evaluate the
energetic difference between isomers. Moreover, we have used the crystallographic
coordinates for the theoretical analysis of the noncovalent interactions present in the solid
state. The interaction energies were calculated with correction for the basis set superposition
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error (BSSE) by using the Boys–Bernardi counterpoise technique.46 In order to reproduce
47
solvent effects, we have used the conductorꢀlike screening model COSMO, which is a
variant of the dielectric continuum solvation models.48
Conclusions
Two
homologous
Schiffꢀbase
ligands,
(H2L1)
namely
and
(E)ꢀ2ꢀ((2ꢀ(2ꢀhydroxyꢀ
(E)ꢀ2ꢀ((3ꢀ(2ꢀhydroxyꢀ
ethylamino)ethylimino)methyl)phenol
ethylamino)propylimino)methyl)phenol (H2L2) have been purposefully designed and utilized
in making four cobalt complexes in presence of two pseudohalides SCNꢀ and N3 .
ꢀ
Combination of H2L1 and N3 yields dinuclear cobalt(III) complex, whereas all other
ꢀ
cobminations produce mononuclear species. Thiocyanate containg complexes (1 and 3) are
stereochemically more interesting as on changing H2L1 to H2L2, orientation of two SCNꢀ
groups change from transꢀ to cis. All those experimentally observed facts have explecitly
rationalized by thorough DFT calculations and thereby established that the different
nuclearity and cisꢀtrans stereochemistry are the result of cooperative outcome of ligand
backbone and pseudohalide coꢀligand effects. All four complexes exhibit good catecholase
like activity with varying degree where the dinuclear complex (2) exhibits maximum
efficiency. The catecholase like activity is most probably follow the radical pathway as is
evident from EPR analysis. Our present study opens an avenue for extensive further
investigation of catecholase like activity of cobalt(III) complexes to unveil the finer details of
the mechanistic pathway involved in that catalysis.
Acknowledgement:
A.M is thankful to CSIRꢀJRF fellowship for providing fellowship [Sanction number:
09/028(0959)/2015ꢀEMRꢀI]. S.D is thankful to UGC and University of Calcutta [Sanction
number: UGC/485/Fellow (univ)] for providing fellowship. SG is thankful to SERB, India for
providing National Post Doctoral Fellowship (NPDF) [Sanction number: PDF/2016/000566].
Financial assistance from DSTꢀWB (Sanction memo no. 681(sanc)/ST/P/S&T/15Gꢀ8/2016 dt
09/11/2016) to DD has been duly acknowledged. The authors wish to thank University of
Calcutta for providing the facility of the singleꢀcrystal Xꢀray diffractometer from the DST
FIST program and ESIꢀMS spectrophotometer from the DST PURSE and Indian Association
for the Cultivation of Science for providing EPR facility.
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References
1
2
3
4
E. Vinck, E. Carter, D. M. Murphy , D. S. Van, Inorg. Chem., 2012, 51, 8014.
T. Kurahashi , H. Fujii, Inorg.Chem., 2013, 52, 3908.
M. Lashanizadegan , Z. Zareian,Catal. Lett., 2011, 141, 1698.
M. Volpe, H. Hartnett, J. W. Leeland, K. Wills, M.Ogunshun, B. J. Duncombe, C.
Wilson ,J. B. Love, Inorg.Chem., 2009, 48, 5195.
5
6
7
T. Honda, T. Kojima and S.Fukuzumi, J. Am. Chem. Soc., 2012, 134, 4196.
P. K. Mascharak,Coord. Chem. Rev, 2002, 225, 201.
A. Nishinaga, T. Yamada, H. Fujisawa, K. Ishizani, H. Ihara, T. Matsuura, J. Mol.
Catal. A.1998, 48, 249.
8
T. KurodaꢀSowa, M. Lamm, A. L. Rheingold, C. Frommen, W. M. Reiff, M.
Nakano, A. L. Maniero, LꢀC. Brunel, G. Christou, D. N. Hendrickson, Inorg.
Chem. 2001, 40, 6469.
9
S. Ganguly, R. Mondal, Cryst. Growth Des. 2015, 15, 5, 2211.
P. Chakraborty, J. Adhikary, S. Samanta, D. Escudero, A. C. Castro, M. Swart, S.
Ghosh, A. Bauzá, A. Frontera, E. Zangrando, D. Das, Cryst. Growth Des. 2014,
14, 4111.
10
11
I. Majumder, P. Chakraborty, J. Adhikary, H. Kara ,E. Zangrando, A. Bauza, A.
Frontera, D. Das, ChemistrySelect. 2016, 3, 615.
12
13
14
P. Braunstein, F. Naud, Angew. Chem. Int. Ed. 2001, 40, 680.
R. Mukherjee, Coord. Chem. Rev. 2000, 203, 151.
R. Dorta, E. D. Stevens, N. M. Scott, C. Costabile, L. Cavallo, Carl D.Hoff, S. P.
Nolan, J. Am. Chem. Soc. 2005, 127, 2485.
15
16
K. D. Benkstein, J. T. Hupp, C. L. Stern, J. Am. Chem. Soc. 1998, 120,12982.
A. Banerjee, S. Ganguly, T. Chattopadhyay, K. S. Banu, A. Patra, S.Bhattacharya,
E.Zangrando, D. Das, Inorg. Chem. 2009, 48, 8695.
17
18
C. Gerdemann, C. Eicken, HꢀJ. Galla, B. Krebs, J. Inorg. Biochem. 2002, 89, 155.
C. Belle, C. Beguin, I. GautierꢀLuneau, S. Hamman, C. Philouze, J. L. Pierre, F.
Thomas, S.Torelli, Inorg. Chem. 2002, 41, 479.
19
20
S. Mukherjee, T. Weyhermuller, E. Bothe, K. Wieghardt, P. Chaudhuri, Dalton
Trans. 2004, 38423.
M. Mitra , A. Maji, K. Ghosh,. G. Kaur, A.Roy Choudhury, CꢀH.Lin , J. Ribas ,
R. Ghosh, Polyhedron, 2013,61,15.
24

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21
22
A. Biswas, L. K. Das, M.G. B. Drew, G. Aromí, P. Gamez, A.Ghosh, Inorg.
Chem. 2012, 51, 7993.
A. Hazari, L. K. Das, R. M. Kadam, A. Bauzá, A. Frontera, A. Ghosh, Dalton
Trans., 2015,44, 3862.
23
24
S. K. Dey, A. Mukherjee, New J. Chem., 2014, 38,4985.
M. Das, R. Nasani, M. Saha, S. M. Mobin, S. Mukhopadhyay, Dalton Trans.
2015, 44, 2299.
25
26
27
S. K. Dey, A. Mukherjee, Coordination Chemistry Reviews, 2016, 310, 80.
P. Seth, M. G. B. Drew, A. Ghosh, J. Mol. Catal. A: Chem. 2012, 365, 154.
P. Chakraborty, J. Adhikary, B. Ghosh, R. Sanyal, S. Chattopadhyay, A. Bauzá,
A. Frontera, E. Zangrando,and D. Das, Inorg. Chem. 2014, 53, 8257.
I. Majumder,P. Chakraborty, S. Das, H. Kara, S. Chattopadhyay, E. Zangrando, D.
Das, RSC Adv. 2015, 5, 51290.
28
29
30
P. Chakraborty, I. Majumder, K. S .Banu, B. Ghosh, H. Kara, E. Zangrando, D.
Das, Dalton Trans. 2016, 45, 742.
J. Adhikary, A. Chakraborty, S. Dasgupta, S. Chattopadhyay, R. Kruszynski, A.
TrzesowskaꢀKruszynska, S. Stepanović, M. GrudenꢀPavlović, M. Swart, D. Das,
Dalton Trans, 2016, 45, 12409.
31
32
33
34
35
36
37
A. Guha, K. S. Banu, A. Banerjee, T. Ghosh, S. Bhattacharya, E. Zangrando, D.
Das, J.Mol.Catal.A:Chem., 2011, 338, 51.
T. Ghosh, J. Adhikary, P. Chakraborty, P. K. Sukul, M. S. Jana, T. K. Mondal, E.
Zangrando, D. Das, Dalton Trans.2014, 43, 841.
A. Guha, T. Chattopadhyay, N. D. Paul, M . Mukherjee, S. Goswami, T. K.
Mondal, E. Zangrando, D. Das, Inorg. Chem. 2012, 51, 8750.
R. Sanyal, S. K. Dash, S. Das, S. Chattopadhyay, S. Roy, D. Das, J Biol Inorg
Chem. 2014, 19, 1099.
S. Dasgupta, J. Adhikary, S. Giri, A. Bauzá, A. Frontera, D. Das, Dalton Trans.,
2017, 46, 5888.
A. Banerjee, A. Guha, J. Adhikary, A. Khan, K. Manna, S. Dey, E. Zangrando, D.
Das, Polyhedron , 2013, 60 ,102.
D. Dey, A. B. Roy, A. Ranjani, L. Gayathri, S. Chandraleka, D. Dhanasekaran, M.
A. Akbarsha, C.ꢀY. Shen, HꢀL.Tsai, M. Maji, N. Kole, B. Biswas, J. Chem. Sci.,
2015, 127, 649.
25

Dalton Transactions
Page 26 of 27
View Article Online
DOI: 10.1039/C7DT03040A
38
39
K.Nakamoto, Infrared and Raman Spectra of Inorganic and Coordination
Compounds.John Wiley & Sons, New York, 5th edition, 1997.
A. B. P Lever, Inorganic Electronic Spectroscopy, Elsevier, New York, 1968, pp
507.
40
41
S. K. Dey, P. Mitra, A. Mukherjee, Cryst. Growth Des. 2014, 15, 706.
R. Modak, Y. Sikdar, S. Mandal, S. Goswami, Inorg. Chem. Commun. 2013, 37,
193.
42
43
JꢀH. Qiu, Z.ꢀR. Liao, X.ꢀG. Meng, L. Zhu, Z.ꢀM. Wang, K.ꢀB. Yu, Polyhedron.
2005, 24, 1617.
J. Adhikary, P. Chakraborty, S. Das, T. Chattopadhyay, A. Bauzá, S.
Chattopadhyay, B. Ghosh, F. A. Mautner, A. Frontera, D. Das, Inorg. Chem.,
2013, 52, 1344.
44
45
S. Dasgupta, I. Majumder, P. Chakraborty, E. Zangrando, A. Bauzá, A. Frontera,
D. Das, Eur. J. Inorg. Chem. 2017, 2017, 133.
R. Ahlrichs, M. Bär, M. Hacer, H. Horn , C. Kömel, Chem. Phys. Lett., 1989, 162,
165.
46
47
48
S. B. Boys , F. Bernardi, Mol. Phys., 1970, 19, 553.
A. Klamt , G. Schüürmann, J. Chem. Soc., Perkin Trans., 1993, 2, 799.
A. Klampt, WIREs Comput. Mol. Sci., 2011, 1, 699.
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Table of Contents
Ligand backbone effect of homologous Schiff-bases in combination with influences of SCN-
-
and N3 are instrumental in controlling nuclearity and stereochemistry of catecholase active
cobalt(III) complexes.