A rare cobalt(III) paramagnetic derivative incorporating 1-alkyl-2-[(o-thioalkyl)phenylazo]imidazole (SMeaaiNEt): EPR, redox and magnetic interpretation

Article abstract of DOI:10.1016/j.ica.2017.03.015

The condensation of 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole (SMeaaiNEt), Co(ClO₄)₂, 6H₂O and NaN₃ in methanol affords a rare Co(III) paramagnetic complex [Co(SMeaaiNEt)(N₃)₃] (1). Single crystal X-ray diffraction study of complex 1 reveals that the Co(III) possesses a distorted octahedral environment. The EPR study interprets an unusual high-spin Co(III) species with configuration t_2g⁴e_g² and S?=?2. The temperature dependent magnetic interpretation agrees with the existence of intermolecular antiferromagnetic coupling on the paramagnetic Co(III) center. A cyclic voltammetry study displays for complex 1 two quasi-reversible and one irreversible responses at the negative direction which may be assigned to different reduction systems. DFT computation using optimized geometry is governed to explain the electronic nature of cobalt derivative which is in accordance with the experimental evidence.

Full text of DOI:10.1016/j.ica.2017.03.015

Accepted Manuscript
Research paper
A rare cobalt(III) paramagnetic derivative incorporating 1-alkyl-2-[(o-thioalk-
yl)phenylazo]imidazole (SMeaaiNEt): EPR, redox and magnetic interpretation
Soumendranath Nandi, Kuheli Das, Amitabha Datta, Suman Roy, Eugenio
Garribba, Takashiro Akitsu, Chittaranjan Sinha
PII:
S0020-1693(16)30721-6
http://dx.doi.org/10.1016/j.ica.2017.03.015
ICA 17475
DOI:
Reference:
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
19 October 2016
3 March 2017
8 March 2017
Please cite this article as: S. Nandi, K. Das, A. Datta, S. Roy, E. Garribba, T. Akitsu, C. Sinha, A rare cobalt(III)
paramagnetic derivative incorporating 1-alkyl-2-[(o-thioalkyl)phenylazo]imidazole (SMeaaiNEt): EPR, redox and
magnetic interpretation, Inorganica Chimica Acta (2017), doi: http://dx.doi.org/10.1016/j.ica.2017.03.015
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A rare cobalt(III) paramagnetic derivative incorporating
-alkyl-2-[(o-thioalkyl)phenylazo]imidazole (SMeaaiNEt) : EPR,
redox and magnetic interpretation
1
a
a
*,b
a
Soumendranath Nandi , Kuheli Das , Amitabha Datta , Suman Roy , Eugenio
c
d
*,a
Garribba , Takashiro Akitsu , Chittaranjan Sinha
a
Department of Chemistry, Jadavpur University, Kolkata – 700032, India
Institute of Chemistry, Academia Sinica, Nankang, Taipei - 11529, Taiwan
b
c
Dipartimento di Chimica and Centro Interdisciplinare per lo Sviluppo della Ricerca
Biotecnologica e per lo Studio della Biodiversità della Sardegna, Università di
Sassari, Via Vienna 2, I-07100 Sassari, Italy
d
Department of Chemistry, Faculty of Science, Tokyo University of Science
1
-3 Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan
*
Authors for correspondence.
E-mail: c_r_sinha@yahoo.com (C. Sinha); amitd_ju@yahoo.co.in (A. Datta)
Keywords: Co(III) complex / 1-alkyl-2-{(thioalkyl)arylazo}imidazole / EPR / VTM

A B S T R A C T
The condensation of 1-alkyl-2-{(o-thioalkyl)phenylazo}imidazole (SMeaaiNEt),
4 2 2 3
Co(ClO ) , 6H O and NaN in methanol affords a rare Co(III) paramagnetic complex
[
Co(SMeaaiNEt)(N
3 3
) ] (1). Single crystal X-ray diffraction study of complex 1
reveals that the Co(III) possesses a distorted octahedral environment. The EPR study
4
2
g
interprets an unusual high-spin Co(III) species with configuration t2g e and S = 2.
The temperature dependent magnetic interpretation agrees with the existence of
intermolecular antiferromagnetic coupling on the paramagnetic Co(III) center. A
Cyclic voltammetry study displays for complex 1 two quasi-reversible and one
irreversible responses at the negative direction which may be assigned to different
reduction systems. DFT computation using optimized geometry is governed to
explain the electronic nature of cobalt derivative which is in accordance with the
experimental evidence.
___________________________________________________________

1
. Introduction
There has been a continuous interest in the chemistry of metal complexes of
imidazole and related heterocycles [1-4]. There are two basic reasons among the
researchers to concentrate on imidazole type systems: biochemical ubiquity and an
alternative to polypyridines. The metal complexes of polypyridines have received
much attention because of rich electrochemistry, interesting optical properties,
bioinorganic chemistry and catalysis [5-10]. This has led to the modification of the
ligand system inserting different substituents, presence of other donor centers etc
[
11-14]. Ligand synthesis using imidazole as heterocyclic backbone is of much
advantage because of the biochemical importance of this molecule [15,16]. Imidazole
carries meta-related two N centers of different basicity and can bind strongly heavy
metal ions [17,18]. We have designed a surface modified extractant by anchoring
imidazole to polystyrene by azo group (–N=N–) and have been used for the separation
of heavy metals from drinking water, environmental samples, medicinal samples and
ores, minerals [19]. The fundamental property of interaction between metal ions and
organic ligands has been utilized in the design of functional materials. Azoimidazoles
is one such system. It has also been used to extract anions through protonation of
imidazole motif and subsequent interaction with anions via hydrogen bonding [20].
The exo-bidentate behavior of the ligand has been eliminated by N(1)-alkylation. The

coordination chemistry of 1-alkyl-2-(arylazo)imidazoles (RaaiR′) has been studied by
us [21-27] and others [28,29] using transition metals. In RaaiR′, the active function is
the azoimine group (–N=N–C=N–) which is isoelectronic with diimine function
(
–N=C–C=N–). The non-transition metal complexes of arylazoimidazole has been
reported earlier [30-33]. The Group 12 metal complexes of RaaiR′ show both
monodentate imidazole-N and chelating N,N′-donor ligands [30-34]. Co(III)
6
complexes may exist in diamagnetic low-spin (t2g ) and/or paramagnetic high-spin
4
2
n+
(
t
2g
e
g
) octahedral geometry. In most cases [Co(III)L
6
]
octahedral complexes are
3
-
3 3 2 3 6
diamagnetic. Other than CoF , [CoF (H O) ] and [CoF ] recent literature shows few
Co(III) complexes with N, O donor ligands that may exhibit temperature dependent
paramagnetism [36-38]. Herein, we report the azido-Co(III) complex
incorporating1-alkyl-2-[(othioalkyl)phenylazo]imidazole (SMeaaiNEt) (1). Complex
1
is spectroscopically characterized and structurally confirmed by single crystal X-ray
diffractometry. Variable temperature magnetic measurement confirms the existence of
strong antiferromagnetic coupling on the Co(III) center. The redox and EPR
spectrometric studies are also reported.
2
. Experimental
2.1. Materials

All chemicals and solvents were of reagent grade and used as received.
Co(ClO
4
)
2
.6H
2
O, o-(amino)thiophenol, methyl iodide (MeI), ethyl iodide (EtI), NaN
3
are purchased from E. Merck, India. All experiments are carried out under N
2
atmosphere. The ligand is prepared by coupling of o-(thioalkyl)phenyldiazonium ion
obtained by diazotization of o-(thioalkyl)aniline) and imidazole at pH 7 followed by
(
N(1)-alkylation using alkyl iodide in presence of NaH in dry THF under inert
conditions [39].
Physical measurements
Microanalytical data (C, H, and N) were collected on a Perkin–Elmer 2400 CHNS/O
elemental analyzer. FTIR spectra were recorded on a Perkin-Elmer RX-1
-1
spectrophotometer in the range 4000–400 cm as KBr pellets. Electronic spectra were
measured on a Lambda 25 (U.V.–Vis.–N.I.R.) spectrophotometer in methanol. EPR
spectra were recorded from 0 to 10000 Gauss in the temperature range 77-298 K with
an X-band (9.4 GHz) Bruker EMX spectrometer equippedwith an HP 53150A
microwave frequency counter. The magnetic properties were investigated with a
Quantum Design MPMS-XL superconducting quantum interference device
magnetometer (SQUID) at an applied field 0.5 T in a temperature range 5-300 K.
Powder samples were measured in a pharmaceutical cellulose capsule.

Electrochemical measurements were performed using computer-controlled PAR
model 250 VersaStat electrochemical instruments with Pt-disk electrodes. All
measurements were carried out under nitrogen environment at 298 K with reference to
4 4
SCE in acetonitrile using [nBu N][ClO ] as supporting electrolyte. The reported
potentials are uncorrected for junction potential.
3 3
Synthesis of [Co(SMeaaiNEt)(N ) ] (1)
1
-Ethyl-2-[o-(thiomethyl)phenylazo]imidazole (SMeaaiNEt) (0.2 g,0.81 mmol) in
4 2 2
methanol (15 ml) was added drop wise to Co(ClO ) .6H O (0.3 g, 0.82 mmol) in the
2 3
same solvent (10 ml) at 298 K under N environment. To this solution NaN (0.10 g,
1.52 mmol) was added in small volume of water. The solution was stirred for 3 hrs.
Orange-brown solution was then filtered off and N gas was bubbled to reduce its
2
volume to 10 ml. The solution was then kept into refregerator for 12 hrs. Dark brown
mass was precipitated at the bottom of the container and filtered. Residue was then
washed with methanol-water (1:1, v/v) and shining dark brown crystals were
separated out after few days on slow evaporation of the solvent. Then good shaped
block crystals were air-dried before X-ray diffraction analysis. Yield was 0.22 g
(
60%). Anal. Calc. forC12
H14CoN13S: C, 33.41; H, 3.27; N, 42.19. Found: C, 33.66; H,
3.41; N, 41.87%. The Scheme 1 depicts the synthesis of the ligand.

Scheme 1. (i) Dry EtOH/Na, RX; (ii) NaNO
2
2 3
/HCl, 0-5°C; (iii) Imidazole, Na CO
/
/
solution (pH ~ 7); (iv) THF/NaH, R X (R = Me, R = Et).
X-ray crystallography
The crystal structure of 1 was determined by X-ray diffraction method. Crystal
data and experimental details for data collection and structure refinement are reported
in Table 1. Intensity data and cell parameters were recorded at 298(2) K on a Bruker
Breeze (MoKα radiation λ = 0.71073 Å) equipped with a CCD area detector and a
graphite monochromator. The ω: 2θ scan technique was applied within a θ range of
1.62−27.47°. No significant crystal decay was observed. The raw frame data were
processed using SAINT and SADABS to yield the reflection data file [40,41]. The
structure was solved by Direct Methods using the SIR97 program [42] and refined on
2
F
o
by full-matrix least-squares procedures, using the SHELXL-97 program [43] in
the WinGX suite v.1.80.05 [44]. All non-hydrogen atoms were refined with

anisotropic atomic displacements. The hydrogen atoms were included in the
refinement at idealized geometry and refined “riding” on the corresponding parent
2
2
atoms. The weighting scheme used in the last cycle of refinement was w = 1/ [σ F +
o
2
2
o
2
(
0.0520P) + 0.3154P], where P = (F
+ 2F )/3. Crystallographic data (excluding
c
structure factors) for the structure reported have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication no. CCDC-1499217 for 1
and can be obtained free of charge on application to the CCDC, 12 Union Road,
Cambridge, CB2IEZ, UK (fax: +44-1223-336-033; e-mail deposit@ccdc.cam.ac.uk or
http://www.ccdc.cam.ac.uk).
Table 1. Crystallographic data of compound 1.
Empirical formula
Formula weight
Temperature
Wavelength (Å)
Crystal system
Space group
a, Å
12
C H14CoN13S
431.35
298(2)
0.71073
Triclinic
P-1
8.3359(10)
8.879(2)
b, Å
c, Å
13.3259(14)
77.966(16)
α, deg

β, deg
γ, deg
72.018(9)
69.633(14)
3
Volume, Å
873.8(2)
Z
2
-
3
D
calc (mg m )
1.639
-1
µ(Mo Kα) (mm )
1.118
Crystal size
0.46× 0.40 × 0.32
440
F(000)
θ range for data collection
Reflections collected / unique
1.62−27.47
4013 / 3445 [R(int) = 0.0175]
3445 / 0 / 246
R1 = 0.0299, wR2 = 0.0776
R1 = 0.0403, wR2 = 0.1002
0.381 and -0.311
Data / restraints / parameters
b
Final R indices [F
R indices (all data)
Largest diff. Peak and hole, e.Å
o o
>4σ(F )]
-3
a
2
o
2 2
Goodness-of-fit S = [Σw(F
-F
c
) / (n-p)]1/2, where n is the number of reflections
b
and p the number of parameters.
R
1
o
= Σ║F │-│F
c
║/Σ│F
o
│, wR
2
=
2
2 2
2 2 1/2
[
o c o
Σ[w(F -F ) ]/Σ[w(F ) ]] .

Results and discussion
Synthesis and formulation
Co(ClO
4
)
2
.6H
2
O
reacts
with
1-alkyl-2-[o-(thiomethyl)phenylazo]imidazole
(
[
(
SMeaaiNEt) and NaN
3
(1:1:2 moleproportion) in methanol to generate
Co(SMeaaiNEt)(N ] (1) which is isolated as dark brown crystals on slow cooling
3 3
)
Scheme 2). The composition of the complex is supported by micro-analytical data.
Complex 1 is soluble in methanol, ethanol, chloroform, dichloromethane and
acetonitrile but insoluble in hexane, benzene, and toluene. The IR spectra of 1 is
determined on comparing with the free ligand and some reported cobalt(II) complexes
of arylazoimidazoles [45,46]. The characteristic strong transmission band at
-1
2
050-2115 cm is referred to νN
3
that suggests the terminal azide bonding
undoubtedly [47]. Moderately intense stretching bands at 1570-1600 and 1420–1452
-1
cm are observed due to ν(C=N) and ν(N=N), respectively, for the coordinated
SMeaaiNEt ligand.
4 2 2 3 3 3
Co(ClO ) .6H O + SMeaaiNEt + 3NaN → [Co(SMeaaiNEt)(N ) ]
Scheme 2. Reaction scheme for the synthesis of complex 1.
Molecular structure

Single-crystal X-ray diffraction analysis reveals that complex 1 crystallizes in the
ꢀ
triclinic space group P1. Selected bond distances and bond angles are given in Table
. The asymmetric unit consists of three azide anions and ligand SMeaaiNEt
coordinated to a cobalt center, featuring a mononuclear complex. The reaction is
2
4 2
started taking Co(ClO ) as metal salt; however, at the end a Co(III) metal complex is
formed; so, air O
2
might be the oxidizing agent during synthesis. Two nitrogen atoms
(
N2 and N4) and one sulfur atom (S1) belonging to ligand L coordinate with the metal
center in a chelating manner, while the other three positions are occupied by three
nitrogen atoms (N5, N8 and N11) from three different azide ions (see Figure 1). As
shown in Figure 1, the Co1(II) center adopts a six-coordinated {CoN
5
S} distorted
octahedral geometry.
Figure 1. The ORTEP view of complex 1. The ellipsoids are drawn with 30%
probability level.

The Co1-N distances in 1 lie in the range of 1.899(19)-1.970(2) Å which are
2
comparable with reported distances of Co(III)-N(sp ) length (1.89-2.02 Å) [48-50].
The paramagnetic Co(III) complexes show longer bond length because of electron
2
population in e
g
level [51]. The Co(II)-N(sp ) distances lie in the range of 2.02-2.15 Å
which is longer than Co(III) complexes; either in diamagnetic or paramagnetic nature.
The Co(II)-N(azo) distance in the family of 1-alkyl-2-(arylazo)imidazole complexes
belongs in the range of 2.33-2.52 Å [52-55]. The bond parameters in the present
complex well fit to Co(III) oxidation state. The Co1-S distance 2.239(7) Å is also
comparable with earlier literature of thioether-salicylaldimines [50]. A supramolecular
network is formed through the cooperation between the monomeric units. Only two
C-H···N hydrogen bonds are detected of distances C(6)-H(6)…N(7) = 2.51 and
C(12)-H(12A)…N(11) = 2.45 Å and π···π interactions of about 3.704 Å between the
monomeric units helps in stabilizing the framework (Figures 2a and 2b).

Figure 2. (a) Weak interactions like C−H···N hydrogen bonding (orange) and π···π
interactions (dark pink) can be observed between the monomeric units; (b) view of the
framework along the b axis.
Table 2. Selected bond distances and bond angles of complex 1.
Co(1)- N(4)
Co(1)- N(2)
Co(1)- N(5)
Co(1)- N(11)
Co(1)- N(8)
Co(1)- S(1)
1.8989(19)
1.9142(18)
1.915(2)
N(4)- Co(1)- N(2)
N(4)- Co(1)- N(5)
N(2)- Co(1)- N(5)
N(4)- Co(1)- N(11)
N(2)- Co(1)- N(11)
N(5)- Co(1)- N(11)
80.54(8)
173.58(8)
93.06(9)
88.55(9)
90.11(9)
91.10(10)
1.957(2)
1.970(2)
2.2387(7)
N(4)- Co(1)- N(8)
N(2)- Co(1)- N(8)
N(5)- Co(1)- N(8)
N(11)- Co(1)- N(8)
N(8)-Co(1)-S(1)
88.62(9)
90.74(9)
91.86(10)
176.87(9)
86.89(7)
N(4)-Co(1)-S(1)
N(2)- Co(1)- S(1)
N(5)- Co(1)- S(1)
N(11)-Co(1)-S(1)
87.28(6)
167.65(6)
99.13(7)
91.65(7)
Electronic spectra
The electronic spectra of the ligand and complex 1 were recorded in HPLC grade
acetonitrile solution. Visible region of the complex spectrum shows three transitions:
the transitions are 600-675, 450-515, 385-425 nm along with two transitions in UV
region; 355-375, 240-255 nm. Based on the low intensity and low energy nature the
bands are considered to be d–d transitions in an octahedral geometry. The high intense
transition <430 nm may be assigned to MLCT transitions.
Theoretically generated structures of complex 1 are used to calculate composition

and energy of the functions to explain the electronic properties. The orbital energies
alongwith contributions from the ligands and metal are given in ESI (Tables S1 and S2).
Figure 3 depicts the selected occupied and unoccupied frontier orbitals. The HOMO of 1 is
-
constituted by Co (22%), ligand, SMeaaiNEt (40%), and N
3
(38%). The other occupied
-
MOs (HOMO-2, HOMO-3 etc) are mainly contributed from N
3
(>80%). Unoccupied
MOs are contributed from SMeaaiNEt (>95%). The calculated transitions are grouped in
Table S2. The intensity of these transitions is assessed from oscillator strength (f). Here the
visible region (400-570 nm) transitions are assigned to HOMO-6→LUMO+3,
HOMO-8→LUMO etc. The calculated transitions at 470-570 nm are weak (f, 0.0118–
0.0934) and are assigned to a mixture of LMCT (ligand-to-metal charge transfer) and ILCT
(intra-ligand charge transfer). An intense band is observed at 450 nm which is ILCT band.
HOMO-1; E, -5.22 eV; N
3
, 19%; Co, 35%;
HOMO; E, -4.7 eV; N
3
, 38%; Co, 22%; NNS,
NNS, 46%
40%

LUMO; E, -4.44 eV; N
3
, 17%; Co, 14%;
LUMO+1; E, -2.44 eV; N
3
, 01%; Co,
NNS, 69%
00%;NNS , 99%
(
a)
HOMO-1; E, -5.95 eV; N
3
, 81%; Co, 13%;
3
HOMO; E, -5.69 eV; N , 31%; Co, 61%;
NNS, 06%
NNS, 08%
LUMO; E, -5.27 eV; N
3
, 46%; Co, 48%;
3
LUMO+1; E, -5.2 eV; N , 47%; Co, 49%;
NNS, 06%
NNS, 04%
(
b)
Figure 3. Contour plots of some selected (a) α- and (b) β- molecular orbitals of 1.
EPR spectra
EPR spectra of the polycrystalline complex 1 are recorded in the temperature range
77-298 K. The spectra at 77, 140 and 298 K are reported in Figure 4. Almost all of
the octahedral Co(III) complexes have diamagnetic ground state and only few
3
-
3 2 3 6
exceptions, such as [CoF (H O) ] and [CoF ] , are known [48]. Therefore, the
6
electronic configuration is t2g and the spin state is S = 0; for this state no EPR signal
is expected. In contrast, Figure 4 shows that in the range examined a strong EPR

spectrum can be revealed; absorptions of the microwave radiations are observed from
Figure 4. X-band EPR spectra of the polycrystalline complex 1 at: (a) 298, (b) 140
and (c) 77 K. The spectra are recorded with the same instrumental gain.
0
to 5000 G and resonances at g 3.6, 2.3 and 2.0 (at 77 K) and at 3.6 and 2.0 plus a
shoulder at 1.8 (298 K) are well evident. The spectral pattern does not change
significantly with the temperature, but from 77 to 298 K a significant weakening of
the signal intensity is detected (cfr. traces a and c of Figure 4). The results can be
interpreted on the basis of an unusual high-spin Co(III) species with configuration
4
2
2g g
t e and S = 2. EPR spectra of other systems with S = 2, such as high-spin Fe(II)
and high-spin Mn(III) complexes, support our experimental results [49,50]. It has
been pointed out that the chance to detect EPR signals for non-Kramer doublets

increases for S≥ 2 and, in particular, the transition within the highest non-Kramer
doubletis always by far the easiest to be detected and is often the only observe
transition; however, in most of the cases the spectra provide insufficient information
for the determination of the Hamiltonian parameters (and this is the case) [50]. The
decrease of the EPR signal intensity from 77 to 298 K gain (the three spectra in
Figure 4 are reported using the same instrumental gain) is in agreement with the
VTM measurements, which indicate the population of the S = 0 state with increasing
the temperature.
Complex 1 was dissolved in two types of solvent: a weakly coordinating solvent
3
such as CH CN and a coordinating solvent such as DMF. EPR spectra (shown in
Figure 5) are very different with respect to those recorded in the solid state. In both
the cases no signal is revealed (the gain is the same used for the solid samples), and
6
this means that in solution the electronic configuration t2g and the spin S = 0 are

Figure 5. Anisotropic X-band EPR spectra of the complex 1 dissolved in: (a) DMF
and (b) CH CN. The spectra are recorded with the same instrumental gain used in
Figure 4.
3
favored. Therefore, it is probable that solid stat effects stabilize the anomalous
high-spin state, whereas in solution the behavior is that usual for Co(III) complexes.
Magnetic property
M M
The magnetic property of complex 1 in the form of χ T vs T plot (χ is the molar
M
magnetic susceptibility) is shown in Figure 6. The value of χ T at 300 K is 2.39 emu
-1
mol K which defines high spin Co(III), a typical value for cobalt (III) ion, as
6
expected. In general, Co(III) exists as diamagnetic (low-spin), t2g and paramagnetic
4
2
(
high-spin), t2g
e
g
electronic configuration. However, Co(III) paramagnetic
complexes are fewer [59] than those of huge number of diamagnetic Co(III)
complexes. The present example is one of the rare case of
1
-alkyl-2-{(o-thioalkyl)phenylazo}imidazole Co(III) high-spin paramagnetic complex.
-1
M
With lowering of temperature there is an increasing of χ T to 7.25 emu mol K at 12
-
1
K and then a rapid decrease to 4.15 emu mol K at 5 K. This feature is quite
interesting and

Figure 6. Temperature dependence of χ
M
vs T of 1. Inset shows χ T vs T plot.
M
stipulates noticeable intermolecular antiferromagnetic interaction. We could come into
conclusion that the concerned data clearly supports the mononuclear high-spin Co(III)
6
24
complex in octahedral symmetry (d ; HS, S=2). Figure 6 is evident with the
calculated magnetic moment 4.37 BM at 300 K (theoretical value 4.89 BM [51].
Redox study
Cyclic voltammetry is governed to examine the redox nature of the complex in
acetonitrile solution having the potential range –1.6 to 1.2 V vs SCE electrode. A
representative voltammogram is shown in Figure 7. The complex displays no
characteristic response at the positive part in the redox diagram. On scanning to
negative direction (0.0 to -1.6 V) three redox responses are observed at ~ -0.4; -0.8

and -1.4 V. Two of the reductive couples (~ -0.4; -0.8 V) are quasi-reversible (∆Ep ≥
100 mV) while third one remains at -1.4 V as irreversible. The couples at negative to
-
SCE are reductive in nature and first two reductions are referred to azo/azo and
-
=
azo /azo respectively [52]. The irreversible reduction at very high negative potential
(
-1.4 V) may be considered electron accommodation to azido dominated redox level.
Cyclic voltammetric behaviour of the complexes is readily accountable from DFT
calculation. Unoccupied MOs are significantly dominated by azoimine function, thus
reduction may refer to electron accommodation at azo dominated orbital of the ligand. So
the assignment, azo reductions are justified. The LUMO and other unoccupied MOs are
t
Figure 7. Cyclic voltammogram of complex 1 in MeCN solution (0.1 NBu
4
ClO
4
)
using Pt-milli working electrode, Pt-wire auxiliary and Ag/AgCl reference electrode
under nitrogen at 25 °C). SMeaaiNEt dominated (>95%), so reduction is as usual,

.
. N
N
N
+ e
N
.
Conclusion
Azido-cobalt(III)-1-alkyl-2-[(othioalkyl)phenylazo]imidazole (SMeaaiNEt) complex
is afforded and systematically characterized by X-ray crystallography and several
spectroscopic techniques. Temperature and solvent dependent EPR spectra are
recorded confirming an unusual high-spin Co(III) derivative and well comparable
with other high-spin Fe(II) and Mn(III) complexes. Temperature dependent magnetic
study reveals the presence of strong antiferromagnetic coupling on the paramagnetic
Co(III) center. This phenomenon is very uncommon and probably the first example of
the Co(III) derivative coupled with imidazole moiety and monodentate orientation of
three azide molecules. Further investigations on DNA cleavage and fluorescence
cell-imaging using substituted imidazole assisted cobalt derivatives are currently
being carried out in our laboratories.
Acknowledgements
Financial support from University Grants Commission, CAS-UGC, New Delhi, India
is thankfully acknowledged.

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lGRAPHICALABSTRACT
A rare cobalt(III) paramagnetic derivative incorporating
-alkyl-2-[(o-thioalkyl)phenylazo]imidazole (SMeaaiNEt) : EPR,
redox and magnetic interpretation
1
a
a
*,b
a
Soumendranath Nandi , Kuheli Das , Amitabha Datta , Suman Roy , Eugenio
c
d
*,a
Garribba , Takashiro Akitsu , Chittaranjan Sinha
1
-alkyl-2-{(o-thioalkyl)phenylazo}imidazole
(
SMeaaiNEt), employed a Co(III) derivative is
afforded. The spectroscopic properties are
carried out and DFT optimized geometry is also
included to explain the electronic nature. EPR
spectra strongly supports the unusual high-spin
Co(III) species.