Synthesis, structure and magnetic property of a dinuclear cobalt(II/III) complex with a reduced Schiff base ligand

Article abstract of DOI:10.1016/j.poly.2020.114756

A dinuclear mixed valence cobalt(II/III) complex, [(N₃)Co^IIIL(μ-CH₃COO)Co^II(N₃)]?CH₃OH with a N₂O₄ donor compartmental reduced Schiff base ligand, H₂L [(1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol)], has been synthesized and characterized by spectral and elemental analyses. Cobalt(III) is placed in the inner N₂O₂ compartment whereas cobalt(II) is present in the outer O₄ compartment of the ligand. Structure of the complex is confirmed by single crystal X-ray crystallography. The magnetic susceptibility measurement confirms that the complex belongs to localized class-I mixed valence system with isolated S = ³/₂ ion and shows Curie-Weiss paramagnetism.

Full text of DOI:10.1016/j.poly.2020.114756

Polyhedron 190 (2020) 114756
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, structure and magnetic property of a dinuclear cobalt(II/III)
complex with a reduced Schiff base ligand
a
b
b
a,
⇑
Abhisek Banerjee , Santiago Herrero , Ángel Gutiérrez , Shouvik Chattopadhyay
a
Department of Chemistry, Inorganic Section, Jadavpur University, Kolkata 700032, India
Departamento de Química Inorgánica, Facultad de Ciencias Químicas, Universidad Complutense de Madrid, Ciudad Universitaria, Madrid 28040, Spain
b
a r t i c l e i n f o
a b s t r a c t
III
II
Article history:
Received 2 July 2020
Accepted 13 August 2020
Available online 18 August 2020
3 3 3 3 2 4
A dinuclear mixed valence cobalt(II/III) complex, [(N )Co L(m-CH COO)Co (N )]∙CH OH with a N O donor
compartmental reduced Schiff base ligand, H
has been synthesized and characterized by spectral and elemental analyses. Cobalt(III) is placed in the
inner N compartment whereas cobalt(II) is present in the outer O compartment of the ligand.
2
L [(1,3-propanediyl)bis(iminomethylene)bis(6-ethoxyphenol)],
O
2 2
4
Structure of the complex is confirmed by single crystal X-ray crystallography. The magnetic susceptibility
Keywords:
Mixed valence
Cobalt
measurement confirms that the complex belongs to localized class-I mixed valence system with isolated
3
S =
2
/ ion and shows Curie-Weiss paramagnetism.
Ó 2020 Elsevier Ltd. All rights reserved.
Dinuclear
Reduced Schiff base
Magnetic behaviour
1
. Introduction
Study of the magnetic properties of di and trinuclear transition
to the Robin-Day classification viz. class-I, class-II and class-III [19].
The most renowned mixed valence cobalt complex is Co , a
3 4
O
class-I type, in which cobalt(III) centers are octahedral and low
spin, whereas cobalt(II) centers are tetrahedral and high spin
[20]. Magnetic properties of these complexes were not studied in
detail; rather their catalytic activities were investigated
[10–12,16–18]. Few mixed valence cobalt complexes have been
prepared with hydroxyl rich ligands and their magnetic properties
were investigated [21,22].
In the present work, we have synthesized a mixed valence
2 4
cobalt(II/III) complex with a N O donor compartmental reduced
Schiff base ligand. The complex has been characterized by spectral
and elemental analyses. Its structure has been confirmed by single
crystal X-ray diffraction analysis. The magnetic property of the
complex has also be explored.
metal complexes of Schiff bases has been an interesting research
area in the field of materials science since a long time [1,2]. Easy
synthetic routes, extensive stability and flexibility make the use
of Schiff bases so much popular as ligand [3,4]. Recently, reduced
Schiff bases have also been used to prepare transition metal com-
plexes [5]. Different types of magnetic behaviors, e.g., ferromag-
netic, antiferromagnetic, metamagnetic, single molecular
magnetism (SMM), spin canting and spin flop have been observed
in many such complexes of copper, nickel, iron and manganese
[
6-9]. Magnetism of dinuclear cobalt complexes, on the other hand,
were less investigated probably because of the diamagnetic nature
of low-spin cobalt(III) complexes [10–12]. Cobalt(II) complexes are
suitable for magnetic study, but it is difficult to stabilize cobalt(II)
in presence of strong field N-donor ligands. However recently a
cobalt(II) SMM with only N-donor ligands has been reported in liter-
ature [13]. Cobalt may, however, form mixed valence cobalt(II/III)
complexes via partial oxidation of cobalt(II) precursors and many
di and trinuclear mixed valence cobalt(II/III) complexes were
reported in literature [10–18]. Depending on the extent of elec-
tronic communication between the different metal sites, mixed
valence compounds have been divided into three classes according
2
. Experimental section
2.1. Materials
All chemicals used were purchased from Sigma-Aldrich and
were of reagent grade. They were used without further
purification.
Caution!!! Although no problems were encountered in this
work, organic ligands in the presence of azide are potentially
explosive. Only a small amount of the material (not more than
10 mmol) should be prepared and it should be handled with care.
⇑
Corresponding author.
E-mail address: shouvik.chem@gmail.com (S. Chattopadhyay).
https://doi.org/10.1016/j.poly.2020.114756
277-5387/Ó 2020 Elsevier Ltd. All rights reserved.
0

2
A. Banerjee et al. / Polyhedron 190 (2020) 114756
2
2
.2. Synthesis
method and refined by full-matrix least squares on F2 using the
SHELXL-18/1 package [23]. Non-hydrogen atoms were refined with
anisotropic thermal parameters. Hydrogen atoms attached to
nitrogen and oxygen atoms in the complex were located by differ-
ence Fourier maps and were kept at fixed positions. Multi-scan
empirical absorption corrections were applied to the data using
the program SADABS [24]. A summary of the crystallographic data
has been given in Table 1. Selected bond lengths and bond angles
have been given in Table 2 and Table S1 (Supplementary informa-
tion), respectively. It is to be mentioned here that there is a disor-
der in the position of one ethyl group attached to O(3) and two sets
of positions {C(1), C(2) and C(25), C(26)} were refined with occu-
pancies of x and 1 À x with x converging to 0.502(9).
2
.2.1. Synthesis of the reduced Schiff base ligand, H L [(1,3-
propanediyl)bis(iminomethylene)bis(6-ethoxyphenol)]
0 mL methanol solution of 3-ethoxysalicylaldehyde (4 mmol,
.66 g) and 1,3-propanediamine (2 mmol, 0.22 mL) was refluxed
for 2 h to prepare a potential hexadentate N donor Schiff base
{N,N’-bis(3-ethoxysalicylidene)propane-1,3-diamine}.
Then the solution was cooled to 0 °C and solid sodium borohydride
4.00 mmol, 0.15 g) was added gently to the methanol solution
2
0
2 4
O
a
ligand,
2
H L
(
with constant stirring. The resulting solution was acidified with
glacial acetic acid (10 mL) and placed under reduced pressure in
a rotary evaporator (~60 °C). The residue was dissolved in water
(
15 mL) and extracted with dichloromethane (15 mL) using a sep-
arating funnel. The ligand solution in dichloromethane was dried
using anhydrous sodium acetate and then dichloromethane was
3
. Results and discussion
evaporated under reduced pressure and the ligand, H
extracted in methanol. The methanol was evaporated under
reduced pressure to get the ligand, H L.
Yield: 0.46 (~62.45%). Anal. Calc. for
FW = 374.47): C, 67.3; H, 8.0; N, 7.5%. Found: C, 67.2; H, 7.9; N,
2
L, was
3
.1. Synthesis
2
The potential hexadentate compartmental reduced Schiff base
g
21 30 2 4
C H N O
2
ligand, H L, was synthesised by facile condensation of 1,3-propane-
diamine with 3-ethoxysalicylaldehyde in 1:2 ratio followed by
reduction with sodium borohydride in methanol under constant
(
1
7
6
.7%. H NMR (DMSO-D6, 300 MHz) (ppm) d: 1.360–1.211 [m,
H, methyl CH of ethoxy parts; 3.991–3.921 [m, 4H, methylene
3
2
stirring at 0 °C [16–18]. This reduced Schiff base, H L, on reaction
CH
CH
2
of ethoxy parts], 3.797–3.775 [d, J = 6.6 Hz, 4H, methylene
of aldehyde part (adjacent to amine nitrogen)], 2.562–2.475
with cobalt(II) acetate tetrahydrate followed by the addition of
sodium azide as co-ligand in methanol gave rise to the complex.
The synthetic procedure of the complex has been shown in
Scheme 1.
2
[
2
m, 4H, methylene CH (adjacent to amine nitrogen) of diamine],
1
6
.605–1.560 [m, 2H, methylene CH
.780–6.593 (m, 6H, aromatic CH).
2
(central) of diamine part],
III
II
2.2.2. Synthesis of the complex [(N
3
)Co L(m-CH
3
COO)Co (N
3 3
)]∙CH OH
3.2. Structure description
A methanol solution (10 mL) of cobalt(II) acetate tetrahydrate
1.00 mmol, 0.25 g) was added to the reduced tetradentate Schiff
base ligand, H L, (1.00 mmol, 0.37 g) with constant stirring for
(
X-ray crystal structure determination reveals that it crystallizes
2
in the monoclinic space group, P2 /c. Perspective view of the com-
1
ca. 1 h. A solution of sodium azide (0.92 mmol, 0.06 g) in metha-
nol/water solution (10 mL in a 4:1 ratio) was then added to it
and stirring was continued for about 2 h more. Dark brown crystals
appeared after 3–4 days on slow evaporation of the filtrate in an
open atmosphere and X-ray quality single crystals were collected
from the product.
plex along with the selective atom labelling scheme has been
shown in Fig. 1. H L, is a potential hexadentate compartmental
2
reduced Schiff base having inner N O and outer O compartments
2
2
4
with Co(1) center occupying the inner N O cavity and Co(2) occu-
2
2
pying the outer O4 cavity. This is an example of a mixed valence
complex where cobalt centers in the neutral dinuclear core are of
different oxidation states i.e. +3 and +2, and this assignment can
be confirmed by total charge balance considerations, interatomic
distances of Co-N and Co-O and BVS (Bond valence sum) calcula-
tions [25–30]. The relative interatomic distances from cobalt(III)
Yield: 0.25 g (~75.24%, based on cobalt). Anal. Calc. for C24
35
H -
Co N O (FW = 665.46): C, 43.2; H, 5.2; N, 16.8%. Found: C, 43.3; H,
2 8 7
À1
5
2
.1; N, 16.9%. FT-IR (KBr, cm ): 3185 (
m
N-H), 2980–2895 (
m
C-H),
3
À1
026 (
m
N3), 2055 (
m
N3). UV–Vis, kmax (nm), [
CN), 618 (6.25 Â 10 ), 365 (2.80 Â 10 ), 238
e
max (dm mol
À1
2
3
cm )] (CH
3
4
(
1.5 Â 10 ).
Table 1
Crystal data and refinement details of the complex.
2
.3. Physical measurements
Formula
C
24
H
35Co
665.46
Monoclinic
P2 /c
2 8 7
N O
Elemental analyses (carbon, hydrogen and nitrogen) were per-
Formula Weight
Crystal System
Space group
a(Å)
b(Å)
c(Å)
formed using a Perkin Elmer 240C elemental analyzer. IR spectrum
in KBr (4500–500 cm ) was recorded with a Perkin Elmer Spec-
trum Two spectrophotometer. Electronic spectrum in acetonitrile
À1
1
15.705(6)
9.114(3)
19.934(7)
91.998(2)
2851.87(3)
4
1.550
1.221
1380
(
200–800 nm) was recorded on a Perkin Elmer Lambda 35 UV–vis-
ible spectrophotometer. Quantum Design MPMSXL SQUID
Superconducting Quantum Interference Device) magnetometer
A
b(°)3
V(Å )
(
Z
was used to measure the variable-temperature magnetic proper-
ties. H NMR spectrum were recorded on a 300 MHz Bruker FT
NMR spectrometer using DMSO-D6 as the solvent; chemical shifts
À3
d
(calc) [g cm
]
1
À1
m [mm
F(000)
]
(d) are given in ppm.
Total Reflections
Unique Reflections
Observed data [I > 2
48,470
6596
5584
r
(I)]
2.4. X-ray crystallography
R(int)
0.030
#
*
R1, wR2 (all data)
0.0401, 0.0881
0.0317, 0.0837
0.489, À0.416
#
A suitable single crystal single crystal of the complex was used
*R1, wR2 ([I > 2
r(I)]
À3
Residual Electron Density (eÅ
)
for data collection using a ‘Bruker D8 QUEST area detector’ diffrac-
tometer equipped with graphite-monochromated Mo K radiation
k = 0.71073 Å). The molecular structure was solved by direct
*
| and #wR2 =
|2-|F
2 2
a
R1 =
.
R
||F
o
c
|-|F ||/R
|F
o
R
w(|F
o
c
| ) /Rw|
2
1/2
(
F
o
| )

A. Banerjee et al. / Polyhedron 190 (2020) 114756
3
Table 2
Selected Bond lengths (Å) of the
complex.
Co(1)-O(1)
Co(1)-O(2)
Co(1)-O(5)
Co(1)-N(1)
Co(1)-N(2)
Co(1)-N(3)
Co(2)-O(1)
Co(2)-O(2)
Co(2)-O(3)
Co(2)-O(4)
Co(2)-O(6)
Co(2)-N(4)
1.946(12)
1.958(13)
1.929(12)
1.986(1)
1.978(1)
1.922(2)
2.027(13)
2.024(13)
2.284(1)
2.314(3)
2.063(14)
1.997(3)
center, Co(1) (3O, 3 N) lie in the range 1.920–1.986 Å, while those
from cobalt(II) center, Co(2) (5O, N) are in the range
.997–2.310 Å. In this complex, both cobalt centers adopt distorted
1
1
octahedral geometry. The geometry of cobalt(II) is actually in
between octahedral and trigonal prism (as could be identified from
SHAPE analysis) [31]. The cobalt(III) center, Co(1), is coordinated
by two amine nitrogen atoms, N(1) and N(2) and two phenoxy oxy-
gen atoms, O(1) and O(2), of the deprotonated reduced Schiff base
which constitute the equatorial plane. The fifth coordination site is
filled by a nitrogen atom, N(3), of terminal azide, whereas an oxy-
gen atom, O(5), of the bridging acetate moiety coordinates at the
sixth site. Similarly for cobalt(II) center, Co(2), the equatorial plane
consists of four oxygen atoms [two phenoxy oxygen atoms, O(1)
and O(2), and two ethoxy oxygen atoms, O(3) and O(4)]. A nitrogen
atom, N(4), of another terminal azide coordinates at the fifth site
whereas the sixth coordination is filled by an oxygen atom, O(6),
of the bridging acetate moiety (given in Table S1, Supplementary
Information), which are being slightly deviated from the ideal val-
ues of 90° for the cis angles and 180° for the trans angles. The
intramolecular separation between Co(1) and Co(2) is obtained
as 2.980(5) Å. The distance is not satisfactorily short to infer any
metal–metal bonding [16,32,33]. The saturated six membered che-
late ring, Co(1)-N(1)-C(10)-C(11)-C(12)-N(2), represents a half
chair conformation with puckering parameters [34], q(2) = 0.553
Fig. 1. Perspective view of the complex with selective atom labelling scheme. Non
coordinated methanol molecule and hydrogen atoms have been omitted for clarity.
Only one disorder position of the ethoxy side arm is shown.
3.4. Supramoloecular interactions
Two hydrogen atoms, H(1) and H(2), available in the ligand part
are efficient for hydrogen bonding. Of these, H(1), attached to an
amine nitrogen atom, N(1), is hydrogen bonded with a symmetry
a
related oxygen atom, O(7) , of the solvent methanol molecule
{
symmetry transformation a = x,1 + y,z}; and H(2), attached to an
amine nitrogen atom, N(2), is hydrogen bonded with the symmetry
a
related azide nitrogen atom, N(8) , {symmetry transformation
a
=
x,1 + y,z} of the neighbouring molecule. The azide nitrogen
atom, N(4), is involved in hydrogen bonding interaction with the
a
symmetry related hydrogen atom, H(7) , attached to an oxygen
a
a
atom, O(7) , {symmetry transformation = x,1 + y,z} of the neigh-
bouring solvent methanol molecule. All these interactions led to
the construction of a chain like structure (Fig. 2). The details of
hydrogen bonding interactions have been given in Table 3.
(
3) Å, u = 184.5(8)°.
In addition, CAHÁÁÁ
The hydrogen atom, H(12A), attached to carbon atom, C(12), is
interaction with symmetry
related (symmetry transformation = 1-x,1/2 + y,1/2-z) phenyl
ring, [C(14)-C(15)-C(16)-C(17)-C(18)-C(19)] (Fig. 3). The details of
p interaction is also prevalent in the complex.
3
.3. BVS calculation
involved in inter-molecular CAHÁÁÁ
p
b
The bond valence sum (BVS) calculations were performed to
calculate the oxidation state of cobalt centers in the prepared com-
plex. The results are in good agreement for confirming the exis-
tence of mixed valence states of cobalt in the complex. The BVS
values are calculated as 3.04 and 2.01 for the Co(1) and Co(2) cen-
ters. Thus this bond valence sum calculative strategy strongly sup-
ports the assignment of mixed valence states of cobalt (+3 and +2)
in the complex.
these CAHÁÁÁ
p interactions have been shown in Table 4.
3.5. Hirshfeld surface analyses
Hirshfeld surfaces [35–37] and the 2D-fingerprint [38–40] plots
of the complex were calculated by using Crystal Explorer software
Scheme 1. Synthesis of ligand and the complex. Non coordinated methanol molecule has been omitted for clarity.

4
A. Banerjee et al. / Polyhedron 190 (2020) 114756
Fig. 2. Perspective view of one dimensional chain through hydrogen bonding interaction in the complex. Only the relevant hydrogen atoms have been shown for clarity.
Symmetry transformation: a = x,1 + y,z.
Table 3
Hydrogen bond distances (Å) and angles (◦) for the complex.
D–HÁÁÁA
D-H
HÁÁÁA
2.15(3)
2.46 (2)
2.04(3)
DÁÁÁA
2.998(2)
3.270(3)
2.899(3)
\D-HÁÁÁA
161(2)
161(4)
175(3)
Symmetry transformation
a
a
a
N(1)-H(1)ÁÁÁO(7)
N(2)-H(2)ÁÁÁN(8)
O(7)-H(7)ÁÁÁN(4)
0.88(2)
0.85(2)
0.87(3)
= x,1 + y,z.
D = donor; H = hydrogen; A = acceptor.
Fig. 3. Perspective view of the supra-molecular dimer formed by inter-molecular CAH∙∙∙
shown in the figure. Symmetry transformation: = 1-x,1/2 + y,1/2-z.
p
interactions with selective atom labelling scheme. Only relevant atoms have been
b
Table 4
Geometric features (distances in Å and angles in °) of the CAHÁÁÁ
p
interactions obtained for the complex.
CAHÁÁÁCg(ring)
C(12)-H(12A)ÁÁÁCg(9)
HÁÁÁCg(Å)
2.55
CAHÁÁÁCg
159
CÁÁÁCg (Å)
3.467(2)
Symmetry transformation
b
b
= 1-x,1/2 + y,1/2-z.
Cg(9) = Center of gravity of the ring [C(14)- C(15)-C(16)-C(17)-C(18)-C(19)].
[
41]. Hirshfeld surface analysis has been explored in order to
other than hydrogen bonds. Thus Hirshfeld surface analysis serves
as a powerful tool by which the intermolecular interactions of the
complex have been quantified.
Two-dimensional fingerprint plots (Fig. 5) obtained from Hirsh-
feld surface analysis may also be useful in order to get quantitative
information about the individual contribution of such supramolec-
ular interactions in the crystal packing. Intermolecular interactions
appear as distinct spikes in this plot. Complementary regions are
observable in the two-dimensional fingerprint plots where one
enhance the significance of the nature of the interactions between
molecules in crystal lattice. The Hirshfeld surfaces have been
mapped over dnorm (range À0.1 Å to 1.5 Å) shape index and curved-
ness (Fig. 4). Graphical plots of the molecular Hirshfeld surfaces
mapped with dnorm used a red-white-blue colour scheme, where
red highlights shorter contacts, white is used for contacts around
the Van der Walls separation, and blue is for longer contacts. The
intense circular depressions (deep red) seen on the surfaces indi-
cates the hydrogen bonding contacts. The small extent of area
and light colour on the surface indicates weaker and longer contact
molecule act as donor (d
e i e i
> d ) and the other as an acceptor (d < d ).
In the fingerprint plots the most dominant interactions have been

A. Banerjee et al. / Polyhedron 190 (2020) 114756
5
Fig. 4. Hirshfeld surfaces mapped with dnorm (left), shape index (middle) and curvedness (right) for the complex.
Fig. 5. Fingerprint plot: Full (a), resolved into H∙∙∙C/C∙∙∙H (b), H∙∙∙N/N∙∙∙H (c) and H∙∙∙O/O∙∙∙H (d) contacts contributed to the total Hirshfeld Surface area of the complex.
observed for N∙∙∙H/H∙∙∙N contacts i.e. 27.3% of the total Hirshfeld
surface followed by C∙∙∙H/H∙∙∙C contacts with contribution of
with the usual values for isolated cobalt(II) ions [42], where the
spin–orbit coupling renders values of 4.3–5.2 b. On lowering the
temperature, the T value decreases to a minimum value of 1.75
cm K mol at 2 K that corresponds to a magnetic moment of
1
4.0% of the total Hirshfeld surface. The contribution of interac-
v
3
À1
tions coming from O∙∙∙H contacts are comparatively less i.e. 5.9%.
3
.75 b, in the range for a spin only magnetic moment in a high spin
7
3.6. Magnetic measurements
d ion. This behaviour is compatible with a Curie-Weiss paramag-
net, as shown in Fig. 7. On this basis the plot of
ature yields a straight line with slope 0.3559(5) mol cm
intercept –0.19(9) K, R = 0.9998. These values correspond to an
À1
v
versus temper-
À3 À1
The magnetic susceptibility of the complex has been measured
K
and
2
in the temperature range of 2–300 K under a constant magnetic
field of 1 T. The T vs. T plot of the data also show these features
Fig. 6), with a room temperature value of 2.84 cm K mol that
v
average magnetic moment of 4.74(2) b, supporting the expected
3
À1
3
(
behaviour of isolated S =
/
2
ions. This plot is compatible with a
remains approximately constant on cooling up to 50 K. This value
corresponds to a magnetic moment of 4.77 b, higher than the the-
oretical value for three unpaired electrons (3.88 b), but consistent
small spin–orbit coupling and/or a zero field splitting contribution,
since the cobalt(II) environment is very regular with the two axial
and two equatorial bond distances close to 2 Å, while the other two

6
A. Banerjee et al. / Polyhedron 190 (2020) 114756
Scheme 2. Different types of protons of the ligand, H
spectrum.
L appeared in 1H NMR
2
Fig. 6. Temperature dependence of
using the parameters described in the text.
vT. The solid line represents the best fitting
that the imine group of the Schiff base is reduced. The bands
corresponding to alkyl CAH stretching occur in the range of
À1
2
990–2895 cm has been noticed in the IR spectrum of the com-
plex. Most often metal-carboxylates show two absorption bands in
À1
the IR spectrum around 1413 and 1556 cm due to symmetric and
anti-symmetric stretching vibrations, respectively [52,53]. In the
current case, strong and sharp absorption bands at 1416 and
À1
1
560 cm have been observed which are attributed to symmetric
and antisymmetric stretching vibrations of the carboxylate groups
respectively [54]. A very strong band is obtained (which is
À1
À1
bifurcated at 2026 cm and 2055 cm ) for azide groups [17]. IR
spectrum of the complex has been provided in the Fig. S1
(
Supplementary Information).
An intense absorption band at 365 nm may be assigned as
charge transfer transitions from the coordinated ligand to the
cobalt(III) center (LMCT) [55]. A broad absorption bands at
6
(
18 nm may be attributed to one of the two expected transitions
A ? T1g and A ? T2g) for any low-spin cobalt(III) in dis-
1g 1g
1
1
1
1
torted octahedral geometry [17]. However, this band may also be
considered as d-d transition band of cobalt(II) center [31]. How-
ever, any other bands originating from d-d transition is obscured
by the high intensed LMCT transition [56]. High energy absorption
band around 238 nm may be assigned to intra ligand p–p* transi-
Fig. 7. Plot of the inverse of susceptibility vs. temperature. The solid line represents
the fitting of the data with the parameters reported in the text. The inset shows the
temperature variation of the susceptibility and the corresponding fitting.
tion [57]. Electronic spectrum of the complex has been given in the
Fig. S2 (Supplementary Information). The complex does not exhibit
any IVCT band on the time scale of the electronic transition, and
this justifies that the complex essentially belongs to class-I loca-
lised mixed valence complex [58,59].
equatorial distances of around 2.2 Å can be mainly attributed to
the distortion induced by the steric requirements of the ethoxy
groups, more than to the influence of the metal ion configuration
Scheme 2 refers to the assignment of different types of protons
1
1
2
of the ligand, H L, found in H NMR spectrum. In the H NMR spec-
trum of the ligand, a multiplet peak for the methyl protons [a + b] of
the ethoxy part of 3-ethoxysalicylaldehyde moiety have been
noticed in the range 1.360–1.211 ppm. Signals for the aromatic pro-
tons of the 3-ethoxysalicylaldehyde moiety have been observed as a
multiplet in the range 6.780–6.593 ppm. The benzyl protons
[
43–46]. To account for these contributions the experimental data
in Fig. 6 were fitted using PHI [47]. The Hamiltonian used in the fit-
ting process corresponds to the sum of the Curie behaviour for the
3
2
isolated S =
/
2
plus a zero field splitting term: H = gÁbÁS + DÁS
z
,
where b is the Bohr magneton and D the zero field splitting
paremeter. The best-fitted values were g = 2.39(1) and |D| = 5.3
1) cm , with R = 0.9991. The zero field splitting parameter
appears in the usual range for slightly distorted octahedral cobalt
II) ions [21,48–50].
[
HNCH
3.775 ppm. Signals for three different kind of methylene protons
OCH (c) + OCH (d)], [HNCH (g) + HNCH (h)] and [CH (i)] present
in the ligand appear as multiplet in the range 3.991–3.921 ppm,
2 2
(e) + HNCH (f)] appear as doublet at 3.797 and
À1
2
(
[
2
2
2
2
2
(
2
.562–2.475 ppm and 1.605–1.560 ppm respectively.
3.7. IR, electronic and NMR spectra
4
. Conclusion
The IR and electronic spectra are in good agreement with the
crystal structure of the complex. A moderately sharp band at
In the present work, we have reported the synthesis, structure
and magnetic property of a dinuclear mixed valence cobalt(II/III)
complex. Cobalt(III) is essentially low-spin in the complex and
À1
3
185 cm has been observed in the IR spectrum. This band is
assigned to the NAH stretching vibration [51], confirming the fact

A. Banerjee et al. / Polyhedron 190 (2020) 114756
7
therefore does not contribute any magnetic moment due to the
absence of unpaired electron in it. The room temperature magnetic
moment of the complex is 4.77 b, which is although considerably
higher than the theoretical value for three unpaired electrons
[8] S. Naiya, S. Biswas, M.G.B. Drew, C.J. Gómez-García, A. Ghosh, Inorg. Chem. 51
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561.
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93.
[12] S.K. Dey, A. Mukherjee, New J. Chem. 38 (2014) 4985.
(
[
(
4
(
3.88 b), but this value is not unusual for a cobalt(II) complex
[
due to the presence of spin–orbit coupling. The geometry of
cobalt(II) is severely distorted from octahedral geometry. The vari-
able temperature magnetic susceptibility data were fitted using
1
[
13] K. Ghosh, K. Harms, A. Bauza, A. Frontera, S. Chattopadhyay, CrystEngComm 20
2018) 7281.
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(
the program PHI and the best-fitted values were g = 2.22 and |D|
[
À1
=
8.6 cm . With the coordination geometry of the cobalt(II) and
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4 (2015) 3862.
[17] A. Banerjee, S. Chattopadhyay, Polyhedron 177 (2020) 114290.
(
the D value, it is likely that the complex may exhibit SMM behavior
or at least field induced SMM behavior). We are currently trying to
[
(
4
prepare a series of complexes of this type and will try to check
their potential application as SMM. The work is in progress to
improve the yield of the reaction and to develop more systems
based on this strategy to generalize the concept.
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Abhisek Banerjee: He synthesized the complex and character-
ized it by spectral and elemental analysis and performed all neces-
sary works.
Santiago Herrero and Ángel Gutiérrez: They jointly performed
the magnetic study of the complex.
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Declaration of Competing Interest
[
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Pryce, Inorg. Chem. 49 (2010) 10214.
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to influence the work reported in this paper.
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Acknowledgments
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A. B. thanks the UGC, India, for awarding a Junior Research Fel-
lowship. S. H. thanks the Comunidad de Madrid (project B2017/
BMD-3770). S. C wishes to thank the RUSA 2.0 program of the
Government of India, operating at Jadavpur University under
which they each received ‘‘Research Support to Faculty Members”
for Research Thrust Areas ‘‘Research in Advance Materials”; Sanc-
tion Ref. no. R-11/755/19 dated 27.06.2019.
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Supplementary information (SI) available: Hirshfeld Surface
Analysis, Table S1 and Figures from S1-S2. CCDC 1832082 contains
the supplementary crystallographic data for the complex. Supple-
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