New complexes of Ni(II) and Co(III) with a Schiff-base ligand derived from o-vanillin. Crystal structure, magnetic and catalytic properties of a dissymmetric binuclear nickel(II) complex

Article abstract of DOI:10.1016/j.poly.2018.05.007

A binuclear complex, [Ni₂L₂(NO₃)(H₂O)(CH₃CN)]ClO₄·CH₃CN (1), has been obtained using a Schiff-base ligand (HL) derived from o-vanillin and 4-(2-aminoethyl)morpholine. The crystal

Full text of DOI:10.1016/j.poly.2018.05.007

Accepted Manuscript
New complexes of Ni(II) and Co(III) with a Schiff-base ligand derived from o-
vanillin. Crystal structure, magnetic and catalytic properties of a dissymmetric
binuclear nickel(II) complex
Vlad Andrei Neacşu, Cătălin Maxim, Augustin M. Mădălan, Mihaela
Hillebrand, María del Camino González-Arellano, Stéphane Soriano, Eva
Rentschler, Marius Andruh
PII:
S0277-5387(18)30227-4
https://doi.org/10.1016/j.poly.2018.05.007
POLY 13152
DOI:
Reference:
To appear in:
Polyhedron
Received Date:
Accepted Date:
1 March 2018
1 May 2018
Please cite this article as: V.A. Neacşu, C. Maxim, A.M. Mădălan, M. Hillebrand, M. del Camino González-Arellano,
S. Soriano, E. Rentschler, M. Andruh, New complexes of Ni(II) and Co(III) with a Schiff-base ligand derived from
o-vanillin. Crystal structure, magnetic and catalytic properties of a dissymmetric binuclear nickel(II) complex,
Polyhedron (2018), doi: https://doi.org/10.1016/j.poly.2018.05.007
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New complexes of Ni(II) and Co(III) with a Schiff-base ligand derived from o-
vanillin. Crystal structure, magnetic and catalytic properties of a
dissymmetric binuclear nickel(II) complex
a
a
a
b
Vlad Andrei Neacșu , Cătălin Maxim , Augustin M. Mădălan , Mihaela Hillebrand , María del
c
d
e
a,*
Camino González-Arellano , Stéphane Soriano , Eva Rentschler , Marius Andruh
a.
Inorganic Chemistry Laboratory, Faculty of Chemistry, University of Bucharest, Str. Dumbrava Roșie
nr. 23, 020464-Bucharest, Romania, E-mail: marius.andruh@dnt.ro
b
Department of Physical Chemistry, Faculty of Chemistry, University of Bucharest
c
Departamento de Química Orgánica y Química Inorganíca, Facultad de Farmacia, Universidad de
Alcalá, Campus Universitario, Autovía A2, 33.600, 28871 Alcalá de Henares, Madrid, Spain
d.
Instituto de Física, Universidade Federal Fluminense, Niterói, Rio de Janeiro, 24020-140, Brazil
e.
Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg University Mainz Duesbergweg
10–14, 55128- Mainz, Germany
Dedicated to Professor Spyros Perlepes, a great scientist and friend
ABSTRACT
A binuclear complex, [Ni
2
L
2
(NO
3
)(H
2
O)(CH
3
CN)]ClO
4
·CH CN (1), has been obtained using a
3
Schiff-base ligand (HL) derived from o-vanillin and 4-(2-aminoethyl)morpholine. The crystal
structure of 1 has been solved. Both Ni(II) ions are hexacoordinated, but they display different
coordination spheres. The exchange interaction between the two nickel ions is antiferromagnetic
-
1
(
J = -7.9±0.2 cm ; H = -JS
catalyst in the epoxidation of various olefins. The reaction of the same ligand with a mixture of
cobalt(II) perchlorate and nitrate affords mononuclear Co(III) complex,
CoL (H O)]ClO ·CH OH (2).
1 2
S ), in line with the DFT calculations. Compound 1 was tested as a
a
[
2
2
4
3
Keywords: nickel complexes; cobalt complexes; Schiff-base ligands; magnetic properties;
catalysis
1

1
. Introduction
The interest in the chemistry of oligonuclear complexes of nickel(II) arises from their relevance
in molecular magnetism, model bioinorganic chemistry, and catalysis. Numerous binuclear
complexes have been synthesized and employed as models for the investigation of the factors
governing the nature (ferro- or antiferromagnetic) and strength of the exchange interactions
between the Ni(II) ions mediated by various bridges, e. g. phenoxido [1], azido [2], cyanato and
thiocyanato [2a,3], carboxylato [4] etc. The magneto-structural correlations have been supported
by DFT calculations [1a,b,d]. The bioinorganic chemistry of nickel started with the discovery of
urease, an enzyme that catalyzes the hydrolysis of urea [5], the active site containing two nickel
ions bridged by one carboxylato and one hydroxido group. This discovery prompted chemists to
synthesize model compounds for urease [6], as well as new compounds able to catalyze various
reactions, e. g. epoxidation of aliphatic, aromatic, and terminal olefins [7], hydrolysis of esters
under ambient conditions [8], oligomerization of ethylene [9], and polymerization of olefins
[
10].
The Schiff-base ligands derived from o-vanillin generate a very rich coordination
chemistry [11]. In this paper we report on a new dissymmetric binuclear Ni(II) complex (1),
which is obtained using a Schiff-base proligand resulted from the condensation reaction between
o-vanillin and 4-(2-aminoethyl)morpholine (HL). Its spectral, magnetic, and catalytic properties
in epoxidation reactions of olefins have been investigated. This ligand was already employed by
Mohanta et al. to obtain a binuclear Ni(II) complex with azido bridges [12], by Su et al. to obtain
mononuclear complexes of Co(III) [13], and by Dai et al. to obtain a binuclear Cd(II) complex
[
14]. We also present here the crystal structure of a mononuclear Co(III) complex (2), which is
obtained by reacting the proligand HL with a mixture of cobalt (II) nitrate and perchlorate.
2
. Experimental part
2
.1. Synthesis
All chemicals used for the present study were purchased from commercial sources and used
without further purification.
2
2 2 3 2 3 4 3
.1.1. Synthesis of [Ni L (NO )(H O)(CH CN)]ClO ·CH CN 1
A solution of 45.57 mg 4-(2-aminoethyl)morpholine (0.35 mmol) in 10 mL acetonitrile was
added dropwise under continuous stirring to a solution of 53.25 mg o-vanillin (0.35 mmol) in 15
2

mL acetonitrile. The solution rapidly turned from colorless to bright yellow. After 15 minutes,
5.42 mg triethylamine (0.35 mmol) were added in order to deprotonate the Schiff-base ligand.
After another 30 minutes, a solution of Ni(NO ·6H O (50.89 mg, 0.175 mmol) and
Ni(ClO ·6H O (64 mg, 0.175 mmol) in 10 mL acetonitrile was added dropwise, the color of the
3
3
)
2
2
4
)
2
2
solution changing to dark green. The solution was stirred for another 30 minutes and by slow
evaporation of the solution at room temperature, in 10-14 days, dark green rectangular crystals
−1
were obtained, suitable for X-Ray diffraction. IR (KBr disk/cm ): 3418(w), 2953(w), 2308(w),
1
636(m), 1604(w), 1545(w), 1450(s), 1406(m), 1384(s), 1302(s), 1240(m), 1219(s), 1143(w), 1109(s),
092(s), 970(w), 927(w), 900(w), 865(w), 786(w), 749(w), 624(m). Elemental analysis: calculated
1
for C32
H46ClN
7
Ni
2
O14: C 42.44, H 5.19, N 10.83 %; found: C 42.05, H 5.12, N 10.80 %.
2
.1.2. Synthesis of [CoL
2
(H O)]ClO ·CH OH 2
2
4
3
A solution of 45.57 mg 4-(2-aminoethyl)morpholine (0.35 mmol) in 10 mL methanol was added
dropwise under continuous stirring to a solution of 53.25 mg o-vanillin (0.35 mmol) in 15 mL
methanol. The solution rapidly turned from colorless to bright yellow. After 15 minutes, 35.42
mg triethylamine (0.35 mmol) were added in order to deprotonate the Schiff-base ligand. After
3
0 minutes, a solution of Co(NO
3
)
2
·6H
2
O (50.93 mg, 0.175 mmol) and Co(ClO
4
)
2
·6H O (64.04
2
mg, 0.175 mmol) in 10 mL methanol was added dropwise, the color of the solution changing to
dark brown. The solution was stirred then for 30 minutes and, by slow evaporation at room
−1
temperature, dark brown needle-like crystals were obtained. IR (KBr disk/cm ): 3562(w),
3359(w), 2972(w), 2863(w), 2354(w), 2310(w), 1644(m), 1622(s), 1603(m), 1548(w), 1472(m),
1449(m), 1404(w), 1385(w), 1323(s), 1251(s), 1226(s), 1197(w), 1112(s), 1088(s), 1013(m), 974(w),
931(w), 913(w), 861(w), 776(w), 748(m), 737(m), 668(w), 624(w). Elemental analysis: calculated for
C
29
H
44ClN CoO12: C 47.34, H 5.99, N 7.62 %; found: C 47.09, H 8.41, N 6.10 %.
4
Caution! Perchlorate salts are potentially explosive and they should be handled in small
quantities. The synthesis was carried out at the mmol scale and the crystals were grown by slow
evaporation at room temperature.
3

2
.2. Physical measurements
The IR spectra (KBr pellets) were recorded on a Bruker Tensor 37 spectrophotometer in the
-1
4
000-400 cm region and the UV-Vis spectra were recorded with a Jasco V-670
spectrophotometer.
Magnetic susceptibility measurements on a polycrystalline sample of 1 were carried out on a
Quantum Design SQUID magnetometer in the temperature range 1.9–300 K. The diamagnetic
corrections for the compound were estimated using Pascal’s constants. The magnetic data were
also corrected for diamagnetic contributions of the sample holder.
2
.3. X-ray crystallographic analysis
Crystals were measured on STOE IPDS II single crystal diffractometer, using graphite-
monochromated Mo Kα radiation (λ = 0.71073 Å). The structures were solved by direct methods
2
and refined by full-matrix least-squares techniques based on F . The non-H atoms were refined
with anisotropic displacement parameters. The crystallographic data are collected in Table 1.
2.4. Computational details
The DFT calculations for 1 were performed on the geometries obtained from the X-ray crystal
structure, without other optimization, using two functionals, UB3LYP [15] and UB3PW91 [16],
and two atomic basis sets, LANL2DZ [17] and TZVP [18]. The energies of the Broken
Symmetry (EBS, S = 0) and High Spin (EHS, S = 2) states were calculated using the procedure of
the fragments as implemented in the Gaussian09 program [19] and further checked for their
stability.
2.5. Catalytic properties
In a typical experiment, an ampoule was charged with 3-chloroperbenzoic acid (0.1 mmol),
olefin (0.035 mmol), and nickel catalyst (compound 1) dissolved in acetonitrile (2.5, 5.8 or 10
mmol %). The reaction was carried out with stirring at room temperature for different times. The
resultant mixture was diluted and analyzed by GC-MS. GC-MS was performed using an Agilent
GS-MS turbo system (5975-7820A) model equipped with a HP-5MS capillary column (30 m x
0
4
.25 mm x 0.25 µm), under the following conditions: cyclooctene, styrene, and trans-stilbene:
0˚C, ramp 10˚C/min until 250˚C, held 2 min, solvent delay at 0.0-3.0 min. Retention times:
4

peak at 5.04 min cyclooctene and at 8.20 min epoxide; peak at 4.90 min styrene and at 7.58 min
epoxide; peak at 16.17 min trans-stilbene and at 16.29 min epoxide. Cyclohexene: 40˚C, ramp
1
0˚C/min until 250˚C, held 2 min, solvent delay at 3.50-3.65 min. Retention times: peak at 2.53
min cyclohexene and at 4.42 min epoxide. 1-Hexene: 35˚C, ramp 10˚C/min until 250˚C, held 2
min, no solvent delay. Retention times: peak at 2.05 min 1-hexene and at 4.05 min epoxide.
3
. Results and Discussion
The new compounds have been synthesized in situ, following a two-step procedure: in the first
step the proligand HL (Scheme 1) was obtained by reacting o-vanillin and 4-(2-
aminoethyl)morpholine; in the next step, the deprotonated ligand was reacted with a mixture of
Ni(NO
3
)
2
·6H
2
O and Ni(ClO
4
)
2
·6H
2
O salts for compound 1, and, respectively, a mixture of
Co(NO
3
)
2
·6H
2
O and Co(ClO
4
)
2
·6H
2
O for compound 2.
3
.1. Spectral properties
The FTIR spectra of compounds 1 and 2 show the characteristic bands of the azomethine group
-1
-1
(
1636 cm and 1622 cm respectively), and the uncoordinated perchlorate ion (1109 and 624
-1
-1
cm for 1, respectively 1112 and 624 cm for 2). In the case of compound 1 the FTIR spectrum
-1
also shows the characteristic band of the nitrato ligand (1384 cm ). The diffuse reflectance
electronic spectrum of 1 (Figure 1) clearly shows that the Ni(II) ions are hexacoordinated: the
3
3
3
3
two bands with maxima at 878 nm and 594 nm are assigned to the A
2
→ T
2
and A
2
→ T
1
transitions, respectively (assuming the O symmetry for the two nickel ions) [20]. The spin
3
1
forbidden transition, A → E, is observed at 760 nm.
2
3
.2. Description of the crystal structure
Compound 1 crystalizes in the monoclinic P2
1
/c space group. Its structure consists of non-
centrosymmetric binuclear cations, uncoordinated perchlorate ions, and solvent molecules. A
view of the complex cation is shown in Figure 2. The two anionic Schiff bases act differently as
ligands. One of them (A) is coordinated simultaneously to the two Ni(II) ions (chelated with the
nitrogen atoms and the phenoxido oxygen to Ni2 and with the methoxy group to Ni1); the other
one (B) acts as a NNO tridentate ligand towards Ni1 (the two nitrogen atoms and the phenoxido
oxygen), the methoxy group being uncoordinated. The nickel ions are bridged by the phenoxido
5

oxygen atom (from A) and by the bidentate nitrato ligand. Both Ni(II) ions display a pseudo-
octahedral stereochemistry. Ni1 is coordinated by the two nitrogen and the terminal phenoxido
oxygen atoms from ligand B, two oxygen atoms from the bridging nitrato and phenoxido groups,
and by the methoxy oxygen from ligand A. Ni2 is coordinated by two nitrogen atoms arising
from the organic ligand A, two oxygen atoms from the bridging nitrato and phenoxido groups,
one water molecule, and one acetonitrile molecule. The two Ni–N distances involving the
azomethine nitrogen atoms (Ni1–N2 = 1.980(3); Ni2–N3 = 1.987(3) Å) are shorter than those
involving the morpholine nitrogen atoms (Ni1–N1 = 2.172(3); Ni2–N4 = 2.271(3) Å). The
shortest and longest Ni-O distances involve the terminal phenoxido oxygen atom (Ni1–O8 =
1
.983(2) Å) and, respectively, the methoxy oxygen atom (Ni1–O6 = 2.140(2) Å). The
intramolecular distance between the nickel ions is 3.514 Å and the value of the bridging angle,
Ni1–O4-Ni2, is 117.7º. The shortest intermolecular distance between the nickel ions is 7.514 Å.
Compound 2 crystalizes in the monoclinic P2 /n space group. Its structure consists of
1
mononuclear cations, uncoordinated perchlorate ions, and solvent molecules. A view of the
complex cation is shown in Figure 3. One organic molecule acts as a tridentate chelating ligand
(
through the two nitrogen atoms and the phenoxido oxygen atom); the other one acts as a
bidentate chelating ligand (the nitrogen atom from the azomethine group and the phenoxido
oxygen). The cobalt ion displays an octahedral stereochemistry, being coordinated by three
nitrogen and two oxygen atoms from the organic ligands and by an aqua ligand. The Co-N and
Co-O distances vary between 1.871 and 2.064 Å, confirming the oxidation state of the cobalt ion
(
+3). The cobalt(III) complex reported by Su et al., [CoL
2
(N )], has a similar structure, but the
3
water molecule is replaced by the monodentate azido ligand [13].
3
.3 Magnetic properties
M
The temperature dependence of the χ T product for compound 1 is shown in Figure 4. The value
3
-1
of χ
M
T at room temperature (2.30 cm mol K) corresponds to two S = 1 uncoupled Ni(II) ions
(
M
g = 2.16). By decreasing the temperature, χ T decreases slowly down to 80 K, then more and
3
-1
more, reaching 0.10 cm mol K at 2 K. This behavior suggests the occurrence of an
antiferromagnetic coupling of the two Ni(II) ions. The magnetic data have been analyzed using
the following Hamiltonian: H = -JS
1
S
2
(S
1
= S
2
= 1). The temperature dependence of the molar
magnetic susceptibility is then given by eq. (1):
6

ꢄ
ꢄ
ꢉ
ꢊꢉ
ꢂꢃ ꢅ
2ꢈ + 10ꢈ
ꢌ
ꢆꢇ
ꢀꢁ
=
∙
,
ꢊꢉ
ꢋ =
ꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢍꢎ1ꢏ
ꢉ
ꢆꢇ
1 + 3ꢈ + 5ꢈ
-1
The best fit to the data is obtained with the following parameters: J = -7.9±0.2 cm ; g =
.19±0.02. Since the intermolecular distances between the paramagnetic centers are quite large,
2
we did not include a Weiss term in eq. (1).
To our knowledge, except for compound 1, only one binuclear complex with one phenoxido and
one nitrato bridge is described, but its magnetic properties have not been investigated [21a]. The
few compounds existing in literature and characterized from the magnetic point of view are bi-
and trinuclear species with two phenoxido and one nitrato bridges [21b-d]. In these compounds,
the Ni-O(phenoxido)-Ni angles vary between ~93.2º and ~96.9º, smaller than in 1 and favoring a
ferromagnetic coupling (accidental orthogonality of the magnetic orbitals). Nanda et al. have
shown that, for bis-phenoxido-bridged Ni(II) complexes, values of this angle larger than 97º lead
to antiferromagnetic interactions [1g,h]. The value of the Ni-O(phenoxido)-Ni angle in 1 is
1
17.7º, therefore the antiferromagnetic coupling of the Ni(II) ions is not surprising.
3
.4. DFT calculations
The J value for compound 1 can be calculated according to the eqs. (2-4) [22], using the energy
values for the high (EHS) and low spin states (EBS - Broken Symmetry):
2
J = 2(EBS - EHS)/S max
(2)
(3)
(4)
2
2
J = 2(EBS – EHS)/(<S >HS - <S >BS
)
J = 2(EBS - EHS)/S(S+1)
2
2
In eq. (2), <S >HS and <S >BS are the expectation values of the spin-squared operator in the two
states, HS and BS respectively. In our case, S = S = 1, S = Smax= S + S = 2. The calculated J
1
2
1
2
values, using the three formulas, are gathered in Table 4. Both functionals and basis sets led to
similar J values, in a qualitative agreement with the experimental one; a comparison of the
values calculated by the three equations shows that eq. (4) predicts the lowest J value, which is
close to the experimental one. In the BS state, regardless of the method used, the positive and
7

negative spin densities are concentrated on the two paramagnetic Ni(II) ions and on their close
surroundings, as can be seen in Figure 5; for example, at the UB3LYP/TZVP level, the values
are (+1.646) and (-1.661) respectively.
3
.5. Catalytic properties
The catalytic epoxidation of various olefins was performed with MCPBA (3-chloroperbenzoic
acid) in the presence of Ni-complex (compound 1) under mild conditions [7,23-25]. The oxidant
MCPBA was added to a mixture of olefin, catalyst, and acetonitrile. Blank runs (in the absence
of catalyst) provided almost negligible conversions. The results of the epoxidation reactions are
summarized in Table 5. Quantitative conversions were obtained for cyclic olefins, such as
cyclohexene and cyclooctene (entries 1-2) in very mild conditions: room temperature, short
times (5-10 min) and 1 mol %, under milder conditions than those in literature [7,23]. In
addition, the epoxides were the only products obtained, no by-products were detected, therefore
free radical oxidation reactions were not involved in this epoxidation [23,26,27]. Terminal
olefins are substrates difficult to oxidize [28], even in harder conditions: 60 min and 10 mol %, a
low conversion (entry 3) was obtained.
Styrene was oxidized to its corresponding epoxide with good conversions (68 and 93 %,
entries 4 and 5, respectively). In terms of selectivity, styrene oxide is the major product (≈ 90%),
some amounts of others products being also obtained: benzaldehyde (4.0%) and
phenylacetaldehyde (≈ 6%). Trans-stilbene was converted to trans-stilbene oxide (46 and 49%,
entries 6 and 7, respectively) and benzaldehyde (4.51 and 6.73%, entries 6 and 7, respectively),
but 2-phenylacetophenone was not detected; for olefins containing aromatic rings, the substrates
produced aldehyde and ketone, but our catalyst, in the case of trans-stilbene, is more selective
than others [7,23]. Formation of aldehydes and ketones indicates that the reaction mechanism
implies nickel(III)-oxo or peroxyl radical intermediates [23,28], and the presence of
chlorobenzene supports this proposal. A higher amount of catalyst has a major influence for
styrene (68 vs. 93%, entries 4 and 5, respectively) but not for trans-stilbene (41 vs 46%, entries 6
and 7, respectively). The reason may be that because of the bulky steric hindrance of the phenyl
group, it is unfavourable for the alkene to access the active nickel centre.
8

4
. Conclusions. In conclusion, we described herein two new complexes of Ni(II) and Co(III)
with a Schiff-base ligand derived from o-vanillin. The nickel derivative is a rare example of
dissymmetric binuclear complex, featuring one phenoxido and one nitrato bridges. The exchange
interaction between the nickel(II) ions was found moderately strong antiferromagnetic, in line
with DFT calculations. This compound acts as an efficient catalyst in epoxidation reactions of
olefins.
5
. Acknowledgements. Financial support from the University of Bucharest (Project 741) is
gratefully acknowledged. C. G.-A. gratefully acknowledges the support from the Spanish
Ministerio de Economía y Competitividad (project CTQ2014-55005-P).
6
. Supplementary material
CCDC 1826839 and 1839534 contain the supplementary crystallographic data for 1 and 2. These
data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
9

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12

Table 1. Crystallographic data, details of data collection and structure refinement parameters for
and 2.
1
Compound
1
2
Chemical formula
C
32
H
46Ni
2
N
7
O14Cl
C
29
H
44CoN O12Cl
4
-1
M (g mol )
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
905.63
200(2)
0.71073
735.06
173(2)
0.71073
monoclinic
monoclinic
P 2 /c
1
1
P 2 /n
10.1085(2)
33.0735(3)
11.9323(4)
90
17.3009(10)
10.5552(4)
18.0734(12)
90
b (Å)
c (Å)
α (°)
β (°)
108.497(5)
90
103.793(5)
90
γ (°)
3
V (Å )
3783.16(18)
4
3205.3(3)
4
Z
-3
D
c
(g cm )
1.590
1.143
1888
1.523
-1
µ (mm )
0.689
F(0 0 0)
1544
2
Goodness-of-fit (GOF) on F
0.981
0.805
Final R
, wR
1
, wR
2
[I > 2 σ(I)]
0.0433, 0.1110
0.0587, 0.1216
0.0522, 0.1257
0.0834, 0.1437
0.728, -0.592
R
1
2
(all data)
-3
Largest difference in peak and hole (e Å ) 0.447, -0.639
13

Table 2. Selected bond lengths (Å) and angles (°) for 1
Bond lengths
Ni1 - O2
Ni1 - O4
Ni1 - O6
Ni1 - O8
Ni1 - N1
Ni1 - N2
Ni2 - O1
Ni2 - O4
Ni2 - O5
Ni2 - N3
Ni2 - N4
Ni2 - N5
Bond angles
2.089(2)
2.059(2)
2.140(2)
1.983(2)
2.172(3)
1.980(3)
2.081(2)
2.048(2)
2.070(2)
1.987(3)
2.271(3)
2.080(3)
Ni1 - O4 - Ni2
N1 - Ni1 - N2
N1 - Ni1 - O2
N1 - Ni1 - O4
N1 - Ni1 - O6
N1 - Ni1 - O8
N2 - Ni1 - O2
N2 - Ni1 - O4
N2 - Ni1 - O6
N2 - Ni1 - O8
O2 - Ni1 - O4
O2 - Ni1 - O6
O2 - Ni1 - O8
O4 - Ni1 - O6
O4 - Ni1 - O8
O6 - Ni1 - O8
O1 - Ni2 - O4
O1 - Ni2 - O5
O1 - Ni2 - N3
O1 - Ni2 - N4
O1 - Ni2 - N5
O4 - Ni2 - O5
O4 - Ni2 - N3
O4 - Ni2 - N4
O4 - Ni2 - N5
O5 - Ni2 - N3
O5 - Ni2 - N4
O5 - Ni2 - N5
N3 - Ni2 - N4
N3 - Ni2 - N5
N4 - Ni2 - N5
117.73(10)
83.90(11)
94.27(10)
100.32(10)
89.27(10)
175.02(10)
85.74(10)
169.51(10)
92.95(10)
91.12(10)
103.40(9)
176.07(9)
85.44(10)
77.59(9)
84.58(9)
90.88(10)
91.34(9)
86.51(9)
175.98(10)
94.23(10)
83.03(10)
86.62(9)
91.65(10)
173.14(10)
88.16(10)
96.34(11)
97.69(10)
168.19(11)
82.60(11)
94.39(11)
88.56(11)
14

Table 3. Selected bond lengths (Å) and angles (°) for 2
Bond lengths
Co1 – N1
Co1 – N2
Co1 – N3
Co1 – O2
Co1 – O5
Co1 – O7
Bond angles
1.902(3)
2.064(3)
1.953(2)
1.871(2)
1.874(2)
1.943(3)
O2 – Co1 – O5
O2 – Co1 – N1
O5 – Co1 – N1
O2 – Co1 – O7
O5 – Co1 – O7
N1 – Co1 – O7
O2 – Co1 – N3
O5 – Co1 – N3
N1 – Co1 – N3
O7 – Co1 – N3
O2 – Co1 – N2
O5 – Co1 – N2
N1 – Co1 – N2
O7 – Co1 – N2
N3 – Co1 – N2
91.77(10)
94.66(10)
84.38(11)
88.32(10)
173.75(10)
89.39(11)
85.02(10)
94.68(11)
179.00(11)
91.55(11)
179.78(11)
88.03(10)
85.23(11)
91.87(10)
95.09(10)
15

-1
Table 4. Exchange coupling constants (cm ) for compound 1
Functional
Atomic
Basis Set
Landl2dz
TZVP
(EHS − EBS) (EHS − EBS) J (eq.2) J (eq.3) J (eq.4)
-
1
(Ha)
(cm )
UB3LYP
UB3LYP
UB3PW91
UB3PW91
-0.0001013 -22.22473376 -11.11
-0.0001046 -22.94873792 -11.47
-0.0001018 -22.33443136 -11.17
-0.0001034 -22.68546368 -11.34
-11.11
-11.47
-11.17
-11.34
-7.41
-7.65
-7.44
-7.56
Landl2dz
TZVP
a
Table 5. Epoxidation of olefins by MCPBA with complex 1 as a catalyst.
Time
b
Entry Olefin
Catal. (mmol %)
Conv. (%) Selec. (%)
(
min)
1
2
3
Cyclooctene
1
10
5
98.5
100
16
Epoxide
Epoxide
Epoxide
Epoxide
Cyclohexene
1-hexene
1
10
60
90.65
5.35
4
5
2.5
5.7
60
60
68
93
Benzaldehyde
Phenylacetaldehyde 4.00
Styrene
Epoxide
90.00
6.00
Benzaldehyde
Phenylacetaldehyde 4.00
Epoxide
95.49
4.51
6
7
2.5
5.7
60
60
46
49
Benzaldehyde
Epoxide
Trans-stilbene
92.70
7.30
Benzaldehyde
a
Reactions conditions: MCPBA (0.1 mmol), olefin (0.035 mmol) and nickel catalyst dissolved in acetonitrile
b
(
2.5, 5.8 or 10 mmol %). Based on olefins.
16

Scheme 1. Structure of the Schiff-base proligand, HL.
17

CAPTION TO THE FIGURES
Figure 1. Diffuse reflectance spectrum of 1.
Figure 2. Perspective view of the binuclear complex cation in crystal 1. Hydrogen atoms have
been omitted for clarity.
Figure 3. Perspective view of the mononuclear complex cation in crystal 2. Hydrogen atoms
have been omitted for clarity.
Figure 4. χ T vs. T curve for compound 1.
M
Figure 5. Spin density in the BS state of complex 1 (isosurface cutoff value = 0.001).
18

Figure 1
Figure 2
19

Figure 3
20

Figure 3
Figure 4
Figure 5
21

GRAPHICAL ABSTRACT
22

SYNOPSIS TOC
A novel dissymmetric binuclear Ni(II) complex has been obtained using a Schiff-base ligand derived
from o-vanillin. Its magnetic, spectroscopic and catalytic properties have been investigated
23