Antiferro- to ferromagnetic crossover in diphenoxido bridged NiII2MnII complexes derived from N2O2 donor Schiff base ligands

Article abstract of DOI:10.1016/j.poly.2016.05.021

Three new trinuclear Ni^II-Mn^II complexes have been synthesized using three different "metalloligands" [NiL¹], [NiL²] and [NiL³] derived from the Schiff bases H₂L¹ = N,N′-bis(salicylidene)-1,3-pentanediamine, H₂L² = N,N′-bis(salicylidene)-1,3-propanediamine and H₂L³ = N,N′-bis(salicylidene)-1,3,-diaminopropan-2-ol), respectively. In all three complexes, [(NiL¹)₂Mn(OOCPh)₂(H₂O)₂]·CH₃OH (1), [(NiL²)₂Mn(OOCPh)₂(CH₃OH)₂]·CH₃OH (2) and [(NiL³)₂Mn(OOCPh)₂(H₂O)₂]·CH₃OH (3), in addition to the double phenoxido bridge, the two terminal Ni^II atoms are linked to the central Mn^II by means of a syn-syn bridging benzoate, giving rise to a linear structure. Complex 1 with Ni-O-Mn angle of 97.35° exhibits antiferromagnetic interactions (J_Ni-Mn = -0.60 cm^-1) whereas ferromagnetic exchange is observed in 2 and 3 (J_Ni-Mn = +2.00 and +1.10 cm^-1 respectively) having Ni-O-Mn angle 97.34° (in 2), 97.27° (in 3). Theoretical calculations have been performed in order to understand the effect of structural parameters that can tune the magnetic properties of this type of complexes such as small differences in the Ni-O-Mn angle and/or slight variations in intermolecular contacts within the crystal.

Full text of DOI:10.1016/j.poly.2016.05.021

Accepted Manuscript
Antiferro- to ferromagnetic crossover in diphenoxido bridged NiII MnII com-
2
plexes derived from N2O2 donor Schiff base ligands
Piya Seth, Albert Figuerola, Jesús Jover, Eliseo Ruiz, Ashutosh Ghosh
PII:
S0277-5387(16)30164-4
DOI:
http://dx.doi.org/10.1016/j.poly.2016.05.021
POLY 11995
Reference:
Polyhedron
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Accepted Date:
2 April 2016
3 May 2016
Please cite this article as: P. Seth, A. Figuerola, J. Jover, E. Ruiz, A. Ghosh, Antiferro- to ferromagnetic crossover
in diphenoxido bridged NiII MnII complexes derived from N2O2 donor Schiff base ligands, Polyhedron (2016), doi:
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http://dx.doi.org/10.1016/j.poly.2016.05.021
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Antiferro- to ferromagnetic crossover in diphenoxido bridged NiII MnII
2
complexes derived from N2O2 donor Schiff base ligands
Piya Seth,a,b Albert Figuerola,*c,d Jesús Jover,c,e Eliseo Ruiz,c,e Ashutosh Ghosh*a
a
Department of Chemistry, University College of Science, University of Calcutta, 92, A.P.C. Road, Kolkata-700
009, India; e-mail: ghosh_59@yahoo.com
b
Sister Nibedita Govt. General Degree College for Girls, Hastings House, 20B, Judges Court Road, Kolkata-
700027.
c
Departament de Química Inorgànica, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain;
e-mail: albert.figuerola@qi.ub.edu
d
Institut de Nanociència i Nanotecnologia (IN2UB), Universitat de Barcelona, Martí i Franquès 1-11, 08028
Barcelona, Spain
e
Institut de Recerca de Química Teòrica i Computacional, Universitat de Barcelona, Diagonal 645, E-08028
Barcelona, Spain
Abstract
Three new trinuclear NiII-MnII complexes have been synthesized using three different
“metalloligands” [NiL1], [NiL2] and [NiL3] derived from the Schiff bases H2L1= N,N'-
bis(salicylidene)-1,3-pentanediamine, H2L2= N,N'–bis(salicylidene)-1,3-propanediamine and
H2L3= N,N'-bis(salicylidene)-1,3,-diaminopropan-2-ol), respectively. In all three complexes,
[(NiL1)2Mn(OOCPh)2(H2O)2]·CH3OH (1), [(NiL2)2Mn(OOCPh)2(CH3OH)2]·CH3OH (2) and
[(NiL3)2Mn(OOCPh)2(H2O)2]·CH3OH (3), in addition to the double phenoxido bridge, the two
terminal NiII atoms are linked to the central MnII by means of a syn-syn bridging benzoate, giving
rise to a linear structure. Complex 1 with Ni-O-Mn angle of 97.35º exhibits antiferromagnetic
interactions (JNi−Mn = -0.60 cm-1) whereas ferromagnetic exchange is observed in 2 and 3 (JNi−Mn
= +2.00 and +1.10 cm-1 respectively) having Ni-O-Mn angle 97.34º (in 2), 97.27º (in 3).
Theoretical calculations have been performed in order to understand the effect of structural
parameters that can tune the magnetic properties of such complexes such as small differences in
the Ni-O-Mn angle and/or slight variations in intermolecular contacts within the crystal.
Keywords: Manganese; Nickel; Heterometallic complexes; Magnetic properties; Crossover
angle
1

1. Introduction
Synthesis of homometallic complexes of NiII with salen type Schiff base ligands with a variety of
bridging ligands is well documented over the last few decades due to their interesting magnetic
properties [1], catalytic activity [2] and biological relevance [3]. Octahedral NiII Schiff base
complexes with oxido/phenoxido bridges possess magnetic interactions covering a broad range,
from antiferromagnetism to ferromagnetism and their magneto-structural correlations reveal
interesting trends [4]. The major factor controlling the exchange coupling (J) is the
oxido/phenoxido bridging (Ni–O–Ni) angle. From the experimental observations and theoretical
calculations, it has been found that as Ni–O–Ni angle increases from 90º, the ferromagnetic
coupling decreases and becomes antiferromagnetic at ca. 93.5º for µ2-O bridged dinuclear NiII
complexes [5].
Introduction of heterometal in NiII-Schiff base complexes using “metalloligand” approach is
currently of research interest because it may not only drastically change the topologies but also
the catalytic, photoluminescent and magnetic properties [6]. Among these complexes, a handful
of NiII-MnII complexes have been synthesized and structurally characterized [7,8]. However,
magnetic properties of only few of these complexes were studied [8]. We therefore took an
initiative to synthesize some NiII-MnII complexes with salen type Schiff bases so that we can
establish the dependence of magnetic exchange coupling on structural parameters, especially on
the phenoxido bridging (Ni-O-Mn) angle. Recently, we reported some linear trinuclear
phenoxido and syn-syn carboxylato bridged NiII-MnII complexes with salen type Schiff bases
where the phenoxido bridging angles range from 96.43−98.51º [9]. It has been found that a linear
correlation exists between Ni-O-Mn angle and JNi-Mn values. From the experimental and
theoretical results we proposed that the antiferromagnetic to ferromagnetic crossover angle
should be ca. 98º for this type of complexes. To verify our predictions, we would like to
synthesize similar type of NiII-MnII complexes having identical bridging modes with Ni-O-Mn
angle close to 98º that would provide with an opportunity to study the effect of small variation of
bridging angle on magnetic coupling.
Herein, we report the synthesis, crystal structure, and magnetic properties of three new
phenoxido and syn-syn benzoato bridged NiII-MnII complexes derived from three closely related
Schiff base ligands H2L1= N,N'-bis(salicylidene)-1,3-pentanediamine, H2L2= N,N'–
2

bis(salicylidene)-1,3-propanediamine and H2L3= N,N'-bis(salicylidene)-1,3,-diaminopropan-2-ol.
The complexes are (1),
[(NiL1)2Mn(OOCPh)2(H2O)2]·CH3OH
[(NiL2)2Mn(OOCPh)2(CH3OH)2]·CH3OH (2) and [(NiL3)2Mn(OOCPh)2(H2O)2]·CH3OH (3).
The Ni-O-Mn values for these complexes are 97.35º (in 1), 97.34º (in 2), 97.27º (in 3). Variable
temperature magnetic susceptibility measurements exhibit clear antiferromagnetic interactions
between NiII and MnII ions in 1, while ferromagnetic exchange is observed in 2 and 3.
Theoretical DFT calculations have been performed in order to analyze the fact that small
differences in the Ni-O-Mn angle can tune the magnetic properties of such complexes.
2. Experimental
2.1. Starting materials
Salicylaldehyde, 1,3-diaminopentane, 1,3-diaminopropane, 1,3-diaminopropan-2-ol, and benzoic
acid were purchased from Lancaster and were of AR grade and used without further purification.
Manganese benzoate [Mn(OOCPh)2·4H2O] was synthesized by a reported procedure [10a].
2.2. Synthesis of the Schiff-Base Ligands N,N'-bis(salicylidene)-1,3-pentanediamine
(H2L1), N,N'–bis(salicylidene)-1,3-propanediamine (H2L2), and N,N'-bis(salicylidene)-
1,3,-diaminopropan-2-ol (H2L3)
Three di-Schiff base ligands, H2L1, H2L2 and H2L3 were synthesized in our laboratory by
standard methods [10b]. Salicylaldehyde (1.05mL, 10 mM) was mixed with respective
diammines viz. 1,3-diaminopentane (0.596 mL, 5 mM), 1,3-propanediamine (0.42 mL, 5 mM),
1,3-diaminopropan-2-ol ( 0.295 g, 5 mM) in methanol (20 mL) and the resulting mixtures were
refluxed for ca. 1.5 h and allowed to cool to room temperature. The desired yellow crystalline
ligands were filtered off from each solution, washed with methanol, and dried in a vacuum
desiccator containing anhydrous CaCl2.
2.3. Synthesis of the ‘metalloligands’ [NiL1], [NiL2] and [NiL3]
Three metalloligands have been prepared by following the same procedure. A mixture of the
required di-Schiff base ligand H2L1 (1.54 g, 5mM), H2L2 (1.432 g, 5 mM) and H2L3 (1.49 g,
5mM) in methanol and aqueous ammonia solution (10 mL, 20%) were added to a methanolic
3

solution (20 mL) of Ni(ClO4)2·6H2O (1.825 g, 5 mM) to prepare the desired ‘metalloligand’
[NiL1], [NiL2] and [NiL3], respectively as previously reported [11].
2.4.
Synthesis
of
complexes
[(NiL1)2Mn(OOCPh)2(H2O)2]·CH3OH
(1),
[(NiL2)2Mn(OOCPh)2(CH3OH)2]·CH3OH (2) and [(NiL3)2Mn(OOCPh)2(H2O)2]·CH3OH (3)
To a 20 mL methanolic solution of respective metalloligands i.e. [NiL1] (0.734 g, 2mM), [NiL2]
(0.680g, 2mM), [NiL3] (0.710 g, 2mM), a 1:10 H2O-MeOH (v/v, 10 mL) mixture of
Mn(OOCPh)2·4H2O (0.370 g, 1 mM) was added drop wise. The resulting mixture was stirred for
ca 1 h at room temperature. It was filtered and the filtrate was kept in a beaker inside a
desiccator. X-ray quality single-crystals of 1-3 appeared at the wall of the respective beakers on
evaporation of the solvent after 2-3 days.
Complex 1: Yield: 0.860 g (76%) C54H62N4O12Ni2Mn (1131.40): calcd C, 57.32; H, 5.52; N,
4.95; found C, 57.24; H, 5.49; N, 4.88. IR (KBr pellet, cm−1) 1630 ν(C=N), 1554 νas(COO), 1471
νs(COO).
Complex 2: Yield: 0.746 g (68%) C52H53N4O12Ni2Mn (1098.30): calcd C, 56.86; H, 4.86; N,
5.10; found C, 56.71; H, 4.82; N, 4.95. IR (KBr pellet, cm−1) 1630 ν(C=N), 1557 νas(COO), 1401
νs(COO).
Complex 3: Yield: 0.786 g (71%) C50H54N4O14Ni2Mn (1107.29): calcd C, 54.23; H, 4.92; N,
5.06; found C, 54.21; H, 4.90; N, 4.92. IR (KBr pellet, cm−1) 1635 ν(C=N), 1564 νas(COO), 1474
νs(COO).
2.5. Physical measurements
Elemental analyses (C, H, and N) were performed using a Perkin-Elmer 240C elemental
analyzer. IR spectra in KBr (4000–500 cm−1) were recorded using a Perkin-Elmer RXI FTIR
spectrophotometer. Temperature-dependent molar susceptibility measurements of polycrystalline
samples of 1-3 were carried out at the ‘‘Servei de Magnetoquímica (Universitat de Barcelona)’’
in a Quantum Design SQUID MPMSXL susceptometer with an applied field of 3000 and 198 G
in the temperature ranges 2–300 and 2–30 K, respectively.
4

2.6. Computational details
To calculate the exchange interactions, a phenomenological Heisenberg-Dirac-van Vleck
Hamiltonian was used, excluding the terms relating to magnetic anisotropy, to describe the
exchange coupling in a general polynuclear complex:
ˆ ˆ
H = − J S S
b
ˆ
∑
(1)
ab
a
a<b
ˆ
ˆ
Sa
Sb
Jab
where
and
are the spin operators of the different paramagnetic cations. The
parameters
are the pairwise coupling constants between the paramagnetic centres of the molecule. Basically,
we need to calculate the energy of n+1 spin distributions for a system with n different exchange
coupling constants [12]. These energy values allow us to build up a system of n equations in
which the J values are the unknowns. In the present study, three calculations were performed in
order to obtain the two exchange coupling constants of the MnNi2 complexes. They correspond
to the high-spin S = 9/2 state, one S = 1/2 wave function flipping the spin of the central
manganese atom, and finally one S = 5/2 with the spin inversion of the two external nickel
atoms. Theoretical Calculations were performed with the hybrid B3LYP functional [13] as
implemented in Gaussian09 code [14] which employs a procedure that allows us to determine
individually the local charges and multiplicities of the atoms, including the ligand field effects
[15].
2.7. Crystal data collection and refinement
Suitable single crystals of complexes 1-3 were mounted on a Bruker-AXS SMART APEX II
diffractometer equipped with a graphite monochromator and Mo-Kα (λ = 0.71073 Å) radiation.
The crystals were positioned at 60 mm from the CCD. 360 Frames were measured with a
counting time of 10 s. The structures were solved by the Patterson method using the SHELXS
97. Subsequent difference Fourier synthesis and least-square refinement revealed the positions of
the remaining non-hydrogen atoms that were refined with independent anisotropic displacement
parameters. Hydrogen atoms were placed in idealized positions and their displacement
parameters were fixed to be 1.2 times larger than those of the attached non-hydrogen atom.
Absorption corrections were carried out using the SADABS program [16]. All calculations were
carried out using the SHELXS 97 [17], SHELXL 97 [18], PLATON 99 [19], ORTEP-32 [20]
5

and WinGX system Ver-1.64 [21]. Data collection, structure refinement parameters and
crystallographic data for the three complexes are given in Table 1.
3. Results and Discussion
3.1. Syntheses and IR spectra of the complexes
Three new trinuclear heterometallic NiII-MnII benzoato bridged complexes derived from three
different tetradentate Schiff base ligands have been synthesized. For this purpose, we have first
prepared the required Schiff bases in the laboratory following the reported procedure [10b] and
then synthesized the respective ‘metalloligands’ [NiL1], [NiL2] and [NiL3] using these Schiff
bases. These ‘metalloligands’ on reaction with Mn(OOCPh)2·4H2O (0.370 g, 1 mM) in H2O-
MeOH solvent yielded the desired linear trinuclear diphenoxido and benzoato bridged complexes
1-3 (Scheme 1). Besides elemental analysis, all three complexes were characterized by IR
spectroscopy. All three complexes exhibit a strong and sharp band at 1630-1635 cm–1, due to
azomethine ν(C=N). Other peaks due to asymmetric and symmetric stretching of carboxylate are
observed at 1554, 1471 cm–1 (in 1) 1557, 1401 cm–1 (in 2) 1564, 1474 cm–1 (in 3) respectively.
H
X
R
N
N
H
X
R
OH
Ni(ClO4)2.6H2O
NH3/ MeOH
HO
Y
N
N
HO
Ni
O
H
X
N
O
O
C-Ph
R
Mn(OOCPh)2·4H2O
H2O/MeOH
O
O
Mn
Ni
N
Ph-C
O
O
Ni
O
OH
O
O
N
N
Y
X=H; R= C2H5; Y= H in 1
X=H; R=H; Y=Me in 2
X=OH; R=H; Y= H in 3
R
X
H
Scheme 1. Formation of complexes 1–3.
6

3.2. Structure descriptions of the complexes
All three complexes consist of similar structures containing the two terminal NiII and a central
MnII atoms in a linear disposition. The X-ray crystal structure of 1 reveals that it consists of a
centrosymmetric trinuclear unit [(NiL1)2Mn(OOCPh)2(H2O)2]·CH3OH. An ORTEP diagram of 1
is shown in Figure 1 and the selected bond lengths and bond angles are summarized in Table 2.
Here, the six-coordinated manganese is in a distorted octahedral environment and is bonded to
four oxygen atoms from the two metalloligands [NiL1], at distances ranging between 2.154(3)-
2.168(2) Å that form the basal plane of the MnII. The trans axial positions are occupied by the
oxygen atom of the syn-syn bridging benzoate (1κO:2κO′) at a distance 2.225(2) Å.
The two terminal nickel atoms are bonded to four donor atoms (O(1), O(2), N(1), N(2)) of the
ligand L1, which makes the basal plane with Ni-N distance 2.025(4)-2.048(3) Å and Ni-O
distance 2.023(2)-2.031(2) Å. One of the axial positions is occupied by oxygen atom O(4) of the
syn-syn bridging benzoate at a distance 2.052(3) Å. The other axial position of the nickel atom is
bonded to the oxygen atom O(5) of a water molecule at a distance of 2.174(3) Å completing an
octahedral geometry around NiII. The Root-mean-square (r.m.s) deviation shown by four donor
atoms in the basal plane from their mean plane is 0.013 Å while the Ni atom is deviated by
0.078(5) Å from the plane towards the carboxylato oxygen O(4). In this complex Ni···Mn
distance is 3.146(1) Å and the two Ni-O-Mn bridging angle 97.26(9) and 97.47(9)˚.
Figure 1. ORTEP-3 view of 1 with ellipsoids at 20% probability.
7

Complex 2 consists of two similar centrosymmetric trinuclear units 2A and 2B having the same
composition [(NiL2)2Mn(OOCPh)2(CH3OH)2]·CH3OH. An ORTEP diagram of 2A is shown in
Figure 2 and selected bond length and bond angles are summarized in Table 2. Here, both the
units contain a six-coordinate central MnII in a distorted octahedral environment along with two
six-coordinated octahedral NiII with equivalent geometries at terminal positions. The manganese
atom is bonded to four oxygen atoms from the two ligands L2, at distances ranging between
2.170(2)- 2.176(2) Å in 2A and 2.162(2)- 2.168(2) Å in 2B, that form the basal plane of the MnII.
Two trans axial positions are occupied by the oxygen atoms O(3) (in 2A) and O(8) (in 2B) of the
syn-syn bridging benzoate at distances of 2.223(2) and 2.183(2) Å in 2A and 2B, respectively.
The nickel atoms are bonded to four donor atoms (O(1), O(2), N(1), N(2) in 2A and (O(6), O(7),
N(3), N(4) in 2B) of the ligand L2, making up the equatorial plane with Ni–O distances in the
range of 2.020(2)-2.033(2)Å in 2A, 2.015(2)-2.018(2)Å in 2B and Ni–N distances of 2.023(2)-
2.029(2)Å in 2A, 2.023(2)-2.024(2)Å in 2B. One of the axial positions is occupied by oxygen
atom (O(4) in 2A, O(9) in 2B) of the syn-syn bridging benzoate at distances of 2.079(2) and
2.051(2) Å, respectively. The other axial positions of the nickel atoms are bonded to the oxygen
atom of the solvent methanol at distances of 2.151(2) Å in 2A and 2.253(3) Å in 2B. The mean
deviations of four donor atoms in the basal plane from their respective mean plane are 0.0019 Å
(in 2A), 0.00015 Å (in 2B) while the Ni atom is deviated by 0.029(1) Å to the direction of the
axial O(4) in 2A and 0.081(1) Å towards O(9) in 2B. Ni···Mn distance is 3.173 Å in 2A and
3.124 Å in 2B. Two Ni-O-Mn bridging angles are 97.98(8), 98.15(8)˚ in 2A and 96.57(8),
96.65(8)˚ in 2B.
8

Figure 2. ORTEP-3 view of 2A with ellipsoids at 20% probability. There are two trimers with
equivalent structures, only one is shown.
Complex 3 has the chemical composition [(NiL3)2Mn(OOCPh)2(H2O)2]·CH3OH and its structure
is very similar with 1. An ORTEP diagram of 3 is shown in Figure 3 and the selected bond
length and bond angles are summarized in Table 2. Here the central manganese is bonded to four
oxygens from the two metalloligands [NiL3], at distances ranging between 2.167(3)-2.192(3) Å
that form the basal plane of the MnII. The trans axial positions are occupied by the oxygen atom
of the syn-syn bridging benzoate (1κO:2κO′) at a distance 2.224(3) Å.
The two terminal nickel atoms are bonded to four donor atoms (O(1), O(2), N(1), N(2)) of the
ligand L3, which makes equatorial plane with Ni-N distance 2.022(4) - 2.025(4) Å and Ni-O
distance 2.014(3)- 2.030(3) Å. One of the axial positions is occupied by oxygen atom O(4) of the
syn-syn bridging benzoate at a distance 2.059 (3)Å and the other axial positions is bonded to the
oxygen atom O(5) of a water molecule at a distance 2.193(4) Å which is slightly longer than that
of 1. The r.m.s deviation shown by four donor atoms in the basal plane from their respective
mean plane is 0.026 Å while the Ni atom is deviated by 0.027(1) Å from the plane towards the
carboxylato oxygen O(4). In this complex Ni…Mn distance is 3.159(1) Å and the two Ni-O-Mn
bridging angle 97.26(1) and 97.57(1)˚.
9

Figure 3.The structure of 3 with ellipsoids at 30% probability.
3.3. Magnetic Properties
Magnetic measurements in complex 1 clearly confirm that an antiferromagnetic exchange is
operating between NiII and MnII ions within this complex. On the contrary, the magnetic
interaction is ferromagnetic in nature for complexes 2 and 3. Temperature-dependent molar
susceptibility measurements on polycrystalline samples of 1-3 were carried out in an applied
field of 0.3 T in the temperature range 1.9-300 K. The data are shown in the χMT versus T plot in
Figure 4, where χM is the molar magnetic susceptibility and T is the absolute temperature. The
room temperature values of χMT for compounds 1-3 are 6.60, 6.64 and 6.66 cm3mol-1K
respectively, slightly higher than the 6.4 cm3mol-1K value expected for non-interacting NiII-MnII-
NiII trinuclear units. The χMT values measured for complex 1 are kept approximately constant
down to 100 K, temperature below which they start decreasing gradually reaching a value of
4.10 cm3mol-1K at 2 K. On the other hand, for complexes 2 and 3, the χMT values increase with
decreasing temperature until they reach a maximum of 7.28 cm3mol-1K at 15 K for 2 and 8.44
cm3mol-1K at 5.5 K for 3. Below these temperatures, the value of χMT drops sharply. In order to
quantitatively interpret these data, simulations of the experimental curves were done by using the
MAGPACK program as shown in Figure 4 [22]. A Hamiltonian of the type H=−J[S1S2+S1S3],
where S1 = SMn and S2=S3=SNi, was used for the simulations. In the model, the crystallographic
10

equivalence of the two NiII ions in the trinuclear unit was considered by assigning one single g
value for that ion. Additionally, one single set of magnetic parameters was deduced for each of
the studied compounds, regardless of the presence of two non-equivalent Ni2Mn trinuclear
molecules in the unit cell in 2. Simulations were carried out including a zero field splitting (D)
value for the two NiII ions and considering that the exchange coupling between these two
terminal ions was zero (JNi-Ni = 0 cm-1). Moreover, a term accounting for intermolecular
interactions (zJ’) was also included. The best agreement between experimental and simulated
curves was obtained with the following sets of parameters: gNi = 2.10, gMn = 2.00, DNi = 4.0 cm-1,
JNi-Mn = -0.60 cm-1 and zJ’ = -0.05 cm-1 for complex 1; gNi = 2.10, gMn = 2.00, DNi = 4.0 cm-1, JNi-
Mn = 2.00 cm-1 and zJ’ = -0.40 cm-1 for complex 2; and gNi = 2.10, gMn = 2.00, DNi = 4.0 cm-1, JNi-
Mn = 1.10 cm-1 and zJ’ = -0.08 cm-1 for complex 3.
Figure 4. Thermal dependence of the χMT for complexes 1-3. Symbols represent experimental
data while straight lines represent the simulations obtained from the parameters indicated in the
main text.
We recently reported a magnetostructural study on similar diphenoxido-bridged NiII -MnII
2
coordination complexes.9 A linear dependency was found between the JNi-Mn value and the Ni-O-
Mn angle of the monodentate phenoxido bridges, from which a value of the crossover angle from
ferro to antiferromagnetic exchange could be assigned. This value corresponds approximately to
11

98° and apparently indicates that the family of NiII-MnII complexes supports ferromagnetic
interactions up to angles higher than those observed among other known MM' diphenoxido-
bridged complexes, except for the MnIIIMnIII family of compounds [23]. Three new diphenoxido-
bridged NiII -MnII complexes (1-3) which have been presented in this work, we have described
2
the synthesis and structural characterization possess analogous skeleton to that of previously
reported molecules. Thus, it is expected for them to follow a magnetic behavior in agreement
with the previously mentioned linear dependency. At first glance, the experimental JNi-Mn values
seem to be consistent with it, showing that these complexes have magnetic exchange couplings
of either ferro- or antiferromagnetic nature but always with low magnetic constants in agreement
with the values of their Ni-O-Mn angles close to 98°, as shown in Table 3. However, a close look
at the data reveals one main discrepancy: the largest ferromagnetic JNi-Mn exchange constant
corresponds to complex 2, although this displays an intermediate Ni-O-Mn angle with respect to
complexes 1 and 3. Yet, the very similar Ni-O-Mn angles shown by the three complexes, the
difference between the lowest and highest values being 0.08°, do not allow extracting reliable
conclusions based only on the previously reported magnetostructural correlation. Additionally,
complex 2 contains two non-equivalent molecules in the unit cell with slightly different
structural parameters, which will therefore lead to substantially different magnetic exchange
constants. Nevertheless, the contribution of each molecule to the bulk average magnetic behavior
cannot be ascertained from the measurement performed on crystalline powder. Thus, theoretical
calculations have been addressed to better understand the systems.
The experimental (exp) and calculated (calc) JNi-Mn magnetic exchange constants for complexes
1-3 are displayed in Table 3, together with their corresponding Ni-O-Mn angle values. The
calculations provide average JNi-Mn values that follow the same trend observed for the
experimental ones in all three complexes, confirming that the most ferromagnetic JNi-Mn constant
corresponds to complex 2, albeit its intermediate Ni-O-Mn angle. Remarkably, the two non-
equivalent molecules in complex 2 show significantly different values of the Ni-O-Mn angle,
being these 98.07° and 96.61° respectively. Accordingly, calculations performed on single
molecules provided an antiferromagnetic JNi-Mn constant for the former (-0.45 cm-1) and a larger
ferromagnetic one (+2.16 cm-1) for the latter, in complete agreement with the expected behavior.
Indeed, only JNi-Mn > 0 have been obtained from calculations in complexes with Ni-O-Mn angles
below 98°, and only antiferromagnetic couplings have been calculated for complexes with Ni-O-
12

Mn angles above 98°, as shown in Figure 5, suggesting a crossover angle at ca. 98°, in complete
agreement with our previous work.9 All in all, these results evidence the relevance of the Ni-O-
Mn angle dictating the strength and nature of the magnetic exchange interaction in such
complexes, and further confirm a ferro to antiferromagnetic crossover angle at around 98° for
diphenoxido-bridged NiII -MnII coordination compounds. The small deviations from the linear
2
dependency evidence however the presence of secondary structural factors that further tune the
magnetic properties of such complexes such as small differences in the Ni-O-Mn angle and/or
slight variations in intermolecular contacts within the crystal.
Figure 5. Linear variation of the calculated JNi-Mn values and the Ni-O-Mn angles of the µ2-
phenoxido bridging ligands for complexes 1-3 and for complexes reported in ref 9. Both
parameters have been considered independently for non equivalent molecules contained in
complex 2 of this work and complexes 1 and 2 of ref. 9. Additionally, an octahedral coordination
environment has been considered in the calculation for NiII ions in complex 2 of ref. 9 for ease of
comparison (more details can be found in ref. 9). The linear fit of the data yields an adjusted R2
value of 88.9%.
13

4. Conclusions
Three new diphenoxido and syn-syn benzoate bridged NiII-MnII complexes derived from three
different salen type Schiff base ligands are synthesized and characterized. All three have similar
trinuclear linear structures comprised of a central octahedral MnII and two terminal octahedral
NiII atoms having very slight variations in average phenoxido bridging angles (97.27-97.35°).
The dependence between magnetic exchange coupling (JNi-Mn) and phenoxido bridging angle
(Ni-O-Mn) has been verified theoretically for this type of complexes, confirming that small
differences in this structural parameter are responsible for ferro- or antiferromagnetic interaction
between the two metal centers within the complex.
Acknowledgements
We are thankful to Prof. Michael G. B. Drew, School of Chemistry, The University of Reading,
U.K., for helpful discussions on the crystallographic part. We thank DST-FIST, India funded
Single Crystal Diffractometer Facility at the Department of Chemistry, University of Calcutta,
Kolkata, India. The authors thank Department of Science and Technology (DST), New Delhi,
India, for financial support (SR/S1/IC/0034/2012). P.S is thankful to UGC for research
fellowship [UGC/52/Jr. Fellow (Enhancement) dated 17.01.2013]. A.F acknowledges financial
support from the Spanish Ministerio de Economía y Competitividad (MINECO) through
CTQ2012-32247 and for a Ramón y Cajal Fellowship (RYC-2010-05821), and from the regional
Generalitat de Catalunya authority (2014SGR-129). E.R. also thanks Generalitat de Catalunya
for an ICREA Academia award. The authors thankfully acknowledge the computer resources,
technical expertise and assistance provided by the CSUC (Consorci de Serveis Universitaris de
Catalunya).
Notes and References
CCDC 1437810-1437812 contain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
14

[1] a) R. Biswas, Y. Ida, M. L. Baker, S. Biswas, P. Kar, H. Nojiri, T. Ishida, A. Ghosh, Chem.–
Eur. J. 19 (2013) 3943–3953; b) R. Biswas, S. Mukherjee, P. Kar, A. Ghosh, Inorg. Chem., 51
(2012) 8150–8160.
[2] a) K. Yamaguchi, S. Koshino, F. Akagi, M. Suzuki, A. Uehara, S. Suzuki, J. Am. Chem. Soc.
119 (1997) 5752–5753; b) A. Biswas, L. K. Das, M. G. B. Drew, G. Aromí, P. Gamez, A.
Ghosh, Inorg. Chem. 51 (2012) 7993–8001.
[3] a) R. N. Patel, A. Singh, V. P. Sondhiya, Y. Singh, K. K. Shukla, D. K. Patel, R. Pandey, J.
Coord. Chem. 65 (2012) 795–812; b) S. Ciurli, in Metal Ions in Life Sciences, ed. A. Sigel, H.
Sigel, R. K. O. Sigel, John Wiley & Sons, Chichester, vol. 2 (2007) 241–278.
[4] a) K. K. Nanda, R. Das, L. K. Thompson, K. Venkatsubramanian, K. Nag, Inorg. Chem. 33
(1994) 5934–5939; b) R. Biswas, P. Kar, Y. Song, A. Ghosh, Dalton Trans. 40 (2011) 5324–
5331; c) R. Biswas, S. Giri, S. K. Saha, A. Ghosh, Eur. J. Inorg. Chem. (2012) 2916–2927.
[5] A. Burkhardt, E. T. Spielberg, S. Simon, H. Gçrls, A. Buchholz, W. Plass, Chem. Eur. J. 15
(2009) 1261–1271.
[6] a) C. Arici, D. Ulku, O. Atakol, Anal. Sci. 18 (2002) 959–960; b) M. Sari, O. Atakol, I.
Svoboda, Anal. Sci.: X-ray Struct. Anal. Online 21 (2005) x205–x206; c) O. Atakol, H. Nazir, C.
Arici, S. Durmus, I. Svoboda, H. Fuess, Inorg. Chim. Acta 342 (2003) 295–300; d) S. Ghosh, S.
Mukherjee, P. Seth, P. S. Mukherjee, A. Ghosh Dalton Trans. 42 (2013) 13554-13564; e) L. K.
Das, A. Biswas, C. J. Gómez-García, M. G. B. Drew, A. Ghosh Inorg. Chem. 53 (2014)
434−445; f) H.-P. Jia, W. Li, Z.-F. Ju, J. Zhang, Inorg. Chem. Commun. 10 (2007) 397–400.
[7] a) F. Ercan, O. Atakol, Acta Crystallogr., Sect. C: Cryst. Struct. Commun. 54 (1998)
1268−1270; b) F. Ercan, O. Atakol, C. Arici, I. Svoboda, H. Fuess, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun. 58 (2002) m193−m196; c) O. Atakol, H. Nazir, Z. Durmus, I. Svoboda,
H. Fuess, Anal. Sci. 18 (2002) 493; d) H. Chen, C. B. Ma, D. Q. Yuan, M.-Q. Hu, H.-M. Wen,
Q.-T. Liu, C.-N. Chen, Inorg. Chem. 50 (2011) 10342−10352; e) P. Seth, L. K. Das, M. G. B.
Drew, A. Ghosh, Eur. J. Inorg. Chem. (2012) 2232–2242.
15

[8] a) A. K. Sharma, F. Lloret, R. Mukherjee, Inorg. Chem. 46 (2007) 5128−5130; b) T.
Kobayashi, T. Yamaguchi, H. Ohta, Y. Sunatsuki, M. Kojima, N. Re, M. Nonoyama, N.
Matsumoto, Chem. Commun. (2006) 1950−1952.
[9] P. Seth, A. Figuerola, J. Jover, E. Ruiz, A. Ghosh, Inorg. Chem. 53 (2014) 9296-9305.
[10] a) W. Ferenc, Gazz. Chim. Ital. 125 (1995) 23–26; b) J. Reglinski, S. Morris, D. E.
Stevenson Polyhedron, 21 (2002) 2167−2174.
[11] M. G. B. Drew, R. N. Prasad, R. P. Sharma, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun. 41 (1985) 1755−1758.
[12] a) E. Ruiz, P. Alemany, S. Alvarez, J. Cano, J. Am. Chem. Soc. 119 (1997) 1297-1303; b)
E. Ruiz, Struct. Bond. 113 (2004) 71; c) E. Ruiz, A. Rodríguez-Fortea, J. Cano, S. Alvarez, P.
Alemany, J. Comp. Chem. 24 (2003) 982-989; d) E. Ruiz, S. Alvarez, J. Cano, V. Polo, J. Chem.
Phys. 123 (2005) 164110; e) E. Ruiz, A. R. Fortea, J. Tercero, T. Cauchy, C. Massobrio, J.
Chem. Phys. 123 (2005) 074102.
[13] A. D. Becke, J. Chem. Phys. 98 (1993) 5648–5652.
[14] Gaussian 09 (Revision D01): M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M.
A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson, H. Nakatsuji,
M. Caricato, X. Li, H. P. Hratchian, A. F. zmaylov, I. J. Bloino, G. Zheng, J. L. Sonnenberg, M.
Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O.
Kitao, H. Nakai, T. Vreven, J. J. A. Montgomery, J. E. Peralta, F. Ogliaro, M. Bearpark. J. J.
Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov, R. Kobayashi, J. Normand, K. Raghavachari,
A. Rendell, J. C. Burant, S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene, J.
E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E. Stratmann, O.
Yazyev, A. J. Austin, C. Cammi, J.W. Pomelli, R. Ochterski, R. L. Martin, K. Morokuma, V. G.
Zakrzewski, G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels, O. Farkas, J.
B. Foresman, J.V. Ortiz, J. Cioslowski, D. J. Fox, Wallingford, CT, 2009. Using a guess function
generated with the Jaguar 7.0 code, Jaguar 7.0: Schrödinger, LLC, New York, 2007.
[15] a) G. Vacek, J. K. Perry, J.-M. Langlois, Chem. Phys. Lett. 310 (1999) 189–194; b) A.
Schaefer, C. Huber, R. Ahlrichs, J. Chem. Phys. 100 (1994) 5829 –5835.
16

[16] SAINT, version 6.02, SADABS, version 2.03, Bruker AXS, Inc., Madison, WI, 2002.
[17] G. M. Sheldrick, SHELXS-97, Program for solution of crystal structures, University of
Göttingen, Germany, 1997.
[18] G. M. Sheldrick, SHELXL-97, Program for refinement of crystal structures, University of
Göttingen, Germany, 1997.
[19] A. L. Spek, Acta Crystallogr., Sect. A: Fundam. Crystallogr. 46 (1990) C34.
[20] L. J. Farrugia, J. Appl. Crystallogr. 30 (1997) 565.
[21] L. J. Farrugia, J. Appl. Crystallogr., 32 (1999) 837.
[22] a) J. J. B. Almenar, J. M. C. Juan, E. Coronado, B. S. Tsukerblat, J. Comput. Chem. 22
(2001) 985-991; b) J. J. B. Almenar, J. M. C. Juan, E. Coronado, B. S. Tsukerblat, Inorg. Chem.
38 (1999) 6081-6088.
[23] a) Z. Lu, M. Yuan, F. Pan, S. Gao, D. Zhang, D. Zhu, Inorg. Chem. 45 (2006) 3538−3548;
b) G. Bhargavi, M. V. Rajasekharan, J.-P. Costes, J.-P Tuchagues Polyhedron 28 (2009)
1253−1260; c) P. Kar, P. M. Guha, M. G. B. Drew, T. Ishida, A. Ghosh Eur. J. Inorg. Chem.
(2011) 2075–2085; d) S. Naiya, S. Biswas, M. G. B. Drew, C. J. Gómez-García, A. Ghosh Inorg.
Chem. 51 (2012) 5332−5341.
Table 1. Crystal data and structure refinement of complexes 1-3.
1
2
3
Formula
C54H62N4O12Ni2Mn C52H53N4O12Ni2Mn C50H54N4O14Ni2Mn
Formula weight
Space group
1131.40
P-1
1098.30
P-1
1107.29
C2/c
Crystal system
Triclinic
10.991(5)
11.355(5)
12.237(5)
74.224(5)
70.492(5)
69.382(5)
1326.6(1)
Triclinic
Monoclinic
17.497(5)
12.968(5)
21.787(5)
90.00
97.574(5)
90.00
a/ Å
b/ Å
c/ Å
α/°
β/°
γ/°
10.745(5)
11.523(5)
21.366(5)
103.842(5)
102.060(5)
93.906(5)
2492.4(17)
3
4900(3)
V/Å
Z
1
2
4
17

Dcalc/g cm-3
Absorption coeff.(µ) mm-1
F(000)
1.416
1.002
591
1.464
1.064
1140
1.501
1.086
2300
R(int)
0.027
0.029
0.034
θ range (deg)
Total reflections
Unique reflections
I>2σ(I)
1.8, 29.1
20950
1.0, 26.4
29717
1.9, 26.4
29165,
4968
6883
4906
9891
8015
4285
R1, wR2
Temp (K)
0.0530, 0.1586
293
0.0394, 0.1106,
293
0.0576, 0.1891
293
Table 2. Dimensions in the metal coordination spheres in 1-3 (distances,Å, angles,°).
1
2A
3
2.031(2)
2.023(2)
2.052(3)
2.174(3)
2.025(4)
2.048(3)
2.154(3)
2.168(2)
2.225(2)
2.020(2)
2.033(2)
2.079(2)
2.151(2)
2.023(2)
2.029(3)
2.176(2)
2.170(2)
2.223(2)
2.014(3)
2.030(3)
2.059(3)
2.193(4)
2.022(4)
2.025(4)
2.192(3)
2.167(3)
2.224(3)
Ni(1)−O(1)
Ni(1)−O(2)
Ni(1)−O(4)
Ni(1)−O(5)
Ni(1)−N(1)
Ni(1)−N(2)
Mn(1)−O(1)
Mn(1)−O(2)
Mn(1)−O(3)
82.46(9)
93.50(9)
88.21(1)
91.03(1)
82.15(7)
93.08(8)
88.67(9)
91.09(9)
82.56(11)
92.14(11)
90.97(12)
91.16(13)
O(1)−Ni(1)−O(2)
O(1)−Ni(1)−O(4)
O(1)−Ni(1)−O(5)
O(1)−Ni(1)−N(1)
O(1)−Ni(1)−N(2)
O(2)−Ni(1)−O(4)
O(2)−Ni(1)−O(5)
O(2)−Ni(1)−N(1)
O(2)−Ni(1)−N(2)
170.66(1) 172.37(11) 172.87(13)
91.75(9)
91.07(1)
172.69(1) 173.09(9) 173.01(13)
89.53(1) 90.39(11) 90.31(13)
92.70(8)
89.29(8)
93.79(11)
90.14(12)
O(4)-Ni(1)-O(5) 176.87(1) 177.52(9) 175.28(13)
96.66(1) 96.32(12) 95.96(15)
N(1)−Ni(1)−N(2)
O(4)-Ni(1)-N(2)
91.53(1) 88.90(10) 88.19(14)
O(5)-Ni(1)-N(1) 85.38(13) 89.11(9)
86.88(14)
O(5)-Ni(1)-N(2) 87.14(13) 89.59(10) 89.17(15)
O(1)-Mn(1)-O(2) 76.39(8)
O(1)-Mn(1)-O(3) 87.82(9)
75.57(7)
88.77(7)
75.50(10)
90.38(10)
O(1)-Mn(1)-O(2)a 103.61(8) 104.43(7) 104.50(10)
O(1)-Mn(1)-O(3)a 92.18(8)
91.23(7)
89.62(10)
18

O(2)-Mn(1)-O(3) 87.41(8)
83.76(7)
85.07(10)
O(1)a-Mn(1)-O(2) 103.61(8) 104.43(7) 104.50(10)
O(2)-Mn(1)-O(3)a 92.59(8)
O(1)a-Mn(1)-O(3) 92.18(9)
O(2)a-Mn(1)-O(3) 92.59(8)
O(1)a-Mn(1)-O(2)a 76.39(8)
O(1)a-Mn(1)-O(3)a 87.82(9)
96.24(7)
91.23(7)
96.24(7)
75.57(7)
88.77(7)
98.15(8)
97.98(8)
94.93(10)
89.62(10)
94.93(10)
75.50(10)
90.38(10)
97.26(11)
97.57(11)
97.47(9)
97.26(9)
Ni(1)−O(1)−Mn(1)
Ni(1)−O(2)−Mn(1)
a represents symmetry element 2-x,1-y,1-z for 1, 1-x,-y,1-z for 2A, 3/2-x,1/2-y,1-z for 3.
2B
2B
Ni(2)-O(6)
Ni(2)-O(7)
Ni(2)-O(9)
Ni(2)-O(10)
Ni(2)-N(3)
2.015(2)
2.018(2)
2.051(2)
2.253(3)
2.024(2)
Ni(2)-N(4)
Mn(2)-O(7)
Mn(2)-O(8)
Mn(2)-O(6)
2.023(2)
2.162(2)
2.183(2)
2.168(2)
O(6)-Ni(2)-O(7) 83.39(8) O(6)b-Mn(2)-O(8) 94.36(7)
O(6)-Ni(2)-O(9) 94.55(8) O(6)b-Mn(2)-O(7) 103.45(7)
O(6)-Ni(2)-O(10) 88.56(9) O(6)b-Mn(2)-O(7)b 76.55(7)
O(6)-Ni(2)-N(3) 90.28(9) O(6)b-Mn(2)-O(8)b 85.64(7)
O(6)-Mn(2)-O(7) 76.55(7) O(7)b-Mn(2)-O(8)b 87.81(7)
O(7)-Ni(2)-O(9) 94.76(8) O(6)-Mn(2)-O(8) 85.64(7)
O(7)-Ni(2)-O(10) 89.56(10) O(7)-Mn(2)-O(8) 87.81(7)
O(7)-Ni(2)-N(3) 172.34(9) Ni(2)-O(6)-Mn(2) 96.57(8)
O(7)-Ni(2)-N(4) 89.54(8) Ni(2)-O(7)-Mn(2) 96.65(8)
O(7)-Mn(2)-O(8)b 92.20(7)
b represents symmetry element 1-x,1-y,2-z for 2B.
19

Table 3. Selected Structural Parameters of µ2-Phenoxido-Bridged Ni2Mn Complexes,
Ordered by Decreasing Value of their Average Ni-O-Mn Angle.
Ni-O-Mn angle /
Compound
JNi-Mn (exp) / cm-1 JNi-Mn (calc) / cm-1
deg
[MnII(NiIIL)2(OAc)4(H2O)2]8a
-0.30
-0.60
+2.00
-
-3.37 (-0.13)
+0.51 (-0.31)
+0.86
102.31
Complex 1
97.35
97.34
98.07
96.61
97.27
86.38
Complex 2
2A
2B
-0.45 (-0.31)
+2.16 (-0.30)
+0.71 (-0.30)
+8.26 (-0.30)
-
Complex 3
[MnII(NiIIL)2]·2CH3OH8b
+1.10
+9.30
In the JNi-Mn (calc) column, the numbers in brackets correspond to the calculated JNi-Ni values, that is the magnetic
exchange constants between NiII ions that belong to the same molecule.
20

Antiferro- to ferromagnetic crossover in diphenoxido bridged NiII MnII
2
complexes derived from N2O2 donor Schiff base ligands
Piya Seth, Albert Figuerola, Jesús Jover, Eliseo Ruiz, Ashutosh Ghosh

Antiferro- to ferromagnetic crossover in diphenoxido bridged NiII MnII
2
complexes derived from N2O2 donor Schiff base ligands
Piya Seth, Albert Figuerola, Jesús Jover, Eliseo Ruiz, Ashutosh Ghosh
Three new Ni(II)-Mn(II) complexes, derived from different Schiff base ligands, having very
slight variations in average phenoxido bridging angles (97.27-97.35°) have been synthesized
in order to analyze that small difference in structural parameters can be responsible for ferro-
to antiferromagnetic crossover in this type of complexes.