One ferromagnetic and two antiferromagnetic dinuclear nickel(II) complexes derived from a tridentate N,N,O-donor schiff base ligand: A density functional study of magnetic coupling

Article abstract of DOI:10.1002/ejic.201200028

Three new dinuclear Ni^II complexes, [Ni₂L ₂(NO₃)₂] (1), [Ni₂L ₂(NO₂)₂] (2), and [Ni₂L ₂(CH₃COO)₂(H₂O)

Full text of DOI:10.1002/ejic.201200028

Job/Unit: I20028
/KAP1
Date: 25-04-12 14:58:33
Pages: 13
FULL PAPER
DOI: 10.1002/ejic.201200028
One Ferromagnetic and Two Antiferromagnetic Dinuclear Nickel(II)
Complexes Derived from a Tridentate N,N,O-Donor Schiff Base Ligand:
A Density Functional Study of Magnetic Coupling
[a]
[b]
[b]
[a]
Rituparna Biswas, Sanjib Giri, Shyamal K. Saha, and Ashutosh Ghosh*
Keywords: Nickel / Schiff bases / O ligands / Magnetic properties / Density functional calculations
Three new dinuclear NiII complexes, [Ni
Ni (NO ] (2), and [Ni (CH COO) (H
been synthesized by using a tridentate Schiff base ligand, 2-
{[3-(dimethylamino)propyl]imino}methyl)phenol (HL), along
with a nitrate, nitrite, or acetate ion, respectively, as co-li-
gand. These three complexes were characterized by spectral
analysis, X-ray crystallography, and variable-temperature
L
(NO
O)] (3), have
)
] (1),
an antiferromagnetic intradimer interaction in complexes 1
2
2
3
2
–
1
[
2
L
2
2
)
2
2
L
2
3
2
2
and 2 with J values of –20.34(5) and –25.25(4) cm , respec-
tively, whereas complex 3 shows a dominant ferromagnetic
–
1
(
exchange coupling with J = 19.11(9) cm . DFT calculations
were performed, and the theoretically obtained J values of
–
1
–19.99 (for 1), –24.19 (for 2) and 18.81 cm (for 3) corroborate
very well the experimental results. An attempt has also been
magnetic susceptibility measurements. The structural analy-
ses revealed that the Ni ions are coordinated by the depro- Ni–O–Ni angles on the coupling constants of the Ni com-
made to correlate the effect of Ni···Ni distances and bridging
II
II
tonated chelating tridentate Schiff base and possess a dis-
torted octahedral geometry in all three complexes. Com-
plexes through DFT calculations. The relative energy calcu-
lations show that the diphenoxido-bridged complexes are
stable at larger bridging angles, and consequently the cou-
pling is antiferromagnetic, whereas with an additional water
plexes 1 and 2 are two di-μ
2
-phenoxido-bridged species in
which the nitrate and nitrite act as chelating co-ligands.
However, in complex 3, in which the acetate anion is mono- bridge, the formation of complexes with the Ni–O–Ni bridg-
dentate, an additional water bridge is present along with two
-phenoxido bridges making the complex a face-sharing bi-
ing angle in the ferromagnetic region is energetically profit-
able.
μ
2
octahedron. Magnetic susceptibility measurements indicate
ionic co-ligands.[6–10] Magneto-structural correlations of
such species have been made, and interesting trends have
Introduction
The structural and magnetic properties of dinuclear ni- emerged. Ferromagnetic interactions have been found to
ckel(II) complexes with a variety of bridging ligands have prevail in octahedrally coordinated dimeric nickel(II) com-
[
11]
received considerable attention over the past two decades plexes with end-on azide
mainly because of their relevance in biological systems (as end-to-end thiocyanate
and cyanate bridges as well as
and selenocyanate bridges. In
[
12,13]
evidenced by the many existing biochemical polynuclear the case of the phenoxido-bridged dinuclear nickel(II) com-
[
1]
active complexes) and because of increasing interest in plexes, the major factor controlling the exchange coupling
[2]
[14]
molecule-based and single-molecule magnets. Dinuclear is the bridging Ni–O–Ni angle.
On the basis of experi-
μ-O–nickel(II) complexes with mixed N,O donor sets have mental results, it has been proposed that in the case of
been extensively investigated due to their potential to act as phenoxido-bridged nickel(II) complexes, the spins on the
[
3–5]
II
structural, electronic, and catalytic models for urease.
The salicylaldehyde-derived tridentate N,N,O donor Schiff angles are less than ca. 93.5 and 99.0°,
bases, which can bridge two metal ions through the phe- the μ and μ bridging modes of the phenoxido oxygen
Ni ions interact ferromagnetically if the average Ni–O–Ni
[
15]
depending upon
2
3
noxido oxygen atom, have been used in the synthesis of atoms, and for larger angles, the spin delocalization of the
II
polynuclear Ni complexes along with various bridging an- magnetic orbitals will be enhanced thereby giving rise to
[
16]
antiferromagnetic interactions.
To design ferromagnetic
II
phenoxido-bridged Ni complexes, it is thus necessary to
make the bridging angle less than these critical values. Most
of the dinickel(II) complexes involving an Ni O -bridging
[
[
a] Department of Chemistry, University College of Science,
University of Calcutta,
9
2, A.P.C. Road, Kolkata 700009, India
2
2
E-mail: ghosh_59@yahoo.com
b] Department of Materials Science, Indian Association for the moiety that are reported in the literature are antiferromag-
Cultivation of Science,
Jadavpur, Kolkata 700032, India
[7,17,18]
netically coupled.
To the best of our knowledge, of
the structurally characterized diphenoxido-bridged dinu-
clear nickel(II) complexes, only two are known to show fer-
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201200028.
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1

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R. Biswas, S. Giri, S. K. Saha, A. Ghosh
FULL PAPER
romagnetic coupling.[
19]
Very recently we reported two
II
more Ni compounds containing two μ -phenoxido and
2
one water bridge, which predominantly exhibited ferromag-
[
20]
netic interactions.
In that report we proposed that the
presence of the additional water bridge was very important
to lowering the bridging angles to below the critical value
and consequently to making the exchange coupling ferro-
magnetic.
In this paper we report on the synthesis, crystal struc-
tures, and magnetic properties of three new diphenoxido-
bridged dinickel(II) complexes, [Ni L (NO ) ] (1),
2
2
3 2
[
Ni L (NO ) ] (2), and [Ni L (CH COO) (H O)] (3), by
2 2 2 2 2 2 3 2 2
using a tridentate Schiff base ligand, 2-({[3-(dimeth-
ylamino)propyl]imino}methyl]phenol (HL), along with ni-
trate, nitrite, or acetate, respectively, as co-ligand. We have
previously found that the carboxylate ion can stabilize an
additional water bridge between the two nickel atoms with
the help of strong hydrogen bonds.[ As other oxo anions,
for example, nitrate or nitrite, also have the potential to
form hydrogen bonds, these anions were chosen for this in-
vestigation. It was found that compounds 1 and 2 are anti-
ferromagnetically coupled, whereas compound 3, which
contains an additional water bridge, is ferromagnetically
coupled. Several groups have rationalized the magnetic be-
20]
Scheme 1. Synthesis of complexes 1–3.
IR and UV/Vis Spectra of Complexes 1–3
II
II
havior of Cu and Ni complexes through DFT calcula-
[
21]
tions.
For complexes 1–3, a DFT study (using a combi-
The IR spectra of complexes 1–3 show a strong and
nation of the hybrid B3LYP functional and the TZVP basis sharp band due to azomethine ν(C=N) at 1644, 1644, and
–1
set) resulted in the successful determination of the nature 1635 cm , respectively. For complex 1, the characteristic
of the magnetic exchange interactions. The variation in the strong peak of the coordinated nitrate anion is observed
coupling constants with bridging angle Ni–O–Ni was also at 1289 cm–1 for the asymmetric stretching vibration. For
computed taking complexes 1–3 as models. The relative en- complex 2, absorption bands at 1290, 1200, and 1050 cm–1
ergy calculations substantiated the importance of the ad- are tentatively assigned to ν (NO ), ν (NO ), and δ(NO ),
s
2
as
2
2
[
23]
–1
ditional water bridge in obtaining such species with bridg- respectively.
The presence of a band near 3400 cm in
ing angles in the ferromagnetic region. To the best of our the spectrum of 3 indicates the presence of a water mole-
knowledge, although theoretical studies showing the depen- cule. The broad nature of the band is probably due to the
dence of the coupling constant J on the Cu–O–Cu angle participation of these water molecules in hydrogen bonding.
II
–1
in hydroxido/phenoxido-bridged Cu complexes have been The IR spectral bands in the 1300–1650 cm region are
performed in detail,[ such investigations with nickel com- difficult to assign due to the presence of several absorption
22]
plexes have not yet been reported.
bands from both the Schiff base and the carboxylato li-
gands. Nevertheless, by comparing the IR spectra of this
II
Ni complex with those of 1 and 2 with other anions, the
–1
strong bands at 1548 and 1580 cm may be assigned to the
antisymmetric stretching mode of the carboxylate group,
whereas the bands at 1450 and 1412 cm–1 can be assigned
to the symmetric stretching modes of the carboxylato li-
gands in complex 3.
Results and Discussion
Synthesis of Complexes 1–3
The electronic spectra of compounds 1–3 were recorded
The monocondensed tridentate Schiff base ligand HL [2- in methanol solution. The electronic spectra show absorp-
({[3-(dimethylamino)propyl]imino}methyl)phenol] reacted tion bands at 637 and 1012 nm (for 1), 640 and 1025 nm
smoothly with nickel(II) nitrate and nickel(II) acetate in (for 2), and 644 and 1022 nm (for 3). These bands have been
3
3
methanolic solution in a 1:1 molar ratio to yield complexes assigned to the spin-allowed transitions A gǞ T g and
2
1
3
3
1
and 3, respectively (Scheme 1). Complex 2 was synthe-
A gǞ T g(P), respectively. The higher-energy d–d bands
2 2
sized by adding a methanolic solution of Ni(ClO ) ·6H O are obscured by strong ligand-to-metal charge-transfer
4
2
2
to a methanolic solution of the Schiff base ligand (HL) fol- transitions. Moreover, the intense UV absorption bands ob-
lowed by the addition of an aqueous methanolic solution served at 365, 366, and 367 nm for complexes 1–3, respec-
of NaNO in a 1:1:1 molar ratio. An equimolar amount of tively, have been assigned to LǞM charge-transfer transi-
2
triethylamine was then added in each case to deprotonate tions, which are characteristic of transition-metal complexes
[
24]
the Schiff base.
with Schiff base ligands.
2
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Antiferro- and Ferromagnetic Dinuclear Nickel(II) Complexes
Description of the Crystal Structures of Complexes 1–3
cepting ability of the imine (C=N) functions, which in turn
weakens the bond mutually trans to it as both of them com-
pete for the same metal d orbital for back-bonding stabili-
zation. The four donor atoms O(11), N(23), O(41), and
O(42) describe the basal planes of the Ni(1) atom of com-
plexes 1 and 2. The deviations of these coordinating atoms
from the least-square mean plane through them are
Compounds [Ni L (NO ) ] (1) and [Ni L (NO ) ] (2)
2
2
3
2
2
2
2 2
The crystal structures of both 1 and 2 consist of di-μ2-
phenoxido-bridged discrete centrosymmetric dimeric units
of formula [Ni L (NO ) ] and [Ni L (NO ) ], respectively
2
2
3 2
2
2
2 2
(Figure 1). Selected bond lengths and angles are presented
0
0
.019(2), –0.018(3), –0.029(3), and 0.028(2) Å (for 1) and
.033(2), –0.032(2), –0.050(2), and 0.049(2) Å (for 2),
in Tables 1 and 2. In both complexes the nickel atoms are
hexacoordinated with an octahedral environment that is
significantly distorted primarily by the small bite angles of
respectively. The displacement of the Ni(1) atom from the
same plane towards the axially coordinated O(11)Ј atom is
0.012(3) and 0.029(1) Å for complexes 1 and 2, respectively.
No classic hydrogen bonds are found in either complex 1
or 2.
5
9.41(9) and 57.90(9)° at the bidentate chelating nitrate
2
2
(κ O,OЈ) and nitrite (κ O,OЈ) ions in 1 and 2, respectively.
In addition, each metal center is bonded to the three donor
atoms of the deprotonated chelated Schiff base ligand L
3
(
1κ N,NЈ,O:2κO) through the secondary amine nitrogen
Table 1. Bond lengths and angles in the metal coordination spheres
atom N(23), the imine nitrogen atom N(19), and the phen-
oxido oxygen atom O(11) as well as to a bridging phen-
oxido oxygen atom O(11)Ј [Ј: 2 – x, 1 – y, 1 – z (1) and
[a]
of complex 1.
Bond length [Å]
Bond angle [°]
Ni(1)–O(11)
Ni(1)–N(19)
Ni(1)–N(23)
Ni(1)–O(11)Ј
Ni(1)–O(41)
2.008(2)
2.009(3)
2.121(3)
2.091(2)
2.218(3)
2.135(2)
O(11)–Ni(1)–N(19)
O(11)–Ni(1)–N(23)
O(11)–Ni(1)–O(11)Ј
N(19)–Ni(1)–N(23)
O(11)Ј–Ni(1)–N(19)
O(11)Ј–Ni(1)–N(23)
Ni(1)–O(11)–Ni(1)Ј
O(41)–Ni(1)–O(42)
O(41)–Ni(1)–N(23)
O(41)–Ni(1)–O(11)
O(41)–Ni(1)–O(11)Ј
O(41)–Ni(1)–N(19)
O(42)–Ni(1)–N(19)
O(42)–Ni(1)–N(23)
O(42)–Ni(1)–O(11)
O(42)–Ni(1)–O(11)Ј
92.64(10)
103.91(11)
80.69(7)
87.00(11)
172.17(10)
98.54(11)
99.31(8)
59.41(9)
161.05(9)
94.95(9)
86.15(10)
90.38(11)
88.92(9)
101.76(10)
154.34(11)
95.32(8)
1
/2 – x, 1/2 – y, 1 – z (2)] from the symmetry-related Schiff
3
base ligand (1κO:2κ N,NЈ,O) with bond lengths similar to
those observed in related compounds.[ As is usually found
25]
II
in this type of double oxido-bridged Ni dimers, the Ni O
core is slightly asymmetric, because each Ni ion is closer Ni(1)–O(42)
2
2
II
to the phenoxido oxygen atom of L [Ni(1)–O(11) 2.008(2)
(for 1) and 2.014(2) Å (for 2); Table 1] that is chelated to it
than to the phenoxido oxygen atom of the symmetry-re-
lated Schiff base ligand [Ni(1)–O(11)Ј 2.091(2) (for 1) and
2
3
.104(2) Å (for 2)]. The two Ni atoms are separated by
.124(2) and 3.156(2) Å, and the Ni(1)–O(11)–Ni(1)Ј bridge
angles are 99.31(8) and 100.01(7)° for 1 and 2, respectively.
The tridentate ligand coordinates to the metal ion in a fa-
cial configuration in both 1 and 2. Note that Ni(1)–O(11)
and Ni(1)–N(19) are the two shortest bonds, and bonds
trans to N(19) [Ni(1)–O(11)Ј] are significantly lengthened in
both structures (Tables 1 and 2). The shortening of the bridged dinuclear complexes of Ni containing a similar
Ni(1)–N(19) bond as well as the lengthening of the bond type of N,N,O donor tridentate Schiff base along with vari-
trans to it seems to stem from the better p-electron-ac- ous anions, but only four have nitrate or nitrite as co-ligand.
[a] Symmetry operator Ј: 2 – x, 1 – y, 1 – z.
A CSD search revealed that there are many phenoxido-
II
Figure 1. ORTEP views of the asymmetric unit of 1 (left) and 2 (right) with ellipsoids at the 30% probability level.
Eur. J. Inorg. Chem. 0000, 0–0
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R. Biswas, S. Giri, S. K. Saha, A. Ghosh
Table 2. Bond lengths and angles in the metal coordination spheres water molecule O(3) and two μ -phenoxido oxygen atoms
FULL PAPER
2
[
a]
of complex 2.
O(11) and O(26). Each of the two metal centers, Ni(1) and
Ni(2), present a distorted octahedral environment, being
coordinated to the deprotonated chelating Schiff base li-
gand through the secondary amine nitrogen atoms N(23)
and N(38), the imine nitrogen atoms N(19) and N(34), and
the phenoxido oxygen atoms O(11) and O(26), respectively,
in a facial configuration with typical bond lengths
Bond length [Å]
Bond angle [°]
Ni(1)–O(11)
Ni(1)–N(19)
Ni(1)–N(23)
Ni(1)–O(11)Ј
Ni(1)–O(41)
Ni(1)–O(42)
2.014(2)
2.017(2)
2.138(3)
2.104(2)
2.201(3)
2.116(3)
O(11)–Ni(1)–N(19)
O(11)–Ni(1)–N(23)
O(11)–Ni(1)–O(11)Ј
N(19)–Ni(1)–N(23)
O(11)Ј–Ni(1)–N(19)
O(11)Ј–Ni(1)–N(23)
Ni(1)–O(11)–Ni(1)Ј
O(41)–Ni(1)–O(42)
O(41)–Ni(1)–N(23)
O(41)–Ni(1)–O(11)
O(41)–Ni(1)–O(11)Ј
O(41)–Ni(1)–N(19)
O(42)–Ni(1)–N(19)
O(42)–Ni(1)–N(23)
O(42)–Ni(1)–O(11)
O(42)–Ni(1)–O(11)Ј
92.29(8)
103.33(8)
79.99(7)
85.18(9)
172.14(9)
97.97(7)
100.01(7)
57.90(9)
159.37(9)
96.98(8)
89.04(7)
90.44(8)
89.78(9)
101.85(9)
154.82(7)
96.58(7)
[
7,26]
(Table 3).
The carboxylate oxygen atoms O(41) and
O(51) of the terminally coordinated monodentate acetate
ions, the oxygen atom O(3) of the water molecule, and the
bridging phenoxido atoms O(26) and O(11) complete the
hexacoordination of Ni(1) and Ni(2), respectively. Thus, the
two nickel atoms are linked through three oxygen bridges
to form a face-shared bi-octahedron with an Ni···Ni dis-
tance of 2.872(1) Å, which is significantly shorter than
those in complexes 1 and 2 (3.124 and 3.156 Å) and other
similar dinuclear nickel(II) complexes with only the two
[a] Symmetry operator Ј: 1/2 – x, 1/2 – y, 1 – z.
[
14,17,27,28]
phenoxido bridges.
angles, Ni(1)–O(11)–Ni(2) and Ni(1)–O(26)–Ni(2), are
6.30(11) and 87.18(10)°, respectively, and the water bridg-
The two phenoxido bridging
[7,10]
Of these, three are dinuclear
and the remaining one is
[
7]
8
polynuclear. The structures of the three dinuclear com-
plexes are very similar to those of 1 and 2, whereas in the
polynuclear species the dimeric units are further joined to-
gether by a nitrite bridge to form a one-dimensional
ing angle, Ni(1)–O(3)–Ni(2), is 86.71(12)°. Each bridging
phenoxido oxygen atom is asymmetrically bound with one
Ni–O bond slightly longer [Ni(1)–O(26) 2.145(3) Å, Ni(2)–
O(11) 2.172(3) Å] than the other [Ni(1)–O(11) 2.025(3) Å,
Ni(2)–O(26) 2.019(3) Å]. The Ni–O(water) bonds are iden-
tical within experimental error [Ni(1)–O(3) 2.092(3) Å,
Ni(2)–O(3) 2.091(3) Å], and these distances are comparable
to those found in other reported aqua-bridged dinuclear
[
7]
chain. Although in the majority of such complexes the
tridentate Schiff base coordinates meridionally, in the com-
plexes with nitrate or nitrite as co-ligand it is in a facial
configuration. The chelating coordination of the nitrate or
nitrite, which must span the cis position, seems to be re-
sponsible for the rather unusual facial coordination of the
Schiff base ligand, with a folded conformation in these
complexes.
II
[19,29,30]
Ni complexes, which are in the range 2.09–2.25 Å.
The four donor atoms O(11), N(19), O(41), and O(3) de-
scribe the basal plane of Ni(1) and the deviations of these
coordinating atoms from the least-square mean plane
through them are –0.083(3), 0.072(4), –0.067(3), and
Compound [Ni L (H O)(CH COO) ]·H O (3)
2
2
2
3
2
2
0
0
.078(3) Å, respectively. The Ni(1) atom is displaced
.123(1) Å from the same plane. The basal bond lengths
The structure of 3 is shown in Figure 2 together with the
atomic numbering scheme Selected bond lengths and angles
are presented in Table 3. The crystal structure of 3 consists
of a discrete dinuclear unit of formula [Ni L (H O)(CH -
around the Ni(1) atom are in the range of 2.017(4)–
.092(3) Å. The apical bond lengths Ni(1)–O(26) and
2
2
2
2
3
Ni(1)–N(23) are 2.145(3) and 2.155(4) Å, respectively, the
O(26)–Ni(1)–N(23) bond angle being 172.54(14)°. Similarly,
COO) ]·H O. The dinuclear unit is formed of two indepen-
2
2
dent nickel atoms, labeled Ni(1) and Ni(2), bridged by one
Figure 2. (a) ORTEP view of the asymmetric unit of 3 with ellipsoids at the 30% probability level. (b) Face-sharing bi-octahedron repre-
sentation of complex 3.
4
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Antiferro- and Ferromagnetic Dinuclear Nickel(II) Complexes
in the coordination sphere of Ni(2), the basal plane consists oxygen atoms O(43) and O(53), respectively, of the ter-
of O(3), O(26), O(51), and N(34) with the bond lengths in minally coordinated acetate anions with D···A distances of
[
20,31]
the range of 2.000(4)–2.091(3) Å. The apical bond lengths 2.566(5) and 2.493(5) Å
(see Table S2 in the Support-
Ni(2)–O(11) and Ni(2)–N(38) are 2.172(3) and 2.159(4) Å, ing Information).
respectively, the O(11)–Ni(2)–N(38) bond angle being
Comparison of the structural parameters of complex 3
1
72.96(14)°. Deviation of the coordinating atoms O(3), with those of the four previously reported similar dinuclear
II
[19,20]
O(26), O(51), and N(34) from the least-square mean plane Ni complexes,
through them are 0.082(3), –0.085(3), –0.070(4), and water bridges, revealed that the double bridging Ni–μ2-
.073(4) Å, respectively, and that of the Ni(2) atom from O(phenoxido)–Ni (ca. 85–92°, ca. 1.9–2.1 Å) and Ni–
with both di-μ -O(phenoxido) and
2
0
the same plane is –0.149(1) Å. The two hydrogen atoms μH O–Ni (ca. 81–87°, ca. 2.0–2.3 Å) angles and distances
2
H(3A) and H(3B) of the bridging water molecule partici- are comparable. The Ni···Ni distances are also very similar
pate in strong intramolecular hydrogen bonding with the (ca. 2.8–2.9 Å).
Table 3. Bond lengths and angles in the metal coordination spheres
of complex 3.
Magnetic Properties
Bond length [Å]
Bond length [Å]
The thermal variations of the product of the molar mag-
II
netic susceptibility and the temperature (χ T) per two Ni
M
Ni(1)–O(11)
Ni(1)–O(26)
Ni(1)–O(3)
Ni(1)–O(41)
Ni(1)–N(19)
Ni(1)–N(23)
2.025(3)
2.145(3)
2.092(3)
2.055(3)
2.017(4)
2.155(4)
Ni(2)–O(11)
Ni(2)–O(26)
Ni(2)–O(3)
Ni(2)–O(51)
Ni(2)–N(34)
Ni(2)–N(38)
2.172(3)
2.019(3)
2.091(3)
2.033(3)
2.000(4)
2.159(4)
ions for compounds 1–3 are displayed in Figures 3 and 4
[χM vs. T plots are given in Figures S1 (for 1 and 2) and S2
for 3) in the Supporting Information]. As can be seen, the
(
three compounds show χ T values at room temperature of
M
3
–1
ca. 2.3–2.4 cm Kmol , in agreement with the expected
Bond angle [°]
Bond angle [°]
II
value for two noninteracting Ni S = 1 ions (the expected
3
–1
O(11)–Ni(1)–N(19) 89.43(14)
O(11)–Ni(1)–N(23) 102.83(13) O(26)–Ni(2)–N(38) 104.42(13)
O(11)–Ni(1)–O(41) 166.92(12) O(26)–Ni(2)–O(51) 164.53(14)
O(41)–Ni(1)–N(23) 88.89(13)
O(26)–Ni(1)–N(19) 100.51(13) O(11)–Ni(2)–N(34) 99.08(15)
O(26)–Ni(1)–O(41) 88.50(11) O(11)–Ni(2)–O(51) 87.04(13)
O(26)–Ni(1)–N(23) 172.54(14) O(11)–Ni(2)–N(38) 172.96(14)
O(3)–Ni(1)–O(11) 79.45(12)
O(3)–Ni(1)–O(41) 93.49(11)
O(26)–Ni(2)–N(34) 90.51(14)
spin-only value is 2.0 cm Kmol , g = 2). Compounds 1
and 2 present very similar behavior on lowering the tem-
perature: χ T shows a smooth decrease at higher tempera-
M
O(51)–Ni(2)–N(38) 89.19(15)
tures and a more pronounced decrease as the temperature
is further lowered to reach values very close to zero at 2 K
(
Figure 3). Compound 3 shows different behavior: χ T
M
O(3)–Ni(2)–O(11) 76.22(12)
O(3)–Ni(2)–O(51) 92.19(13)
O(3)–Ni(2)–O(26) 78.82(11)
O(51)–Ni(2)–N(34) 97.58(16)
N(34)–Ni(2)–N(38) 87.30(16)
O(11)–Ni(2)–O(26) 78.64(10)
Ni(2)–O(11)–C(15) 119.80(3)
O(3)–Ni(2)–N(34) 168.96(14)
O(3)–Ni(2)–N(38) 98.01(14)
gradually increases to reach
a
maximum value of
3
–1
3
.45 cm Kmol at 15 K followed by a pronounced drop to
Ni(1)–(O3)–Ni(2)
86.71(12)
3
–1
O(3)–Ni(1)–O(26) 76.03(12)
O(41)–Ni(1)–N(19) 97.13(14)
N(19)–Ni(1)–N(23) 86.75(15)
O(11)–Ni(1)–O(26) 79.15(11)
Ni(1)–O(11)–C(15) 128.2(3)
Ni(1)–O(11)–Ni(2) 86.30(11)
Ni(1)–O(26)–Ni(2) 87.18(10)
O(3)–Ni(1)–N(19) 168.77(14)
O(3)–Ni(1)–N(23) 97.16(14)
reach values of 2.94 cm Kmol at 2 K (Figure 4). These
results indicate that compounds 1 and 2 present an antifer-
romagnetic Ni–Ni exchange coupling inside its dimeric
structure, whereas complex 3 is typical of a system that ex-
hibits dominant intramolecular ferromagnetic exchange
coupling with the drop in χ T at lower temperatures due
M
to zero-field splitting (ZFS) of the ground state (S = 2) and/
or possible interactions between the dimers.
M
Figure 3. Plots of χ T vs. T for complex 1 (left) and 2 (right). The points are the experimental data with the solid line generated from
the fitted curve.
Eur. J. Inorg. Chem. 0000, 0–0
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5

Job/Unit: I20028
/KAP1
Date: 25-04-12 14:58:33
Pages: 13
R. Biswas, S. Giri, S. K. Saha, A. Ghosh
FULL PAPER
The magnetic properties of 1 and 2 were analyzed by a
theoretical model considering the interaction between two
S = 1 spin centers. We fitted the magnetic properties of
compounds 1 and 2 to a simple S = 1 dimer model derived
from the isotropic Hamiltonian with H = –JS S [Equa-
1
2
[
32]
tion (1)].
(
1)
The parameters N, β, and k in Equation (1) have their
usual meanings, J is the singlet–triplet splitting, and ρ is the
relative content for the paramagnetic impurity in which the
spin state S = 1 is assumed. The χ T versus T curves were
M
least-squares fitted by minimizing the function R =
2
2
Figure 4. Plot of χ
imental data with the solid line generated from the fitted curve.
M
T vs. T for complex 3. The points are the exper-
Σ[(χ T)
– (χ T)
] /Σ(χ T)
. The best-fitting pa-
M
exp.
M
calcd.
M
exp.
1
–
rameters are J = –20.34(5) cm , g = 2.24(9), and ρ =
–
6
–1
1.2(2)% with R = 3.6ϫ10 (for 1) and J = –25.25(4) cm ,
–
6
g = 2.27(8), and ρ = 1.3(1)% with R = 1.7ϫ10 (for 2)
coupling, ZFS and interdimer coupling are present, but
their correct evaluation is not possible due to their close
(Table 4).
To achieve a good data fitting for compound 3, we fitted
[
7,33]
relationship.
the magnetic data to Equation (2) taking the Weiss constant
θ) as an additional parameter to include the interdimer
interaction (zJЈ) term as well as the anisotropy term (D).
The antiferromagnetic exchange observed in compounds
(
1
and 2 leads to a diamagnetic ground spin state in these
compounds, as confirmed by the isothermal magnetization
measurements at 2 K, which show values of Ͻ0.1 μ at high
B
fields (Figure 5). In contrast, the ferromagnetic coupling of
compound 3 leads to S = 2 ground spin states, which is
(
2)
–1
The best-fitting parameters are J = 19.11(9) cm , g = confirmed by the isothermal magnetization measurements
–
5
2
.217(5), and θ = –0.074 K with R = 1.29ϫ10 (Table 4). at 2 K (Figure 5). Because there are interdimer antiferro-
Note that the addition of only the anisotropy term (D) in magnetic interactions (in compound 3) and zero-field split-
the spin Hamiltonian provided poor data fitting at low tem- ting, the magnetization values at 5 T are slightly smaller
perature. Thus, it can be concluded that, besides intradimer than the expected values of ca. 4 μB.
Table 4. Magnetic and structural parameters of compounds 1–3.
Complex
Nature of mag-
netic coupling
Experimental Phenoxido-bridged Ni–O–Ni
J values [cm ] angles [°]; distances [Å]
Water-bridged Ni–O–Ni angles
[°]; distances [Å]
Ni···Ni distances [Å]
–1
[
[
[
Ni
Ni
Ni
2
L
2
(NO
(NO
(CH
3
)
2
] (1)
] (2)
COO)
antiferromagnetic –20.34(5)
antiferromagnetic –25.25(4)
99.31(8); 2.008(2), 2.091(2)
100.01(7); 2.014(2), 2.104(2)
86.30(11), 87.18(10); 2.025(3),
–
–
3.124
3.156
2.872
2
L
2
2
)
2
2
L
2
3
2 2
(H O)] (3)
ferromagnetic
19.11(9)
86.71(12); 2.092(3), 2.091(3)
2.144(3), 2.172(3), 2.019(3)
Figure 5. Field dependence of molar magnetizations for compounds 1–3 at 2 K.
6
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Job/Unit: I20028
/KAP1
Date: 25-04-12 14:58:33
Pages: 13
Antiferro- and Ferromagnetic Dinuclear Nickel(II) Complexes
Magneto-Structural Correlation and Theoretical
Interpretation by DFT Methods
should show moderate antiferromagnetic coupling, in
agreement with experimental results. In compound 3, the
Ni–O–Ni bond angles are considerably smaller [Ni(1)–
II
In octahedral Ni , the d
x2–y2
and dz orbitals each contain (O3)–Ni(2) 86.71(12)°, Ni(1)–O(11)–Ni(2) 86.30(11)°, and
2
an unpaired electron. Therefore, for the diphen- Ni(1)–O(26)–Ni(2) 87.18(10)°; Figure 6], and this explains
oxido-bridged compounds 1 and 2, only the d orbitals the observed ferromagnetic coupling in the complex.
x2–y2
of the metal atom along with the local orbitals of the bridg-
To achieve a better understanding of the magneto-struc-
ing ligands are involved in the super-exchange pathways, tural interrelation, we used DFT calculations with the
whereas for 3, the magnetic orbitals, composed of both the broken-symmetry approach to calculate J values theoretic-
d
x2–y2
and dz orbitals of nickel(II) and ligand local orbitals, ally. The J values calculated for complexes 1–3 are in good
2
participate in super-exchange phenomena. The magneto- agreement with the experimental results (Table 4). The
structural correlations for the μ -oxido/phenoxido-bridged theoretically obtained J values are –19.99 (for 1), –24.19
2
II
–1
Ni complexes based on the magnetic measurements of (for 2), and 18.81 cm (for 3), which reveals antiferromag-
structurally characterized species indicate ferromagnetic netic coupling in complexes 1 and 2 and ferromagnetic cou-
coupling below the critical Ni–O–Ni angle of 93.5° and pling in complex 3. Thus, the calculated values reproduce
above which the exchange coupling is expected to be anti- the experimental trends correctly. Moreover, we have also
ferromagnetic. The majority of the reported diphenoxido- performed DFT calculations to gain a better insight into
bridged dinuclear nickel(II) complexes show strong antifer- the angular dependence of the exchange coupling interac-
–
1
romagnetic interactions (–20 Ͼ J Ͼ –100 cm ) as the bridg- tions of complexes 1–3. The two diphenoxido-bridged dinu-
ing angle is larger than the critical value.[
14,15,18,34,35]
To the clear complexes 1 and 2 allowed us to simplify the study of
best of our knowledge, ferromagnetic behavior has been the magneto-structural correlations, because they have only
found in only seven μ2-phenoxido-bridged com- one exchange pathway through the μ -phenoxido oxygen
2
[
15,19,20,30,36]
plexes
terized. The Ni–O–Ni bond angles in compounds 1 and 2 by changing the Ni···Ni distance and keeping the rest of the
99.31(8) and 100.01(7)°, respectively] indicate that they structure unaltered. The change in the Ni···Ni separation is
that have also been structurally charac- atom. The DFT calculations for complex 1 were performed
[
Figure 6. Structures of the NiII environments in (a) 1, (b) 2, and (c) 3 with the bridging bond lengths [Å] and angles [°].
Figure 7. Dependence of (a) the calculated exchange coupling constant and (b) the relative energy on the phenoxido-bridged Ni–O–Ni
angle.
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7

Job/Unit: I20028
/KAP1
Date: 25-04-12 14:58:33
Pages: 13
R. Biswas, S. Giri, S. K. Saha, A. Ghosh
FULL PAPER
clearly proportionate to the change in Ni–O–Ni bond angle. change interaction coming from the μ -OH bridge. First,
2
2
A clear dependence of the exchange coupling constant on we performed calculations based on density functional
the Ni–O–Ni angle has been found and is represented in theory (see Computational Methodology in the Exp. Sect.)
Figure 7a.
by changing the Ni···Ni distance of complex 3 (Figure 8a).
From the curve it is clear that on increasing the Ni–O– As a result, all three bridging angles [ЄNi–OH –Ni, ЄNi–
2
1
2
Ni bridging angle (starting from 78°) first the magnitude O(Ph )–Ni, and ЄNi–O(Ph )–Ni] changed simultaneously,
of J increases and then decreases passing through a maxi- and this resulted in considerable changes in the coupling
mum value at about 90°. The parabolic dependence of the constant (J), as shown in Figure 8b for the ЄNi–OH –Ni
2
exchange coupling on the Ni–O–Ni angle clearly shows angle. The plots indicate a nearly linear relationship of J
that ferromagnetic interactions are expected only when with the bond angle/bond length with a slight bending at
the bridging angles are in the range 84–96°. This type of both ends. Earlier we discussed the parabolic nature of the
parabolic relationship of J with the bond angle has also value of J with the bond angle. In Figure 8, we used a rela-
[
22b]
II
II
been found by Ruiz et al.
in azido-bridged Cu , Ni , tively narrow bond angle range. So here the bending feature
and Mn complexes. The relative energy calculations may arise from the parabolic nature of the overall curve.
Figure 7b) indicate that the possibility of obtaining the From Figure 8 it is apparent that the ferromagnetic cou-
II
(
complex on the left side of the parabola with a relatively pling significantly decreases with increasing Ni···Ni dis-
small Ni–O–Ni angle (Ͻ89°) is extremely remote because tance, which causes larger phenoxide and water bridging
of the high instability, and therefore it is unlikely to be angles. The critical Ni···Ni distance was found to be ca.
synthesized. Figure 7b also indicates a flat minimum for 3.11 Å and that of the ЄNi–OH –Ni and ЄNi–O(phenox-
2
the relative energies at larger bond angles, and as a result ido)–Ni bridging angles are ca. 91° (see Table S1 in the Sup-
complexes with a range of large bond angles should be porting Information). The relative energy calculations (Fig-
stable.
ure 8c) show that complexes with smaller bond angles for
II
The magnetic behavior of complex 3 is governed by two this kind of triple-bridged Ni system can be synthesized
dominant factors: (1) The super-exchange pathway through because of their higher stability in this lower range of Ni–
the μ -phenoxido oxygen atom and (2) another super-ex- O–Ni angles.
2
Figure 8. (a) Magnetic coupling constant for complex 3 as a function of the Ni···Ni distance and (b) Ni–OH
c) relative energy as a function of the Ni–OH –Ni bridging angle.
2
–Ni bridging angle, and
(
2
8
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Job/Unit: I20028
/KAP1
Date: 25-04-12 14:58:33
Pages: 13
Antiferro- and Ferromagnetic Dinuclear Nickel(II) Complexes
To have an idea of the contribution of the water bridge dependence of the coupling constant with increasing water
to the overall coupling, calculations were also performed on bridging angle at a bond angle limit of Ϯ8° from its most
a model complex of 3, removing the water bridge from the stable position. Thus, we conclude that in comparison with
structure without making any changes to the bond angle or complexes 1 and 2, the relatively small phenoxido-bridged
the distances of phenoxido bridges. The calculated value of Ni–O–Ni angle gains stability from the water bridging in
–
1
J then becomes –12.98 cm , which indicates an antiferro- complex 3.
magnetic interaction in the model, although our previous
The Mulliken spin population analysis (Tables S3 and
calculations with compound 1 as a model complex show S4) indicates that a significant spin (ca. 0.64 e) is delocal-
that the coupling should be ferromagnetic for the diphe- ized through the ligand, whereas the rest of the spin (ca.
noxido bridging angle of ca. 86–87°. The change in geome- 3.36 e) is carried by the central nickel atoms for the high-
try from distorted octahedron to square-pyramidal on re- spin state of 1 and 2. Here, the spin carried by the phen-
moval of the water bridge seems responsible for the appar- oxido oxygen atom is ca. 0.80 e in the high-spin state and
ent disagreement in exchange coupling. It has been docu- Ϯ0.01 e in the broken-symmetry state. Although in complex
mented that, in the cases of mixed bridged polynuclear spe- 3 the spin density on the phenoxido-bridged oxygen atoms
cies, the overall exchange coupling constant cannot be as- is approximately the same as in complexes 1 and 2, in the
cribed to the algebraic sum of contributions from different broken-symmetry state of complex 3, a very small spin den-
[
37]
bridges.
sity (0.004 e) on the water-bridged oxygen atom signifies
Finally, to check the influence of the bridging water mo- polarization competition between the two nickel atoms with
lecule on the values of J, we changed only the Ni–OH2 α and β spin density, respectively.
bond length keeping the other structural parameters
To know the magnetic couplings (J) in the optimized
[
Ni···Ni distance and Ni–O(phenoxido)–Ni bond angles] structures of all three compounds 1–3, we performed geo-
constant. As a result, the Ni–OH –Ni bridging angle metrical optimization at the B3LYP/TZVP level of DFT.
2
changed, and calculations were performed within the range The optimized geometrical parameters for the three com-
80–105°. The result is shown in Figure 9.
plexes show good agreement with their corresponding X-
The plot suggests that starting from 80° the ferromag- ray crystallographic data (Table S5). The J values calculated
netic coupling increases upon increasing the water bridging from the optimized and X-ray structures are listed in
angle and after passing through a maximum at θ ≈ 93° the Table 5. Comparison of the data clearly shows that the J
value of J decreases. This shows that ferromagnetic cou- values of the optimized structures are underestimated by ca.
pling preferably occurs in the lower range of Ni–OH –Ni 28%, although it can be said that these values are in agree-
2
angles, and a maximum was found at ca. 93°. The relative ment with the experimentally obtained J values. These devi-
energy plot (Figure 9b) shows an inverted unsymmetrical ations from the corresponding experimental J values may
parabolic feature with a minimum at ca. 84.5°. Thus, in this be accounted for by slight differences in the bridging angles
case, complexes with a water bridging angle between 80 and and also in the bridging bond lengths in the optimized
89° are relatively stable, but in this range the value of J structures.
decreases with decreasing bond angle. This type of mag- In summary, the theoretical calculations corroborate well
neto-structural correlation, in which the J value increases the experimental findings that the antiferromagnetic inter-
II
with increasing bond angle, is expected to occur for com- action between the Ni centers in complexes 1 and 2 takes
plexes in which the bond angles are on the left side (positive place through the phenoxido bridges, whereas the ferromag-
slope) of the parabolic coupling constant versus bond angle netic interaction in complex 3 occurs through the phen-
[
22b]
relationship.
Note that compound 3 shows a positive oxido and water bridges. We carried out calculations to
2
Figure 9. Dependence of (a) the calculated exchange coupling constant and (b) the relative energy on the Ni–OH –Ni bridging angle.
Eur. J. Inorg. Chem. 0000, 0–0
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9

Job/Unit: I20028
/KAP1
Date: 25-04-12 14:58:33
Pages: 13
R. Biswas, S. Giri, S. K. Saha, A. Ghosh
FULL PAPER
Table 5. Comparison of experimental, theoretical, and optimized J values.
Complex
Experimental J values
Theoretical J values calculated
from X-ray structure [cm ]
Theoretical J values calculated from
–1
–1
–1
[cm ]
optimized structure [cm ]
[Ni
[Ni
[Ni
2
2
2
L
2
L
2
L
2
(NO
(NO
3
2
)
)
2
] (1)
] (2)
–20.34
–25.25
+19.11
–19.994
–24.192
+18.811
–14.073
–17.326
+13.88
2
3 2 2
(CH COO) (H O)] (3)
determine the influence of the Ni–O(phenoxido)–Ni bridg- Experimental Section
ing angles in complex 1 by varying the Ni···Ni distance. The
Materials: The diamine and salicylaldehyde were purchased from
Lancaster Chemical Co. All other reagents were reagent-grade and
used without further purification.
results show a parabolic dependence of the values of J on
the Ni···Ni distance or the phenoxido bridging angle. The
relative stability calculations show that these kinds of com-
pounds are stable when the phenoxido-bridged Ni–O–Ni
angle is larger, and consequently the coupling becomes anti-
ferromagnetic. However, in the case of complex 3, due to
the presence of water-bridging, stability is achieved at rela-
tively small Ni–O(phenoxido)–Ni angles. The dependence
Physical Measurements: Elemental analyses (C, H, and N) were
performed with a 2400 series II CHN analyzer. IR spectra (4500–
–
1
5
00 cm ) in KBr pellets were recorded with a Perkin–Elmer RXI
FT-IR spectrophotometer. Electronic spectra (1400–350 nm) in
CH OH (for 1–3) were recorded with a Hitachi U-3501 spectropho-
tometer. The magnetic measurements were carried out at the
3
of the coupling constant on the water bridging angle shows “Servei de Magnetoquimica (Universitat de Barcelona)” on poly-
that the most stable structure lies in the positive slope re- crystalline samples (20 mg) with a Quantum Design SQUID
gion of an unsymmetrical parabolic curve. Thus, the value MPMSXL susceptometer in applied fields of 7000 and 400 G in
the temperature ranges of 2–300 and 2–30 K, respectively. The field
of J increases with the bond angle in this region.
dependence of the magnetization measurements were performed
with the same instrument at 2 K. The experimental magnetic
susceptibility data are corrected for the diamagnetism estimated
Conclusions
[37a]
from Pascal’s tables
and sample holder calibration.
Three new dinuclear NiII complexes have been synthe- Synthesis of the Schiff Base Ligand 2-({[3-(Dimethylamino)-
sized by using a tridentate N,N,O donor Schiff base ligand, propyl]imino}methyl)phenol (HL): The Schiff base was prepared by
the condensation of salicylaldehyde and N,N-dimethyl-1,3-prop-
2
-({[3-(dimethylamino)propyl]imino}methyl)phenol, and an
20]
–
–
–
anediamine in methanol as reported earlier.[
(NO ] (1): Ni(NO ·6H
compound 3, as well as the diphenoxido bridges from the dissolved in methanol (10 mL) was added to a methanolic solution
anionic co-ligand, NO , NO , or CH COO . Compounds
1
3
2
3
and 2 present diphenoxido-bridged complexes whereas in Synthesis of [Ni
2
L
2
3
)
2
3
)
2
2
O (1.455 g, 5 mmol)
(
10 mL) of the ligand HL (5 mmol) with constant stirring followed
Schiff base ligand, a water molecule acts as a bridge be-
tween the two Ni ions. The strong hydrogen bond between
II
by the addition of triethylamine (0.70 mL, 5 mmol). The color of
the solution turned deep green. The solution was left to stand in
air until plate-shaped green X-ray quality single crystals of complex
appeared at the bottom of the vessel on slow evaporation of the
solvent. Yield: 1.14 g; 70%. IR (KBr pellet): ν˜ = 1644 (νC=N),
the bridging water molecule and the uncoordinated oxygen
atom of the acetate group seems to stabilize the structure
of 3. The magnetic study revealed that compounds 1 and 2
are antiferromagnetically coupled, as is expected from the
Ni–O–Ni bridging angles [99.31(8) and 100.01(7)°]. How-
1
–
–1
1
289 (νNO ) cm . UV/Vis (CH
3
3
OH): λmax = 365, 637, 1012 nm.
Ni O (651.99): calcd. C 44.21, H 5.26, N 12.89; found
C
24
H
34
N
6
2 8
ever, compound 3 is ferromagnetically coupled, as indicated C 44.10, H 5.20, N 12.97.
by the smaller bridging angles [86.71(12), 86.30(11), and
Synthesis of [Ni
2 2 2 2 4 2 2
L (NO ) ] (2): Ni(ClO ) ·6H O (1.828 g, 5 mmol),
87.18(10)°]. The experimental magnetic behavior of com-
dissolved in methanol (10 mL) was added to a methanolic solution
plexes 1–3 was corroborated by DFT calculations, which (10 mL) of the Schiff base HL (5 mmol) with constant stirring fol-
serve as an efficient tool for understanding the magnetic lowed by the addition of triethylamine (0.70 mL, 5 mmol). Then a
interaction pathways of the complexes. A combination of methanol/water solution (9:1, v/v) of NaNO (0.345 g, 5 mmol) was
2
added with slow stirring. The solution was left to stand overnight
in air in which time block-shaped light-green X-ray quality single
crystals of complex 2 appeared. Yield: 1.16 g; 75%. IR (KBr pellet):
DFT calculations and magnetic studies have allowed us to
deduce the dependence of the exchange coupling constant
J on the bridge identity, the metal–metal separation, and
the bond angles subtended at the bridging atoms in the di-
–
1
ν˜ = 1644 (νC=N), 1290 (ν
s
NO
2
), 1200 (νasNO
2
) cm . UV/Vis
Ni (619.99):
(
CH OH): λmax = 366, 640, 1025 nm. C24
3
H
34
N
6
2 6
O
nuclear nickel complexes having either μ -phenoxido or
2
calcd. C 46.50, H 5.53, N 13.56; found C 46.31, H 5.25, N 13.12.
Synthesis of [Ni (CH COO) (H O)] (3): Ni(OAc) ·4H
1.240 g, 5 mmol) dissolved in hot methanol (10 mL) was added to
both μ -phenoxido and μ -water bridges. However, from the
2
2
2
L
2
3
2
2
2
2
O
relative energy point of view, the diphenoxido-bridged com-
plexes are highly unstable in the lower bond angle range,
(
a methanolic solution (10 mL) of the ligand HL (5 mmol) and the
mixture stirred for ca. 10 min. Triethylamine (0.70 mL, 5 mmol)
was added, the color of the solution turned deep green, and a green
precipitate separated within 1 h. The green solid was then removed
II
whereas in the triple-bridged Ni complexes such small
angles can be obtained easily, which indicates the impor-
tance of the additional bridge in making them stable in the
lower bridging angle region and consequently the coupling by filtration, washed with diethyl ether, and redissolved in CH CN.
3
ferromagnetic.
The solution was left to stand overnight in the air, which resulted
10
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Job/Unit: I20028
/KAP1
Date: 25-04-12 14:58:33
Pages: 13
Antiferro- and Ferromagnetic Dinuclear Nickel(II) Complexes
in the precipitation of deep-green, X-ray-quality single crystals of
convergence criterion (Grid4).[49] The “resolution of identity” (RI)
approximation with auxiliary TZV/J coulomb fitting basis sets were
also used to increase the speed of the calculations. For the SCF
complex 3. Yield: 1.09 g; 65%. IR (KBr pellet): ν˜ = 3400 (br.,
–1
[50]
νOH), 1635 (νC=N), 1580 (νasC=O), 1450 (ν
CH OH): λmax = 367, 644, 1022 nm. C56
s
C=O) cm . UV/Vis
4
Ni O15 (1346.18): calculations, we have taken into account all the experimental struc-
(
3
H
86
N
8
calcd. C 49.97, H 6.44, N 8.32; found C 49.55, H 6.38, N 8.16.
tures without further geometrical optimization. In the DFT calcu-
lations on angle dependence we modified the angle keeping the rest
of the structure frozen and then performed the SCF calculations.
To check the changes in J in the optimized structures, we per-
formed a geometrical optimization at the B3LYP/TZVP level of
theory. Then the SCF calculations of the optimized structure and
J value extraction were performed by using the same method as
used in previous calculations.
Crystallographic Data Collection and Refinement: Suitable single
crystals of each complex were mounted on a Bruker SMART dif-
fractometer equipped with a graphite monochromator and Mo-K
λ = 0.71073 Å) radiation. The structures were solved by the Pat-
α
(
[38]
terson method by using SHELXS97. Subsequent difference Fou-
rier synthesis and least-squares refinement revealed the positions
of the remaining non-hydrogen atoms. The non-hydrogen atoms
were refined with independent anisotropic displacement param-
eters. All the hydrogen atoms were placed in idealized positions,
and their displacement parameters were fixed at 1.2 times larger
than those of the attached non-hydrogen atoms except for the hy-
drogen atoms on C(6) in 1 and 2, and on C(7) and C(21) in 3 and
on the water oxygen atoms O(3) and O(8) in 3, which were located
in the difference Fourier map. Successful convergence was indicated
by a maximum shift/error of 0.001 for the last cycle of the least-
squares refinement. All calculations were carried out by using
E
bs – Ehs
J =
(3)
1 2 1
2S S + S
Supporting Information (see footnote on the first page of this arti-
cle): Results of DFT calculations, given in Tables S1, S3 and S4,
hydrogen bonding in complex 3, shown in Table S2; selected bond
lengths and angles of 1–3 in Table S5, Figures S1 and S2 with χ
vs. T plots of complexes 1–3.
M
[
38]
[39]
[40]
[41]
SHELXS97, SHELXL97, PLATON99, ORTEP-32, and
WinGX systemVer-1.64.[ Data collection and structure refine-
ment parameters as well as the crystallographic data for the three
complexes are given in Table 6. CCDC-852926 (for 1), -852927 (for
42]
Acknowledgments
2
), and -852928 (for 3) contain the supplementary crystallographic
We thank the Council of Scientific and Industrial Research (CSIR)
and the Government of India [Senior Research Fellowships to
R. B. and S. G., Sanction no. 09/028(0746)/2009-EMR-I and 09/
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.
080(0639)/2009-EMR-I]. Crystallography was performed at the De-
partment of Science & Technology – Fund for Improvement of S&
T Infrastructure in Higher Educational Institutions (DST-FIST),
India-funded Single Crystal Diffractometer Facility at the Depart-
ment of Chemistry, University of Calcutta. S. K. S. acknowledges
the DST – Centre for Nanotechnology, Indian Association for the
Cultivation of Science (IACS) for financial support. We are thank-
ful to Dr. Carmen Diaz, Departament de Química Inorgànica, Uni-
versitat de Barcelona, Marti i Franques 1-11, 08028 Barcelona,
Spain.
Table 6. Crystallographic data for complexes 1–3.
1
2
3
Empirical formula
C H N Ni O
24 34 6 2 8
C H N Ni O
24 34 6 2 6
C
56 86 8 4 15
H N Ni O
M
651.95
619.95
monoclinic
1346.09
monoclinic
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
V [Å ]
triclinic
¯
P1 (No. 2)
8.736(5)
9.403(5)
9.964(5)
109.039(5)
94.159(5)
112.664(5)
695.3(6)
1
C2/c (No. 15)
20.780(5)
17.503(5)
7.915(5)
90
111.980(5)
90
2670(2)
4
C2/c (No. 15)
18.746(4)
12.756(3)
28.761(8)
90
107.871(3)
90
6546(3)
4
1.366
1.199
2840
0.057
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11

Job/Unit: I20028
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Date: 25-04-12 14:58:33
Pages: 13
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Published Online: ᭿
12
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Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: I20028
/KAP1
Date: 25-04-12 14:58:33
Pages: 13
Antiferro- and Ferromagnetic Dinuclear Nickel(II) Complexes
Dinuclear Nickel(II) Complexes
R. Biswas, S. Giri, S. K. Saha,
A. Ghosh* ....................................... 1–13
One Ferromagnetic and Two Antiferro-
magnetic Dinuclear Nickel(II) Complexes
Derived from a Tridentate N,N,O-Donor
Schiff Base Ligand: A Density Functional
Study of Magnetic Coupling
Keywords: Nickel / Schiff bases / O ligands /
Magnetic properties / Density functional
calculations
Of the three dinuclear NiII complexes syn-
thesized, the two double-phenoxido-
bridged complexes are antiferromagne-
tically coupled, whereas the third with an
additional water bridge is ferromagnetic. A
theoretical study has been performed to
show the influence of the Ni–O–Ni bond
angle on the exchange coupling constants.
Eur. J. Inorg. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
13