Polynuclear nickel(II) complexes with salicylaldimine derivative ligands

Article abstract of DOI:10.1016/j.ica.2012.09.037

The reaction of pentadentate salicylaldimine ligand 2-((2-(2-(2- hydroxybenzylideneamino)ethylthio)ethylimino)methyl)phenol (H₂L) and its related hydrogenated derivative 2-((2-(2-(2-hydroxybenzylamino)ethylthio) ethylamino)methyl)phenol (H

Full text of DOI:10.1016/j.ica.2012.09.037

Inorganica Chimica Acta 394 (2013) 741–746
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Inorganica Chimica Acta
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Polynuclear nickel(II) complexes with salicylaldimine derivative ligands
a
b,
Moussa Dieng a, Ousmane Diouf a, Mohamed Gaye a, , Abdou Salam Sall , Paulo Pérez-Lourido
⇑
⇑
,
Laura Valencia b, Andrea Caneschi c, Lorenzo Sorace c
a Department of Chemistry, University Cheikh Anta Diop, Dakar, Senegal
b Departamento de Química Inorgánica, Facultade de Química, Universidad de Vigo, 36310 Vigo, Pontevedra, Spain
c Dipartimento di Chimica ‘‘U. Schiff’’ and INSTM Research Unit, Università di Firenze, Via della Lastruccia 3, 50019 Sesto Fiorentino, FI, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 23 April 2012
Received in revised form 26 September 2012
Accepted 26 September 2012
Available online 12 October 2012
The reaction of pentadentate salicylaldimine ligand 2-((2-(2-(2-hydroxybenzylideneamino)ethylthio)
ethylimino)methyl)phenol (H2L) and its related hydrogenated derivative 2-((2-(2-(2-hydroxybenzylami-
no)ethylthio)ethylamino)methyl)phenol (H4L1) with hydrated nitrate and perchlorate nickel(II) salts
afforded polynuclear metal complexes. These complexes were characterized by elemental analysis, IR
and UV–Vis spectroscopy, molar conductance and variable temperature magnetic measurements. Single
crystal X-ray diffraction of [(NiL)2]ꢀCH3OHꢀ4H2O (1) and [Ni3(H2L1)2(NO3)2] (3) complexes has revealed
the presence of an octahedral coordination geometry around the nickel ion. The magnetic data indicate
that a moderate antiferromagnetic interaction is present in complexes 1 and 3.
Keywords:
Nickel
Polynuclear
Salicylaldimine
Antiferromagnetic
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
(Scheme 1), which have large receptor cavities with N and S donor
sites suitably disposed to encapsulate one or more metal ions,
Studies involving the chelation and coordination of ligands de-
rived from salicylaldehyde to transition metal centers containing a
flexible tridentate ligand have been an ongoing area of active
research. In recent years, much attention has been given to the
synthesis of acyclic ligands that can give rise to dinuclear or
polynuclear metal complexes with interactions between the metal
centers [1,2]. Salicylaldehyde has been used as precursor of a high
number of acyclic ligands with several different donor sites using
different amines [3–5]. The formation of acyclic complexes
depends on the dimension of the cavities, on the flexibility of the
arms, on the nature of the donor atoms and on the complexing
properties of the anions acting as counter ions [6]. Attention has
been devoted to the study of spectroscopic properties and crystal
structures [7,8].
Some metalloproteins contain metal ions such as Ni(II) or Cu(II)
where the coordination spheres present N and S donor sets. These
features have led to increased interest in the synthesis of com-
plexes with mixed N,S donating chelates as structural models of
the active sites [9,10]. In this paper, we report our work with acy-
clic ligands derived from the salicylaldehyde precursor and 2-(2-
aminoethylthio)ethanamine. In this case, we have prepared the
acyclic H2L and its related hydrogenated derivative H4L1 ligands
resulting in di- or trinuclear complexes. The complexation capacity
of these acyclic ligands towards the first row transitional metal
Ni(II) ion has been investigated.
2. Experimental
2.1. Physical measurements
Elemental analyses were carried out using a LECO CHNS-932
instrument. The IR spectra were recorded as KBr discs on a Bruker
IFS-66 V spectrophotometer (4000 to 400 cmꢁ1). The UV–Vis spec-
tra were run on a Shimadzu UV-2501 PC Recording Spectropho-
tometer (1000 to 200 nm). The FAB mass spectra were recorded
using a Micromass Autospec spectrometer using 3-nitrobenzyl
alcohol as the matrix. The 1H and 13C NMR spectra of the Schiff
bases were recorded in CDCl3 on a BRUKER 500 MHz spectrometer
at room temperature using TMS as an internal reference. The molar
conductance of 10ꢁ3 M solutions of the metal complexes in DMF
was measured at 25 °C using a WTW LF-330 conductivity meter
with a WTW conductivity cell. Magnetic measurements were per-
formed in the temperature range of 2–300 K by using a Cryogenic
S600 SQUID magnetometer in an applied magnetic field of
1000 Oe. Raw data were corrected for the diamagnetism of the
sample holder, measured in the same temperature and field range,
and the intrinsic contribution of the sample, estimated by Pascal’s
constants.
⇑
Corresponding authors.
E-mail addresses: mlgayeastou@yahoo.fr (M. Gaye), paulo@uvigo.es
(P. Pérez-Lourido).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.09.037

742
M. Dieng et al. / Inorganica Chimica Acta 394 (2013) 741–746
–CH2–S–), 3.8 (t, 4H, –CH2–N–), 4.9 (s, 2H, HN–), 3.8 (t, 4H, Ar–
CH2–N–), 6.8–7.4 (m, 8H, HAr), 12.25 (s, (broad), 2H, –OH) ppm.
13C NMR (CDCl3) d 158.07, 128.87, 128.42, 122.19, 119.16, 116.46
(CAr), 52.20 (–CH2–N), 46.84 (Ar–CH2–N–), 31.81 (–CH2–S–) ppm.
2.4. Synthesis of the complexes – General procedure
N
S
OH
OH
NH
S
OH
To a refluxing methanolic solution (10–20 mL) of the perchlo-
rate or nitrate metal salt (2 mmol), a solution of the corresponding
ligand (1 mmol) in methanol (15–30 mL) was slowly added. The
solution was stirred at room temperature for 2 h and then let stand
to cool. The precipitate obtained was isolated by vacuum filtration,
washed with cold methanol and dried over anhydrous P4O10. In the
case of complexes 1 and 3, no precipitate from the mixture solution
was formed, thus the resultant green solutions were filtered. Crys-
tals of [(NiL)2]ꢀCH3OHꢀ2H2O (1) and [Ni3(H2L1)2(NO3)2] (3), were
obtained by slow evaporation of the green solution after 3 days.
N
NH
OH
2.4.1. [(NiL)2]ꢀCH3OHꢀ4H2O (1)
Anal. Calc. for C37H44Ni2N4O7S2: C, 53.0; H, 5.3; N, 6.7; S, 7.6.
Found: C, 53.0; H, 5.3; N, 6.6; S, 7.6%. Yield: 39%. IR (KBr, cmꢁ1):
3489m, 3024w, 2911m, 2858m, 1627s, 1595s, 1547s, 1469m,
H2L
H4L1
Scheme 1.
1289s, 1100m, 894m, 788m, 759s, 592m. Km = 127 cm2
X
ꢁ1 molꢁ1
in DMF. UV–Vis (k, nm) (e
, Mꢁ1 cmꢁ1) 325(3), 350(1.204), 360(3),
2.2. Chemicals and starting materials
395(0.586), 430(0.643), 485(0.783), 540 (0.849), 620(1.109),
790(1.915), 890(1.921), 910(1.979). Color: green.
2-(2-Aminoethylthio)ethanamine, salicylaldehyde, sodium tet-
rahydroborate and hydrated nitrate and perchlorate salts Ni(II)
salts were commercial products (from Alfa and Aldrich) and were
used without further purification. Solvents were of reagent grade
and were purified by the usual methods.
Caution: Although no problems were encountered during the
course of this work, attention is drawn to the potentially explosive
nature of the perchlorate salts.
2.4.2. [Ni2L](NO3)2 (2)
Anal. Calc. for C18H18Ni2N4O8S: C, 38.1; H, 3.2; N, 9.9; S, 5.7.
Found: C, 38.3; H, 3.5; N, 9.8; S, 5.8%. Yield: 36%. IR (KBr, cmꢁ1):
3316f, 3253f, 3159tf, 2935tf, 1626m, 1594m, 1547m, 1471m,
1444m, 1422m, 1380s, 1323w, 1305m, 1286m, 1270m, 1196m,
1154f, 1126f, 1063m, 1039m, 1019f, 976f, 964m, 892m, 856f,
816f, 784m, 766m, 759m, 739m, 693m, 676f, 638f, 592m, 553m.
Color: green.
2.3. Synthesis of the ligands
2.4.3. [Ni3(H2L1)2(NO3)2] (3)
2.3.1. H2L
Anal. Calc. for C36H44Ni3N6O10S2: C, 45.0; H, 4.6; N, 8.7; S, 6.7.
Found: C, 45.0; H, 4.6; N, 8.7; S, 6.6%. Yield: 25%. IR (KBr, cmꢁ1):
3277s, 3038m, 2833s, 1577s, 1526w, 1424s, 1335m, 1278m,
2-(2-Aminoethylthio)ethanamine (4.17 g, 34.7 mmol) dissolved
in 30 mL of ethanol was refluxed with an ethanolic solution of sal-
icylaldehyde (8.47 g, 69.4 mmol), in the presence of few drops of
glacial acetic acid [11]. The resulting yellow solution was refluxed
for 3 h. On cooling to room temperature a separated yellow precip-
itate was formed. It was thoroughly washed with ether and dried
over P4O10. Anal. Calc. for C18H20N2O2S: C, 65.8; H, 6.1; N, 8.5; S,
9.8. Found: C, 65.5; H, 6.1; N, 8.5; S, 9.9%. Yield: 87.4%. M.P.:
1082s, 1039s, 983s, 870s, 752s. Km = 42 cm2
X
ꢁ1 molꢁ1 in DMF.
UV–Vis (k, nm)
(e
,
Mꢁ1 cmꢁ1
)
335(0.802), 360(0.865),
550(0.311),725(0.548), 925(0.740). Color: green.
2.5. X-ray data collection, structure determination, and refinement
75 °C. MS (FAB, m/z): 329 [H2L]+. IR (KBr, cmꢁ1): 3354s (
3135m, 3052m, 1149s, 1069m, 955s, 891s ( CH); 2854s (
1633s ( C@N); 1577s, 1526w, 1418s ( C@C); 1244m (
C–O). 1H
m
m
O–H);
CH2);
The details of the X-ray crystal structure solution and refine-
ment are given in Table 1. Measurements were made on a Bruker
SMART CCD Area Detector. All data were corrected for Lorentz
and polarization effects. Empirical absorption correction was ap-
plied. Complex scattering factors were taken from the program
package SHELXTL [13]. The structures were solved by direct methods,
which revealed the position of all non-hydrogen atoms. All the
structures were refined on F2 by a full-matrix least-squares
procedure using anisotropic displacement parameters for all non-
hydrogen atoms [14]. All hydrogen atoms were located in their
calculated positions and refined using a riding model. Molecular
graphics were generated using ORTEP-3 [15].
m
m
m
m
NMR (CDCl3) d 2.9 (t, 4H, –CH2–S–), 3.8 (t, 4H, –CH2–N@), 8.4 (s,
2H, HC@N–), 6.8–7.4 (m, 8H, HAr), 12.25 (s (broad), 2H, –OH)
ppm. 13C NMR (CDCl3) d 166.06 (–C@N–), 161.04, 132.41, 132.25,
131.49, 118.69, 117.03 (CAr), 59.40 (–CH2–N–), 33.45 (–CH2–S–)
ppm.
2.3.2. H4L1
H2L (5.08 g, 15.5 mmol) was dissolved at 0 °C in 70 mL of meth-
anol and (1.76 g, 46.4 mmol) of NaBH4 was added in small portions
[12]. The white precipitate which was formed during the reaction
was isolated by filtration. The solid product was washed with sev-
eral portions of diethylether and dried in a vacuum dessicator over
P4O10. Anal. Calc. for C18H24N2O2S: C, 65.0; H, 7.3; N, 8.4; S, 9.6.
Found: C, 65.1; H, 7.3; N, 8.4; S, 9.7%. Yield: 97%. M.P.: 103 °C.
3. Results and discussion
The acyclic Schiff bases H2L and H4L1 were prepared in a good
yield. The synthesis of H2L was achieved in a one step procedure
using the direct condensation of salicylaldehyde with 2-(2-amino-
ethylthio)ethanamine, and H4L1 was obtained by reducing H2L in
MS (FAB, m/z): 333 [H4L1]+. IR (KBr, cmꢁ1): 3354s (
3038m, 1082s, 983s, 870s ( CH); 2833s ( CH2); 1577s, 1526w,
1461s, 752s ( C@C); 1278m (
C–O). 1H NMR CDCl3 d 2.9 (t, 4H,
mO–H); 3277m,
m
m
m
m

M. Dieng et al. / Inorganica Chimica Acta 394 (2013) 741–746
743
Table 1
Crystal data and structure refinement for [(NiL)2]ꢀCH3OHꢀ4H2O (1) and [Ni3(H2L1)2(NO3)2] (3).
(1)
(3)
Empirical formula
Formula weight
T (K)
C
37H48N4O9S2Ni2
C36H44N6O10S2Ni3
961.02
293(2)
874.33
293(2)
k (Å)
Crystal system
Space group
0.71073
orthorhombic
Pbcn
0.71073
monoclinic
P21/c
Unit cell dimensions
a (Å)
b (Å)
13.8664(18)
14.8691(19)
21.014(3)
11.573(4)
18.768(6)
10.027(3)
111.141(6)
2031.5(11)
2
1.571
1.542
996
c (Å)
b (°)
V (Å3)
4332.6(10)
4
1.340
1.018
Z
Dcalc (Mg/m3)
Absorption coefficient (mmꢁ1
F(000)
)
1832
Crystal size (mm)
h range for data collection (°)
Index ranges
Reflections collected
Independent reflections
Completeness to theta (°)
Absorption correction
0.34 ꢂ 0.34 ꢂ 0.23
0.20 ꢂ 0.17 ꢂ 0.10
1.94–25.02
1.89–25.07
ꢁ16 6 h 6 16, ꢁ17 6 k 6 17, ꢁ24 6 l 6 24
30106
3832 (Rint = 0.0416)
100% (25.02)
ꢁ13 6 h 6 13, ꢁ22 6 k 6 22, ꢁ11 6 l 6 11
15498
3594 (Rint = 0.0612)
99.9% (25.07)
empirical
empirical
Maximum and minimum transmission
Refinement method
0.7995 and 0.7234
full-matrix least-squares on F2
3832/0/242
0.8611 and 0.7480
full-matrix least-squares on F2
3594/0/267
Data/restraints/parameters
Goodness-of-fit on F2
1.100
1.053
Final R indices [I > 2
R indices (all data)
r
(I)]
R1 = 0.0672, wR2 = 0.2205
R1 = 0.0906, wR2 = 0.2586
1.604 and ꢁ0.324
R1 = 0.0397, wR2 = 0.0771
R1 = 0.0825, wR2 = 0.0997
0.438 and ꢁ0.366
Largest difference in peak and hole (e Åꢁ3
)
methanol with sodium borohydride. The mass spectra of the two
ligands present an intense peak at m/z 329 and 333, respectively,
corresponding to the molecular ions of the protonated ligands.
The presence of phenol hydroxyl and imine moiety in the free li-
gand H2L were confirmed by the appearance in the IR spectrum
the IR of the nitrate complex 2, information regarding the possible
bonding modes of the nitrate group was obtained. For example, the
bands at 1422 and 1323 cmꢁ1 are due to
m
(N@O) (
5), respectively, of the coordinated nitrate. The s(NO2) (
tected at 1029 cmꢁ1. These facts are characteristic of bidentate
bridging nitrate ligands [16,17]. The separation 5 has
1 ꢁ
been used as criterion of differentiation between mono and biden-
tate chelating nitrates, with increasing as the coordination
m
1) and
m
as(NO2)
(m
m
m2) is de-
of an intense broad band centered at ca. 3354 cmꢁ1
(m
O–H), a strong
band at 1640 cmꢁ1 mC@N and bands of medium intensity at 1577,
1526 and 1461 cmꢁ1 C@C). In the IR spectrum of the H4L1 no band
D
m
=
m
m
(m
Dm
assignable to mC@N was observed. This fact confirms the reduction
of H2L. The 1H NMR spectra of the ligands are comparable and
show the reduction of the imine group. Indeed, the signal at d
8.4 ppm observed in the spectrum of H2L corresponding to
(HC@N), disappears in the spectrum H4L1 while two new signal ap-
pear at d 4.9 and 3.8 ppm, representative of –NH– and Ar–CH2–N,
respectively. The 13C NMR spectrum of H2L shows a signal at d
166.06 ppm which represent the carbon atom of the imine C@N
group. This peak shifts to d 46.84 ppm upon reduction of H2L to
H4L1. The peaks at d 161.04 and 158.07 ppm represent the aromatic
Cipso of the OH of the phenol in H2L and H4L1 spectra, respectively.
The coordination ability of H2L and H4L1 towards hydrated per-
chlorate and nitrate salts of Ni(II) in 2:1 metal:ligand molar ratio
was studied by mixing methanol solutions of the corresponding li-
gand and metal salts. In all cases, the complexes appear to be air
stable and, except complex 2, soluble in common organic solvents.
These complexes were characterized by elemental analysis, IR and
UV–Vis spectroscopy, molar conductivity and magnetic measure-
ments, except 2 due to its low solubility in common solvents men-
tioned above.
changes from mono to bidentate and/or bridging modes [18]. The
magnitude of this separation for this complex (99 cmꢁ1) is indica-
tive of a bidentate bridging nitrate. Also, the characteristic band
near 1380 cmꢁ1, typical of non-coordinated nitrate group is ob-
served [19]. Therefore it can be concluded the probably presence
of both, coordinated and ionic nitrate, counter ions in complex 2.
The IR spectrum of the complex [Ni3(H2L1)2(NO3)2] (3) exhibits
bands assignable to a bidentate bridging nitrate moiety. Additional
band assignable to N–H stretching vibration was observed at
3227 cmꢁ1
.
The electronic spectra of the complexes 1 and 3 were recorded
in freshly prepared DMF solutions. A fairly symmetrical new band
is observed for 1. This band disappears in the complex from the li-
gand treated with NaBH4 in order to reduce the C@N group to a
saturated moiety. Therefore, the absorption at 405 nm must be
associated with the C@N chromophore coordinated to the metal
ion through the nitrogen atom. An intense band was also observed
at 335 nm. It was absent for the free ligand and is assigned to
charge transfer between the coordinated ligand and the metal ions.
The electronic spectrum of 1 exhibits four bands at 540, 620,
790 and 910 nm, while the electronic spectrum of 3 shows three
band at 550, 725 and 925 nm. These values are typical of
octahedral Ni(II) complexes and they can accordingly be attributed
The elemental analysis are in good agreement with the ex-
pected values for neutral complexes. In the IR spectra of the com-
plexes, the C@N band shift towards lower frequency on
complexation of H2L by Ni(II) ion, appearing near 1620 cmꢁ1 in
the spectra of 1 and 2, suggesting an interaction between the metal
and the imine nitrogen atom. The hydroxyl groups of water and
methanol lattice molecules appear near 3490 cmꢁ1 for 1 [16]. From
3
3
to T2g 3A2g
,
3T1g(F) 3A2g and T1g(P) 3A2g transitions [20].
These results are in agreement with the X-ray crystal structure
which displays the metal ion in
environment.
a
distorted octahedral

744
M. Dieng et al. / Inorganica Chimica Acta 394 (2013) 741–746
Molar conductivities were measured for freshly prepared solu-
tions in DMF and after standing for 2 weeks. The conductivities in-
creased very slightly with time for all the complexes. The
conductance value of complex 1 lies in the range observed for
2:1 electrolytes (130–170 cm2
X
ꢁ1 molꢁ1). For the trinuclear Ni(II)
complex, 3, the conductance is 42 cm2
X
ꢁ1 molꢁ1 indicative of a
neutral complex in DMF solution [21].
Crystals of [(NiL)2]ꢀCH3OHꢀ4H2O (1) and [Ni3(H2L1)2(NO3)2] (3)
suitable for X-ray diffraction were obtained by slow evaporation
of the corresponding solutions.
3.1. Crystal structure of [(NiL)2]ꢀCH3OHꢀ4H2O (1)
The molecular structure of [(NiL)2] is shown in Fig. 1a together
with the atomic numbering scheme adopted and selected bond
lengths and angles. The compound crystallizes in the centrosym-
metric space group Pbcn. The asymmetric unity shows half mole-
cule as the dimer lies in a crystallographic binary axis. The
structure is dinuclear, with the two nickel(II) centers joined by
two phenolate groups acting as a bridge. The geometry around
the metal ion can be described as slightly distorted octahedral,
with a N2SO3 core comprised by the five donor atoms of one li-
gand: two amine nitrogen, one sulfur atom and the two phenolate
groups (one acting as terminal and the other as bridge with the
other metal ion). The sixth position is occupied by the bridging
phenolate oxygen of the other ligand molecule. The equatorial
plane of the octahedron is formed by N(2)–S(1)–O(1)–O(2)#1
(rms 0.0631) with the Ni ion 0.0243 Å out of this plane. The axial
positions are occupied respectively by one N of one amine and
the O of one phenolate bridge group, 174.6(2)° [N(1)–Ni(1)–O(2)].
The shortest bond distance to the nickel ion corresponds to the
terminal phenolate oxygen, Ni(1)–O(1), 2.024(5) Å, and the longest
bond distance to the sulfur atom, Ni(1)–S(1), 2.5717 Å. The amine
distances, Ni(1)–N(1), 2.046(7) Å and Ni(1)–N(2), 2.0333(6) Å, are
in the range of the bridge phenolate oxygen atoms, Ni(1)–O(2),
2.050(5) Å.
Fig. 1b. Hydrogen bond interaction of one water molecule with methanol and
phenolate groups in [(NiL)2]ꢀCH3OHꢀ4H2O (1).
[Ni(dpmap)(H2O)]2(ClO4)2ꢀ3(CH3)2CO] (dpmap is 2-{[[di(2-pyri-
dyl)methyl](methyl)-amino] methyl}phenol) [22].
Disordered water molecules are present in the structure. O1w
and O3w lies also in the crystallographic binary axis. O1W, inter-
acts through hydrogen bonding with methanol molecules and the
terminal O1 phenolate groups (Fig. 1b). [O1Wꢀ ꢀ ꢀO1S 2.649 Å],
[O1Wꢀ ꢀ ꢀO1 2.502 Å].
3.2. Crystal structure of [Ni3(H2L1)2(NO3)2] (3)
The molecular structure of the complex [Ni3(H2L1)2(NO3)2] is
illustrated in Fig. 2 together with selected bond lengths and angles.
The figure shows a trinuclear centrosymmetric complex, with the
three nickel ions in linear array joined by two ligands molecules
through phenolate bridge groups and two bidentated nitrate moi-
eties. The geometry about all of the Ni(II) ions can be regarded as
distorted octahedral. The two terminal Ni ions are in a N2SO3 core,
being coordinated by the donor atoms of one ligand molecule –
two secondary amine nitrogen atoms, two bridge phenolate groups
and the terminal sulfur atom- and one oxygen atom from a biden-
tade bridging nitrate moiety. Two nitrogen atoms, N(1) and N(2)
and two oxygen atoms O(1) and O(2) from the ligand form the
equatorial plane of the distorted octahedron (rms 0.0056) with
the Ni ion 0.0445 Å out of it. Thus, the axial positions are occupied
by the sulfur atom of the ligand, S(1) and the oxygen O(1N) from
the bidentate bridge nitrate, [O(1N)–Ni(1)–S(1), 172.96(9)°]. The
Ni–N distances [Ni(1)–N(1), 2.095(4) Å and Ni(1)–N(2),
2.086(4) Å] are comparable to those found for the octahedral
complex [Ni(ampy)2(NO3)2] (ampy is 2-aminomethylpyridine)
[2.0811(11) Å] [23]. The Ni–Ophenolate distances [Ni(1)–O(1),
2.011(3) Å and Ni(1)–O(2), 2.034(3) Å] are in the order of similar
complexes [24]. The nickel nitrate distance [Ni(1)–O(1N),
2.158(3) Å] and the longest coordination distance to the sulfur
atom, [Ni(1)–S(1), 2.3748(15) Å] are comparable with the values
found for similar nickel octahedral complexes [25,26].
The two Ni ions are separated by 3.1538 Å, a distance too long
to consider an intermetallic interaction, with a bridge angle of
100.6(2)° [Ni(1)–O(2)–Ni(1)#1]. These parameters are comparable
to those found for similar dinuclear nickel complexes, for example
The central nickel ion, Ni(2), presents an O6 distorted octahe-
dral environment, being coordinated by the bridging phenolate
oxygen atoms of the two ligand molecules that constitutes the
equatorial plane [O(1)–O(2)–O(1)#1–O(2)#1, rms 0.000] with
Ni(2) seated in that plane. The axial positions are occupied by
two oxygen atoms from a different bidentate bridge nitrate moiety.
The Ni(2)–Ophenolate distances are similar, [Ni(2)–O(2), 1.994(3) Å
Fig. 1a. Crystal structure of [(NiL)2]ꢀCH3OHꢀ4H2O (1). Selected bond lengths (Å) and
angles (°): Ni(1)–O(1) 2.024(5), Ni(1)–N(2) 2.033(6), Ni(1)–N(1) 2.046(7), Ni(1)–
O(2)#1 2.048(5), Ni(1)–O(2) 2.050(5), Ni(1)–S(1) 2.572(2), O(1)–Ni(1)–N(2) 95.9(3),
O(1)–Ni(1)–N(1) 86.7(2), N(2)–Ni(1)–N(1) 97.1(3), O(1)–Ni(1)–O(2)#1 96.0(2),
N(2)–Ni(1)–O(2)#1 159.3(2), N(1)–Ni(1)–O(2)#1 100.4(2), O(1)–Ni(1)–O(2)
88.4(2), N(2)–Ni(1)–O(2) 85.8(2), N(1)–Ni(1)–O(2) 174.6(2), O(2)#1–Ni(1)–O(2)
77.7(2), O(1)–Ni(1)–S(1) 166.59(15), N(2)–Ni(1)–S(1) 81.1(2), N(1)–Ni(1)–S(1)
80.72(18), O(2)#1–Ni(1)–S(1) 90.94(15), O(2)–Ni(1)–S(1) 104.35(15). Symmetry
transformations used to generate equivalent atoms: #1 ꢁx, y, ꢁz + 1/2.
and Ni(2)–O(1), 2.002(3) Å] and shorter than the Ni(2)–Onitrate
,
2.188(3) Å, which is comparable to those found in octahedral

M. Dieng et al. / Inorganica Chimica Acta 394 (2013) 741–746
745
Fig. 3. Experimental (full squares) and best fit
v
T
(emu K molꢁ1
)
vs.
T
data
(continuous line) for the dinuclear complex [(NiL)2]ꢀCH3OHꢀ4H2O (1).
11,23-dimethyl-3,7,15,19-tetraazatricyclo [19.3.1.19,13] hexaco-
sa-1(25),9,11,13(26),21,23-hexaene-25,26-diolate) [37,38] and
[Ni2(sym-hmp)2](BPh4)2.3.5DMF.0.5(2-PrOH) (where [H(sym-hmp)]
is 2,6-bis[(2-hydroxyethyl)methylaminomethyl]-4-methyl-phenol
Fig. 2. Crystal structure of [Ni3(H2L1)2(NO3)2] (3). Selected bond lengths (Å) and
angles (°): Ni(1)–O(1) 2.011(3), Ni(1)–O(2) 2.034(3), Ni(1)–N(2) 2.086(4), Ni(1)–
N(1) 2.095(4), Ni(1)–O(1N) 2.158(3), Ni(1)–S(1) 2.3748(15), Ni(2)–O(2)#1 1.994(3),
Ni(2)–O(2) 1.994(3), Ni(2)–O(1) 2.002(3), Ni(2)–O(1)#1 2.002(3), Ni(2)–O(2N)#1
2.188(3), Ni(2)–O(2N) 2.188(3), O(1)–Ni(1)–O(2) 81.13(11), O(1)–Ni(1)–N(2)
171.61(14), O(2)–Ni(1)–N(2) 90.91(15), O(2)–Ni(1)–N(1) 172.85(14), N(2)–Ni(1)–
N(1) 95.85(17), O(1)–Ni(1)–O(1N) 89.94(12), N(1)–Ni(1)–O(1N) 89.97(14),
O(2)–Ni(1)–S(1) 96.00(9), N(2)–Ni(1)–S(1) 87.06(13), N(1)–Ni(1)–S(1) 86.69(11),
O(1N)–Ni(1)–S(1) 172.96(9), O(2)#1–Ni(2)–O(2) 180.0(3), O(2)#1–Ni(2)–O(1)
97.66(12), O(2)–Ni(2)–O(1)#1 97.66(12), O(1)–Ni(2)–O(1)#1 180.0(2), O(2)–
Ni(2)–O(2N)#1 95.98(11), O(2)#1–Ni(2)–O(2N) 95.98(11), O(2)–Ni(2)–O(2N)
84.02(11), O(1)#1–Ni(2)–O(2N) 92.82(11), O(2N)#1–Ni(2)–O(2N) 180.0(2).
Symmetry transformations used to generate equivalent atoms: #1 ꢁx, ꢁy, ꢁz.
[39] show
a relatively stronger antiferromagnetic interaction
J = ꢁ67.1 cmꢁ1 and J = ꢁ69.7 cmꢁ1, respectively. Thus, as complex
1
shows two bridges between the nickel atoms, with Ni–
(Ophenolate)2–Ni angles of 100.64°, the magnitude of the antiferro-
magnetic interaction between the nickel centers is fully in the
expected range.
3.3.2. Magnetic properties of complex 3
Temperature dependence of the
complex 5 is shown on Fig. 4. The value of
v
T plots for the trinuclear Ni(II)
v
T is 3.50 emu K molꢁ1
at 300 K and is a little higher than the spin-only value for three
S = 1 spins with g = 2.00 (2.97 emu K molꢁ1) [40] and at 2 K the
v
[Ni2(pamap)2(NO3)]NO3, (Hpamap is N-(2-hydroxy)benzyl-N-methyl-
N0-(2-pyridyl)methyl-1,3-propanediamine) (2.188(2) Å) [29].
Few nitrate complexes of nickel, where the nitrate group
adopted bidentate bridging mode of coordination were found in
the literature [24,27] with respect to the monodentate or bidentate
chelating mode [28–33]. The distance between Ni ions is 3.015 Å,
shorter than that found for complex 1, but also longer than can
be considered an intermetallic interaction.
T is 0.90 emu K molꢁ1. Upon cooling from 300 to 100 K, the
vT
values steadily decrease. Below 100 K, the
vT values rapidly de-
crease with further cooling, suggesting that a dominant antiferro-
magnetic interaction between adjacent nickel(II) centers is
operative. Indeed, the interaction between the two terminal Ni(II)
cations was assumed to be negligible owing to the large distance
(3.0151(9) Å) and the long path between them. The magnetic anal-
ysis was then carried out by using the isotropic spin Hamiltonian
ˆ
ˆ
ˆ
ˆ
ˆ
ˆ
H = J[S1 ꢀ S2 + S2 ꢀ S3], (where the two terminal Ni are identified by
3.3. Magnetic properties
ˆ
ˆ
S1 and S3 while the central Ni atom is named S2). It is interesting
3.3.1. Magnetic properties of complex 1
For the dinuclear complex, the room temperature value of
vT
1.97 emu K molꢁ1, (Fig. 3) is a little lower than those expected
for two isolated Ni(II) ions (2.0 emu K molꢁ1, g = 2.00) [34]. On
cooling the
vT decreases regularly, with a more rapid descent be-
low 100 K, reaching a value of 0.02 emu K molꢁ1 at 2 K. This behav-
ior clearly points to antiferromagnetic interactions being active
within the molecule, with a small fraction of paramagnetic impu-
rity accounting for the residual paramagnetism at low tempera-
ture. A satisfactory fit, shown in Fig. 3, was obtained by using the
ˆ
Van Vleck equation derived by the Hamiltonian H = ꢁJS1 ꢀ S2 + glB
B ꢀ S and including a small fraction of paramagnetic impurity, with
best fit values g = 2.123 0.004, J = ꢁ66.4 0.6 cmꢁ1
, %imp =
1.5 0.2. Some authors have reported the magnetic behavior of
phenolate bridged nickel (II) complexes. They have suggested that
the phenolate group transmits an antiferromagnetic contribution
[35–37]. They showed a linear relationship between exchange
interaction owing the value of Ni–(Ophenolate)2–Ni bridge angle.
The dinuclear complexes [Ni2(L)(pyridine)2](ClO4)2 (where L is
Fig. 4. Experimental (full squares) and best fit
(continuous line) for the dinuclear complex [Ni3(H2L1)2(NO3)2] (3).
vT ) vs. T data
(emu K molꢁ1

746
M. Dieng et al. / Inorganica Chimica Acta 394 (2013) 741–746
to note that in this approach the ground state cannot be the
diamagnetic one, so that a meaningful model has to include a
correction to take into account possible zero field splitting effects
and/or intermolecular interactions:
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Appendix A. Supplementary material
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CCDC 868781 and 868782 contain the supplementary crystallo-
graphic data for [(NiL)2]ꢀCH3OHꢀ4H2O (1) and [Ni3(H2L1)2(NO3)2]
(3), respectively. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via http://
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2012.09.037.