The first triple phenoxido-bridged triangular NiIICu II2 complexes with a N2O2 donor di-Schiff base and pseudohalide (N(CN)2- or NCS -) ligands: Structural analyses an

Article abstract of DOI:10.1016/j.poly.2012.12.019

Two triangular tri-nuclear, hetero-metallic copper(II)-nickel(II) complexes, [(CuL)₂Ni{N(CN)₂}₂]·H ₂O (1) and [(CuL)₂Ni(NCS)₂]·H ₂O (2) have been synthesized by reacting "ligand

Full text of DOI:10.1016/j.poly.2012.12.019

Polyhedron 51 (2013) 96–101
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
The first triple phenoxido-bridged triangular NꢀiIICuII complexes with a N2O2
2
donor di-Schiff base and pseudohalide (N(CN)2 or NCSꢀ) ligands: Structural
analyses and magnetic properties
a,
Saptarshi Biswas a, Carmen Diaz b, , Ashutosh Ghosh
⇑
⇑
a Department of Chemistry, University College of Science, University of Calcutta, 92, A.P.C. Road, Kolkata 700009, India
b Departament de Química Inorgànica, Facultat de Química, Universitat de Barcelona, Martí i Franquès 1-11, 08028 Barcelona, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
Two triangular tri-nuclear, hetero-metallic copper(II)-nickel(II) complexes, [(CuL)2Ni{N(CN)2}2]ꢁH2O (1) and
[(CuL)2Ni(NCS)2]ꢁH2O (2) have been synthesized by reacting ‘‘ligand complex’’ [CuL] with Ni(ClO4)2 in
presence of polyatomic anions, dicyanamide (dca) or thiocyanate in methanol–water medium, where H2L
is a N2O2 donor di-Schiff base derived from 1,3-propanediamine and 2-hydroxyacetophenone. Both the
complexes have been structurally and magnetically characterized. In both complexes, two [CuL] units coor-
dinate to a nickel atom through the coordination of the phenoxido oxygen atoms forming triple phenoxido
bridges between each Cu(II) and Ni(II). A couple of terminal dca or N-bonded thiocyanate ions complete the
distorted octahedral geometry around Ni(II) in 1 and 2 respectively. Variable temperature magnetic suscep-
Received 6 November 2012
Accepted 26 December 2012
Available online 2 January 2013
Keywords:
NiIICuII complexes
2
Di-Schiff base ligand
Crystal structures
Magnetic properties
tibility measurements show the presence of moderate antiferromagnetic exchange interactions mediated
P
through the phenoxido bridges with J values (H = ꢀJ SiSi+1) of ꢀ49 and ꢀ42 cmꢀ1 for 1 and 2 respectively.
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
compounds the ligands are not salen type N2O2 donor; instead they
contain an additional coordinating group such as methoxy, ethoxy
The area of hetero-metallic polynuclear complexes have at-
tracted attention of the chemists not only for their interesting
architectures and topologies, but also for their applications in a
wide range of fields such as magnetism [1–5], photoluminescence
[6,7] and multifunctional molecular materials [8,9]. There are sev-
eral strategies for building the hetero-metallic coordination com-
plexes. Among them, use of previously formed metal complexes
having potentially bridging groups is found to be very effective
ones. For example, neutral complexes of salen type di-Schiff bases
(salen = N,N0-ethylenebis(salicylideneimine)) with divalent transi-
tion metal ions can coordinate to a second metal ion to afford var-
ious hetero-metallic compounds [10–19]. Such ‘‘Schiff base
complex as a ligand’’ approach has been applied successfully by
several groups including ours to construct many hetero-metallic
complexes with interesting structures and magnetic properties
[20–24]. Since Cu(II) chelates are the most stable ones among the
divalent first row transition metals, they have been widely used
for this purpose leading to several hundreds of hetero-nuclear spe-
cies with different transition metal ions. Among them, twenty four
are MCu2 type trinuclear species and only three [25–27] of them
contain Ni(II) as the central atom. However, in all these three
or carboxylate at the other o-position to the phenoxido oxygen.
Moreover, in two of these complexes only single oxido bridge
and in the other one double oxido bridge are formed between
the terminal Cu(II) and central Ni(II). Besides these, one more dou-
ble oxido bridged NiCu2 compound is reported but with an amino-
alkoxide ligand [28].
Herein, we report the synthesis, crystal structure and magnetic
properties of two new NiCu2 species [(CuL)2Ni{N(CN)2}2]ꢁH2O (1)
and [(CuL)2Ni(NCS)2]ꢁH2O (2) with the di-Schiff base ligand H2L
(N,N0-bis(
a-methylsalicylidene)-1,3-propanediamine, Scheme 1).
The complexes are the first examples of NiCu2 cluster with salen
type ligand. The novelty of the complexes also lies in that the nick-
el atom is coordinated by two [CuL] units through unprecedented
triple phenoxido-bridge between Ni(II) and each Cu(II) atoms. The
variable temperature molar susceptibility measurements of both
the complexes show the presence of antiferromagnetic behavior
between the NiII and the CuII ions within the cluster.
2. Experimental
2.1. Starting materials
⇑
Corresponding authors. Tel.: +91 9433344484; fax: +91 33 2351 9755 (A.
Ghosh).
The 2-hydroxyacetophenone and 1,3-propanediamine were
purchased from Lancaster and were of reagent grade. They were
used without further purification.
E-mail addresses: carme.diaz@qi.ub.es (C. Diaz), ghosh_59@yahoo.com (A.
Ghosh).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.12.019

S. Biswas et al. / Polyhedron 51 (2013) 96–101
97
X
X
O
Cu
O
Cu
Ni
N
N
Cu(ClO4)2
in MeOH
N
N
Ni(ClO ) ,
4 2 NaX
in MeOH/ H2O
N
N
Cu
O
O
O
O
HO
OH
N
N
Ni-X
[CuL]
H2L
1 Ni-N(CN)2
2 Ni-NCS
1-2
Scheme 1. Synthetic route to 1 and 2.
Caution! Perchlorate salts of metal complexes with organic li-
gands are potentially explosive. Only a small amount of material
should be prepared and it should be handled with care.
2.5. Crystallographic data collection and refinement
Suitable single crystals of both the complexes were mounted on
a Bruker-AXS SMART APEX II diffractometer equipped with a
graphite monochromator and Mo K
a (k = 0.71073 Å) radiation.
2.2. Synthesis of the Schiff base ligand (H2L) and the ligand complex
[CuL]
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 using Patterson method by using the SHELXS97. Subsequent
difference Fourier synthesis and least-square refinement revealed
the positions of the remaining non-hydrogen atoms that were re-
fined with independent anisotropic displacement parameters.
Hydrogen atoms were placed in idealized positions and their dis-
placement 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 [30]. All calculations were car-
ried out using SHELXS97 [31], SHELXL97 [32], PLATON99 [33], ORTEP-32
[34] and WinGX system Ver-1.64 [35]. Data collection and struc-
ture refinement parameters and crystallographic data for the four
complexes are given in Table 1.
The di-Schiff-base ligand, H2L was prepared by usual methods
[29]: 5 mmol of 1,3-propanediamine (0.42 mL) were mixed with
10 mmol of 2-hydroxyacetophenone (1.20 mL) in methanol
(10 mL). The resulting solution was refluxed for ca. 2 h and allowed
to cool. The yellow colored methanolic solution was used directly
for complex formation.
To a methanolic solution (10 mL) of Cu(ClO4)2ꢁ6H2O (1.852 g,
5 mmol), was added a methanolic solution of H2L (5 mmol,
20 mL) to prepare the ligand complex [CuL], as reported earlier
[29].
2.3. Synthesis of the complexes [(CuL)2Ni{N(CN)2}2]ꢁH2O (1) and
[(CuL)2Ni(NCS)2]ꢁH2O (2)
3. Results and discussion
5 mL of an aqueous solution of Ni(ClO4)2ꢁ6H2O (0.365 g,
1 mmol) was added to a methanolic solution (30 mL) of the ‘‘ligand
complex’’ [CuL] (0.784 g, 2 mmol) followed by 5 mL of an aqueous
solution of sodium dicyanamide (0.178 g, 2 mmol) or sodium thio-
cyanate (0.159 g, 2 mmol) for complexes 1 and 2, respectively.
Upon stirring, in both the cases microcrystalline solid started to
separate immediately. The stirring was continued for 30 min and
then filtered. The filtrate was allowed to stand overnight to yield
the brown (for both 1 and 2) X-ray quality single crystals at the
bottom of the vessel.
3.1. Synthesis, IR and UV–Vis absorption considerations
The Schiff-base ligand (H2L) and its Cu(II) complex, [CuL] were
synthesized by the reported procedure [29]. The trinuclear com-
plexes [(CuL)2Ni{N(CN)2}2]ꢁH2O (1) and [(CuL)2Ni(NCS)2]ꢁH2O (2)
were prepared simply by reacting [CuL] with Ni(ClO4)2 (2:1 molar
ratios) in presence of polyatomic anion Xꢀ (Xꢀ = dicyanamide (dca)
or thiocyanate) in methanol/water medium (3:1, v/v) (Scheme 1).
Besides elemental analysis, both complexes were initially char-
acterized by IR spectra. The precursor ‘‘ligand complex’’ [CuL] is
neutral and does not have any counter anion but the synthesized
Compound 1: Yield: 1.112 g. (63%). Anal. Calc. for C42H42Cu2-
NiN10O5 (952.65): C, 52.95; H, 4.44; N, 14.70. Found: C, 53.08; H,
4.67; N, 14.67%. kmax (solid, reflectance): 378, 605, 1100 nm. IR
(KBr pellet, cmꢀ1):
m(C@N) 1595; m(N(CN)2) 2264, 2222, 2156.
Table 1
Crystal data and structure refinement for complexes [(CuL)2Ni{N(CN)2}2]ꢁH2O (1) and
Compound 2: Yield: 1.044 g. (59%). Anal. Calc. for C40H42Cu2-
NiN6O5S2 (936.73): C, 51.29; H, 4.52; N, 8.97. Found: C, 51.41; H,
4.69; N, 8.79%. kmax (solid, reflectance): 368, 607, 1100 nm. IR
[(CuL)2Ni(NCS)2]ꢁH2O (2).
Complex
1
2
(KBr pellet, cmꢀ1):
m(C@N) 1596 m(NCS) 2055.
Formula
Formula weight
Space group
Crystal system
a (Å)
C
42H42Cu2NiN10O5
C40H42Cu2NiN6O5S2
936.73
C2/c
monoclinic
23.249(5)
10.194(5)
16.763(5)
94.924(5)
3958(2)
4
952.65
C2/c
monoclinic
23.243(6)
10.478(3)
17.247(5)
97.024(4)
4169(2)
4
2.4. Physical measurements
b (Å)
c (Å)
Elemental analyses (C, H and N) were performed using a Perkin-
Elmer 2400 series II CHN analyzer. IR spectra in KBr pellets (4000–
500 cmꢀ1) were recorded using a Perkin-Elmer RXI FT- IR spectro-
photometer. The electronic absorption spectra in the solid state
(1200–200 nm) were recorded with a Hitachi U-3501 spectropho-
tometer. Temperature-dependence molar susceptibility measure-
ments of powdered samples of 1 and 2 were carried out at the
‘‘Servei de Magnetoquimica (Universitat de Barcelona)’’ in a Quan-
tum Design SQUID MPMSXL susceptometer with an applied field of
10000 and 500 G in the temperature range of 2–300 and 2–30 K,
respectively.
b (°)
V (Å3)
Z
Dcalc (g cmꢀ3
)
1.518
1.569
l
(mmꢀ1
Rint
Number of unique data
Data with I > 2 (I)
R1 on I > 2 (I)
wR2 on I > 2 (I)
Goodness-of-fit (GOF) value
)
1.516
0.0586
3896
1.697
0.0877
3292
1603
0.0984
0.3093
0.946
r
2396
r
0.0436
0.0989
1.030
r

98
S. Biswas et al. / Polyhedron 51 (2013) 96–101
complexes contain anions (coordinated N(CN)2ꢀ or NCSꢀ in 1 and 2
Table 2
Bond distances (Å) and angles (°) around the metal centers in complexes 1 and 2.
respectively). Therefore, the appearance of the characteristic peaks
for dca m
C–N at 2264, 2222 and 2156 cmꢀ1 in the IR spectra of com-
Complex
Atoms
1
2
Distance (Å)
Distance (Å)
plex 1 indicates its formation. On the other hand, IR spectra of 2
show a sharp peak at 2055 cmꢀ1 in the spectrum corroborating
the presence of N-bonded thiocyanate. The rest of the spectral pat-
terns and band positions of adduct and the precursor, [CuL] is very
similar. In both the complexes, a strong and sharp band due to the
Cu1–O1
Cu1–O2
Cu1–N1
Cu1–N2
Cu1–O1a
Ni1–O1
Ni1–O2
Ni1–N3
Cu1–Ni1
1.906 (3)
1.914 (2)
1.938(3)
1.962(4)
2.713(3)
2.219(2)
1.992(3)
2.014 (3)
2.987(1)
1.885(7)
1.878(6)
1.917(12)
1.957(12)
2.664(7)
2.230(7)
2.003(7)
1.980(9)
2.988(2)
azomethine m(C@N) group of the Schiff base appears at 1595 and
1596 cmꢀ1 for complexes 1 and 2 respectively. In the IR spectra
of both complexes, the broad band near 3430 cmꢀ1 is due to the
O–H stretching of the water molecules.
Angle (°)
83.2(1)
90.3(1)
165.9(1)
67.2(1)
166.2(1)
89.9(1)
72.4(1)
98.9(2)
116.3(1)
98.9(1)
73.8(1)
97.8(1)
73.1(1)
83.4(1)
167.0(1)
103.3(1)
151.6(1)
96.3(1)
92.6(1)
Angle (°)
82.8(3)
91.2(5)
165.5(4)
67.8(3)
164.7(4)
89.7(4)
73.9(3)
99.0(5)
116.8(4)
98.3(3)
71.7(3)
163.8(3)
71.9(3)
82.7(3)
96.7(3)
95.9(3)
148.5(3)
105.0(3)
96.6(4)
The solid state electronic spectra of both the complexes shows
two absorption band near 378 and 368 nm for 1 and 2, respec-
tively, attributed to ligand-to-metal charge transfer transitions. Be-
sides this band, a single broad absorption band is observed in the
visible region for both complexes at 605 and 607 nm for 1 and 2,
respectively. The spin allowed d–d transition 3A2g ? 3T1g(F) is very
usual for octahedral Ni(II) complexes. This band is typical of d–d
transitions for both the Cu(II) and Ni(II) ions. At very lower energy
region, a very broad and low intense band appears for both the
complexes near ꢂ1100 nm for 3A2g ? 3T2g transition.
O1–Cu1–O2
O1–Cu1–N1
O1–Cu1–N2
O1–Cu1–O1a
O2–Cu1–N1
O2–Cu1–N2
O1a–Cu1–O2
N1–Cu1–N2
O1a–Cu1–N1
O1a–Cu1–N2
O1–Ni1–O2
O1–Ni1–N3
O1–Ni1–O1a
O1–Ni1–O2a
O1–Ni1–N3a
O2–Ni1–N3
O2–Ni1–O2a
O2–Ni1–N3a
N3–Ni1–N3a
3.2. Description of structures
3.2.1. [(CuL)2Ni{N(CN)2}2]ꢁH2O (1) and [(CuL)2Ni(NCS)2]ꢁH2O (2)
The single crystal X-ray analyses reveal that two structures are
very similar containing discrete triangular units which consist of
two [CuL] units, one nickel ion, two pseudohalides anions (dca
for 1 and thiocyanate for 2) and two molecules water as solvent
with 50% occupancy. In both structures a crystallographic twofold
axis passes through the nickel atom. The ORTEP views of the com-
plexes are shown in Fig. 1 and the bond distances and angles are
given in Table 2. Both Cu(II) ions in the trinuclear unit present a
penta-coordinated square pyramidal geometry where the basal
plane is formed by the two imine N atoms N(1) and N(2), and
the two phenoxido O atoms, O(1) and O(2), of the Schiff base
(Fig. 1). The two [CuL] units in both the complexes are held to-
gether not only by Ni(II) ions but also through the semi-coordina-
tion of one of the phenoxido groups of one unit, O(1), to the axial
position of the Cu(II) ion of the other [CuL] unit with Cu(1)–O(1)a
distances of 2.713(3) and 2.664(7) Å for 1 and 2 respectively; (sym-
metry operation a = ꢀx, y, 1/2ꢀz and 1ꢀx, y, 1/2ꢀz for 1 and 2
respectively) completing, in this way, the square pyramidal geom-
etry. This semi-coordination leads to short CuꢁꢁꢁCu distances
(3.685(2) and 3.627(3) Å in 1 and 2, respectively). The r.m.s. devi-
ations of the four basal atoms from the mean plane passing
Symmetry operation a = ꢀx, y, 1/2ꢀz and 1ꢀx, y, 1/2ꢀz for complexes 1 and 2,
respectively.
through them are 0.192 and 0.205 Å for 1 and 2, respectively.
The metal atom is 0.001(1) and 0.016(1) Å from this plane towards
the axially coordinated oxygen atom for 1 and 2, respectively. The
tetrahedral distortion in the basal plane is apparent since one pair
of diagonal donor atoms clearly lies below the plane while the
other pair is above the plane with the metal ion nearly in the mean
plane. The dihedral angles between the two planes [N(1)–Cu(1)–
O(1) and N(2)–Cu(1)–O(2)] is 16.25° for complex 1 and 17.52° for
complex 2 compares with 0° for a perfectly square-planar arrange-
ment and 90° for a perfect tetrahedral arrangement. The Addison
parameter (s) [36] of the Cu atom is 0.005 and 0.013 for 1 and 2,
respectively; indicating that the distortion towards trigonal
bipyramid geometry is small for both the complexes. It is to be
noted that the average Cu–O bond distances in the [CuL] units of
Fig. 1. ORTEP view of the trinuclear complex 1 (left) and 2 (right). Ellipsoids are drawn at 30% probability level. The dotted bonds show the weak Cu–O interactions.

S. Biswas et al. / Polyhedron 51 (2013) 96–101
99
Fig. 2. Hydrogen bonding interactions in the complex 1.
both the complexes are slightly greater than that of the mono-nu-
clear complex [29].
Fig. 4. Coordination spheres of the trinuclear core of both the complexes.
In the two complexes, the nickel atom lies on a twofold axis and
is bonded to two N atoms from two terminal dca or two N-bonded
thiocyanate ligands in 1 and 2, respectively, and to four phenoxido
oxygen atoms from two [CuL] units in a distorted octahedral
arrangement. These six bond distances around the Ni(II) ion are
in the range 1.980(9)–2.230(7) Å (Table 2). The three trans angles
are significantly smaller than 180° in both the complexes and lies
in the range 148.5(3)–167.0(1)°. On the other hand the six cis an-
gles are in the range of (71.7(3)–105.0(3)°). It is to be noted that
the longest bond distances at Ni(1)–O(1) = 2.219(2) and
2.230(7) Å and smallest cis angles at O(1)–Ni(1)–O(1)a = 73.1(1)°
for 1 and O(1)–Ni(1)–O(2) = 72.3(3)° for 2, are associated with
values of 1.75 emu molꢀ1 K for 1 and 1.67 emu molꢀ1 K for 2, very
near to the expected value (1.75 emu molꢀ1 K; g = 2) for two non-
interacting CuII and one NiII ions. The
vMT value gradually de-
creases on lowering the temperature to reach a plateau of ca.
0.02 emu molꢀ1 K at 10 K for 1 and 0.06 emu molꢀ1 K at 17 K for
2. The decrease observed in the vMT value when lowering the tem-
perature suggests the presence of moderate antiferromagnetic
interactions between the NiII and the CuII ions. The plateau at
low temperatures suggests the presence of an S = 0 spin ground
state and confirms the presence of antiferromagnetic behavior be-
tween the NiII and the CuII ions inside the cluster.
The structure reveals that the trinuclear triangular complex con-
tains two symmetry-related copper(II) ions and one nickel(II) ion.
The two pairs of metal ions CuꢁꢁꢁNi and the pair CuꢁꢁꢁCu, in the trinu-
clear core, are diphenoxido bridged. The metal ions occupy the cor-
ners of an isosceles triangle, thus there are two possible exchange
interactions, JNi–Cu and JCu–Cu (Fig. 4). The two identical Ni–Cu
magnetic interactions, JNi–Cu involves three oxygen atoms (two
symmetry related O(1) and one O(2) atoms of the phenoxido-bridge
ligands) whereas Cu–Cu exchange interactions are through two
O(1) atoms (Fig. 4). However, the O(1) atoms are weakly bonded
in the axial position to the CuII ions with Cu(1)–O(1)a
the l3-phenoxido atom, O(1). The unique feature of the structures
is that complexes 1 and 2 are the first report of triple oxido bridged
between Cu(II) and Ni(II) in such hetero-metallic compounds with
l3-phenoxido bridges with two copper and one nickel atom. How-
ever, similar bridging system has been observed recently in Cu(II)–
Mn(II) compounds [23].
The packing of the complexes 1 is controlled by hydrogen bond-
ing interactions. The hydrogen atom (H1W) of the water molecule
(O1W) is H-bonded with the non-coordinated terminal nitrogen
atom N(5) of the dca anion with donor–acceptor distance of
2.77(1) Å (Fig. 2). The hydrogen atoms of the water molecule in
complex 2 were not found in the Fourier map, so it could not be
fixed.
distance = 2.713(3) Å for
1 and 2.664(7) Å for 2, thus the
interactions between the two CuII ions and between the two NiII
through one of the O(1) atoms should be negligible. This consider-
ation agrees with the magnetic experimental results (
v
MT ffi 0 at
3.3. Magnetic properties
2 K). Therefore, the superexchange between the two pair of phe-
noxido-bridged between the adjacent CuII and NiII ions govern the
magnetic behavior. In order to investigate the magnetic behavior
The temperature dependence of vMT and v for complexes 1 and
2 are shown in Fig. 3 respectively. They show room temperature
0.028
1.8
0.008
0.007
1.5
0.024
1.2
0.020
-
0.9
0.006
2.0
0.6
T
0.005
0.016
1.5
χ
0.3
0.004
1.0
0.0
0.012
/uemol
0
50 100 150 200 250 300
T / K
χ
χ
0.003
0.5
T
0.008
0.004
χ
0.002
0.0
0
50 100 150 200 250 300
T / K
0.001
0
50 100 150 200 250 300
T / K
0
50
100 150 200 250 300
T / K
Fig. 3. vM versus T plot. Inset
vMT versus T plot. The solid lines represent the best fit to the experimental data, left for complex 1 and right for complex 2.

100
S. Biswas et al. / Polyhedron 51 (2013) 96–101
Table 3
Magnetic and structural parameters of Ni(II)–Cu(II) complexes with double phenoxido bridges and trinuclear core [NiIICuII2] consist of oxido bridged.
CCDC code
J (cmꢀ1
)
Cu–O (Å)
Ni–O (Å)
Cu–O–Ni (°)
Nuclearity
Refs.
ZOJFEJ
ꢀ90
1.908/1.890
–
2.062/2.073
–
99.77/99.95
–
2
2
2
2
2
2
2
2
2
2
2
4
3
3
3
[37]
[38]
[39]
[40]
[41]
[42]
[43]
[44]
[45]
[46]
[47]
[48]
[48]
[49]
[25]
POQMEN
QADWOH
LOQHAB
BIHZEX
ꢀ82
ꢀ236
+20.0
ꢀ94.7
ꢀ96
1.927/1.921
2.005/2.281
1.894/1.897
2.083/2.266
1.908/1.925
1.978/1.960
1.892/1.908
1.940/1.937
–
2.069/2.141
2.075/2.018
2.024/2.017
1.841/1.832
2.044/2.177
2.000/2.035
2.063/2.107
2.005/2.026
–
98.35/96.15
101.88/94.76
98.75/98.90
104.05/97.61
96.94/92.13
101.88/101.28
94.10/92.23
97.84/97.22
100.9
NIPFCU
UDUWEV
LINWIO
DEWPAW
XANNOP
UKIPOT
ꢀ12
ꢀ47
ꢀ15.7
ꢀ48
ꢀ201
ꢀ229.8
ꢀ260
ꢀ237.2
ꢀ50.6
KAHVAQ
KAJFEG
1.953
2.037
101.13
1.966/1.958
1.956/1.959
1.888/1.930
1.888/1.883
1.921
1.952
1.906/1.914
1.885/1.878
2.036/2.013
2.026/2.025
2.203/2.239
2.216/2.255
2.109/2.029
2.060/2.065
2.219/1.992
2.230/2.003
100.66/101.76
101.67/101.56
102.42/99.81
101.94/100.71
124.45
123.76
99.74/92.48
100.64/92.72
GIWYEQ
IXAZUCb
UHODOLa,b
ꢀ25.4
ꢀ22.8
ꢀ49
3
3
3
3
[26]
[27]
This work
This work
ALETUHa,b
1b
2b
ꢀ42
a
Single Ni–Cu oxido bridge.
b
Trinuclear NiIICuII complex.
2
an isotropic Heisenberg–Didac–van Vleck (HDVV) Hamiltonian for-
malism (Eq. (1)) was used in the approach.
1.883–2.281 Å, 1.832–2.275 Å and 92.13–124.45°, respectively).
These considerations impede to make magneto-structural correla-
tions for the exchange parameters.
^
^
^
^ ^
H ¼ ꢀJðSS1SS2 þ SS2SS3
Þ
ð1Þ
4. Conclusions
The magnetic susceptibility deduced from the Hamiltonian is
given in Eq. (2), where N, g, b and k have their usual meanings
The use of a [CuL] complex as a ligand towards Ni(II) ions (H2-
L = tetradentate di-Schiff base) has yielded two very similar trinuꢀ-
clear triangular complexes of formula [(CuL)2Ni(X)2], X = N(CN)2
(1) and NCSꢀ (2). The unique feature of the complexes is that they
are the first examples of trinuclear NiII–CuII2 species where the NiII
is bridged with each CuII through triple phenoxido bridges. The
magnetic coupling through the oxido bridges is in both cases mod-
erate antiferromagnetic leading to spin ground states of S = 0.
These coupling constants are within the range of existing similar
Ni–Cu complexes with oxido bridges.
ꢀ
ꢁ
Nb2g2
1þ5expð4J=kTÞþexpð2J=kTÞ
vM
¼
ð2Þ
kT 3þ5expð4J=kTÞþexpðꢀ2J=kTÞþ3expð2J=kTÞ
The increase of the vM versus T curves at very low temperatures
is due to the presence of paramagnetic impurities (Fig. 3, inset). To
take into account it, we introduce the parameter in the expres-
sion of the magnetic susceptibility (Eq. (3)).
q
Nb2g2
3kT
vM0
¼
vMð1 ꢀ
qÞ þ
x3:5q
þ Na
ð3Þ
N
= 400 Â 10ꢀ6 cm3 molꢀ1
.
a
Acknowledgments
The best fitted curves are plotted in Fig. 3 along with the exper-
imental data. The best fit parameters obtained are J = ꢀ49 cmꢀ1
,
We thank CSIR, India for awarding a Senior Research Fellowship
(Sanction No. 09/028(0732)/2008-EMR-I) to S. Biswas. Crystallog-
raphy was performed at the DST-FIST, India-funded Single Crystal
Diffractometer Facility at the Department of Chemistry, University
of Calcutta and the Spanish Government (Grant CTQ2009-07264).
g = 2.17,
q
= 0.51% and R = 1.61 Â 10ꢀ8 for
1 and g = 2.06,
J = ꢀ42 cmꢀ1
,
q
= 2.61% and R = 6.15 Â 10ꢀ7 for 2 (where R is the
P
P
2
agreement factor defined as ½ð
v
MTÞexp ꢀ ð
v
MTÞcalcŠ2=
ðv
MTÞexp).
The magnitude of the antiferromagnetic J value is very similar
for both complexes, and this result agrees with their analogous
structural parameters (see structural part and Tables 2 and 3). Con-
sidering that complexes 1 and 2 are the first examples in which the
NiII and the CuII ions are linked through a triple phenoxido bridges,
attempts have been made to compare their J values with related
systems reported in the literature. In Table 3, we have assembled
the J values together with the main structural parameters of struc-
turally and magnetic characterized dinuclear NiII–CuII complexes
[37–48] with double phenoxido bridges, and trinuclear complexes
with oxido-bridged [NiIICuII2] core [25–27,48,49]. We can conclude
that there is no clear relationship between the J values with only
one of the structural parameters or a combination of all of them.
This is a reasonable conclusion taking into account that the
complexes related in Table 3 have different structures, different
nuclearity, different kind of oxido-bridges ligands and different
number of these oxido-bridged ligands, thus the structural
parameters show a wide range values (the Cu–O distances, the
Ni–O distances and the Cu–O–Ni angle are in the range of
Appendix A. Supplementary data
CCDC 903864 and 903865 contain the supplementary crystallo-
graphic data for 1 and 2, respectively. These data can be obtained
free of charge via http://www.ccdc.cam.ac.uk/conts/retriev-
ing.html, or from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033;
or e-mail: deposit@ccdc.cam.ac.uk.
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