Synthesis, structure and magnetic property of an asymmetric chlorido bridged dinuclear copper(II) complex containing a didentate Schiff base

Article abstract of DOI:10.1016/j.poly.2014.12.031

A dinuclear complex, [Cu₂(μ-Cl)₂Cl₂(pbba)₂] (1) [pbba = N-((pyridin-2-yl)benzylidene)benzylamine], has been isolated from the reaction of a 1:1 M ratio of CuCl₂·2H₂O and pbba in MeOH soluti

Full text of DOI:10.1016/j.poly.2014.12.031

Polyhedron 89 (2015) 39–44
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis, structure and magnetic property of an asymmetric chlorido
bridged dinuclear copper(II) complex containing a didentate Schiff base
Somnath Choubey a, Subhasis Roy a, Soumi Chattopadhayay a, Kishalay Bhar a, Joan Ribas b,
Montserrat Monfort b, , Barindra Kumar Ghosh a,
⇑
⇑
a Department of Chemistry, The University of Burdwan, Burdwan 713104, India
b Departament de Química Inorgánica, 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:
A dinuclear complex, [Cu2(l-Cl)2Cl2(pbba)2] (1) [pbba = N-((pyridin-2-yl)benzylidene)benzylamine], has
Received 19 September 2014
Accepted 14 December 2014
Available online 14 January 2015
been isolated from the reaction of a 1:1 M ratio of CuCl2ꢀ2H2O and pbba in MeOH solution at room tem-
perature. Compound 1 has been characterized using microanalytical, spectroscopic, thermal and other
physico-chemical results. Single crystal X-ray diffraction measurements show that each metal center
in 1 adopts a distorted square pyramidal geometry with a CuN2Cl3 chromophore ligated through two
N atoms of pbba and two bridging and one terminal chloride atom. The centrosymmetric dinuclear unit
Keywords:
Dinuclear copper(II)
Asymmetric chlorido bridge
Schiff base
X-ray structure
Ferromagnetism
contains an asymmetric di-l-chlorido bridge. Variable-temperature magnetic susceptibility measure-
ments indicate weak intramolecular ferromagnetic coupling (J = +5.02 0.13 cmꢁ1) through chlorido
bridges and weak intermolecular antiferromagnetic (J0 = ꢁ0.32 0.01 cmꢁ1) interactions among the dinu-
clear entities, coupled with weak zero-field splitting arising from the S = 1 ground state.
Ó 2015 Published by Elsevier Ltd.
1. Introduction
some of our earlier work, we reported the syntheses, characteriza-
tion and magnetic properties of some copper(II) compounds in com-
Dinuclear copper(II) complexes with monoatomic bridges, such
as halides, have been the center of attraction due to their interesting
structures, catalytic and magnetic properties [1–9], and also as
models for the active sites of biomolecules [10]. Depending on the
nature of the co-ligands, chlorido bridged compounds [11] with pla-
bination with pseudohalido/carboxylato/hydroxido bridging units
and Schiff base/amine spacers of varied denticities [27]. In view of
the importance of the copper(II) compounds and our interest in
magneto-structural correlations of transition metal complexes, we
wished to extend such work to copper(II) chloride in combination
with a didentate Schiff base, N-((pyridin-2-yl)benzylidene)benzyl-
amine (pbba; Scheme 1). We have successfully isolated and charac-
terized one neutral dinuclear copper(II) chlorido complex of the
nar Cu(l-Cl)2Cu bridging loops show different molecular structures
[9,12–20] with varied bond distances and angles. The crystalline
architectures of these compounds are found to be interesting due
to the variations of the nature of forces such as weak intramolecular
and/or intermolecular interactions. The magnetic super-exchange
pathways [9,12–19] in these compounds depend on structural
parameters, such as Cu–Cl and Cuꢀ ꢀ ꢀCu distances, Cu–Cl–Cu angles
and of course on the nature of the magnetic orbitals. This reflects
that the structural parameters have great influence on the magnetic
properties, so a detailed knowledge of these parameters is essential
for magneto-structural/-chemical correlations. Several theoretical
analyses [21–26] have been carried out to untangle this behavior
and a range of magnetic interactions, like ferromagnetic (F) and
antiferromagnetic (AF) exchanges, have been found [9,12–19]. In
type [Cu2(l-Cl)2Cl2(pbba)2] (1). Details of the synthesis, crystal
structure, thermal and magnetic behaviors of this compound are
described below.
2. Experimental
2.1. General remarks and physical measurements
2.1.1. Materials
High purity 2-benzoylpyridine (Lancaster, UK), benzylamine
(Spectrochem, India) and copper(II) chloride dihydrate (E. Merck,
India) were purchased from their respective concerns and used
as received. The Schiff base N-((pyridin-2-yl)benzylidene)benzyl-
amine (pbba) was prepared following a reported method [28]. All
⇑
Corresponding authors. Tel.: +91 342 2533913; fax: +91 342 2530452.
E-mail addresses: montserrat.monfort@antares.qi.ub.es (M. Monfort), barin_1@
yahoo.co.uk (B.K. Ghosh).
http://dx.doi.org/10.1016/j.poly.2014.12.031
0277-5387/Ó 2015 Published by Elsevier Ltd.

40
S. Choubey et al. / Polyhedron 89 (2015) 39–44
Table 1
other chemicals and solvents used were AR grade. The synthetic
reactions and work-up were done in the open air.
Crystallographic data and structure refinement for 1.
Complex
1
Formula
C
38H32N4Cl4Cu2
2.1.2. Physical measurements
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
813.58
monoclinic
C2/c
21.319(5)
12.495(5)
15.790(6)
90
122.12(4)
90
3562(3)
0.71073 Å
1.517
Elemental analyses (carbon, hydrogen and nitrogen) were per-
formed on a Perkin–Elmer 2400 CHNS/O elemental analyzer. The
IR spectrum (KBr disc, 4000–400 cmꢁ1) was recorded using a Per-
kin–Elmer FTIR model RX1 spectrometer. Thermal behavior was
examined with a Perkin–Elmer Diamond TG/DT analyzer, with
heating from 30 to 700 °C under nitrogen. Ground state absorption
(in DMF) was measured with a Shimadzu model UV-2450 UV–VIS
spectrophotometer. Variable-temperature magnetic measure-
ments were carried out with a Quantum Design SQUID MPMS-XL
susceptometer working in the 2–300 K temperature range. The
magnetic field was 0.1 T. The diamagnetic corrections were evalu-
ated from Pascal’s constants.
a
(°)
b (°)
c
(°)
V (Å3)
k (Å)
qcalcd (g cmꢁ3
)
Z
4
T (K)
293(2)
1.528
l
(mmꢁ1
)
F(000)
1656
Crystal size (mm3)
h ranges (°)
0.20 ꢂ 0.16 ꢂ 0.06
1.982–28.364
ꢁ28,28/ꢁ16,16/ꢁ21,21
28029
4428
0.9135 and 0.7488
4428/0/217
2.2. Synthesis of [Cu2(l-Cl)2Cl2(pbba)2] (1)
h/k/l
Reflections collected
Independent reflections
Tmax and Tmin
Pbba (124.5 mg, 0.4571 mmol) in MeOH (5 ml) was added
slowly to a CuCl2ꢀ2H2O (77.9 mg, 0.4569 mmol) solution (10 ml)
in the same solvent. After filtration through a fine glass-frit, the
supernatant green solution was kept in air for slow evaporation.
Green rectangular crystals of 1 were deposited within two days,
which were separated by filtration and dried in vacuo over silica
gel indicator. Yield: 650.9 mg (80%). Anal. Calc. for C38H32N4Cl4Cu2
(1): C, 56.10; H, 3.96; N, 6.89%. Found: C, 56.00; H, 3.85; N, 6.78%.
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
1.107
Final R indices [I > 2
R indices (all data)
r
(I)]
R = 0.0462 and wR = 0.1308
R = 0.0771 and wR = 0.1648
1.560 and ꢁ0.604
Largest peak and hole (eÅꢁ3
)
Weighting scheme: R =
R
||Fo| ꢁ |Fc||/
R
|Fo|, wR = [
R
w(F2o ꢁ F2c)2/
R , calcd
w(F2o)2]1/2
2(F2o) + (0.0894P)2]; where P = (Fo2 + 2F2c)/3.
IR (KBr, cmꢁ1):
nm): 280, 707, 917.
m
(C@C) + m(C@N) 1613, 1593, 1571. UV–Vis (kmax/
w = 1/[
r
3. Results and discussion
2.3. X-ray data collection and structure refinement
3.1. Synthesis and spectroscopic studies
A single crystal of 1 suitable for X-ray analysis was selected from
those obtained by slow evaporation of a methanol solution at room
temperature. Diffraction data were collected on a Bruker SMART
CCD area-detector diffractometer using graphite monochromated
The Schiff base pbba was prepared by refluxing benzylamine
and 2-benzoyl pyridine in a 1:1 M ratio in dehydrated ethanol.
The neutral didentate chelator is of the (Ni, Np) type where Ni
and Np are N(imine) and N(pyridine) donor centers, respectively.
Mo Ka radiation (k = 0.71073 Å). Intensity data were reduced using
The penta-coordinated dinuclear compound [Cu2(l-Cl)2Cl2(pbba)2]
SAINT [29] and the empirical absorption corrections were performed
with the SADABS [30] program. The structure was solved by SHELXS-97
[31] and refined by full-matrix least-squares methods based on |F|2
using the program SHELXL-97 [31]. All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were placed in calculated
positions and constrained to ride on their parent atoms. All non-
hydrogen atoms were refined with anisotropic displacement
parameters, whereas hydrogen atoms were located geometrically
and refined using a standard riding model. Materials for publication
were prepared using PLATON [32], DIAMOND [33] and MERCURY 3.1 [34]
programs. A summary of the crystallographic data and structure
determination parameters for 1 is given in Table 1.
(1) was obtained in the one-pot reaction of a 1:1 M ratio of CuCl2-
ꢀ2H2O and the Schiff base (pbba) in MeOH solution at room tem-
perature (Scheme 2).
Complex 1 was characterized by microanalytical (C, H and N),
spectroscopic and other physicochemical results. The microanalyt-
ical data are in good conformity with the formulation. The moisture-
insensitive compound is stable over long periods of time in powdery
and crystalline states, and is soluble in MeOH, EtOH, MeCN, DMF
and DMSO, but is insoluble in water. In IR spectrum, m(C@N) plus
m
(C@C) stretching frequencies [20] of the metal bound Schiff base
are observed in the range 1620–1570 cmꢁ1 [35]. The complex dis-
plays multiple absorption bands and a shoulder in the 200–
1100 nm range. A green solution of 1 shows a broad band at
707 nm assignable to the d–d transition ðdxz; dyz ! dx2 Þ with a
ꢁy2
low-energy shoulder at 917 nm, consistent with the square pyrami-
dal (sp) geometry [36a] of the copper(II) centers. Additionally, a
sharp band at 280 nm may be assigned to a ligand-based transition
[36b].
i
N
Ni
CH2
Ni
Np
Cl
Cu
p
Cl
Cl
i
Np
N
N
MeOH
1:1
CuCl2.2H2O
+
Cu
Cl
Np
p
N
Ni
Scheme 1. (Ni,Np) donor set in pbba.
Scheme 2. Schematic representation of the reaction.

S. Choubey et al. / Polyhedron 89 (2015) 39–44
41
3.2. Description of the crystal structure of [Cu2(l-Cl)2Cl2(pbba)2] (1)
In order to define the coordination sphere conclusively, a single-
crystal X-ray diffraction study of 1 was made. An ORTEP represen-
tation of 1 and perspective views of the packing diagrams are
shown in Figs. 1–3. Selected bond distances and angles relevant
to the coordination spheres can be found in Table 2 and non-cova-
lent interaction parameters are given in Table 3.
The structure of 1 consists of a centrosymmetric dinuclear unit,
[(Cl)Cu(pbba)(l-Cl)2-Cu(pbba)(Cl)], with di-l-chlorido bridges
(Fig. 1). Each copper(II) center, bound by the unsymmetrical diden-
tate N-donor Schiff base pbba, is linked to each other through two
bridging chloride units, Cl2 and its symmetry equivalent Cl2a
(where a = 1/2 ꢁ x, 1/2 ꢁ y, 1 ꢁ z), affording
a square planar
arrangement for the Cu( -Cl)2Cu core with a crystallographic inver-
l
sion center. The bridging is to an appreciable extent unsymmetrical
in nature with different Cu–Cl bond distances [Cu–Cl2 2.2660(14) Å
and Cu–Cl2a 2.6330(12) Å; Table 2]. The fifth coordination site
around each copper(II) is occupied by a terminal Cl1 atom with a
Cu1–Cl1 distance of 2.2733(13) Å. The Cuꢀ ꢀ ꢀCu non-bonding dis-
tance within the complex is 3.5195(15) Å. Two different bridging
angles in the four-membered loop are: Cl2–Cu1–Cl2a 88.46(5)°
and Cu1–Cl1–Cu1a 91.54(5)°. Each copper(II) center adopts a dis-
Fig. 2. Square pyramidal coordination environment of the two copper(II) centers
showing the SP-I configuration in complex 1.
torted square pyramidal (s = 0.37) geometry [37] with one imine
N atom (N2), one pyridine N atom (N1) of pbba, one terminal Cl
atom (Cl1) and one bridging Cl atom (Cl2) forming the base of the
pyramid and the other bridging Cl atom (Cl2a) occupy the apical
position (Fig. 2). It is worth noting that for the Cu1 center, Cl2a occu-
pies the basal position of the square pyramid and Cl2 is in the apical
position, whereas in the case of the other copper (Cu1a) center, Cl2
is in the basal plane and Cl2a is in the apical position. The terminal Cl
atoms Cl1/Cl1a reside in basal arrangements around both Cu
centers.
To be succinct, the geometry of the complex consists of two
square pyramids sharing one base-to-apex edge (SP-I in Scheme 3),
but with nearly parallel basal planes [9]. The axial–equatorial con-
figuration of the two Cl bridges is depicted clearly in Fig. 2. The
copper(II) centers deviate by 0.250 Å from the mean plane. Among
the four equatorial atoms, N1 and Cl2 deviate (N1: 0.311 Å and N3:
0.233 Å) towards the apical Cl2a atom, whereas N2 and Cl1 show a
considerable deviation (N2: 0.305 Å and Cl1: 0.239 Å) in the oppo-
site direction to Cl2a from the mean plane.
Fig. 3. Perspective view of the 2D sheet structure of 1 formed through weak
intramolecular C–Hꢀ ꢀ ꢀCl and C–Hꢀ ꢀ ꢀN hydrogen bonds (sky blue dotted lines) and
intermolecular C–Hꢀ ꢀ ꢀ
p interactions (green dotted lines). (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of
this article.)
basal planes [9,12–16] are tabulated in Table 4. The two unequal
Cu–Cl distances in 1 are shorter compared to those reported in the
literature [9,12–16]. It is important to mention that the bridging
Cu–Cl–Cu angle in 1 is remarkably larger [91.54(5)°] than the aver-
age value [89.40(5) Å] for those complexes; consequently, the
Cuꢀ ꢀ ꢀCu separation is longer (3.5195 Å) than those found in the
reported [9,12–16] dichlorido bridged copper(II) complexes
(Table 4).
Similardinuclear copper(II) complexeshaving a Cu(l-Cl)2Cu core
with square pyramidal copper(II) centers and with nearly parallel
Structure of 1 is stabilized by different kinds of intramolecular
C–Hꢀ ꢀ ꢀCl and C–Hꢀ ꢀ ꢀN hydrogen bonds (Table 3). The weak C–
Hꢀ ꢀ ꢀCl hydrogen bonds between the terminal and bridging chloride
units (Cl1 and Cl2) and H atoms (H1 and H13B) of the pyridine and
Table 2
Selected bond distances (Å) and bond angles (°) in 1.
Bond distances
Bond angles
Cu1ꢁN1
Cu1–N2
Cu1–Cl1
Cu1–Cl2a
Cu1–Cl2
2.005(3)
2.063(3)
2.2733(13)
2.6330(12)
2.2660(14)
N2–Cu1–N1
N2–Cu1–Cl2a
N1–Cu1–Cl2a
N1–Cu1–Cl1
N2–Cu1–Cl1
Cl2–Cu1–Cl2a
Cu1–Cl2a–Cu1
79.33(12)
94.27(9)
172.85(9)
92.58(10)
150.47(9)
88.46(5)
91.54(5)
Fig. 1. PLATON view of [Cu2(l-Cl)2Cl2(pbba)2] (1). Displacement ellipsoids are drawn at
the 50% probability level.
Symmetry code: a = 1/2 – x, 1/2 – y, 1 ꢁ z

42
S. Choubey et al. / Polyhedron 89 (2015) 39–44
Table 3
Hydrogen bond and C–Hꢀ ꢀ ꢀ
3.3. Thermal study
p interaction parameters (Å, °) for 1.
To examine the thermal stability of compound 1, thermogravi-
Hydrogen bond parameters (Å, °)
D–Hꢀ ꢀ ꢀA
D–H Hꢀ ꢀ ꢀA Dꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA Symmetry code
metric analysis (TGA) was made between 40 and 800 °C in a static
atmosphere of nitrogen. The TG curve (Fig. S1) shows that com-
pound 1 is stable up to 203 °C and then gradual decomposition
(obs.: 78.18%, calcd.: 83.98%) occurs in the 203–572 °C tempera-
ture range, corresponding to the removal of the four halido and
two Schiff base ligands. The residue after heating above 600 °C cor-
responds to the formation of metallic copper (obs.: 18.79%, calcd.:
15.65%).
C1–H1ꢀ ꢀ ꢀCl1
0.93 2.76 3.234(5) 113
C13–13Bꢀ ꢀ ꢀCl2a 0.97 2.75
3.224(5) 111
2.875(5) 102
1/2 ꢁ x, 1/2 ꢁ y, 1 ꢁ z
C19–H19ꢀ ꢀ ꢀN2
0.93 2.53
C–Hꢀ ꢀ ꢀ
p
interactions (Å, °)
D–Hꢀ ꢀ ꢀA
D–H Hꢀ ꢀ ꢀA Dꢀ ꢀ ꢀA
D–Hꢀ ꢀ ꢀA Symmetry code
x, 1 ꢁ y, ꢁ 1/2 + z
C8–H8ꢀ ꢀ ꢀCg5
0.93 2.64 3.476(5) 150
Cg(5): C(14)–C(15)–C(16)–C(17)–C(18)–C(19)
3.4. Magnetic properties
L
L
L
Cu
Cl
L
L
The magnetic behavior (Fig. 4) of 1 was investigated in the 2–
Cl
L
L
Cl
Cu
L
300 K temperature range. The room temperature (300 K)
(0.875 cm3 molꢁ1 K) increases (0.93 cm3 molꢁ1 K) continuously
down to 10 K and then decreases (0.76 cm3 molꢁ1
at 2 K)
vMT value
Cl
Cl
Cu
Cu
L
Cu
Cu
L
L
L
L
Cl
SP-II
L
K
L
L
L
L
SP-I
(Fig. 4a). This is indicative of an S = 1 ground state for the dinuclear
complex. The overall feature is characteristic of a weak intramolec-
ular ferromagnetic (F) exchange and a very weak intermolecular
antiferromagnetic (AF) interaction coupled presumably with a very
weak zero-field splitting (D) of the S = 1 ground state. The fitting of
the susceptibility data is carried out following the Bleaney–Bowers
formula [Eq. (1)] [1, p. 104] considering the mean field approach as
arising from the intermolecular interactions and with use of ORIGIN
v.7.0 software [38]; the temperature independent paramagnetism
(TIP) parameter is the standard for two copper(II) ions [for each
SP-III
Scheme 3. Different conformations of dichlorido bridged square pyramidal dinu-
clear copper(II) complexes.
–CH2 groups of the Schiff base (Table 3) are in operation to
strengthen the molecular architecture of the dinuclear unit in 1.
The intramolecular C–Hꢀ ꢀ ꢀN hydrogen bonds between the imine
N atom (N2) and the H atom (H19) of the benzene ring of pbba fur-
ther stabilize the dinuclear moiety. These dinuclear units are asso-
copper(II),
v
= 60 ꢂ 10ꢁ6 cm3 molꢁ1] [1, p. 8].
2 expðJ=kBTÞ
Ng2b2
vM
¼
ꢀ
ð1Þ
ciated with each other through weak intermolecular C–Hꢀ ꢀ ꢀ
p
kBT 1 þ 3 expðJ=kBTÞ
interactions (C8–H8ꢀ ꢀ ꢀCg5, symmetry code = x, 1 ꢁ y, ꢁ1/2 + z),
leading to the formation of a 2D sheet structure stabilizing the
entire crystal lattice (Fig. 3); the phenyl H atom (H8) and the phe-
nyl ring of pbba (Cg5: C14–C15–C16–C17–C18–C19) are involved
in such interactions.
The Hamiltonian used is H = ꢁJS1S2. The best-fit parameters
obtained are: J = +5.02 0.13 cmꢁ1, J0 (intermolecular + D) = ꢁ0.3
2
0.01 cmꢁ1, g = 2.12 0.01 and R = 1.0 ꢂ 10ꢁ4; the R factor is
defined as Ri[(
vmT)obsꢁ(
v v
mT)calc]2/Ri[( mT)obs]2.
Table 4
Comparative structural and magnetic properties of binuclear copper(II) chloride complexes with a planar Cu(l-Cl)2Cu core and SP-I configuration similar to complex 1.
Compound
Axial Cu–Cl distance, R (Å)
Cu–Cl–Cu angle,
a
(°)
a
/R (°/Å)
Cuꢀ ꢀ ꢀCu separation (Å)
J-value# (cmꢁ1
)
Refs.
[Cu2(
[Cu2(
[Cu2(
[Cu2(
l
l
l
l
-Cl)2(LH)2](ClO4)2
-Cl)2(LOMe)2](ClO4)2
-Cl)2(LMe)2](ClO4)2
-Cl)2(LCl)2](ClO4)2
2.896
2.831
2.844
2.830
2.732
2.818
2.677
2.83
2.696
2.906
2.629
2.806
2.922
2.640
2.657
2.581
2.846
2.831
2.72
86.21
85.08
87.11
87.30
84.83
84.863
84.46
93.63
89.73
88.6
88.1
85.82
94.7
86.435
88.81
88.2
95.27
91.1
29.769
30.053
30.629
30.848
31.050
30.115
31.550
33.0
33.283
30.489
33.511
30.584
32.409
32.740
33.425
34.17
3.542
3.449
3.526
3.522
3.382
3.498
3.337
3.753
3.510
3.612
3.437
3.479
3.86
3.376
3.494
3.396
3.825
3.693
3.510
3.736
3.458
4.089
3.5195
+0.257
+0.306
+0.327
+0.188
ꢁ0.274
ꢁ6.91
+43.2(5)
+8.72
ꢃ 0
[12a]
[12a]
[12a]
[12a]
[9]
[CuCl(HL1)]2ꢀH2O
[Cu2Cl2(qsalBr)2]ꢀDMF
[CuCl(HL2)]2ꢀH2O
[12b]
[12c]
[13a]
[13b]
[13c]
[13d]
[14a]
[14b]
[14b]
[14c]
[15a]
[15b]
[15c]
[16a]
[16b]
[16c]
[16d]
Our work
[{Cu(l
-Cl)2(Opo)(pzPh)}2]
[CuCl2(ppmma)]2
[CuCl2(PyTn)]2
[Cu2Cl4(Mebta)4]
[Cu2(amp)2Cl4]
+13.73
+3.35
ꢁ9.4
[CuCl2(HL3)]2(ClO4)2
[Cu2Cl2(L4)2](ClO4)2
[CuCl(L5)]2(ClO4)2
[CuCl(L6)]2(ClO4)2
[CuCl(Hfsaaep)]2
[CuCl(Pypep)]2ꢀ2H2O
+10.70
ꢁ1.95
+0.58
+1.14
+0.15
33.475
32.170
33.1
29.30
31.50
ꢁ2.32
ꢁ2.95
ꢁ8.34
+3.15
ꢁ2.8
[{Cu(
l
-Cl)2(terpy)}2](PF6)2
89.9
88.5
86.13
96.8
91.54
[CuCl2(tmso)]2
[CuCl2(dmen)]2
[Cu2Cl4(tmen)2]
3.020
2.734
3.147
2.633
30.759
34.766
[Cu2(l
-Cl)2Cl2(pbba)2]
+5.02
#
Hamiltonian H = ꢁJS1S2 where LX = N,N-bis[(3,5-dimethylpyrazole-1-yl)methyl]benzylamine (X = H, OMe, Me, Cl); HL1 = N-(2-hydroxyethyl)-5-nitrosalicylaldimine);
HqsalBr = 8-(5-bromo-salicylideneamino)quinoline; H2L2 = [2-((E)-(2-hydroxy-ethylimino)methyl)-4-bromophenol]; pzPh = 3-phenyl-pyrazolyl; OpoH = 2-hydroxypyridine-N-
oxide; ppmma = phenyl-N-[(pyridine-2-yl)methylene]methaneamide; PyTn = 2-(pyrazol-1-yl)-2-thiazoline; Mebta = 1-methylbenzotriazole; amp = 5-amino-methyl-3-methyl-
pyrazole; L3 = 1,5-bis(pyridin-4-ylmethyl)-1,5-diazacyclooctane; L4 = 1-(pyridin-2-ylmethyl)-1,4-diazacycloheptane; L5 = 1-(Imidazol-4-ylmethyl)-1,5-diazacyclooctane;
L6 = 1-(2-pyridylmethyl)-1,5-diazacyclooctane; H2fsaaep = 3-[N-2-(pyridylethyl)formimidoyl]salicylic acid; PypepH = N-(2-(4-imidazolyl)ethyl)-pyridine-2-carboxamide; ter-
py = 2,20;60,200-terpyridine; tmso = tetramethylene sulfoxide; dmen = N,N0-dimethylethylenediamine and tmen = N,N,N0,N0-tetramethylethylenediamine.

S. Choubey et al. / Polyhedron 89 (2015) 39–44
43
quotient
a
/R, where
a
is the Cu–Cl–Cu bridging angle, and R is the
longer out-of plane Cu–Cl bond distance. It was found that for val-
0.92
0.88
0.84
0.80
0.76
ues of this quotient /R (°/Å) lower than 32.6 and higher than 34.8,
a
the exchange interaction is antiferromagnetic. For values falling
between these limits it is ferromagnetic. In the case of complex
1, the value of the quotient a/R is 34.766 °/Å suggesting a ferro-
magnetic interaction between the two copper(II) ions.
A theoretical study by Mrozinski and co-workers [13d] has
established a correlation of the magnetic coupling and the param-
eters
magnetic coupling is ferromagnetic. With the
= 91.54(5)° and R = 2.2660(14) Å] of complex 1, a small ferro-
a
and R; for small
a
values and short Cu–Cl distances (R), the
χ
a
and R values
(a)
[a
magnetic coupling is predicted, which is in agreement with the
experimental result (J = +5.02 0.13 cmꢁ1). An examination
0
50
100 150 200 250 300
(Table 4) of the
a and R values of the reported dichlorido bridged
T / K
SP-I type of copper(II) complexes [9,13–16] and complex 1 reflects
that the major reason for ferromagnetic coupling in 1 is the much
2.0
1.5
1.0
0.5
0.0
shorter R value [2.2660(14) Å], although the much higher
a value
[91.54(5)°] is likely to decrease the magnitude of the ferromagnetic
coupling.
4. Conclusion
β
One neutral dichlorido bridged dinuclear copper(II) compound
containing an unsymmetrical didentate (N,N) Schiff base as an
end-capping ligand has been isolated. Structural analysis reveals
that each copper(II) center, with a distorted square pyramidal
geometry in the compound 1, is linked to each other by asymmet-
(b)
ric di-
1 is stabilized by intramolecular C–Hꢀ ꢀ ꢀCl and C–Hꢀ ꢀ ꢀN hydrogen
bonds and intermolecular C–Hꢀ ꢀ ꢀ interactions forming a 2D sheet
l-chlorido bridges in the SP-I conformation. The structure of
0
10000 20000 30000 40000 50000
H / G
p
structure. Variable-temperature magnetic susceptibility measure-
ment shows weak intramolecular ferromagnetic coupling through
the chlorido bridges and weak intermolecular antiferromagnetic
interactions among the dinuclear entities coupled with weak
zero-field splitting arising from the S = 1 ground state. A compari-
son of the magnetic behavior of 1 with related dichlorido bridged
dinuclear copper(II) complexes containing mono-, di- and triden-
tate N-/O-donor ligands with similar Cu(l-Cl)2Cu cores reveals a
good magneto-structural correlation and untangles the nature of
the interactions.
Fig. 4. (a) Plot of the vMT vs. T for 1. Solid line indicates the best fit (see text) and (b)
plot of the reduced magnetization (M/Nb) vs. H at 2 K for 1.
The reduced molar magnetization at 2 K is given in Fig. 4b. The
tendency for saturation magnetization at 5 T is close to 2.0 Nb, as
expected for an S = 1 ground state. The curve does not follow the
Brillouin formula for S = 1 (ground state) and g = 2.1 due to the
magnetic exchange and zero-field splitting parameters.
Dichlorido bridged dinuclear copper(II) complexes have been
studied by differentresearchgroups toestablish magneto-structural
correlations [21–26]. These show that the exchange coupling con-
Acknowledgments
stant J depends on the value of the Cu–Cl–Cu bridging angle (a), as
well as on the distance of the longer axial Cu–Cl bond (R). However,
these parameters are not the only ones that play an important role in
determining the magnetic coupling; the different arrangements of
the magnetic orbital of copper(II) have a great influence on the mag-
netic behavior of dinuclear copper(II) complexes [9,12–19].
B. K. Ghosh thanks the CSIR and DST, New Delhi, India for finan-
cial support. S. Choubey, S. Chattopadhayay and K. Bhar are grate-
ful to CSIR and S. Roy to UGC, New Delhi, India for fellowships. M.
Monfort and J. Ribas acknowledge the financial support from the
Spanish Government (GrantCTQ2012/30662).
The geometry around the metal(II) center in these compounds
is generally a square pyramid with a different degree of distortion
towards a trigonal bipyramid. The literature shows that the two
square pyramids give rise to three types of geometries (Scheme 3):
(i) square pyramids sharing one base-to-apex edge but with parallel
basal planes (SP-I) [9,12–16], (ii) square pyramids sharing a basal
edge with coplanar basal planes (SP-II) [17,18] and (iii) square pyr-
amids sharing one base-to-apex edge with the two bases nearly
perpendicular to one another (SP-III) [19a]. Generally, dichlorido
bridged dinuclear copper(II) complexes with SP-I and SP-II config-
urations lead to ferromagnetic or antiferromagnetic coupling,
depending on the nature of co-ligands, but the comparatively rare
SP-III geometry shows ferromagnetic coupling.
Appendix A. Supplementary data
CCDC 1004055 contains the supplementary crystallographic
data for compound 1. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the
Cambridge Crystallographic Data Centre, 12 Union Road, Cam-
bridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at http://dx.doi.org/10.
1016/j.poly.2014.12.031.
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