Effect of the counter-anion on the structural and magnetic properties of a copper(II) complex with 2-[(bis(2-pyridylmethyl)amino)methyl]-4-methyl-6- (methylthio)phenol

Article abstract of DOI:10.1016/j.poly.2013.01.005

A new 2-[(bis(2-pyridylmethyl)amino)methyl]-4-methyl-6-(methylthio)phenol copper^II perchlorate, complex, [Cu₂(μ-SL) ₂](ClO₄)₂ (1), was synthesized and magnetically and structurally characterized. The complex consists of two similar but not equivalent [Cu₂(μ-SL)₂]²⁺ bimetallic cations designed as P and Q. Cation P has a square-base pyramidal cupric centre bonded to an approximately trigonal bipyramidal one, while cation Q has two equivalent square-base pyramidal copper centres, related by an inversion center. The cupric centres in both units are bridged by two phenolate oxygen atoms from two deprotonated HSL molecules, defining a central Cu₂O₂ core. Each Cu^II centre has a N₃O₂ coordination sphere. Magnetic studies done for (1) show an overall weak antiferromagnetic behavior. The best fit of the experimental data was obtained using a modified Bleaney-Bowers equation with g₁ = g₂ = 2.05, J_P = -13.4 cm^-1 and J_Q = +5.22 cm^-1 for P and Q, respectively. The properties of the new complex are compared to those reported for the hexafluorophosphate complex with the same ligand, in terms of the effect of the distortion caused by the use of a different anion.

Full text of DOI:10.1016/j.poly.2013.01.005

Polyhedron 51 (2013) 180–185
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Effect of the counter-anion on the structural and magnetic properties
of a copper(II) complex with 2-[(bis(2-pyridylmethyl)amino)methyl]-
4-methyl-6-(methylthio)phenol
b
J. Manzur a,c, , H. Mora , V. Paredes-García b,c, A. Vega b,c, M.A. Novak d
⇑
a Universidad de Chile, Facultad de Ciencias Físicas y Matemáticas, Santiago, Chile
b Universidad Andres Bello, Facultad de Ciencias Exactas, Departamento de Ciencias Químicas, Santiago, Chile
c CEDENNA, Santiago, Chile
d Instituto de Física, Universidad Federal de Rio de Janeiro, Rio de Janeiro, Brazil
a r t i c l e i n f o
a b s t r a c t
new 2-[(bis(2-pyridylmethyl)amino)methyl]-4-methyl-6-(methylthio)phenol copperII perchlorate,
complex, [Cu2( -SL)2](ClO4)2 (1), was synthesized and magnetically and structurally characterized. The
complex consists of two similar but not equivalent [Cu2(
-SL)2]2+ bimetallic cations designed as P and
Article history:
A
Received 24 August 2012
Accepted 7 January 2013
Available online 16 January 2013
l
l
Q. Cation P has a square-base pyramidal cupric centre bonded to an approximately trigonal bipyramidal
one, while cation Q has two equivalent square-base pyramidal copper centres, related by an inversion
center. The cupric centres in both units are bridged by two phenolate oxygen atoms from two deproto-
nated HSL molecules, defining a central Cu2O2 core. Each CuII centre has a N3O2 coordination sphere. Mag-
netic studies done for (1) show an overall weak antiferromagnetic behavior. The best fit of the
experimental data was obtained using a modified Bleaney–Bowers equation with g1 = g2 = 2.05, JP = -
ꢀ13.4 cmꢀ1 and JQ = +5.22 cmꢀ1 for P and Q, respectively. The properties of the new complex are com-
pared to those reported for the hexafluorophosphate complex with the same ligand, in terms of the
effect of the distortion caused by the use of a different anion.
Keywords:
Dicopper(II) complex
Magnetism
Structure
Counteranion effect
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
Coordination modes observed in this type of bis(l-phenoxo)
bridged dimeric copper(II) complexes include equatorial–equato-
rial, axial–equatorial and mixed modes depending on the length
of the arms. The geometries around the cooper(II) centres vary
from square base pyramidal to bipyramidal, and pseudo octahe-
dral. From a magnetic point of view, the exchange interaction be-
tween the copper(II) centres also varies from moderate
antiferromagnetic to weak ferromagnetic. In all these complexes
the counteranion was hexafluorophospate. Hexafluorophosphate,
tetrafluoroborate and perchlorate anions are generally chosen as
counterions due to experimental reasons, since these permit the
isolation of single crystals suitable for X-ray diffraction structural
studies, because of their potential to form crystalline solids with
large complex cations. In this sense, they are expected to have no
effect on the complex cation properties. Contrary to what is in-
ferred, there exists strong evidence that changes in the counteran-
ion may lead to very important modifications in the structure and
properties of the obtained compounds [18–20]. For example, sev-
eral nickel(II) complexes bridged by azido anions have been re-
ported with different amine ligands. When 1,3-propanediamine
and its 2,20-dimethyl derivative are used, trans 1-D antiferromag-
netic systems are always obtained [19] with ClO4ꢀ and PF6ꢀ; while
an antiferromagnetic dinuclear complex is obtained [18] with
Tripodal aminophenol derivatives act as polydentate ligands
giving rise to different mono- or polymetallic species, depending
on the experimental conditions [1–13]. Dimeric copper(II) species
bridged by one or two deprotonated phenoxo ligands have been re-
ported by several authors, and the magnetic properties have been
rationalized, taking into account the structural parameters and the
coordination modes of the phenoxo group to the copper centres
(axial or equatorial) [1,2,12,13]. Usually, the axial coordination
mode has been observed for systems with the 5,5,6 sequence of
the chelate rings, while for a ring sequence of 6,6,6, the equatorial
position of the phenolate ligand is favored. The axial or equatorial
preferences of the phenolate group have been attributed mainly to
the steric effect imposed by the smaller rings [14–17].
In previous works [1] we have reported the structural and mag-
netic properties of dimeric copper(II) complexes with several tripo-
dal pyridylalkylaminophenol ligands, with different length of each
arm of the tripodal ligand (Scheme 1).
⇑
Corresponding author at: Universidad de Chile, Facultad de Ciencias Físicas y
Matemáticas, Santiago, Chile.
E-mail address: jmanzur@ing.uchile.cl (J. Manzur).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.01.005

J. Manzur et al. / Polyhedron 51 (2013) 180–185
181
2.1.3. Single-crystal X-ray diffraction
CH3
OH
CH3
The crystal structure of [Cu2(l-SL)2](ClO4)2 (1) at room temper-
ature was determined by X-ray diffraction measurements on a
prismatic 0.49 ꢁ 0.18 ꢁ 0.07 mm3 single crystal. Data collection
N
R
N
S
CH3
was run on SMART CCD diffractometer, using
x-scans. Data reduc-
CH2
(CH2)n
Py
(CH2)m
OH
CH2
tion was done with SAINT [23], while the structure solution by direct
methods, completion and refinement was conducted with SHELXL
[24]. Empirical absorption corrections were applied using SADABS
[25]. The hydrogen atoms positions were calculated after each cy-
cle of refinement with SHELXL using a riding model for each struc-
ture, with C–H distance varying from 0.93 to 0.97 Å. Uiso(H)
values were set equal to 1.2 Ueq of the parent carbon atom
(1.9 Ueq for Methyl). During the final stages of the refinement it
was clear there was disorder on the three non-equivalent uncoor-
dinated charge balancing perchlorate anions. The perchlorate an-
ions associated to Cl1 and Cl2 centres were modeled using two
positions, labeled A and B, for the four oxygen atoms. They were
then refined and finally held constant at 0.43/0.57(A/B) and 0.36/
0.64(A/B) respectively. For the third perchlorate anion, associated
to Cl3, the disorder was modeled using six positions for the four
oxygen atoms, restricted to add 4. The occupancies were finally
held constant at 0.85, 0.50, 0.84, 0.65, 0.48 and 0.68 for O10,
O11, O12, O13, O14 and O15 respectively. Additional data collec-
tion and refinement details are given in Table 1.
N
Py
N
R = H, SCH3
n = 1, 2
HSL
m = 1, 2
Scheme 1. Tripodal pyridylalkylaminophenols used as ligands.
[B(C6H5)4]ꢀ. When the amine ligand is ethylenediamine, an ꢀantifer-
romagnetic dinuclear complex [18] was reported with PF6 and a
ꢀ
ferromagnetic dinuclear one with ClO4 [20]. The obtained results
are explained by the different sizes of the counteranion, which
forces different kinds of packing in each case, resulting in changes
in the structure, and therefore in the properties.
We have obtained a new dimeric copper(II) complex with the
HSL2 ligand using ClO4ꢀ as the counteranion instead of PF6ꢀ, as re-
ported earlier. This work described the structural and magnetic
characterization of this new complex; a comparison is made ꢀwith
the properties of the one reported previously, with PF6 as
counteranion.
2.1.4. Magnetic susceptibility
The ZFC and FC magnetic susceptibility measurements at vari-
able temperature, in the range of 2.0–291 K, were performed on
a microcrystalline sample using a Cryogenics SX600 SQUID magne-
tometer at 0.02 and 0.25 kOe. Diamagnetic corrections (estimated
from Pascal constants) [26] and sample holder contributions were
taken into account. The fit was performed minimizing the agree-
2. Experimental
All reagents were reagent grade and used without further puri-
fication, unless stated otherwise. Solvents were of HPLC quality
and were used as received. Elemental analyses for C, H, and N were
performed at CEPEDEQ (University of Chile) on a Fison-Carlo Erba
EA 1108 model analyzer. Copper was determined by atomic
absorption spectroscopy. IR spectra were obtained as KBr pellets
on a Bruker Vector 22 instrument. 1H NMR spectra were recorded
in CDCl3 on a Bruker AMX-300 NMR spectrometer. Chemical shifts
are reported as d values downfield of an internal Me4Si reference.
P
P
2
2
1=2
ment factor R ¼ ½
ðvMTobs
ꢀ
vMTcalcÞ =
ð
vMTobsÞ ꢂ
.
3. Results and discussion
3.1. Synthesis
The complex was obtained straight forward by reaction of the li-
gand with CuCl2 in a 1 to 1 M ratio in the presence of triethylamine as
2.1. Syntheses
Table 1
2.1.1. 2-[(Bis(2-pyridylmethyl)amino)methyl]-4-methyl-6-
(methylthio)-phenol (HSL)
The ligand was sinthesized by a Mannich reaction of 2-(methyl-
thio)-p-cresol [21] with bis(2-pyridylmethyl) amine [22], parafor-
maldehyde, and 2-(methylthio)-p-cresol in 57% yield, as
described previously [2]. 1H NMR (CDCl3) for HSL: d 11.4 (1H,
Crystal data and structure refinement details for (1).
Complex
Formula weight
Crystal system
Space group
a (Å)
1
1054.97
monoclinic
P21/n
13.1509(14)
13.3134(14)
21.806(2)
74.191(2)
86.641(2)
66.190(2)
3355.1(6)
b (Å)
c (Å)
broad, OH), 8.58 (2H, d, pyridine
a protons), 7.63 (2H, t), 7.36
(2H, d) and 7.16 (2H, t) (pyridine protons), 6.92 (1H, s), and 6.72
(1H, s) (phenylprotons), 3.86 (4H, s, CH2Py), 3.75 (2H, s, CH2Ph),
2.46 (3H, s, CH3S), 2.26 (3H, s, CH3Ph).
a
(°)
b (°)
c
(°)
0
V (AÅ3)
Z (Z0)
6(3)
1.566
1.228
1626.0
3.40–50.36
ꢀ15 6 h 6 15
–15 6 k 6 15
–26 6 l 6 26
21262, 11908
(0.0482), 7640
961
2.1.2. [Cu2(l-SL)2](ClO4)2
d (g cmꢀ3
)
)
CuCl2 (0.27 g, 2 mmol) was added to a solution of the ligand HSL
(2 mmol) and triethylamine (2 mmol) in methanol (10 mL), and
the mixture was refluxed for 60 min. Excess tetra-n-butylammo-
nium perchlorate was added to the solution, and the crystalline
product precipitated immediately. Recrystallization from an aceto-
nitrile–methanol mixture affords crystals suitable for X-ray struc-
tural studies.
l
(mmꢀ1
F(000)
h (°)
Index ranges
Ntot, Nuniq
(Rint), Nobs
Refinement parameters
Goodness-of-fit (GOF) on F2
R1, wR2 (obs)
IR (cmꢀ1, KBr pellets): 2920 (s, m), 2858 (s, w), 1609 (s, s), 1575 (s,
w), 1457 (s, s), 1094 (s, vs), 860 (s, w), 802 (s, m), 768 (s, m), 623 (s, s).
1.029
UV–Vis (methanol): 485 nm (e e
= 400 Mꢀ1); 754 nm ( = 200 Mꢀ1).
0.0679, 0.1415
0.1101, 0.1609
0.909 and ꢀ0.845
R1, wR2 (all)
Maximum and minimum
Anal. Calc. for C42H44Cu2Cl2N6O10S2: C, 47.78; H, 4.20; N, 7.96;
Dq
Cu, 12.04. Found: C, 48.3; H, 4.18; N, 7.84; Cu, 12.35%.

182
J. Manzur et al. / Polyhedron 51 (2013) 180–185
It is important to note that according to the crystal structure
there are two P cations for each Q cation within the unit cell. In
both cations, the cupric centres are bridged by two phenolate oxy-
gen from two deprotonated HSL molecules, defining a central
Cu2O2 core, while the three remaining nitrogen atoms complete
the coordination sphere of each cupric centre, leading to pentaco-
ordination. Therefore, each copper(II) centre has a N3O2 environ-
ment. However, their coordination geometry differs slightly;
while Cu1 and Cu3 could be well described as a slightly distorted
square-base pyramids, with
[27], the geometry around Cu2 is rather intermediate between a
square-base pyramid and trigonal bipyramid, with equal to
s values of 0.11 and 0.20 respectively
s
0.57. In summary, cation P has a square-base pyramidal cupric cen-
tre (Cu1) bonded to an approximately trigonal bipyramidal one
(Cu2), while cation Q has two square-base pyramidal centres
(Cu3 and Cu3i). The structural parameters of cation Q are very sim-
ilar to those observed for the copper ions in the complex with the
same ligand reported earlier, [Cu2L2](PF6)2, using hexafluorophos-
phate as the counterion instead of perchlorate [2]. It is interesting
to note that for each cupric centre there exists a sulfur atom from
the SCH3 substituent on one of the arms in HSL ligand, which is
correctly placed in the proper direction to complete an octahedral
environment. However, the rather long copper–sulfur distances,
2.812(2) Å (Cu1ꢃ ꢃ ꢃS101), 3.137(2) Å (Cu2ꢃ ꢃ ꢃS1) and 2.929(2) Å
(Cu3ꢃ ꢃ ꢃS201i), suggest this is probably the result of the steric de-
mands of the ligand, precluding to qualify the coordination geom-
etry as octahedral. A reasonable alternative description would be
as pseudo or distorted octahedrons.
In contrast to what was observed for Q, with a strictly planar
Cu2O2 core (because of the inversion centre), unit P presents a cen-
tral core; which is not strictly planar, with deviations to the least-
squares plane of ꢀ0.067(1) Å, ꢀ0.076(1) Å, 0.066(1) Å and
0.076(1) Å for Cu1, Cu2, O1 and O101, respectively.
Both units display rather distorted central Cu2O2 parallelo-
grams, with short distances of 1.941(4) Å (Cu1–O101), 1.919(4) Å
(Cu2–O1) and 1.931(3) Å (Cu3–O201i) and long ones of 2.432(4)
Å (Cu1–O1), 2.140(3) Å (Cu2–O101) and 2.352(4) Å (Cu3–O201).
The corresponding angles are 93.7(2)° (Cu2–O1–Cu1), 102.9(2)°
(Cu1–O101–Cu2) for P, and 98.2(2)° (Cu3i–O201–Cu3) for
Q
(i = 2 ꢀ x, 1 ꢀ y, ꢀz). The copper to copper distance is 3.194(1) Å
for P and 3.245(1) Å for Q.
Finally, it is relevant to note that the phenolate group, which is
highly planar, it is not coplanar with the central Cu2O2 plane. In
fact, the phenolate groups lie at opposite sides of the central plane.
The angle defined by the central Cu2O2 plane and the O–C vector is
27.6° (O1–C16) and 16.9° (O101–C116) for P and 31.4° for Q. Be-
sides, the phenolate moeity is rotated in relation to the Cu2O2 core
by 33.4° (O1) and 23.4° (O101) for P and 34.9° for Q. These struc-
tural parameters have been reported to influence the magnetic
coupling between the cupric centres in binuclear copper com-
plexes bridged by phenolate groups [28]. Table 2 shows a summary
of the most relevant bond distances and angles as determined from
the X-ray diffraction.
Mono-, bi- and trinuclear copper complexes have been de-
scribed for the HSL ligand [1,2]. In all these complexes the ligand
also behaves as a tetracoordinating moiety with a N3O donor set.
The coordination geometry of the metal center in the mononuclear
complex, [Cu(HSL)Cl]PF6 has been described as slightly distorted
square pyramidal with the apical position occupied by the hydro-
xyl group of the phenol. In this mononuclear complex the ligand
is protonated, contrary to the results observed for the reported
complex, and for other similar systems in which the ligand is
deprotonated. As already mentioned, the structural parameters
for the reported dimeric centrosymmetric complex [Cu2(SL)2](PF6)2
[2] are very similar to those found for unit Q. The axial position is
occupied by the phenoxo group, while another phenoxo group
Fig. 1. Molecular structure diagram for cations
asymmetric unit of I, including partial numbering scheme. Displacement ellipsoids
at the 33% level of probability.
P (a) and Q (b) within the
a base; the crystalline product was precipitated after addition of ex-
cess tetra-n-butylammonium perchlorate.
3.2. Structural description
The crystal structure determined for (1) shows two similar, but
not equivalent [Cu2(l
-SL)2]2+ bimetallic cations. One of them, con-
taining Cu1 and Cu2, is pseudo-centrosymmetric, while the other,
containing Cu3 and Cu3i (i: 2 ꢀ x, 1 ꢀ y, ꢀz), is strictly centrosym-
metric. We will refer in the following as cation P to the first, and
cation Q to the second. Both units are depicted in Fig. 1a and b
respectively. The asymmetric unit of the compound contains one
and a half cationic [Cu2(
counter balancing perchlorate anions.
l
-SL)2]2+ units, and three uncoordinated

J. Manzur et al. / Polyhedron 51 (2013) 180–185
183
Table 2
Selected bond distances (Å) and bond angles (°) for (1).
Cu1–O1
Cu1–O101
Cu1–N1
Cu1–N2
Cu1–N3
2.432(4)
1.941(4)
2.008(5)
2.025(4)
1.993(5)
2.812(2)
3.194(1)
Cu2–O1
1.919(4)
2.140(3)
2.024(5)
2.006(4)
2.071(5)
3.137(2)
Cu2–O101
Cu2–N101
Cu2–N102
Cu2–N103
Cu2ꢃ ꢃ ꢃS1
Cu1ꢃ ꢃ ꢃS101
Cu1ꢃ ꢃ ꢃCu2
Cu3–O201
Cu3–N201
Cu3–N203
Cu3ꢃ ꢃ ꢃCu3i
2.352(4)
2.023(5)
1.986(5)
3.245(1)
Cu3201i
1.931(3)
2.033(4)
2.929(2)
Cu3–N202
Cu3ꢃ ꢃ ꢃS201i
O101–Cu1–N1
O101–Cu1–N2
O101–Cu1–N3
N1–Cu1–N2
N1–Cu1–N3
N2–Cu1–N3
N1–Cu1–O1
N2–Cu1–O1
N3–Cu1–O1
O1–Cu2–O101
O1–Cu2–S1
97.7(2)
167.3(2)
98.9(2)
82.3(2)
160.7(2)
83.7(2)
100.8(2)
90.4(2)
92.4(2)
85.2(2)
69.0(1)
118.6(1)
152.3(1)
O1–Cu2–N101
O1–Cu2–N102
O1–Cu2–N103
N101–Cu2–N102
N101–Cu2–N103
N102–Cu2–N103
N101–Cu2–O101
N102–Cu2–O101
N103–Cu2–O101
O101–Cu1–O1
N101–Cu2–S1
93.74(2)
167.8(2)
109.7(2)
80.6(2)
133.6(2)
Fig. 2. Plot of the
shows the best fit of the data.
v
MT product vs. T for of [Cu2(
l
-SL)2](ClO4)2 (1). The solid line
81.7(2)
121.3(2)
88.5(2)
100.7(2)
77.1(1)
72.1(1)
79.6(2)
completely compensated spin value as expected for an antiferro-
magnetic ground state with S = 0 and, it is lower than the value
of 0.75 cm3 molꢀ1 K expected for two uncoupled copper(II) ions.
N102–Cu2–S1
O101–Cu2–S1
N103–Cu2–S1
Since two similar but not equivalent [Cu2(l
-SL)2]2+ bimetallic
O201i–Cu3–N201
O201i–Cu3–N203
N201–Cu3–N202
O201i–Cu3–O201
N203–Cu3–O201
102.6(2)
93.5(2)
82.3(2)
81.8(2)
101.2(2)
O201i–Cu3–N202
N203–Cu3–N201
N203–Cu3–N202
N201–Cu3–O201
N202–Cu3–O201
171.3(2)
159.2(2)
83.5(2)
94.2(2)
90.8(2)
cations (P and Q) are present in the crystal structure, in a 2 to 1 ra-
tio, the variable temperature susceptibility data were fitted using
the following expression:
vM ¼ 2vM
þ
vM
Q
ð1Þ
T
P
Cu2–O1–Cu1
93.7(2)
98.2(2)
Cu1–O101–Cu2
102.9(2)
Cu3i–O201–Cu3
where vM and vM correspond to the contribution of cations P and
P
Q
i
Symmetry labels : 2 ꢀ x, 1 ꢀ y, ꢀz.
Q to the total magnetic susceptibility. The magnetic susceptibility
contributions were modeled by the Bleaney–Bowers expression,
using the isotropic exchange Hamiltonian (H = ꢀJS1ꢃS2) for the two
interacting S = 1/2 centres [29],
from a second copper ion occupies the fourth basal position to
form an unsymmetrically bridged Cu2O2 core. Taki et al. [7] re-
ported the X-ray structure of a dimeric copper(II) complex with
an analogous ligand having a 4-tert-butyl substituent on the phe-
nol ring instead of a methyl, L1H = (2-methylthio-4-tert-butyl-6-
[{bis(pyridin-2-ylmethyl)-amino}methyl] phenol). The complex,
[CuII2(L1ꢀ)2](PF6)(ClO4), consisted of two non-equivalent five-coor-
dinated copper(II) ions having square pyramidal geometry with a
ꢀ
ꢁ
2Ng2b2
kBT
1
vM
¼
ð2Þ
i
3 þ expðꢀJi=kBTÞ
This expression was used assuming that, although both binu-
clear copper units [Cu2(
l
-SL)2]2+ present the same coordination
sphere (CuN3O2), the different distortions in each binuclear units
should produce different exchange interactions and therefore dif-
ferent magnetic exchange constants. Phuengphai et al. [30] also
used an expression with two different J values (one for each dinu-
clear unit present in the compound) to fit the experimental mag-
netic data of
different phosphato-bridged dinuclear units, [Cu2(phen)2(
H2PO4–O,O0)2(H2PO4)2][Cu2(phen)2( -H2PO4–O,O0)(
-H2PO4–O)(l-
HPO4–O)]2 (H2O)9 (phen = 1,10-phenanthroline). The best fit of the
experimental data was obtained from Eq. (2) (Fig. 2) using
g1 = g2 = 2.05, JP = ꢀ13.4 cmꢀ1 and JQ = 5.22 cmꢀ1 with R = 7.5 ꢁ
10ꢀ5. These results show that the magnetic exchange between
the copper(II) centres within the cationic species P and Q is rather
weak.
Literature data show that the magnetic behavior of bis(
oxo)dicopper(II) complexes is modulated mainly by the bridging
angle Cu–O(Ph)–Cu [31,32]. Usually, bis( -phenoxo)dicopper(II)
complexes exhibit moderate to strong antiferromagnetic spin cou-
pling between copper(II) ions, with bridging angles greater than
97°, while weak antiferromagnetic or ferromagnetic exchange
interactions, which is scarce in this type of compounds, is rational-
ized in terms of different structural parameters [28,33–36]. In the
case of pentacoordinated CuII ions the most frequently found
geometries are square pyramid or trigonal bipyramid. The mag-
netic orbitals (i.e., the orbitals that contain the unpaired electrons)
N3O2 donor set (s = 0.06 and 0.04 for the two copper ions). In this
compound, the pyridine nitrogen atom acts as the axial ligand for
one copper ion, whereas the phenolate oxygen atom serves as the
axial ligand for the second copper ion. Thus, one phenolate oxygen
is the equatorial ligand for both copper ions, while the other phe-
nolate oxygen acts as the equatorial ligand for one of them, and as
the axial ligand for the second one, bridging the copper atoms in a
equatorial–axial fashion, as in the Q unit of the reported complex.
a
CuII coordination compound containing two
l-
l
l
3.3. Magnetic susceptibility characterization
The thermal dependence of the magnetic susceptibility for (1),
at applied fields of 0.02 and 0.25 kOe, was obtained in a tempera-
ture range of 2.5–291 K. A complete reversibility between ZFC and
FC measurements and no field dependence of the magnetic suscep-
tibility was observed.
l-phen-
l
Fig. 2 shows the
vMT (T) plot at 0.25 kOe. At 291 K the value of
v
MT is 1.59 cm3 molꢀ1 K, which is very close to the expected value
for four non-interacting copper(II) centres (1.50 cm3 molꢀ1K). This
value remains almost invariant till approximately 70 K. From this
temperature the value of
vMT decreases markedly reaching a value
of 0.69 cm3 molꢀ1 K at 2.5 K. This behavior can be associated with
antiferromagnetic interactions between the copper(II) centres at
temperatures lower than 70 K. It is important to note, that the va-
lue of 0.69 cm3molꢀ1K obtained at 2.5 K, does not correspond to a
are dx2
and dz2 , respectively. The magnetic interaction may occur
ꢀy2
in an equatorial–equatorial, axial–axial or equatorial–axial

184
J. Manzur et al. / Polyhedron 51 (2013) 180–185
arrangement, depending on the magnetic orbitals involved, result-
ing in a rather strong (first two arrangements) or a weak magnetic
exchange (last arrangement) [33–36].
The magnitude of the magnetic exchange interactions between
copper(II) ions in binuclear complexes is dependent upon the orbi-
tal ground-state configuration of the copper(II) ions. Strong mag-
the phenyl group of the phenoxo moiety for [Cu2L2](PF6)2 is out of
the Cu2O2 plane, with the angle between the plane and the O–C vec-
tor of 21.7°, while for [Cu2(SL)2](PF6)2 is 51.6°. Thus the more planar
system, corresponding to [Cu2(L)2](PF6)2, presents an antiferromag-
netic exchange interaction.
In the case of [Cu2(l-SL)2](ClO4)2 (1) reported in this work, cat-
netic exchange interactions require both good
orientation of the magnetic orbitals, and good superexchange
pathways provided by the bridging atom orbitals.
In compound (1) cation Q, is characterized by a centrosymmet-
ric unit formed by two copper(II) ions with a slightly distorted
square pyramid geometry (s = 0.21) and Cu–O(Ph)–Cu angles of
r
-bonding
ion P is also formed by two square base pyramidal CuII centres
bridged in axial–equatorial fashion by two phenoxo groups with a
more distorted geometry for the CuII ions, resulting in a non cent-
rosymetric Cu2O2 moiety. The angles between the Cu2O2 plane and
O1–C16 and O101–C116 vectors correspond to 27.6° and 16.9°
respectively. The second magnetic exchange constant of
ꢀ13.9 cmꢀ1 can be ascribed to the exchange interaction through
98.2°, and an axial–equatorial coordination mode of the phenolate
ions to the CuII ions. If we take into account the relevance of the
Cu–O(Ph)–Cu angle in the observed magnetic behavior, it can be
anticipated that the planar Q cation should be characterized by
an antiferromagnetic interaction (Cu–O–Cu angle = 98.2°). How-
ever, the axial–equatorial coordination mode of both phenoxo li-
gands produces unfavorable overlap between the magnetic
orbitals, canceling the antiferromagnetic interaction and leading
to an overall weak ferromagtic exchange. Therefore, cation Q can
be related with JQ = +5.22 cmꢀ1. The reported J value for the analo-
gous complex with hexafluorophosphate as counteranion, [Cu2-
the more planar phenoxo bridge with
a Cu–O–Cu angle of
102.85° present in cation P, while the less planar with the more ac-
cute Cu–O–Cu angle of 94.5°, would be less effective mediating the
magnetic exchange.
4. Conclusions
A new CuII complex has been prepared with the tripodal ligand
2-[(bis(2-pyridylmethyl)amino)methyl]-4-methyl-6-(methylthio)-
phenol and perchlorate as the anion. The structural and magnetic
properties analyzed, comparing these with the ones of previously
reported complex, obtained with hexafluorophophate as the coun-
terion. For this species the axial-equatorial bridging mode of the
two phenolate bridges explains the weak ferromagnetic interaction
between the copper centres, while complex (1) consists of two
similar but not equivalent dinuclear copperII units, P and Q, being
Q structurally and magnetically very similar to the reported one,
while P is asymmetric and accounts for the overall weak antiferro-
magnetic behavior observed in this complex. Apparently, the size
and shape of the counteranion influence the coordination and
bridging mode of the ligand, resulting in important structural
changes and hence modifying the magnetic properties of the ob-
tained complex.
SL2](PF6)2, is +3.4 cmꢀ1
On the other hand, cation P has two copper centres; Cu1 exhib-
its square pyramid geometry ( = 0.11) while Cu2 presents an
approximately trigonal bipyramid geometry ( = 0.57). Both copper
.
s
s
ions are bridged by two phenoxo groups in axial–axial and equato-
rial–equatorial coordination modes having Cu–O(Ph)–Cu bond an-
gles of 94.05° and 102.85°, respectively. This configuration of the
phenoxo bridges would favor antiferromagnetic exchange between
the copper ions. Nevertheless, the non-planarity of the Cu2O2 moi-
ety (hinge distortion = 7.13°) together with the out of plane shift of
the phenyl ring (27.6° and 16.9°), and the rotation of the phenyl
ring respect to the Cu2O2 plane (33.4° and 23.4°) reduce the mag-
netic interaction [28] resulting in a low magnetic exchange con-
stant, J, of ꢀ13.4 cmꢀ1
. It is possible to conclude that the
geometry distortions around the Cu2O2 core result in a poor orbital
overlap through the phenoxo bridges, despite being axial–axial or
equatorial–equatorial.
Acknowledgments
Financial support from Project FONDECYT 1050484 and Proyec-
to Basal FB0807 (CEDENNA) is gratefully acknowledged.
Although magnetostructural correlations for dinuclear
bis(phenoxo)-bridged CuII complexes show a large dependence of
the coupling on the bridging Cu–O–Cu angle, the J value in non pla-
nar systems also is dependent on the following structural parame-
Appendix A. Supplementary material
ters (i) large out-of-plane shifts for the phenoxo group (s angle),
CCDC 896774 contains the supplementary crystallographic data
for [Cu2(l-SL)2](ClO4)2 (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,
Cambridge CB2 1EZ, UK; fax: +44 1223-336-033; or e-mail:
deposit@ccdc.cam.ac.uk.
which reduce the antiferromagnetic term; (ii) large hinge distor-
tions (i.e., Cu–O–Cu–O) cancel the antiferromagnetic contributions,
and can lead to ferromagnetic coupling at small Cu–O–Cu angles;
(iii) a syn conformation of the phenoxo groups favors the antiferro-
magnetic contribution; (iv) for small
s angles, the rotation of the
phenyl rings with respect to the Cu2O2 framework results in an in-
crease of the antiferromagnetic interaction.
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