A rare polymeric azido-bridged copper(II) chain with a pentameric repeating unit: Synthesis, structure and magnetic properties

Article abstract of DOI:10.1016/j.poly.2012.10.031

The novel polymeric chain copper(II) complex [Cu₄(μ-Mesalpn) ₂(μ_1,1,1-N₃)₂(μ_1,1- N₃)₂Cu]_n (1) was prepared by the reaction of Cu(NO₃)₂

Full text of DOI:10.1016/j.poly.2012.10.031

Polyhedron 50 (2013) 45–50
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A rare polymeric azido-bridged copper(II) chain with a pentameric repeating unit:
Synthesis, structure and magnetic properties
b
c
c
Aliakbar Dehno Khalaji a, , Smail Triki , Juan M. Clemente-Juan , Carlos J. Gómez-García
⇑
a Department of Chemistry, Faculty of Science, Golestan University, Gorgan, Iran
b UMR CNRS 6521, Chimie, Electrochimie Moléculaires, Chimie Analytique, Université de Bretagne Occidentale, BP 809, 29285 Brest Cedex, France
c Instituto de Ciencia Molecular (ICMol), Parque Científico, Universidad de Valencia, 46980 Paterna, Valencia, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The novel polymeric chain copper(II) complex [Cu4(
l
-Mesalpn)2(
l
1,1,1-N3)2(
l
1,1-N3)2Cu]n (1) was pre-
Received 11 August 2012
Accepted 14 October 2012
Available online 2 November 2012
pared by the reaction of Cu(NO3)2Á3H2O with Mesalpn in the presence of an excess of NaN3. A single-
crystal X-ray diffraction study showed an unusual 1D polymeric chain based on pentanuclear Cu5 units
with both l1,1,1-N3 and l1,1-N3 bridges, and with three independent Cu(II) ions presenting three different
coordination numbers (4, 5 and 6). The magnetic susceptibility data show the presence of dominant anti-
ferromagnetic interactions.
Keywords:
Copper(II) complex
Single-crystal
Ó 2012 Elsevier Ltd. All rights reserved.
Pentanuclear
1D polymeric chain
1. Introduction
(Scheme 1-h, six examples, one with Cu) [2]. Besides these coordi-
nation modes, there are also many complexes with double azido
In recent years, the field of polynuclear copper(II) complexes
with Schiff base ligands in the presence of the azide anion as a
bridging ligand has been an area of intense study, not only for their
interesting molecular structures but also because they have poten-
tial applications and constitute ideal systems for understanding
the nature of magnetic interactions [1–7]. The flexibility in the
coordination versatility of the azido ligand is clearly shown by its
capacity to act either as terminal monodentate (Scheme 1a) or as
a bridging bi-, tri- and tetra-dentate linker in different transition
metal complexes (Scheme 1b–j) [8–12]. Thus, a careful search in
the CCDC database (updated Nov-2011) shows a total of 1448
deposited structures of complexes with terminal N3 ligands with
any metal and a total of 345 complexes with Cu (Scheme 1-a).
When acting as bi-dentate, the azido ligand may bind two metals
bridges, either l1,1 (Scheme 1i, 400 examples, 172 with Cu) or
l1,3 (Scheme 1j, 77 examples, 33 with Cu).
Of course, the final coordination mode of the azide ion in a com-
plex will depend on its geometry, on the nature of the other co-
ligands present, on the central metal atom and on its oxidation
state [1–23]. Besides, the azido ligand is also used as a ligand to
study the interaction between small molecules and the metal cen-
tre of metalloenzymes [24,25]. It is well established that the nature
of the magnetic interaction depends on the coordination mode of
the bridging azido group [14,26]. In Cu complexes, the interaction
is strongly ferromagnetic when the coordination mode of azido is
end-on (
magnetic when the coordination mode of azido is end-to-end
1,3) [30,31]. In the case of asymmetric bridges (involving long
and short Cu–N bonds) the situation is less studied since there
are less examples. Thus, in asymmetric 1,1-N3 bridges the cou-
pling may vary from weak ferro to weak antiferromagnetic,
whereas in asymmetric 1,3-N3 bridges the coupling ranges from
l1,1) [27–29], while the interaction is strongly antiferro-
(l
via only one terminal N atom (end-on = EO or
with 1030 reported metallic complexes, 377 with Cu) or with the
two terminal N atoms (end-to-end = EE or 1,3) (Scheme 1-c, with
l1,1) (Scheme 1-b,
l
l
638 examples, 173 with Cu). When the azido ligand is connected to
l
three metals atoms, the two possible tridentate bridging coordina-
weak ferro to strong antiferromagnetic [14].
tion modes are
l
1,1,1 (Scheme 1d, 79 known examples, 16 with Cu)
According to the literature on copper(II) complexes, multiden-
tate Schiff bases have proven to be effective auxiliary ligands to
stabilize multinuclear copper(II) complexes, as shown for some re-
cently reported azido-bridged tetranuclear copper(II) complexes
[15,32–34]. In this work we show how by using the Schiff base
ligand Mesalpn and changing the synthetic conditions, we have
and l1,1,3 (Scheme 1e, 73 examples, 31 with Cu). Finally, although
less common, there are also some examples where the azido ligand
is linked to four metals atoms. In this case, the three possible coor-
dination modes are l1,1,1,1 (Scheme 1f, nine examples, one with
Cu), l1,1,1,3 (Scheme 1g, four examples, one with Cu) and l1,1,3,3
obtained
pentameric Cu5 repeating unit, formulated as [Cu4(
1,1,1-N3)2( 1,1-N3)2Cu]n (1).
a
new polymeric copper(II) chain complex with
a
l
-Mesalpn)2
⇑
Corresponding author. Tel./fax: +98 171 2245882.
E-mail addresses: alidkhalaji@yahoo.com, ad.khalaji@gu.ac.ir (A.D. Khalaji).
(l
l
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.10.031

46
A.D. Khalaji et al. / Polyhedron 50 (2013) 45–50
2.3. Physical measurements
Fourier transform infrared spectra were recorded as a KBr disk
on a FT-IR Perkin-Elmer spectrophotometer. Elemental analyses
were carried out using a Heraeus CHN–O-Rapid analyser.
2.4. Magnetic measurements
Variable temperature magnetic susceptibility measurements
were carried out in the temperature range 2–300 K with an applied
magnetic field of 0.1 T on a polycrystalline sample (m = 3.73 mg)
with a Quantum Design MPMS-XL-5 SQUID magnetometer. The
susceptibility data were corrected for the sample holders, previ-
ously measured using the same conditions, and for the diamag-
netic contributions of the salt, as deduced using Pascal’s constant
tables (
v
dia = À519.5 Â 10À6 emu molÀ1) [36].
2.5. X-ray structure determination
A black single crystal was placed at the top of a glass fibre with
silicone grease and mounted on an Xcalibur 2 CCD diffractometer
(Oxford Diffraction) fitted with graphite monochromated Mo K
a
radiation (k = 0.71073 Å). Data were collected at 170 K. The struc-
ture was solved by direct methods and successive Fourier differ-
ence syntheses, and was refined on F2 by weighted anisotropic
full-matrix least-square methods [37]. Except the disordered N7
(N7A and N7B) and N8 (N8A and N8B) atoms, which were refined
isotropically, all other non-hydrogen atoms were refined aniso-
tropically, while the hydrogen atoms were calculated and therefore
included as isotropic fixed contributors to Fc. Data collection and
data reduction were done with the CRYSALIS-CCD and CRYSALIS-RED pro-
grams [38]. All other calculations were performed with standard
procedures (WINGX) [39]. Crystal data, structure refinement and col-
lection parameters are listed in Table 1. Selected bond lengths and
angles are given in Table 2.
Scheme 1. Bonding modes of the azido ligand with the total number of known
complexes with any metal and with Cu.
2. Experimental
2.1. General procedure
All the used reagents were commercially available, reagent
grade and used as received without any further purification. The
tetradentate Schiff base ligand Mesalpn (Scheme 2) was synthe-
sized by mixing 2-hydroxyacetophenone and propane-1,3-diamine
in a 2:1 M ratio in ethanol, according to the literature method [35].
CAUTION! Nitrate salts of metal complexes with organic ligands
and azide ions are potentially explosive. Only small quantities of
these complexes should be prepared and they should be handled
with care.
3. Results and discussion
3.1. FT-IR spectra
The FT-IR spectrum of [Cu4(l-Mesalpn)2(l1,1,1-N3)2(l1,1-N3)
2Cu]n showed strong absorption bands at 2142 and 2054 cmÀ1
,
2.2. [Cu4(l-Mesalpn)2(l1,1,1-N3)2(l1,1-N3)2Cu]n (1)
To 50 mL of a methanolic solution of Cu(NO3)2Á3H2O (1.2 g,
5 mmol) was added 0.61 g (2 mmol) of MesalpnH2 dissolved in
20 mL of acetone, and the resulting solution was stirred for 1.5 h.
Then, NaN3 (0.72 g, 12 mmol) dissolved in 5 mL of H2O was slowly
added to the above solution and the resulting brown solution was
stirred further for 5 min. The solution was left at room tempera-
ture, resulting in the precipitation of black crystals after 2 weeks.
These were collected by filtration and washed with small amounts
of methanol and air dried (mass = 0.652 g, yield = 55% based on
Table 1
Crystallographic data for [Cu4(
l
-Mesalpn)2(
l
1,1,1-N3)2(
l
1,1-N3)2Cu]n (1).
C38H40Cu5N22O4
Empirical formulaa
Formula weight
Crystal system, Space group
a (Å)
b (Å)
c (Å)
V (Å3)
Z
1186.62
orthorhombic, Pbcn
12.0222(5)
18.822(0)
19.4522(8)
4401.7(3)
4
2396
2.447
22845
3151
F(0 0 0)
Cu). FT-IR (KBr):
(CH@N) 1624(s);
C, 38.46; H, 3.39; N, 25.97. Found: C, 38.39; H, 3.45; N, 26.04%.
m(CH) 3047(w), 2932(w);
m(N3) 2142(s), 2054(s);
l
(mmÀ1
)
m
m(M–N) 424(w). Anal. Calc. for C38H40Cu5N22O4:
Measured reflections
Independent reflections
Rint
0.0865
Reflections with I > 2
r
(I)
2095
Parameters
307
0.0419
0.0985
0.976
R[F2 > 2
wR(F2)c
r
(F2)]b
H
3C
CH3
N
N
Goodness-of-fit (GOF) on F2d
D
qmax
,
D
qmin (eÅÀ3
)
1.033, À0.652
a
b
c
The asymmetric unit contains 0.5 of the chemical formula.
OH HO
P
R1
=
|Fo À Fc|/Fo.
P
P
wR2 = { [w(Fo À Fc2)2]/ [w(Fo2)2]}1/2
.
2
P
d
2
Goodness-of-fit = { [w(Fo À Fc2)2]/(Nobs À Nvar)}1/2
.
Scheme 2. The chemical structure of Schiff base ligand Mesalpn.

A.D. Khalaji et al. / Polyhedron 50 (2013) 45–50
47
Table 2
Selected bond distances (Å) and angles (°) in [Cu4(l-Mesalpn)2(l1,1,1-N3)2(l1,1-N3)2Cu]n (1).
Cu1–O1
Cu1–O2
Cu1–N1
Cu1–N2
Cu1–N3
N1–C1
N1–C8
N2–C10
1.962(4)
1.955(4)
1.981(4)
1.959(5)
2.241(5)
1.282(7)
1.481(7)
1.475(7)
1.139(7)
1.210(7)
86.53(17)
91.78(16)
159.01(17)
178.11(17)
92.21(18)
88.89(17)
81.27(19)
121.1(2)
79.14(18)
100.6(2)
103.82(5)
133.5(3)
108.6(2)
Cu2–N6
Cu2–N9
Cu2–N3(a)
Cu2–N3
Cu2–O2
N6–N7B
N6–N7A
N7A–N8A
N7B–N8B
N10–N9
2.1093(7)
2.198(8)
2.213(6)
2.362(6)
2.005(3)
1.2212(11)
1.2190(11)
1.1494(11)
1.1505(11)
1.222(10)
172.4(2)
79.7(2)
79.7(2)
172.36(19)
97.6(5)
160.65(15)
98.95(11)
91.36(10)
105.22(19)
93.56(19)
115.4(3)
Cu2–O1(a)
Cu3–N6(b)
Cu3–N6
Cu3–N9
Cu3–N9(b)
N10–N11
C11–N2
O2–C17
O1–C7
2.012(3)
1.9542(6)
1.9542(6)
1.968(6)
1.968(6)
1.145(10)
1.295(7)
1.327(7
N4–N5
N4–N3
1.350(6)
O2–Cu1–N2
O2–Cu1–O1
N2–Cu1–O1
O2–Cu1–N1
N2–Cu1–N1
O1–Cu1–N1
O2–Cu1–N3
N2–Cu1–N3
O1–Cu1–N3
N1–Cu1–N3
N6(b)–Cu3–N6
C17–O2–Cu2
Cu1–O1–Cu2(a)
N6(b)–Cu3–N9
N6–Cu3–N9
N6–Cu2–N9
71.37(17)
92.63(17)
78.78(17)
167.70(14)
101.6(2)
77.28(16)
84.40(16)
103.78(14)
174.7(2)
O2–Cu2–N3(a)
O1(a)–Cu2–N3(a)
N6–Cu2–N3(a)
N9–Cu2–N3(a)
O2–Cu2–N3
N6(b)–Cu3–N9(b)
N6–Cu3–N9(b)
N9–Cu3–N9(b)
O2–Cu2–O1(a)
O2–Cu2–N6
O1(a)–Cu2–N3
N6–Cu2–N3
O1(a)–Cu2–N6
O2–Cu2–N9
N9–Cu2–N3
O1(a)–Cu2–N9
C17–O2–Cu1
Cu1–O2–Cu2
N3(a)–Cu2–N3
C7–O1–Cu1
82.75(19)
114.8(3)
126.1(3)
111.1(2)
C7–O1–Cu2(a)
Symmetry codes:
(a)
1 À x, Ày, 2 À z.
(b)
1 À x, y, 3/2 À z.
due to the asymmetric stretching vibration of N3, and clearly
proves the presence of both l1,1 and 1,1,1-N3 bridging modes of
the azido ligand [32–34,40–43]. The strong characteristic absorp-
tion of the CH@N group was also detected at 1624 cmÀ1
angles when the polyhedron is viewed as a square pyramid; for a
perfectly square-pyramidal geometry, is equal to zero, and it be-
comes unity for a perfectly trigonal bipyramid geometry [49–53].
l
s
.
Finally, the Cu3 ion is coordinated to four nitrogen atoms from four
l
1,1 azido groups (N6, N9, N6⁄ and N96⁄) to form an almost perfect
square planar geometry with Cu–N bond distances of 1.9542(6) and
3.2. Description of the structure of [Cu4(l-Mesalpn)2(l1,1,1-N3)2(l1,1-
1.968(6) Å (Table 1). The two different 1,1 [N6–N7–N8 (N6–N7A–
l
N3)2Cu]n (1)
N8A and N6–N7B–N8B disordered units) and N9–N10–N11] and
the l1,1,1 (N3–N4–N5) bridging azido ligands are quasi-linear
(N6–N7A–N8A = 167.1(15)°, N6–N7B–N8B = 176.2(17)°, N9–N10–
N11 = 176.4(9)° and N3–N4–N5 = 178.8(6)°), as is usually observed
in azido ligands. The structure of 1 shows a total of four different
connected CuÁ Á ÁCu pairs: Cu1Á Á ÁCu2 = 3.265(1) Å (through the phe-
The asymmetric unit of compound 1 contains two Cu(II) ions lo-
cated at general positions (Cu1 and Cu2) and one Cu(II) ion located
on a special position (Cu3) (Fig. 1, top). The formula unit contains,
thus, two Cu1, two Cu2 and one Cu3 atom. These five Cu(II) ions are
connected through l1,1 and l1,1,1-N3 bridges and through the two
phenoxido groups of the Mesalpn ligand to yield a doubly deco-
noxido O2 and
a
l
1,1,1-N3 bridges), Cu1Á Á ÁCu2⁄ = 3.229(1) Å
(through the phenoxido O1 and a
l
1,1,1-N3 bridges), Cu2Á Á ÁCu2⁄ =
rated 1D polymeric copper(II) complex (Fig. 1, bottom).
3.435(1) Å (through a double
3.202(1) Å (through a double l1,1-N3 bridge) (Fig. 1).
l
1,1,1-N3 bridge) and Cu2Á Á ÁCu3 =
Interestingly, the coordination numbers (and, therefore, the
geometries) of the three Cu ions are different: Cu1 is pentacoordi-
nated with a square pyramidal geometry, Cu2 is hexacoordinated
with an octahedral geometry and Cu3 is tetracoordinated and pre-
sents a square planar geometry. Although this fact is rare, it is not
unique. In fact, among the several thousands of azido complexes,
the CCDC data base shows seven other examples of azido-bridged
complexes containing Cu ions with coordination numbers of 4, 5
and 6 [44–48].
The bridging Cu1–O1–Cu2⁄ and Cu1–O2–Cu2 bond angles
(108.6(2)° and 111.1(2)°, respectively) are similar and are larger than
those reported in the tetranuclear copper(II) complexes [Cu4(
alen)2( 1,1-N3)2(N3)2] (98.95(3)° and 105.47(3)°) [34], and [Cu4(
Mesalen)2( 1,1-N3)2(N3)2(H2O)2] (99.6(1)° and 105.6(1)°) [34]. In
contrast, the two Cu–N–Cu bond angles through the double 1,1azido
l-Mes-
l
l-
l
l
bridges (Cu3–N6–Cu2 = 103.91(3)° and Cu3–N9–Cu2 = 100.3(3)°)
are similar to those reported in the tetranuclear copper(II) complexes
The Cu2 ions are coordinated to two phenoxido oxygen atoms
(O1 and O2⁄) of two different Mesalpn Schiff bases (with Cu–O bond
distances of 2.012(3) and 2.005(3) Å, respectively) and to four nitro-
gen atoms from two l1,1 (N6 and N9) and two l1,1,1 (N3 and N3⁄)
azido groups to form a slightly distorted octahedral geometry (with
Cu–N bond distances of 2.1093(7), 2.198(8), 2.362(6) and
2.213(6) Å, respectively). The Cu1 ions are located in the inner cav-
ity of the Mesalpn ligand and present a distorted square pyramidal
geometry where the basal plane is formed by two phenoxido oxygen
atoms of the Schiff base (O1 and O2, with Cu-O bond distances of
1.962(4) and 1.955(4) Å, respectively) and two imine nitrogen
atoms from one Mesalpn ligand (N1 and N2, with Cu–N bonds dis-
tances of 1.981(4) and 1.959(5) Å, respectively). The axial position
[Cu4(
1,1-N3)2(N3)2] (101.17(3)°) [34] and [Cu4(
(N3)2(H2O)2] (101.6(2)°) [32]. Also the three Cu–N–Cu bond angles
through the
l-salen)2(l1,1-N3)2(N3)2] (103.3(2)°) [15], [Cu4(l-Mesalen)2
(l
l-Mesalpn)2(l1,1-N3)2
l1,1,1-azido bridge (Cu1–N3–Cu2 = 90.3(2)°, Cu2–N3–
Cu2⁄ = 97.3(2)° and Cu1–N3–Cu2⁄ = 92.9(2)°) are similar to those re-
portedinthe polynuclear copper(II) complex[Cu6(N3)12(aem)2]n [18].
Finally, it is worth mentioning that although there are many Cu(II)
chaincomplexeswithazidobridges, thedecoratedchaintopologyob-
served in compound 1 has never been observed before in azido-
bridged Cu complexes.
3.3. Magnetic properties
is occupied by a nitrogen atom from one
Cu–N3 = 2.241(5) Å). The distortion in the square pyramidal geom-
etry is clearly shown by the Addison parameter, = 0.318;
= (b À )/60], where b and are the two greatest basal plane
l1,1,1azido group (N3, with
The temperature dependence of the product of the molar mag-
s
netic susceptibility times the temperature,
vmT, per five Cu ions
[
s
a
a
shows a room temperature value of ca. 2.3 emu K molÀ1, which is

48
A.D. Khalaji et al. / Polyhedron 50 (2013) 45–50
Fig. 1. ORTEP perspective views of the title compound: the asymmetric unit with the atomic labelling scheme and the metal environments (top); ORTEP of the one-
dimensional structure along the [001] direction (bottom). Code of equivalent positions: (a) 1 À x, Ày, 2 À z; (b) 1 À x, y, 3/2 À z;(c) x, Ày, À1/2 + z; (d) 1 À x, y, 5/2 À z;(e) x, Ày,
1/2 + z.
the expected vale for five independent S = 1/2 Cu(II) ions with
g ꢀ 2.2 (Fig. 2). When the temperature is decreased, the
vmT prod-
2.5
2.0
1.5
1.0
0.5
0.0
uct shows a progressive decrease to reach a plateau of ca.
experimental
J4 model
0.4 emu K molÀ1 in the temperature range of ca. 30–10 K. Below
ca. 10 K the
vmT value shows an additional decrease and reaches
J2 model
a value of ca. 0.3 emu K molÀ1 at 2 K. This behaviour indicates
the presence of predominant antiferromagnetic interactions in
compound 1. This antiferromagnetic coupling is also clearly seen
0.020
0.018
0.016
0.014
0.012
0.010
0.008
in the thermal variation of
at ca. 100 K (inset in Fig. 2) followed by a divergence at lower tem-
peratures, corresponding to the plateau observed in the mT plot.
vm, which shows a rounded maximum
v
A close inspection of the chain structure of compound 1 shows
the presence of four different Cu–Cu exchange pathways (Cu1–
Cu2, Cu1–Cu2⁄, Cu2–Cu2⁄ and Cu2⁄–Cu3, Fig. 3a). Accordingly, in
a first approach we can have used a magnetic model including
these four exchange coupling constants (J12, J21, J22 and J23, model
J4, Fig. 3b). In this model, J12 and J21 represent the Cu1–Cu2
and Cu1–Cu2⁄ magnetic coupling through the phenoxido and
0
50 100 150 200 250 300
T (K)
0
50
100
150
T (K)
200
250
300
1,1,1-N3 bridges, J22 is the Cu2–Cu2⁄ coupling through the double
Fig. 2. Thermal variation of the
Inset shows the thermal variation of
best fit to the J4 and J2 models, respectively (see text). (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of
this article.)
vmT product per five Cu(II) ions in compound 1.
l
l
1,1,1-N3 bridge and J23 is the Cu2⁄–Cu3 coupling through the dou-
vm. Red and blue solid lines correspond to the
ble
l1,1-N3 bridge (Fig. 3b). With this model we have been able to
reproduce the magnetic data of compound 1 by using a 10 Cu(II)

A.D. Khalaji et al. / Polyhedron 50 (2013) 45–50
49
Fig. 3. (a) Structure of the Cu chain in compound 1. Only the bridging and terminal coordinated atoms are shown. (b) Scheme of the magnetic exchange pathways.
centre closed-chain model [35], corresponding to two pentameric
–Cu3–Cu2–(Cu1)2–Cu2– units, with the following set of parame-
ters: g = 2.212, J12 = À71.4 cmÀ1, J21 = À20.7 cmÀ1, J22 = 54.9 cmÀ1
and J23 = 0.27 cmÀ1 (red line in Fig. 2). Note that although the mod-
el reproduces the magnetic properties very well, the number of
parameters is quite high.
In order to reduce the number of adjustable parameters, we can
consider, in a first approach, that the Cu1–Cu2 and Cu1–Cu2⁄ path-
ways are very similar. In fact, both are formed by a phenoxido
experimentally. Furthermore, a detailed analysis of the Cu–N bond
distances in this double 1,1-N3 bridge reveals a slight asymmetry,
l
with two short (Cu3–N6 = 1.9542(6) and Cu3–N9 = 1.968(6) Å) and
two long (Cu2–N6 = 2.1093(7) and Cu2–N9 = 2.198(8) Å) Cu–N
bond distances. Interestingly, the two long bond distances are close
to the crossing point (ca. 2.05 Å) from ferro- to antiferro-magnetic
coupling [1]. Finally, an additional aspect that is also responsible
for a decrease in the magnetic coupling through this bridge is the
lack of planarity of the Cu(N)2Cu central unit, which presents a
dihedral angle of ca. 17°.
bridge and a
l1,1,1-N3 bridge with similar bond distances and an-
gles and, therefore, we have assumed that both are identical
(J12 = J21 in Fig. 3b). Furthermore, since the fit to the J4 model gives
a very small Cu2-Cu3 coupling constant (J23 = 0.27 cm-1), we can
assume that this coupling is negligible as compared with all the
others, and accordingly we have fixed J23 = 0. This simplified model
including only two different J values (model J2) is also able to sat-
isfactorily reproduce the magnetic properties of compound 1 with
g = 2.149, J12 = J21 = À56.1 cmÀ1 and J22 = 15.8 cmÀ1 (blue line in
Fig. 2).
Although l1,1,1-N3 bridges are scarcer and there is no magneto-
structural correlation with this kind of bridge, the ferromagnetic
coupling found in the J22 bridge is similar to those observed in
other
The coupling constants J12 and J21 correspond to the two differ-
ent bridges connecting Cu1 and Cu2: the 1,1,1-N3 and the -phe-
noxido bridges. On one hand, the 1,1,1-N3 bridge is slightly
l1,1,1-N3 bridges [58,59].
l
l
l
asymmetric and presents long Cu–N bond distances (Cu1–
N3 = 2.241(5) Å, Cu2-N3⁄ = 2.213(6) Å and Cu2–N3 = 2.362(6) Å),
and therefore it is expected to give weak antiferromagnetic cou-
plings. On the other hand, the phenoxido bridge is expected to
originate an antiferromagnetic coupling when the Cu–O–Cu bond
angles are larger than ca. 96° [60–69]. In compound 1 these angles
are 108.6(2)° and 111.1(2)° (Table 2), and therefore both coupling
constants are expected to be moderate to strong and antiferromag-
netic, in agreement with the values found in both models.
Finally, it is worth mentioning that although the first model,
using four different J values, reproduces the magnetic properties
of compound 1 better, a much simpler model with only two J val-
ues is also able to reproduce the magnetic properties of the chain
compound 1 very satisfactorily. The deviations in this J2 model
are probably due to the fact that J12 might be different to J21 (as ob-
served in the J4 model) rather than to the assumption that J23 is
equal to zero.
The presence of a plateau of ca. 0.4 emu K molÀ1 at low temper-
atures has to be attributed to the presence of a very small coupling
constant connecting Cu3 with the rhombs containing Cu1 and Cu2,
leading to almost isolated Cu3 ions. Although the plateau could
also be due to the presence of spin frustration in the Cu1Cu2
rhomb [54], the presence of a ferromagnetic coupling, J22, along
the short diagonal of the rhomb excludes this possibility.
The values found for the coupling constants can be well corre-
lated with the many previous magneto-structural correlations
and theoretical calculations [1,55–57]. These correlations and the-
oretical calculations predict that for double symmetric
l1,1-N3
bridges (as J23) the main parameters controlling the magnetic cou-
pling are the Cu–N–Cu bond angles and Cu–N bond distances, be-
sides the geometry of the Cu complex. Thus, the magnetic coupling
is expected to be ferromagnetic and strong when the Cu–N–Cu
bond angle is small. This coupling decreases as the Cu–N–Cu angle
increases and becomes antiferromagnetic for angles of ca. 104°
(theoretically) [57] and ca. 108° (experimentally) [1]. Interestingly,
in compound 1 the Cu–N–Cu bond angles defining J23 are within
this critical range (Cu3–N6–Cu2 = 103.91(3)° and Cu3–N9–
Cu2 = 100.3(3)°) and, therefore, the coupling through this double
4. Conclusions
The use of the Schiff base ligand Mesalpn with azido ligands and
Cu(II) ions has yielded an unprecedented azido bridged Cu(II) chain
with alternating Cu(II) monomers and Cu4 rhombs connected
l1,1-N3 bridge is expected to be very weak, as observed

50
A.D. Khalaji et al. / Polyhedron 50 (2013) 45–50
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Acknowledgments
The authors acknowledge the CNRS (Centre National de la
Recherche Scientifique), the EU (MAGMANet Network of excel-
lence), the Spanish Ministerio de Economía y Competitividad
(Projects Consolider-Ingenio in Molecular Nanoscience CSD2007-
00010 and CTQ-2011-26507), the Generalitat Valenciana (Project
PROMETEO 2009/095) and the Golestan University for partial sup-
port of this work.
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Appendix A. Supplementary material
CCDC 904882 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-
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