Two tetranuclear copper(II) complexes with open cubane-like Cu 4O4 core framework and ferromagnetic exchange interactions between copper(II) ions: Structure, magnetic properties, and density functional study

Article abstract of DOI:10.1002/ejic.201301515

Two alkoxo-bridged copper(II) tridentate Schiff base complexes [{Cu(H ₂L1)}₄] (1) [H₂L1 = N-(2-hydroxyethyl)-3,5-di- tert-butylsalicylaldimine] and {Cu(H₂L2)}₄ (2) [H ₂L2 = N-(2-hydroxyethyl)-4-methoxysalicylaldimine] have been synthesized and structurally and magnetically characterized. X-ray diffraction studies show that 1 and 2 are tetranuclear alkoxo-bridged copper(II) complexes that contain a rather distorted Cu₄O₄ cubane core of 4+2 type (four short and two long Cu?Cu distances). The coordination of each copper ion can be described as a distorted square pyramid with one nitrogen and four oxygen atoms from three ligands. Variable-temperature magnetic susceptibility measurements on the two tetranuclear complexes 1 and 2 in the range 2-300 K indicate ferromagnetic exchange coupling between copper(II) centers. The magnetic susceptibility data were analyzed by using a simple two-J model with J′ and J″ representing the magnetic exchange couplings through the short and long Cu?Cu exchange pathways, respectively. The J values were as follows: J′ = +28.7 cm^-1 and J″ = +7.8 cm^-1 for 1, and J′ = +39.8 cm^-1 and J″ = +10.2 cm^-1 for 2. The sign and magnitude of the exchange coupling constants were justified on the basis of the structural geometric factors of the bridging Cu(O)₂Cu fragments, the overlap of the magnetic orbitals, and DFT calculations. Two alkoxo-bridged copper(II) tridentate Schiff base complexes were synthesized and structurally and magnetically characterized. Magnetic susceptibility measurements on the tetranuclear complexes indicate ferromagnetic exchange coupling between copper(II) centers. The sign and magnitude of the exchange coupling constants were justified on the basis of several factors including DFT calculations. Copyright

Full text of DOI:10.1002/ejic.201301515

FULL PAPER
DOI:10.1002/ejic.201301515
Two Tetranuclear Copper(II) Complexes with Open
Cubane-Like Cu4O4 Core Framework and Ferromagnetic
Exchange Interactions between Copper(II) Ions: Structure,
Magnetic Properties, and Density Functional Study
Elif Gungor,*[a] Hulya Kara,[a] Enrique Colacio,*[b] and
Antonio J. Mota[b]
Keywords: Copper / Schiff bases / Magnetic properties / Density functional calculations
Two alkoxo-bridged copper(II) tridentate Schiff base com-
plexes [{Cu(H2L1)}4] (1) [H2L1 = N-(2-hydroxyethyl)-3,5-di-
tert-butylsalicylaldimine] and {Cu(H2L2)}4 (2) [H2L2 = N-(2-
hydroxyethyl)-4-methoxysalicylaldimine] have been synthe-
sized and structurally and magnetically characterized. X-ray
diffraction studies show that 1 and 2 are tetranuclear alkoxo-
bridged copper(II) complexes that contain a rather distorted
Cu4O4 cubane core of 4+2 type (four short and two long
Cu···Cu distances). The coordination of each copper ion can
be described as a distorted square pyramid with one nitrogen
and four oxygen atoms from three ligands. Variable-tempera-
ture magnetic susceptibility measurements on the two tetra-
nuclear complexes 1 and 2 in the range 2–300 K indicate fer-
romagnetic exchange coupling between copper(II) centers.
The magnetic susceptibility data were analyzed by using a
simple two-J model with JЈ and JЈЈ representing the magnetic
exchange couplings through the short and long Cu···Cu ex-
change pathways, respectively. The J values were as follows:
JЈ = +28.7 cm–1 and JЈЈ = +7.8 cm–1 for 1, and JЈ = +39.8 cm–1
and JЈЈ = +10.2 cm–1 for 2. The sign and magnitude of the
exchange coupling constants were justified on the basis of
the structural geometric factors of the bridging Cu(O)2Cu
fragments, the overlap of the magnetic orbitals, and DFT cal-
culations.
length of the Cu–O bonds within the cubane unit. Thus,
Cu4O4 cubane complexes with four long Cu–O distances
between two dinuclear subunits are classified as type I,
whereas those with long Cu–O distances within each dinu-
clear subunit are classified as type II.
Introduction
Polynuclear copper(II) complexes have attracted much
attention during recent decades owing to their interesting
architectures and potential applications in fields such as co-
ordination polymers,[1] magnetochemistry,[2] bioinorganic
chemistry,[3] and catalysis.[4] Among them, cubane-like
Cu4O4 complexes that contain hydroxo, alkoxo, or phenoxo
bridges are relatively common[5] and have been studied from
a magneto-structural point of view with experimental and
theoretical approaches.[6] Two classifications of Cu4O4 cub-
ane-like complexes have been proposed on the basis of their
structural features. Chronologically, the first one was sug-
gested by Mergehenn and Haase,[7] who classified these
compounds into two types (I and II), depending on the
The second one was proposed by Alvarez et al.[6] and
uses the Cu···Cu distances within the cubane unit to classify
the Cu4O4 complexes into three types (see Scheme 1): (i)
2+4, which is equivalent to type I and has two short and
four long Cu···Cu distances, (ii) 4+2, which contains four
short and two long Cu···Cu distances and when the sym-
metry is S4 would be equivalent to type II, and (iii) 6+0,
which contains six similar Cu···Cu distances.
[a] Department of Physics, Faculty of Science and Art, Balikesir
University,
10145 Balikesir, Turkey
E-mail: egungor@balikesir.edu.tr
http://w3.balikesir.edu.tr/~egungor
http://w3.balikesir.edu.tr/~hkara
[b] Departamento de Química Inorgánica, Universidad de
Granada,
18071 Granada, Spain
E-mail: ecolacio@ugr.es
Scheme 1. Structural types of Cu4O4 cubane complexes classified
according to the Cu···Cu distances. Short Cu···Cu distances (solid
lines), long Cu···Cu distances (hashed lines), short Cu–O bond
lengths (bold lines), and long Cu–O distances (dashed lines).
http://inorganica.ugr.es
http://www.ugr.es/local/mota
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201301515.
Eur. J. Inorg. Chem. 2014, 1552–1560
1552
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Although the analysis of the magneto-structural data for
Cu4O4 cubane complexes has allowed the understanding of
the main structural factors that govern the magnetic ex-
change coupling in this type of system,[6a] no simple mag-
neto-structural correlations could be established for them.
Moreover, there is a contradictory result for 4+2 type
complexes because the sign of the experimental magnetic
exchange coupling through the long Cu···Cu pathways is
generally opposite to that obtained from DFT calcula-
tions.[6a] Therefore, more examples of this type of complex
are needed, not only to clarify this point but also to support
previous results. In connection with this, we are reporting
here the synthesis, crystal structure, magnetic properties,
and DFT calculations of two new examples of ferromag-
netically coupled tetranuclear copper(II) complexes with
open cubane-like Cu4O4 core framework. Interestingly, for
these complexes, the sign and magnitude of the experimen-
tal magnetic coupling constants agree well with those pre-
dicted from DFT calculations for 4+2 Cu4O4-type com-
plexes.
Figure 2. ORTEP drawing of complex 2 with atom labeling. Ther-
mal ellipsoids have been drawn at 30% probability level (hydrogen
atoms are omitted for clarity).
Table 1. Crystal data and structure refinement compound 1 and 2.
1
2
Chemical formula
Mr
T
C68H100Cu4N4O8
1355.68
293(2)
C40H44Cu4N4O12
1026.95
100(2)
Results and Discussion
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
monoclinic
P21/c
24.6826(7)
15.1397(6)
19.6794(6)
90
95.160(3)
90
7324.1(4)
4
triclinic
P1
¯
Crystal Structure Description of 1 and 2
11.5022(4)
11.9664(4)
16.1999(6)
81.022(2)
71.223(2)
72.461(2)
2008.63(13)
2
The structures of 1 and 2 are illustrated in Figures 1 and
2. The crystallographic data, conditions used for the inten-
sity data collection, and some features of the structure re-
finement are listed in Table 1. Selected bond lengths and
angles are listed in Table 2.
γ [°]
V [Å3]
Z
ρcalcd. [gcm–1]
1.230
1.196
1.698
2.158
μ [mm–1]
Reflections collected 33530
34111
Independent reflec-
tions
17010
14193
Data/parameters
GoF on F2
R indices [IϾ2σ(I)]
5992/688
0.9
R1 = 0.0715,
wR2 = 0.2148
9250/545
1.02
R1 = 0.0325,
wR2 = 0.0755
In the main structural unit of 1 and 2, it is seen that the
Cu4O4 core consists of four alkoxo-bridged copper atoms
to give an approximately cubic array of alternating copper
and oxygen atoms that occupy the corners of the cube. All
copper(II) centers are pentacoordinate with an NO4 donor
set from the Schiff base ligands. For a pentacoordinate
metal center, the distortion of the coordination environ-
ment from trigonal bipyramidal (TBP) to square pyramidal
(SP) can be evaluated by the Addison distortion index (τ)
defined as τ = (α – β)/60, in which α and β are the two
largest coordination angles, and τ = 0 for perfect SP and 1
for ideal TBP.[23] The structural distortion indexes of Cu1,
Cu2, Cu3, and Cu4 atoms were found to be τCu1 = 0.0016,
Figure 1. ORTEP drawing of complex 1 with atom labeling. Ther-
mal ellipsoids have been drawn at 30% probability level (hydrogen
atoms are omitted for clarity).
The crystal structure of 1 has been reported previously τCu2 = 0.024, τCu3 = 0.027, and τCu4 = 0.016 for 1, and τCu1
at room temperature.[8] We report here a redetermination of = 0.024, τCu2 = 0.027, τCu3 = 0.015, and τCu4 = 0.024 for 2,
1 in detail. The precision of the unit-cell dimensions was respectively. Therefore, the coordination polyhedron of each
improved by an order of magnitude. The unit-cell volume copper(II) center is best described as distorted square py-
decreased by approximately 771.9 Å3 for 1.[8]
ramidal. The slight distortion in the basal plane may be
Eur. J. Inorg. Chem. 2014, 1552–1560
1553
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Table 2. Some selected bond lengths [Å] and angles [°] for 1 and 2. Magnetic Properties of Complexes 1 and 2
1
2
The temperature dependence of χMT (χM is the molar
magnetic susceptibility per Cu4 unit) for 1 and 2 in the
range 300–2 K and at an applied field of 1000 Oe is shown
in Figure 3.
Cu1–O1
Cu1–O2
Cu1–O5
Cu1–O7
Cu1–N1
Cu2–O2
Cu2–O3
Cu2–O4
Cu2–O5
Cu2–N2
Cu3–O5
Cu3–O6
Cu3–O7
Cu3–O4
Cu3–N3
Cu4–O4
1.868(4)
1.953(4)
1.939(4)
2.478(4)
1.907(4)
1.960(4)
1.905(4)
1.960(4)
2.401(4)
1.914(7)
1.968(4)
1.872(4)
1.967(4)
2.470(4)
1.925(6)
1.938(4)
1.960(4)
1.873(4)
2.506(4)
1.914(6)
105.450(1)
96.440(1)
91.005(1)
106.100(1)
88.450(1)
97.160(1)
88.890(1)
98.730(1)
107.920(1)
100.840(1)
91.310(1)
107.800(2)
1.913(1)
1.988(1)
1.963(2)
2.323(1)
1.932(2)
1.947(2)
1.902(1)
1.966(1)
2.575(1)
1.938(3)
1.966(1)
1.895(1)
1.999(2)
2.282(1)
1.933(2)
1.946(2)
1.956(1)
1.890(1)
2.600(1)
1.928(2)
109.500(9)
94.080(7)
89.130(7)
102.460(8)
89.950(7)
104.150(7)
87.310(7)
104.890(8)
108.430(9)
95.020(7)
92.260(8)
101.230(9)
Cu4–O7
Cu4–O8
Cu4–O2
Cu4–N4
Figure 3. Temperature dependence of χMT for 1 and 2.
Cu1–O2–Cu2
Cu1–O2–Cu4
Cu1–O5–Cu2
Cu1–O5–Cu3
Cu1–O7–Cu3
Cu1–O7–Cu4
Cu2–O2–Cu4
Cu2–O4–Cu3
Cu2–O4–Cu4
Cu2–O5–Cu3
Cu3–O4–Cu4
Cu3–O7–Cu4
The χMT value at room temperature for 1 and 2 (1.66
and 1.68 cm3 mol–1 K, respectively) is slightly higher than
that expected for four uncoupled Cu2+ ions (S = 1/2) with
g = 2.0 (1.50 cm3 mol–1 K). When the temperature is low-
ered, χMT steadily increases to reach a maximum at 8 K
(2.78 cm3 mol–1 K) for 1 and at 6 K (2.78 cm3 mol–1 K) for
2, respectively. Below the temperature of the maximum, the
χMT value decreases to 2 K to reach values of 2.25 and
3.01 cm3 mol–1 K for 1 and 2, respectively.
This behavior is due to a significant intratetranuclear fer-
romagnetic coupling between the copper(II) ions, which
leads to a S = 2 ground state. The decrease in χMT at low
temperatures suggests the existence of zero-field splitting ef-
fects (ZFS) of the S = 2 ground state and/or intermolecular
antiferromagnetic interactions.
Complexes 1 and 2, which exhibit an open cubane-like
Cu4O4 structure with four short and two long Cu···Cu dis-
tances (see Figure 4), belong to the 4+2 type. A close in-
spection of the structure of 1 and 2 reveals that their respec-
tive 4+2 Cu4O4 cubane units are rather asymmetric, so that
six different J values should be taken into account to ana-
lyze the magnetic data. However, to avoid overparametriz-
ation, we have assumed that the exchange coupling con-
stants between the copper(II) ions that involve short Cu··Cu
distances are equivalent and described by JЈ, whereas those
that involve long Cu··Cu distances are described by JЈЈ (see
Figure 4).
attributed to the strain imposed by the ligand to the metal
center during coordination.
Cu···Cu distances on different cubic faces of 1 and 2 are
also different; they vary from 3.058 to 3.378 Å, which are
quite comparable to those values of the similar tetramer
copper(II) complexes reported in the literature.[5d,6b,6c] The
basal plane of the square pyramid is constructed by the
phenolate oxygen atom, the imine nitrogen atom, and two
μ3-alkoxide oxygen atoms, whereas the apical position is oc-
cupied by another μ3-alkoxide oxygen atom. Cu1, Cu2, Cu3,
and Cu4 deviate from the NO3 basal planes by 0.062, 0.056,
0.060, and 0.069 Å for 1, and 0.142, 0.105, 0.108, and
0.091 Å for 2, respectively, towards the apical ligand atom.
The basal Cu–O and Cu–N bond lengths of 1 and 2 are
in the range 1.868(4)–1.999(2) Å and 1.907(4)–1.938(3) Å,
respectively, which lie well within the range of reported val-
ues for corresponding bond lengths of other copper(II) tet-
ranuclear cubane clusters.[5d,5s] The axial Cu–O bond
lengths are in the range 2.401(4)–2.506(4) Å for 1 and
2.282(18)–2.600(17) Å for 2. The elongated of the Cu–O ax-
ial bonds can be explained by Jahn–Teller distortions,
which is typical for copper(II) d9.
In keeping with the above considerations, the experimen-
tal magnetic susceptibility data for 1 and 2 were analyzed
by using the following two-J isotropic Hamiltonian
[Equation (1)].
H = –JЈ(SCu1SCu2 + SCu1SCu3 + SCu2SCu4 + SCu3SCu4) –
Finally, before proceeding to the magnetic characteriza-
tion, we note that the powder patterns for bulk microcrys-
talline samples of 1 and 2 were consistent with the exclusive
JЈЈ(SCu1SCu4 + SCu2SCu3
) (1)
This model implies that exchange interactions between
presence of the phase identified in the single-crystal experi- the CuII ions that belong to the short and long Cu··Cu dis-
ment (Figures S1 and S2 in the Supporting Information).
tances are averaged in each case. A zJ parameter was in-
Eur. J. Inorg. Chem. 2014, 1552–1560
1554
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
+28.7 cm–1, JЈЈ = +7.8 cm–1, g = 2.036, and zJ = –0.25 cm–1
for 1 and JЈ = +39.8 cm–1, JЈЈ = +10.2 cm–1, g = 2.025, and
zJ = –0.02 cm–1 for 2. It is worth mentioning that intermo-
lecular interactions and the ZFS effects of the ground state
have a similar effect on the magnetic properties at low tem-
perature and consequently are strongly correlated. There-
fore, the extracted zJ values can be considered the upper
limit for the intercubane interactions. The experimental JЈ
and JЈЈ coupling constants reported for 4+2 Cu4O4 cubane-
like complexes (Table 3) are ferromagnetic and antiferro-
magnetic, respectively, with only one exception along each
of the series of coupling constants.
Although the sign of JЈЈ determined for 1 and 2 seems
to be in contradiction with the reported experimental val-
ues, DFT calculations carried out by Alvarez et al. on mod-
els of 4+2 systems agree with our results as they always
found weakly ferromagnetic JЈЈ coupling constants, which
were practically independent of the geometry. To support
the experimental values of JЈ and JЈЈ for compounds 1 and
2 and to calculate the “remaining” possible J values for
these compounds (as indicated elsewhere, the Cu4O4 cubane
unit is rather asymmetric, with six different exchange path-
ways), DFT calculations were carried out on the X-ray
structures as found in the solid state. The calculated J val-
ues for 1 and 2 are given in Scheme 2.
The values of JЈmean (average value of the calculated J1,
J2, J5, and J6 calculated exchange coupling constant) and
JЈЈmean (average value of the calculated J3 and J4) are
respectively +30.2 and +4.45 cm–1 for 1 and +36 and
+6.8 cm–1 for 2 (see Scheme 2). The sign and relative magni-
Figure 4. (a) A view of the Cu4O4 core of 1 and 2 with (b) the
exchange coupling pattern.
cluded to account for intercubane magnetic interactions by tude of these interactions are in good accord with the exper-
using the molecular-field approximation, and an average g imental results, which indicate that JЈ and JЈЈ are both fer-
value was assumed for the whole Cu4O4 unit. The Hamilto- romagnetic and larger for 2 than for 1. Moreover, as ex-
nian was numerically diagonalized using the MAGPACK pected, JЈЈ is weakly ferromagnetic and much weaker than
program.[24] The best-fit parameters were as follows: JЈ = JЈ.
Table 3. Structural and magnetic data for 1, 2, and a series of related compounds.
Complex
Class
Cu···Cu [Å]
Cu–O [Å]
Cu–O–Cu [°]
J [cm–1]
Ref.
[{Cu(H2L1)}4]
4+2
4+2
4+2
4+2
4+2
4+2
4+2
4+2
4+2
4+2
4+2
4+2
4+2
4+2
4+2
4+2
4+2
3.114–3.378
3.058–3.384
3.108–3.615
3.129–3.307
3.229–3.486
3.021–3.492
3.070–3.419
3.103–3.458
3.114–3.415
3.124–3.512
3.176–3.523
2.961–3.333
3.127–3.503
3.095–3.413
3.108–3.615
3.150–3.410
3.293–3.315
1.868–1.968
1.890–1.999
1.930–2.00
1.934–2.010
1.934–1.971
1.920–1.970
1.950–1.990
1.930–1.970
1.900–1.970
1.960–2.00
1.920–1.980
1.894–1.907
1.928–2.099
1.886–1.984
1.894–2.000
1.920–1.990
1.967–1.980
88.45–107.97
89.95–109.50
85.80–106.10
86.20–112.10
86.20–112.10
87.30–109.80
88.30–104.00
88.80–105.80
88.80–107.70
88.80–104.40
88.80–108.80
97.10–101.0
100.0–107.0
102.00–109.40
104.80–106.10
108.00–110.10
113.06
+28.7, +7.8
+ 39.8, +10.2
+72, –35.2
–6.40, –10.90
+13.60, –34.90
+41, –19.80
+33.30, –15.60
+14.70, –18.40
+15.20, –9.40
+57, –14
+80, –9
+2.16, –103.40
+1, –65
+33, –15.80
+36, –17.60
+89.80, –32.60
–37.46, –2.45
this work
[{Cu(H2L2)}4]
this work
[Cu4(hsae)4]·2H2O·4MeCN[a]
[Cu4(dpd-H)4(ClO4)2(H2O)2]2
[5m]
[b]
[5o]
[5v]
[5n]
[5s]
[5s]
[5u]
[5t]
[5j]
[Cu4(L1)4]·Na·ClO4
[c]
[Cu4(MeCOCHCMe=NCH2CHO)4]
[Cu4(L2)2(OMe)2]·2H2O·THF[d]
[Cu4(L2)2(OH)2]·6H2O[d]
[Cu4(L3)4][e]
[Cu4(L4)4]·9MeOH[f]
[Cu4Br4(CH2CH2NEt2)4]·4CCl4
[Cu4(L5)4]4H2O[g]
[5b]
[5y]
[5d]
[5k]
[5c]
[5z]
[Cu4(NH3)4(HL6)4][CdBr4]Br2·3dmf·H2O[h]
[Cu4(L7)4]·5CH3OH·H2O[i]
[Cu4(hsae)4]·2H2O·4CH3CN[a]
[Cu4(hpda)4](ClO4)4·H2O[j]
[Cu4(HL8)4]DMF[k]
[a] H2hsae: 2-(4-hydroxysalicylideneamino)-1-ethanol. [b] dpd-H: the hydrated gem-diol form [(C5H4N)2CO(OH), dpd-H] of di-2-pyr-
idylketone. [c] H2L1: NЈ-(2-hydroxy-3-methoxybenzylidene)benzohydrazide. [d] H2L2: N,NЈ-(2-hydroxypropane-1,3-diyl)bis(salicylald-
imine). [e] H2L3: ethyl 2-[N-(2-hydroxycyclohexyl)aminomethylene]-3-oxobutanoate. [f] H2L4: Schiff base of pyridoxal and 2-amino-1-
phenylpropan-1-ol. [g] H2L5: 2-(3-methoxysalicylideneamino)benzyl alcohol. [h] H2L6: Schiff base of cadmium oxide in the air-exposed
solution of ammonium bromide and diethanolamine in dimethylformamide (dmf). [i] H2L7: 2-(5-fluorosalicylideneamino)ethanol.
[j] H2hpda: N-(2-hydroxyethyl)-1,3-propanediamine. [k] H3L8 = NЈ-(2-hydroxy-3-methoxybenzylidene)-2-hydroxybenzohydrazide.
Eur. J. Inorg. Chem. 2014, 1552–1560
1555
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Scheme 2. Calculated Ji values inside the Cu4O4 unit as found in the crystal structures of complexes 1 and 2.
It should be noted at this point that both experimental[25] copper atom). This disposition of the Cu–O–Cu bridge
and theoretical[25h,25i,6a,26] studies have shown that the leads to a very small overlap between the magnetic orbitals
major factor that controls the magnetic exchange interac- and, consequently, very weak ferromagnetic or antiferro-
tion in hydroxo- and alkoxo-bridged polynuclear copper(II) magnetic interactions are experimentally observed. There-
complexes is the value of the Cu–O–Cu angle (θ), and an fore, only the equatorial–equatorial Cu–O–Cu bridge will
almost linear variation of J with θ has been established for be operative in transmitting the exchange interaction, with
dinuclear complexes, the crossing point between antiferro- its sign and magnitude mainly depending on the θ and τ
magnetic and ferromagnetic interactions being located at angles. These short Cu–O–Cu exchange pathways have θ
approximately 98°.[25a] DFT calculations carried out on di- angles in the ranges 105.45–107.92° (average value 106.81°)
hydroxo- and dialkoxo-bridged model structures that con- and 101.20–109.50° (average value 105.4°) and average τ
tain a planar Cu2(μ-O2) skeleton predicted antiferromag- angles of 45.4 and 46.3° for 1 and 2, respectively. Although
netic interactions for Cu–O–Cu angles (θ) larger than 92° the experimental magneto-structural correlations for dialk-
when the τ angle (out-of-plane displacement of the carbon oxo-bridged dinuclear copper(II) complexes[25] predict weak
atom bonded to the oxygen bridging atom from the Cu2O2 to medium antiferromagnetic interactions for the θ and τ
plane) was zero. Dihydroxo and dialkoxo complexes exhib- angles observed for 1 and 2 (the effects of θ and τ are not
ited antiferromagnetic interactions for the whole range of complementary as the large θ values favor antiferromag-
the Cu–O–Cu angle (θ) when the τ angles were smaller than netic interactions, whereas the large τ values favor ferro-
40°.[26c,26d] Moreover, a correlation was established between magnetic interactions); however, the calculated and experi-
θ and τ, which showed that small values of θ are associated mental J1 values, as indicated above, are ferromagnetic. As
with the largest values of τ. Therefore, the AF coupling is was shown by Alvarez et al. from DFT calculations,[6a] this
favored when θ increases and τ diminishes.
discrepancy can be explained by the presence of chelate li-
The calculated and experimental JЈ and JЈЈ values for 1 gands attached to the alkoxo bridge, which could introduce
and 2, as well as the difference between them, can be justi- an additional exchange pathway between the copper(II)
fied on the basis of the above magneto-structural corre- atoms. These additional pathways would ultimately be re-
lations and the overlap between the magnetic orbitals along sponsible for the overall ferromagnetic interactions ob-
the magnetic exchange pathways. Within the Cu4O4 cubane served for 1 and 2.
unit, each Cu(O)2Cu bridging fragment with short Cu···Cu
The calculated J1–J6 coupling constants for 1 and 2 (see
distances in the ranges 3.114–3.174 and 3.058–3.174 Å for Scheme 2) are in line with that predicted for the above mag-
1 and 2, respectively, exhibits two different Cu–O–Cu brid- neto-structural correlations. For 1, the larger J values corre-
ges: one that connects equatorial positions on the neigh- spond to the short exchange pathways Cu1–O2–Cu2 and
boring square-pyramidal copper(II) atoms with Cu–O dis- Cu1–O5–Cu3, which are described by J1 and J2, respec-
tances of approximately 1.95 Å, and the other one linking tively, and have the smaller θ (105.45 and 106.10°, respec-
equatorial and apical positions on neighboring copper(II) tively) and larger τ (46.1 and 45.01°, respectively) angles.
atoms, with Cu–Oapical distances in the ranges 2.401–2.506 The short exchange pathways Cu3–O7–Cu4 and Cu2–O4–
and 2.282–2.600 Å, for 1 and 2, respectively (see dotted Cu4, which are described by J6 and J5, respectively, have
lines in Figure 4). The latter type of Cu–O–Cu bridge in- larger θ (107.80 and 107.92°, respectively) and smaller τ
volves one apical position on the square-pyramidal coordi- angles (44.16 and 44.99°, respectively) than the exchange
nation sphere of the copper atom, in which the density of pathways described by J1 and J2. The increase in θ and the
the unpaired electron is very small (the unpaired electron is decrease in τ favor the antiferromagnetic contribution to
located in the dx2–y2 orbital, which lies in the basal plane the magnetic coupling, thus reducing the global ferromag-
and is directed toward the ligand atoms coordinated to the netic interaction (mean J value of 37.05 cm–1 for the ex-
Eur. J. Inorg. Chem. 2014, 1552–1560
1556
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
change pathways described by J1 and J2 and 23.4 cm–1 for differences in the Schiff base ligands. Thus, complex 2,
those described by J6 and J5). In the case of 2, the larger J which shows smaller θ and bigger τ values than 1, presents
values are found for the short Cu1–O5–Cu3 and Cu3–O7– a larger JЈ value, as expected from the experimental and
Cu4 exchange pathways, which are described by J2 and J6, calculated magneto-structural correlation for alkoxo-
respectively, and characterized by the smaller θ (102.46 and bridged dinuclear copper(II) complexes.[6a,25,26]
101.23°) and larger τ angles (51.5 and 49.3°). The other two
The spin-density distribution for 1 and 2 (the spin den-
short exchange pathways in 2, Cu1–O2–Cu2 and Cu2–O4– sity of 1 is given as an example in Figure 5, whereas that of
Cu4, which are described by J1 and J5, respectively, have 2 is given in the Supporting Information) clearly shows that
larger θ (109.5 and 108.42°, respectively) and smaller τ the spin density of the copper(II) atoms has the shape of a
angles (40.1 and 44.5°, respectively) than the Cu1–O5–Cu3 dx2–y2 orbital and it is σ delocalized on the donor atoms
and Cu3–O7–Cu4 exchange pathways and consequently ex- directly attached to the metal. As expected, the delocaliza-
hibit smaller J values (mean J value of 50.95 cm–1 for the tion is more important for the atoms directly bound to the
exchange pathways described by J2 and J6 and 21.05 cm–1 CuII atoms. Moreover, the spin density is mainly found at
for those described by J1 and J5). The difference between the metal, as expected if they are the magnetic centres (see
the two couples of mean J values corresponding to the Table 4).
short Cu–O–Cu exchange pathways in 1 and 2 are bigger
for the latter (29.9 cm–1 vs. 13.6 cm–1) because it also exhib-
Table 4. Selected values of the spin density for complexes 1 and 2.
its a larger difference between the corresponding mean val-
ues of the θ angle (108.96 and 101.84° for 2 and 105.77 and
107.86° for 1).
The Cu(O)2Cu bridging fragments with long Cu···Cu dis- Cu3
tances (Cu2–O4–Cu3 and Cu1–O7–Cu4) contain two equa-
torial-axial bridges and therefore weak ferromagnetic or
antiferromagnetic interactions little dependent on the geo-
metrical factors, are expected. The experimental and calcu-
lated weak ferromagnetic interactions extracted for 1 and 2
agree with this prediction and match well in sign and mag-
nitude with those calculated by other authors.[6a]
1
2
Cu1
Cu2
0.6222
0.6273
0.6327
0.6256
0.1570
0.1620
0.1564
0.1600
0.0919
0.0931
0.0974
0.0930
0.1104
0.1091
0.1116
0.1133
0.6311
0.6254
0.6306
0.6193
0.1757
0.1540
0.1655
0.1568
0.0979
0.0938
0.0958
0.0967
0.1064
0.1077
0.1070
0.1118
Cu4
O1alcoholate
[a]
O2alcoholate
O3alcoholate
O4alcoholate
O1phenolate
O2phenolate
O3phenolate
O4phenolate
N1
It is worth noting that the ligands used for preparing 1
and 2 are very similar, with both being NO2 tridentate che- N2
late bridging Schiff bases. Therefore, the differences be-
tween the JЈ values observed for 1 and 2 should mainly
N3
N4
[a] The labels 1–4 for oxygen and nitrogen refer to the atom that
belongs to the ligand coordinating the corresponding copper atom
(1–4).
arise from their differences in θ and τ angles rather than to
Conclusion
Two new Cu4O4 cubane-like complexes were prepared
from two closely related NO2 chelate tridentate bridging
Schiff base ligands. Experimental magnetic studies showed
that complexes 1 and 2 exhibit dominant ferromagnetic
coupling. Complexes 1 and 2 exhibit a rather distorted open
cubane-like Cu4O4 structure with four short and two long
Cu···Cu distances and therefore belong to the 4+2 type. Al-
though six different J values should be taken into account
to analyze the magnetic data, we have assumed that the
exchange coupling constants between the copper(II) ions
that involve short Cu···Cu distances are equivalent and de-
scribed by JЈ, whereas those which involve long Cu···Cu
distances are described by JЈЈ. The values of the magnetic
exchange coupling constant extracted from the experimen-
tal susceptibility data were as follows: JЈ = +28.7 cm–1, JЈЈ
= +7.8 cm–1 for 1, and JЈ = +39.8 cm–1, JЈЈ = +10.2 cm–1
for 2. DFT calculations on the structures of 1 and 2 as
found in the solid state afforded J values that agree well
with the experimental ones. Moreover, the six calculated J
Figure 5. View of the calculated spin-density distribution for the
quintuplet state of 1. Gray shapes correspond to positive spin
densities. The isodensity surface corresponds to a cutoff value of
0.0015 ebohr–3.
Eur. J. Inorg. Chem. 2014, 1552–1560
1557
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
X-ray Structural Determination: Diffraction measurements were
carried out with an Oxford Diffraction Xcalibur3 diffractometer at
293 K for 1 and with a Bruker Apex II Kappa CCD diffractometer
at 100 K for 2 by using graphite-monochromated Mo-Kα radiation
(λ = 0.71073 Å). The intensity data were integrated using the AP-
EXII program.[9] Absorption corrections were applied on the basis
of equivalent reflections using SADABS.[10] The structures were
solved by direct methods and refined using full-matrix least-squares
against F2 using SHELXL.[11] All non-hydrogen atoms were as-
signed anisotropic displacement parameters and refined without
coupling constants for the Cu4O4 unit in 1 and 2 follow
the trend predicted by the magneto-structural correlations
previously established for dialkoxo-bridged dicopper(II)
complexes (the ferromagnetic interaction decreases with the
increase in the Cu–O–Cu bridging angle (θ) and with the
decrease in the τ angle that describes the out-of-plane dis-
placement of the carbon atom bonded to the oxygen bridg-
ing atom from the Cu2O2 plane). To the best of our knowl-
edge, complexes 1 and 2 are the first examples of 4+2
Cu4O4 complexes in which both coupling constants (JЈ and positional constraints. Hydrogen atoms were included in idealized
positions with isotropic displacement parameters constrained to 1.5
times the Uequiv of their attached carbon atoms for methyl hydrogen
atoms, and 1.2 times the Uequiv of their attached carbon atoms for
all others. A possible disorder in the ethanolamine portion of the
ligand and one methoxy group of 1 has been considered. However,
the nineteen carbon atoms of methoxy groups were refined iso-
tropically owing to their high thermal motion.
JЈЈ) are ferromagnetic, and thus in good agreement with
previous DFT calculations that predicted a positive sign for
JЈЈ.
Experimental Section
Physical Measurements: All chemical reagents and solvents were
purchased from Merck or Aldrich and used without further purifi-
cation. Elemental (C, H, N) analyses were carried out by standard
methods with a LECO, CHNS-932 analyzer. FTIR spectra were
measured with a Perkin–Elmer Model Bx 1600 instrument with the
samples as KBr pellets in the 4000–400 cm–1 range. The tempera-
ture dependence of the magnetic susceptibility of polycrystalline
samples was measured between 2 and 300 K at a field of 1.0 T
using a Quantum Design model MPMS computer-controlled
SQUID magnetometer. The synthetic route of the ligand and com-
plexes are outlined in Scheme 3.
Powder X-ray measurements were performed using Cu-Kα radia-
tion (λ = 1.5418 Å) with a Bruker-AXS D8-Avance diffractometer
equipped with a secondary monochromator. The data were col-
lected in the range 5° Ͻ 2θ Ͻ 50° in θ–θ mode with a step time of
n s (5 s Ͻ n Ͻ 10 s) and a step width of 0.03°.
Computational Details: All theoretical calculations were carried out
at the DFT level of theory using the hybrid B3LYP exchange-corre-
lation functional,[12–14] as implemented in the Gaussian 03 pro-
gram.[15] A quadratic convergence method was employed in the
self-consistent field (SCF) process.[16] The triple-ξ quality basis set
proposed by Ahlrichs and co-workers has been used for all
atoms.[17] Calculations were performed on the complexes built from
the experimental geometries. The electronic configurations used as
starting points were created using the Jaguar 7.6 software.[18] The
approach used to determine the exchange coupling constants for
polynuclear complexes has been described in detail elsewhere.[19–22]
To calculate nJi exchange coupling constants of a polynuclear com-
plex, we must perform at least n + 1 energy calculations of different
spin configurations that correspond to single-determinant Kohn–
Sham solutions.[21] Therefore, seven calculations are necessary for
complex 1 to obtain the values of five exchange coupling constants
(see Table 3). However, additional electronic configurations have
been calculated to verify possible errors or shortcomings in the
computational procedure. The values of the Ji constants were ob-
tained by a fit-process from the energy found for the chosen spin
configurations.
Scheme 3. The ligands H2L1 and H2L2 used in this study.
Synthesis of H2L1 and H2L2 Ligands: The tridentate Schiff base
ligand H2L1 was synthesized from 3,5-di-tert-butyl-2-hydroxybenz-
aldehyde and ethanolamine in a 1:1 molar ratio in hot methanol
according to the method reported previously.[8] H2L2 was prepared
in a similar way by using 2-hydroxy-4-methoxybenzaldehyde in hot
methanol. The ligands H2L1 and H2L2 evaluated in this study are
outlined in Scheme 3. For H2L1: Yellow crystals, yield 80%.
C17H27O2N (277.40): calcd. C 73.60, H 9.81, N 5.04; found C
72.25, H 9.02, N 5.12. For H2L2: Brown crystals, yield 80%.
C10H13O3N (195.21): calcd. C 61.52, H 6.71, N 7.17; found C
60.23, H 6.17, N 6.98.
CCDC-826612 (for 1) and -826610 (for 2) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.”
Synthesis of Complex 1 and 2: Complexes 1 and 2 were prepared
by the addition of copper(II) acetate monohydrate (0.199 g,
1 mmol) in hot methanol (20 cm3) to the appropriate ligand (H2L1
and H2L2) (1 mmol) in hot methanol (30 cm3). Triethylamine
(Et3N; 1 mmol) was then added to the resulting solution. The mix-
ture was warmed to 65 °C and stirred for 15 min. A green solution
was obtained, which was allowed to stand at room temperature for
several weeks to afford green crystals. Complex 1: Green crystals,
yield 75%. C68H100Cu4N4O8 (1355.68): calcd. C 60.24, H 7.43, N
Supporting Information (see footnote on the first page of this arti-
cle): Powder XRD patterns for 1 and 2, and view of the calculated
spin-density distribution for the quintuplet state of 2. Also includes
the relationships derived from the difference between the energy of
the HS state and that of the BS states, from which the Ji parameters
can be calculated, and the spin-density distribution for complex 2.
Acknowledgments
4.13; found C 60.20, H 7.52, N 4.18. IR (KBr): ν = 3306, 2956,
˜
2870, 2380, 1645, 1449, 1115, 535, 475 cm–1. Complex 2: Green
The authors are grateful to the Research Funds of Balikesir Uni-
versity (grant number BAP-2010/33) and The Scientific and Tech-
crystals, yield 75%. C40H44Cu4N4O12 (1026.95): calcd. C 46.78, H
˙
4.32, N 5.46; found C 46.12, H 4.34, N 5.10. IR (KBr): ν = 3053,
nological Research Council of Turkey (TUBITAK) (grant number
˜
2922, 2830, 2361, 1648, 1595, 1240, 579, 485 cm–1.
TBAG-108T431) for the financial support. H. K. thanks the Nato-
Eur. J. Inorg. Chem. 2014, 1552–1560
1558
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
Z. Anorg. Allg. Chem. 2007, 633, 351–353; h) C. Maxim, T. D.
Pasatoiu, V. C. Kravtsov, S. Shova, C. A. Muryn, R. E. P. Win-
penny, F. Tuna, M. Andruh, Inorg. Chim. Acta 2008, 361,
3903–3911; i) L. Merz, W. Haase, J. Chem. Soc., Dalton Trans.
1978, 11, 1594–1598; j) R. Mergehenn, L. Merz, W. Haase, J.
Chem. Soc., Dalton Trans. 1980, 17, 1703–1709; k) M. Nihei,
N. Hoshino, T. Ito, H. Oshio, Polyhedron 2003, 22, 2359–2362;
l) H. Oshio, Y. Saito, T. Ito, Angew. Chem. 1997, 109, 2789–
2791; m) H. Oshio, Y. Saito, T. Ito, Angew. Chem. 1997, 109,
2789; Angew. Chem. Int. Ed. Engl. 1997, 36, 2673–2675; n) L.
Walz, H. Paulus, W. Haase, J. Chem. Soc., Dalton Trans. 1983,
657–664; o) Y. M. Li, J. J. Zhang, R. B. Fu, S. C. Xiang, T. L.
Sheng, D. Q. Yuan, X. H. Huang, X. T. Wu, Polyhedron 2006,
25, 1618–1624; p) L. Schwabe, W. Haase, J. Chem. Soc., Dalton
Trans. 1985, 1909–1913; q) N. Matsumoto, I. Ueda, Y. Nishida,
S. Kida, Bull. Chem. Soc. Jpn. 1976, 49, 1308–1312; r) A. Mu-
kherjee, R. Raghunathan, M. K. Saha, M. Nethaji, S. Ramase-
sha, A. R. Chakravarty, Chem. Eur. J. 2005, 11, 3087–3096; s)
H. Astheimer, F. Nepveu, L. Walz, W. Haase, J. Chem. Soc.,
Dalton Trans. 1985, 315–320; t) R. Wegner, M. Gottschaldt, H.
Görls, E. G. Jager, D. Klemm, Chem. Eur. J. 2001, 7, 2143–
2157; u) J. Chakraborty, S. Thakurta, G. Pilet, D. Luneau, S.
Mitra, Polyhedron 2009, 28, 819–825; v) E. A. Buvaylo, V. N.
Kokozay, O. Y. Vassilyeva, B. W. Skelton, J. Jezierska, L. C.
Bruneland, A. Ozarowski, Inorg. Chem. 2005, 44, 206–216; w)
M. L. Liu, J. M. Dou, J. Z. Cui, D. C. Li, D. Q. Wang, J. Mol.
Struct. 2012, 1011, 140–144.
a) E. Ruiz, S. Alvarez, A. Rodríguez-Fortea, P. Alemany, J.
Mater. Chem. 2006, 16, 2729–2735; b) E. Ruiz, S. Alvarez, A.
Rodríguez-Fortea, P. Alemany, Y. Pouillon, C. Massobrio, J. S.
Miller, M. Drillon Eds (Eds.), Electronic Structure and Mag-
netic Behavior in Polynuclear Transition-Metal Compounds, vol.
2, Wiley-VCH, Weinheim, Germany, 2001; c) E. Ruiz, A.
Rodríguez-Fortea, P. Alemany, S. Alvarez, Polyhedron 2001, 20,
1323–1327.
R. Mergehenn, W. Haase, Acta Crystallogr., Sect. B 1977, 33,
1877–1882.
S. Jammi, T. Punniyamurth, Eur. J. Inorg. Chem. 2009, 2508–
2511.
B1-TUBITAK for funding and Prof. Guy Orpen (School of Chem-
istry, University of Bristol, UK) for his hospitality. The authors are
also very grateful to Dr. Yasemin Yahsi (The University of Balike-
sir) for the X-ray measurement, and Dr. Lorenzo Sorace and Dr.
Andrea Caneschi (Department of Chemistry, University of Flor-
ence) for SQUID measurements. E. C. and A. M. offer their thanks
to the Spanish Ministerio de Economía y Competitividad (MI-
NECO) (project number CTQ-2011-24478/BQU), the Junta de An-
dalucía, and the University of Granada for financial support. The
authors would also like to thank the Centro de Supercomputación
de la Universidad de Granada for computational resources.
[1] a) G. R. Newkome, E. He, C. N. Moorefield, Chem. Rev. 1999,
99, 1689–1746; b) S. Leininger, B. Olenyuk, P. J. Stang, Chem.
Rev. 2000, 100, 853–907; c) J. Y. Lu, Coord. Chem. Rev. 2003,
246, 327–347; d) A. Y. Robin, K. M. Fromm, Coord. Chem.
Rev. 2006, 250, 2127–2157; e) C. J. Adams, M. A. Kurawa, M.
Lusi, A. G. Orpen, CrystEngComm 2008, 10, 1790–1795; f) M.
Chang, M. Chung, B. S. Lee, C. H. Kwak, J. Nanosci. Nano-
technol. 2006, 6, 3338–3342; g) S. G. Kang, H. Kim, S. Bang,
Inorg. Chim. Acta 2013, 396, 10–13.
[2] a) O. Kahn, Molecular Magnetism, VCH Publishers, New
York, 1993; b) O. Kahn, Acc. Chem. Res. 2000, 33, 647–657; c)
E. Coronado, P. Day, Chem. Rev. 2004, 104, 5419–5448; d) Z.
Lu, T. Fan, W. Guo, J. Lu, C. Fan, Inorg. Chim. Acta 2013,
400, 191–196; e) C. M. Liu, R. G. Xiong, D. Q. Zhang, D. B.
Zhu, J. Am. Chem. Soc. 2010, 132, 4044–4045; f) G. Karotsis,
S. Kenedy, S. J. Teat, C. M. Beavers, D. A. Fowler, J. J. Morales,
M. Evangelisti, S. J. Dalgarno, E. K. Brechin, J. Am. Chem.
Soc. 2010, 132, 12983–12990; g) J. Zhang, P. Teo, R. Pattacini,
A. Kermagoret, R. Welter, G. Rogez, T. S. A. Hor, P.
Braunstein, Angew. Chem. 2010, 122, 4545; Angew. Chem. Int.
Ed. 2010, 49, 4443–4446; h) E. Gungor, H. Kara, Inorg. Chim.
Acta 2012, 384, 137–142; i) M. F. Haddow, H. Kara, G. R.
Owen, Inorg. Chim. Acta 2009, 362, 3502–3506; j) Y. Elerman,
H. Kara, A. Z. Elmali, Naturforsch. Teil A 2003, 58, 363–372.
[3] a) R. Huber, Angew. Chem. 1989, 101, 849; Angew. Chem. Int.
Ed. Engl. 1989, 28, 848–869; b) E. I. Solomon, U. M. Sunda-
ram, T. E. Machonkin, Chem. Rev. 1996, 96, 2563–2606; c) P.
Gamez, P. G. Aubel, W. L. Driessen, J. Reedijk, Chem. Soc.
Rev. 2001, 30, 376–385; d) E. I. Solomon, R. K. Szilagyi, S.
DeBeer George, L. Basumallick, Chem. Rev. 2004, 104, 419–
458; e) G. Henkel, B. Krebs, Chem. Rev. 2004, 104, 801–824; f)
Y. Zhao, T. Gong, Z. Yu, S. Zhu, W. He, T. Ni, Z. Guo, Inorg.
Chim. Acta 2013, 399, 112–118; g) L. Tjioe, A. Meininger, T.
Joshi, L. Spiccia, B. Graham, Inorg. Chem. 2011, 50, 4327–
4339; h) S. S. Bhat, A. A. Kumbhar, H. Heptullah, A. A. Khan,
V. V. Gobre, S. P. Gejji, V. G. Puranik, Inorg. Chem. 2011, 50,
545–558.
[4] a) R. Wegner, M. Gottschaldt, H. Görls, E. Jäger, D. Klemm,
Chem. Eur. J. 2001, 7, 2143–2157; b) M. M. Dıaz-Requejo, P. J.
Pérez, Chem. Rev. 2008, 108, 3379–3394; c) A. M. Kirillov,
M. V. Kirillova, A. J. L. Pombeiro, Coord. Chem. Rev. 2012,
256, 2741–2759; d) S. Löw, J. Becker, C. Würtele, A. Miska, C.
Kleeberg, U. Behrens, O. Walter, S. Schindler, Chem. Eur. J.
2013, 19, 5342–5351; e) E. Safaei, A. Wojtczak, E. Bill, H.
Hamidi, Polyhedron 2010, 29, 2769–2775; f) E. Safaei, M. M.
Kabir, A. Wojtczak, Z. Jaglicic, A. Kozakiewicz, Y. I. Lee, In-
org. Chim. Acta 2011, 366, 275–282.
[5] a) H. H. Monfared, J. Sanchiz, Z. Kalantari, C. Janiak, Inorg.
Chim. Acta 2009, 362, 3791–3795; b) J. W. Lu, Y. H. Huang, S.
Lo, H. H. Wei, Inorg. Chem. Commun. 2007, 10, 1210–1213; c)
X. S. Tan, Y. Fujii, R. Nukada, M. Mikuriyaand, Y. Nakano,
J. Chem. Soc., Dalton Trans. 1999, 2415–2416; d) X. F. Yan, J.
Pan, S. R. Li, H. Zhou, Z. Q. Pan, Z. Anorg. Allg. Chem. 2009,
635, 1481–1484; e) A. Burkhardt, E. T. Spielberg, H. Görlsand,
W. Plass, Inorg. Chem. 2008, 47, 2485–2493; f) Y. Xie, H. Jiang,
A. S.-C. Chan, Q. Liu, X. Xu, C. Dud, Y. Zhu, Inorg. Chim.
Acta 2002, 333, 138–143; g) V. T. Yilmaz, V. Kars, C. Kazak,
[6]
[7]
[8]
[9]
SAINT, v. 760A, Bruker-AXS, Inc., Madison, Wisconsin,
USA, 2002.
G. M. Sheldrick, SADABS, v. 2008/1, University of Göttingen,
Germany, 2003.
G. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
A. D. Becke, Phys. Rev. A 1988, 38, 3098–3100.
[10]
[11]
[12]
[13]
[14]
[15]
C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785–789.
A. D. Becke, J. Chem. Phys. 1993, 98, 5648–5652.
M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
M. A. Robb, J. R. Cheeseman, J. J. A. Montgomery, T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tom-
asi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani, N. Rega,
G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratch-
ian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gom-
perts, R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C.
Pomelli, J. W. Ochterski, P. Y. Ayala, K. Morokuma, G. A.
Voth, P. Salvador, J. J. Dannenberg, V. G. Zakrzewski, S. Dap-
prich, A. D. Daniels, M. C. Strain, O. Farkas, D. K. Malick,
A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q.
Cui, A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov,
G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. L. Martin,
D. J. Fox, T. Keith, M. A. Al–Laham, C. Y. Peng, A. Nanayak-
kara, M. Challacombe, P. M. W. Gill, B. Johnson, W. Chen,
M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian 03, revision
C02, Gaussian Inc, Wallingford CT, 2004.
[16]
[17]
G. B. Bacskay, Chem. Phys. 1981, 61, 385–404.
A. Schäfer, C. Huber, R. Ahlrichs, J. Chem. Phys. 1994, 100,
5829–5835.
[18]
Jaguar 76, Schrödinger, Inc., Portland OR, 2009.
Eur. J. Inorg. Chem. 2014, 1552–1560
1559
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
[19] E. Ruiz, J. Cano, S. Alvarez, P. Alemany, J. Comput. Chem.
1999, 20, 1391–1400.
[20] E. Ruiz, S. Alvarez, A. Rodríguez-Fortea, P. Alemany, Y. Pouil-
lon, C. Massobrio, Magn. Mol. Mater. II 2001, 227–279.
[21] E. Ruiz, A. Rodríguez-Fortea, J. Cano, S. Alvarez, P. Alemany,
J. Comput. Chem. 2003, 24, 982–989.
edes da Silva, J. Sanchiz, M. N. Kopylovich, A. J. L. Pombeiro,
Inorg. Chem. 2008, 47, 162–175; g) L. J. Farrugia, D. S. Mid-
dlemiss, R. Sillanpää, P. Seppälä, J. Phys. Chem. A 2008, 112,
9050–967; h) P. Seppälä, E. Colacio, A. J. Mota, R. Sillanpää,
Inorg. Chim. Acta 2010, 363, 755–762; i) P. Seppälä, E. Colacio,
A. J. Mota, R. Sillanpää, Dalton Trans. 2012, 41, 2648–2658.
[22] E. Ruiz, S. Alvarez, J. Cano, V. Polo, J. Chem. Phys. 2005, 123,
164110/1–164140/7.
[23] A. W. Addison, T. N. Rao, J. Reedijk, J. Van Rijn, G. C. Ver-
schoor, J. Chem. Soc., Dalton Trans. 1984, 1349–1356.
[24] J. J. Borrás-Almenar, J. M. Clemente-Juan, E. Coronado, B. S.
Tsukerblat, J. Comput. Chem. 2001, 22, 985–991.
[25] a) V. H. Crawford, H. W. Richardson, J. R. Wasson, D. J.
Hodgson, W. E. Hatfield, Inorg. Chem. 1976, 15, 2107–2110; b)
L. Merz, W. Haase, J. Chem. Soc., Dalton Trans. 1980, 875–
879; c) L. Walz, H. Paulus, W. Haase, J. Chem. Soc., Dalton
Trans. 1985, 913–920; d) L. Walz, W. Haase, J. Chem. Soc.,
Dalton Trans. 1985, 1243–1248; e) T. Lindgren, R. Sillanpää,
K. Rissanen, L. K. Thompson, C. J. O’Connor, G. A.
Van Albada, J. Reedijk, Inorg. Chim. Acta 1990, 171, 95–102;
f) A. M. Kirillov, Y. Y. Karabach, M. Haukka, M. F. C. Gu-
[26]
See, for example: a) H. Astheimer, W. Haase, J. Chem. Phys.
1986, 85, 1427–1432; b) M. Handa, N. Koga, S. Kida, Bull.
Chem. Soc. Jpn. 1988, 61, 3853–3857; c) E. Ruiz, P. Alemany,
S. Alvarez, J. Cano, J. Am. Chem. Soc. 1997, 119, 1297–1303;
d) E. Ruiz, P. Alemany, S. Alvarez, J. Cano, Inorg. Chem. 1997,
36, 3683–3688; e) H. Hu, D. Zhang, Z. Chen, C. Liu, Chem.
Phys. Lett. 2000, 329, 255–260; f) H. Hu, Y. Liu, D. Zhang, C.
Liu, THEOCHEM 2001, 546, 73–78; g) H. Hu, X. Yang, Z.
Chen, THEOCHEM 2002, 618, 41–46; h) A. Rodríguez-
Fortea, E. Ruiz, P. Alemany, S. Alvarez, Monatsh. Chem. 2003,
134, 307–316; i) C. J. Calzado, D. Maynau, J. Chem. Phys.
2011, 135, 194704.
Received: December 2, 2013
Published Online: February 24, 2014
Eur. J. Inorg. Chem. 2014, 1552–1560
1560
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim