Synthesis, crystal structures and magnetic characterization of heterodinuclear CuIIGdIII and CuIITb III Schiff base complexes

Article abstract of DOI:10.1016/j.ica.2011.09.017

Preparation, crystal structures and magnetic properties of new heterodinuclear Cu^IIGd^III (1) and Cu^IITb ^III (2) complexes [CuLn(L)(NO₃)₂(H ₂O)₃MeOH]NO₃·MeOH

Full text of DOI:10.1016/j.ica.2011.09.017

Inorganica Chimica Acta 378 (2011) 288–296
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Inorganica Chimica Acta
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Synthesis, crystal structures and magnetic characterization of heterodinuclear
CuIIGdIII and CuIITbIII Schiff base complexes
b
c
a
Beata Cristóvão a, , Julia Kłak , Barbara Miroslaw , Liliana Mazur
⇑
a Department of General and Coordination Chemistry, Maria Curie-Sklodowska University, Maria Curie-Sklodowska sq. 2, 20-031 Lublin, Poland
b Faculty of Chemistry, University of Wrocław, F. Joliot Curie 14, 50-383 Wrocław, Poland
c Department of Crystallography, Faculty of Chemistry, Maria Curie-Sklodowska University, Maria Curie-Sklodowska sq. 3, 20-031 Lublin, Poland
a r t i c l e i n f o
a b s t r a c t
Preparation, crystal structures and magnetic properties of new heterodinuclear CuIIGdIII (1) and CuIITbIII
(2) complexes [CuLn(L)(NO3)2(H2O)3MeOH]NO3ꢀMeOH (where Ln = Gd, Tb) with the hexadentate Schiff-
Article history:
Received 10 April 2011
Received in revised form 31 August 2011
Accepted 5 September 2011
Available online 12 September 2011
base
compartmental
ligand
N,N0-bis(5-bromo-3-methoxysalicylidene)propylene-1,3-diamine
(H2L = C19H20N2O4Br2) (0) have been described. Crystal structure analysis of 1 and 2 revealed that they
are isostructural and form discrete dinuclear units with dihedral angle between the O1Cu1O2 and
O1Gd1/Tb1O2 planes equal to 2.5(1)° and 2.6(1)°, respectively. The variable-temperature and variable-
field magnetic measurements indicate that the metal centers in 1 and 2 are ferromagnetically coupled
(J = 7.89 cmꢁ1 for 1). Crystal and molecular structure of the Schiff base ligand (0) has been also reported.
The complex formation changes the conformation of Schiff base ligand molecule.
Keywords:
Heterodinuclear complexes
Schiff base
Crystal structure
Magnetic properties
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
[2,16,24,26,42,43]. In comparison to the studies of Cu–Gd hetero-
nuclear systems [1–4,9,12,14–21,24,26,27,39–43] the magnetic
The heteronuclear 3d–4f complexes attract much attention due
to their interesting magnetic properties, as well as, for investigat-
ing the nature of magnetic exchange interactions between lantha-
nide and transition metal atoms and their exploitable applications.
They are used as magnets, high-temperature superconductors,
molecular sensors or luminescent materials [1–16]. The most of re-
ported 3d–4f complexes have been derived from bicompartmental
Schiff-base ligands having an inner site with N2O2 chelating cen-
ters binding 3d cations (radii 0.75–0.6 Å) and outer O2O2 coordina-
tion site which is larger than the inner one and able to
accommodate greater, oxophilic, 4f lanthanide ions (radii 1.06–
0.85 Å) [1,3,6,14–34]. A search in the literature revealed that the
architectural study on 3d–4f compounds has been well developed
properties of Cu–Tb coordination compounds have been much less
investigated [1,35,44–50]. We have undertaken study on heteronu-
clear 3d–4f complexes in order to investigate the influence of the
structural parameters on the nature and magnitudes of the ex-
change interactions and gain more information on the magnetic
properties of Cu(II)–Ln(III) compounds. In our study we have syn-
thesized new heterodinuclear CuIIGdIII (1) and CuIITbIII (2) com-
pounds [CuLn(L)(NO3)2(H2O)3MeOH]NO3ꢀMeOH, by using the
hexadentate Schiff base compartmental ligand N,N0-bis(5-bromo-
3-methoxysalicylidene)propylene-1,3-diamine. We determined
crystal structures of the free ligand and complexes, measured their
magnetic susceptibilities in the temperature range of 1.8–300 K as
well as measuring the variation of the magnetization (M) at 2 K as a
function of the field (H) up to 5 T.
but little is known about the exchange coupling parameter (JLn–M
)
[1,10,18–30]. The paramagnetic rare earth ions Ln(III) (except of
Gd(III)) are characterized by an anisotropic magnetic moment
leading to difficulty in analyzing JLn–M [1,4–6,14,35–38]. The mag-
netic research of polynuclear Cu–Gd compounds came to the con-
clusion that the exchange interaction within the Cu–Gd ions is in
most cases ferromagnetic [3,14–21,24,30,39–43] but Costes et al.
reported examples of complexes in which this interaction is anti-
ferromagnetic [42,43]. Moreover the geometrical factors have been
found to influence the nature of exchange coupling
2. Experimental
2.1. Materials
All chemicals and solvents used for the synthesis were of com-
mercially available reagent grade and were used without further
purification.
The Schiff base ligand N,N0-bis(5-bromo-3-methoxysalicylid-
ene)propylene-1,3-diamine (H2L = C19H18Br2N2O4) (0) has been
synthesized by the 2:1 condensation of 5-bromo-2-hydroxy-3-
methoxybenzaldehyde and 1,3-diaminopropane in methanol
⇑
Corresponding author.
E-mail address: beata.cristovao@poczta.umcs.lublin.pl (B. Cristóvão).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.09.017

B. Cristóvão et al. / Inorganica Chimica Acta 378 (2011) 288–296
289
according to the reported procedure [11,24]. The Schiff base was
separated as yellow needles and recrystallized twice from metha-
nol. The compound is stable at room temperature and has been
characterized by elemental analysis, FTIR spectroscopy and single
crystal X-ray structural analysis. Anal. Calc. for C19H18Br2N2O4: C,
45.61; H, 4.00; N, 5.60. Found: C, 45.32; H, 3.76; N, 5.67%.
are disordered in structures 1 and 2 into two almost equally occu-
pied positions (sof’s = 0.584(6):0.416(6) in 1 and 0.606(6):0.394(6)
in 2), whereas atom C8 was treated as unaffected by disorder. The
coordinates of C10/C10A and C8/C8A in 1 and C10/C10A and C9/
C9A in 2 were refined with the same anisotropic displacement
parameters (constrains were applied with EADP instruction).
Hydrogen atoms from water and methanol molecules were found
in difference Fourier map and refined isotropically. Distances O–
H in water molecules were restrained in 2 by DFIX instruction to
0.8 Å with an estimated standard deviation 0.05. All remaining
H-atoms were positioned geometrically and allowed to ride on
their parent atoms, with Uiso(H) = 1.2/1.5 Ueq(C). A summary of
the conditions for the data collection and the structure refinement
parameters are given in Table 1. The molecular plots were drawn
with ORTEP3 for Windows [56], Mercury [57] and Diamond [58].
2.2. Synthesis of the complexes
Compounds 1 and 2 were obtained in a similar way. For in-
stance, to prepare 1, a mixture of Schiff base ligand H2L (0.4 mmol,
0.1999 g) and Cu(OAc)2ꢀH2O (0.4 mmol, 0.0799 g) in methanol
(30 ml) was vigorous stirred for 30 min at room temperature. Then,
a methanol solution of Gd(NO3)3ꢀ6H2O (0.2 mmol, 0.0903 g) was
added dropwise, and the mixture was kept stirring for another
30 min at ambient temperature. The solution was filtered to re-
move the suspended materials and kept in the low temperature
for very slow evaporation. After a few days green crystals suitable
for X-ray diffraction were appeared which were collected by filtra-
tion, washed with cold methanol and dried. Terbium(III) nitrate
was prepared from Tb4O7 (0.05 mmol, 0.0374 g) with nitric acid.
Anal. Calc. for C21H32N5O18Br2CuGd (1023.12) (1): C, 24.64; H,
3.13; N, 6.84; Cu, 6.21; Gd, 15.38. Found: C, 25.04; H, 2.87; N,
6.83; Cu, 6.43; Gd, 15.62%. Anal. Calc. for C21H32N5O18Br2CuTb
(1024.80) (2): C, 24.61; H, 3.13; N, 6.84; Cu, 6.21; Tb, 15.52. Found:
C, 24.19; H, 2.94; N, 6.84; Cu, 6.46; Tb, 15.71%.
3. Results and discussion
3.1. Infrared spectra
The FTIR spectrum of the Schiff base ligand, H2L (0) shows
strong absorption band at 1636 cmꢁ1 which is characteristic for
the azomethine m(C@N) group. In the spectra of the complexes 1
and 2 this band is shifted to lower wavenumbers and appears at
1628 cmꢁ1 indicating the participation of the azomethine nitrogen
in coordination to metal [1,59–64]. A strong band observed at
1252 cmꢁ1 in free Schiff base spectrum has been assigned to phe-
2.3. Physical measurements
nolic m(C–O) stretching vibration. On complexation, this band ap-
pears at lower frequency 1240 cmꢁ1, confirming the involvement
of the phenolic oxygen in the metal–ligand bonding. [60,63,64].
This is in accord with the X-ray structural data. The structural
determination of 1 and 2 (see below) show that, the Schiff base acts
as hexadentate chelating ligand coordinated to metal ions through
two nitrogen and four oxygen atoms. The strong band at
1384 cmꢁ1 is present only in the spectra of the complexes and
The contents of carbon, hydrogen and nitrogen in the analyzed
compounds were determined by elemental analysis using a CHN
2400 Perkin Elmer analyser.
The contents of copper and lanthanides were established using
ED XRF spectrophotometer (Canberra-Packard).
The FTIR spectra of complexes were recorded over the range of
4000–200 cmꢁ1 using M-80 spectrophotometer (Carl Zeiss Jena).
Samples for IR spectra measurements were prepared as KBr discs.
The magnetization of the CuIIGdIII (1) and CuIITbIII (2) powdered
samples was measured over the temperature range of 1.8–300 K
using a Quantum Design SQUID – based MPMSXL-5-type magne-
tometer. The superconducting magnet was generally operated at
a field strength ranging from 0 to 5 T. Measurements sample of
compounds were made at magnetic field 0.5 T. The SQUID magne-
tometer was calibrated with the palladium rod sample. Corrections
are based on subtracting the sample – holder signal and contribu-
tion vD estimated from the Pascal’s constants [51] and equal
420 ꢂ 10ꢁ6 cm3 molꢁ1 for CuIIGdIII (1) and 408 ꢂ 10ꢁ6 cm3 molꢁ1
for CuIITbIII (2), respectively and the temperature independent
can be assigned to vibrations of the nitrate group
m(NO3)
[1,59,65]. In the FTIR spectra of the 1 and 2 the broad medium
bands with the maximum around 3430 cmꢁ1 may be attributed
to the OH stretching vibrations of water molecules,
m(O–H)
[1,59,60]. On the basis of crystal structures of these compounds
we know that the water molecules are present in the complexes
and they are bonded to the lanthanide(III) ions. The occurrence
of two bands at ca. 572 and 448 cmꢁ1 respectively, which are not
seen in the spectrum of the free Schiff base ligand, gives further
evidence for M–O and M–N interaction. The selected FTIR bands
of the free Schiff base ligand 0 and compounds 1 and 2 are listed
in Supporting Information, Table S1.
paramagnetism of the Cu2+ centers equal +60 ꢂ 10ꢁ6 cm3 molꢁ1
.
3.2. Crystal structure description
2.4. Single crystal X-ray analysis
3.2.1. Description of crystal and molecular structure of the free Schiff
base ligand 0
The crystallographic measurements were performed on an
Oxford Diffraction Xcalibur CCD diffractometer with the graphite-
A search of the Cambridge Structural Database (CSD, Version
5.32 with updates November 2010 and February 2011 [70] re-
vealed only six crystal structures with N,N0-bis(5-bromo-2-hydro-
xy-3-methoxybenzylidene)-1,3-diaminopropane (0) as a ligand
(Refcodes: FOBBEE, FOBBII, TEHROO, WAQDEX, XUJRIE and XUJ-
ROK). However, there is no crystal structure deposition of the free
ligand in the CSD. Here, we report the crystal structure of 0 in
100 K (Table 1). The atomic numbering scheme is shown in
Fig. 1. The single crystal X-ray analysis confirmed the molecular
structure of ligand 0 with favoured enolimine over ketonamine
form (Table 2). The complex formation changes the conformation
of ligand molecule mainly through the bending of propylene-1,3-
diamine bridge and rotation of aromatic rings (Table 2). In the solid
monochromatized Mo K
ature of 100(2) K. Data sets were collected using the
a
radiation (k = 0.71073 Å) at the temper-
scan
x
technique, with an angular scan width of 1.0°. The programs
CRYSALIS CCD and CRYSALIS RED [52] were used for data collection, cell
refinement and data reduction. The data were corrected for Lorentz
and polarization effects. A multi-scan absorption correction was
applied for 1 and in case of 2 and 0 – the analytical absorption cor-
rection based on the indexing of the crystal faces [53]. The struc-
tures were solved by direct methods using SHELXS-97 and refined
by the full-matrix least-squares on F2 using the SHELXL-97 [54] (both
operating under WINGX [55]). All non-hydrogen atoms were refined
with anisotropic displacement parameters. The C9 and C10 atoms

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B. Cristóvão et al. / Inorganica Chimica Acta 378 (2011) 288–296
illustrated in Figs. 2 and 3. The central part of the coordination core
in 1 and 2 is occupied by Cu(II) and Gd(III)/Tb(III) ions. The metal
ions are bridged via two phenolic oxygen atoms from organic li-
gand. The inner salen-type cavity is occupied by Cu(II) ion. Lantha-
nide ions are present in the open, larger space of the
compartmental ligand. The M–O(phenolate) bond distances for
copper(II) and gadolinium(III)/terbium(III) ions are in accordance
with the values reported for related 3d–4f coordination com-
pounds (Table 2) [28,35,69]. The CuOOGd/Tb core including two
phenoxo oxygen atoms is essentially planar with the largest devi-
ation from mean plane being 0.021 and 0.022 Å for Cu ion in 1 and
2, respectively. The dihedral angle between the Cu1O1O2 and Gd1/
Tb1O1O2 planes is equal to 2.5(1)° in 1 and 2.6(1)° in 2. The Cu1–
Gd1/Tb1 distances are quite short: 3.539(1) and 3.522(4) Å, in 1
and 2, respectively.
Fig. 1. Molecular structure of 0 with atomic labels. The displacement ellipsoids
were drawn at the 50% probability level.
state the molecule of 0 has bent conformation with dihedral angle
between two rings being 83°, while in 1 and 2 these angles are
equal to 26°. Both hydroxyl O1/O2 atoms form intramolecular
hydrogen bonds to N1/N2 atoms. The adjacent molecules interact
The coordination polyhedron of the lanthanide cation has a shape
resembling distorted tricapped trigonal prism (Fig. 4). It is formed by
four O atoms of the polydentate Schiff base ligand, two
g
2 chelating
O atoms from a nitrate anion, and three O atoms from aqua ligands.
The lanthanide–oxygen bond lengths depend on the chemical nat-
ure of the O atoms (methoxy, nitrate, aqua or phenoxo). They vary
from 2.358(3) Å for Tb–O(aqua) to 2.537(2) Å for Gd–O(methoxy)
(Table 2). These values are similar to the bond lengths reported ear-
lier [15,21,24]. In the title complexes the copper is surrounded by six
donor atoms. The equatorial N2O2 donors from the Schiff base ligand
are nearly planar with the largest deviation from the mean plane
being 0.189 Å for O1 atom in 1 and 0.197 Å for atom O2 in 2. Addi-
tionally, two oxygen atoms: one from methanol molecule and one
from monodentate nitrate ion, are coordinated to the apical position
of the Cu(II) center – resulting in an octahedral coordination envi-
ronment. The crystal structures of these two novel complexes are
stabilized by strong intermolecular hydrogen bonds (Table 3) be-
tween aqua, nitrate and methanol molecules. In the crystal lattice
the adjacent molecules are held together by classical intermolecular
hydrogen bonds involving the coordinated water molecules and
noncoordinatedOatomsofthemonodentatenitrateligand(Table3).
The uncoordinated nitrate ion and methanol molecule are also con-
nected by hydrogen bond. The molecules form layers perpendicular
through weak C–H. . .O/N, C–H. . .p, and C–H. . .Br interactions
(Table 3).
3.2.2. Description of the structure of 1 and 2
The elemental analyses and infrared spectral data for the CuII–
GdIII (1) and CuII–TbIII (2) coordination compounds are consistent
with the crystal structures determined by single crystal X-ray dif-
fraction (Table 1). The title compounds [CuLn(C19H18N2O4Br2)
(NO3)2(H2O)3MeOH]NO3ꢀMeOH (where Ln = Gd, Tb) are isostructur-
al with very small lattice distortion index eA = 0.00024 [66]. The iso-
structurality indices calculated for
orthogonalization indicate very close similarity between these two
crystal structures (
= 0.0025; Ii(50) = 96.6%; Ivmax = 99.6%) [67].
1 and 2 with Löwdin
P
Crystals of 1 and 2 are composed of discrete dinuclear cations
with a salen-type Schiff base ligands. In the asymmetric unit there
are additionally one uncoordinated nitrate anion and one methanol
molecule. The propylene bridge of organic ligand in both com-
plexes is disordered over two almost equally occupied positions.
A view of these units including the atomic numbering scheme is
Table 1
Crystallographic data, details of data collection and structure refinement parameters for the Schiff base ligand (H2L) 0 and compounds 1 and 2.
Crystal data
0
1
2
Empirical formula
Formula weight
Temperature (K)
Crystal system
Space group
a (Å)
C
19H20Br2N2O4
C21H32Br2CuGdN5O18
1023.12
100(2)
monoclinic
P21/n
9.978(2)
16.753(2)
19.921(3)
90
C21H32Br2CuTbN5O18
1024.80
100(2)
monoclinic
P21/n
9.955(1)
16.720(1)
19.859(1)
90
500.19
100(2)
triclinic
P1
4.592(1)
14.682(1)
15.694(1)
113.88(1)
93.39(1)
ꢀ
b (Å)
c (Å)
a
(°)
b (°)
90.22(3)
90.20(1)
c
(°)
96.70(1)
954.3(1)
2
90
3330.0(9)
4
90
3305.5(1)
4
V (Å3)
Z
Crystal form/color
Crystal size (mm)
plate/yellow
0.40 ꢂ 0.30 ꢂ 0.15
1.741
block/green
0.46 ꢂ 0.32 ꢂ 0.27
2.041
block/green
0.42 ꢂ 0.40 ꢂ 0.32
2.059
Dcalc (g cmꢁ3
)
l
(mmꢁ1
)
4.275
5.096
5.267
Absorption correction
h range (°)
Reflections collected
Independent reflections (Rint
Reflections observed (I > 2r(I))
analytical
2.62–25.24
5980
3459 (0.0297)
2769
multi-scan
2.59–28.28
27961
8182 (0.0267)
6872
analytical
2.64–28.28
15076
8188 (0.0248)
6680
)
Data/restrains/parameters
3459/0/244
1.052
8182/0/480
0.978
8188/6/468
0.999
Goodness-of-fit (GOF) on F2
R1, wR2 [I > 2
R1, wR2 (all data)
qmin (e Åꢁ3
)
r
(I)]
0.0540, 0.1544
0.0631, 0.1574
1.84, ꢁ0.75
0.0210, 0.0470
0.0276, 0.0477
1.40, ꢁ0.75
0.0339, 0.0811
0.0418, 0.0824
2.47, ꢁ1.94
D
qmax
,
D

B. Cristóvão et al. / Inorganica Chimica Acta 378 (2011) 288–296
291
Table 2
Selected geometric parameters (Å, °) in the coordination environments of the metal center.
0
Bond lengths
N1–C7
O1–C1
1.277(1)
1.344(8)
N2–C11
O2–C12
1.276(1)
1.345(7)
Torsions
C7–N1–C8–C9
N1–C8–C9–C10
C8–C9–C10–N2
ꢁ109.0(6)
166.7(4)
ꢁ176.2(4)
C9–C10–N2–C11
C9–C10–N2–C11
C10–N2–C11–C17
108.3(6)
108.3(6)
ꢁ175.4(5)
1
Bond lengths
Gd1–O1
Gd1–O2
Gd1–O3
Gd1–O4
Gd1–O8
Gd1–O9
Gd1–O5
Gd1–O6
2.387(2)
2.398(1)
2.537(2)
2.513(2)
2.483(2)
2.510(2)
2.369(2)
2.387(2)
Gd1–O7
Cu1–N1
Cu1–N2
Cu1–O1
Cu1–O2
Cu1–O11
Cu1–O17
Cu1–Gd1
2.382(2)
1.997(2)
1.969(2)
1.955(1)
1.993(2)
2.532(2)
2.509(2)
3.539(1)
Angles
Cu1–O1–Gd1
Cu1–O2–Gd1
O1–Gd1–O2
Torsions
108.81(6)
107.06(6)
64.06(5)
O1–Gd1–O3
O2–Gd1–O4
a
63.69(5)
64.71(5)
2.5(1)
N1–C8–C9–C10
60.8(6)
C8–C9–C10–N2
ꢁ82.3(7)
a
– dihedral angle between the Cu1O1O2 and Gd1O1O2 planes.
2
Bond lengths
Tb1–O1
Tb1–O2
Tb1–O3
Tb1–O4
Tb1–O8
Tb1–O9
Tb1–O5
Tb1–O6
2.372(2)
2.378(2)
2.528(2)
2.502(2)
2.461(2)
2.494(3)
2.358(3)
2.377(3)
Tb1–O7
Cu1–N1
Cu1–N2
Cu1–O1
Cu1–O2
Cu1–O11
Cu1–O17
Cu1–Tb1
2.361(3)
1.989(3)
1.961(3)
1.951(2)
1.995(2)
2.537(3)
2.501(3)
3.522(4)
Angles
Cu1–O1–Tb1
Cu1–O2–Tb1
O1–Tb1–O2
Torsions
108.74(9)
106.95(9)
64.42(8)
O1–Tb1–O3
O2–Tb1–O4
a
63.81(7)
64.81(8)
2.6(1)
N1–C8–C9–C10
61.3(8)
C8–C9–C10–N2
ꢁ81.0(9)
a
– dihedral angle between the Cu1O1O2 and Tb1O1O2 planes.
Fig. 2. Molecular structure of 1 with atomic labels. The displacement ellipsoids
Fig. 3. Molecular structure of 2 with atomic labels. The displacement ellipsoids
were drawn at the 50% probability level.
were drawn at the 50% probability level.

292
B. Cristóvão et al. / Inorganica Chimica Acta 378 (2011) 288–296
Table 3
Hydrogen bonding geometry.
D–H. . .A
D–H (Å)
H. . .A (Å)
D. . .A (Å)
D–H. . .A (°)
0
O1–H1. . .N1
O2–H2. . .N2
C9–H9B. . .O3(i)
C18–H18A. . .N2(i)
C9–H9A. . .Br2(ii)
C18–H18A. . .O3(iii)
0.84
0.84
0.99
0.98
0.99
0.98
0.98
0.98
1.86
1.83
2.63
2.67
2.95
2.44
2.50
2.66
2.601(6)
2.576(6)
3.485(8)
3.397(9)
3.659(7)
3.193(7)
3.445
146.4(3)
146.8(3)
144.4(3)
131.6(3)
129.2(3)
133.0(3)
148
(iv)
C18–H18B. . .cg1
C19–H19C. . .cg2(iv)
3.162
163
Symmetry codes: (i) ꢁx, ꢁy, ꢁz; (ii) ꢁx, ꢁy, 1 ꢁ z; (iii) ꢁ1 ꢁ x, ꢁy, ꢁz; (iv) ꢁ1 + x, y, z; cg1 – centroid between atoms C1, C2; cg2 – centroid between atoms C12, C13.
1
O5–H5A. . .O18
O5–H5B. . .O11
O5–H5B. . .O13
O5–H5B. . .N4
O7–H7B. . .O17
O6–H6B. . .O14
0.81(3)
0.78(3)
0.78(3)
0.78(3)
0.99(4)
0.72(3)
0.77(3)
0.86(3)
0.74(4)
0.80(3)
0.80(3)
0.80(3)
0.93
1.86(3)
1.99(3)
2.54(3)
2.62(3)
2.08(4)
2.08(3)
1.93(3)
1.81(3)
2.12(4)
2.01(3)
2.58(3)
2.65(3)
2.41
2.657(3)
2.757(3)
3.148(3)
3.371(3)
2.847(3)
2.761(3)
2.693(3)
2.663(3)
2.845(3)
2.785(2)
3.207(3)
3.424(3)
3.324(3)
3.400(3)
3.347(7)
3.261(11)
3.500(4)
3.530(3)
168.9(6)
169.4(6)
135.5(6)
162.8(6)
171.8(8)
157.7(6)
171.9(6)
168.7(6)
171.7(8)
162.5(6)
136.1(6)
161.2(6)
168
O7–H7A. . .O12(i)
O6–H6A. . .O13(i)
O18–H18. . .O16(ii)
O17–H17. . .O16(iii)
O17–H17. . .O15(iii)
O17–H17. . .N5(iii)
C3–H3. . .O12(iv)
C7–H7. . .O10(v)
C8–H8A. . .O15(v)
C10–H10A. . .O8(vi)
C16–H16. . .O13(vi)
C19–H19B. . .O9(vii)
0.93
0.97
0.97
0.97
2.51
2.47
2.34
2.69
162
150
158
147
0.96
2.58
172
Symmetry codes: (i) x ꢁ 1, y, z; (ii) x + 1, y, z; (iii) 1/2 ꢁ x, y + 1/2, 1/2 ꢁ z; (iv) 3/2 ꢁ x, y ꢁ 1/2, 1/2 ꢁ z ; (v) 1/2 + x, 1/2 ꢁ y, 1/2 + z; (vi) 3/2 ꢁ x, 1/2 + y, 1/2 ꢁ z; (vii) 1 ꢁ x,
1 ꢁ y, ꢁz.
2
O5–H5A. . .O18
O5–H5B. . .O11
O5–H5B. . .O13
O5–H5B. . .N4
O7–H7B. . .O17
O6–H6B. . .O14
0.74(3)
0.77(3)
0.77(3)
0.77(3)
0.79(4)
0.74(4)
0.84(4)
0.83(4)
0.84
0.84
0.84
0.84
0.95
1.91(3)
1.99(3)
2.54(4)
2.61(3)
1.95(4)
2.04(4)
1.87(4)
1.84(4)
2.01
1.95
2.57
2.62
2.39
2.653(4)
2.743(4)
3.146(4)
3.356(4)
2.729(3)
2.751(3)
2.685(4)
2.663(4)
2.843(4)
2.782(4)
3.201(4)
3.422(4)
3.322(4)
3.398(4)
3.344(6)
3.230(19)
3.494(5)
3.525(5)
176.3(4)
166.4(4)
137.3(4)
163.5(4)
173.6(5)
161.9(5)
163.1(4)
168.9(5)
171
171
133
160
167
O7–H7A. . .O12(i)
O6–H6A. . .O13(i)
O18–H18. . .O16(ii)
O17–H17. . .O16(iii)
O17–H17. . .O15(iii)
O17–H17. . .N5(iii)
C3–H3. . .O12(iv)
C7–H7. . .O10(v)
C8–H8A. . .O15(v)
C10–H10A. . .O8(vi)
C16–H16. . .O13(vi)
C19–H19B. . .O9(vii)
0.95
0.99
0.99
0.95
2.48
2.45
2.29
2.67
162
150
159
146
0.98
2.55
172
Symmetry codes: (i) x ꢁ 1, y, z; (ii) x + 1, y, z; (iii) 1/2 ꢁ x, y + 1/2, 1/2 ꢁ z; (iv) 3/2 ꢁ x, y ꢁ 1/2, 1/2 ꢁ z ; (v) 1/2 + x, 1/2 ꢁ y, 1/2 + z; (vi) 3/2 ꢁ x, 1/2 + y, 1/2 ꢁ z; (vii) 1 ꢁ x, 1 ꢁ y, ꢁz.
ꢁ1
to the c crystallographic axis (Fig. 5). Between layers in the crystal
structure the weak hydrogen bonds C–H. . .O and additionally inter-
molecular contacts between O10(nitrate) and Br2 atoms being
shorter than sum of van der Waals radii (3.292(3) and 3.287(3) Å
for 1 and 2, respectively) (symmetry code ꢁx + 1, ꢁy + 1, ꢁz) appear.
These contacts do not conform to the rules of halogen bond because
theC–Br. . .O angle is ca 80°. However, the short Br. . .O distances may
be attributed to anisotropic distribution of electron density around
the halogen nucleus [70]. The intermolecular interactions give an
extended three-dimensional network but do not lead to short inter-
nuclear contacts with the shortest separations between metal ions
being observed for Cuꢀ ꢀ ꢀTb 7.543(4) Å and Cuꢀ ꢀ ꢀGd 7.557(3) Å.
vm and vmT product versus T are given in Fig. 6. The thermal
dependence of vmꢁ1 obeys the Curie–Weiss law in the whole tem-
perature range with h = 1.7 K and C = 8.19 cm3 molꢁ1 K. At 300 K,
v
mT is equal to 8.16 cm3 K molꢁ1 which roughly corresponds to
the value (
v
mT = 8.25 cm3 K molꢁ1) expected for the two isolated
CuII (S = 1/2) and GdIII (4f7, J = 7/2, L = 0, S = 7/2, S7/2) ions, with a
8
g value assumed to be equal to 2. When the temperature is low-
ered,
vmT product remains constant until 120 K and then slightly
increases, reaching a maximum of 9.63 cm3 K molꢁ1 at 10 K, and
then decreases to 7.80 cm3 K molꢁ1 at 2 K. The behavior observed
in the 300–10 K range is indicative of a ferromagnetic interaction
between the GdIII and CuII ions. The facts that the maximum
v
mT
value at 10 K is slightly lower than expected value
(10 cm3 molꢁ1 K) for total spin state S = 4, and the
mT values are
3.3. Magnetic properties
v
decreased at low temperatures may be attributed to zero-field
splitting (ZFS) effects of the S = 4 ground state and/or antiferro-
magnetic interactions between heterobinuclear entities in crystal
The magnetic properties of CuIIGdIII (1) were studied over the
temperature range of 1.8–300 K. Plots of magnetic susceptibility

B. Cristóvão et al. / Inorganica Chimica Acta 378 (2011) 288–296
293
ꢁ1
Fig. 6. Temperature dependence of experimental
vmT (s) and vm (d) vs. T for
complex 1. The solid lines is the calculated curve derived from Eqs. (1) and (2).
15g24 þ 7g23 expðꢁ4J=kTÞ
Fd
¼
ð1Þ
ð2Þ
9 þ 7 expðꢁ4J=kTÞ
4Nb2TFd
þ NaT
Fig. 4. A view of coordination polyhedron in 2. The disordered part of propylene
bridge with lower occupation factor was omitted for clarity.
v
mT ¼
kT ꢁ J0Fd
where b is the Bohr magneton, g is Lande factor, k is Boltzman’s con-
lattice. The GdIII with an 8S7/2 single-ion ground state does not pos-
sess a first-order orbital moment [51]. Thus the contributions of
the orbital angular momentum and the anisotropic effect do not
need to be taken into consideration. Considering the occurrence
of intramolecular magnetic interactions (J) and intermolecular
interactions (J0) [9,71] the coupling of the spin momentum of GdIII
and CuII ions is described by the spin Hamiltonian
H ¼ ꢁJSCuSGd ꢁ J0SCuSGd. Taking into consideration the g values
associated with the low-lying levels E(4) = 0 and E(3) = 4J,
g4 = (7gGd + gCu)/8, and g3 = (9gGd ꢁ gCu)/8 [72] we obtain the fol-
lowing theoretical expression (1) and (2) [24]:
stant, and N is the temperature-independent paramagnetism. A
a
least-squares fitting of the experimental data between 10 and
200 K (solid lꢁin1e in Fig. 6) leads to J = 7.89(1) cmꢁ1
,
J0 = ꢁ0.066(1) cm
,
gCu = 2.02(2),
gGd = 1.98(1)
and
N
a
= 2.76 ꢂ 10ꢁ6 cm3 molꢁ1 with
a
good agreement factor
R =
R
(v
expT ꢁ
v
calcT)2/
R
(v
expT)2 (R = 1.10 ꢂ 10ꢁ4). This fitting indi-
cates an intradimer Cu–Gd ferromagnetic interaction. The analysis
also reveals very weak intermolecular antiferromagnetic interaction
propagated through extended networks formed by hydrogen bonds.
To confirm the nature of the ground state of 1, we investigated the
variation of the magnetization, M, with respect to the field, at 2 K.
Fig. 5. View of molecular layers perpendicular to c crystallographic axis in crystal structure of 2. The hydrogen atoms were omitted for clarity. Dashed lines indicate
intermolecular Br. . .O contacts.

294
B. Cristóvão et al. / Inorganica Chimica Acta 378 (2011) 288–296
ꢁ1
Fig. 8. Temperature dependence of experimental
complex 2.
vmT (h) and vm (j) vs. T for
Fig. 7. Field dependence of the magnetization for complex 1. The solid line is the
Brillouin function curve for a S = 4 state of CuII–GdIII unit; dashed line is the
Brillouin function for two independent S = 1/2 and S = 7/2 systems.
Gd–O (bridging atom) directions, one concludes easily that the lar-
ger the bending network the smaller the value of these parameter J,
and consequently, the weaker the ferromagnetic coupling is. In an
attempt to find some structural characteristic, which could corre-
late with the magnetic behavior in the CuO2Gd bridging network,
we analyzed some the CuIIGdIII dinuclear complexes reported in
the literature [2,3,8,14,15,21,24,28,30,42,68,73–78]. There is some
correlation between JCuGd and the intramolecular Cu. . .Gd distance
and this can be fitted to an exponential function such that –
J = A exp(BdCu. . .Gd) where A = 6.409 ꢂ 104 and B = ꢁ2.833 with J in
cmꢁ1 and Cu. . .Gd distance between the two metal centers in Å
[79]. Using the value of Cu. . .Gd = 3.539(1) Å as found in the present
Table 4
The comparison of the structural and magnetic data for a series of some CuIIGdIII
complexes.
Compound
Cu. . .Gd aa (°)
(Å)
J
Refs.
(cmꢁ1
)
LCu(Me2CO)Gd(NO3)3
CuLGd(NO3)3]ꢀMe2CO
LCu(Me2CO)Gd(NO3)3
L2Cu(MeOH)Gd(NO3)3
L4Cu(OCMe2)Gd(NO3)3
CuGd(H2O)(NO3)(ems)2
LCu(O2COMe)Gd(thd)2
[LCu(Me2CO)Gd(NO3)3]2
Cu(salabza)Gd(hfac)3
CuGdLCl2(H2O)4Clꢀ2H2O
CuGd(hfa)3(salen)(meim)
GdCu(OTf)(bdmap)2(H2O)THF
CuL1Gd(NO3)3
3.475
3.428
3.427
3.484
3.523
3.306
3.473
3.375
3.248
3.51
3.252
3.31
3.65
3.62
3.345
12.7
12.9
11.8
12.5
16.6
24.5
19.1
11
47.4
1.7
39.6
0.6
7.3
7.0
5.6
6.8
4.8
1.88
3.5
7.4
16
15
26
28
28
2
14
77
79
78
30
76
44
44
80
this
work
complex 1, this relationship leads to a value of Jcalc = 14.5 cmꢁ1
which poorly match the experimental value 7.89 cmꢁ1. It was also
noted that the JCuGd values and the dihedral angle defined by
,
0.8
a
10.1
1.42
ꢁ0.04
3.5
ꢁ0.49
3.36
7.89
the two O–Cu–O and O–Gd–O planes of the CuO2Gd bridging core
a
could be correlated by an exponential function, J = A expꢁB with
A = 11.5 and B = 0.054 [24]. According to this correlation, J should
6.1
39.1
20.5
CuGdL2(H2O)(NO3)3
CuGd(hmp)2(NO3)3(H2O)2
[CuLGd(L)(NO3)2(H2O)3MeOH]NO3ꢀMeOH 3.539
be ca. 10 cm–1 for 1 (
a = 2.52°). In the obtained complex 1 the inter-
action is ferromagnetic (J = 7.89 cmꢁ1) as it is for reported dipheno-
lato-bridged CuIIGdIII dinuclear complexes which yield J values
varying from 1.0 to 10.1 cmꢁ1 [2,14–16,28,30,42,74–78]. The exper-
imental value of 7.89 cm–1 is not very different from this hypothe-
sis. The intermolecular shortest metal–metal distance in 1 is large
enough to consider the dinuclear core as magnetically isolated,
the extended networks formed by hydrogen bonds take part in
the intermolecular antiferromagnetic interaction and may cause
deviation from this magneto-structural relationship. However, this
correlation revealed that the increase of the interaction parameter
2.52
a
Dihedral angle between planes OCuO and OGdO.
The results are shown in Fig. 7, where molar magnetization M is ex-
pressed in lB units. The saturation magnetization is close to 8 lB
.
The magnetization data have been compared with the sum of the
Brillouin functions of isolated GdIII and CuII, as well as with the Brill-
ouin function of the S = 4 pair state. The experimental magnetiza-
tions of 1 is greater than for two independent S = 1/2 and S = 7/2
system and very close with the Brillouin function of S = 4 state.
These results confirm the ferromagnetic interaction between GdIII
and CuII and demonstrating that the low temperature decrease of
J
can be related to
(J = 0.8 cmꢁ1) when
the literature [76], it appears that the highest exchange parameters
(J = 10.1 cmꢁ1) are associated with the lowest value
(1.78°) The
a
decrease in
a and tends to vanish
a
approaches a value of 47.4° [77]. Based on
a
comparisons of the structural and magnetic characteristics in the
CuO2Gd bridging network reported in the literature are listed in Ta-
ble 4. Increasing the distortion from planarity of similar bridging
system causes a decrease of J values.
vmT is not due to ZFS effects and there exists antiferromagnetic
interactions between neighboring dinuclear units. The complex 1
considered in this work exhibits ferromagnetic JCu–Gd interactions,
as in the majority of previously published CuIIGdIII complexes
[2,3,8,14,15,21,24,26,28,30,42,68,73–78]. The ferromagnetic char-
acter of the magnetic interaction within the GdO2Cu systems has
been attributed [30,42] to the coupling between the ground and
the excited configuration of GdIII–CuII in which an electron has been
transferred from the singly occupied 3d copper orbital to an empty
5d gadolinium orbital. Given that their largest values would be
associated with the gadolinium 5d orbitals oriented along the two
The magnetic susceptibility
v
mT of CuIITbIII (2) has been also
measured in the temperature range of 1.8–300 K in a 0.5 T of ap-
plied magnetic field. The data obtained for complex 2 are repre-
sented in Figs. 8 and 9. The values Curie and Weiss constants
determined from the relation 1/
1.8–300 K are equal to 12.71 cm3 molꢁ1 and 1.96 K, respectively.
At the room temperature, the mT product is equal to
12.61 cm3 molꢁ1 K, which is slightly larger than the value
vm = f(T) over temperature range
v

B. Cristóvão et al. / Inorganica Chimica Acta 378 (2011) 288–296
295
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2011.09.017.
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14.61 cm3 molꢁ1 K at 10 K. The profile of the
is strongly suggestive of the occurrence a ferromagnetic CuII–TbIII
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v
mT gradually increases to reach
a value of
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Appendix A. Supplementary material
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