N,N′-bis(5-bromo-2-hydroxy-3-methoxybenzylidene)-1,3-diaminopropane Cu-4f-Cu and Cu-4f complexes: Synthesis, crystal structures and magnetic properties

Article abstract of DOI:10.1016/j.poly.2011.12.013

Synthesis, crystal structures and magnetic studies of new heterotri- and heterodinuclear complexes having general formulae [Cu₂Ln(L) ₂(NO₃)(H₂O)₂](NO₃) ₂·3H₂O (where L

Full text of DOI:10.1016/j.poly.2011.12.013

Polyhedron 34 (2012) 121–128
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
N,N0-bis(5-bromo-2-hydroxy-3-methoxybenzylidene)-1,3-diaminopropane
Cu–4f–Cu and Cu–4f complexes: Synthesis, crystal structures and magnetic
properties
b
c
Beata Cristóvão a, , Barbara Miroslaw , Julia Kłak
⇑
a Department of General and Coordination Chemistry, Maria Curie-Sklodowska University, Maria Curie-Sklodowska sq. 2, 20-031 Lublin, Poland
b Department of Crystallography, Faculty of Chemistry, Maria Curie-Sklodowska University, Maria Curie-Sklodowska sq. 3, 20-031 Lublin, Poland
c Faculty of Chemistry, University of Wrocław, F. Joliot Curie 14, 50-383 Wrocław, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 July 2011
Accepted 15 December 2011
Available online 23 December 2011
Synthesis, crystal structures and magnetic studies of new heterotri- and heterodinuclear complexes hav-
ing general formulae [Cu2Ln(L)2(NO3)(H2O)2](NO3)2ꢀ3H2O (where Ln = Ce (1), Pr (2), Nd (3) and La (4)),
and [CuLn(L)(NO3)2(H2O)3MeOH]NO3ꢀMeOH (where Ln = Dy (5) and Er (6)), respectively involving the
Schiff base (H2L) as main ligand are reported. The heterotrinuclear complexes crystallize in the mono-
clinic space group C2/c with the molecule lying on the twofold axis (Z0 = 0.5), while the dinuclear
complexes (5 and 6) form monoclinic crystals with space group P21/n. The lanthanide(III) cation in
CuII–LnIII–CuII core is 10-coordinated, whereas in dinuclear compounds the coordination number for
Ln(III) ion is only nine. The polyhedra formed around terminal Cu(II) ions in 1–3 have a shape of deformed
tetragonal pyramid with water molecule in apical position. In crystals 5 and 6 the Cu(II) has octahedral
coordination. The temperature dependence of the magnetic susceptibility and the field-dependent mag-
netization indicated that the interaction between CuII and LnIII ions is antiferromagnetic for Ln = Ce, Pr
and Nd and ferromagnetic for Ln = Dy and Er.
Keywords:
Heterotrinucelar complexes
Heterodinucelar complexes
Schiff base
Crystal structure
Magnetic properties
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
predicted theoretically that coupling of 4fn ions with other para-
magnetic species will be antiferromagnetic for n < 7 and ferromag-
Schiff base ligands obtained from salicylaldehyde and its deriv-
atives are largely used for the synthesis of metal complexes having
application in bioinorganic chemistry, catalysis and magnetochem-
istry [1–7]. The molecular structure of these ligands – the kind, the
number and the position of the donor atoms influence the number
of metal ions within homo- and heteronuclear compounds
[1,5,8–12]. Additional coordinating groups (for example: methoxy)
attached to salicylaldehyde yield compartmental Schiff base
ligands which have an inner coordination site with two N-donor
and two O-donor chelating centers suitable for the complexation
of transition metal ions, and outer coordination site with four O-
donor atoms that is capable of incorporating larger oxophilic ions,
such as rare earth elements [5,9–11,13–18]. The Ln(III) ions (except
for La, Gd and Lu) have a large orbital contribution to the total
magnetic moment, which makes the understanding of the 3d–4f
interaction complicated [6,13,19–25]. In the reported 3d–4f
compounds, where the nature or magnitude of the interactions
has been determined, the majority of them contain Gd(III) as the
lanthanide counterpart [6,9–11,15–17,26–29]. Kahn et al.
netic for n > 7 [30,31].
The studies of the crystal structure and magnetic interaction in
di- and polynuclear metal 3d–4f complexes are crucial in the devel-
opment of the coordination chemistry and magnetochemistry. As a
continuation of our research in the present paper we report synthe-
sis, molecular and crystal structures (except 4) and magnetic
properties of four novel heterotrinuclear [Cu2Ce(L)2(NO3)(H2O)2]
(NO3)2ꢀ3H2O (1), [Cu2Pr(L)2(NO3)(H2O)2](NO3)2ꢀ3H2O (2) [Cu2
Nd(L)2(NO3)(H2O)2](NO3)2ꢀ3H2O (3) and [Cu2La(L)2(NO3)(H2O)2]
(NO3)2ꢀ3H2O (4) and two heterodinuclear [CuDy(L)(NO3)2(H2O)3
MeOH]NO3ꢀMeOH (5) and [CuEr(L)(NO3)2(H2O)3MeOH]NO3ꢀMeOH
(6) compounds with the Schiff base ligand N,N0-bis(5-bromo-3-
methoxysalicylidene)propylene-1,3-diamine (H2L, Scheme 1).
2. Experimental
2.1. Synthesis
2.1.1. Materials
The reagents and solvents used for synthesis were commercially
available from Aldrich Chemical Company and Polish Chemical Re-
agents. They were used as received without further purification.
⇑
Corresponding author.
E-mail address: beata.cristovao@poczta.umcs.lublin.pl (B. Cristóvão).
0277-5387/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2011.12.013

122
B. Cristóvão et al. / Polyhedron 34 (2012) 121–128
(KBr, cmꢁ1): 3420m, 1628s, 1560w, 1468s, 1384s, 1288s, 1236m,
1220m, 1076w, 788m, 756w, 692w, 628w, 448w.
2.1.6. [Cu2La(L)2(NO3)(H2O)2](NO3)2ꢀ3H2O (4)
Yield: 180 mg/58%. Anal. Calc. for
C38H46N7O22Br4Cu2La
(1538.05) (4): C, 29.67; H, 2.99; N, 6.38; Cu, 8.26; La, 9.03. Found:
C, 28.96; H, 3.03; N, 6.25; Cu, 8.32; La, 8.81%. Selected FTIR bands
(KBr, cmꢁ1): 3440m, 1624s, 1552w, 1468s, 1384s, 1296s, 1240s,
1220m, 1100w, 1068m, 1028w, 848w, 788m, 756w, 692m, 628w,
568w, 468w.
2.1.7. [CuDy(L)(NO3)2(H2O)3MeOH]NO3ꢀMeOH (5)
Yield: 105 mg/52%. Anal. Calc. for
C21H32N5O18Br2CuDy
Scheme 1. Structure of ligand molecule H2L.
(1028.38) (5): C, 24.50; H, 3.11; N, 6.81; Cu, 6.17; Dy, 15.80. Found:
C, 25.75; H, 2.92; N, 6.84; Cu, 6.32; Dy, 15.48%. Selected FTIR bands
(KBr, cmꢁ1): 3426m, 2928w, 2848w, 1628vs, 1560w, 1476s, 1384s,
1240s, 1096w, 1072m, 1012w, 966w, 852w, 820w, 792m, 762m,
696w, 572m, 540w, 448m.
2.1.2. N,N0-bis(5-bromo-3-methoxysalicylidene)propylene-1,3-
diamine, H2L
The Schiff base (C19H18Br2N2O4) abbreviated as H2L was ob-
tained by the 2:1 condensation of 5-bromo-2-hydroxy-3-methoxy-
benzaldehyde and 1,3-diaminopropane in methanol according to
the reported procedure [11,12,17]. Anal. Calc. for C19H18Br2N2O4:
C, 45.61; H, 4.00; N, 5.60. Found: C, 45.37; H, 3.84; N, 5.57%. FTIR
(KBr, cmꢁ1): 34520w, 1636s, 1574w, 1476s, 1440w, 1392w,
1252s, 1096m, 1068w, 1016w, 968m, 864m, 852m, 836m, 756m.
1H NMR (DMSO-d6, d ppm): –CH@N–, 8.50; Ar–OH, 13.78; H–Ar,
7.10, 7.20 (doublet AB); –OCH3, 3.79; –CH2–N–, 3.68 (triplet); –
CH2–, 2.03 (quintet).
2.1.8. [CuEr(L)(NO3)2(H2O)3MeOH]NO3ꢀMeOH (6)
Yield: 110 mg/55%. Anal. Calc. for
C21H32N5O18Br2CuEr
(1033.14) (6): C, 24.39; H, 3.10; N, 6.76; Cu, 6.16; Er, 16.35. Found:
C, 25.75; H, 2.57; N, 6.20; Cu, 6.33; Er, 15.17%. Selected FTIR bands
(KBr, cmꢁ1): 3426m, 2928w, 2848w, 1628vs, 1560w, 1476s, 1384s,
1240s, 1096w, 1072m, 1012w, 966w, 852w, 820w, 792m, 762m,
696w, 572m, 540w, 448m.
2.2. Methods
2.1.3. [Cu2Ln(L)2(NO3)(H2O)2](NO3)2ꢀ3H2O, (Ln = Ce 1, Pr 2, Nd 3, La 4)
and [CuLn(L)(NO3)2(H2O)3MeOH]NO3ꢀMeOH (Ln = Dy 5, Er 6)
The 1–6 complexes were prepared according the same experi-
mental procedure, so that only the cerium(III) entity (1) will be
described. The Schiff base ligand H2L (0.4 mmol, 0.1999 g) was dis-
solved in methanol (20 mL) at room temperature. Then copper(II)
acetate monohydrate (0.4 mmol, 0.0799 g) followed by cerium(III)
nitrate hexahydrate (0.2 mmol, 0.0868 g) were added to the yellow
homogeneous solution which was stirred, yielding a clear green
solution. The solution was filtered and kept undisturbed during a
few days at low temperature in the fridge until green crystals were
formed. They were isolated by filtration, washed with cold metha-
nol and air-dried. We have failed to obtain well-shaped single crys-
tals of the lanthanum(III) complex 4 but we have succeeded in
doing so for the cerium(III) 1, praseodymium(III) 2 and neodym-
ium(III) 3 complexes, that turned out to be isostructural. It is worth
to note that using the same 3d/4f ratio and synthesis conditions we
have obtained different products: trinuclear complexes in the case
of light lanthanides(III) 1–4 and dinuclear ones in the case of heavy
lanthanides(III) 5, 6.
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 1H NMR spectra of the Schiff base ligand was recorded in
DMSO-d6 solution using Bruker Avance spectrometer (range 0–16
d ppm).
The FTIR spectra of complexes were recorded over the range of
4000–400 cmꢁ1 using M-80 spectrophotometer (Carl Zeiss Jena).
Samples for FTIR spectra measurements were prepared as KBr
discs.
The magnetization of the CuII–CeIII–CuII (1), CuII–PrIII–CuII (2),
CuII–NdIII–CuII (3), CuII–LaIII–CuII (4), CuII–DyIII (5) and CuII–ErIII
(6) powdered samples was measured over the temperature range
of 1.8–300 K using a Quantum Design SQUID – based MPMSXL-5-
type magnetometer. The superconducting magnet was generally
operated at a field strength ranging from 0 to 5 T. Measurements
were made at magnetic field 0.5 T. The SQUID magnetometer
was calibrated with the palladium rod sample. Corrections are
based on subtracting the sample – holder signal and contribution
vD estimated from the Pascal’s constants [32].
Yield: 180 mg/59%. Anal. Calc. for C38H46N7O22Br4Cu2Ce (1)
(1539.66.): C, 29.64; H, 2.99; N, 6.37; Cu, 8.25; Ce, 9.10. Found:
C, 29.76; H, 2.79; N, 6.34; Cu, 8.10; Ce, 8.72%. Selected FTIR bands
(KBr, cmꢁ1): 3444m, 1624s, 1552w, 1468s, 1384s, 1292s, 1240s,
1220m, 1068w, 788m, 756w, 692w, 628w, 448w.
2.3. X-ray crystal structure determination
The X-ray diffracted intensities were measured from single
crystals on an Oxford Diffraction Xcalibur CCD diffractometer with
2.1.4. [Cu2Pr(L)2(NO3)(H2O)2](NO3)2ꢀ3H2O (2)
Yield: 190 mg/62%. Anal. Calc. for
C38H46N7O22Br4Cu2Pr
the graphite-monochromatized MoK
100(2) K for 1 and 3 and on an Oxford Diffraction Xcalibur Atlas
Gemini ultra diffractometer with monochromatized CuK radia-
tion (k = 1.54184 Å) at 293(2) K for 2, 5 and 6. Data sets were col-
lected using the scan technique. The programs CRYSALIS CCD and
a radiation (k = 0.71073 Å) at
(1540.45) (2): C, 29.62; H, 2.99; N, 6.37; Cu, 8.25; Pr, 9.15. Found:
C, 30.04; H, 2.85; N, 6.24; Cu, 8.02; Pr, 9.40%. Selected FTIR bands
(KBr, cmꢁ1): 3440m, 1628s, 1468s, 1384s, 1288s, 1238m, 1220m,
1076w, 788m, 756w, 692w, 628w, 448w.
a
x
CRYSALIS RED [33] were used for data collection, cell refinement and
data reduction. A multi-scan absorption correction was applied
for 1 and 3, while for 2, 5 and 6 – the analytical absorption correc-
tion based on the indexing of the crystal faces was performed [34].
The structures were solved by direct methods using SHELXS-97 and
2.1.5. [Cu2Nd(L)2(NO3)(H2O)2](NO3)2ꢀ3H2O (3)
Yield: 170 mg/55%. Anal. Calc. for
C38H46N7O22Br4Cu2Nd
(1543.78) (3): C, 29.57; H, 2.98; N, 6.35; Cu, 8.24; Nd, 9.34. Found:
C, 29.86; H, 2.86; N, 6.30; Cu, 8.22; Nd, 9.27%. Selected FTIR bands

B. Cristóvão et al. / Polyhedron 34 (2012) 121–128
123
Table 1
Crystallographic data for crystals 1–3 and 5–6.
1
2
3
5
6
Empirical formula
Formula weight
T (K)
C
38H46Br4Cu2N7O22Ce
C38H46Br4Cu2N7O22Pr
1540.45
293(2)
C38H46Br4Cu2N7O22Nd
1543.78
100(2)
C21H32Br2CuN5O18Dy
1028.38
293(2)
C21H32Br2CuN5O18Er
1033.14
293(2)
1539.66
100(2)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
monoclinic
C2/c
16.841(1)
13.805(1)
21.683(1)
93.72(1)
monoclinic
C2/c
16.958(1)
14.082(1)
21.788(1)
93.99(1)
monoclinic
C2/c
16.884(1)
13.700(1)
21.720(1)
94.10(1)
5011.1(6)
4, 0.5
monoclinic
P21/n
9.952(1)
16.826(1)
20.178(1)
90.62(1)
3378.6(1)
4, 1
monoclinic
P21/n
9.936(1)
16.808(1)
20.159(1)
90.71(1)
3366.3(2)
4, 1
b (°)
V (Å3)
5030.2(2)
4, 0.5
5190.3(2)
4, 0.5
Z, Z0
Crystal form/color
Crystal size (mm)
block/green
0.30 ꢂ 0.20 ꢂ 0.16
2.033
block/green
0.48 ꢂ 0.20 ꢂ 0.18
1.971
block/green
0.38 ꢂ 0.24 ꢂ 0.20
2.046
block/green
0.41 ꢂ 0.20 ꢂ 0.12
2.022
block/green
0.40 ꢂ 0.35 ꢂ 0.20
2.039
Dcalc (g cmꢁ3
)
l
(mmꢁ1
)
4.992
12.383
5.139
15.985
8.795
Absorption correction
h Range (°)
multi-scan
3.47–27.48
19474/5745 (0.0386)
5745/339
1.520
analytical
4.07–67.12
47926/4629 (0.0396)
4629/344
multi-scan
2.62–27.48
18790/5718 (0.0555)
5718/341
analytical
3.42–67.22
37080/6030 (0.0400)
6030/442
1.028
analytical
3.42–67.17
236595/6011 (0.0586)
6011/439
Reflections collected/unique (Rint
Data/parameters
)
Goodness-of-fit (GOF) on F2
1.067
1.283
1.103
R1, wR2 [I > 2
R1, wR2 (all data)
r
(I)]
0.0440, 0.0861
0.0567, 0.0874
0.0285, 0.0774
0.0294, 0.0781
0.0564, 0.1310
0.0731, 0.1351
0.0299, 0.0734
0.0320, 0.0751
0.0291, 0.0733
0.0298, 0.0737
Extinction coefficient
D
qmax
,
D
qmin (e Åꢁ3
)
1.415, ꢁ1.503
0.637, ꢁ0.635
2.267, ꢁ1.079
1.164, ꢁ1.288
1.202, ꢁ1.15
refined by the full-matrix least-squares on F2 using the SHELXL-97
[35] (both operating under WinGX [36]). Non-hydrogen atoms
with except of disordered C and O atoms were refined with aniso-
tropic displacement parameters.
The C9 atoms of the propyl bridge in all structures are disor-
dered over two positions with sof’s for the major part being
0.75(1), 0.61(1), 0.61(2), 0.54(1) and 0.52(1) in 1–3, 5 and 6,
respectively. In the asymmetric units of 1 and 3 in the outer sphere
of complex there are 1.5 water molecules. In 1 one H2O molecule is
disordered over two positions with sof’s 0.65 and 0.35. The second
water (sof = 0.5) is disordered over two positions by the twofold
axis. In 3 in the outer sphere 1.5 water molecules occupy two posi-
tions with sof’s 0.75. Hydrogen atoms of water molecules in the
inner coordination sphere were found in the difference Fourier
map. The water molecules in the outer sphere are disordered and
theirs H atoms were not found. All remaining H-atoms were posi-
tioned geometrically and allowed to ride on their parent atoms,
with Uiso(H) = 1.2/1.5 Ueq(C and O). A summary of the conditions
for the data collection and the crystal structure refinement param-
eters are given in Table 1. The molecular plots were drawn with
ORTEP3 for Windows [37], Mercury [38] and Diamond [39].
Fig. 1a. Schematic diagram of trinuclear complexes 1–3.
is that the complexes are dicationic [(LCu(H2O))2Ln(NO3)]2+ and
the charge is neutralized by two nitrate ions in the outer coordina-
tion sphere. The crystal structures are hydrates with three water
molecules (1.5 per asymmetric unit) disordered in channels along
Z crystallographic axis (Fig. 2).
3. Results and discussion
The CuII ions occupy the N2O2 cavity. The coordination polyhe-
dron has classical distorted square pyramidal geometry with water
molecule in the apical position (Fig. 3). The dihedral angles
between two N2O2 planes of the Schiff-base ligands are close to
30° (Table 2). Two O4 cavities of Schiff base ligands form kind of
capsule for the Ln ion. The coordination sphere of the cation is
3.1. Description of crystal and molecular structure of the complexes 1–
3 and 5–6
The trinuclear complexes [Cu2Ln(L)2(NO3)(H2O)2](NO3)2ꢀ3H2O
(where Ln = Ce (1), Pr (2) and Nd (3), L = C19H18N2O4Br2) of 1–3
are isostructural and crystallize in the monoclinic space group
C2/c. Their schematic diagram is given in Fig. 1a. The crystal struc-
ture with atom numbering scheme of 1 is shown in Fig. 1b (atom
numbering scheme is analogs for compounds 2 and 3). Details of
the relevant data collection and refinement are summarized in
Table 1. The selected bond lengths and angles are given in Table
2. The complexes of 1–3 are isostructural and crystallize in the
monoclinic space group C2/c. These compounds are heterotrinu-
clear monomers built up around a twofold axis that passes through
the LnIII cation and bisects the nitrate ligand so only half of mole-
cule is symmetrically independent, Z0 = 0.5. One distinctive feature
filled by the bidentate (g
2-chelating) nitrate group. Ten ligand O
atoms around the Ln(III) ion form polyhedron in shape of three
face- and one edge-capped trigonal bipyramid (Figs. 4). The dihe-
dral angles (a) between the (O1Cu1O2) and (O1Ln1O2) planes
are ca. 17° (Table 2). The complexes form chiral two-blade propel-
ler-like left- and right-handed CuIILnIIICuII units as in structures re-
ported by Wang et al. [14]. However, the crystals are racemates.
The intramolecular separations Cu1ꢀ ꢀ ꢀLn1 and Cu1ꢀ ꢀ ꢀCu1i
(symmetry code (i) ꢁx + 1, y, ꢁz + 1/2) being ca. 3.6 and 7.2 Å,
respectively (Table 2), are within the normal range of values for
polynuclear Cu–Ln complexes [9,26].

124
B. Cristóvão et al. / Polyhedron 34 (2012) 121–128
Fig. 1b. Molecular structure and atom numbering scheme of complex 1, displace-
ment ellipsoids were drawn at 50% probability level, hydrogen spheres are drawn
with an arbitrary radius; the disordered part of propylene bridge, water molecules
and nitrate anion from the outer coordination sphere were omitted for clarity.
Fig. 3. Coordination polyhedra of Cu and Nd cations in the trinuclear complex 3.
distorted octahedral. The Cu2+ ion is held within the inner N2O2
compartment of the Schiff base ligand. The apical vertices of the
deformed octahedron are occupied by one methanol and one ni-
trate oxygen atoms. The dihedral angle between Cu1O1O2 and
Ln1O1O2 (where Ln1 = Dy, Er) is equal to 2.9(1)° 5 and 2.8(1)° 6,
respectively that is in accordance with the values reported for sim-
ilar compounds [11]. The Cu1–O and Cu1–N bond distances in the
equatorial N2O2 square plane of copper cation for 5 and 6 are very
similar and lie in the ranges 1.949(2)–1.983(2) and 1.959(3)–
1.986(3) Å, respectively, while in the apical position the Cu1–O
bond distances are longer (Table 3). The lanthanide–oxygen bond
lengths depend on the chemical nature of the O atoms (methoxy,
nitrate, aqua or phenoxo). They vary from 2.323(3) Å for
Er1–O8(aqua) to 2.524(2) Å for Dy1–O3(methoxy) (Table 3). The
Ln–O(phenolate) average bond distance decrease in order of lan-
thanide radius contraction: Gd (2.392(5) Å) [11] > Tb (2.375(2) Å)
[11] > Dy (2.367(2) Å) > Er (2.345(5) Å).
3.2. Magnetic properties
Fig. 2. View along channels with disordered water molecules formed in crystal 1.
Hydrogen atoms were omitted for clarity.
The magnetic properties of the heterotrinuclear complexes,
CuII–CeIII–CuII (1), CuII–PrIII–CuII (2) and CuII–NdIII–CuII (3) were
The Ln–O bond lengths depend on the nature of the oxygen
atoms. The distances increase in sequence phenolato < nitra-
to < methoxo (from 2.405(4) to 2.636(3) Å).
determined over the temperature range of 1.8–300 K. Plots of mag-
ꢁ1
netic susceptibility vm and
vmT product versus T are given in
Fig. 5. The experimental
vmT values at room temperature (1.54
for 1, 2.24 for 2 and 2.23 cm3 K molꢁ1 for 3) approximately corre-
Two Cu(II) and one Ln(III) ions are arranged nearly in a line,
with a Cu1–Ln1–Cu1ii (symmetry code (ii): 1/2 ꢁ x, 1/2 + y, 1/
2 ꢁ z) angles close to 172° (Table 2). Between nitrato ions and
water molecules forms extensive network of hydrogen bonds.
Intermolecular Mꢀ ꢀ ꢀM separations in the CuIILnIIICuII structures
indicate well separation of the trinuclear 3d–4f–3d cores (Table 2).
The heterodinuclear complexes [CuLn(L)(NO3)2(H2O)3MeOH]
NO3ꢀMeOH (where Ln = Dy (5) and Er (6)) are isostructural with
CuII–GdIII and CuII–TbIII coordination compounds reported by us
earlier [11] (space group P21/n). Their schematic diagram is given
in Fig. 4a. The crystal structure with atom numbering scheme of
5 is shown in Fig. 4b (atom numbering scheme is analogs for com-
pound 6). The crystallographic data and experimental details are
summarized in Table 1. The selected bond distance and angle
values for structures are presented in Table 3. The lanthanide(III)
cations in 5 and 6 are nine-coordinated by one bidentate nitrate
ion, three water oxygen atoms and four oxygen atoms of the Schiff
base. The coordination environment around the copper(II) site is
ÀÀ
ÁÂ
spond to the calculated ones
v
mT ¼ Nb2=3k 2gC2uSCuðSCu þ 1Þþ
g2LnJLnðJLn þ 1ÞꢃÞ for uncoupled metal ions (1.55, 2.35 and
2.38 cm3 K molꢁ1, respectively). The
v
mT decreases by lowering
the temperature to 0.519 for 1, 0.406 for 2 and 0.249 cm3 K molꢁ1
for 3 in 1.8 K. This decrease could be caused by crystal field effect,
as well as cooperative antiferromagnetic interactions of CuII–LnIII
pairs. The susceptibility data obey the Curie–Weiss law. Negative
value of Weiss constants could also confirm the weak antiferro-
magnetic exchange coupling between the metal ions (ꢁ6.8 K for
1, ꢁ9.3 K for 2 and ꢁ18.7 K for 3). These results are consistent with
the empirical studies concerning heterometallic 3d–4f compounds,
in which the 4f ions display a spin–orbit coupling [18,19,30,31,40–
45]. A final conclusion on the nature of the exchange interaction in
compounds cannot be drawn, since the magnetic properties of this
type of systems are not only due to the coupling between the 3d
and 4f metal ions, but also to the thermal depopulation of the Stark
sublevels of the 4f ions.

B. Cristóvão et al. / Polyhedron 34 (2012) 121–128
125
magnetization M is expressed in lB units. The compounds do not
reach the saturation in the applied field range and magnetization
in 5 T is equal only to 1.95 lB for 1, 1.82 lB for 2 and 1.16 lB for
3. These values are much lower than the simulated values calcu-
lated with the Brillouin function for two Cu(II) ions and one Ln(III)
ion, which do not interact. This further indicates that all complexes
behave as an antiferromagnet. Unfortunately, the quantitative
description of the magnetic properties of heterometallic complexes
containing lanthanide(III) ions is not an easy task because of the li-
gand-field effect and spin–orbit coupling of the Ln(III) ion [19,31].
The magnetic susceptibility of CuII–LaIII–CuII (4) has been also
measured in the temperature range of 1.8–300 K in a 0.5 T applied
magnetic field. The data obtained for complex are represented in
Fig. 7. At the room temperature, the
vmT product is equal to
0.884 cm3 molꢁ1 K and it is consistent with only two S = 1/2 cop-
per(II) centers. Lanthanum(III) with an 1S0 single-ion ground state
is diamagnetic. In this compound, the intramolecular Cuꢀ ꢀ ꢀCu dis-
tance is certainly large and may preclude any significant magnetic
interactions between the copper centers in trinuclear complex.
Fig. 4a. Schematic diagram of dinuclear complexes 5 and 6.
However, below 10 K, small but discernable drop in the
to 0.711 cm3 K molꢁ1 at 1.8 K was also noted. The thermal depen-
dence of is mT characteristic of a small antiferromagnetic interac-
vmT values
v
tion since no maximum appears in the vm versus T curve until
1.8 K. This apparent weak antiferromagnetic interaction may be
mediated by the diamagnetic La(III) center. The examples in the lit-
erature [26] show, that the diamagnetic lanthanum(III) center are
capable of mediating magnetic exchange between the copper(II)
in trinuclear complexes.
The magnetization curve for 4 measured at 2 K was reproduced
with the Brillouin function for two centers of SCu = 1/2 (Fig. 8) and
confirm our previous assumption.
To estimate the magnitude of interaction we use the following
equation for the magnetic susceptibility for two exchange coupled
copper(II) ions [46]. The data have been fit to a model which
~
~
assume the exchange Hamiltonian to be H ¼ ꢁ2JS1 ꢀ S2. The suscep-
tibility is then predicted to be:
ꢀ
ꢁ
2Nb2g2
3kT
1
3
Fig. 4b. Molecular structure and atom numbering scheme of complex 5, displace-
ment ellipsoids were drawn at 50% probability level, hydrogen spheres are drawn
with an arbitrary radius; the methanol molecule and nitrate anion from the outer
coordination sphere were omitted for clarity.
vm
¼
1 þ exp ðꢁ2J=kTÞ
ð1Þ
and the symbols have usual meaning. Least-squares fitting of the
experimental data in whole temperature range leads to J = ꢁ0.42
(2) cmꢁ1, gCu = 2.16(2), as indicated by the solid curve in Fig. 7.
To confirm the nature of the ground state of 1, 2 and 3, we
investigated the variation of the magnetization, M, with respect
to the field, at 2 K. The results are shown in Fig. 6, where molar
The agreement factor
R
is equal 9.38 ꢂ 10ꢁ5 (R =
R
(v
expT ꢁ
v
calcT)2/ expT)2). The result of calculations may be indicative of
R(v
Table 2
Selected bond lengths, angles, intra- and intermolecular distances in complexes of 1, 2 and 3 (Å, °).
Bond/distance (Å)
1
2
3
Angle (°)
1
2
3
Ln1–O1
Ln1–O2
Ln1–O3
Ln1–O4
2.441(3)
2.512(3)
2.636(3)
2.628(3)
2.587(3)
1.961(3)
1.953(3)
2.323(4)
1.971(4)
1.967(4)
3.618(1)
7.218(1)
7.298(1)
8.749(1)
10.888(1)
2.432(2)
2.507(2)
2.628(2)
2.625(2)
2.570(3)
1.961(2)
1.953(2)
2.378(3)
1.973(3)
1.963(3)
3.613(1)
7.210 (1)
7.446 (1)
8.891(1)
11.021(1)
2.405(4)
2.495(4)
2.596(4)
2.615(3)
2.547(5)
1.952(4)
1.948(4)
2.327(5)
1.979(5)
1.954(5)
3.598(1)
7.179(1)
7.252(1)
8.708(1)
10.872(1)
O1–Cu1–O2
O2–Cu1–N2
O1–Cu1–N2
O2–Cu1–N1
O1–Cu1–N1
N2–Cu1–N1
O2–Cu1–O5
O1–Cu1–O5
N2–Cu1–O5
N1–Cu1–O5
Cu1ꢀ ꢀ ꢀLn1ꢀ ꢀ ꢀCu1ii
a
78.6(1)
93.1(1)
158.0(2)
169.1(1)
91.6(1)
97.8(2)
91.7(1)
105.2(1)
95.3(1)
86.4(2)
171.7(1)
17.4(2)
28.3(1)
78.3(1)
93.1(1)
158.2(1)
169.3(1)
92.0(1)
97.6(1)
92.0(1)
104.9(1)
95.3(1)
86.0(1)
172.0(1)
17.4(1)
28.4 (1)
78.2(2)
93.2(2)
157.3(2)
169.0(2)
91.7(2)
97.9(2)
91.4(2)
105.7(2)
95.2(2)
87.1(2)
172.4(1)
16.2(2)
25.6(1)
Ln1–O6
Cu1–O1
Cu1–O2
Cu1–O5
Cu1–N1
Cu1–N2
Cu1–Ln1
Cu1ꢀ ꢀ ꢀCu1i
Cu1ꢀ ꢀ ꢀCu1ii
Cu1ꢀ ꢀ ꢀLn1ii
Ln1ꢀ ꢀ ꢀLn1ii
b
Ln1 = Ce1 for 1, Nd1 for 2, Pr1 for 3;
ꢁz + 1/2; ii1/2 ꢁ x, 1/2 + y, 1/2 ꢁ z.
a
– dihedral angle between the Cu1O1O2 and Ln1O1O2 planes; b – dihedral angle between two N2O2 planes; symmetry codes: iꢁx + 1, y,

126
B. Cristóvão et al. / Polyhedron 34 (2012) 121–128
Table 3
Selected bond lengths, angles, intra- and intermolecular distances in complexes of 5
and 6 (Å, °).
Bond/distance (Å)
5
6
Angle (°)
5
6
Ln1–O1
Ln1–O2
Ln1–O3
Ln1–O4
Ln1–O5
Ln1–O6
Ln1–O8
Ln1–O9
Ln1–O10
Cu1–N1
Cu1–N2
Cu1–O1
Cu1–O2
Cu1–O11
Cu1–O14
Cu1–Ln1
2.365(2) 2.341(2) Cu1–O1–Ln1 108.6(1) 108.7(1)
2.369(2) 2.349(2) Cu1–O2–Ln1 107.3(1) 107.2(1)
2.524(2) 2.510(2) O1–Ln1–O2
2.497(2) 2.484(2) O1–Ln1–O3
2.450(3) 2.428(3) O2–Ln1–O4
64.3(1)
63.9(1)
64.9(1)
2.9(1)
64.7(1)
64.2(1)
65.2(1)
2.8 (1)
2.493(3) 2.473(3)
2.345(3) 2.323(3)
2.352(2) 2.332(2)
2.371(2) 2.346(2)
1.986(3) 1.986(3)
1.960(3) 1.959(3)
1.951(2) 1.949(2)
1.983(2) 1.983(2)
2.604(3) 2.600(3)
2.552(3) 2.557(3)
3.513(1) 3.495(1)
a
ꢁ1
Fig. 7. Temperature dependence of experimental
vmT (s) and vm (d) vs. T for
complex 4. The solid line is the calculated curve derived from Eq. (1).
Ln1 = Dy1 for 5, Er1 for 6;
a
– dihedral angle between the Cu1O1O2 and Ln1O1O2
planes.
Fig. 8. Field dependence of the magnetization for complex 4 (s) at 2 K. The solid
line is the Brillouin function curve for a two independent S = 1
/
of CuII–LaIII–CuII
2
unit.
ꢁ1
Fig. 5. Temperature dependence of experimental
complex 1,
mT (h) and vmꢁ1 (j) vs. T for complex 2 and
for complex 3.
v
mT (s) and vm (d) vs. T for
v
v
mT (4) and vmꢁ1 (N) vs. T
weak interactions between copper centers for reason of large dis-
tance Cuꢀ ꢀ ꢀCu in the trinuclear unit.
The tempꢁe1rature dependences of the magnetic susceptibility
v
mT and vm of the two heterodinuclear complexes, CuII–DyIII
(5) and CuII–ErIII (6) are represented in Fig. 9. At the room temper-
ature, the
v
mT product is equal to 14.92 cm3 molꢁ1 K for (5) and
11.49 cm3 molꢁ1 K for 6, which correspond the values (14.54 and
11.83 cm3 molꢁ1 K, respectively) expected for a pair of noninter-
acting Cu(II) (S = 1/2) and Dy(III) (4f9, J = 15/2, S = 5/2, L = 5,
6H15/2) or Er(III) (4f11, J = 15/2, S = 3/2, L = 6, 4I15/2) ions. As the tem-
perature is lowered,
vmT gradually increases to reach a value of
18.73 cm3 molꢁ1 K for 5 and 12.26 cm3 molꢁ1 K for 6 at 10 K. The
profile of the
vmT versus T curves are strongly suggestive of the
occurrence a ferromagnetic CuII–LnIII interaction in the 10–300 K
temperature range. Positive value of Weiss constants could addi-
tionally confirm the ferromagnetic exchange coupling between
the metal ions (6.9 K for 5 and 2.3 K for 6). Below 10 K, the
vmT val-
ues are decreased to 11.84 cm3 K molꢁ1 for 5 and 9.23 cm3 molꢁ1
K
for 6 at 1.8 K which may be attributed to zero-field splitting (ZFS)
effects and/or intermolecular interactions. For the both complexes,
the ground state of dysprosium(III) and erbium(III) ions have a
first-order angular momentum [18,19,30], so that the magnetic
properties of the CuII–LnIII couples are not appropriate to a simple
analysis based on a spin Hamiltonian comprising only isotropic ex-
change [13]. Additional difficulties may arise from the crystal field
Fig. 6. Field dependence of the magnetization for complex 1 (s), 2 (h) and 3 (4) at
2 K. The solid line is the Brillouin function curve for a three independent S = 1
of
/
2
CuII–CeIII–CuII unit; dashed line is the Brillouin function for two independent S = 1
/
2
and one S = 1 of CuII–PrIII–CuII unit; dotted line is the Brillouin function for two
independent S = 1 and one S = 3 of CuII–NdIII–CuII unit.
/
2
/
2

B. Cristóvão et al. / Polyhedron 34 (2012) 121–128
127
4. Conclusion
The salen-like ligand N,N0-bis(5-bromo-3-methoxysalicylid-
ene)propylene-1,3-diamine can effectively stabilize heterotri- (Cu–
4f–Cu) and heterodinuclear (Cu–4f) complexes. The coordination
compounds 1–3 are isostructural and crystallize in the monoclinic
space group C2/c. Although, compound 4 gave no single crystals of
quality suitable for X-ray structural analysis, we imply similar struc-
ture as in crystals of 1–3 on the basis of analogies in elemental com-
position and FTIR spectra. Their crystal structure is built of trinuclear
dicationic units of [(LCu(H2O))2Ln(NO3)]2+ with nitrate ions in the
outer coordination sphere neutralizing the charge. The molecules
havechiraltwo-bladepropeller-likeshape, however,theycrystallize
as racemates. In the crystal net there are channels along Z crystallo-
graphicaxis filled with disordered watermolecules. The heterodinu-
clear 5 (Dy) and 6 (Er) compounds are isostructural with other heavy
lanthanide(III) complexes (Gd and Tb [11]). It is worth to study other
lanthanide(III) complexes to establish the boundary radius value of
Ln(III)ionforformingdifferenttypesofstructures.Themeasurement
of variable-temperature magnetic susceptibility reveals antiferro-
magnetic interaction between spin carriers in the heterotrinuclear
complexes, CuII–CeIII–CuII (1), CuII–PrIII–CuII (2), CuII–NdIII–CuII (3)
and ferromagnetic coupling in the heterodinuclear complexes,
CuII–DyIII (5) and CuII–ErIII (6). The magnetic data obtained for CuII–
LnIII–CuII (4) shows the weak antiferromagnetic exchange coupling
between the copper ions through the diamagnetic La(III) center.
ꢁ1
Fig. 9. Temperature dependence of experimental
vmT (s) and vm (d) vs. T for
ꢁ1
complex 5 and
vmT (h) and vm (j) vs. T for complex 6.
Appendix A. Supplementary data
CCDC 832420, 858067, 832421, 858065 and 858066 contain the
supplementary crystallographic data for 1, 2, 3, 5 and 6. These data
can be obtained free of charge via http://www.ccdc.cam.ac.uk/con-
ts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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Fig. 10. Field dependence of the magnetization for complex 5 (s) and 6 (h) at 2 K.
The solid line is the Brillouin function curve for a two independent S = 1
of CuII–DyIII unit; dashed line is the Brillouin function for two independent S = 1
and S = 3 of CuII–ErIII unit.
/
2 and S = 5
/
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