Novel sandwich triple-decker dinuclear NdIII-(bis-N,N′-p- bromo-salicylideneamine-1,2-diaminobenzene) complex

Article abstract of DOI:10.1016/j.poly.2013.04.010

In the search of new multifunctional molecular materials, the present paper introduces the work performed with the Salen-type Schiff base: bis-N,N′-p-bromo-salicylideneamine-1,2-diaminobenzene (H₂bsph), to attain novel coordination complexes co

Full text of DOI:10.1016/j.poly.2013.04.010

Polyhedron 64 (2013) 203–208
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Novel sandwich triple-decker dinuclear
NdIII-(bis-N,N0-p-bromo-salicylideneamine-1,2-diaminobenzene) complex
Ahmed M. Abu-Dief a, Raúl Díaz-Torres b, Eva Carolina Sañudo b, Laila H. Abdel-Rahman a,
,
⇑
Núria Aliaga-Alcalde c,
⇑
a Chemistry Department, Faculty of Science, Sohag University, 82524 Sohag, Egypt
b Departament de Química Inorgànica, Universitat de Barcelona, Diagonal 645, 08028 Barcelona, Spain
c ICREA-Institut de Ciència de Materials de Barcelona (ICMAB-CSIC), Campus de la UAB, 08193 Bellaterra, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
In the search of new multifunctional molecular materials, the present paper introduces the work per-
formed with the Salen-type Schiff base: bis-N,N0-p-bromo-salicylideneamine-1,2-diaminobenzene (H2-
bsph), to attain novel coordination complexes containing lanthanides centers (LnIII). So far, our studies
have shown that the combination in acetone of the well-known H2bsph ligand, a base and NdIII(NO3)3-
ꢀ6H2O, results in a yellow solid which crystalline forms has been suitable for X-ray diffraction studies.
As a result, a novel NdIII system has been achieved, with formula [Nd2(bsph)3(H2O)]ꢀ2CH3Cl (1). The archi-
tecture of 1 encloses two metal centers inserted among three Schiff bases (2NdIII:3(bsph2ꢁ)) resembling a
sandwich-shape, is a rare example of triple-decker coordination species with only few similar systems
described in the literature. The magnetic properties of 1 have been examined as well as the luminescence
activity; the latest was compared with H2bsph for better interpretation.
Received 24 January 2013
Accepted 3 April 2013
Available online 11 April 2013
‘‘Dedicated with admiration to Professor
George Christou on the occasion of his 60th
birthday’’
Keywords:
Lanthanide complex
Schiff base
Luminescence
Magnetism
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
as sterochemical models in coordination chemistry and in general,
easy to prepare and therefore, a rich variety of them are available
In recent years considerable efforts have been directed toward
the rational design of multifunctional molecular species using LnIII
complexes. The appealing properties of such family of metals,
mainly magnetic and fluorescent, and their potential use in topics
like molecular magnetism, fluorescence, gas absorption, telecom-
munications, probes in biology and sensing, among others, portray
them as highly promising materials in the development of new
technologies [1–5]. However, it is complicated to anticipate final
structures based on LnIII ions because they often display high and
variable coordination numbers and flexible coordination geome-
tries [6]. One of the most successful strategies to solve this issue
has been the use of rigid conjugated chelating units, as phthalocy-
anines and porphyrins [7–9], to encapsulate such metallic centers
providing the so-called ‘‘double-, triple-,. . . and multi-decker’’
structures. A number of these molecular species have being proved
relevant as single-ion magnets, single-molecule magnets [10] or
because their visible and/or Near-IR luminescent emissions [11].
With the same aim in mind, studies with Salen-type Schiff base
ligands are presently performed. These molecules are well-known
for research purposes [12–15]. Several dinuclear [d–4f] systems
containing Schiff bases have been discussed over the last years,
where the transition metal center was first encapsulated by the li-
gand and the lanthanide was used as terminal metallic center [16–
19]. Related to salen-type ligands, [3d–4f] polynuclear clusters
(nuclearity > 2) with all kind of morphologies have described as
well [20–22]. During the last years, the number of homometallic
LnIII species has risen. However, there is still a limited number of
LnIII–Salen systems, so far they have been described some mono-
nuclear systems and mostly polynuclear entities [23–25]. Due to
their novelty, there is also a lack of control the number of LnIII
and ligands per structure. As it was stressed in 2005 by Yang and
Jones [26] and later by the same group and others [25,27–30],
these systems can also formed multi-decker structures the same
way than the most rigid ligands described above [7–9]. It is worth
mentioning that few examples of such LnIII–Salen systems are pub-
lished and from them even less depict ‘‘real sandwich structures’’
[25–26,29–30]. They are called this way because the number of
LnIII centers is always inferior by one figure to the ligand, which
protect the metallic centers well packed among these organic
units. Herein, we do introduce a new sandwich triple-decker dinu-
clear complex. In this regard, the present work focuses on the Salen
ligand H2bsph, and presents a new [NdIII2(bsph)3(H2O)] complex
⇑
Corresponding authors.
E-mail addresses: lailakenawy@hotmail.com (L.H. Abdel-Rahman), nuria.aliaga@
icrea.cat (N. Aliaga-Alcalde).
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.04.010

204
A.M. Abu-Dief et al. / Polyhedron 64 (2013) 203–208
that display paramagnetic behaviors as well as luminescent prop-
erties in the near-IR region. This work shows our preliminary steps
towards the creation of a family of [LnIII2L3X] complexes (L = Schiff
bases; X = solvent molecule), where the asymmetry of the LnIII ions
involved and their final properties, could provide relevant proper-
ties already found in other dinuclear LnIII systems with regards to
their application in emerging research areas as nanospintronics
[31].
2.3. Physical measurements
C, H and N analyses were performed with a Perkin-Elmer 2400
series II analyzer. Infrared spectra (4000–400 cmꢁ1) were recorded
from KBr pellets on a Bruker IFS-125 FT-IR spectrophotometer.
Absorption spectra were recorded with 1 nm resolution for all
cases on a Cary 100 Bio UV-spectrophotometer.
2.4. Structure determination
Single crystal diffraction data for complex 1 were collected on a
yellow plate on a Bruker APEXII SMART diffractometer at the Fac-
ultat de Química, Universitat de Barcelona, using a microfocus Mo
2. Experimental
Starting materials were purchased from Aldrich and all manip-
ulations were performed using materials as received.
ka
radiationsource. The structures were solved by direct methods
(
SHELXS97) andrefined on F2
(SHELX-97). Hydrogen atoms were in-
cluded on calculatedpositions, riding on their carrier atoms.
2.1. Preparation of ligand H2bsph
2.5. Fluorescence data
H2bsph was synthesized according literature methods [32].
4.04 g of 5-bromosalicylaldehyde (20 mmol) were dissolved in
60 ml of ethanol and heated to reflux. On the other hand, 1,2-Phen-
ylenediamine (1.08 g, 10 mmol) was dissolved in 50 ml of ethanol.
The mixture of both solutions was refluxed for 4 h and orange
Fluorescence emission spectra in the solid state and in solution
were carried out on a Horiba–Jobin–Yvon SPEX Nanolog-TM and a
Cary Eclipse spectrofluorimeter. Distilled THF and HPLC MeCN
were employed and concentrations of ligand H2bsph and com-
pound 1 were 10ꢁ6 and 10ꢁ5 M, respectively. The experiments
were performed in aerobic conditions and at room temperature;
slits used were of 5 nm for all the experiments (solid sample and
in solution).
crystals were formed during the reflux. Yield: 85%. IR (m )
/cmꢁ1
1612s, 1563m, 1473s, 1347w, 1273s, 1186m, 979w, 915w,816m
755m, 700w, 568w, 454w. Elemental Anal. Calc. for H2bsph
(C20H14N2Br2O2): C, 50.85; H, 2.85; N, 5.97. Found: C, 50.76;
H, 2.99; N, 6.06%.
2.6. Magnetic experiments
Magnetic experiments using SQUID were performed in the
‘‘Unitat de Mesures Magnètiques (Universitat de Barcelona)’’ on a
polycrystalline sample of complex 1 with a Quantum Design SQUID
MPMS-XL magnetometer working in the 2.0–300 K range. The
magnetic fields were 0.02 T (from 2.0 to 30 K) and 0.3 T (from 30
to 300 K). The diamagnetic corrections were evaluated from Pas-
cal’s constants.
2.2. Synthesis of [Nd2(bsph)3(H2O)]ꢀ2CH3Cl (1ꢀ2CH3Cl)
NaOH (0.32 g, 8 mmol in 10 ml water) was added to a solution
of H2bsph (1.90 g 4 mmol) in acetone and the resulting one was
stirred during 15 min. Then, 0.87 g Nd(NO3)3ꢀ6H2O (2 mmol) dis-
solved in 30 mL of water were added slowly to the initial mixture.
The resulting solution was stirred for a couple of hours and. The
resulting yellow precipitate was filtered, washed with H2O and
dried with Et2O. Yellow crystals were obtained layering CHCl3 with
2.7. Crystal structure of [Nd2(bsph)3(H2O)]ꢀ2CH3Cl] (1ꢀ2CH3Cl)
Et2O. Yield: 74%. IR (m
/cmꢁ1) 1636m, 1611m, 1578w, 1519m,
1459m, 1163m, 977w, 825w, 753w, 697w, 636w, 542w, 473w,
456w. Elemental Anal. Calc. for Ndbsph (C60H42N6Br6O9Nd2) C,
41.20; H, 2.42; N, 4.80. Found: C, 41.24; H, 2.39; N, 4.76%.
Labeled ORTEP representations of 1 are depicted in Fig. 1. Rele-
vant crystallographic data of the complex are collected in Tables 1
and 2. Complex 1 crystallizes in the monoclinic space group P21/c
Fig. 1. (Left) POV-Ray labeled ORTEP representation of [Nd2(bsph)3(H2O)]ꢀ2CH3Cl (1); H atoms have been removed to simplify, C atoms are in grey, Nd in purple, N in dark blue,
O in red and Br in orange. (Right) Labeled scheme of the core of 1. (Color online.)

A.M. Abu-Dief et al. / Polyhedron 64 (2013) 203–208
205
the molecule (in a wing or butterfly shape) [26,30], whereas the
central bsph2ꢁ ligand is the less distorted (see explanation below).
Both NdIII ions are sandwiched among the three bsph2ꢁ forcing the
twist of the two outer ones (Fig. 1 left). The intramolecular Nd1–
Nd2 distance is 3.945 Å, in the range of other Nd tripe/tetra-decker
Nd complexes [26,30]. As mentioned above, Nd1 is heptacoordi-
nated and displays a distorted mono-capped octahedron geometry
(Fig. 1 right); binds to two nitrogen atoms (N3, N4) from one of the
external bsph2ꢁ ligands and five oxygen atoms (O1–O3, O5–O6):
two of them from the former ligand (O1, O2) and the rest from a
molecule of water (O5w) and the central bsph2ꢁ unit (O3–O6) that
acts as a bridge between the two Nd centers. Nd1–N3 and Nd1–N4
are 2.557 and 2.553 Å, respectively, meanwhile the Nd1–Ox (X = 1–
3, 5–6) bond lengths are found between 2.234 and 2.451 Å; in
agreement with reported NdIII ions coordinated to similar Salen-
type Schiff bases [25,30].
The defined geometry of Nd1 provided the longest angles of
158.22° and 163.71° for O1–Nd1–O3 and O2–Nd1–O6, in that or-
der. N3–Nd1–O5 and N4–Nd1–O5 were found of 152.77° and
142.89°, correspondingly. Finally, the bridging angle O3–Nd1–O6,
formed by two oxygen atoms from the central ligand and Nd1
ion was 70.61°. On the other hand, Nd2 is octacoordinated contain-
ing four nitrogens (N1–N2, N5–N6) and four oxygen atoms (O3–
O4, O6–O7); displays a distorted square antiprism geometry where
each square contains equal number of nitrogen and oxygen atoms
(described as Nd2–Ny and Nd2–Ox). Even though there are several
differences with Nd1, overall the bending of the peripheral bsph2ꢁ
ligand is similar to the former. The bond distances Nd2–Ny (y = 1–
2, 5–6) are from 2.552 to 2.657 Å, longer than those found for Nd1
however, the Nd2–Ox (x = 3–4, 6–7) are of similar range between
2.292 and 2.442 Å. The bond angles around Nd2 are also in agree-
ment with the already mentioned distorted geometry, being Ox–
Nd2–Ox0 angles between 70.75° and 97.67°, the shorter corre-
sponding to the O3–Nd2–O6 bridging angle very similar in value
with the reported for Nd1. Angles between Ny–Nd2–Ny0 are found
between 139.31° and 59.86°. Finally, Nd1–O3–Nd2 and Nd2–O6–
Nd1 were found of 110.0° and 108.5°, in that order. A more detailed
number of bond distances and angles for 1 are listed in Table 2.
Additional features of such structure are (i) the quasi-parallel
mode of their aromatic rings to accommodate the two NdIII centers
(Fig. 2 left; although Caromaticꢀ ꢀ ꢀCaromatic distances always superior
to 3.4 Å), where one of the outer and the inner bsph2ꢁ units show
a similar disposition meanwhile the third one is the most distorted
and twisted among the three; and (ii) the bend of the ligands to al-
low the final disposition of the metal centers providing a compact
structure (Fig. 2 right) similarly to other lanthanides with more re-
stricted ligands as phtalocyaninates or porphyrines [7–9].
Table 1
Crystal data and structure refinement for complex 1.
Empirical formula
C62H34Br6Cl6N6Nd2O7 (1)
Formula weight
T (K)
Crystal system
Space group
a (Å)
1955.62
101(2)
monoclinic
P21/c
15.2328(7)
18.6384(9)
23.4772(12)
90.00
96.029(3)
90.00
6628.7(6)
4
1.968
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (mg/mm3)
l
(mmꢁ1
)
5.466
3764.0
F(000)
Crystal size (mm3)
0.13 ꢂ 0.13 ꢂ 0.05
2.68–56.72°
ꢁ20 6 h 6 20,
ꢁ24 6 k 6 22,
ꢁ30 6 l 6 31
49323
15745 (0.0793)
15745/0/803
0.997
2H
Index ranges
Reflections collected
Independent reflections (Rint
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indexes [I P 2
Final R indexes [all data]
Largest difference in peak/hole (e Åꢁ3
)
r(I)]
R1 = 0.0946, wR2 = 0.2622
R1 = 0.1378, wR2 = 0.3001
3.23/ꢁ7.10
)
Table 2
Relevant bond lengths and angles for complex 1, respectively.
Distances (Å)
Angles (°)
Nd1
Nd1
Nd1
Nd1
Nd1
Nd1
Nd1
Nd1
Nd2
Nd2
Nd2
Nd2
Nd2
Nd2
Nd2
Nd2
Nd2
O1
O2
O3
O5w
O6
N3
N4
O3
N1
N2
O4
O6
O7
N5
N6
3.9455(9)
2.233(7)
2.302(8)
2.424(8)
2.451(8)
2.420(8)
2.558(9)
2.554(9)
2.393(8)
2.570(9)
2.552(9)
2.348(7)
2.442(8)
2.291(7)
2.657(9)
2.654(9)
Nd2
Nd1
O1
O1
O1
O2
O2
O2
O3
O6
N4
O3
N2
O4
O4
O6
O6
O7
O7
O7
N6
O3
O6
Nd1
Nd2
O2
N3
N4
O5w
N3
N4
O5w
O3
110.0(3)
108.5(3)
99.8(3)
71.6(3)
120.1(3)
84.5(3)
118.6(3)
72.1(3)
74.7(3)
70.6(3)
63.3(3)
70.8(3)
63.3(3)
122.7(3)
71.4(3)
100.2(3)
67.3(3)
71.0(3)
112.4(3)
97.7(3)
59.9(3)
Nd1
Nd1
Nd1
Nd1
Nd1
Nd1
Nd1
Nd1
Nd1
Nd2
Nd2
Nd2
Nd2
Nd2
Nd2
Nd2
Nd2
Nd2
Nd2
N3
O6
N1
N1
N2
N5
N6
N1
N2
O4
To characterize the bending of the three ligands two planes
were defined per ligand taking into account the Br and the N and
N5
Torsion angles (°)
O6 Nd1 O3 Nd2
O3 Nd1 Nd2 O6
ꢁ3.2(3)
ꢁ174.8(4)
with the asymmetric unit containing four molecules of 1 and eight
molecules of solvent (CHCl3). Complex 1 contains two NdIII centers
(Nd1 and Nd2) with coordination numbers seven and eight respec-
tively; both centers have different binding environments with re-
spect to the bsph2ꢁ ligands and Nd1 coordinates additionally to a
molecule of H2O. All these facts prevent from further intramolecu-
lar elements of symmetry. The final structure, [2Nd:3(bsph2ꢁ):H2-
O], contains three bsph2ꢁ ligands: two on the peripheral sides
limiting and isolating each molecule from the neighbors (being
the shortest Ndꢀ ꢀ ꢀNd distance 5.829 Å) and one inner ligand acting
as a bridge between the two metal centers. To allow the formation
of such complex, the peripheral ligands bend towards the center of
Fig. 2. Ball and stick representation showing the almost parallel alignment of two
of the bsph2ꢁ ligands that form each complex Nd atoms are in purple, C in grey, H in
light grey, N in dark blue, O in red and Br in bright orange. (Color online.)

206
A.M. Abu-Dief et al. / Polyhedron 64 (2013) 203–208
O atoms from each half side of the ligand. Then, the angle formed
by both planes was calculated. If the ligands will be disposed in a
single plane the final angle would it be 0° or nearby. The highest
the angle, the most distorted the ligand. This way, measuring the
peripheral ligands, Br5O4N2 and Br6O7N1 provided an angle of
38.24° being the most distorted; it was followed by the 34.03°
formed with the Br2O2N4 and Br1O1N3 planes. The central ligand
displayed an angle of 11.04°, corresponding to the less distorted
one, using the planes described by the following atoms: Br4O3N5
and Br3O6N6 (Fig. 2 right).
some transition metals proved [33–34], the reactivity of such or-
ganic unit with LnIII remained unexplored until now [35]. In this
paper, systems 1 was characterized in the solid state by Infrared,
elemental analysis and X-ray diffraction. The infrared spectrum
agrees with the pattern of other analogous systems. This way,
the m
(C@N) stretching moiety (1636 cmꢁ1 (1)) shifts to higher wave-
numbers compared with the free H2bsph (1612 cmꢁ1) [36]. Other
sharp bands were found around 1611, 1519 and 1164 cmꢁ1 which
intensities decreased progressively, assignable to the m(C@C)
stretching vibrations from the ligand upon coordination. Below
825 cmꢁ1 only weak bands were observed, none of them assign-
Comparison of the distances and angles of compound 1 with
previous systems in the literature provides primary information.
There are only three other structures of LnIII displaying ‘‘real’’ sand-
wich triple-decker dinuclear complexes, [Ln2(L2ꢁ)3(X)](where
L = Salen-type Schiff bases and X = solvent molecule) [25,29–30].
Two of them having NdIII [25,30] as it is the case of complex 1 with
different Salen-type Schiff base ligands (L) and also different mol-
ecules of solvents attached (X = MeOH). The third system differs on
the organic unit as well as on the metal center (YbIII) [29]. Taking
into account the work presented here (1) and the other two [Nd2(-
L2ꢁ)3(X)] species [25,30], a list of comparative values has been
made showing some of their similarities and differences. Table 3
shows some of the most remarkable parameters of the three sys-
tems. From the point of view of the crystal data and refinement
parameters, complex 1 displays the same number of molecules
per unit cell as the other two systems but its volume is higher
and has also a different space group. Complexes from Refs.
[25,30] contain two different dinuclear clusters in the unit cell
comparing with 1. Regarding distances and angles, Ndx–Oy–Ndz
angles are similar in the three systems, although complex 1 shows
the shortest Nd–Nd distance compared with Ref. [25] and an inter-
mediate value compared with Ref. [30]. Interestingly, 1 contains
the shortest intermolecular Ndꢀ ꢀ ꢀNd distance comparing with the
other two (Table 3).
able to m(M–O/N). The elemental analysis corroborated the 2 M:3L
coordination (where M and L stand for metal and ligand) and final-
ly the crystal structures provided precise description of the final
arrangement.
As it has been mentioned in the crystallographic section, three
other sandwich triple-decker dinuclear clusters have been previ-
ously described in the literature containing LnIII centers with sim-
ilar ligands to H2bsph. In addition, few triple-, tetra- and even
penta-decker systems have been also achieved [25–30]. It has been
pointed out that the formation of multidecker multimetallic lan-
thanide-Schiff base assemblies depends on different factors: (i)
the stochiometry, being normally used 1:1 or 1:2 (M:L), (ii) the ini-
tial LnIII-salts (where NO3ꢁ, Clꢁ, OAcꢁ, CF3CO3ꢁ, OTfꢁ have been
proposed in different works), (iii) the bases (sometimes absence
of it, Et3N or NaOH), (iv) additional metallic salts (e.g., Zn(OAc)2)
and (v) the solvents or mixtures of solvents used (MeOH,
MeOH:CH2Cl2, MeCN, MeCN:MeOH, MeCN:THF).
So far, our studies have shown that comparing with previous
works, deprotonation of the base with NaOH and the use of ace-
tone as solvent favors dinuclear entities with Nd. Further studies
with additional Ln-salts are in progress to analyze if this could
be extended to the rest of LnIII ions. As it has been said above,
we have made comparisons of the synthetic ways for achieving
the three existing [Nd2L3X] systems. Initial works, related to the
formation of polynuclear LnIII–Salen-type Schiff base ligands,
claimed that different nuclearity among final systems was depend-
ing on the nature of the anions used [26]. From the point of view of
the [Nd2L3X] species, it is clear that the dinuclear structures have
been made with different Ln salts: triflate [25], acetate [30] and ni-
trate (present work). The three [Nd2L3X] compared here have been
also made using different solvents (or mixture of solvents), stochi-
ometries and bases (none [30], Et3N [25] and NaOH (present
work)). Basically, the present work agrees with the idea that poly-
nuclear decker–LnIII systems depend on several aspects but we
would like to stress that there is not a unique and most relevant
factor among the others, and therefore, each LnIII should be studied
in different conditions to determine which of those affect the most
to the nuclearity and final composition of the structures.
3. Discussion
The present work describes the formation of a homodinuclear
complex, [Nd2(bsph)3(H2O] (1), by reacting Nd(NO3)3ꢀ6H2O with
bsph2ꢁ in a ratio 1:2, using acetone as a solvent. Although the free
ligand, H2bsph, has been studied in the past and its behavior with
Table 3
List of the some of the most important crystal data, structure refinement parameters,
distances (Å) and angles (°).
Parameters
Ref. [25]
Ref. [30]
This work (1)
Empirical
formula
Crystal system
Space group
V (Å3)
C
67H54N6Nd2O7 C61H46N6Nd2O7 C62H34Br6Cl6N6Nd2O7
monoclinic
P21
6090.7
4
triclinic
P1
monoclinic
P21/c
3.1. Magnetism
ꢀ
5424.6
4
6628.7
4
The temperature-dependent magnetic susceptibility data for a
crystalline sample of 1 were measured at applied fields of 0.02
(from 1.8 to 30 K) and 0.3 T (from 30 to 300 K) with superimpos-
able results (Fig. 3 Left). Magnetization measurements were car-
ried out at 2 K and in the field range 0–5 T (Fig. 3 Right).
Z
Distances (Å)
Nd1–Nd2
Nd3–Nd4
Ndꢀ ꢀ ꢀNd
3.9605
3.9629
8.190
3.9608
3.9364
7.677
3.9455
–
5.829
Angles (°)
The experimental
vMT value for 1 at room temperature is
Nd1–Ox–Nd2*
Nd1–Ox0–Nd2*
Nd3–Oy–Nd4*
Nd3–Oy0–Nd4*
108.3
110.5
110.2
110.5
109.5
110.6
108.7
109.0
110.0
108.5
–
3.92 cm3 molꢁ1 K, higher than the expected one for two uncoupled
4
NdIII ions in the I9/2 ground state (S = 3/2, L = 6, J = 15/2, g = 8/11,
v
MT = 3.28 cm3 molꢁ1 K) [37]. The graph shows a slope that gradu-
–
ally decreases by lowering temperature arriving to a value of
*
Numbers of x and x0 are 3 and 4 for Refs. [25,30,3,6] for complex 1. Values of y and
2.13 cm3 molꢁ1 K at 1.8 K. The observed behavior of the
vMT of 1
y0 are 10 and 11 for Refs. [3,4]. The ligand in this work is the N,N0-bis(salicylidene)-
1,2-cyclohexanediamine; The Schiff base used in reference 25 was bis-N,N0-p-
bromo-salicylideneamine-1,2-diaminobenzene and in reference 30 was 2,20-[(4,5-
dimethyl-1,2-phenylene)bis(nitrilomethylidyne)]bis[phenol].
could be attributed to weak antiferromagnetic interactions and
the depopulation of the Stark levels [38,39]. The M versus H plot
shows a faster increase at low magnetic fields and a slow linear

A.M. Abu-Dief et al. / Polyhedron 64 (2013) 203–208
207
Fig. 3. (Left)
complex 1.
vMT vs. T (empty dots connected through a line) and vMT vs. logT (empty dots connected through a line, respectively) for complex 1; (right) M vs. H for
Fig. 4. (Left) UV–Vis spectra of 1 at 10–5 M in THF (black line) and MeCN (empty sphere with a black line). (Right) Luminescent spectra of complex 1 in THF (solid line) and
MeCN (empty spheres connected with solid line) solutions, 10–5 M each at room temperature. Normalized emissions are presented in all the cases.
augment at the highest, without complete saturation up to 5 T. The
magnetization value at the highest field is in good agreement with
the expected value for two uncoupled NdIII centers and the lack of
saturation reinforces the idea of a significant anisotropy and/or
low-lying excited states in the system. Alternating current (ac)
experiments without applying dc external fields and with applica-
tion of a small field (0.05 T) were carried out resulting in no slow
relaxation of the magnetization in both circumstances. Published
multi-decker NdIII systems are not reported magnetically, therefore
it is not possible to compare the data obtained with related sys-
tems [25,28,30]. Further theoretical studies should be performed
to provide more insight on the intra molecular exchanges as well
as comparative studies with GdIII analogous to corroborate the pos-
sibility of antiferromagnetism within the two NdIII ions [39] (inset
temperature (concentrations 10ꢁ5 M, Fig. 4 right). Experiments
were performed in the visible and near-IR scope, where the free li-
gand and complex 1 were expected to be luminescent active,
respectively. In the case of H2bsph only broad band with maximum
value at 469 nm was found in THF and 467 nm in MeCN, in that or-
der, when excited at 300 nm (not shown). On the other hand, com-
plex 1 showed a nice pattern in the near-IR range when a
wavelength of 385 nm was used, displaying three emission max-
ima at approximately 894, 1062 and 1337 nm and assigned to
the leaps of 4F3/2 ? 4I9/2, 4F3/2 ? 4I11/2 and 4F3/2 ? 4I13/2, respec-
Fig. 3 Left shows the semilog of vMT versus T, displaying the mag-
netic behavior of complex 1 at the lowest temperatures).
3.2. UV–Vis and luminescence
The UV–Vis spectroscopy of compound 1 was conducted in
MeCN and THF at room temperature (final concentrations
10ꢁ5 M, respectively). Absorption spectra in both solvents show
different patterns (exchange of the molecule of H2O coordinated
to one of the Nd ions by molecules of THF or MeCN, respectively,
could be one of the reasons for such variations) [40]; Fig. 4 shows
the behavior of 1 in both solvents. Complex 1 exhibits absorption
bands at approximately 245 nm, a lower shoulder at 290 and also
a band at 385 nm when the solvent was THF; meanwhile, shifted
bands appear around 250, 270 and 380 nm, when MeCN was used.
Luminescent studies were carried out based on the absorption
bands of free ligand, H2bsph (not shown), and complex 1 at room
Fig. 5. Luminescent spectrum of complex 1 in the solid state at room temperature.
Normalized emission is shown. ⁄Scattering processes.

208
A.M. Abu-Dief et al. / Polyhedron 64 (2013) 203–208
tively (Fig. 4 right). As it is typical for NdIII complexes that display
luminescence, the center band is the most intense. These charac-
teristic emissions are normally related to intramolecular energy
transfer from the ligand to the metal, seen already in other
Salen-type NdIII samples [25,28,30]. Interestingly, the emissions
in THF were always more intense than the emission bands in MeCN
(Fig. 4 right), showing that the intensity is highly quenched in the
latest. In addition, solid luminescence in the near-IR was also per-
formed displaying the same emissions observed in both solvents
by irradiating at the same wavelength, 385 nm (Fig. 5). This fact
reinforces the idea of the ligand behaving as an antenna and fur-
ther intramolecular energy transfer processes.
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Acknowledgements
The authors thank AECID, program 7-PCI-EGIPTE (AP/040924/
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Appendix A. Supplementary data
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CCDC 919669 contains the supplementary crystallographic data
for complex 1. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or e-mail: deposit@ccdc.cam.ac.uk.
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