Dinuclear lanthanide(III) complexes with large-bite Schiff bases derived from 2,6-diformyl-4-chlorophenol and hydrazides: Synthesis, structural characterization and spectroscopic studies

Article abstract of DOI:10.1016/j.poly.2012.06.025

Two Schiff bases (H₃L¹ and H₅L ²), derived from 2,6-diformyl-4-chlorophenol and hydrazides, and their complexes with some lanthanides (Y, La, Nd, Sm, Dy and Er) have been synthesized. These compounds have been characterized by means of elemental analysis, UV-Vis spectroscopy, IR spectroscopy, ¹H and ¹³C NMR (for the organic ligands), molar conductance and room temperature magnetic measurements. Single crystal X-ray analysis of the two complexes [La ₂(H₂L¹)₃(C₂H ₅OH)₂]·(Cl)·(NO₃) ₂·((CH₃)₂CO)₂·(H ₂O)₂ (1) and [Er₂(H₄L ²)₃]·(SCN)₃·(H₂O) (8) has revealed the nature of the structures; the lanthanide(III) ions are intramolecularly bridged by three phenolic oxygen atoms, forming a dinuclear complex. The lanthanum atom is ten-coordinated, while the erbium atom is nine-coordinated. The coordination polyhedron of the erbium complex is best described as a tricapped trigonal prism.

Full text of DOI:10.1016/j.poly.2012.06.025

Polyhedron 43 (2012) 97–103
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Polyhedron
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Dinuclear lanthanide(III) complexes with large-bite Schiff bases derived
from 2,6-diformyl-4-chlorophenol and hydrazides: Synthesis, structural
characterization and spectroscopic studies
Farba Bouyagui Tamboura a, Ousmane Diouf a, Aliou Hamady Barry b, Mohamed Gaye a,
,
⇑
Abdou Salam Sall a
a Department of Chemistry, University Cheikh Anta Diop, Dakar, Senegal
b Department of Chemistry, University of Nouakchott, Nouakchott, Mauritania
a r t i c l e i n f o
a b s t r a c t
Two Schiff bases (H3L1 and H5L2), derived from 2,6-diformyl-4-chlorophenol and hydrazides, and their
complexes with some lanthanides (Y, La, Nd, Sm, Dy and Er) have been synthesized. These compounds
have been characterized by means of elemental analysis, UV–Vis spectroscopy, IR spectroscopy, 1H and
13C NMR (for the organic ligands), molar conductance and room temperature magnetic measurements.
Single crystal X-ray analysis of the two complexes [La2(H2L1)3(C2H5OH)2]ꢀ(Cl)ꢀ(NO3)2ꢀ((CH3)2CO)2ꢀ(H2O)2
(1) and [Er2(H4L2)3]ꢀ(SCN)3ꢀ(H2O) (8) has revealed the nature of the structures; the lanthanide(III) ions are
intramolecularly bridged by three phenolic oxygen atoms, forming a dinuclear complex. The lanthanum
atom is ten-coordinated, while the erbium atom is nine-coordinated. The coordination polyhedron of the
erbium complex is best described as a tricapped trigonal prism.
Article history:
Received 22 April 2012
Accepted 5 June 2012
Available online 23 June 2012
Keywords:
Lanthanide
Hydrazone
Schiff bases
Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction
the size of the metal ions, producing complexes of the type
[Ln2(H2L1)3(C2H5OH)m]ꢀ(Cl)ꢀ (NO3)2ꢀ((CH3)2CO)nꢀ(H2O)p (m = n = p
Studies involving the chelation and coordination of ligands
derived from hydrazone to lanthanide centers containing flexible
multidentate ligands have been an ongoing area of active research.
In recent years, much attention has been given to the syntheses of
acyclic ligands that can give rise to mononuclear or dinuclear
lanthanide complexes with interactions between the metal cen-
ters. It is known that a considerable amount of work has been done
on complexes with hydrazones because of their ability to chelate
with lanthanide ions [1–10]. Hydrazone lanthanide complexes
can be used as electroluminescent devices [11,12], structural
probes [13] and in immunobiological assays [14]. As well as their
paramagnetic and luminescent properties [15–17], the bioactivi-
ties of lanthanides, such as antimicrobial or antitumor, have been
explored over the past decades [18–21]. In addition, some hydra-
zone lanthanide chelates have represented good antioxidant activ-
ities [19,20]. In the course of our studies on the chemistry of
lanthanide compounds, we have prepared and characterized a
number of chelates containing hydrazones as ligands. Herein we
report a series of new lanthanide(III) complexes derived from phe-
nol-based macro-acyclic ligands which each have two similar me-
tal-binding sites sharing a phenolic oxygen atom. Due to the
flexibility of the arms, the cavity size could be adjusted to match
= 2 for (1) and m = n = 0 and p = 1 or 2 for the other complexes)
and [Ln(H4L2)2ꢀ(H2O)t]ꢀ(SCN)3ꢀ (H2O)z (t = 2 and z = 1 for (6); t = 0
and z = 1 or 3 for the other complexes). The crystal structures of
the lanthanum and erbium complexes have been elucidated.
2. Experimental
2.1. Materials and procedures
2,6-Diformyl-4-chlorophenol was synthesized according to the
literature [21] and recrystallized from n-hexane/chloroform;
benzoyl hydrazide, 2-hydroxybenzoyl hydrazide and the lanthanide
nitrate salts were commercial products (from Alfa and Aldrich) and
were used without further purification. Solvents were of reagent
grade and were purified by the usual methods. The analyses for
carbon, hydrogen and nitrogen were carried out using a LECO
CHNS-932 instrument. The IR spectra were recorded as KBr discs
on a Bruker IFS-66 V spectrophotometer (4000–400 cmꢁ1). The mo-
lar conductances of 10ꢁ3 M solutions of the metal complexes in DMF
were measured at 25 °C using a WTW LF-330 conductivity meter
with
a WTW conductivity cell. Room temperature magnetic
susceptibilities of the powdered samples {calibrant Hg[Co(SCN)4]}
were measured using a Johnson Matthey scientific magnetic
susceptibility balance. Melting points were recorded on a Büchi
apparatus and are uncorrected. The 1H and 13C NMR spectra of the
⇑
Corresponding author. Tel.: +221 77 55 55 891; fax: +221 33 82 46 318.
E-mail address: mlgayeastou@yahoo.fr (M. Gaye).
0277-5387/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2012.06.025

98
F.B. Tamboura et al. / Polyhedron 43 (2012) 97–103
H5L2: Yield 83%. M.P. >230 °C. Anal. Calc. for C22H17ClN4O5: C,
Table 1
Crystallographic data and refinement parameters for 1 and 8.
58.36; H, 3.77; N, 12.34; Cl, 7.85. Found: C, 58.35; H, 3.78; N,
12.37; Cl, 7.83%. MS (FAB), m/z: 453. 1H NMR dmso-d6 d (ppm):
7.47 (m, 6H, HAr), 7.60 (m, 2H, –NH), 7.73 (m, 4H, HAr), 8.60 (s,
2H, –N=CH), 12.20 (s (broad), 2H, –OH), 12.70 (s (broad), 1H, –
OH). 13C NMR dmso-d6 d (ppm): 196.52 (–C=O), 163.28 (–C=N),
155.45 (HO–CAr), 144.87, 132.20, 132.78, 128.65, 127.84, 123.55,
122.08 (CAr).
Formula
C76H76La2Cl4N14O21 C69H50Er2Cl3N15O16S3
(1)
(8)
Molecular weight
Crystal system
Space group
T (K)
a (Å)
b (Å)
1941.12
monoclinic
C2/c
1882.29
monoclinic
P21/n
173(2)
21.1020 (6)
18.5070 (7)
23.1880 (9)
90
173(2)
13.14300 (10)
23.0550 (2)
25.5410 (3)
90
c (Å)
2.4. Preparation of the complexes
a
(°)
b (°)
114.4520 (10)
90
8243.5 (5)
4
1.564
1.23
0.71073
892
0.054
0.126
552
96.367 (3)
90
7691.49 (13)
4
1.625
2.43
0.71073
3728
0.053
0.121
966
2.4.1. Complexes of H3L1
c
(°)
V (Å3)
Lanthanide (III) nitrate heptahydrate (1 mmol) in methanol
(20 mL) was added to a suspension of 5-chloro-1,3-diformyl-2-
hydroxybenzene-bis(benzoylhydrazone) (1.5 mmol) in methanol
(80 mL). The mixture was refluxed for 1 h. LiCl (0.1272 g, 3 mmol)
was added. The resulting yellow solution was filtered-off and the
filtrate was kept at 298 K. Yellow crystals began to appear after
three days and were collected by filtration.
Z
Dcalc (g cmꢁ3
)
l
(Mo K
a
) (mmꢁ1
)
k (Å)
F(000)
R
wR
Parameters refined
No. of measured reflections
No. of independent reflections 8574
Goodness-of-fit
[La2(H2L1)3(C2H5OH)2]ꢀ(Cl)ꢀ(NO3)2ꢀ((CH3)2CO)2ꢀ(H2O)2 (1). Crys-
tals suitable for X-ray diffraction were obtained by slow evaporation
of an acetone/ethanol solution of the complex. Yield 55%. Anal. calc.
for[C76H76Cl4N14O21La2]:C, 47.03;H, 3.95;N, 10.10. Found:C, 46.99;
H, 3.93; N, 10.12%. Diamagnetic. KM (S cm2 molꢁ1): 205.
[Nd2(H2L1)3]ꢀ(Cl)ꢀ(NO3)2ꢀ(H2O)2 (2). Yield 65%. Anal. calc. for
[C66H52Cl4Nd2N14O17]: C, 45.47; H, 3.01; N, 11.25. Found: C,
13469
22521
22521
0.87
0.91
1.17
Maximum residual peak
2.54
(e Åꢁ3
)
Minimum residual hole(e Åꢁ3) ꢁ0.91
ꢁ1.57
w2(|F0|2)2]1/2
R .
P
R = ||F0| ꢁ |Fc||)/
R
|F0|, wR = [
R
w2(|F0|2 ꢁ |Fc|2)2/
45.58; H, 3.09; N, 11.19%. leff (l
B): 7.18. KM (S cm2 molꢁ1): 222.
[Sm2(H2L1)3]ꢀ(Cl)ꢀ(NO3)2ꢀ(H2O) (3). Yield 71%. Anal. calc. for
Schiff bases were recorded in CDCl3 on a BRUKER 500 MHz spec-
trometer at room temperature using TMS as an internal reference.
The L-SIMS mass spectra were recorded using a Micromass Auto-
spec spectrometer using 3-nitrobenzyl alcohol as the matrix.
[C66H50Cl4Sm2N14O16]: C, 45.62; H, 2.90; N, 11.28. Found: C,
45.69; H, 3.11; N, 11.37%. leff (l
B): 3.32. KM (S cm2 molꢁ1): 200.
[Dy2(H2L1)3]ꢀ(Cl)ꢀ(NO3)2ꢀ(H2O) (4). Yield 59%. Anal. calc. for
[C66H50Cl4Dy2N14O16]: C, 44.99; H, 2.86; N, 11.13. Found: C,
45.06; H, 2.79; N, 11.23%. leff (l
B): 18.08. KM (S cm2 molꢁ1): 220.
2.2. X-ray crystal structure determination
2.4.2. Complexes of H5L2
Slow evaporation of an ethanol/acetone solution gave X-ray
quality crystals of the two compounds [La2(H2L1)3(C2H5OH)2]ꢀ(Cl)ꢀ
(NO3)2ꢀ((CH3)2CO)2ꢀ(H2O)2 (1) and [Er2(H4L2)3]ꢀ(SCN)3ꢀ(H2O) (8).
Details of the X-ray crystal structure solution and refinement are
given in Table 1. Measurements were made on a Bruker SMART
CCD Area Detector. All data were corrected for Lorentz and polari-
zation effects. An empirical absorption correction was applied.
Complex scattering factors were taken from the program package
To a solution of lanthanide (III) nitrate heptahydrate (1 mmol)
in methanol (10 mL) was added a solution of KSCN (3 mmol) in
10 mL of methanol. The mixture was stirred at room temperature
for 1 h. The white precipitate that formed was discarded by filtra-
tion. The resulting solution was added to a suspension of 5-chloro-
1,3-diformyl-2-hydroxybenzene-bis(20-hydroxybenzoyl
hydra-
zone) (1.5 mmol) in methanol (80 mL) and then the mixture was
refluxed for 1 h. The resulting yellow solution was filtered-off
and the filtrate was kept at 298 K. Yellow crystals began to appear
after 3 days and were collected by filtration.
SHELXTL [22]. The structures were solved by direct methods, which
revealed the position of all non-hydrogen atoms. All the structures
were refined on F2 by a full-matrix least-squares procedure using
anisotropic displacement parameters for all non hydrogen atoms
[23]. The hydrogen atoms were located in their calculated posi-
tions and refined using a riding model. Molecular graphics were
generated using ORTEP-3 [24].
[Y2(H4L2)3]ꢀ(SCN)3ꢀ(H2O)3 (5). Yield 62%. Anal. calc. for
[C69H54Cl3N15O18S3Y2]: C, 47.04; H, 3.09; N, 11.93. Found: C,
46.85; H, 3.15; N, 11.83%. Diamagnetic. KM (S cm2 molꢁ1): 204.
[La2(H4L2)3ꢀ(H2O)2]ꢀ(SCN)3ꢀ(H2O) (6). Yield 65%. Anal. calc. for
[C69H54Cl3N15O18S3La2]: C, 44.52; H, 2.92; N, 11.29. Found: C,
44.47; H, 3.05; N, 11.25%. Diamagnetic. KM (S cm2 molꢁ1): 198.
[Sm2(H4L2)3]ꢀ(SCN)3ꢀ(H2O)3 (7). Yield 61%. Anal. calc. for
[C69H54Cl3N15O18S3Sm2]: C, 43.98; H, 2.89; N, 11.15. Found: C,
2.3. Preparation of the ligands
The ligands were obtained from the condensation of 2,6-difor-
myl-4-chlorophenol and the corresponding hydrazide in a 1:2 M
ratio, in an ethanol medium; two drops of glacial acetic acid was
used as a catalyst. The yellow precipitates obtained were filtered,
washed with ethanol and dried in vacuum over P4O10. The yield
of the Schiff bases was quantitative.
44.05; H, 2.79; N, 11.37%. leff (l
B): 2.22. KM (S cm2 molꢁ1): 240.
[Er2(H4L2)3]ꢀ(SCN)3ꢀ(H2O) (8). Crystals suitable for X-ray diffrac-
tion were obtained by slow evaporation of an acetone/methanol
solution of the complex. Yield 55%. Anal. calc. for [C69H50Cl3N15O16-
S3Er2]: C, 44.03; H, 2.68; N, 11.16. Found: C, 44.10; H, 2.60; N,
11.27. leff (l
B): 16.42. KM (S cm2 molꢁ1): 230.
H3L1: Yield 96%. M.P. 221–225 °C. Anal. Calc. for C22H17ClN4O3:
C, 62.77; H, 4.08; N, 13.33; Cl, 8.46. Found: C, 62.79; H, 4.07; N,
13.31; Cl, 8.42%. MS (FAB), m/z: 421. 1H NMR dmso-d6 d (ppm):
7.47 (m, 6H, HAr), 7.60 (m, 1H, –NH), 7.73 (m, 6H, HAr), 8.60
(s, 2H, –N=CH), 12.20 (s (broad), 1H, –OH), 12.70 (s (broad), 1H, –
OH). 13C NMR dmso-d6 d (ppm): 196.52 (–C=O), 163.28 (–C=N),
155.45 (HO–CAr), 144.87, 132.78, 132.19, 128.65, 127.84, 123.56,
122.08 (CAr).
3. Result and discussion
3.1. Synthesis and spectroscopic studies
Here we have prepared the acyclic Schiff bases H3L1 and H5L2
(Chart 1) following a method well known in the literature. The

F.B. Tamboura et al. / Polyhedron 43 (2012) 97–103
99
Table 3
The UV–Vis data k (nm) and
Cl
Cl
e
(L molꢁ1 cmꢁ1) for the ligands and the complexes.
Compounds k(nm)
H3L1
H5L2
227 (5.36), 271 (3.04) [pH 7], 287 (3.04) [pH 13], 319 (3.19),
345 (1.07), 363 (3.39), 418 (1.30), 438 (1.45)
225 (5.36), 270 (3.08) [pH 7], 285(3.13) [pH 13], 320 (3.15), 345
(1.01), 365 (3.48), 420 (1.25), 440 (1.56)
287 (3.06), 330 (5.2), 370(15,52), 410 (5.3), 530 (5.83)
286 (3.02), 330 (4.2), 370(5,78), 410 (6.5), 530 (0.39)
289 (3.00), 335 (2.50), 365 (1.28), 405 (3.89), 460 (3.35)
285 (2.98), 330 (3.15), 370(12.50), 405 (12.50), 460 (12.50)
287 (3.66), 330 (1.55), 345 (1.20), 360 (1.38), 463 (2.45)
284 (3.54), 335 (2.58), 344 (0.55), 366 (0.98), 461 (1.33)
286 (3.55), 325 (2.50), 340 (0.66), 365 (1.83), 465 (2.30)
285 (3.27), 325 (5.50), 340 (3.89), 360 (3.83), 440 (1.17), 465
(5.83)
N
O
OH
N
O
N
O
OH
N
O
HN
NH
HN
NH
1
2
3
4
5
6
7
8
OH
HO
H3L1
H5L2
Chart 1. Scheme of H3L and H5L
Upon complexation of H3L1 or H5L2 with lanthanide ions, the
C=N bands shift toward lower frequency, appearing in the range
1512–1555 cmꢁ1 in the IR spectra of the complexes, suggesting
an interaction between the metal ion and the imino nitrogen atom.
The hydroxyl groups of water lattice molecules and coordinated
ethanol in the case of 1 appear near 3490 cmꢁ1 [25]. In the com-
plexes from H3L1 information regarding the possible bonding
modes of the nitrate group was obtained. The presence of a band
near 1380 cmꢁ1 indicates that ionic nitrate groups are present
[26]. In the infrared spectra of the complexes from H5L2, a strong
band near 2050 cmꢁ1 appears and confirms the presence of SCNꢁ
as counter-ions in these compounds. Additional bands at ca.
1615 and 3220 cmꢁ1 were observed in the spectra of both com-
plexes and are assignable respectively to coordinated N–C=O and
N–H stretching vibrations, respectively. The water present in all
the complexes is probably lattice and/or coordinated according to
syntheses of the ligands were achieved in a one step procedure
using the direct condensation of 2,6-diformyl-4-chlorophenol with
the appropriate hydrazide in quantitative yields. The mass spectra
of the two ligands present an intense peak at 421 and 453 uma,
corresponding to the molecular ions of [H3L1 + H]+ and
[H5L2 + H]+, respectively. The 1H NMR spectra of the ligands were
recorded in deuterated dimethylsulfoxide. The NMR spectra of
the compounds are comparable and show an added signal for
H5L2. Indeed, the spectrum of H3L1 revealed peaks at 12.2 (HO–
Ar) and 12.7 ppm (HO–C=N), which is indicative of the iminolisa-
tion of one of the two amide groups. This fact is not observable
in the spectrum of H5L2. In this case only signals attributable to
HO–Ar are observable; the amide groups remain stable. The 13C
NMR spectra of the ligands show a signal at d 196.52 ppm which
represent the carbon atom of the carbonyl C=O group. The peaks
at d 155.45 represent the aromatic Cipso of the OH of the phenol
in the spectra of H3L1 and H5L2. The main IR bands are summarized
in Table 2. The IR spectra of the two compounds show moderate-
intensity absorptions at ca. 1620 cmꢁ1 which are attributable to
the broad band at 3460 cmꢁ1
.
The electronic spectral data of the ligands H3L1 and H5L2 and the
complexes are recorded in methanol and the main bands are listed
in Table 3. The assignments are made by a comparison with liter-
ature data [27–29]. The ligands H3L1 and H5L2 show an intense
absorption band respectively at 271 and 270 nm which shift to a
higher wavelength at 287 and 285 nm, respectively, when increas-
ing the pH. This fact is diagnostic of the presence of a phenol group
in the ligands molecules. An intense band is also observed in the
spectra of the ligands near 227 nm and this is assigned to a
m
(C=N). No bands are observed for the free 2,6-diformyl-4-chloro-
phenol or hydrazides indicating that complete condensation has
occurred. The phenol and/or iminol moieties reveal a band at ca.
3400 cmꢁ1. The amide function exhibits strong absorptions,
m(N–
C=O), at ca. 1660 cmꢁ1
.
The reactions of H3L1 and H5L2 with nitrate or thiocyanate
lanthanide salts in 3:2 M ratios were investigated, and the
complexation was performed by mixing ethanol or methanol solu-
tions of both the ligand and metal salt. The products isolated were
dinuclear complexes. In all cases the complexes appear to be air sta-
ble and are soluble in common organic solvents. Crystals suitable for
X-ray analysis were obtained by slow evaporation of solutions of
[La2(H2L1)3(C2H5OH)2]ꢀ(Cl)ꢀ(NO3)2ꢀ((CH3)2CO)2ꢀ(H2O)2 (1) and [Er2
(H4L2)3]ꢀ(SCN)3ꢀ(H2O) (8). All the compounds are characterized by
elemental analysis (C, H, N), IR spectroscopy, molar conductivity,
magnetic measurements and X-ray diffraction for 1 and 8.
p
? p ?
p⁄ transition of the aromatic rings. A p⁄ transition attrib-
uted to the C=N chromophore is observed in the spectra of the li-
gands at 320 nm [29]. In the region 340–440 nm intense bands
are observed and these are assigned to the n ? p⁄ transition in
the carbonyl group. Upon coordination to lanthanide(III) ions these
bands are shifted to lower wavelengths, supporting the coordina-
tion of the hydrazonic moieties via the imino nitrogen and the
carbonyl oxygen atoms to the metal center. In the spectra of the
complexes a new band around 286 nm was observed. This is indic-
Table 2
Vibration frequencies in the infrared spectra of the compounds and their assignments.
Compound
Vibration frequencies (cmꢁ1
(O–H) (N–H)
)
m
m
m
(C=O)
m
(C=N)
m
(Ln–O)
m
(Ln–N)
m
(SCN)
m
(NO3)
H3L1
3447
3489
3462
3498
3475
3489
3450
3462
3475
3453
32 52
3212
3207
3205
3198
3212
3205
3150
3100
3202
1660
1660
1610
1613
1610
1608
1615
1616
1616
1607
1620
1620
1555
1572
1560
1565
1575
1560
1559
1569
–
–
–
–
–
–
–
–
–
–
2054
2050
2052
2054
–
–
H5L2
1
465
480
475
457
475
525
530
459
276
282
278
265
272
475
482
268
1387
1383
1385
1388
–
–
–
–
2
3
4
5
6
7
8

100
F.B. Tamboura et al. / Polyhedron 43 (2012) 97–103
ative of the transformation of the phenol in the phenolate groups
upon reaction with lanthanide(III) ions. No absorption bands due
to f–f transitions could be observed in the visible region of the
spectra. This may be attributed to intense charge-transfer transi-
tions that obscure the f–f bands. The electronic spectral data of
the complexes further support the coordination of the ligand to
the lanthanide through the imino nitrogen, carbonyl oxygen and
phenolate oxygen atoms.
Molar conductivities were measured for freshly prepared solu-
tions in DMF and after standing for two weeks. The conductivities
increased very slightly with time in dmf for all the complexes. The
conductance values lie in the range observed for 3:1 electrolytes
(200–240 cm2
X
ꢁ1 molꢁ1) [30]. The leff value of the lanthanide
complexes show that these are paramagnetic except for complexes
1, 5 and 6, which are diamagnetic in nature. This paramagnetic
behavior is consistent with the presence of unpaired 4f electrons.
The observed leff values are in close proximity to the values for
the free metal ions reported by Van Vleck and Frank [31]. This
shows that the magnetic moments of the Ln3+ ions are not affected
by the ligand field. The 4f-electrons are not involved in the
coordination.
The formulations obtained from the infrared spectra for these
complexes are in accordance with the measured molar conductiv-
ities. The overall observations on the geometrical features found
for all complexes by conductivity and spectroscopic studies are
in complete agreement as that elucidated by X-ray crystallography
for complexes 1 and 8.
Fig. 2. A view of the coordination environment around each LaIII ion in complex 1.
of 2. Two non-coordinated water and acetone molecules per two
La-containing units, intervene as lattice solvent. As is evident from
the structure, the coordination to the lanthanide ion occurs via the
phenolate oxygen rather than the nitrogen atom. In the titled com-
plex, both lanthanide(III) ions have a coordination number of ten,
binding the three imine nitrogen atoms, three neutral oxygen
atoms of the hydrazone, the three phenolate oxygen atoms of the
three ligand molecules and one neutral oxygen atom of the coordi-
nated ethanol molecule. The complex crystallizes in the monoclinic
space group C2/c. The coordination of the hydrazone to La results
in the formation of five and six membered (LaOCNN and LaOCCCN)
3.2. Description of the structures
Partially labelled plots of the dinuclear structures of complexes 1
and 8 are shown in Fig. 1 and Fig. 3, respectively. The coordination
polyhedra of the LaIII and ErIII ions are shown in Figs. 2 and 4. Se-
lected interatomic distances and angles are listed in Tables 4 and 5.
The structure of complex 1 consists of [La2(H2L1)3(C2H5OH)2]3+
discrete entities, nitrate and chloride anions in a NO3ꢁ/Clꢁ ratio
Fig. 1. Crystal structure of the dinuclear complex [La2(H2L1)3(C2H5OH)2]ꢀ(Cl)ꢀ(NO3)2ꢀ((CH3)2CO)2ꢀ(H2O)2 (1), showing partially the atom numbering scheme.

F.B. Tamboura et al. / Polyhedron 43 (2012) 97–103
101
Table 4
atoms at La1 is 358.11°. In this complex, the planes [O2, O3, O5],
[N1, N3, N6] and [O1, O4, O4i] are nearly parallel to each other,
with small dihedral angles of 1.37–2.67°. These planes are perpen-
dicular to the plane [La1, O9, O2], with a dihedral angle of 89.72°.
As reported by Bu et al. [4] for [Ho2(L)3(H2O)](NO3)2ꢀ(OH)ꢀ3.5H2O
(where HL is N,N0-diisonicotinoyl-2-hydroxy-5-methylisophthalal-
dehyde dihydrazone), the coordination polyhedron around each
lanthanum atom can be regarded as a 1333 stacking pattern
(Fig. 2).
In this compound, there is extensive hydrogen bonding leading
to a very complex motif. The uncoordinated water molecules
[corresponding to O11] are hydrogen bonded to either uncoordi-
nated acetone molecules [O10] or nitrate [O6, O7] oxygen atoms,
while the coordinated ethanol molecule [O9] is hydrogen bonded
only to the nitrate oxygen and nitrogen atoms [O8, N7]. The NH
of the hydrazonic moieties of the ligand molecule [N2, N4 and
N5] are hydrogen bonded respectively to the uncoordinated water
molecules [O11], to the chlorine atom of the ligand [Cl3] and to the
oxygen atom of the nitrate ion [O8].
Selected bond lengths (Å) and bond angles (°) of complex 1.
La1AO1
La1AO4
La1AO4i
La1AO2
La1AO3
La1AO5
2.493(3)
2.498(4)
2.507(4)
2.566(4)
2.499(4)
2.528(4)
La1AO9
La1AN1
La1AN3
La1AN6
La1ALa1i
2.627(4)
2.819(5)
2.787(5)
2.787(5)
3.8540(8)
O1ALa1AO4
O1ALa1AO4i
O4ALa1AO4i
La1AO1ALa1i
La1AO4ALa1i
N6ALa1AN1
66.20(11)
66.06(11)
68.50(15)
101.24(18)
100.72(13)
118.05(14)
N6ALa1AN3
N3ALa1AN1
O5ALa1AN6
O3ALa1AN1
O4ALa1AN3
O1ALa1AN1
123.36(15)
116.70(15)
58.93(13)
58.05(13)
61.28(11)
62.02(11)
Symmetry codes: (i) ꢁx + 1, y, ꢁz + 3/2.
Table 5
Selected bond lengths (Å) and bond angles (°) of complex 8.
The structure of complex 8 consists of [Er2(H4L2)3]3+ discrete
entities, thiocyanate anions and one non-coordinated water
molecule per two Er-containing units, intervening as lattice solvent.
The coordination of the hydrazones to Er results in the formation of
five OCNNEr and six NCCCOEr membered chelating rings which
share one Er–N bond. In the two rings, the Er–N bonds have the
largest metal–ligand distances [Er1–N3 = 2.555(4) Å, Er1–O4 = 2.3
22(4) Å, Er1–N7 = 2.555(4) Å]. The Er–O bonds involving the hydraz
onic oxygen have metal–ligand distances comparable in the three
ligand molecules [Er1–O4 = 2.322(4) Å, Er1–O9 = 2.296(3) Å, Er1–
O14 = 2.318(4) Å]. The phenolic oxygen atoms, acting as bridges
between the two Er atoms, have metal–ligand distances in the range
2.256(3)–2.374(3) Å. The Er1ꢀ ꢀ ꢀEr2 distance is 3.4871(4) Å. These
are consistent with those found in other nine-coordinated erbiu-
m(III) complexes [34].
The following bonds are not altered in the complex: C8–O2, C16–
O4, C30–O7, C38–O9, C52–O12 and C60–O14 are short, consistent
with a double bond, and C8–N2, C16–NO4, C30–O6, C38–N8, C52–
N10 and C60–N12 are long, consistent with a single bond. The
remaining bond distances of the hydrazone molecule, as well as
C26–O6, C37–N7 and C29–N5 are slightly different in the three li-
gand molecules. The bond angles of the ligands, which involve the
Er(III) ion, and the bridging oxygen atoms of the ligand are very sim-
ilar for the two erbium(III) metal centers [O1–Er1–O6 = 69.99(12)°;
O6–Er2–O1 = 68.73(12)°; O1–Er1–O11 = 68.63 (12)°; O11–Er2–
O1 = 68.68(12)°; O6–Er1–O11 = 68.75(12)°; O11–Er2–O6 = 70.94
(12)°]. The three sets of donor atoms [(O1, O6, O11); (N3, N7, N11)
and (O4, O9, O14)] (Er1) and [(O1, O6, O11) and (N1, N5, N9) and
(O2, O7, O12)] (Er2) form three planes to lie upon, medium and un-
der the sheets of each erbiumIII center, respectively. Each erbiumIII
ion is positioned on a plane formed by three nitrogen atoms, [N3,
N7, N11] (Er1) and [N1, N5, N9] (Er2). The angle sum subtended
by the three capping atoms is 359.60° at Er1 and 359.58° at Er2. In
this complex the planes around the erbium centers are nearly paral-
lel; e.g. [O1, O6, O11], [N11, N3, N7] and [O4, O9, O14] are nearly
parallel to each other with dihedral angles of 1.48–8.66°. Both erbiu-
m(III) atoms in the complex are nine-coordinated, being bound to
three oxygen atoms of carbonyl groups, three nitrogen atoms of
the azomethine groups and three phenolate oxygen atoms. The
three thiocyanate moieties act as counter ions. The water molecule
remains uncoordinated. Two possible coordination polyhedra with
nine vertexes are known. The coordination polyhedra around each
erbium atoms are better described as a distorted tricapped trigonal
prisms with three hydrazones nitrogen atoms forming the three
face caps: N3, N7, and N11 for Er1 and N1, N5 and N9 for Er2 (Fig. 3).
In this compound, there is extensive intramolecular hydrogen
bonding. Indeed each ligand molecule possesses two free hydroxyl
Er1AO1
Er1AO6
Er1AO11
Er1AO4
Er1AO9
Er1AO14
Er1AN3
Er1AN7
Er1AN11
Er1AEr2
2.257(3)
2.319(4)
2.377(3)
2.317(4)
2.295(4)
2.316(4)
2.558(5)
2.553(4)
2.584(4)
3.4871(4)
Er2AO1
Er2AO6
Er2AO11
Er2AO2
Er2AO7
Er2AO12
Er2AN1
Er2AN5
Er2AN9
2.353(3)
2.290(4)
2.274(4)
2.337(4)
2.348 (4)
2.369(4)
2.594(4)
2.577(4)
2.605(4)
O1AEr1AO6
O1AEr1AO11
O6AEr1AO11
N3AEr1AN7
N3AEr1AN11
N7AEr1AN11
O4AEr1AN3
O9AEr1AN7
O14AEr1AN11
O1AEr1AN3
O6AEr1AN7
O11AEr1AN11
Er1AO1AEr2
Er1AO11AEr2
69.93(12)
68.65(12)
68.69(12)
126.96(14)
111.12(14)
121.52(14)
62.56(14)
63.35(13)
62.74(13)
68.87(13)
66.71(13)
64.43(13)
98.28(13)
97.13(13)
O1AEr2AO6
O1AEr2AO11
O11AEr2AO6
O2AEr2AN1
N1AEr2AN5
N1AEr2AN9
N5AEr2AN9
O7AEr2AN5
O12AEr2AN9
O1AEr2AN1
O11AEr2AN9
O6AEr2AN5
Er2AO6AEr1
68.80(12)
68.81(12)
71.00(12)
63.17(13)
125.70(14)
112.06(14)
121.82(14)
63.81(13)
62.72(13
64.64(13)
67.98(13)
67.99(13)
98.32(13)
chelating rings. In the complex the La–N bonds involving the
hydrazone nitrogen atoms show the largest metal–ligand distances
(La1–N6 = 2.786(5) Å, La1–N3 = 2.787(5) Å and La1–N1 = 2.819(5)
Å). The La–O bonds involving the hydrazonic oxygen atoms are
in the range 2.499(4)–2.566(4) Å and are comparable to those
found in hydrazonic complexes [32]. The phenolate oxygen atoms
acting as bridges have bonds distances in the range 2.493(3)–
2.507(4) Å and are comparable to the values in the complex
[La2(2,6-DNP)6(H2O)4]ꢀ4H2O (where 2,6-DNP is 2,6-dinitrophenol)
[33]. The largest metal–oxygen bond distance in the complex is
found in the bond of La with the oxygen atom of the ethanol
solvent molecule (La1–O9 = 2.627(4) Å). The Laꢀ ꢀ ꢀLa distance is
3.8540(8) Å. The C14–N18 distance and its related symmetry are
consistent with a single bond while the C22–N19 and C14–O3 dis-
tances and their related symmetries are consistent with double
bond character. The bond angles of the ligands, which involve
the La(III) ion and the bridged oxygen atoms of the ligand, are in
the range 66.09(11)–68.50(15)°. The three sets of donor atoms
[(O1, O4, O4i); (N1, N3, N6) and (O2, O3, O5)] form three planes
to lie upon, medium and under the sheets of the lanthanumIII cen-
ters, respectively. The oxygen atom of the coordinated ethanol
molecule, O9, is over the plane formed by O2, O3 and O5. The LaIII
ion is positioned on a plane formed by three nitrogen atoms, N1,
N3 and N6. The angle sum subtended by these three nitrogen

102
F.B. Tamboura et al. / Polyhedron 43 (2012) 97–103
Fig. 3. (a) Crystal structure of the dinuclear complex [Er2(H4L2)3]ꢀ(SCN)3ꢀ(H2O) (8) where one ligand molecule, a water molecule and thiocyanate counter-ions are omitted for
clarity.(b) Crystal structure of the dinuclear complex showing partially the atom numbering scheme.
groups which are hydrogen bonded with the nitrogen or oxygen
atoms of the hydrazonic moieties. There is also established
hydrogen bonding between these hydroxyls groups with the
uncoordinated water molecules and free thiocyanates anions. The
NH of the hydrazonic moieties of the ligand molecules are hydro-
gen bonded to the uncoordinated hydroxyl groups of the ligand
and to the uncoordinated thiocyanate anions through the sulfur
atom.
In the literature, for a series of lanthanide complexes, the
repulsion between ligand molecules in the coordination sphere
increases when the size of the lanthanides ions decreases [35–38].
The averaged Ln–N and Ln–O bond distances in complex 1
(2.798(5) and 2.515(4) Å (Ln=La)) are larger than those in complex
8 (2.578(4) and 2.321(4) Å (Ln=Er)), and the averaged O–Ln–N angle
in complex 1 (61.65(12)°) is smaller than that found in complex 8
(66.77(13)°). These results are consistent with the reduced size of
the ionic radius on going from La3+ to Er3+. The larger LaIII ion
(rLa3+ = 1.16 Å) [39] forms longer coordination bond distances with
the donor atoms of the Schiff base ligands and smaller chelate an-
gles than does the ErIII ion which has a smaller ionic radius
(rEr3+ = 1.00 Å) [39]. This has the result of reducing the coordination
number and seeing the structure change. When comparing com-
plexes 1 and 8 we note that the separation of La1ꢀ ꢀ ꢀLa1i, in complex
1 is 0.3669 Å, higher than the Er1ꢀ ꢀ ꢀEr2 separation in complex 8. Bu
et al. [4] report a similar observation when comparing [Ho2(L)3(-
H2O)](NO3)2ꢀ(OH)ꢀ3.5H2O and [Lu2(L)3](OH)3 (where HL is N,N0-dii-
sonicotinoyl-2-hydroxy-5-methylisophthalaldehyde dihydrazone);
the Hoꢀ ꢀ ꢀHo separation is 0.1438 Å, higher than the Luꢀ ꢀ ꢀLu separa-
tion. We can note that the decrease in ionic radius is correlated to
increased repulsions between the ligands in the complex.

F.B. Tamboura et al. / Polyhedron 43 (2012) 97–103
103
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Supplementary data CCDC 871848 and 871849 contains the
supplementary crystallographic data for [La2(H2L1)3(C2H5OH)2]ꢀ
(Cl)ꢀ(NO3)2ꢀ((CH3)2CO)2ꢀ(H2O)2 (1) and [Er2(H4L2)3]ꢀ(SCN)3ꢀ(H2O)
(8), respectively. 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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