One-pot metal template synthesis, crystal structures and spectroscopic properties of self-assembled rare earth metal ion complexes of salicylaldimine ligands

Article abstract of DOI:10.1016/j.ica.2016.08.045

The one-step metal-promoted condensation reaction of salicylaldehyde with diethylenetriamine in the presence of rare earth metal ions carried out in the same experimental conditions produces two types of salicylaldimine complexes. The compounds were chara

Full text of DOI:10.1016/j.ica.2016.08.045

Accepted Manuscript
One-pot metal template synthesis, crystal structures and spectroscopic proper-
ties of self-assembled rare earth metal ion complexes of salicylaldimine ligands
Izabela Pospieszna-Markiewicz, Wanda Radecka-Paryzek, Maciej Kubicki,
Zbigniew Hnatejko
PII:
S0020-1693(16)30498-4
http://dx.doi.org/10.1016/j.ica.2016.08.045
ICA 17239
DOI:
Reference:
Inorganica Chimica Acta
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24 February 2016
4 August 2016
28 August 2016
Please cite this article as: I. Pospieszna-Markiewicz, W. Radecka-Paryzek, M. Kubicki, Z. Hnatejko, One-pot metal
template synthesis, crystal structures and spectroscopic properties of self-assembled rare earth metal ion complexes
of salicylaldimine ligands, Inorganica Chimica Acta (2016), doi: http://dx.doi.org/10.1016/j.ica.2016.08.045
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One-pot metal template synthesis, crystal structures and spectroscopic
properties of self-assembled rare earth metal ion complexes of
salicylaldimine ligands
Izabela Pospieszna-Markiewicz∗, Wanda Radecka-Paryzek, Maciej Kubicki, Zbigniew
Hnatejko
Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 60-780 Poznań, Poland
___________________________________________________________________________
Abstract
The one-step metal-promoted condensation reaction of salicylaldehyde with
diethylenetriamine in the presence of rare earth metal ions carried out in the same
experimental conditions produces two types of salicylaldimine complexes. The compounds
were characterized by spectroscopic data (ESI-MS, IR, UV/Vis, luminescence) and X-ray
crystallography. The complexes contain the deprotonated tetradentate C11H16N3O=(L1)1- N-
(salicylidene)-diethylenetriamine or pentadentate C18H19N3O2=(L2)2- N,N’-bis(salicylidene)-
diethylenetriamine ligand as a result of the [1+1] or [2+1] Schiff base condensation,
respectively. The metal ions are bonded to all the potential nitrogen and oxygen donor atoms.
The crystal structures of the complexes reveal two different supramolecular architectures: a
monomer in [Tm(C11H16N3O)2]NO3⋅CH3OH complex with formation of a two-dimensional
self-assembled network and a dimer in [M2(C18H19N3O2)2(NO3)2] complexes (M = Y3+,
Eu3+or Lu3+), although in all cases the metal ions are eight-coordinated with distorted square
antiprism geometry.
Keywords: Rare earth metal ions; Self-assembly; Schiff base complexes; Crystal structures
___________________________________________________________________________
∗
Corresponding author: Izabela Pospieszna-Markiewicz (E-mail: izap@amu.edu.pl,; Tel.: +48618291715)
1

1. Introduction
Metal complexes of Schiff base salen-type chelating ligands with N and O potential donor
atoms are called metallo-salens. They are stable in solution and in the solid state [1]. The
salen-type ligands can coordinate to various d- and f-block metal cations. The rare earth metal
ion (yttrium and lanthanides) Schiff base complexes are of special interest due to their
potential use in organic light-emitting diodes, as luminescent molecular probes, as a new
generation of functional materials, in catalysis, as single-molecule magnets (SMM) [2-8], in
biological applications [9-11]. Many supramolecular structures of salen-type rare earth metal
ion complexes are known, sometimes with unexpected and unusual coordination framework
[2,3,12-21]. This may be due to the difficulties in controlling the coordination environment
around these metal ions which display high and variable coordination numbers with low
stereochemical preference. Recently we reported the metal promoted in situ synthesis and the
structural details of salicylaldimine lanthanide nitrate complexes derived from salicylaldehyde
and flexible aliphatic or rigid aromatic diamines which self-assemble into an infinite one- or
two-dimensional coordination polymers, finite monomers and dimers with an unusual
coordination mode [17-19]. The salen-type ligands with N2O2 set of potential donor atoms
exist in these complexes in neutral form and use exclusively the oxygen atoms as donors with
the nitrogen atoms not being involved in the coordination [17-21]. In order to extend our
study on influence of the nature of diamine spacer on supramolecular array, we used
diethylenetriamine as precursor with additional nitrogen atom as potential donor. Here we
describe the template synthesis, single crystal X-ray structure determination and
characterization of rare earth metal ion salicylaldimine complexes containing tetradentate N-
(salicylidene)-diethylenetriamine with N3O set of donor atoms or pentadentate N,N’-
bis(salicylidene)-diethylenetriamine ligand with N3O2 donor system. Two types of the
2

complexes have been isolated as a result of a self-organization process starting from Schiff
base [1+1] or [2+1] condensation of salicylaldehyde and diamine in the presence of rare earth
metal ions (Scheme S1, Supplementary material). Contrary to our earlier findings the metal
ions in these complexes are bonded to all the potential nitrogen and oxygen donor atoms of
the deprotonated ligands.
2. Experimental
2.1. Materials
Y(NO3)3⋅6H2O, Eu(NO3)3⋅5H2O, Tm(NO3)3⋅6H2O, Lu(NO3)3⋅6H2O, salicylaldehyde and
diethylenetriamine were used as received from Aldrich Chemical Company.
2.2. Physical measurements
The compounds were characterized using microanalyses (CHN), IR, ESI-MS, and
single crystal X-ray structural analysis.
IR spectra were recorded using KBr pellets in the range of 4000-400 cm-1 on a Bruker IFS
66v/S spectrophotometer. Mass spectra were recorded using electrospray ionization (ESI)
techniques. Electrospray mass spectra were determined in methanol using a Waters
Micromass ZQ spectrometer. Microanalyses (CHN) was obtained using a Perkin-Elmer 2400
CHN micro analyzer. Ultraviolet–visible (UV–Vis) spectra of the compounds in ethanol (at
concentration of 2⋅10-5 M) were measured using Shimadzu UV PC 2401 spectrophotometer.
Luminescence spectra (scanned from 200 to 660 nm) were recorded on a Hitachi F 7000
spectrofluorometer with a 1 cm quartz cell at room temperature. Both of the excitation and
emission band widths were 2.5 nm.
2.3. Synthesis of the complexes. General procedures.
3

[Tm(C11H16N3O)2]NO3⋅CH3OH; [M2(C18H19N3O2)2(NO3)2] (M=Y3+, Eu3+, Lu3+)
To a mixture of appropriate metal(III) nitrate (0.1 mmol: 46 mg Tm(NO3)3⋅6H2O for 1, 38 mg
Y(NO3)3⋅6H2O for 2, 43 mg Eu(NO3)3⋅5H2O for 3, 47 mg Lu(NO3)3⋅6H2O for 4) in methanol
(10 mL) and salicylaldehyde (0.2 mmol, 16 µL) in methanol (5 mL), diethylenetriamine (0.1
mmol, 11 µL) in methanol (5 mL) was added dropwise (30 min) with stirring. The reaction
was carried out under air for 48 hours at room temperature, which resulted in formation of
clear yellow solution. The solution volume was then reduced to 5 mL by roto-evaporation.
Dark-yellow single crystals suitable for X-ray diffraction analysis were formed by slow
diffusion of dichloromethane or n-hexane (1a) into reaction sample at 4°C over a period of 6-
8 weeks. Single crystals were filtered via suction filtration and air dried.
[Tm(C11H16N3O)2]NO3·CH3OH (1)
Yield: 43mg, 0.063 mmol, 63%. Anal.: Calcd. for C23H36N7O6Tm (675.52 g mol-1): C, 40.89;
H, 5.37; N, 14.51. Found: C, 42.08; H, 4.99; N, 14.71%. ESI-MS: m/z = 580
[Tm(C11H16N3O)2]+, 205 [C11H16N3O]-. IR (KBr): ν = 3435 (OH), 3322, 3281, 3230 (NH),
-
2425 (OH◌◌◌N), 1631 (C=N), 1608 (C=C), 1763, 1474, 1384, 1347, 825 (NO3 ), 1257 (C–
O), 570 (Tm–N), 485 (Tm–O) cm-1. UV-Vis (EtOH): λmax/nm (ε/dm3 mol-1 cm-1) 254
(1.55⋅104), 325 (0.52⋅104).
[Y2(C18H19N3O2)2(NO3)2] (2)
Yield: 60 mg, 0.065 mmol, 66%. Anal.: Calcd. for C36H38N8O10Y2 (920.56 g mol-1): C, 46.97;
H, 4.16; N, 12.17. Found C, 46.91; H, 4.19; N, 12.13%. ESI-MS: m/z = 709
[Y(C18H20N3O2)2]+, 398 [Y(C18H19N3O2)]+, 522 [Y(C18H20N3O2)2(NO3)2]-, 312
[C18H21N3O2+H]+. IR (KBr): ν = 3418 (OH), 3272, 3070, 3014 (NH), 1635 (C=N), 1597
4

-
(C=C), 1779, 1742, 1483–1326, 826, 817 (NO3 ), 1273 (C–O), 556 (Y–N), 480 (Y–O) cm-1.
UV-Vis (EtOH): λmax/nm (ε/dm3 mol-1 cm-1) 258 (3.09⋅104), 346 (1.58⋅104).
[Eu2(C18H19N3O2)2(NO3)2] (3)
Yield: 65 mg, 0.062 mmol, 62%. Anal.: Calcd. for C36H38N8O10Eu2 (1044.66 g mol-1): C,
41.31; H, 3.66; N, 10.71. Found C, 41.53; H, 3.61; N, 10.68%. ESI-MS: m/z = 773
[Eu(C18H20N3O2)2]+, 586 [Eu(C18H20N3O2)2(NO3)2]-, 312 [C18H21N3O2+H]+. IR (KBr):
ν = 3428 (OH), 3258, 3151, 3037 (NH), 1633 (C=N), 1595 (C=C), 1767, 1738, 1472–1303,
-
830, 819 (NO3 ), 1273 (C–O), 560 (Eu–N), 483 (Eu–O) cm-1. UV-Vis (EtOH): λmax/nm (ε/dm3
mol-1 cm-1) 261 (2.63⋅104), 348 (1.66⋅104).
[Lu2(C18H19N3O2)2(NO3)2] (4)
Yield: 71 mg, 0.065 mmol, 65%. Anal.: Calcd. for C36H38N8O10Lu2 (1092.68 g mol-1): C,
39.57; H, 3.51; N, 10.26. Found C, 39.61; H, 3.59; N, 10.29%. ESI-MS: m/z = 795
[Lu(C18H20N3O2)2]+, 312 [C18H21N3O2+H]+. IR (KBr): ν = 3424 (OH), 3257, 3162, 3042
-
(NH), 1631 (C=N), 1596 (C=C), 1767, 1753, 1471–1326, 827, 818 (NO3 ), 1276 (C–O), 572
(Lu–N), 488 (Lu–O) cm-1. UV-Vis (EtOH): λmax/nm (ε/dm3 mol-1 cm-1) 259 (2.19⋅104), 347
(1.05⋅104).
2.4. Synthesis of the N,N’-bis(salicylidene)-diethylenetriamine, H2L2=C18H21N3O2
The N,N’-bis(salicylidene)-diethylenetriamine (H2L2) has been obtained for comparison by
Schiff base [2+1] condensation reaction of salicylaldehyde and diethylenetriamine using
method described earlier for N,N’-bis(salicylidene)-ethylenediamine with some modifications
[22]. To a solution of salicylaldehyde (320 µL, 4 mmol) in a mixed solvent of toluene (15
5

mL) and diethyl ether (5 mL), diethylenetriamine (220 µL, 2 mmol) in THF (15 mL) was
added dropwise with stirring. The reaction was carried out for 3 h at 50°C. The yellow
solution was acidified with glacial acetic acid to pH 6 and after 0.5 h the mixture was cooled.
The solution volume was then reduced to 5 mL by roto-evaporation. Precipitation was carried
out by addition of diethyl ether (5 mL). The yellow solid was filtered off and dried in air.
Yield: 252 mg, 0.809 mmol, 81%. Anal.: Calcd. for C18H21N3O2 (311.38 g mol-1): C, 69.43;
H, 6.80; N, 13.49. Found C, 69.11; H, 6.65; N, 13.19%. ESI-MS: m/z = 310 [C18H21N3O2-H]-,
312 [C18H21N3O2+H]+. IR (KBr): ν = 3389 (OH), 2575 (OH◌◌◌N), 1628 (C=N), 1582
(C=C), 1281 (C–O) cm-1. UV-Vis (EtOH): λmax/nm (ε/dm3 mol-1 cm-1) 255 (0.44⋅104), 313
(0.16⋅104), 402 (0.05⋅104).
Scheme 1. Schiff base ligand H2L2
2.5. X-ray crystallography
Diffraction data were collected by the ω-scan technique on Agilent Technologies four-
circle SuperNova diffractometer with Atlas CCD detector, equipped with Nova microfocus
CuKα radiation source (λ = 1.54178 Å), for 2 and 3 at room temperature, for 1, 1a and 4 at
130(1) K. The data were corrected for Lorentz-polarization as well as for absorption effects
[23]. Precise unit-cell parameters were determined by a least-squares fit of reflections of the
highest intensity, chosen from the whole experiments. The structures were solved with SIR92
6

[24] and refined with the full-matrix least-squares procedure on F2 by SHELXL-2013 [25].
The scattering factors incorporated in SHELXL97 were used. All non-hydrogen atoms were
refined anisotropically, N-H hydrogen atoms in 1 were found in difference Fourier maps and
isotropically refined, all other hydrogen atoms were placed in idealized positions and refined
as ‘riding model’ with isotropic displacement parameters set at 1.2 times Ueq of appropriate
carrier atoms. In the structures of 2 and 4 the large voids were filled with diffused electron
density; as the modeling of solvent molecules was in these cases unsuccessful, the SQUEEZE
procedure [26] was applied. Crystals of 3 were found to be two-component twins and this was
taken into account both in data reduction and structure refinement. These crystals were of
poor quality, and the diffraction finished quickly – therefore the data found up to 1.1Å
resolution were only collected. As this structure is isostructural with previously reported for
Nd3+ complex [27] we will not discuss it in detail (Crystal data for 1-4 complexes,
Supplementary material).
3. Results and discussion
3.1. Synthesis, ESI mass and IR spectroscopy
The salen-type rare earth metal ion complexes containing either N-(salicylidene)-
diethylenetriamine for Tm3+ (1) or N,N’-bis(salicylidene)-1,5-diethylenetriamine for Y3+ (2),
Eu3+ (3) or Lu3+ (4) were prepared in situ through the one-step Schiff base condensation
reaction of salicylaldehyde with diethylenetriamine in the presence of appropriate nitrate salt
acting as a template. It should be noted here that, although these complexes were synthesized
by the template procedure, the free N,N’-bis(salicylidene)-diethylenetriamine ligand was also
obtained separately for comparison.
7

The complexes were characterized by ESI mass spectroscopy and IR spectral analysis.
The mass spectra of complexes showed mass fragmentation pattern which fits well with the
formula suggested by elemental and X-ray analyses. The ESI mass spectra exhibit mass peak
corresponding to the free ligand as a result of demetalation process. The mass spectrum of
ligand H2L2 showed molecular ion peaks at m/z = 310 [C18H21N3O2-H]-, 312
[C18H21N3O2+H]+ which matched the C18H21N3O2 ligand formula. The infrared spectra of the
complexes provide some information regarding the bonding mode of the ligand and nitrate
counterions. All IR spectra of complexes exhibit three bands at 3322-3014 cm-1 region
attributable to NH vibrations of amine groups. The IR spectrum of ligand H2L2 exhibits the
bands at 3389 cm-1 and 2557 cm-1 characteristic of O-H stretching vibration and OH···N=C
moiety, respectively. The presence of these bands in the ligand indicates that hydrogen atom
of the phenol is involved in intramolecular H-bonding with the imine nitrogen. The IR
spectrum of Tm3+ complex 1 displays a band at 3435 cm-1 corresponding to OH vibration in
the MeOH molecules. The band at 2425 cm-1 is attributed to the presence of intermolecular
hydrogen bonds between NH groups and nitrate oxygen atoms, involving also solvent
molecules which is consistent with crystallographic data. All IR spectra of compounds exhibit
characteristic absorption band at around 1630 cm-1 attributed to C=N stretching mode
confirming the Schiff base formation. The shift of this band to higher frequency, observed in
the spectra of the complexes compared to the free ligand confirms the coordination of the
nitrogen atom of azomethine group to the rare earth ions. The spectrum of complex 1 exhibits
two strong bands at 1384 and 825 cm-1, suggesting the ionic nature of nitrate anion The
spectra of the complexes 2, 3 and 4 display vibrations indicative of coordinated nitrate groups.
The ν(N−O) stretching frequencies are observed at 1488-1303 cm-1 region. The range of
splitting confirms the bidentate coordinating behavior of the nitrate groups [28]. The ν(C−O)
phenolic frequency observed as a band at 1281 cm-1 for the ligand H2L2, is shifted in the
8

complexes thus suggesting the participation of the oxygen atom of the deprotonated hydroxyl
group in the formation of the M−O bonds. The metal complexes are also characterized by
appearance of new bands at 572-556 cm-1 and 488-480 cm-1 which are assigned to ν(M−N)
and ν(M−O) bending frequencies, respectively.
3.2. Crystal structure
-
The complex [Tm(L1)2]+·NO3 has been obtained in two different crystal forms:
orthorhombic Pbca 1 and monoclinic P21/n 1a, the latter ones crystallizes with two structural
units (Table 1a A, B) in the asymmetric part of the unit cell. Interestingly, in both of these
crystals there are additional solvent (methanol) molecules (one per asymmetric unit in 1, two
in 1a). The crystals 1 and 1a were obtained from the same synthesis, but were crystallized in
two different vials. The crystals 1 and 1a were of irregular form and differed from each other
in shade and shape (Fig. S1, Supplementary material). The geometric features of the
complexes are almost identical; Tm3+ cations are eight-coordinated by one oxygen and three
nitrogen atoms from two ligand molecules (Fig. 1), the nitrate counteranions are not involved
in coordination.
9

Fig. 1. A perspective view of the [Tm(L1)2]+ cation in 1; ellipsoids are drawn at the 50%
probability level, hydrogen atoms are shown as spheres of arbitrary radius.
The coordination geometry in each case can be described as distorted square antiprism: N11
and N14 atoms from two ligand molecules are approximately coplanar, and the mean plane is
almost parallel to the plane created by O1 and N8 atoms. Also the Tm-ligand bond lengths are
similar in two molecules. Table 1a lists relevant geometrical data for the complexes. In the
crystal structures hydrogen bond networks between NH groups and nitro oxygen atoms,
involving also solvent molecules, are influencing the architecture of the crystals (Fig. 2, Table
S1, Supplementary material).
10

Table 1
Geometrical parameters (Å); (a) – type 1, (b) – type 2.
(a)
1 (M=Tm)
1a (M=Tm)
A
2.171(5)
2.155(5)
2.468(7)
2.487(6)
2.521(6)
2.511(6)
2.511(7
2.514(6)
B
M-O1A
M-O1B
M-N8A
M-N8B
M-N11A
M-N11B
M-N14A
M-N14B
2.177(2)
2.172(2)
2.503(3)
2.482(3)
2.504(3)
2.512(3)
2.538(3)
2.555(3)
2.173(5)
2.150(6)
2.501(7)
2.521(6)
2.509(7)
2.502(7)
2.521(7)
2.527(7)
(b)
2 (M=Y)
3 (M=Lu)
2.157(3)
2.279(3)
2.243(3) ii
2.408(3)
2.463(3)
2.455(4)
2.488(4)
2.494(4)
3.6680(4) ii
4 (M=Eu)
2.28(4)
M-O1A
M-O17A
M-O17A
M-O2B
M-O3B
M-N8A
M-N11A
M-N14A
M···M
2.1716(16)
2.3131(14)
2.2891(14)i
2.4913(16)
2.4548(16)
2.4961(19)
2.5280(18)
2.5408(19)
3.7283(4) i
2.36(3)
2.36(3)iii
2.51(4)
2.52(3)
2.56(4)
2.60(4)
2.54(4)
3.835(6) iii
Symmetry codes: i 1/2-x,1/2-y,-z, ii ½-x,1/2-y,1-z; iii –x,2-y,-z
11

(a)
(b)
Fig. 2. 2-D layer structure in 1 constructed by hydrogen bonding as seen along x (a) and z (b)
directions.
For the second type of complexes, with (L2)2- ligand, we have found two different crystal
structures, both created by the neutral dimeric units, which can be described as M2(L2)2(NO3)2
12

(M=Y3+, Eu3+or Lu3+). Relevant geometrical data are presented in Table 1b. One of these
forms – monoclinic P21 – was described earlier for Nd complex [27], and now we obtained
isomorphic structure for Eu3+ (3) prepared in completely different in situ method. Complexes
of Y3+ (2) and Lu3+ (4) crystallize in yet another form, C2/c monoclinic. Again, the geometry
of the complexes is almost identical in these crystals (Fig. 3); they are binuclear di-O bridged,
centrosymmetric dimers. In both forms the crystals are exactly Ci-symmetrical, as they
occupy special positions in their respective space groups. The rare earth metal ions are 8-
coordinated, this time by one N3O2 system from (L2)2 ligand molecule, bridging oxygen from
another (L2)2- and two oxygen atoms from the nitrate anion, and the coordination geometry is
distorted square antiprism. Fig. S2 (Supplementary material) shows the crystal structure of
[Y2(C18H19N3O2)2(NO3)2] 2; the large gaps which are filled with the diffused electron density
(disordered solvents, for instance) are clearly seen.
13

Fig. 3. A perspective view of the [Y2(L2)2(NO3)2] centrosymmetric complex in 2; ellipsoids
are drawn at the 50% probability level, hydrogen atoms are shown as spheres of arbitrary
radius. The unlabeled atoms are related to the labelled ones with symmetry operation -x+1/2,
-y+1/2, -z.
3.3. Electronic absorption spectra and luminescence properties
14

Absorption and emission spectra of ligand H2L2 and complexes 1-4 were recorded at
concentration of 2⋅10-5 M in ethanol solvent at ambient temperature. The absorption maxima
bands (λmax) and the molar absorption coefficients (ε) are listed in Table 2 and selected
spectra are presented in Fig. 4.
5
4
3
1
4
2
H L2
2
1
0
250
300
350
400
450
500
λ [nm]
Fig. 4. The UV-Vis absorption spectra of the ligand H2L2 and complexes 1 and 4 in ethanol
solution.
The absorption of ligand H2L2 is characterized by two main bands at λmax=255 and 313 nm.
These absorption bands are ascribable to π-π* transitions involving both the benzene ring and
azomethine group [29,30]. Upon complexation, in 2-4 these bands are red-shifted to 258-261
and 346-348 nm compared to those of free ligand. The very low intensity absorption band at
λ=402 nm observed in H2L2 may belong the n-π* transition of the C=N group which overlaps
with intramolecular charge transfer from phenyl ring. In the case of complex 1 with (L1)1-, the
main absorption bands are located at 254 and 325 nm. The f-f transitions of the lanthanide(III)
ions are very weak and were not observed in the absorption spectra of the complexes.
15

Table 2
Electronic spectral data of ligand H2L2 and complexes 1-4.
Compound
Absorption
Excitation
Emission
λabs/nm (ε⋅104/dm3⋅mol-1⋅cm-1)
λex/nm
λem/nm
H2L2
255 (0.44), 313 (0.16), 402 (0.05)
254 (1.55), 325 (0.52)
360
362
348
361
353
433
437
442
440
435
1
2
3
4
258 (3.09), 346 (1.58)
261 (2.63), 348 (1.66)
259 (2.19), 347 (1.05)
The photoluminescent properties of all the complexes along with the H2L2 ligand were also
studied. The excitation wavelengths were selected from excitation spectra of the complexes.
Upon excitation at 360 nm, a blue emission with broad spectral profile centered at about 433
nm was observed for Schiff base ligand. The luminescence spectra of 1-4 complexes, shown
in Fig. 5, only exhibited free ligand emission bands centered at 437, 442, 440 and 435 nm
respectively. The luminescence of these compounds is most likely caused by π-π* or n-π*
intra-ligand transitions [31,32]. The intramolecular energy transfer from the ligand triplet state
to excited states of lanthanide(III) ions is one of the factors influencing the luminescence
properties of lanthanide(III) complexes [33]. The spectrum of the Eu3+ complex 3 does not
exhibit bands characteristic of metal-centered emission. The absence of emission bands of
Eu3+ ions may be due to the quenching through an intra-ligand and ligand-to-europium
charge-transfer excited states [34].
16

1200
1100
1000
900
800
700
600
500
400
300
200
100
0
600
500
400
300
200
100
0
1
2
3
4
200 220 240 260 280 300 320 340 360 380 400
λ [nm]
1
2
3
4
H L2
2
400
440
480
520
560
600
640
λ [nm]
Fig. 5. Emission and excitation spectra of studied compounds in ethanol solution.
4. Conclusion
The rare earth nitrate complexes of N-(salicylidene)-diethylenetriamine or N,N’-
bis(salicylidene)-1,5-diethylenetriamine are formed in situ through the self-assembly process
in the metal-induced [1+1] or [2+1] Schiff base condensation reaction of salicylaldehyde with
diethylenetriamine. Crystal structure determination reveals the formation of the monomer in
case of thulium(III) N-(salicylidene)-diethylenetriamine complex with 1:2 metal to ligand
stoichiometry, where the Schiff base acts as deprotonated tetradentate ligand with N3O set of
donor atoms. The hydrogen bonding leads to formation of a 2-D self-assembled network. The
crystal structure of N,N’-bis(salicylidene)-1,5-diethylenetriamine rare earth metal ion
complexes is made of the neutral dimeric units involving the deprotonated ligand with N3O2
donor set, with the voids which are filled with the disordered solvent molecules. Their
17

bonding properties influence the resulting supramolecular architecture. In both types of these
complexes the metal ions are eight coordinated with distorted square antiprism geometry. The
metal ions are bonded to all the potential nitrogen and oxygen donor atoms of the
deprotonated ligands. This type of coordination is in a marked contrast to the neutral
exclusively O–donor type of coordination observed in related salicylaldimine lanthanide
complexes [17-21]. These results confirm the effectiveness of rare earth elements in self-
assembly of the components leading to the formation of compounds with unusual structures,
although the final product of this process may be difficult to predict.
Appendix A. Supplementary data
Crystallographic data has been deposited with the Cambridge Crystallographic Data Centre,
Nos. CCDC 144775 (1), CCDC 1447755 (1a), CCDC 1447756 (2), CCDC 1447757 (3) and
CCDC 1447758 (4) . Copies of this information may be obtained free of charge from: The
Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK. Fax: +44(1223)336-033, e-
mail:deposit@ccdc.cam.ac.uk, or www: http://www.ccdc.cam.ac.uk
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21

The self-assembled metal-promoted synthesis of salicylaldimine complexes of rare earth
metal ions is described. Two types of Schiff base complexes reveal two different
supramolecular architectures: a monomer in [Tm(C11H16N3O)2]NO3⋅CH3OH complex with
formations of a two-dimensional network and a dimer in [M2(C18H19N3O2)2(NO3)2]
complexes (M
=
Y3+, Eu3+or Lu3+). The complexes contain N-(salicylidene)-
diethylenetriamine deprotonated ligand with N3O set of donor atoms or N,N’-
bis(salicylidene)-diethylenetriamine deprotonated ligand with N3O2 donor system.
22

• Two types of rare earth ion complexes are formed in metal template Schiff base [1+1]
or [2+1] condensation of salicylaldehyde and diethylenetriamine.
• The complexes were characterized by spectroscopic methods.
• Solid-state structures were determined by single crystal X-ray diffraction.
• The metal ions are eight-coordinated with a distorted square antiprism geometry.
• The absorption and emission spectra of compounds were studied at room temperature.
23