Synthesis, crystal structure, antioxidation and fluorescence of two lanthanide
complexes with a noncyclic polyether Schiff base ligand
XINKUI SHI, SHANSHAN MAO, KESHENG SHEN, HUILU WU and XIA TANG
School of Chemical and Biological Engineering, Lanzhou Jiaotong University,
Lanzhou, Gansu, 730070, P. R. China
Two
lanthanide
(Sm
and
La)
complexes
with
the
Schiff
base
ligand
bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine (Bod) have been synthesized and
characterized
by
physico-chemical
and
spectroscopic
methods.
[Sm(Bod)(NO3)3]
{bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine samarium(III) trinitrate} (1) is a discrete
mononuclear
species
and
{bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine
[La(Bod)(NO3)3(DMF)]n
dimethylformamide
lanthanum(III)
trinitrate}n (2) formed an inorganic coordination polymer. In the two complexes, the metal ions
are both ten-coordinate and the geometric structure around the Ln(III) ions can be described as
distorted hexadecahedral. An antioxidant assay in vitro shows that complexes 1 and 2 exhibit
better scavenging activity than both the ligand and the usual antioxidants on hydroxyl and
superoxide radicals. Under excitation at room temperature, a red shift in the fluorescence band of
the ligand in the complexes compared with that of the free ligand can be attributed to
coordination of the rare earth ions to the ligand. Furthermore, 1 produced characteristic Sm(III)
luminescence, which indicates the ligand Bod is a good organic chelator to absorb energy and
transfer it to the Sm3+ ion.
Keywords: Bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine; Lanthanide complex; Crystal
structure; Antioxidant; Fluorescence
Corresponding author. Emails: [email protected]; [email protected]
1
1. Introduction
Schiff bases are a very important class of compounds because of their ability to form stable
complexes with many different transition and rare-earth metal ions in various oxidation states via
N and O atoms [1-4]. Aguiari et al. have synthesized a series of flexible cyclic and acyclic Schiff
bases derived from functionalized polyamines to verify the influence of the different
coordinating moieties on metal ion recognition and to study the stability and the properties of
complexes containing d- or f-metal ions. In particular, by condensation in hot methanol of
2,3-dihydroxy-,
2-hydroxy-3-methoxy-
1,2-diaminoethane,
or
2-hydroxy-3-ethoxy-benzaldehyde
1,3-diaminopropane,
with
1,5-diamino-3-oxapentane,
1,8-diamino-3,6-dioxaoctane and 1,11-diamino-3,6,9-trioxaundecane, macroacyclic ligands have
been obtained. However, structurally characterized hexadentate Schiff-base lanthanide
complexes are very rare [5]. Mononuclear and homo- or heteropolynuclear complexes with
compartmental acyclic or macrocyclic Schiff bases have been widely studied because of their
potential application in magnetism, luminescence and new functional materials, in which pore
size, coordination forms, and functionality could be varied [6-8]. The Schiff base complexes
have also been used as biological models to understand the structures of biomolecules and
biological processes [9, 10].
In recent decades, lanthanide complexes with organic ligands have been attracting great
attention as advanced optical materials for progressive technologies due to their useful practical
applications in telecommunications, OLED-devices, and solar energy conversion, as well as in
bio-sciences [11-14]. It was shown by Weissman that ligands in organolanthanide complexes
play the role of antenna to harvest and transmit the excitation energy to lanthanide ion [15]. The
luminescent intensities of the lanthanide metal complexes are strongly dependent on the
efficiency of the organic ligand to absorb UV light, energy transfer from the ligand to metal, and
lanthanide metal luminescence [16-18].
An excess of activated oxygen species in the forms of superoxide anion (O2-∙) and
hydroxyl radical (OH∙), generated by normal metabolic processes, may cause various diseases
2
such as carcinogenesis, drug-associated toxicity, inflammation, atherogenesis, and aging in
aerobic organisms [19-21]. The potential value of antioxidants has prompted investigators to
search for the cooperative effects of metal complexes and natural compounds for improving
antioxidant activity and cytotoxicity [22, 23].
Our recent studies have focused on the use of a tetradentate Schiff base ligand,
bis(N-salicylidene)-3-oxapentane-1,5-diamine, to coordinate to Ln(III) ions to improve
DNA-binding behavior and antioxidant ability [24]. As part of our continuing studies, we herein
report the synthesis, crystal structure, antioxidant character and fluorescence of two lanthanide
complexes with a hexadentate Schiff-bases ligand Bod. We believe that by choosing Bod as a
chelating ligand it is possible to induce and enhance the fluorescent properties, and improve
antioxidant activity of the lanthanide complexes. Information obtained from this study will be
helpful in the development of some new antioxidants and optical materials.
2. Experimental
2.1. Materials and methods
All chemicals were of analytical grade. Nitroblue tetrazolium nitrate (NBT), methionine (MET),
o-vanillin and riboflavin (VitB2) were obtained from Sigma-Aldrich Co. (USA) and used without
purification. 3-Oxapentane-1,5-diamine was made based on a preparation described [25].
C, H and N elemental analyses were determined using a Carlo Erba 1106 elemental
analyzer. IR spectra were recorded from 4000–400 cm−1 with a Nicolet FT-VERTEX 70
spectrometer using KBr pellets. Conductance measurements were made with a DDS-307 type
conductivity bridge using 3×10-3 mol L-1 solutions in DMF at room temperature. The
fluorescence spectra were recorded on a LS-55 spectrofluorophotometer. Electronic spectra were
taken on a Lab-Tech UV Bluestar spectrophotometer. The antioxidant activities using the
hydroxyl radical (OH∙) and superoxide radical (O2-∙) were measured in a water-bath with a 722sp
spectrophotometer.
3
2.2. Preparation of bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine (Bod)
o-Vanillin (1.82 g, 12 mmol) in EtOH (5 mL) was added dropwise to a 5 mL EtOH solution of
3-oxapentane-1,5-diamine (0.52 g, 5 mmol). After the completion of addition, the solution was
stirred for an additional 4 h at 78 °C. After cooling to room temperature, the precipitate was
filtered off. The product was dried in vacuo and obtained as a yellow crystalline solid. Yield:
1.59 g (68.0%). Anal. C20H24O5N2: calcd. C, 64.50; H, 6.50; N, 7.52 %; found: C, 64.30; H, 6.51;
N, 7.51 %. Selected IR data (KBr, ν/cm-1), 1629(νC=N), 1256(νC-O-C), 1047(νOH). UV-Vis (DMF):
λ = 271, 330 nm. Λm (DMF, 297 K): 1.7 S cm2 mol−1.
2.3. Preparation of [Sm(Bod)(NO3)3] {bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine
samarium(III) trinitrate} (1)
To a stirred solution of Bod (0.372 g, 1 mmol) in MeOH (5 mL) was added Sm(NO3)3(H2O)6
(0.1776 g, 1 mmol) in MeOH (5 mL). A yellow sediment was generated rapidly. The precipitate
was filtered off, washed with MeOH and absolute Et2O, and dried in vacuo. The dried precipitate
was dissolved in DMF to form a yellow solution. Yellow block crystals of [Sm(Bod)(NO3)3]
suitable for X-ray diffraction studies were obtained by vapor diffusion of diethyl ether into the
solution for few weeks at room temperature. Yield: 0.3121 g (56.8%). Anal. SmC20H24N5O14:
calcd. C, 33.89; H, 3.41; N, 9.88 %; found: C, 33.91; H, 3.39; N, 9.78 %. Selected IR data: (KBr
ν/cm-1), 1182 (νC-O-C), 1032(νOH), 1385(νNO3), 1654 (νC=N). UV-Vis (DMF): λ = 271, 355 nm.
Λm (DMF, 297 K): 7.6 S cm2 mol−1.
2.4.
Preparation
of
{bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine
[La(Bod)(NO3)3(DMF)]n
dimethylformamide
lanthanum(III)
trinitrate}n (2)
To a stirred solution of Bod (0.372 g, 1 mmol) in MeOH (5 mL) was added La(NO3)3(H2O)6
(0.1732 g, 1 mmol) in MeOH (5 mL). A yellow sediment was generated rapidly. The precipitate
was filtered off, washed with MeOH and absolute Et2O, and dried in vacuo. The dried precipitate
4
was dissolved in DMF to form a yellow solution. Pale yellow block crystals of 2 suitable for
X-ray diffraction measurement were obtained by vapor diffusion of diethyl ether into the solution
for two weeks at room temperature. Yield: 0.2933 g (53.8%). Anal. LaC23H31N6O15: calcd. C,
35.90; H, 3.93; N, 10.92 %; found: C, 35.88; H, 3.95; N, 10.90 %. Selected IR data: (KBr ν/cm-1),
1174 (νC-O-C), 1037(νOH), 1389(νNO3), 1655 (νC=N). UV-Vis (DMF): λ = 279, 361 nm. Λm (DMF,
297 K): 6.9 S cm2 mol−1.
2.5. X-ray structure determination
A suitable single crystal was mounted on a glass fiber and the intensity data were collected on a
Bruker SMART APEX diffractometer with graphite-monochromated Mo Kα radiation (λ =
0.71073 Å) at 296 K. Data reduction and cell refinement were performed using SAINT programs
[26]. The absorption corrections were carried out by the empirical method. The structure was
solved by direct methods and refined by full-matrix least-squares against F2 using SHELXTL
software [27]. All hydrogens were found in difference electron maps and were subsequently
refined in a riding-model approximation with C–H distances from 0.93 to 0.97 Å and Uiso (H) =
1.2 Ueq(C) or Uiso (H) = 1.5 Ueq(C). A summary of parameters for the data collections and
refinements are given in table 1. Selected bond lengths and angles of 1 and 2 are listed in table 2
and table S1.
2.6. Hydroxyl radical scavenging activity
The hydroxyl radicals in aqueous media were generated through a Fenton-type reaction [28, 29].
Aliquots of the reaction mixture (3 mL) contained 1 mL of 0.1 mM aqueous safranin, 1 mL of
1.0 mM aqueous EDTA–Fe(II), 1 mL of 3% aqueous H2O2, and a series of quantitative
microadditions of solutions of the test compound. The mixture without the tested compound was
used as the control. The reaction mixtures were incubated at 37 C for 30 min in a water-bath.
Absorbance at 520 nm was measured and the solvent effect was corrected throughout. The
scavenging effect for HO∙ was calculated from the following expression:
5
Scavenging effect % = (Asample - Ar) / (Ao - Ar) × 100%
where Asample is the absorbance of the sample in the presence of the tested compound, Ar is the
absorbance of the blank in the absence of the tested compound and Ao is the absorbance in the
absence of the tested compound and EDTA-Fe(II).
2.7. Superoxide radical scavenging activity
A non-enzymatic system containing 1 mL 9.9×10-6 M VitB2, 1 mL 1.38×10-4 M NBT and 1 mL
0.03 M MET was used to produce superoxide anion (O2-∙), and the scavenging rate of O2-∙ under
the influence of 0.1–1.0 μM of the tested compound was determined by monitoring the reduction
in the rate of transformation of NBT to monoformazan dye. The specific method proceeded
following the procedure described [30]. The reactions were monitored at 560 nm with a UV/Vis
spectrophotometer, and the rate of absorption change was determined. The percentage inhibition
of NBT reduction was calculated using the following equation [31]: percentage inhibition of
NBT reduction = (1-k’/k) × 100, where k’ and k represent the slopes of the straight line of
absorbance values as a function of time in the presence and absence of the SOD mimic
compound (SOD is superoxide dismutase), respectively.
3. Results and discussion
Scheme 1 summarizes the multi-step procedure leading to the ligand Bod. In the present
investigations, Bod and its complexes were synthesized and characterized by different physical
and chemical techniques. The complexes are soluble in polar aprotic solvents such as DMF and
DMSO, partially soluble in water, ethanol and methanol, but insoluble in Et2O and petroleum
ether. Elemental analysis shows that their compositions are [Sm(Bod)(NO3)3] and
[La(Bod)(NO3)3(DMF)]n, which was confirmed by the crystal structure analysis.
6
Scheme 1. Synthetic route for Bod.
3.1. X-ray structure determination of complexes
3.1.1. Crystal structure of 1. Complex 1 crystallized in the triclinic space group P-1.
Unexpectedly, two imine nitrogen atoms of this ligand did not take part in coordinating with the
metal ion and the complex was observed to be a mononuclear structure. The asymmetric unit
consists of discrete [Sm(Bod)(NO3)3] species without any additional solvent molecules (figure 1).
Each Sm(III) ion adopted a distorted hexadecahedron geometry and is ten-coordinate with four
oxygen atoms from two hydroxyl oxygen atoms and two methoxyl oxygen atoms of the ligand
and six oxygen atoms from three bidentate nitrate counterions. This is similar to other reports on
Schiff-base
lanthanide
complexes
[Ln(H2L1)(NO3)3]
(H2L1
=
N,N’-bis-(3-methoxysalicylidene)ethylene-1,2-diamine, Ln3+ = Sm3+, Nd3+, Eu3+, Pr3+, Gd3+,
Tb3+,
Dy3+,
Ho3+,
Er3+)
[32-37],
[Ln(H2L2)(NO3)3]
(H2L2
=
N,N’-bis(3-methoxysalicylideneimino)diethylenetriamine, Ln3+ = La3+, Nd3+) [38]. Bod acts as a
deprotonated tetradentate ligand with the O2O2 set of donor atoms capable of effective
coordination. This is different from other reports on Schiff-base lanthanide complexes
[Pr(H2L1)(NO3)3]n and [(L1)Pr(NO3)] [39]. The bond length ranges for Sm-Onitrate, Sm-Omethoxyl,
and Sm-Ohydroxyl are 2.482(4)-2.644(5) Å, 2.667(4)-2.740(4) Å and 2.322(4)-2.376(4) Å,
respectively. Of the three distinct bond types, Sm-Omethoxyl exhibits the longest bond length,
while Sm-Ohydroxyl has the shortest bond length and Sm-Onitrate possesses an intermediate bond
length.
7
As shown in figure 2, two benzene rings from two contiguous [Sm(Bod)(NO3)3] located
in the same line are in a parallel position, so the geometry of the complex ion is propagated into
an infinite 1-D chain via interligand π···π interactions (d = 3.750(0) Å). The non-classical
CH···O hydrogen-bonding interactions play important roles in crystal packing in the complex.
Neighboring chains are connected by C(5)-H···O(2) [C(5)-O(2) 3.263(6) Å] hydrogen bonds,
thus generating an infinite 2-D layer.
3.1.2. Crystal structure of 2. Figure 3 shows the ORTEP structure of [La(Bod)(NO3)3(DMF)]n
with atom labeling. Based on the single-crystal X-ray analysis, 2 crystallizes in the triclinic space
group P-1 and possesses a 1-D ribbon framework built from an extended array of ten-coordinate
La3+ centers and the ligand. Bod bridges each pair of La(III) ions via two La-O (hydroxy) and
one La-O (methoxyl) bonds, and one methoxyl O-atom is left uncoordinated. Each La(III) ion,
adopting a distorted hexadecahedral geometry, is 10-coordinate with two phenolic oxygen atoms
from different ligands, one methoxy oxygen atom, six oxygen atoms from three bidentate nitrate
ions and one DMF oxygen atom, while the nitrogen atoms of the imines remain uncoordinated
(figure 3). One methoxy oxygen atom coordinates to the La(III) ion because of the shorter La-O
(methoxy) bond length (2.794(6) Å), whereas another methoxy oxygen atom remains
uncoordinated to La(III) ion resulting in the longer La-O(1) (3.004(8) Å) distance. The structure
of 2 is similar with other reports on Schiff-base lanthanide complexes [Sm(H2L1)(NO3)3(MeOH)]
(H2L1 = N,N’-bis-(3-methoxysalicylidene)ethylene-1,2-diamine) [37], [(H2L3)La(NO3)3(MeOH)]
(H2L3 = N,N’-bis(3-methoxysalicylidene)propane-1,2-diamine)) [40], but with slightly different
from the reported 1D spiral Schiff base lanthanide complex [(H2L1)Ln(NO3)3·H2O] (Ln3+ =
La3+, Pr3+) [39], in which it was proposed that the Ln(III) ion was only coordinated by
deprotonated phenolic oxygen atoms without complexation of the oxygen atom from the
neighboring methoxy group.
In figure 4, it is shown that each ligand and La(III) ion bridge together to form an
inorganic polymer. Hydrogen-bonding interactions are also very significant for 2. The
8
C(8)-H(8)···O(13) [C(8)-O(13) 3.258(9) Å] hydrogen bonding interactions between two chains
led to the formation of a 2-D supramolecular network as shown in figure 4.
We examined the known salen-type Schiff base lanthanide complexes and arrived at the
following conclusions. (i) Most of the lanthanide complexes with a hexadentate Schiff base
ligand (via reaction of o-vanillin and 1,2-diamines) are mononuclear complexes [32-38], and
only a small part of them are coordination polymers [37, 40]. (ii) In 1D spiral salen-type Schiff
base lanthanide complexes, the coordination bridging mode of the ligands is different. For
tetradentate Schiff-base ligands (derived from salicylide and 1,2-diamines), two hydroxy oxygen
atoms of each ligand act as a bidentate linker bridging between two Ln3+ ions [33, 41], while for
hexadentate Schiff-base ligands (derived from o-vanillin and diamines), two hydroxy oxygen
atoms and one methoxyl oxygen atom of each ligand act as a tridentate linker bridging between
two Ln3+ ions, and one methoxyl oxygen atom of the ligand is left uncoordinated [37, 40].
(iii) From the above research content, it can also be found that the same ligand with different rare
earth ions formed the different structures of the complexes. The size of the rare earth ions (La(III)
0.103 nm, Sm(III) 0.0958 nm) might impact the structure of the complexes. The heavy rare earth
ions form mononuclear complexes, and the light rare earth ions form polynuclear complex. This
is mainly attributed to the “lanthanide contraction effect”. This conclusion is consistent with our
previous findings in lanthanide complexes with bis(N-salicylidene)-3-oxapentane-1,5-diamine
[24].
To determine whether the crystal structures are truly representative of the bulk materials
used for property studies, powder X-ray diffraction (PXRD) experiments were carried out for the
complexes. The PXRD experimental and as-simulated patterns are shown in figure S1. The
crystalline samples of 1 and 2 gave a positive match between the experimental and simulated
PXRD patterns, indicating that the bulk synthesized material and the crystals are homogeneous.
9
3.2. IR and electronic spectra
In the free ligand Bod, a strong band is found at 1629 cm-1 along with a weak band at 1255 cm-1.
By analogy with the previously assigned bands, the former can be attributed to ν(C=N), while the
latter can be attributed to ν(C-O-C). These bands shifted ca. 20 ~ 80 cm-1 in the complexes, which
can be attributed to coordination of the ligand. Bands at 1385-1389 cm−1 in the complexes
indicate bidentate nitrate [42], in agreement with X-ray diffraction.
The electronic spectra of the ligands and the metal complex were recorded in DMF
solution at room temperature. The UV bands of Bod (271, 330 nm) are marginally shifted in the
complexes. Two absorption bands are assigned to π→π* (benzene) and π→π* (C=N) transitions.
3.3. Hydroxyl radical scavenging activity
The plots of hydroxyl radical scavenging effects (%) of the ligand and complexes have been
depicted in figure 5. The complexes show inhibitory activity and the suppression ratio for OH∙
increases with increasing complex concentration. Usually, mannitol and vitamin C are used as
the standard antioxidants for comparison [43]. The 50% inhibitory concentration (IC50) values of
mannitol and vitamin C are about 9.6×10-3 and 8.7×10-3 M, respectively. According to the
antioxidant experiments, the IC50 of the ligand and 1 and 2 are 8.60×10-5, 6.82×10-6 and
8.7×10-6 M in figure 5 (a), (b), (c). The results suggest that the complexes exhibit better
scavenging activity than the ligand, as well as mannitol and vitamin C. Due to the observed IC50
values, 1 and 2 can be considered as a potential drugs to eliminate the hydroxyl radical [44, 45].
3.4. Superoxide radical scavenging activity
As another significant assay of antioxidant activity, superoxide radical (O2-∙) scavenging activity
of the title complexes has been investigated. The complexes and the ligand have good superoxide
radical scavenging activity. The concentration of the complex which causes 50% inhibition of
NBT reduction is reported as IC50. As can be seen from figure 5, the IC50 values for the
complexes were determined by plotting the graph of percentage inhibition of NBT reduction
10
against the increase in the concentration of the complexes. The ligand and 1 and 2 show IC50
values of 2.05×10-4, 3.78×10-5 and 3.47×10-5 M, respectively, in figure 5 (d), (e), (f). The value
of IC50 of vitamin C for superoxide radical scavenging effect is 1.12×10-4 M. The complexes
have better superoxide radical scavenging activity than the ligand and vitamin C. The results
indicate that 1 and 2 also exhibit good superoxide radical scavenging activity and may be
inhibitors (or drugs) to scavenge superoxide radical (O2−·) in vivo which needs further
investigation.
The lower IC50 values observed in hydroxyl radical and superoxide radical scavenging
assays did demonstrate that 1 and 2 have good scavenging effects for hydroxyl radical (OH∙) and
superoxide radical (O2-∙).
3.5. Fluorescence studies
The ability to transfer energy from ligand-centered to metal-centered states is important in the
design of lanthanide(III) photonic devices [46, 47].
Presented in table 3 are the data from the fluorescence emission spectra of the ligand and
its complexes in DMF solution (1×10-5 mol L-1) and in the solid state, which were studied at
room temperature. As shown in figure 6, the emission peak of the ligand is observed at 460 nm
(π-π*) in solvent (figure 6(a)) and 338 nm (π-π*) in the solid state (figure 6(d)). Among the
complexes studied, the emission spectrum of the Sm(III) complex in DMF was measured for
excitation at 357 nm. The emission spectrum is shown in figure 6(b). Emission bands were
observed at 476, 566, 599 and 645 nm and are attributed to π-π* transition, f-f transitions
4
G5/26H5/2 (zero–zero band: forbidden transition), 4G5/26H7/2 (magnetic dipole transition)
and 4G5/26H9/2 (electric dipole transition), respectively. 4G5/26H9/2 transition intensity was
1.5 times larger than 4G5/26H7/2 transition intensity. The full width at half-maxim (FWHM) of
the 4G5/26H9/2 transition was 7 nm. The narrow and strong emission of the 4G5/26H9/2
transition is due to the asymmetric ten-coordinate structure related to the special odd parity [48].
Based on the data we can learn the emission peaks which appear near 566, 599 and 645 nm are
11
the emission peaks of Sm(III) [49]. The emission of 1 produced characteristic Sm(III)
luminescence, which indicated an effective match of the orbital energy levels between the ligand
and Sm(III) ion. The intense emission peaks of 1 in the solid state appear near 490 nm (π-π*) in
figure 6(e) and the fluorescence of the Sm(III) ion was not observed due to the effect of diffuse
reflection of the metal ions. The intense emission peak of 2 is observed at 464 nm (π-π*) in
solvent (figure 6(c)) and 521 nm (π-π*) in solid state (figure 6(f)). For 2, La(III) has no 4f
electrons and has a closed-shell electron configuration. Therefore, the energy absorbed by Bod
cannot be transferred to La(III) ions by an intramolecular energy transfer processes, however it
relaxes through its own lower energy levels, due to the mismatch of the orbital energy levels
between the ligand and La(III) ions.
The red shift in the fluorescence band of the ligand in the complexes compared with the
free ligand can be attributed to coordination of the rare earth ions to the ligand, which results in
an increase of the delocalization of electrons and reduction of the energy gaps between the π-π*
molecular orbitals of the ligand [50-53]. Energy transfer between the Schiff base ligand and the
rare earth ion appears to follow the well-known intramolecular energy transfer mechanism
exhibited by lanthanide Schiff-base complexes [54].
4. Conclusion
The lanthanide (Sm(III) and La(III)) nitrate complexes of the Schiff base ligand
bis(3-methoxysalicylidene)-3-oxapentane-1,5-diamine (Bod) have been synthesized and
structurally characterized by elemental analysis, molar conductivity, IR spectra and UV–Vis
spectra. Complexes 1 and 2 exhibited potential antioxidant activity against OH∙ and O2-∙ radicals
in in vitro studies. These findings clearly indicate that the Ln(III) complexes have potential
practical applications of antioxidants, which warrants further in vivo experiments and
pharmacological assays. In addition, 1 exhibits the characteristic luminescence of Sm(III) ions
whereas 2 shows only the fluorescence characteristics of Bod. This indicates that Bod is a good
organic chelator to absorb and transfer energy to Sm(III) ions.
12
Supplementary material
Crystallographic data (excluding structure factors) for 1 and 2 have been deposited with the
Cambridge Crystallographic Data Center as supplementary publication CCDC 998536 and
998537. Copies of the data can be obtained free of charge on application to the CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK.
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was supported by the National Natural Science Foundation of China (Grant No.
21367017); Natural Science Foundation of Gansu Province (Grant No. 1212RJZA037) and
Graduate Student Innovation Projects of Lanzhou Jiaotong University.
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17
Figure 1. (Left) Molecular structure and atom numberings of 1 with hydrogen atoms omitted for
clarity. (Right) Distorted hexadecahedron environment described by donor atoms around the
central Sm3+ atom as illustrated in the polyhedral view.
18
Figure 2. Packing structure of 1.
19
Figure 3. (Upper) Molecular structure and atom numberings of 2 with hydrogen atoms omitted
for clarity. (Lower) Distorted hexadecahedral environment described by donor atoms around the
central La3+ atom as illustrated in the polyhedral view.
20
Figure 4. Packing structure of 2.
21
Figure 5. Plots of antioxidation properties for the ligand and the complexes. (a) Ligand
(b) [Sm(Bod)(NO3)3] (c) [La(Bod)(NO3)3(DMF)]n of the hydroxyl radical-scavenging effect (%);
(d) Ligand (e) [Sm(Bod)(NO3)3] (f) [La(Bod)(NO3)3(DMF)]n of the superoxide
radical-scavenging effect (%).
22
Figure 6. The photoluminescent emission spectra (solid and solvent in DMF) of the ligand and
the complexes. (a) Ligand (b) [Sm(Bod)(NO3)3] (c) [La(Bod)(NO3)3(DMF)]n in DMF solvent;
(d) Ligand (e) [Sm(Bod)(NO3)3] (f) [La(Bod)(NO3)3(DMF)]n in solid-state.
23
Table 1. Crystal data and structure refinement for 1 and 2.
Complex
1
2
Molecular formula
Molecular weight (gm-1)
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
α (°)
β (°)
γ (°)
Volume (Å3)
Z
T(K)
D (calculated) (g·cm−3)
Absorption coefficient (mm−1)
F(000)
Crystal size (mm)
θ range for data collection (°)
Reflections collected
Independent reflections
Index ranges
SmC20H24N5O14
708.8
Triclinic
P-1
LaC23H31N6O15
770.45
Triclinic
P-1
9.513(13)
9.720(13)
15.33(2)
77.541(16)
84.219(14)
74.545(16)
1333(3)
2
296(2)
1.766
2.281
702
0.41 × 0.37 × 0.30
1.36 to 25.50
8985
4962 [R(int) = 0.0253]
-11<=h<=11,
-8<=k<=11,
-18<=l<=18
Full-matrix least-squares on F2
4818 / 0 / 363
1.049
R1 = 0.0306, wR2 = 0.0737
R1 = 0.0389, wR2 = 0.0824
0.857 and -0.691
11.14(2)
14.98(3)
15.09(3)
61.42(2)
72.620(19)
83.35(2)
2109(7)
2
296(2)
1.213
1.070
776
0.39 × 0.36 × 0.32
2.19 to 25.50
13477
7652 [R(int) = 0.0600]
-13<=h<=13,
-18<=k<=18,
-18<=l<=15
Full-matrix least-squares on F2
7652 / 367 / 410
0.934
R1 = 0.0576, wR2 = 0.1358
R1 = 0.1015, wR2 = 0.1483
1.071 and -0.8528
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
Final R1 and wR2 [I > 2σ(I)]
R indices (all data)
Largest diff. peak and hole (e Å-3)
24
Table 2. Selected bond distances (Å) for 1 and 2.
Selected bond lengths (Å)
Ln-Onitrate
Ln-Ohydroxyl
Ln-Omethoxyl
1
Sm(1)-O(2)
Sm(1)-O(4)
Sm(1)-O(5)
Sm(1)-O(6)
Sm(1)-O(8)
Sm(1)-O(10)
Sm(1)-O(13)
Sm(1)-O(14)
Sm(1)-O(11)
Sm(1)-O(12)
2
2.557(4)
2.644(5)
2.552(5)
2.482(4)
2.553(5)
2.525(5)
2.322(4)
2.376(4)
2.740(4)
2.667(4)
Ln-ODMF
La(1)-O(7)
La(1)-O(8)
La(1)-O(10)
La(1)-O(11)
La(1)-O(13)
La(1)-O(14)
La(1)-O(2)#1
La(1)-O(4)
La(1)-O(5)
La(1)-O(1)#1
La(1)-O(15)
Symmetry transformations used to generate equivalent atoms: #1 x+1,y,z
25
2.638(6)
2.670(6)
2.671(6)
2.615(7)
2.616(7)
2.723(6)
2.454(5)
2.426(5)
2.794(6)
3.004(8)
2.534(6)
Table 3. Luminescence spectra data of the Schiff base ligand Bod and its complexes in DMF at room
temperature.
Solvent
λex(nm)
λem(nm)
Stokes
shift
(nm)
Ligand
Complex 1
371
357
Complex 2
349
460
476
566
599
645
464
89
119
209
242
288
115
Compound
Solid
λem(nm)
Stokes
shift
(nm)
Assignment
200
355
338
490
138
135
π-π*
π-π*
392
521
129
π-π*
Assignment
λex(nm)
π-π*
π-π*
4
G5/2→6H5/2
4
G5/2→6H7/2
4
G5/2→6H9/2
π-π*
26