Heterobimetallic 3d–4f Zn(II)–Ln(III) (Ln?=?Sm, Eu, Tb and Dy) complexes with a N2O4 bisoxime chelate ligand and a simple auxiliary ligand Py: Syntheses, structures and luminescence properties

Article abstract of DOI:10.1016/j.poly.2017.02.040

Four new 3d–4f heterobinuclear complexes [Zn(L)Sm(Py)(NO₃)₃] (1), [Zn(L)Eu(OAc)(NO₃)₂] (2), [Zn(L)Tb(Py)(NO₃)₃] (3) and [Zn(L)Dy(OAc)(NO₃)₂] (4); Py?=?pyridine; H

Full text of DOI:10.1016/j.poly.2017.02.040

Accepted Manuscript
Heterobimetallic 3d–4f Zn(II)–Ln(III) (Ln = Sm, Eu, Tb and Dy) complexes
with a N2O4 bisoxime chelate ligand and a simple auxiliary ligand Py: Syntheses,
structures and luminescence properties
Cai-Hong Tao, Jian-Chun Ma, Li-Chun Zhu, Yang Zhang, Wen-Kui Dong
PII:
S0277-5387(17)30162-6
DOI:
http://dx.doi.org/10.1016/j.poly.2017.02.040
POLY 12507
Reference:
Polyhedron
To appear in:
Received Date:
Revised Date:
Accepted Date:
23 January 2017
25 February 2017
27 February 2017
Please cite this article as: C-H. Tao, J-C. Ma, L-C. Zhu, Y. Zhang, W-K. Dong, Heterobimetallic 3d–4f Zn(II)–
Ln(III) (Ln = Sm, Eu, Tb and Dy) complexes with a N2O4 bisoxime chelate ligand and a simple auxiliary ligand Py:
Syntheses, structures and luminescence properties, Polyhedron (2017), doi: http://dx.doi.org/10.1016/j.poly.
2017.02.040
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Heterobimetallic 3d–4f Zn(II)–Ln(III) (Ln = Sm, Eu, Tb and Dy)
complexes with a N2O4 bisoxime chelate ligand and a simple auxiliary
ligand Py: Syntheses, structures and luminescence properties
Cai-Hong Tao, Jian-Chun Ma, Li-Chun Zhu, Yang Zhang, Wen-Kui Dong*
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070,
P. R. China
______________________________________________________________________________
Abstract
Four new 3d–4f heterobinuclear complexes [Zn(L)Sm(Py)(NO3)3] (1), [Zn(L)Eu(OAc)(NO3)2]
(2), [Zn(L)Tb(Py)(NO3)3] (3) and [Zn(L)Dy(OAc)(NO3)2] (4); Py = pyridine; H2L =
6,6'-dimethoxy-2,2'-[ethylenedioxybis(nitrilomethylidyne)]diphenol) have been successfully
prepared by the one-pot reaction of H2L with zinc(II) acetate, lanthanide(III) nitrate and a simple
auxiliary ligand Py. Although the heterobinuclear complexes 1−4 are prepared in the same
reaction condition, the auxiliary ligand Py doesn’t coordinate to the Zn(II) center of the
complexes 2 and 4. Instead, the bridging µ-acetato ligand is present in the complexes 2 and 4.
The coordination of the auxiliary ligand Py in the complexes 1 and 3 leads to the smaller
distortion of square pyramidal coordination site of Zn(II), the higher coplanarity between the
planes of ZnO(phenoxo)2 and LnO(phenoxo)2, and the longer Zn···Ln distance compared with
the complexes 2 and 4. Moreover, the ligand (L)2– can selectively sensitize Sm(III) ion from
among Sm(III), Eu(III), Tb(III) and Dy(III) ions, although these complexes would often exhibit
f–f luminescence.
Keywords: N2O4 bisoxime ligand; 3d–4f complex; Synthesis; Structure; Luminescence
______________________________________________________________________________
1. Introduction
Salen-type transition metal complexes are used as precursors in the syntheses of
oligometallic complexes [1,2] because of the high coordination ability of the phenoxo groups
*Corresponding author. Tel: +86 931 4938703; Fax: +86 931 4938703.
E-mail address: dongwk@126.com (W.-K. Dong)
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which can bridge two metal centers in a µ2-M–O–M fashion. Many homo- and
heteropolymetallic complexes have been synthesized with Salen-type ligands [3,4]. When
3-alkoxy groups are introduced in salicylidene moieties, an O4 coordination site composed of the
alkoxy groups and phenoxo oxygen atoms is produced in addition to the N2O2 site. The O4 site of
3-alkoxy Salen-type ligands is suitable for lanthanide ions to obtain 3d–4f heteronuclear
complexes [5]. These 3d–4f heterometallic complexes have been widely studied because of their
potential application in magnetism and luminescence [5]. The luminescence properties of Ln(III)
complexes are of considerable interest due to their potential applications in materials science and
bioassays [6]. Various complexes of Eu(III) and Tb(III), which emit a strong visible luminescence,
have been extensively studied. Several Zn(III)–Ln(III) heterometallic complexes of Salen-type
ligands have also been reported to exhibit a visible or NIR luminescence [7].
Herein, we report the syntheses and crystal structures of four new heterobinuclear complexes
[Zn(L)Sm(Py)(NO3)3] (1), [Zn(L)Eu(OAc)(NO3)2] (2), [Zn(L)Tb(Py)(NO3)3] (3) and
[Zn(L)Dy(OAc)(NO3)2] (4). The complexes 1-4 were characterized by elemental analyses, IR
spectra, UV-Vis spectra, X-ray single crystal diffraction, and luminescence spectroscopy. The Py
was selected as a simple auxiliary ligand owing to its availability and application in the building
of Salen-type complexes. Though many homo or heteronuclear complexes have been studied
using Salen-type or Salamo-type N2O2 compounds over the past two decades [8], few
Salamo-type 3d−4f heteromultinuclear complexes have been reported [4l].
2. Experimental Section
2.1 Materials and instrumentation
2-Hydroxy-3-methoxybenzaldehyde (99%) was purchased from Alfa Aesar. The other
reagents and solvents were purchased from Shanghai Darui Chemical Fine Chemicals
Company. All chemicals were of analytical grade and used without further purification. C,
H, and N analyses were obtained using a GmbH VarioEL V3.00 automatic elemental analysis
instrument. Melting points were obtained by the use of a microscopic melting point apparatus
1
made in Beijing Taike Instrument Limited Company, and the thermometer was uncorrected. H
NMR spectra were recorded using a Mercury-400BB spectrometer at 400 MHz and 13C NMR
spectra were recorded using a Mercury-600BB spectrometer at 150 MHz. IR spectra were
2

recorded on a VERTEX70 FT-IR spectrophotometer, with samples prepared as KBr (4000-400
cm-1) pellets. UV–Vis absorption spectra were recorded on a Shimadzu UV-2550 spectrometer.
Luminescence spectra in solution and solid state were recorded on a Perkin-Elmer LS-55
spectrometer. The luminescence decays in solid state were recorded using a pumped dye laser
(Lambda Physics model FL2002) as the excitation source.
2.2
Synthesis
and
characterization
of
6,6'-dimethoxy-2,2'-[ethylenedioxybis(nitrilomethylidyne)]diphenol (H2L)
The ligand H2L was synthesized according to the reported procedure [9]. Synthetic route to
the ligand H2L is shown in Scheme 1. The infrared and UV spectra of the H2L were almost
consistent with the literature. Mp 132-134 °C. Anal. calc. for C18H20N2O6: C, 59.99; H, 5.59; N,
7.77%. Found: C, 60.21; H, 5.65; N, 7.58%. 1H NMR (400 MHz, CDCl3): δ 3.90 (s, 6 H), 4.50 (s,
4 H), 6.82 (dd, J = 7.8, 1.8 Hz, 2 H), 6.85 (t, J = 8.0 Hz, 2 H), 6.90 (dd, J = 7.8, 1.8 Hz, 2 H),
8.25 (s, 2 H), 9.75 (s, 2 H). 13C NMR (150 MHz, CDCl3): δ 56.2 (CH3), 73.2 (CH2), 113.6 (CH),
116.6 (C), 119.7 (CH), 122.3 (CH), 147.2 (C), 148.0 (C), 152.2 (CH=N). IR (KBr; cm–1): 3134
(m), 2956 (m), 2897 (m), 1605 (s), 1578 (m), 1473 (s), 1423 (s), 1362 (m), 1315 (m), 1256 (s),
1171 (w), 1055 (s), 970 (w), 928 (s), 835 (m), 775 (s), 729 (s), 675 (s), 621 (s), 586 (w), 540 (w).
UV–Vis (CH3OH), λmax (nm) [εmax (dm3 mol–1 cm–1)]: 223 (5.74 × 104), 271 (3.80 × 104), 317
(1.12 × 104).
Scheme 1. The synthetic route to H2L.
2.3 Syntheses of the complexes 1, 2, 3 and 4
To a stirred solution of H2L (36.0 mg, 0.1 mmol) in chloroform (1 mL) was added
Zn(OAc)2·2H2O (21.9 mg, 0.1 mmol) and Ln(NO3)3·6H2O (0.1 mmol) in methanol (2 mL). After
stirring for 10 min at room temperature, a solution of Py (0.1 mmol) in methanol (0.5 mL) was
added, and the mixture was kept stirring for another 10 min at room temperature. Then the
mixture was filtered and the filtrate was obtained. The crystals suitable for X-ray diffraction
studies were obtained by vapor diffusion of diethyl ether into the filtrate for about four days at
room temperature.
For the complex 1, clear light colourless blocks. Yield: 0.055 g, 66%. Anal. calc. for
3

[Zn(L)Sm(Py)(NO3)3] (C23H23SmN6O15Zn): C, 32.92; H, 2.76; N, 10.01%. Found: C, 32.85; H,
2.71; N, 9.95%. IR (cm–1, KBr): 2949 (w), 1610 (s), 1556 (m), 1508 (s), 1469 (s), 1385 (s), 1290
(s), 1240 (m), 1217 (s), 1172 (w), 1072 (s), 1043 (m), 1022 (m), 970 (m), 939 (m), 922 (w), 850
(m), 814 (w), 783 (w), 740 (s), 700 (w), 661 (w), 619 (m), 524 (w), 520 (w). UV–Vis (CH3OH),
λmax (nm) [εmax (dm3 mol–1 cm–1)]: 229 (5.39 × 104), 279 (3.06 × 104), 349 (1.02 × 104).
For the complex 2, clear light red blocks. Yield: 0.051 g, 67%. Anal. calc. for
[Zn(L)Eu(OAc)(NO3)2] (C20H21EuN4O14Zn): C, 31.66; H, 2.79; N, 7.38%. Found: C, 31.59; H,
2.73; N, 7.30%. IR (cm–1, KBr): 2949 (w), 1610 (s), 1558 (m), 1508 (s), 1465 (s), 1384 (s), 1294
(s), 1240 (m), 1219 (s), 1170 (w), 1074 (s), 1043 (m), 1024 (m), 972 (m), 939 (m), 921 (m), 812
(w), 781 (w), 740 (s), 663 (w), 619 (m), 524 (w). UV–Vis (CH3OH), λmax (nm) [εmax (dm3 mol–1
cm–1)]: 230 (4.72 × 104), 279 (2.57 × 104), 349 (0.84 × 104).
For the complex 3, clear light yellow blocks. Yield: 0.053 g, 63%. Anal. calc. for
[Zn(L)Tb(Py)(NO3)3] (C23H23TbN6O15Zn): C, 32.58; H, 2.73; N, 9.91%. Found: C, 32.51; H,
2.77; N, 9.80%. IR (cm–1, KBr): 2949 (w), 1610 (s), 1558 (m), 1508 (s), 1466 (s), 1382 (s), 1294
(s), 1240 (m), 1217 (s), 1172 (w), 1074 (s), 1043 (s), 1024 (s), 972 (m), 941 (m), 923 (m), 852
(m), 812 (w), 781 (w), 740 (s), 663 (w), 619 (m), 526 (w). UV–Vis (CH3OH), λmax (nm) [εmax
(dm3 mol–1 cm–1)]: 226 (4.51 × 104), 278 (2.33 × 104), 349 (0.69 × 104).
For the complex 4, clear light yellow blocks. Yield: 0.046 g, 60%. Anal. calc. for
[Zn(L)Dy(OAc)(NO3)2] (C20H21DyN4O14Zn): C, 31.23; H, 2.75; N, 7.28%. Found: C, 31.19; H,
2.85; N, 7.20%. IR (cm–1, KBr): 2949 (w), 1610 (s), 1573 (m), 1508 (s), 1465 (s), 1384 (s), 1319
(s), 1294 (s), 1240 (s), 1219 (s), 1099 (w), 1172 (w), 1074 (s), 1043 (s), 1024 (s), 974 (m), 941
(m), 923 (m), 812 (w), 781 (w), 742 (s), 663 (w), 619 (m), 524 (w). UV–Vis (CH3OH), λmax (nm)
[εmax (dm3 mol–1 cm–1)]: 226 (5.78 × 104), 277 (3.03 × 104), 350 (0.91 × 104).
2.4 Crystal structure determination
The single crystals of the complexes 1, 3 and 4 were placed on a Bruker Smart 1000
area detector, while that of the complex 2 was placed on a SuperNova (Dual, Cu at zero, Eos)
diffractometer. The diffraction data were collected using a graphite monochromated Mo Kα
radiation (λ = 0.71073 Å). Data collection and reduction of the complexes 1, 3 and 4 were
performed using the SMART and SAINT software [10], while that of the complex 2 was
performed using the CrysAlisPro software. The structures were solved using the direct
4

method and refined by full-matrix least squares methods on F2 by using the SHELXL-97
program package [11]. Anisotropic thermal parameters were used for the non-hydrogen
atoms and isotropic parameters for the hydrogen atoms. Hydrogen atoms were added
geometrically and refined using a riding model. Crystallographic data and refinement for all
of the complexes are summarized in Table 1. Selected structural parameters are listed in
Table 2.
3. Results and discussion
3.1 Spectral investigation
3.1.1 IR spectra
As shown in Fig. 1, IR spectra of the free ligand H2L and its corresponding complexes 1–4
exhibit the characteristic C=N stretching band. For the free ligand H2L this band appears at 1605
cm-1, while the C=N bands of the complexes 1–4 are observed at 1610 cm-1. The C=N absorption
shifts to higher wavenumbers by 5 cm-1 on going from the free ligand H2L to the complexes [12].
The O-H stretching frequency of the free ligand H2L appears at 3134 cm-1 [4j].
The Ar-O stretching appear as a strong band within 1263-1213 cm-1 range as reported for
similar Salen-type ligands. These bands occur at 1256 cm-1 for H2L, 1217 cm-1 for the complexes
1 and 3, 1219 cm-1 for the complexes 2 and 4. The Ar-O stretching is shifted to lower
wavenumbers, indicating that the M-O bonds are formed between the metal ions and oxygen
atoms of phenolic groups [13].
Four bands in the IR spectra of the complexes 1–4 near 1508, 1290-1294, 1043, and 812-814
cm–1 can be assigned to vibrations of the coordinated nitrate group (respectively the vibrations ν4,
ν1, ν2, and ν6). The difference between the ν4 and the ν1 peaks is ca. 214-218 cm–1, which is
typical for bidentate nitrate groups (monodentate nitrate groups display a much smaller splitting)
[14].
3.1.2 UV-Vis spectra
The absorption spectra of the free ligand H2L and its corresponding complexes 1–4 in
methanol solution show that the spectra of the complexes 1–4 are similar to each other, but are
different from the spectrum of the free ligand H2L (Figure 2). UV-Vis spectrum of the free ligand
H2Lexhibits three absorption peaks at ca. 223, 271 and 317 nm. The absorption peak at 223 and
5

271 nm can be assigned to the π-π* transition of the benzene rings and the absorption peak at 317
nm can be attributed to the intra-ligand π-π* transition of the C=N bonds [12].
Compared with the absorption peak of the free ligand, the corresponding absorption peak of
the complexes 1-4 are bathochromically shifted and are observed at 226-230 and 277-279 nm,
indicating the coordination of metal ions with the (L)2–. Meanwhile, a new absorption peak is
observed at ca. 350 nm in the complexes 1–4, which are assigned to the n-π* charge transfer
transition from the lone pair electron of N atom of C=N group to the benzene rings [15].
3.2 Description of the crystal structures
3.2.1 Structures of the complexes 1 and 3
The crystal structures of the heterobinuclear complexes [Zn(L)Ln(Py)(NO3)3] (Ln = Sm (1),
Tb (3)) are shown in Fig. 3, and selected bond lengths are summarized in Table 2. As shown in
Fig. 3, the structures of the complexes 1 and 3 are similar, only the structure of the
Zn(II)–Sm(III) complex
1 is described in detail. In the crystal structure of the complex 1,
each Zn(II) atom lies in a five-coordinate environment and adopts a distorted square pyramidal
geometry (τ = 0.127) [16], where the inner N2O2 core (N1, N2, O5 and O6) from deprotonated
(L)2– unit, and one terminal N (N3) atom from the coordinated Py at the apical position (Fig. 3a).
The bond lengths of Zn−O(N) are Zn1−O5 = 2.030(5) Å, Zn1−O6 = 2.030(4) Å, Zn1−N1 =
2.074(6) Å, Zn1−N2 = 2.108(7) Å, and Zn1−N3 = 2.042(6)
Å. The Sm(III) atom is
ten-coordinated and adopts a distorted bicapped square antiprism geometry, composed of the
outer O4 cavity (O1, O4, O5 and O6) from deprotonated (L)2– unit and six oxygen atoms from
three bidentate nitrate ligands. The Sm−O bond lengths (2.416(4) and 2.353(5) Å) from the
phenoxo oxygen atoms (O5 and O6) are slightly shorter than those (2.548(6), 2.576(6) or
2.495(6)–2.572(6) Å) from –OMe groups or nitrate ligands. The Zn(II)···Sm(III) distance of the
complex 1 is 3.559(6) Å, slightly longer than that of previous heterodinuclear complex
[LZnSm(OAc)3] [17], in which the apical position of Zn(II) atom was occupied by oxygen atoms
from anions (OAc–), instead of nitrogen atom from the Py in the complex 1. The Zn-O2-Sm
square is nearly planar, with the dihedral angle between the O5–Zn1–O6 and O5–Sm1–O6
planes is 0.46(6)°.
3.2.2 Structures of the complexes 2 and 4
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The crystal structures of the heterobinuclear complexes [Zn(L)Ln(OAc)(NO3)2] (Ln = Eu (2),
Dy (4)) are shown in Fig. 4, and selected bond lengths are summarized in Table 2. Although the
complexes 1–4 are prepared in the same reaction condition, a MeOH-CHCl3 solution of the
ligand H2L, Zn(OAc)2·2H2O, Ln(NO3)3·6H2O and Py in a 1:1:1:1 molar ratio, the auxiliary
ligand Py only coordinates to the complexes 1 and 3. The acetato ligand bridges the Zn(II) and
Ln(III) atoms in a µ2 fashion in the complexes 2 and 4. As shown in Fig. 4, the structures of the
complexes 2 and 4 are similar, and only the structure of the Zn(II)–Eu(III) complex
2 is
described in detail. In the crystal structure of the complex , each Zn(II) atom has a
2
distorted square pyramidal coordination geometry (τ = 0.279) [16], where the equatorial
coordination sites consist of N2O2 donor atoms of the ligand (L)2– with the distances of
Zn1−O2 = 2.052(2) Å, Zn1−O5 = 2.017(2) Å, Zn1−N1 = 2.044(3) Å, and Zn1−N2 = 2.096(3)
Å, and the axial position is occupied by one oxygen atom of µ-acetato ligand with the
distance of Zn1−O8 = 1.977(3) Å. The coordination number of Eu(III) atom is nine,
consisting of four oxygen atoms of two bidentate nitrate ligands, one oxygen atom of
µ-acetato ligand, two phenolato and two methoxy oxygen atoms of deprotonated (L)2– unit
.
Thus, the Eu(III) atom adopts a distorted tricapped trigonal prism coordination geometry. The
Eu−O distances of two nitrate ligands and one µ-acetato ligand are in the range of
2.339(2)–2.507(3) Å (Table 2). The two phenolato and two methoxy oxygen atoms of the
ligand (L)2– unit coordinate to Eu(III) atom, with the distances of Eu1−O1 = 2.585(3) Å,
Eu1−O2 = 2.333(3) Å, Eu1−O5 = 2.352(3) Å, and Eu1−O6 = 2.590(3) Å. Although the
Eu−O distances from the phenolato oxygen atoms (O2, O5) are much shorter than those
from the methoxy oxygens (O1, O6), the bridging mode from the phenolato oxygen atoms
helps to form the binuclear structure. The Zn-O2-Eu square is not planar, as the dihedral
angle between the O2–Zn1–O5 and O2–Eu1–O5 planes is 31.83(6)° which is much larger
than the complexes 1 and 3 (Table 2).
A π···π contact is found in the complexes 2 (3.797(3)
Å) and 4 (3.779(3) Å), but it is not
found in the complexes 1 and 3. Fig. 5 shows the dimeric structure formed by π···π interactions
in 2 [18].
Although the heterobinuclear complexes 1−4 are prepared in the same reaction condition, the
Py unit doesn’t coordinate to the Zn(II) center of the complexes 2 and 4. Instead, the bridging
7

µ-acetato ligand is present in the complexes 2 and 4. This difference in the formation of two
different types of complexes (one with Py and the other with OAc- bridge) might be related to
difference in Lewis acidity. Sm and Tb complexes have lower Lewis acidity, while Eu and Dy
both have higher Lewis acidity [19], thus the Py unit could coordinate to the Zn(II) center of the
complexes 1 and 3, and couldn’t coordinate to that of the complexes 2 and 4. The coordination of
the Py in the complexes 1 and 3 leads to the smaller distortion of square pyramidal coordination
site of Zn(II), the higher coplanarity between the planes of ZnO(phenoxo)2 and LnO(phenoxo)2,
and the longer Zn···Ln distance compared with the complexes 2 and 4 (Table 2).
3.3 Luminescence spectra
The luminescence spectra of the free ligand H2L and its complexes 1−4 in MeOH solution (1
× 10-5 M) at room temperature are shown in Fig. 6.
The luminescence spectrum of the complex [Zn(L)Sm(Py)(NO3)3] (1) under excitation at 350
nm shows three characteristic emission peaks at 560, 596 and 643 nm. These peaks have been
4
6
assigned to the G5/2 to the HJ (J = 5/2, 7/2, 9/2) transitions which are typical emission peaks of
4
Sm(III) ion. The transition at 560 nm, G5/2→6H5/2, has a predominantly magnetic dipole
4
character, whereas the transition at 643 nm, G5/2→6H9/2, is mainly a hypersensitive transition. In
addition, the spectrum shows a broad peak at around 395–460 nm, which has been assigned to the
intraligand fluorescent emission of (L)2–. The Sm(III) ion is excited not by direct metal excitation
but by efficient sensitization by the [Zn(L)] unit. The broad ligand emission at 395–460 nm also
confirms the efficient energy transfer from the ligand to Sm(III) ion [7].
The ligand (L)2– acts as a sensitizer for Sm(III) luminescence in the visible region. The
sensitization process leading to the luminescence is known to proceeds via excitation of the
organic ligand to its singlet excited state. The energy is then transferred to its triplet state by
intersystem crossing, which is followed by energy transfer to the excited state of the Sm(III) ions
to produce the luminescence.
In the luminescence spectra of the complexes 2, 3 and 4 (Fig. 7), only a broad band at around
395–470 nm due to intraligand fluorescence is observed instead of the f–f emission expected for
Eu(III), Tb(III) and Dy(III) ions. In the complex 2, the emission from Eu(III) are quenched and
5
the intraligand fluorescence are also weak which may be due to thermal quenching of the D0
level of Eu(III) by an intramolecular ligand-to-metal charge-transfer (LMCT) process [17]. In the
8

complexes 3 and 4, energy transfer from the ligand to the metal is not efficient, probably because
the energy levels of the excited states of Tb(III) and Dy(III) ions lie higher than that of the
excited state of the [Zn(L)] moiety. Hence, the 3-MeOsalamo ligand (L)2– can selectively
sensitize Sm(III) ion from Sm(III), Eu(III), Tb(III) and Dy(III) ions, although these complexes
would often exhibit f–f luminescence [5]. It has been demonstrated that the Zn(II) ion with d10
configurations would generally not participate in the electron transfer process nor contribute to
sensitization of lanthanide luminescence [1b,20]. Nevertheless, the Zn(II) ion plays an important
role in the [Zn(L)Ln] complexes not only as a structure stabilizer, but also to improve the
efficiency of the antenna chromophores. Here one Tb(III) emission peak (540 nm) of the complex
[Zn(L)Tb (Py)(NO3)3] (3) is superimposed on that of the free ligand H2L. It demonstrate Tb(III)
ion is not sensitized effectively which may be due to a mismatch between the triplet state of the
[Zn(L)] moiety and 5D4 of Tb(III) ion.
Moreover, visible luminescence measurements of the complexes 1−4 in solid state are also
conducted. As shown in Fig. 8, the luminescence spectra of the complex 1 under excitation at 350
nm show three characteristic emission peaks at ca. 564, 598 and 646 nm of Sm(III) ion, and
others are still not characteristic emission of Ln(III) ions. Differences of relative intensity of the
complex 1 in the solid state from that in solution is small, demonstrates that the directional close
stacking of crystal molecules has a small effect on its luminescence.
4
The luminescence decay curve of the G5/2 emitting level of the Zn(II)–Sm(III) complex 1 is
monitored in the 4G5/2→6H7/2 (596 nm) transition. The luminescence decay curve (Fig. 9) can be
fitted mono-exponentially with time constants of microseconds (35.93 µs) of the Sm(III)
emissions in solid state. Because Sm(III) complexes generally show relatively weak f–f emission
with short decays [21], the value of the complex 1 is much lower than those of the bright Eu(III)
and Tb(III) complexes reported previously [5,6].
4. Conclusion
Four Zn(II)–Ln(III) heterobinuclear complexes have been prepared by the one-pot reaction
of the Salamo-type ligand H2L with zinc(II) acetate, lanthanide(III) nitrate and Py. Although the
heterobinuclear complexes 1−4 are prepared in the same reaction condition, the Py only
coordinates in 1 and 3. The acetato ligand bridges the Zn(II) and Ln(III) ions in a µ2 fashion in 2
and 4. A π···π contact is found in 2 and 4, but not in 1 and 3. The Zn(II)–Sm(III) heterobinuclear
9

complex exhibits characteristic emission of Sm(III) ion. The corresponding complexes containing
other lanthanides show only a blue emission due to the ligand. Therefore the Salamo-type ligand
(L)2– can selectively sensitize Sm(III) ion from among Sm(III), Eu(III), Tb(III) and Dy(III) ions.
Acknowledgement
This work was supported by the National Natural Science Foundation of China (21361015),
which is gratefully acknowledged.
Appendix A. Supplementary material
CCDC 1447934, 1447931, 1447930 and 1447928 contain the supplementary crystallographic
data for 1, 2, 3 and 4. These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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(2016) 1095; (e) Y.X. Sun, L. Wang, X.Y. Dong, Z.L. Ren, W.S. Meng, Synth. React.
Inorg. Met. Org. Nano Met. Chem. 43 (2013) 599; (f) Y.X. Sun, W.K. Dong, L. Wang,
L. Zhao, Y.H. Yang, Chinese J. Inorg. Chem. 25 (2009) 1478; (g) X.Y. Dong, Y.X.
Sun, L. Wang, L. Li, J. Chem. Res. 36 (2012) 387.
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J.C. Ma, Y. Zhang, J. Zhang, W.K. Dong, Z. Anorg, Allg. Chem. 641 (2015) 2520; (e)
L. Xu, Y.P. Zhang, J.Y. Shi, W.K. Dong, Chinese J. Inorg. Chem. 23 (2007) 1999; (f)
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Zhao, S.H. Liu, G.H. Liu, X.T. Dong, Synth. React. Inorg. Met. Org. Nano Met.
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12

Table 1
Crystallographic data and refinement parameter for the complexes 1–4
Complex
1
2
3
4
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (°)
β (°)
C23H23SmN6O15Zn
839.19
296(2)
MoKα, 0.71073
orthorhombic
Pna21
16.6132(16)
18.7807(17)
9.4711(10)
90
90
90
2955.1(5)
4
1.886
C20H21EuN4O14Zn
758.74
294.11(10)
MoKα, 0.71073
triclinic
C23H23TbN6O15Zn
847.76
293.33(10)
MoKα, 0.71073
orthorhombic
Pna21
16.5875(4)
18.5310(4)
9.3436(2)
90
C20H21DyN4O14Zn
769.28
173(2)
MoKα, 0.71073
triclinic
P-1
9.2830(7)
9.3329(7)
15.5419(11)
91.742(6)
95.895(6)
98.233(6)
1324.19(17)
2
P-1
9.4811(11)
9.5958(7)
14.3576(19)
90.990(9)
91.289(10)
100.383(8)
1284.2(2)
2
90
90
γ (°)
V (Å3)
2872.06(11)
4
1.961
Z
Dc (g·cm-3)
1.962
3.432
1.929
3.781
µ (mm-1)
2.862
3.363
θ Range (°)
F(000)
2.2 to 25.5
1660
3.3 to 25.7
748
3.3 to 26.0
1672
3.4 to 26.0
754
h/k/l (min, max)
Crystal size (mm)
Reflections collected
-20,16/-22,22/-11,11 -11,11/-11,9/-17,17 -20,19/-13,22/-11,11 -12,11/-11,12/-20,20
0.22 × 0.25 × 0.27
21355/5451
[Rint = 0.050]
5451
0.31 × 0.32 × 0.34
9564/4859
[Rint = 0.034]
4859
0.27 × 0.29 × 0.33
11846/5049
[Rint = 0.050]
5049
0.23 × 0.25 × 0.27
10483/5206
[Rint = 0.031]
5206
Independent reflection
Completeness to θ (%)
Data/restraints/parameter
s
25.49 (99.00)
26.32 (99.72)
26.32 (99.61)
26.32 (99.71)
5451/1/417
4859/0/364
5049/1/417
5206/0/364
Final R indices [I > 2σ R1 = 0.0308,
R1 = 0.0315,
wR2 = 0.0451
R1 = 0.0411,
wR2 = 0.0514
1.003
R1 = 0.0356,
wR2 = 0.0532
R1 = 0.0482,
wR2 = 0.0586
1.017
R1 = 0.0325,
wR2 = 0.0631
R1 = 0.0403,
wR2 = 0.0671
1.040
(I)]
wR2 = 0.0657
R1 = 0.0385,
wR2 = 0.0684
1.035
R indices (all data)
GOF
13

∆ρmax,min (e Å– 3)
-0.47, 0.61
-0.57, 0.72
-0.58, 0.89
-0.74, 0.63
Wen-kui Dong et al.
Table 2
Selected structural parametersa of the complexes 1–4
1
2
3
4
Zn1–N1
Zn1–N2
Zn1–N3
Zn1–O5
Zn1–O6
Sm1–O1
Sm1–O4
Sm1–O5
Sm1–O6
Sm1–O7
Sm1–O9
Sm1–O10
Sm1–O12
Sm1–O13
Sm1–O15
2.074(6)
2.108(7)
2.042(6)
2.030(5)
2.030(4)
2.548(6)
2.576(6)
2.416(4)
2.353(5)
2.572(6)
2.516(6)
2.566(5)
2.516(6)
2.495(6)
2.512(6)
Zn1–N1
Zn1–N2
Zn1–O2
Zn1–O5
Zn1–O8
Eu1–O1
Eu1–O2
Eu1–O5
Eu1–O6
Eu1–O7
Eu1–O9
Eu1–O10
Eu1–O12
Eu1–O13
Eu1···Zn1
τ (Zn)b
2.044(3)
2.096(3)
2.052(2)
2.017(2)
1.977(3)
2.585(3)
2.333(3)
2.352(3)
2.590(3)
2.339(2)
2.482(4)
2.473(3)
2.507(3)
2.491(3)
3.4153(6)
0.279
Zn1–N1
Zn1–N2
Zn1–N3
Zn1–O2
Zn1–O5
Tb1–O1
Tb1–O2
Tb1–O5
Tb1–O6
Tb1–O7
Tb1–O8
Tb1–O10
Tb1–O12
Tb1–O13
Tb1–O15
Tb1···Zn1
τ (Zn)b
2.103(7)
2.066(7)
2.037(7)
2.026(5)
2.027(5)
2.536(6)
2.312(5)
2.380(5)
2.514(6)
2.539(6)
2.480(6)
2.462(7)
2.535(6)
2.452(6)
2.459(6)
3.526(6)
0.095
Zn1–N1
Zn1–N2
Zn1–O2
Zn1–O5
Zn1–O8
Dy1–O1
Dy1–O2
Dy1–O5
Dy1–O6
Dy1–O7
Dy1–O9
Dy1–O10
Dy1–O12
Dy1–O13
2.086(4)
2.047(4)
2.012(3)
2.051(3)
1.988(3)
2.580(3)
2.318(3)
2.286(3)
2.540(3)
2.313(3)
2.449(3)
2.426(3)
2.453(3)
2.455(3)
Dy1···Zn1 3.3764(6)
Sm1···Zn1 3.559(6)
τ (Zn)b
0.308
31.80(6)
τ (Zn)b
0.127
0.46(6)
δc
31.83(6)
δc
δc
δc
0.04(6)
a Distances in Å and angles in
°
.
b τ values are calculated according to ref. [17]. c Dihedral angle between
ZnO(phenoxo)2 and LnO(phenoxo)2 planes.
14

Wen-kui Dong et al.
Figures legends:
Scheme 1. The synthetic route to H2L.
Fig. 1 IR spectra of the free ligand H2L and its complexes 1–4.
Fig. 2 UV-Vis spectra of the free ligand H2L and its complexes 1–4 in CH3OH (1 × 10-5 M).
Fig. 3 View of the molecular structures of the complexes 1 (a) and 3 (b). H atoms are omitted for clarity, and
thermal ellipsoids are drawn at the 30% probability level.
Fig. 4 View of the molecular structures of the complexes 2 (a) and 4 (b). H atoms are omitted for clarity, and
thermal ellipsoids are drawn at the 30% probability level.
Fig. 5 View of the π···π interactions of the complex 2. H atoms are omitted for clarity.
Fig. 6 Luminescence spectrum of the complex 1 in CH3OH (1 × 10-5 M) upon excitation at 350 nm.
Fig. 7 Luminescence spectra of the H2L and its complexes 2, 3 and 4 in CH3OH (1 × 10-5 M) upon excitation
at 350 nm.
Fig. 8 Luminescence spectra of the complexes 1-4 in solid state upon excitation at 350 nm.
Fig. 9 Luminescence decay curve of the complex 1 in the solid state.
15

Wen-Kui Dong et al.
O
O
C
O
C
C
.
NH2NH2 H2O
Br
Br
N OH
N O
O
N
EtOH
EtOH
C
O
C
O
C
O
O
O
N
O
N
OH
2
O
H2L
OH HO
H2N O
O
NH2
EtOH
O
O
Scheme 1
16

Wen-Kui Dong et al.
H2L
1
2
3
4
4000
3500
3000
2500
2000
1500
1000
500
Wavelength (cm-1)
Fig. 1.
17

Wen-Kui Dong et al.
0.6
0.5
0.4
0.3
0.2
0.1
0.0
H2L
1
2
3
4
250
300
350
400
450
Wavelength (nm)
Fig. 2.
18

Wen-Kui Dong et al.
Fig. 3.
19

Wen-Kui Dong et al.
Fig. 4.
20

Wen-Kui Dong et al.
Fig. 5.
21

Wen-Kui Dong et al.
500
400
300
200
100
0
1
400
450
500
550
600
650
Wavelength (nm)
Fig. 6.
22

Wen-Kui Dong et al.
400
300
200
100
0
H2L
2
3
4
400
450
500
550
600
650
Wavelength (nm)
Fig. 7.
23

Wen-Kui Dong et al.
600
500
400
300
200
100
0
H2L
1
2
3
4
400
450
500
550
600
650
Wavelength (nm)
Fig. 8.
24

Wen-Kui Dong et al.
10000
8000
6000
4000
2000
0
Scan Type: Exponential Fit Time Scan
Fit Parameters: Fit = B1exp(-t/t1)
B1 = 0.093
t1 = 35.93 µs
200000
400000
600000
800000
Time (ns)
Fig. 9.
Wen-Kui Dong et al.
25

Graphical Abstract:
Four new 3d–4f heterobimetallic complexes 1–4 have been successfully prepared by the
one-pot method, and characterized structurally. Moreover, the ligand (L)2– can selectively
sensitize Sm(III) ion from among Sm(III), Eu(III), Tb(III) and Dy(III) ions, although these
complexes would often exhibit f–f luminescence.
Wen-Kui Dong et al.
26