Investigating into crystal structures and supramolecular architectures of four newly synthesized hetero-octanuclear [CuII4-LnIII4] (Ln = Sm, Eu, Tb and Dy) complexes produced by a hexadentate bisoxime chelate ligand

Article abstract of DOI:10.1016/j.ica.2020.119823

Four unprecedented 3d-4f hetero-octanuclear family-type complexes [{Cu(L)Ln(NO₃)₃}₂][Cu(L)Ln(NO₃)₃]₂ (Ln = Sm (1), Eu (2), Tb (3) and Dy (4)) were synthesized by an unsymmetric single salamo-like ligand H₂L (6-Methoxy-6′-ethoxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol) with Cu(OAc)₂·H₂O and Ln(NO₃)₃·6H₂O (Ln = Sm, Eu, Tb and Dy), respectively. X-ray crystallography revealed that each hetero-octanuclear 3d-4f metal complexes [{Cu(L)Ln(NO₃)₃}₂][Cu(L)Ln(NO₃)₃]₂ contains one neutral dimer [{Cu(L)Ln(NO₃)₃}₂] unit and two independent [Cu(L)Ln(NO₃)₃] units. At the same time, the four Cu(II) atoms of the complexes 1–4 have four- and five-coordinated configurations, while the four Ln(III) atoms have only one configuration, all of which are ten-coordinated. The structures of the four complexes 1–4 were characterized via elemental analyses, PXRD, FT-IR and UV–Vis spectroscopy. In addition, while studying the crystal structure, the supramolecular interactions and spectral properties of the complexes 1–4 were studied in detail.

Full text of DOI:10.1016/j.ica.2020.119823

Journal Pre-proofs
Research paper
Investigating into Crystal Structures and Supramolecular Architectures of
Four Newly Synthesized Hetero-octanuclear [CuII 4-LnIII 4] (Ln = Sm, Eu, Tb
and Dy) Complexes Produced by a Hexadentate Bisoxime Chelate Ligand
Xiao-Xin An, Zhuang-Zhuang Chen, Hao-Ran Mu, Li Zhao
PII:
DOI:
Reference:
S0020-1693(20)31022-7
https://doi.org/10.1016/j.ica.2020.119823
ICA 119823
To appear in:
Inorganica Chimica Acta
Received Date:
Revised Date:
Accepted Date:
11 May 2020
9 June 2020
9 June 2020
Please cite this article as: X-X. An, Z-Z. Chen, H-R. Mu, L. Zhao, Investigating into Crystal Structures and
Supramolecular Architectures of Four Newly Synthesized Hetero-octanuclear [CuII 4-LnIII 4] (Ln = Sm, Eu, Tb
and Dy) Complexes Produced by a Hexadentate Bisoxime Chelate Ligand, Inorganica Chimica Acta (2020), doi:
https://doi.org/10.1016/j.ica.2020.119823
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Author Contributions:
1. Li Zhao designed the experiments and contributed reagents/materials/analysis tools.
2. Xiao-Xin An ， Zhuang-Zhuang Chen
experiments and analyzed the data.
3. Xiao-Xin An wrote the paper.
and Hao-Ran Mu performed the
Declaration of interests
The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.
☐The authors declare the following financial interests/personal relationships which
may be considered as potential competing interests:
Graphical Abstract
Four unprecedented 3d-4f hetero-octanuclear family-type complexes

[{Cu(L)Ln(NO3)3}2][Cu(L)Ln(NO3)3]2 (Ln = Sm (1), Eu (2), Tb (3) and Dy (4)) were
synthesized and characterized via elemental analyses, PXRD, FT-IR, UV-Vis
spectroscopy. In addition, while studying the crystal structures, the supramolecular
interactions and spectral properties of complexes 1–4 were studied in detail.
SimulatedpatternoftheComplex1
ExperimentedpatternoftheComplex1
1600
HL
2
HL
2
Complex1
Complex2
Complex3
Complex4
1200
800
400
0
Complex1
Complex2
Complex3
Complex4
5
10 15 20 25 30 35 40 45 50
Diffractionangle(2θ)
4000 3500 3000 2500 2000 1500 1000 500
-1
Wavelength(cm )
350
400
450
Wavelength(nm)
500
550
0.12
0.10
0.08
0.06
0.04
0.02
0.00
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.0
O
O
O
O
O
O
N
O
N
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
N
[Cu2+
]
/ [H2L]
N
N
O
O
N
N
O
O
N
O
Cu
O
Cu
Ln
O
Cu
Ln
N
O
O
O
O
O
O
O
O
O
O
Ln
O
Ln
O
O
373 nm
O
N
O
O
N
O
N
O
O
O
N
O
O
N
N
O
O
O
Cu
N
O
O
O
O
O
N
O
O
N
O
O
O
O
O
O
O
O
O
O
O
O
N
O
N
O
250
300
350
400
450
Wavelength (nm)
Investigating into Crystal Structures and Supramolecular
Architectures of Four Newly Synthesized Hetero-octanuclear
[CuII -LnIII ] (Ln = Sm, Eu, Tb and Dy) Complexes Produced
4
4
by a Hexadentate Bisoxime Chelate Ligand

*
Xiao-Xin An, Zhuang-Zhuang Chen, Hao-Ran Mu, Li Zhao
School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou,
Gansu 730070, PR China
ABSTRACT:
Four unprecedented 3d-4f hetero-octanuclear family-type complexes
[{Cu(L)Ln(NO3)3}2][Cu(L)Ln(NO3)3]2 (Ln = Sm (1), Eu (2), Tb (3) and Dy (4))
were synthesized by an unsymmetric single salamo-like ligand H2L
(6-Methoxy-6′-ethoxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol) with
Cu(OAc)2·H2O and Ln(NO3)3·6H2O (Ln = Sm, Eu, Tb and Dy), respectively.
X-ray crystallography revealed that each hetero-octanuclear 3d-4f metal
complexes [{Cu(L)Ln(NO3)3}2][Cu(L)Ln(NO3)3]2 contains one neutral dimer
[{Cu(L)Ln(NO3)3}2] unit and two independent [Cu(L)Ln(NO3)3] units. At the
same time, the four Cu(II) atoms of the complexes 1–4 have four- and
five-coordinated configurations, while the four Ln(III) atoms have only one
configuration, all of which are ten-coordinated. The structures of the four
complexes 1–4 were characterized via elemental analyses, PXRD, FT-IR and
UV-Vis spectroscopy. In addition, while studying the crystal structure, the
supramolecular interactions and spectral properties of the complexes 1–4
* Corresponding authors.
E-mail addresses: zhaoli_72@163.com (L. Zhao).

were studied in detail.
Keywords: Unsymmetric salamo-like ligand; Hetero-octanuclear 3d-4f
complex; Synthesis; Crystal structure; Property
1. Introduction
Salen-like Schiff base ligands are formed by introducing the same
aldehydes at both ends of diamine [1–3]. Their complexes have been widely
studied in the fields of optics [4–9], magnetisms [10–14], biological fields
[15–20], catalyses [21–23] and chemical sensors [24–31]. Salen-like ligands
were introduced into two more electronegative oxygen atoms to form
salamo-like bisoxime ligands [32–37]. The abnormal stability of C=N bond not
only makes the hydrolysis reaction and exchange reaction difficult to occur,
but also the metal complexes formed have novel structures and properties.
One study shows that salamo-like complexes are at least 104 times more
stable than salen-like complexes, which is one of the important reasons why
salamo-like complexes have gradually become a hot topic in modern
coordination chemistry [38–47]. In the process of crystal culture, single
salamo-like small molecule ligands can be used to design and synthesize
one-dimensional chain polymer or MOF structure by adding auxiliary ligands;
and they can also be used as small molecule fluorescence chemical sensors
to identify metal ions; straight chain bissalamo-like ligands will twist in the
process of metal coordination, forming a C-type coordination cavity.

Herein, a family of four unprecedented hetero-octanuclear 3d-4f
complexes [ZnII -LnIII ] (Ln = Sm, Eu, Tb and Dy) were designed and
4
4
synthesized by an unsymmetric single salamo-like ligand (H2L) with
Cu(OAc)2·H2O and Ln(NO3)3·6H2O (Ln = Sm, Eu, Tb and Dy), respectively. In
previous reports, some complexes are monomolecular crystals, others are
dimers, and the rest are coordination polymers and MOFs. Interestingly, the
four complexes synthesized in this paper are same familial, and each
hetero-octanuclear metal complex finally shows one neutral dimer
[{Cu(L)Ln(NO3)3}2] unit and two independent [Cu(L)Ln(NO3)3] units. At the
same time, the four Cu(II) atoms of each complex have two coordination
configuratatoms of four-coordination and five-coordination, while the four
Ln(III) atoms have only one coordination configuration, all of which are
ten-coordination. Each complex has the same coordination pattern, so it can
be called a “family”.
2. Experimental
2.1. Materials and physical measurements
The reagents and raw materials used in this paper were purchased from
commercial suppliers and can be used directly without further purification.
The Bruker APEX-II CCD surface inspection diffractometer (Bruker,
Germany) were used to measure and record the X-ray single crystal
structure for the complexes 1–4. The melting point of the substance was

measured using SGW X-4A Shanghai Jingke Slight Melting Point Instrument
(Shanghai, China). The 1H NMR spectrum of the ligand was measured by an
AVANCE DRX-400 / 600 spectrometer (Brook, Germany) using CDCl3 as
solvent. The elemental analysis of the ligand H2L and its complexes 1–4 was
determined by the GmbH VariuoEL V3.00 automatic element analyzer
(Berlin, Germany) and the IRIS ER/S-WP-1 ICP atomic emission
spectrometer (Berlin, Germany). The D/max-2400 powder X-ray
diffractometer (Rigaku, Japan) were used to record the PXRD experimental
data of the complexes 1–4 in the range of 2θ = 5–50°. The infrared spectra in
the range of 4000–400 cm-1 were recorded on a Vertex 70 FT-IR
spectrophotometer (Bruck, Germany) using KBr as tablet. The electron
absorption spectra of the UV-Vis region of the ligand H2L and its complexes
1–4 were measured using a UV-3900 spectrometer (Tokyo, Japan). The
F-7000 FL 220-240V spectrophotometer (Tokyo, Japan) were used to
measure the liquid fluorescence spectra of the ligand and its complexes 1–4.
2.2. Synthesis of H2L
The
ligand
6-methoxy-6′-ethoxy-2,2′-[ethylenedioxybis(nitrilomethylidyne)]diphenol (H2L) was
synthesized according to the literature [48] (Scheme 1).
An ethanol solution (80 mL) of 3-methoxyrsalicylaldehyde (307.0 mg, 2.0 mmol)
was added dropwise to an ethanol solution (20 mL) of 1, 2-bis(aminooxy)ethane (370.8
mg, 4.0 mmol). The mixed solution was reacted at 45–55°C for 4 h, after distillation
under reduced pressure, the crude product was purified (dichloromethane: ethyl acetate
=
15
:
1)
to
acquire
white
crystalline
solid
of

2-[O-(1-ethoxyamide)]oxime-6-methoxyphenol [49]. Yield: 70.4 %. M.p: 93−94°C.
Anal. Calcd for C10H14N2O4 (%): C, 53.09; H, 6.24; N, 12.38. Found: C, 53.25; H, 6.13;
N, 12.41.
Equimolar 2-[O-(1-ethoxyamide)]oxime-6-methoxyphenol (454.2 mg, 2.0
mmol) and 3-ethoxysalicylaldehyde (333.5 mg, 2.0 mmol) dissolved in ethanol
solution (60 mL), reaction at a temperature of 55–60°C for 6 h to obtain a crude
product, and then recrystallization to obtain white crystals of ligand H2L. M.p:
100−101°C; Yield: 81.9 %. 1H NMR (400 MHz, CDCl3) δ 9.73 (s, 1H, –OH), 9.69 (s,
1H, –OH), 8.26 (s, 2H, –N=CH), 6.91 (dd, J = 7.2, 2.8Hz, 2H, –ArH), 6.88–6.80 (m, 4H,
–ArH), 4.47 (t, J = 4.2 Hz, 4H, –CH2), 4.11 (q, J = 8.4 Hz, 2H, –OCH2), 3.91 (s, 3H,
–OCH3), 1.48 (t, J = 5.6 Hz, 3H, –CH3). Anal. Calc. for C19H22N2O6 (%): C, 60.95; H,
5.92; N, 7.48. Found: C, 61.05; H, 5.90; N, 7.41.
CHO
CHO
O
N
O
O
N
O
N
OH
OH
NH2
OMe
OEt
NH2
O
O NH2
OH
HO
OH
OMe
EtO
OMe
H2L
Scheme 1. Synthetic route to the ligand H2L.
2.3. Synthesis of the complexes 1−4
  −   
      Cu(OAc)2·H2O 
Ln(NO3)3·6H2O        
  

O
N
O
N
Cu(OAc)2·H2O
Ln(NO3)3·6H2O
OH
HO
OMe
EtO
Ln=Sm (1), Eu (2), Tb (3) and Dy (4)
Scheme 2. Self-assembly process of the complexes 1−4.
2.3.1 Synthesis of [{Cu(L)Sm(NO3)3}2][Cu(L)Sm(NO3)3]2 (1)
To a stirred solution of H2L (7.80 mg, 0.20 mmol) in dichloromethane (3 mL)
was added Cu(OAc)2·H2O (4.29 mg, 0.20 mmol) and Sm(NO3)3·6H2O (9.00 mg,
0.20 mmol ) in ethanol (4 mL). Stir for tens of minutes, then filter and seal, and place
in a quiet and dark environment for several weeks to obtain dark green regular
transparent bulk crystals suitable for X-ray single crystal diffraction. For the complex
1: C76H80N20O60Sm4Cu4, yield: 8.7 mg, 41.3%. Elemental analysis (%): Anal. calc.:
C, 29.55; H, 2.61; N, 9.07; Cu, 8.23; Sm, 19.47; found: C, 29.71; H, 2.68; N, 8.91; Cu,
8.27; Sm, 19.63.
2.3.2 Synthesis of [{Cu(L)Eu(NO3)3}2][Cu(L)Eu(NO3)3]2 (2)
The synthesis process of the complex 2 is similar to the method and
process of the complex 1. To a stirred solution of H2L (7.79 mg, 0.20 mmol) in
dichloromethane (3 mL) was added Cu(OAc)2·H2O (4.35 mg, 0.20 mmol) and
Eu(NO3)3·6H2O (9.15 mg, 0.20 mmol ) in ethanol (4 mL). Stir for tens of
minutes, then filter and seal, and place in a quiet and dark environment for
several weeks to obtain dark green regular transparent bulk crystals suitable
for X-ray single crystal line diffraction. For the complex 2: C76H80N20O60Eu4Cu4,
yield: 9.0 mg, 42.3%. Elemental analysis (%): Anal. calc.: C, 29.49; H, 2.60; N,

9.05; Cu, 8.21; Eu, 19.64; found: C, 29.62; H, 2.64; N, 8.97; Cu, 8.26; Eu,
19.79.
2.3.3 Synthesis of [{Cu(L)Tb(NO3)3}2][Cu(L)Tb(NO3)3]2 (3)
The synthesis process of the complex 3 is similar to the method and
process of the complex 1. To a stirred solution of H2L (7.95 mg, 0.20 mmol) in
dichloromethane (3 mL) was added Cu(OAc)2·H2O (4.65 mg, 0.20 mmol) and
Tb(NO3)3·6H2O (9.04 mg, 0.20 mmol ) in ethanol (4 mL). Stir for tens of
minutes, then filter and seal, and place in a quiet and dark environment for
several weeks to obtain dark green regular transparent bulk crystals suitable
for X-ray single crystal line diffraction. For the complex 3: C76H80N20O60Tb4Cu4,
yield: 8.8 mg, 40.7%. Elemental analysis (%): Anal. calc.: C, 29.22; H, 2.58; N,
8.97; Cu, 8.14; Tb, 20.35; found: C, 29.47; H, 2.61; N, 8.85; Cu, 8.24; Tb,
20.52.
2.3.4 Synthesis of [{Cu(L)Dy(NO3)3}2][Cu(L)Dy(NO3)3]2 (4)
The synthesis process of the complex 4 is similar to the method and
process of the complex 1. To a stirred solution of H2L (7.68 mg, 0.20 mmol) in
dichloromethane (3 mL) was added Cu(OAc)2·H2O (4.52 mg, 0.20 mmol) and
Dy(NO3)3·6H2O (9.20 mg, 0.20 mmol) ) in ethanol (4 mL). Stir for tens of
minutes, then filter and seal, and place in a quiet and dark environment for
several weeks to obtain dark green regular transparent bulk crystals suitable

for X-ray single crystal line diffraction. For the complex 4: C76H80N20O60Dy4Cu4,
yield: 9.4 mg, 43.9%. Elemental analysis (%): Anal. calc.: C, 29.09; H, 2.57; N,
8.93; Cu, 8.10; Dy, 20.72; found: C, 29.33; H, 2.60; N, 8.88; Cu, 8.16; Dy,
20.55.
2.4. X-ray structure determination of the complexes −
X-ray single crystal diffraction data of the complexes 1−4 were recorded
using a Bruker APEX-II CCD (complex 1 at 173(2) K, complex 4 at 173(2) K)
and SuperNova (Mo) X-ray Source (complex 2 at 173(2) K, complex 3 at
287(2) K) diffractometer with a monochromatic Mo-Kα radiation (λ = 0.71073
Å), respectively. The single crystal structures were solved via the direct
methods (SHELXS) [50], and all the hydrogen atoms were included at the
calculated positatoms and constrained to ride on their parent atoms.
Reflections were merged by SHELXL according to the crystal class for the
calculation of statistics and refinement. All non-hydrogen atoms were refined
anisotropically via a full-matrix least-squares procedure on F2 with SHELXL
[51]. Data collection and refinements of these complexes were listed in Table
1. CCDC: CCDC–2000461, 2000455, 2000460 and 2000456 for the
complexes 1–4.
Table 1 X-ray crystallographic data for the complexes 1–4.
Complex
1
2
3
4

Empirical formula
C76H80
C76H80Eu4Cu4N20O6 C76H80Tb4Cu4N20O6
C76H80Dy4Cu4N20O6
Sm4Cu4N20O60
0
0
0
Formula weight
T (K)
3089.16
3095.60
3123.44
3137.76
173(2)
173(2)
287(2)
173(2)
Wavelength (Å)
Crystal system
Space group
a (Å)
0.71073
Triclinic
0.71073
Triclinic
0.71073
Triclinic
0.71073
Triclinic
P-1
P-1
P-1
P-1
12.6496(6)
14.2040(7)
16.6253(8)
105.9790(10)
111.0870(10)
101.6650(10)
2523.8(2)
1
12.5969(8)
14.1929(8)
16.6337(9)
106.054(5)
110.979(6)
101.506(5)
2516.5(3)
1
12.5767(7)
14.2475(10)
16.7873(10)
106.778(6)
111.465(5)
100.274(5)
2540.5(3)
1
12.4869(12)
14.1017(13)
16.7276(16)
106.839(2)
111.389(2)
100.209(2)
2489.3(4)
1
b (Å)
c (Å)
α (°)
β (°)
γ (°)
V (Å3)
Z
Dcalc (g∙cm–3)
μ(mm–1)
F (000)
2.033
2.043
2.042
2.093
3.233
3.401
3.684
3.920
1520.0
1524.0
1532.0
1536.0
Crystal size (mm)
0.220
0.160
×
0.190
×
0.18 × 0.14 × 0.12
0.21 × 0.17 × 0.14
0.220
0.160
× 0.190 ×
2θ Range (°)
4.626 to 50.018
6.708 to 52.044
6.754 to 52.044
4.698 to 50.02
Index ranges
–15 h  15
–15  h  15
–15  h 15
–14 h  14

–16 k  14
–17 l  19
17872
–17  k  17
–20  l  17
17366
–17  k  17
–20  l  20
17475
–16 k  16
–19 l  19
16419
Reflectatoms collected
independent reflectato
ms
8838[Rint = 0.0251]
9893[Rint = 0.0478]
9997[Rint = 0.0345]
8689[Rint = 0.0412]
Completeness to θ
99.4% (θ = 25.009)
99.7% (θ = 25.242)
99.7% (θ = 25.242)
99.2% (θ = 25.010)
Data/restraints/paramet 8838 / 0 / 743
ers
9898/40/743
9997/108/752
8689/2329/731
GOF
1.057
1.056
1.052
1.063
Final R1, wR2 indices
0.0395, 0.0930
0.0554, 0.1129
0.0835, 0.1315
0.0431, 0.0964
0.0615, 0.1080
0.0661, 0.1572
0.0819, 0.1661
R1, wR2 indices (all 0.0469, 0.0970
data)
3
3
3
3
-
-
-
-
Largest diff. peak and
hole
2.41 and -1.13e.Å
1.97 and -1.46 e.Å
1.48 and -0.75 e.Å
2.20and -2.15 e.Å
3. Results and Discussion
3.1. PXRD analyses
The PXRD experiments were performed on the complexes 1–4 by
D/max-2400 powder X-ray diffractometer using Cu-Kα radiation in the range
of 2θ = 5–50°. The PXRD data at room temperature on the samples of the
complexes 1–4 well matched the calculated results from single crystal data

were shown in Fig. 1, which confirmed the phase purity and isomorphism of
the complexes 1–4 [52–54].
(a)
SimulatedpatternoftheComplex1
ExperimentedpatternoftheComplex1
5
10 15 20 25 30 35 40 45 50
Diffractionangle(2θ)
(b)
SimulatedpatternoftheComplex2
ExperimentedpatternoftheComplex2
5
10 15 20 25 30 35 40 45 50
Diffractionangle(2θ)

(c)
SimulatedpatternoftheComplex3
ExperimentedpatternoftheComplex3
5
10 15 20 25 30 35 40 45 50
Diffractionangle(2θ)
(d)
SimulatedpatternoftheComplex4
ExperimentedpatternoftheComplex4
5
10 15 20 25 30 35 40 45 50
Diffractionangle(2θ)
Fig. 1. Comparison of the simulated and experimental powder X-ray diffraction (PXRD)
patterns of the complexes 1–4: Complex 1 (a); Complex 2 (b); Complex 3 (c); Complex 4
(d).
3.2 IR spectra analyses
The binding modes were determined by comparing several intense bands
of the ligand H2L and its complexes 1–4 in the infrared spectra (Fig. 2). The
band of the free ligand H2L was observed at 1603 cm−1 correspond to the
stretching vibrations of the C=N bond while the complexes 1–4 were observed
at 1608–1610 cm−1. The spectral changes of the complexes 1–4 indicate that
H2L is coordinated to the metal atoms [55,56]. In addition, the band at 1256

cm−1 in the free ligand H2L can be assigned to a typical Ar–O stretching band.
In the complexes 1–4, the bands shifted to lower frequencies by ca. 29–36
cm−1, indicating that M–O bonds are formed between the metal(II/III) atoms
and oxygen atoms of phenolic groups [57]. The O–H stretching band of the
free ligand H2L was observed at ca. 3419 cm−1 that belongs to the phenolic
hydroxyl group, while the complex 1–4 does not show the O–H stretch band at
3400 cm−1, which is consistent with the results obtained by X-ray single
crystal diffraction [20]. The absorption bands assigned to the coordinated
nitrate groups were observed at about 1461–1494 cm−1 (v1) and 1284–1318
cm−1 (v4) for the complexes 1–4, respectively. The differences between the
strongest absorption band v1 and v4 of nitrate groups lie in ca. 176–183 cm−1,
which very clearly indicate that the coordinated nitrate groups in the
complexes 1–4 are bidentate or monodentate ligands. Anti-symmetric
stretching vibration v3 of the free nitrate group wasn’t observed at 1350–1400
cm−1 in the spectra of the complexes 1–4, which is consistent with the results
of X-ray crystallography, indicating that all nitrates are within a reasonable
coordination sphere [58–60].

HL
2
Complex1
Complex2
Complex3
Complex4
4000 3500 3000 2500 2000 1500 1000 500
-1
Wavelength(cm )
Fig. 2. The IR Spectra of H2L and its complexes 1–4.
3.3. UV-Vis titration experiments
The UV-Vis titration spectra of H2L with Cu(II) ions and [L-Cu2+] with Ln(III)
ions in ethanol solutions are shown in Fig. 3. Take the titration experiment of
the complex 1 as an example, in the UV-Vis titration experiment of H2L with
Cu(II) ions: gradually adding copper acetate solution (1.0 × 10–3 M) to H2L
solution (1.0 × 10–5 M) in small amounts, when the added amount of Cu(II)
ions reached 1.0 equivalent, the absorbance of the solution became stable.
Continue to add Cu(II) ions, the absorbance of the solution remains
unchanged, which indicates that the stoichiometric ratio between Cu(II) : H2L
is 1 : 1. The absorption spectrum of H2L mainly shows two relatively strong
absorption peaks, which appear at about 270 and 319 nm. The former
absorption peak at 270 nm is part of the π–π* transition of the benzene ring

conjugated system, while the latter absorption peak at 319 nm is part of the
π–π* transition of the chromophore C=N group [61–63]. Compared with the
free ligand H2L, the gradual addition of Cu(II) ions changes the absorption
peak. After adding Cu(II) ions, the absorption peak at 270 nm gradually red
shifted to 286 nm, the absorption peak at 319 nm gradually disappeared, and
a new absorption peak appeared at about 373 nm, indicating that Cu(II) ions
coordinate with (L)2– units, and the charge transfer from the ligand to the metal
occurs [34,48].
(a)
(b)

(c)
(d)
(e)
Fig. 3. The UV-Vis titration spectra of H2L (1.0 × 10–5 M) changes after the addition of
Cu(OAc)2·H2O (1.0 × 10–3 M) (a); The UV-Vis titration spectra of [L-Cu2+] changes after
the addition of Sm(NO3)3·6H2O (b), Eu(NO3)3·6H2O (c) Tb(NO3)3·6H2O (d) and

Dy(NO3)3·6H2O (e) (1.0 × 10–3 M).
After adding Sm(III) ions to the [L-Cu2+] complex solution, the absorption
peak at 319 nm decreased slightly, while the original absorption peak at 373
nm shifted to 352 nm. This indicates that the Sm(III) ions has coordinated with
the [L-Cu2+] complex to form a new heteronuclear metal complex [22].
Moreover, the titration results indicate that the coordination ratio of Sm(III) :
[L-Cu2+] is also 1 : 1. The UV-Vis absorption spectra of the complexes 2–4 are
similar, so the same results are obtained. This result is also consistent with
the crystal structure obtained by single crystal diffraction.
3.4. Crystal structure and supra-molecular interaction
Main bond lengths and angles of the complexes 1–4 are presented in
Table S2. The hydrogen bonding interactions (Å,°) of the complexes 1–4 are
summarized in Table S3.
3.4.1 Crystal structure of the complex 1
The complex 1 crystallizes in the triclinic crystal system, space group P-1.
For the complex 1, its structure consists of four fully deprotonated ligand (L)2-
units, four Cu(III) atoms, four Sm(III) atoms, and twelve nitrate groups, they
together displayed the formation of 4 : 4 : 4 (H2L : Cu(II) : Ln(III)) novel
hetero-octanuclear metal complexes, which is completely different from the

structures of 1 : 3, 2 : 3 (L : M) reported earlier in the salamo-like 3d-4f
complexes [64,65]. The final structure is composed of one neutral dimer
[{Cu(L)Sm(NO3)3}2] unit and two independent and equivalent [Cu(L)Sm(NO3)3]
units (Fig. 4(a)). The four Cu(II) atoms in the complex 1 have two coordination
configurations of four-coordinate and five-coordinate, while the four Sm(III)
atoms have only one configuration and all have ten-coordinate. In the
independent [Cu(L)Sm(NO3)3] unit, the Cu(II) atom (Cu1) is located at the
cis-N2O2 coordination site of the ligand (L)2- unit, only two oxime nitrogen
atoms (N1 and N2) and two phenolic oxygen atoms (O2 and O5) participate in
coordination to form a four-coordinate quadrilateral geometric configuration; In
the neutral dimer [{Cu(L)Sm(NO3)3}2] unit, the Cu(II) atom (Cu2) is
five-coordinated, except for the two nitrogen atoms (N7 and N8) and two
oxygen atoms (O26 and O29) from the ligand (L)2- unit, and as the equatorial
plane, its axial position is occupied by one oxygen atom (O21) of the bridged
nitrate group, which acts as a vertex, and finally forms a twisted square
pyramid configuration (τ = 0.08167) [66]. The complex 1 is a symmetrical
structure, and the two Sm(III) atoms (Sm1 and Sm2) of each symmetrical unit
are all ten-coordinated, which is composed of four oxygen atoms in the ligand
(L)2- unit and six oxygen atoms from three bidentate chelate nitrate groups,
each Sm(III) atom is located in an O10 coordination environment, forming a
slightly distorted double-column square anti-prism coordination geometry. The
coordination polyhedron diagram of Cu(II) and Sm(III) atoms of the complex 1

is illustrated in Fig. 4(b).
(a)
(b)
Fig. 4. (a) Molecule structure of the complex 1 (hydrogen atoms are omitted for clarity); (b)
Coordination polyhedrons for Cu(II) and Sm(III) atoms of the complex 1.
In the crystal structure of the complex 1, there are five pairs of
intramolecular hydrogen bonds (Fig. 5(a)) ， followed by C2–H2A···O11 ，
C20–H20A···O19，C21–H21A···O18，C29–H29A···O23 and C29–H29B···O2. At

the same time, through 13 pairs of intermolecular hydrogen bonds
(C1–H1B···O18, C5–H5···O17, C6–H6···O16, C10–H10A···O10
，
C10–H10B···O9 ， C12–H12···O2 ， C14–H14···O2 ， C15–H15···O22 ，
C19–H19B···O12 ， C20–H20B···O14 ， C31–H31···O11 ， C34–H34···O8 and
C35–H35···O9) form a 2-D network structure [43], as depicted in Fig. 5(b). The
3-D supramolecular structure [67] of the complex 1 is observed in Fig. 5(c).
(a)
(b)

(c)
Fig. 5. (a) View of the intramolecular hydrogen bonding interactions of the complex 1; (b)
View of 2-D network structure of the complex 1; (c) View of 3-D supramolecular structure
of the complex 1.
3.4.2 Crystal structure of the complexes 2–4
The crystal structures of the complexes 2–4 are basically similar to that of
the complex 1. The X-ray structures of the complexes 2–4 are shown in the
triclinic crystal system, crystallized in the space group P-1. The crystal
structures of the complexes 2–4 are not discussed in detail.
(a)

(b)
Fig. 6. (a) Molecule structure of the complex 2 (hydrogen atoms are omitted for clarity); (b)
Coordination polyhedrons for Cu(II) and Eu(III) atoms of the complex 2.
(a)
(b)

(c)
Fig. 7. (a) View of the intramolecular hydrogen bonding interactions of the complex 2; (b)
View of 2-D network structure of the complex 2; (c) View of 3-D supramolecular structure
of the complex 2.
The crystal structure of the complex 2 is depicted in Fig. 6(a), and the
coordination polyhedron diagram of Cu(II) and Eu(III) atoms of the complex 2
is shown in Fig. 6(b). In the complex 2, as shown in Fig. 7(a), there are five
pairs of intramolecular hydrogen bonds [43,44] (C1–H1A···O12,
C2–H2A···O13, C10–H10A···O8, C10–H10B···O11 and C21–H21A···O28). In
addition, the two-dimensional network structure (Fig. 7(b)) of the complex 2 is
formed by the interaction of 11 pairs of intermolecular hydrogen bonds,
namely C1–H1B···O23, C4–H4···O19, C6–H6···O22, C12–H12···O28 ，
C15–H15···O26 ， C16–H16···O27 ， C24–H24···O15 ， C29–H29A···O29 ，
C29–H29B···O27，C33–H33···O11 and C35–H35···O7 [68], and finally forming

a 3-D supramolecular structure [69–72] (Fig. 7(c)).
The crystal structure of the complex 3 is presented in Fig. 8(a), and the
coordination polyhedron diagram of Cu(II) and Tb(III) atoms of the complex 3
is shown in Fig. 8(b). Moreover, as shown in Fig. 9(a) and (b), there are four
pairs of intramolecular hydrogen bonds (C18–H18B···O10，C29–H29B···O28，
C37–H37B···O25 and C38–H38C···O31) and six pairs of intermolecular
hydrogen
bonds
(C4–H4···O27,
C5–H5···O31B,
C27–H27···O10,
C32–H32···O7, C34–H34···O3 and C38–H38B···O8) [64] in the molecule of the
complex 3. In addition, the complex 3 visually shows a 3-D perspective [48]
view (Fig. 9(c)).
(a)
(b)

Fig. 8. (a) Molecule structure of the complex 3 (hydrogen atoms are omitted for clarity); (b)
Coordination polyhedrons for Cu(II) and Tb(III) atoms of the complex 3.
(a)
(b)
(c)
Fig. 9. (a) View of the intramolecular hydrogen bonding interaction of the complex 3; (b)

View of 2-D network structure of the complex 3; (c) View of 3-D supramolecular structure
of the complex 3.
The crystal structure of the complex 4 is built in Fig. 10(a), and the
coordination polyhedron diagram of Cu(II) and Eu(III) atoms of the complex 4
is illustrated in Fig. 10(b). In the complex 4, there are three important pairs of
intramolecular hydrogen bonds (C9–H9B···O11, C36–H36B···O26 and
C37–H37C···O15) are formed (Fig. 11(a)). At the same time, the molecules of
the complex 4 form a 2-D network structure [18–20] through 12 pairs of
intermolecular hydrogen bonds (C3–H3···O19, C3–H3···O23, C5–H5···O24,
C11–H11···O26 ， C13–H13···O25 ， C14–H14···O30 ， C22–H22···O10 ，
C23–H23···O13 ， C26–H26···O13 ， C28–H28A···O28 ， C31–H31···O9 and
C37–H37B···O23) (Fig. 11(b)). Furthermore, as shown in Fig. 11(c), the
complex 4 visually shows a 3-D perspective view [48].
(a)

(b)
Fig. 10. (a) Molecule structure of the complex 4 (hydrogen atoms are omitted for clarity);
(b) Coordination polyhedrons for Cu(II) and Eu(III) atoms of the complex 4.
(a)
(b)