Synthesis, crystal structures, fluorescence, electrochemiluminescent properties, and Hirshfeld surface analysis of four Cu/Mn Schiff-basecomplexes

Article abstract of DOI:10.1002/aoc.5712

Four new complexes [Cu(L¹)₂]_n (1), [Mn(L¹)₂]_n (2), [Cu(L²)₂]_n (3), [Mn(L²)₂]_n (4, HL¹ = 2-(((4H-1,2,4-triazol-4-yl)imino)methyl)-4,6-dichlorophenol; HL² = 2-(((4H-1,2,4-triazol-4-yl)imino)methyl)-4,6-dibromophenol) were synthesized by microreaction bottle method. Complexes 1 and 3 and 2 and 4 are isomorphous heterostructures having the same molecular structure. The structures of 1–4 were characterized using single X-ray diffraction, Fourier-transform infrared spectroscopy, powder X-ray diffraction, and thermogravimetric analysis, and their potential applications were analyzed by detecting their fluorescence and electrochemical luminescence (ECL). Hirshfeld surface analysis indicates that X···H (X = Br, Cl) interactions play a crucial role in stabilizing the self-assembly process of 1–4, which show highly intense ECL in N,N-dimethylformamide solution and high thermal stability.

Full text of DOI:10.1002/aoc.5712

Received: 6 February 2020
DOI: 10.1002/aoc.5712
Revised: 19 March 2020
Accepted: 21 March 2020
F U L L P A P E R
Synthesis, crystal structures, fluorescence,
electrochemiluminescent properties, and Hirshfeld surface
analysis of four Cu/Mn Schiff-basecomplexes
Yumei Zeng1 | Haiyang Zhang1 | Yujie Zhang1 | Fanghua Ji1
Jinlu Liang2 | Shuhua Zhang1,3
|
1College of Chemistry and Bioengineering, Guangxi Key Laboratory of Electrochemical and Magnetochemical Functional Materials, Guilin University
of Technology, Guilin, 541004, People's Republic of China
2College of Petroleum and Chemical Engineering, Beibu Gulf University, Qinzhou, 535011, People's Republic of China
3College of Chemistry, Guangdong University of Petrochemical Technology, Maoming, Guangdong, 525000, People's Republic of China
Correspondence
Shuhua Zhang, College of Chemistry,
Abstract
Guangdong University of Petrochemical
Technology, Maoming, Guangdong
525000, People's Republic of China.
Email: zsh720108@163.com
Four new complexes [Cu(L1)2]n (1), [Mn(L1)2]n (2), [Cu(L2)2]n (3), [Mn(L2)2]n
(4,
HL1
=
2-(((4H-1,2,4-triazol-4-yl)imino)methyl)-4,6-dichlorophenol;
HL2 = 2-(((4H-1,2,4-triazol-4-yl)imino)methyl)-4,6-dibromophenol) were syn-
thesized by microreaction bottle method. Complexes 1 and 3 and 2 and 4 are
isomorphous heterostructures having the same molecular structure. The struc-
tures of 1–4 were characterized using single X-ray diffraction, Fourier-
transform infrared spectroscopy, powder X-ray diffraction, and ther-
mogravimetric analysis, and their potential applications were analyzed by
detecting their fluorescence and electrochemical luminescence (ECL).
Hirshfeld surface analysis indicates that X···H (X = Br, Cl) interactions play a
crucial role in stabilizing the self-assembly process of 1–4, which show highly
intense ECL in N,N-dimethylformamide solution and high thermal stability.
Fanghua Ji and Shuhua Zhang, College of
Chemistry and Bioengineering, Guangxi
Key Laboratory of Electrochemical and
Magnetochemical Functional Materials,
Guilin University of Technology, Guilin,
541004, People's Republic of China.
Email: fanghuaji@glut.edu.cn;
zsh720108@163.com
Jinlu Liang, College of Petroleum and
Chemical Engineering, Beibu Gulf
University, Qinzhou, 535011, People's
Republic of China.
K E Y W O R D S
Email: ljinlu@163.com
electrochemical luminescence, fluorescence, polymer, Schiff-base
Funding information
Collaborative Innovation Center for
Exploration of Hidden Nonferrous Metal
Deposits and Development of New
Materials in Guangxi, Grant/Award
Number: GXYSXTZX2017-II-3; the Nature
Science Foundation of China, Grant/
Award Number: 21861014
1 | INTRODUCTION
as they have wide applications in optics,[4–6]
electromagnetism,[7–9] adsorption,[10] and catalysis.[11–15]
The design and synthesis of novel coordination poly-
mer (CP) materials with Schiff base as an organic
ligand have been the hot topic of current research,[1–3]
Currently, the main coordination modes of Schiff bases
are the coordination of metal ions with O and N.[16–20]
Therefore, the choice of an organic ligand determines
Appl Organomet Chem. 2020;e5712.
wileyonlinelibrary.com/journal/aoc
© 2020 John Wiley & Sons, Ltd.
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https://doi.org/10.1002/aoc.5712

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ZENG ET AL.
the nature of the CPs. 1,2,4-Triazole ligand and its
derivatives can bridge transition metal ions through the
N–M coordination mode to obtain high-nuclear com-
pounds and their CPs having unique properties.
3-Amino-1,2,4-triazole was selected as an organic
bridging ligand by Hyunsoo Park, to form four new
CPs with Zn.[19] Yun Gong and his colleagues
used 4-amine-4H-1,2,4-triazole and its derivative
3,5-dimethyl-4-amino-4H-1,2,4-triazole as the main
ligands and combined them with Cu and Ag to form
1D–3D metal organic framework materials. Cu
compounds exhibited better electrocatalytic activity in
generating H2 from water.[17] In this study, 4-amine-
4H-1,2,4-triazole was combined with 3,5-dichloro-
are not the electron transfer resulting from the
original d–d transition but the electron transfer
between the ligand and the metal (LMCT).[30,31] The
fluorescence measurement of the four complexes
revealed that the four complexes had different degrees
of red-shift than the maximum fluorescence intensity
of the ligands: complexes 1 and 2 having red-shifts
about 44–57 nm and complexes 3 and 4 having red-
shifts about 7–10 nm. In addition to the effect of the
C=N bond on the fluorescent properties of the com-
plexes in Schiff bases, it is reasonable to assume that
halogen atoms in salicylaldehyde may cause fluores-
cence quenching.
2-hydroxybenzaldehyde
or
3,5-dibromo-2-hydroxy-
benzaldehyde to form a C=N bond by an aldehyde–
amino-group condensation reaction. The ligands
were coordinated with metal ions (CuII, MnII) under
certain conditions to obtain CPs. That is, four
CPs with CuII and MnII as metal centers were synthe-
sized. Their structures were characterized using
single crystal X-ray diffraction, elemental analysis,
infrared (IR) spectroscopy, and thermogravimetric
analysis.
Electrochemical luminescence (ECL) materials are
now being used in areas of professional field due to
their low background noise and highly sensitive elec-
trochemical response signals.[21] The ECL process uses
a certain pulse of electrical signals to stimulate the
excitation energy of the material and then generates
energy radiation with a certain electrical signal.[22] The
most common solution is to prepare composite mate-
rials, and generally Ru(II) and Ir(II) are suitable metals
for the preparation of CPs.[21–24] All of the previous
methods are expensive and involve complicated experi-
mental procedures. But our synthetic Schiff-base raw
materials and metal salts are both low cost and
efficient.
2 | EXPERIMENTAL
2.1 | Materials and instrumentation
All chemicals were commercially available and used as
received without further purification. The crystal struc-
tures were determined using SuperNova (single source at
offset, Eos, Agilent Technologies, Palo Alto, America) dif-
fractometer and SHELXL crystallographic software of
molecular structures. FT-IR spectra were recorded from
KBr pellets in the range of 4000 to 400 cm-1 on aNicolet
Nexus 470 FT-IR infrared spectrometer (Nicolet, Ameri-
can). The PXRDs of 1-4 were determined by a X0Pert3
Powder
X-ray
powder
diffractometer
(Panaco,Netherlands). TGA measurements were carried
out with heating the crystalline sample from 25 to 900 ꢀC
at a rate of 10 ꢀC·min-1 in N2 atmosphere on a SDT Q600
Thermogravimetric Analyzer (TA, American). ECL prop-
erties and cyclic voltammetry (CV)of compounds 1–4 in
N,N-dimethyformamide(DMF) solution were studied
using MPI-E Electrochemiluminescence Analysis System
(Xi'an Ruimai Analytical Instrument Co., Ltd. Xi'an,
China).
Hirshfeld surface analysis can explain the funda-
mental issue in a material design process from a cer-
tain angle and is widely used as a unique method for
analyzing intermolecular interactions,25–27 using the 2D
fingerprint map. It has also concentrated on the
Hirshfeld surface analysis in the following research.
Fluorescent CP materials can be used to detect the
specific recognition of specific ions, organisms, or
cancer cells because of their strong and stable fluores-
cent properties, large specific surface area, and struc-
tural controllability.[28] Moreover, the excellent
fluorescent luminescence properties of CPs are not so
dependent on external conditions and usually exhibit
good fluorescence intensity at room temperature.[28,29]
Another major factor is that the four new complexes
2.2 | Syntheses
2.2.1 | Synthesis of HL1
A
mixture of 3,5-dichloro-2-hydroxybenzaldehyde
(1.91 g, 10 mmol), 4H-4-amino-1,2,4-triazole (taya,
0.84 g, 10 mmol), and ethanol (20 ml) in a 100 ml
three-necked flask was refluxed at 80ꢀC for 120 min.
The color of the solution changed to brown and was
enriched at 80ꢀC for 2 h. A brown power was obtained
by filtration, washed with hot ethanol (10 ml × 3), and
dried in an oven at 50ꢀC for 24 h (yield: 2.468 g,
ca. 96%, based on taya). Analysis calculated (%) for

ZENG ET AL.
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HL1, C9H6Cl2N4O (Mr = 257.08): C, 42.05; H, 2.35; N,
21.79. Found: C, 41.98; H, 2.42; N, 21.85. The IR data
of HL1 (KBr, cm−1, see Figure S1 in the supporting
information): 3438 m, 3130 m, 1660 w, 1597 s, 1515 s,
1465 s, 1377 m, 1327 s, 1245 s, 1176 m, 1056 s, 868 m,
723 m, 641 w.
of 2 were obtained (yield: 0.066 g, ca 58.1%, based on
HL1). Analysis calculated (%) for 2, C18H10Cl4MnN8O2
(Mr = 567.07): C, 38.13; H, 1.78; N, 19.76. Found: C,
38.10; H, 1.82; N, 19.79. The IR data of 2 (KBr, cm−1, see
Figure S1 in the supporting information): 3143 m, 1603
m, 1515 w, 1465 s, 1346 w, 1214 m, 1163 m, 1057 s,
855 w, 761 m, 629 w.
2.2.2 | Synthesis of HL2
2.2.5 | Synthesis of [Cu(L2)2]n (3)
The method of synthesizing HL2 is similar to that of
synthesizing
2-hydroxybenzaldehyde
HL1,
except
was
that
replaced
brown powder was
3,5-dichloro-
Compound 3 was prepared in a similar way as 1, except
that HL1 was replaced with HL2. Blue bulk crystals of
3 were obtained (yield: 0.080 g, ca 51.2%, based on HL2).
Analysis calculated (%) for 3, C18H10Br4CuN8O2
(Mr = 753.49): C, 28.69; H, 1.34; N, 14.82. Found: C,
28.66; H, 1.37; N, 14.85. The IR data of complex 3 (KBr,
cm−1, see Figure S1 in the supporting information): 3117
m, 1591 s, 1509 m, 1433 s, 1314 w, 1207 m, 1157 m, 1062
s, 962 w, 843 m, 761 s, 623 m.
by
3,5-dibromosalicylaldehyde.
A
obtained by filtration, washed with ethanol (10 ml × 3),
and dried in an oven at 50ꢀC for 24 h (yield: 3.356 g,
ca 97%, based on taya). Analysis calculated (%) for HL2:
C9H6Br2N4O (Mr = 345.98): C, 31.24; H, 1.75; N, 16.19.
Found: C, 31.18; H, 1.82; N, 16.25. The IR data of HL2
(KBr, cm−1, see Figure S1 in the supporting informa-
tion): 3450 s, 3124 m, 3067 m, 1634 w, 1515 s, 1452 m,
1364 s, 1307 s, 1232 s, 1176 s, 1062 s, 962 m, 868 s,
730 m, 623 w.
2.2.6 | Synthesis of [Mn(L2)2]n (4)
Compound 4 was prepared in a similar way as 2, except
that HL1 was replaced with HL2. Red square crystals of
4 were obtained (yield: 0.039 g, ca 52.4%, based on HL2).
Analysis calculated (%) for 4, C18H10Br4MnN8O2
(Mr = 744.88): C, 29.03; H, 1.35; N, 15.04. Found: C,
29.01; H, 1.38; N, 15.09. The IR data of complex 4 (KBr,
cm−1, see Figure S1 in the supporting information): 3130
m, 1591 s, 1509 m, 1459 s, 1370 w, 1226 m, 1151 m, 1056
s, 987 w, 855 w, 755 w, 704 m, 610 w.
2.2.3 | Synthesis of [Cu(L1)2]n (1)
HL1 (0.051 g, 0.2 mmol) was added to a clean 25 ml small
glass bottle. DMF (5 ml) was poured into the glass bottle.
At the same time, Cu(AcO)2·H2O (0.040 g, 0.2 mmol) was
dissolved in 5 ml of deionized water. The two solutions
were then mixed and stirred in the glass bottle for
20 min. Then, the magneton was sucked out by a magnet,
the glass bottle was sealed and placed in an oven at 90ꢀC,
and blue block crystals were obtained after 3 days. The
reaction product was washed with heated DMF (10 ml × 3)
and double-distilled water (10 ml × 3). Blue block crystals
of 1 were obtained (yield: 0.065 g, ca 56.3%, based on
HL1). Analysis calculated (%) for 1, C18H10Cl4CuN8O2
(Mr = 575.68): C, 37.56; H, 1.75; N, 19.46. Found: C,
37.48; H, 1.81; N, 19.53. The IR data of 1 (KBr, cm−1, see
Figure S1 in the supporting information): 3111 m, 1597 s,
1509 m, 1440 s, 1314 w, 1214 m, 1157 m, 1069 s, 849 w,
768 m, 657 w.
2.3 | Crystal structure determination
The diffraction data were collected on a SuperNova with
graphite
monochromated
Mo-Kα
radiation
(λ = 0.71073 Å) at 16 1ꢀC by using the ω scan mode in
the ranges 2.94ꢀ ≤ θ ≤ 25.24ꢀ (1), 2.88ꢀ ≤ θ ≤ 25.01ꢀ (2),
3.07ꢀ ≤ θ ≤ 25.24ꢀ (3), and 2.86ꢀ ≤ θ ≤ 25.24ꢀ (4). The
raw frame data were integrated with the SAINT program.
The structures of 1–4 were determined by direct methods
using SHELXT and refined by full-matrixleast-squares on
F2 using SHELXL-2015 within the OLEX-2 GUI.[32] An
empirical absorption correction using spherical har-
monics was implemented in SCALE3 ABSPACK scaling
algorithm. All non-hydrogen atoms were refined aniso-
tropically. All hydrogen atoms were positioned geometri-
cally and refined using a riding model. Calculations and
graphics were performed using SHELXTL.[33,34] Com-
puter programs used were CrysAlis PRO, Agilent
2.2.4 | Synthesis of [Mn(L1)2]n (2)
The ratio of the metal salt to the ligand was the same as
1, but Mn(AcO)2·4H2O was dissolved in dimethyl sulfox-
ide (DMSO) and stirred for 20 min. Then, 5 ml of double-
distilled water was added, and the reaction flask was
sealed and placed in an oven at 80ꢀC. Red block crystals

4 of 13
ZENG ET AL.
TABLE 1
Crystallographic data for complexes 1–4
Complexes
Formula
Mr
1
2
3
4
C18H10Cl4CuN8O2
575.68
C18H10Cl4MnN8O2
567.07
C18H10Br4CuN8O2
753.49
C18H10Br4MnN8O2
744.88
Crystal size (mm)
Crystal system
Space group
a (Å)
0.20 × 0.19 × 0.13
Monoclinic
P21/c
0.21 × 0.17 × 0.12
Tetragonal
P41212
0.14 × 0.13 × 0.11
Monoclinic
P21/c
0.21 × 0.18 × 0.14
Tetragonal
P41212
12.1734(5)
8.5038(5)
10.4456(5)
90.00
7.6879(2)
7.6879(2)
35.9055(13)
90.00
12.6988(9)
8.7060(5)
10.4404(6)
90.00
7.7367(2)
7.7367(2)
36.6885(16)
90.00
b (Å)
c (Å)
α (ꢀ)
β (ꢀ)
101.328(4)
90.00
90.00
101.410(7)
90.00
90.00
γ (ꢀ)
90.00
90.00
V (Å3)
1060.27(9)
574
2122.13(14)
1132
1131.43(13)
718
2196.07(17)
1420
F(000)
Z
2
4
2
4
Dc (g cm−3
μ (mm−1
θ range (ꢀ)
)
1.803
1.775
2.212
2.253
)
1.57
1.162
8.063
7.915
2.94–25.24
4274/2164
1435
2.88–25.24
21173/1984
1984
3.07–25.24
4519/2332
1733
2.86–25.24
4853/2161
1908
Ref. meas./indep.
Obs. ref. [I > 2σ(I)]
Rint
0.0425
0.0314
0.0324
0.0285
R1 [I ≥ 2σ(I)]a
ωR2 (all data)b
Goof
0.0595
0.0513
0.0510
0.0369
0.1653
0.1303
0.1269
0.0639
0.978
0.0994
1.021
1.062
Δρ (max, min) (eÅ−3
)
0.981, −0.894
0.300, −0.351
1.604, −1.108
0.486, −0.404
aR1 = Σ||Fo|–|Fc||/Σ|Fo|.
bwR2 = [Σw(|Fo2|–|Fc |)2/Σw(|Fo2|)2]1/2
.
2
Technologies, Version 1.171.37.35, SHELXL-15,[33,34] and
Olex2.[32] The crystallographic details for 1–4 are pro-
vided in Table 1. Selected bond lengths and angles for 1–
4 are listed in Table 2.
Complex 1 crystallized in the monoclinic space
group P21/c. As shown in Figure 1, Cu2+ as a central
metal ion coordinated with two oxygen atoms (O1,
O1i) and four nitrogen atoms (N4, N4i, N2ii, N2iii) pro-
vided by four L1 ligands to form a hexacoordinated
octahedral CuN4O2 coordination configuration. The
bond distances of Cu1–O1, Cu1–N4, and Cu1–N2ii
(symmetry code: (ii) x, −y − 0.5, z + 0.5) were
1.947(3), 2.344(4), and 2.049(4) Å, respectively. Note
that the bond length difference around Cu1 may have
been caused by the Jahn–Teller effect[35–37] and that
the L ligand displayed the μ2-L-κ3O1,N1,N2 coordina-
tion mode (Figure 1), which is different from the coor-
dination mode of [Cu(TMP)2(H2O)2] (HTMP is (E)-
3 | RESULT AND DISCUSSION
3.1 | Description of the crystal
structures
3.1.1 | Crystal structures description of
1 and 3
Single crystal X-ray diffraction analysis revealed that
1 and 3 were isomorphic complexes (Figure 1), and
the crystal system (monoclinic) and space group (P21/
c) of 1 and 3 were identical. Therefore, only complex
1 was analyzed.
2-(((4H-1,2,4-triazol-4-yl)
6-methoxyphenol,
μ1-TMP-κ2O1,N1
imino)methyl)-
coordination
mode).[37] Further, the one coordination atom (N1) of
the L ligand was not involved in coordination. In the
ac plane, O1, O1i, N4, N4i, and Cu1 atoms were on

ZENG ET AL.
5 of 13
TABLE 2
Selected bond length (Å) and bond angle (ꢀ) of 1–4
Complexes
M1–O1i
1
2
3
4
1.947(3)
1.947(3)
2.344(4)
2.344(4)
2.049(4)
2.049(4)
180.00(16)
82.08(13)
97.91(13)
97.91(13)
82.09(13)
88.96(14)
91.04(14)
88.96(14)
91.04(14)
180.0
2.052(3)
2.053(3)
2.378(4)
2.378(4)
2.248(5)
2.248(5)
165.0(2)
78.11(14)
92.67(15)
92.67(15)
78.11(14)
86.02(15)
1.941(5)
1.941(5)
2.384(6)
2.384(6)
2.048(6)
2.048(6)
180.0(3)
80.7(2)
99.3(2)
99.3(2)
80.7(2)
89.2(2)
90.8(2)
89.2(2)
90.8(2)
180.0
2.049(4)
M1–O1
2.049(4)
2.408(4)
2.408(4)
2.252(5)
2.252(5)
164.5(2)
78.34(15)
92.02(15)
92.02(15)
78.34(15)
87.80(16)
M1–N4
M1–N4i
M1–N2ii
M1–N2iii
O1–M1–O1i
O1–M1–N4
O1i–M1–N4
O1–M1–N4i
O1i–M1–N4i
O1–M1–N2ii
O1–M1–N2iii
O1i–M1–N2iii
O1i–M1–N2ii
N4i–M1–N4
N2iii–M1–N4
N2ii–M1–N4i
N2ii–M1–N4
N2iii–M1–N4i
N2ii–M1–N2iii
105.41(16)
86.02(15)
105.41(16)
104.9(2)
103.99(16)
87.80(16)
103.99(16)
103.8(2)
93.88(15)
93.88(15)
86.12(15)
86.12(15)
180.0
88.73(16)
88.73(16)
159.39(15)
159.39(15)
82.8(2)
94.5(2)
94.5(2)
85.5(2)
85.5(2)
180.0
88.81(17)
88.81(17)
161.42(17)
161.42(17)
82.6(3)
Symmetry codes: (i) −x + 1, −y, 1 − z; (ii) x, −y − 0.5, z + 0.5; (iii) −x + 1, y + 0.5, 0.5 − z. (i) y − 1, x + 1, −z − 1; (ii) x, y + 1, z; (iii) y, x + 1,
−z − 1. (i) 2 − x, −y, 1 − z; (ii) x, −y − 0.5, z − 0.5; (iii) −x + 2, y + 0.5, 1.5 − z. (i) y, x, 1 − z; (ii) x − 1, y, z; (iii) y, x − 1, 1 − z.
the
same
plane
(the
plane
equation
is
As shown in Figure S2a, each L ligand served as a
bridge to link two adjacent Cu(II) ions and form a
staircase-shaped chain. The length of the step in the
staircase-shaped chains was 10.96 and 10.94 Å for 1 and
3, respectively, which was made up of two 4-amine-4H-
1,2,4-triazole groups of the L ligands and one Cu ion. The
height of the step in the staircase-shaped chains was
4.680 and 4.751 Å for 1 and 3, respectively, which is the
1.6888x + 7.0731y + 5.2207z = 7.8357) because the
bond angles of O1–Cu1–O1i and N4–Cu1–N4i were
also 180ꢀ. As the atoms in the Cu-coordinated octahe-
dral environment were derived from different ligand
groups in four directions, the steric hindrance of each
atom was different, which resulted in a twisted octahe-
dral coordination configuration of copper ions.
FIGURE 1 Molecule structures of 1 and 3

6 of 13
ZENG ET AL.
distance N4···N4i (symmetry code: (i) −x + 1, −y, −z + 1
for 1; 2 − x, −y, 1 − z for 3). The N4···N4i···N4B angle
was 112.4ꢀ and 114.08ꢀ for 1 and 3, respectively (symme-
try code (B) for 1: 1 − x, −1 − y, −z; for 3: x, 1 + y, z − 1).
One-dimensional chains in different directions formed
2D networks by sharing copper atoms (Figure S2b). The
N4···Cu1···N4iii angle was 84.40ꢀ and 85.26ꢀ for 1 and 3,
respectively (symmetry code (iii) for 1: 1 − x, 0.5 + y,
0.5 − z; for 3: 2 − x, 0.5 + y, 1.5 − z). As a result, a rectan-
gular gap was formed in the 2D plane (Figure S2c). The
2D network structure was stacked along the a-axis direc-
tion with a layer spacing of 12.439 Å to form a 3D struc-
ture with the X···π (for 1: Cl2···πe, 3.428(1) Å, symmetry
code: (e) 2 − x, y − 0.5, 1.5 − z; for 3: Br2···πf, 3.277(1) Å,
symmetry code: (f) 1 − x, y − 0.5, 0.5 − z, Figure S2d).
3.1.2 | Crystal structures description of
2 and 4
Single crystal X-ray diffraction analysis revealed that
2 and 4 were isomorphic complexes (Figure 2), and the
crystal system (tetragonal) and space group (P41212) of
2 and 4 were identical. Therefore, only complex 2 was
analyzed.
The metal coordination of 2 and 4 was similar to that
of 1 and 3, but the ligands stretched in different direc-
tions in space. For 1 and 3, the two μ1-L-κ2O1,N1 bid-
entate ligands are center symmetrical with the copper
atom as the center of symmetry. O1–N4–Cu1–N4i–O1i
five atoms formed one plane (Figure 3a). N2ii and N2iii
coordinated with copper atoms from above and below
this plane, respectively. Copper atoms formed a perfect
octahedral configuration (Table 2). The bond angles of
FIGURE 3 Polyhedron of MO2N2 contrast for (a) 1 and (b) 2
O1–Cu1–O1i and N4–Cu1–N4i were 180ꢀ; for 2 and 4, the
two μ1-L-κ2O1,N1 bidentate ligands with the Cu ion con-
structed an obviously distorted tetrahedron (seesaw-
shaped) (Figure 3b). The bond angles of O1–Mn1–O1i
FIGURE 2 Molecule structures of 2 and 4

ZENG ET AL.
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FIGURE 4 1D chain of 2 and 4
and N4–Mn1–N4i were 165.0(2)ꢀ and 104.9(2)ꢀ, respec-
tively (symmetry code: (i) y − 1, x + 1, −z − 1 for 2). In
2 and 4, the other two coordination sites were adjacent in
the distorted octahedron.
of a series of compounds exhibited obvious absorption
peaks as shown in the IR spectrum. The ligands HL1&2
showed a br absorption band at 3448–3450 cm−1(O−H),
because of the stretching vibration adsorption peak of
crystal water molecules in the air or in the complexes.[18]
Bands at 1660 and 1634 cm−1 are attributed to the Schiff
base imine group −CH=N− of the free HL1 and HL2,
respectively, which red-shifted to 1597, 1603, 1591,
1591 cm−1 for 1–4, respectively. The results indicate that
the nitrogen atom of the −CH=N− group in L ligands
was coordinated.[37–39] The C−O stretching vibrations of
the free HL ligands at 1245 and 1232 cm−1 for free HL1
and HL2, respectively, red-shifted to 1214, 1214, 1207,
and 1226 cm−1 for 1–4, respectively, suggesting its partici-
pation in chelation.[35,40] The bands at 3130, 3124, 3111,
3143, 3117, and 3130 cm−1 for HL1, HL2, 1–4, respec-
tively, are attributed to the weak C−H stretching vibra-
tion of the benzene ring, while those at 868, 868,
849, 855, 843, and 855 cm−1 for HL1, HL2, 1–4, respec-
tively, are attributed to the C−X (X = Cl or Br) stretching
vibration. By comparing the IR spectrum of the HL1 and
HL2 ligands with that of the complexes 1–4, we find that
the change in the IR spectrum may have been due to the
change in the density of the electron cloud around the
ligand molecule after the ligands were coordinated to the
metal ions.
Mn1 coordinated with two oxygen atoms (O1, O1i)
and four nitrogen atoms (N4, N4i, N2ii, N3iii) provided by
four different L ligands, and formed a slightly distorted
octahedral MnN4O2 coordination configuration. The
bond distances of Mn1–O1, Mn1–N4, and Mn1–N2ii
(symmetry code: (ii) x, y + 1, z) were 2.053(3), 2.378(4),
and 2.248(5) Å, respectively. The mononuclear Mn(L1)2
unit constructed a 1D chain through an Mn–N coordina-
tion bond which is different from the staircase-shaped
chain of 1 and 3. In the 1D chain of 2 and 4, manganese
atoms were in a straight line while the Mn1···Mn1a dis-
tance was 7.688(1) Å (Figure 4). The 1D chain further
constructed a 2D lattice through Mn–N2 and N2–Mn
bonds. The distance adjacent to the 1D chain was
7.688(1) Å. As a result, there is a square lattice of
7.668 × 7.688 Å and 7.737 × 7.737 Å on the plane for
2 and 4, respectively (Figure S3a), which is different from
the rectangular gap of 1 and 3. The 2D lattice formed 3D
supramolecular network through the X···X interaction
(for 2: Cl2···Cl2E, 3.623(1) Å, symmetry code: (E) −1 − y,
−1 − x, −1.5 − z; for 4: Br2···Br2F, 3.738(1) Å, symmetry
code: (F) 1 − y, 1 − x, 1.5 − z) and C–H···N hydrogen
bonds (for 2: C7–H7···N1G, 3.388(1) Å, symmetry code:
(G) y − 0.5, −0.5 − x, 1.75 + z; for 4: C7–H7···N1G,
3.419(1) Å, symmetry code: (G) 0.5 − y, x− 0.5, 0.25 + z,
Figure S3b).
3.3 | Thermal stability analysis
Under the test conditions of N2 flow rate of 100.0 ml/min
and heating rate of 10ꢀC/min, the thermal stability of
complexes 1–4 was tested from room temperature to
900ꢀC (PXRD has been proven to be a pure phase sample,
Figure S4). Thermogravimetric curves of complexes 1–4
are shown in Figure 5. The four complexes exhibited
3.2 | IR spectrum
The IR spectral data of the ligand HL1&2 and compounds
1–4 are shown in Figure S1. All the characteristic groups

8 of 13
ZENG ET AL.
FIGURE 5 Thermogravimetric curves of 1–4
extremely similar weightlessness behaviors, with com-
plexes 1 and 3, and 2 and 4 being slightly different in sub-
tleties. Complexes 2 and 4 began to decompose at about
329ꢀC, while complexes 1 and 3 began to collapse at
about 220ꢀC, which indicates that 2 and 4 are more stable
than 1 and 3. The decomposition end temperature was
about 720ꢀC, and the remaining products were the
corresponding metal oxides.
intramolecular X (Cl and Br) and the extramolecular
H is indicated in the fingerprint region of the lower-
left corner (donor) of the fingerprint. The interaction
of H inside the molecule with the X (Cl and Br) out-
side the molecule was in the lower-right corner (recep-
tor) fingerprint area, indicating
a clear C–H···X
(Cl and Br) nonconventional hydrogen bond in the
crystal structure of the compounds 1–4. The interaction
C–X(Cl and Br) also plays an important role in the
total 2D fingerprint. The percentage of C–X(Cl and Br)
in compounds 1–4 was 12.7%, 13.4%, 12.8%, and 15.1%,
respectively. The shortest C···X distances were 3.501,
3.408, 3.533, and 3.397 Å for 1–4, respectively. Another
major intermolecular interaction of 1–4 was the H–H
interaction, which is reflected in the middle of the
scattering point of the 2D fingerprint (the percentage
of H–H effect of compounds 1–4 was 13.4%, 10.7%,
12.7%, and 10.6%). The forces of different elements are
summarized in Table 3.
3.4 | Hirshfeld surface analysis
Through the Hirshfeld analysis of the surface effect of
the structural unit, we obtained the 2D fingerprint as
shown in Figure 6. The properties and types of inter-
molecular interactions within the crystal were quanti-
tatively analyzed, and the work of this part was
calculated using the CrystalExplorer 3.1 program.[41]
The acting forces between different elements were
studied separately in the 2D fingerprint, and then the
ratio of the forces of the various parts to research with
the structure was analyzed. For compounds 1–4, X
(Cl and Br)–H accounts for a large proportion of the
entire 2D fingerprint, 21.2%, 16.5%, 20.9%, and 17.0%,
3.5 | Fluorescent properties of 1–4
The luminescent properties of compounds 1–4 and the
respectively.
The
interaction
between
the
free HL1&2 ligands were investigated in DMF solvent

ZENG ET AL.
9 of 13
FIGURE 6 2D fingerprints of various intermolecular forces in 1–4
TABLE 3
Hirshfeld surface calculations (%) for 1–4
Complexes
X·H (X = Cl, Br)
H·H
13.4
10.7
12.7
10.6
C·X
12.7
13.4
12.8
15.1
C·H
11.0
11.4
10.1
10.9
N·X
4.3
8.3
4.1
8.4
N·H
8.5
1
2
3
4
21.2
16.5
20.9
17.0
8.6
8.4
7.9
with a concentration of 5 × 10−5 mol/l (Figure 7). The
maximum absorption wavelength was selected as the
excitation wavelength to test the fluorescence spectrum
of the compounds. A 438 nm wavelength was used to
excite the luminescence of a series of HL1, 1, and
2 with a slit width of 2.5 nm. Upon photoexcitation at
438 nm, the free HL1 ligand was a blue luminescent
compound with the maximum at 470 nm predomi-
nantly assigned to π–π* transition fluorescence. At the
same 438 nm photoexcitation, 1 and 2 exhibited also a
green luminescent emission band at 527 and 514 nm.
Compared to the free ligand HL1, with 57 and 44 nm
red-shifted for 1 and 2, respectively, the emission at
527 and 514 nm and lower fluorescence intensity of
the compounds 1 and 2 probably originated from the
paramagnetic influence of CuII or MnII cations which
are d9 and d5 ions, respectively.[42]
As shown in Figure 7b, upon photoexcitation at
450 nm, the free HL2 ligand exhibited a green lumines-
cent emission peak at 512 nm predominantly also

10 of 13
ZENG ET AL.
FIGURE 7 The fluorescent properties of HL1&2 and 1–4
assigned to π–π* transition fluorescence. At the same
450 nm photoexcitation, 3 and 4 exhibited also a green
luminescent emission peak at 519 and 522 nm. The emis-
sion peaks of 3 and 4 were red-shifted by about 7 and
10 nm for 3 and 4, respectively, compared to the free HL2
ligand. For 3 and 4, lower fluorescence intensity and
redshift relative to HL2 ligand probably originated from
the paramagnetic influence of CuII or MnII cations which
are d9 and d5 ions, respectively.[42] By comparing the
fluorescence intensity of 1 and 2 or 3 and 4, we found
that the fluorescence intensity of compounds 1 or 3 was
lower than that of compounds 2 or 4 constructed with
FIGURE 8 The electrochemical emission spectrum of 1–4

ZENG ET AL.
11 of 13
FIGURE 9 Cyclic voltammetry curves for 1–4
the same ligand, which can be attributed to the electro-
negativity of the substituents and also the electron den-
sity of the ligand as the electronegativity of chlorine is
greater than that of bromine. As a result, the electron
density of ligand HL1 was lower than that of ligand HL2,
which is harmful to the ligand-to-metal charge trans-
fer.[30,36] The unique fluorescent properties of this series
of compounds can be researched as a potential fluores-
cent material.
current were observed. The CV curves for the other three
complexes are similar to that of 1.
For complexes 1–4, the maximum luminous intensity
was about 2850, 2960, 2850, 3100 a.u., respectively. After
seven circulations, the luminous intensities still
maintained stability. In the different metal complexes of
the same ligand, it can be found that the complex of
Mn(II) has a higher maximum luminescence intensity
than that of Cu(II). However, in general, these four com-
pounds have strong and stable luminescent properties
and have great potential application value in the practical
application of electrochemical materials,[39] especially
compound 4.
3.6 | ECL properties of 1–4
The ECL of the pure complexes 1–4 (the phase purity of
1–4 has been checked by PXRD, Figure S4) is shown in
Figure 8. CV was studied to gain insight into the redox
properties of 1–4. Figure 9 shows the experimental results
of CV with glassy carbon disk electrodes modified with
complexes 1–4. For 1, when K2S2O8 was added to the
solution, an oxidation peak in the cathodic current at
−1.5 V and a reduction peak at −0.95 V in the cathodic
We have taken [Ru(bpy)3]3 as a standard[43] for the
ECL yield, resulting in yields of 0.63, 0.66, 0.63, and 0.69
for complexes 1–4, respectively. It is tentatively suggested
that the introduction of the Cu and Mn ions, in particular
Mn ion, could strengthen the spin–orbit coupling effect
and enhance the ECL emission. Compared to Ru-, Ir-, Pt-
, Re-, Os-, and Cd-complexes reported previously,[43–45]
the four complexes as novel polymer ECL materials

12 of 13
ZENG ET AL.
exhibit better economic benefits and environmental
friendliness because copper and manganese are less-tox-
iclow-priced metals.
ORCID
Fanghua Ji https://orcid.org/0000-0002-2101-3930
Shuhua Zhang https://orcid.org/0000-0002-1097-1674
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