Novel salicyloylhydrazone derivatives and corresponding terbium(III) complexes: Synthesis and properties research

Article abstract of DOI:10.1002/bio.3583

Four novel salicyloylhydrazone derivatives and their terbium(III) complexes were synthesized and characterized. The thermal analysis results showed that the terbium(III) complexes possessed good thermal stability. The fluorescence research results showed that the terbium(III) complex substituted by phenyl possessed the best fluorescence intensity among them, and its fluorescence quantum yield was also the highest. The exploration of the electrochemical properties indicated that the introduction of electron-donating groups to the ligand can increase the highest occupied molecular orbital (HOMO) energy levels and decrease the oxidation potential of the corresponding terbium(III) complexes. The introduction of electron-withdrawing groups to the ligand can reduce their HOMO energy levels and increase their oxidation potential. The results showed that the terbium(III) complexes are good candidates for luminescent material.

Full text of DOI:10.1002/bio.3583

Received: 11 August 2018
DOI: 10.1002/bio.3583
Revised: 5 November 2018
Accepted: 9 November 2018
R E S E A R C H A R T I C L E
Novel salicyloylhydrazone derivatives and corresponding
terbium(III) complexes: Synthesis and properties research
1,2
3
2
3
3
|
|
|
|
Rong Xiao
Wei Huang
Xiaoming Xiao
Yanhong Liu
Dongcai Guo
1
College of Educational science, Hunan
Normal University, Changsha, China
Abstract
2
College of Chemistry and Chemical
Four novel salicyloylhydrazone derivatives and their terbium(III) complexes were syn-
thesized and characterized. The thermal analysis results showed that the terbium(III)
complexes possessed good thermal stability. The fluorescence research results
showed that the terbium(III) complex substituted by phenyl possessed the best fluo-
rescence intensity among them, and its fluorescence quantum yield was also the
highest. The exploration of the electrochemical properties indicated that the introduc-
tion of electron‐donating groups to the ligand can increase the highest occupied
molecular orbital (HOMO) energy levels and decrease the oxidation potential of the
corresponding terbium(III) complexes. The introduction of electron‐withdrawing
groups to the ligand can reduce their HOMO energy levels and increase their oxida-
tion potential. The results showed that the terbium(III) complexes are good candidates
for luminescent material.
Engineering, Hunan Normal University,
Changsha, China
3
College of Chemistry and Chemical
Engineering, Hunan University, Changsha,
China
Correspondence
Xiaoming Xiao, College of Chemistry and
Chemical Engineering, Hunan Normal
University, Changsha 410081, China.
Email: xmxiao@hunnu.edu.cn
Dongcai Guo, College of Chemistry and
Chemical Engineering, Hunan University,
Changsha 410082, China.
Email: dcguo2001@hnu.edu.cn
Funding information
Changsha Science and Technology Bureau,
Grant/Award Numbers: kq1701029 and
kq1701164; Hunan Provincial Science and
Technology Department, Grant/Award Num-
ber: 2016SK2064; Innovative Research Team
in University, Grant/Award Number: IRT1238;
Instrument sharing platform of Hunan univer-
sity; National Natural Science Foundation of
China, Grant/Award Numbers: 21341010,
J1210040 and J1103312; Natural Science
Foundation of Hunan Province, Grant/Award
Number: 11JJ5005; China Outstanding Engi-
neer Training Plan for Students of Chemical
Engineering and Technology in Hunan Uni-
versity, Grant/Award Number: MOE‐
No.2011‐40
KEYWORDS
electrochemical properties, fluorescence, salicyloylhydrazone, synthesis, terbium(III) complexes
[
4]
1
|
INTRODUCTION
emissive terbium probe for multiphoton in vitro cell imaging. Ye
et al. reported a terbium complex‐based luminescent probe (BMTA‐
3
+
The luminescence properties of rare earth complexes have drawn
much attention owing to the distinctiveness and diversity of the prop-
erties, and the wide range of applications in many fields. Among rare
Tb ) for the recognition and luminescence detection of hydrogen per-
[
5]
2 2
oxide (H O ) in aqueous solutions. However, salicyloylhydrazone
contains nitrogen and oxygen atoms, and it can coordinate with metal
ions. Their derivatives were reported as excellent ligands and as highly
3+
earth ions, terbium(III) ion (Tb ) has been widely studied. For example,
[
6,7]
Xin et al. reported a new terbium complex (Tb(eb‐PMP) TPPO) with
3
selective Schiff base fluorescent chemosensors.
[
1]
efficient electroluminescence (EL), and they also reported the effect
In order to obtain strong luminescent complexes, researchers
have designed and synthesized a large number of organic ligands
and have tried to explore the effect of different structures or
of the neutral ligands (TPPO, Phen) on the photoluminescence (PL)
[2]
and EL properties of the terbium complexes. Cui et al. reported an
[
8,9]
effective green phosphorescent organic electroluminescent device
constituent groups on the luminescence properties.
However,
[3]
with a terbium complex as the sensitizer. Law et al. reported an
there also existed some problems, such as poor thermal stability,
Luminescence. 2018;1–8.
wileyonlinelibrary.com/journal/bio
© 2018 John Wiley & Sons, Ltd.
1

2
XIAO ET AL.
weak luminescence intensity, etc. These defects limited their applica-
tion fields. Through the modification of the ligand, their solubility,
thermal stability and luminescent properties can be improved, and
in potassium bromide discs by a PER KINGMAKER Spectrum One.
Thermogravimetric analysis (TGA) was carried out on a NETZSCH
STA 409PC thermal gravimetrical analyzer. The fluorescence spectra
were measured using a HIACHI F‐2700 fluorescence magnetometer
at room temperature, using powder samples, and both the excitation
and emission light slits were 5.0 nm. Cyclic voltmeter curves were
tested using three electrodes (a glassy electrode, a platinum electrode
[10,11]
their application potential can also be enhanced.
Therefore, this
method has aroused people's attention, and we also have done some
work in this field.
In this article, on the basis of our preceding work, four novel
hydroelectrical derivatives were synthesized and characterized by
and
a saturated Camelot electrode), with scenery as external
1
13
H‐NMR, C‐NMR and mass spectrometry (MS). The synthetic routes
standard, and nitrite solution as the supporting electrolyte and
−
1
are shown in Scheme 1. Furthermore, terbium(III) complexes were also
prepared, and their structure and composition were explored by molar
conductance, elemental analysis, UV spectra, IR spectra and thermal
analysis. Moreover, their thermal stability, electrochemical properties
and fluorescence properties were also discussed. These complexes will
possibly be used as fluorescent paints, and will be explored in our
future research work.
DMSO as the solvent, the test scanning speed was 100 V s and
the sensitivity was 1 A.
2
.2
|
General synthesis procedure of the
intermediates
2
.2.1
|
Synthesis of compound a
A mixture of menthyl salicylate (50 mmol, 7.60 g) and absolute alcohol
15 mL) was added to a 250 mL three‐necked flask, and then 10 mL of
2
2
|
EXPERIMENTAL
(
hydrazine hydrate was gradually added drop by drop. The reaction
mixture was heated to 80°C and refluxed for 10 h, cooled to room
temperature and filtered. The residue was recrystallized from distilled
.1
|
Materials and method
Pyridine‐2‐formaldehyde (98%), 2‐thiophene formaldehyde (98%),
Tb (99.99%), formaldehyde, dehydrator, mentalist salivary, thora-
[
12]
water, and then a white crystal was obtained.
Yield was 87%.
4
O
7
zine hydrate and other reagents (analytical reagent grade) were pur-
chased from commercial suppliers.
1
–4
2
.2.2
|
Synthesis of compound b
1
13
The H‐ and
sulfoxide (DMSO)‐d
C‐NMR spectra were recorded in dimethyl
/deuterated chloroform (CDCl ) on a Brucker
6
3
Salicylhydrazide (20 mmol, 3.04 g) was dissolved in 20 mL absolute
alcohol in a 250 mL three‐necked flask, and then heated. When the
temperature was stable at 85°C, benzaldehyde (20 mmol, 2.12 g)
was gradually added drop by drop with the reaction lasting for 4 h.
Cooled to room temperature and filtered, then washed several times
spectrometer (400 MHz) with tetramethylsilane (TMS) as an internal
standard. MS was measured with a MAT95XP mass spectrometer.
Melting points of all compounds were determined on an X‐4
binocular microscope. Elemental analysis of the complexes was
carried out on a Varietal 111 (Germany) CHNS analyzer. Molar
conductance was measured using a DDS‐12A conductivity instrument.
Ultraviolet‐visible (UV‐vis) spectra were recorded on a Lab Tech
UV‐2100 magnetometer, with dimethylformamide (DMF) as solvent
1
with hot absolute alcohol. The white solid of compound b was
[
13,14]
2–4
obtained.
The general synthesis procedures of b
were similar
1
to that of b .
−1
1
and reference. Infrared (IR) spectra (400–4000 cm ) were obtained
2‐Hydroxy‐N′‐benzylidene‐2‐benzoylhydrazine (b )
1
A white solid. Yield: 88%. H‐NMR (400 MHz, DMSO‐d
6
) δ 11.84 (s,
2
H), 8.47 (s, 1H), 7.90 (d, J = 7.7 Hz, 1H), 7.79–7.72 (m, 2H), 7.51–
.42 (m, 4H), 7.01–6.93 (m, 2H); MS (EI) m/z (%): 241 (m + 1, 3), 240
7
(
(
m, 18), 138 (3), 137 (36), 121 (100), 120 (52), 119 (9), 93 (17), 92
5), 65 (14).
2
2
‐Hydroxy‐N′‐(pyridine‐2‐methylene)‐2‐benzoylhydrazine (b )
1
A light‐yellow solid. Yield: 81%. H‐NMR (400 MHz, DMSO‐d
6
) δ
1
8
2.02 (s, 1H), 11.67 (s, 1H), 8.64 (d, J = 4.4 Hz, 1H), 8.48 (s, 1H),
.00 (d, J = 7.9 Hz, 1H), 7.89 (dd, J = 19.6, 7.7 Hz, 2H), 7.45 (dd,
J = 12.9, 5.8 Hz, 2H), 7.02–6.93 (m, 2H); MS (EI) m/z (%): 42 (m + 1,
5
6
), 241 (m, 26), 122 (4), 121 (54), 120 (100), 94 (3), 93 (15), 92 (43),
6 (2), 65 (19).
3
2
‐Hydroxy‐N′‐(furan‐2‐methylene)‐2‐benzoylhydrazine (b )
1
A light‐yellow solid. Yield: 84%. H‐NMR (400 MHz, DMSO‐d
6
) δ
11.82 (s, 1H), 11.79 (s, 1H), 8.35 (s, 1H), 7.91–7.81 (m, 2H), 7.44 (t,
SCHEME
1
The synthetic route for the salicyloylhydrazone
derivatives
J = 7.4 Hz, 1H), 6.97 (dd, J = 11.2, 7.3 Hz, 3H), 6.66 (s, 1H); MS (EI)

XIAO ET AL.
3
m/z (%): 231 (m + 1, 5), 230 (m, 30), 138 (2), 137 (19), 121 (100), 110
2‐(2‐(2‐Pyridine‐2‐methylene)carbohydrazide)phenoxy)‐N‐
2
(
59), 94 (3), 93 (17), 81 (4), 66 (2), 65 (18), 52 (5).
phenylacetamide (L )
1
A
light‐yellow powder. Yield: 45%; m.p. 147–150°C. H‐NMR
2
‐Hydroxy‐N′‐(thiophene‐2‐methylene)‐2‐benzoylhydrazine
(400 MHz, DMSO‐d ) δ 12.30 (s, 1H), 10.38 (s, 1H), 8.64 (d,
6
4
(
b )
J = 4.6 Hz, 1H), 8.46 (s, 1H), 8.00 (d, J = 7.9 Hz, 1H), 7.92 (t,
1
A light‐yellow solid. Yield: 85%. H‐NMR (400 MHz, DMSO‐d
1.81 (s, 2H), 8.67 (s, 1H), 7.85 (d, J = 7.7 Hz, 1H), 7.71 (d,
J = 5.0 Hz, 1H), 7.51 (d, J = 3.5 Hz, 1H), 7.44 (t, J = 7.7 Hz, 1H),
6
) δ
J = 7.1 Hz, 1H), 7.81 (dd, J = 7.6, 1.4 Hz, 1H), 7.65 (t, J = 9.5 Hz,
2H), 7.63 (m, 1H), 7.47 (m, 1H), 7.34 (t, J = 7.9 Hz, 2H), 7.23 (t,
J = 7.3 Hz, 1H), 7.18 (t, J = 7.5 Hz, 1H), 7.10 (t, J = 7.4 Hz, 1H), 4.99
1
1
3
7
2
.20–7.14 (m, 1H), 6.97 (dd, J = 12.1, 6.2 Hz, 2H); MS (EI) m/z (%):
(s, 2H); C‐NMR (101 MHz, CDCl ) δ 166.19, 164.63, 156.09,
3
48 (m + 2, 1), 247 (m + 1, 4), 246 (m, 23), 138 (4), 137 (43), 126
152.14, 148.05, 139.12, 137.86, 137.57, 133.22, 129.80, 128.76
(
50), 121 (100), 120 (29),99 (5), 93 (19), 92 (5), 65 (19).
(3C ), 126.01, 124.30 (2C ), 122.25, 120.09 (2C ), 113.63, 68.13;
1
2
3
MS (EI) m/z (%): 376 (m + 2, 1), 375 (m + 1, 3), 374 (m, 10), 255
10), 254 (6), 253 (2), 135 (2), 134 (5), 121 (47), 120 (100), 106 (30),
2 (44),79 (8), 77 (13), 65 (22); Anal. Calcd for C21 : C,
2
.2.3
|
Synthesis of compound c
(
9
18 4 3
H N O
Phenylamine (50 mmol, 4.65 g) and ethylic acid (40 mL) was added to a
00 mL beaker, and then chloroacetyl chloride (50 mmol, 5.60 g) was
67.37; H, 4.85; N, 14.96. Found: C, 67.17; H, 4.60; N, 15.16.
5
added dropwise under an ice bath. The reaction mixture was stirred
for 30 min under an ice bath, and then stirred at room temperature
for another 1 h. The reaction mixture was poured into saturated
sodium acetate solution (200 mL), and then filtered, washed several
times; the residue was recrystallized from the mixed solution of etha-
nol and water. The compound c was obtained.
2‐(2‐(2‐Furan‐2‐methylene)carbohydrazide)phenoxy)‐N‐
3
phenylacetamide (L )
1
A
light‐yellow powder. Yield: 33%; m.p. 153–155°C. H‐NMR
(400 MHz, DMSO‐d ) δ 12.07 (s, 1H), 10.40 (s, 1H), 8.33 (s, 1H),
6
7.91 (s, 1H), 7.80 (d, J = 7.6 Hz, 1H), 7.70 (d, J = 8.3 Hz, 2H), 7.58 (t,
J = 7.9 Hz, 1H), 7.37 (t, J = 7.8 Hz, 2H), 7.25 (d, J = 8.4 Hz, 1H),
7
1
.17 (t, J = 7.5 Hz, 1H), 7.12 (t, J = 7.4 Hz, 1H), 6.96 (d, J = 3.3 Hz,
13
2
.2.4
|
1
–4Synthesis of the salicyloylhydrazone deriva-
3
H), 6.70–6.66 (m, 1H), 4.98 (s, 2H); C‐NMR (101 MHz, CDCl ) δ
tives L
166.44, 163.12, 155.90, 149.40, 144.71, 139.04, 137.76, 133.30,
31.42, 128.86 (3C ), 124.42, 122.22, 120.20 (2C ), 113.91, 113.24,
1
1
2
Salicylhydrazine benzylidene (2.40 g, 10 mmoL) was dissolved in DMF
20 mL) in a 250 mL three‐necked flask. Then, some absolute potas-
sium carbonate (K CO ) was added, heated to 80°C and refluxed for
h. After that, 10 mL of 2‐chloride‐N‐acetyl aniline DMF solution
111.91, 68.10; MS (EI) m/z (%): 365 (m + 2, 1), 364 (m + 1, 4),
363(m, 13), 271 (3), 270 (14), 254 (34), 253 (6), 252 (1), 226 (29),
134 (15), 121 (100), 106 (59), 93 (29), 92 (8), 79 (5), 77 (16), 65 (10);
Anal. Calcd for C20H17N O : C, 66.11; H, 4.72; N, 11.56. Found: C,
(
2
3
1
3
4
was added drop by drop and a little potassium iodide (KI) was also
added, then refluxed for 3 h. Next the mixture was cooled to room
temperature and poured into 300 mL of distilled water, after which
66.21; H, 4.63; N, 11.46.
2‐(2‐(2‐Thiophene‐2‐methylene)carbohydrazide)phenoxy)‐N‐
−1
4
the solution was neutralized with 2 mol L dilute hydrochloric acid.
Subsequently, filtered and washed until the water was neutral. The
residue was dried for three days. Then washed three times and recrys-
phenylacetamide (L )
1
A
light‐yellow powder. Yield: 37%; m.p. 155–157°C. H‐NMR
(400 MHz, DMSO‐d ) δ 12.04 (s, 1H), 10.36 (s, 1H), 8.62 (s, 1H), 7.80
6
1
tallized three times from acetic ether. The white solid compound L
(m, 1H), 7.73 (m, 3H), 7.56 (dd, J = 11.5, 4.3 Hz, 1H), 7.43 (d,
2
–4
was obtained. The general synthesis procedures of L
were similar
J = 3.5 Hz, 1H), 7.35 (t, J = 7.8 Hz, 2H), 7.22 (d, J = 8.3 Hz, 1H), 7.19
13
1
to that of L .
(m, 2H), 7.11 (t, J = 7.5 Hz, 1H), 4.97 (s, 2H); C‐NMR (101 MHz, CDCl3)
δ 166.43, 163.11, 155.87, 144.62, 138.76, 137.86, 133.37, 131.51,
2
‐(2‐(2‐Benzylidene)carbohydrazide)phenoxy)‐N‐
130.93, 129.00, 128.90 (3C ), 127.45, 124.43, 122.21, 120.17 (2C ),
1
2
1
phenylacetamide (L )
113.27, 68.08; MS (EI) m/z (%): 380 (m + 1, 2), 379 (m, 4), 271 (5), 270
(31), 254 (30), 253 (11), 252 (3), 227 (7), 226 (40), 178 (3), 177 (7), 151
(9), 150 (15), 134 (23), 121 (100), 106 (53), 93 (32), 92 (9), 79 (5), 77
(14), 65 (9); Anal. Calcd for C20H17N O S: C, 63.31; H, 4.52; N, 11.07.
1
A white powder. Yield: 54%; melting point (m.p.) 158–160°C. H‐NMR
(
400 MHz, DMSO‐d
6
) δ 12.09 (s, 1H), 10.38 (s, 1H), 8.43 (s, 1H), 7.78
(
d, J = 7.6 Hz, 1H), 7.71 (dd, J = 12.3, 5.2 Hz, 4H), 7.56 (t, J = 7.9 Hz,
3
3
1
1
H), 7.45 (t, J = 9.3 Hz, 3H), 7.33 (t, J = 7.6 Hz, 2H), 7.23 (d, J = 8.3 Hz,
Found: C, 63.50; H, 4.12; N, 11.01.
13
H), 7.17 (t, J = 7.5 Hz, 1H), 7.10 (t, J = 7.6 Hz, 1H), 4.98 (s, 2H); C‐
) δ 167.29, 162.72, 156.04, 148.34,
38.71, 134.68, 133.31, 130.95, 130.67, 129.39 (2C ), 129.38 (2C ),
27.61 (2C ), 124.35, 123.60, 122.27, 119.92 (2C ), 114.41, 68.40;
NMR (101 MHz, DMSO‐d
6
1
1
1
2
|
2
.3
Synthesis of the terbium(III) complexes
3
4
1
MS (EI) m/z (%): 373 (m, 3), 271 (5), 270 (25), 254 (30), 253 (10),
52 (2), 227 (6), 226 (28), 178 (4), 177 (6), 151 (9), 150 (14), 134
27), 121 (100), 106 (56), 93 (48), 92 (10), 77 (20), 65 (13); Anal. Calcd
for C22 : C, 70.76; H, 5.13; N, 11.25. Found: C, 70.41, H, 5.21;
N, 11.29.
Ligand L (0.38 g, 1 mmol) was added into absolute alcohol (50 mL) in
a 250 mL three‐necked flask and heated to 80°C. After being fully dis-
solved, the terbium nitrate alcohol solution (5 mL) was added and
refluxed for 0.5 h. The pH value of the reaction solution was adjusted
2
(
19 3 3
H N O
−1
to 6 by using sodium hydroxide solution (1 mol L ), a white

4
XIAO ET AL.
precipitate was formed. Then the solution was refluxed for 4 h and fil-
tered immediately. Washed three times with hot alcohol and dried.
absorption and transition of the complexes. This analysis indicates that
the ligands coordinate to the terbium(III) ions successfully.
1
The terbium complex with ligand L was obtained. The general synthe-
2
–4
sis procedures of other terbium complexes with ligands L
were sim-
1
ilar to that of the terbium(III) complex with ligand L .
3.3
|
IR spectra analysis
1
–4
The structure of ligands L
and their terbium complexes can be ver-
3
3
|
RESULTS AND DISCUSSION
Elemental analysis of the terbium(III) complexes
ified by IR spectra. The IR data of the ligands and their terbium(III)
complexes are listed in Table 3. Since the IR spectra of all the com-
.1
|
plexes are similar, only the IR spectra of [Tb(NO ) L ]NO ·2H O as
4
3
2
3
2
4
well as its ligand L is selected and shown in Figure 2.
In order to investigate the elemental contents of the terbium(III) com-
plexes, elemental analysis was conducted, and the molar conductivity
was also determined in DMF solution at room temperature. The con-
4
3 2
As shown in Table 3 and Figure 2, the complex [Tb(NO ) L ]
−1
3 2
NO ·2H O exhibits an absorption band at 3459 cm , this is assigned
to the ν(O‐H) stretching vibration and it indicates the existence of
water molecules. Compared to the ν(C=O) stretching vibration absorp-
−3
−1
centration was 10 mol L . The content of terbium elements in com-
plexes are measured by ethylenadiaminetetraacetic acid (EDTA)
titrimetric analysis. The data for all the terbium(III) complexes are listed
in Table 1.
4
−1
4
3 2
tion peak of ligand L at 1697 cm , that of the complex [Tb(NO ) L ]
−1
3 2
NO ·2H O has a red shift of 42 cm and a peak located at 1655 cm
−1
.
Hence the oxygen atom, of the C=O group coordinated to the
As shown inTable 1, the composition of the complexes are consis-
terbium(III) ions, has an electron cloud that moves to the terbium ions
and thus the bond force constant is changed, so the vibration absorp-
tion peak of the carbonyl group exhibits an obvious shift. The ν(N‐
C=O) stretching vibration absorption peak also has a red shift from
1
–4
tent with the formulas of Tb(NO
3
)
3
L
2
·2H O, since the measured
value of elemental contents are in accordance with the theoretical
values. The measured molar conductivity values of the terbium(III)
2
complexes in DMF solution are in the range of 65 to 90 S cm
−1
−1
2
361 cm to 2356 cm , this also implied that the oxygen atom of
−1
mol , indicating that the terbium(III) complexes are 1:1 electrolytes
the N‐C=O group has coordinated to the terbium(III) ions. The
ν(C=N) stretching vibration absorption peak has a red shift from
and a free nitrate ion exists. Therefore, the formulas of the complexes
1–4
are [Tb(NO
3
)
2
L
]NO
3
2
·2H O.
−1
−1
1
601 cm to 1576 cm , indicating that the nitrogen atom of the
C=N group is coordinated to the terbium(III) ions. The complex has
3
.2
|
UV analysis
characteristic absorption peaks of nitrate groups with a strong absorp-
−
1
tion peak at 1385 cm , which showed that the complex has free
1–4
The UV absorption spectra of ligands L
and their terbium(III) com-
nitrate groups. Moreover, the symmetric and antisymmetric absorp-
−1
plexes are recorded in DMF solution. The data are listed in Table 2,
tion peaks of the nitrate groups are located at 1340 cm and
−1
and since the UV spectra of all the terbium(III) complexes are similar,
1 4
1458 cm , and the difference of the vibration frequency (|ν − ν |)
1
−1
only the spectra of L as well as its terbium(III) complex are selected
is less than 200 cm , indicating that the nitrate groups coordinated
to the terbium(III) ions are as bidentate ligands. The earlier mentioned
for illustration, as shown in Figure 1.
1
–4
4
As seen fromTable 2, the absorption bands of ligands L
are dis-
analysis results showed that the ligand L coordinated to the
tributed in the range of 266 to 268 nm and 308 to 326 nm, respec-
tively, and compared to that of the ligands, the maximum absorption
terbium(III) ions successfully, which is consistent with the results of
the earlier analysis.
peaks of the terbium(III) complexes have red shifts. As shown in
1
Figure 1, [Tb(NO
3
)
2
L ]NO
3
2
·2H O has two peaks at 278 nm and
TABLE 2 The UV data of the terbium(III) complexes and corre-
sponding ligands
3
12 nm, which are due to the π → π* and n → π* transitions, respec-
1
tively. Compared with the maximum absorption peaks of ligand L
Complex
Λ
max (nm)
Ligand
Λmax (nm)
1
(
266 nm and 308 nm), that of terbium(III) complex [Tb(NO
3 2
) L ]
1
1
[Tb(NO
[Tb(NO
[Tb(NO
[Tb(NO
3
)
3
)
3
)
3
)
2
2
2
2
L ]NO
3
3
3
3
·2H
·2H
·2H
·2H
2
O
2
O
2
O
2
O
278, 312
278, 312
278, 324
278, 334
L
266, 308
266, 312
266, 318
268, 326
NO ·2H O presents red shifts of 12 nm and 4 nm, respectively. The
3
2
2
2
L ]NO
L
reason may be that the electron delocalization of the conjugated sys-
tem of the terbium(III) complexes is increased and the energy required
for electron transition is decreased, and it is favorable for the energy
3
3
L ]NO
L
4
4
L ]NO
L
TABLE 1 The elemental analysis and molar conductance data of the terbium(III) complexes
Measured value (Theoretical value) (%)
Λ
m
2
−1
Complexes
Carbon
Hydrogen
Nitrogen
Terbium
(S cm mol )
1
[Tb(NO
[Tb(NO
[Tb(NO
[Tb(NO
3
3
3
3
)
2
)
2
)
2
)
2
L ]NO
3
·2H
3
·2H
3
·2H
3
·2H
2
2
2
2
O
O
O
O
35.11 (35.01)
33.18 (33.37)
32.12 (32.26)
31.47 (31.58)
3.12 (3.05)
3.01 (2.91)
2.95 (2.82)
2.55 (2.76)
11.03 (11.14)
12.90 (12.98)
11.39 (11.46)
11.14 (11.05)
21.05 (21.08)
21.02 (21.06)
21.39 (21.37)
20.80 (20.92)
65
68
70
72
2
L ]NO
3
L ]NO
4
L ]NO

XIAO ET AL.
5
1
1
4
4
FIGURE 1 The UV spectra of [Tb(NO
3
)
2
]L NO
3
·2H
2
O (a) and L (b)
3 2 3 2
FIGURE 2 The IR spectra of [Tb(NO ) ]L NO ·2H O (a) and L (b)
TABLE 4 The thermogravimetric data of the terbium(III) complexes
3
.4
|
Thermal analysis
Endothermic Exothermic Residual weight
Complex
peak (°C)
peak (°C)
(theoretical value) (%)
In order to investigate the thermal stability and decomposition process
of the terbium(III) complexes, thermal analysis is carried out under
oxygen atmosphere and the data are shown in Table 4. Since the four
terbium(III) complexes present similar thermal behaviors, only the
1
[
[
[
[
Tb(NO
3
)
2
L ]
115
393, 600
24.00 (24.83)
NO ·2H O
3
2
2
Tb(NO
3
)
2
L ]
113
105
126
449, 609
379, 609
401, 615
24.14 (24.80)
25.00 (25.17)
25.10 (24.97)
NO ·2H O
3
2
3
Tb(NO
3 2
) L ]
thermogravimetric‐differential thermal analysis (TG‐DTA) curve
NO ·2H O
3
2
1
(
Figure 3) of [Tb(NO
3
)
2
]L NO
3
2
·2H O is selected for explanation.
4
Tb(NO
3 2
) L ]
1
From Table 4 and Figure 3, [Tb (NO
3
)
2
]L NO
3
·2H
2
O has a signifi-
NO ·2H O
3
2
cant endothermic peak at 115°C, and there is a mass loss of 4.56%
between 105 and 190°C, that indicated the complex has two crystal
water molecules (theoretical contents value of water is 4.78%). Mean-
while, there was a great weight loss of 49.08% between 190 and
1
ions and the formula of the complex is [Tb(NO
3
)
2
L ]NO
3
2
·2H O, which
is consistent with elemental analysis results. Furthermore, the
terbium(III) complex has an endothermic peak at 115°C, which is due
4
70°C, this is consistent with the theoretical contents value
to the decomposition of crystal water molecules, this does not change
[15]
1
1
(
49.53%) of ligand L . Due to the exothermic oxidation of ligand L ,
there exists an exothermic peak at 393°C. There is a weight loss of
.73% at 470–570°C, due to the decomposition of the free nitrate
ion, and there is also a mass loss of 11.92% between 570 and
50°C, which is assigned to the decomposition of the other two coor-
the structure of the terbium(III) complex.
Additionally, it begins to
degrade at 190°C, that indicated the terbium(III) complex possesses
[16]
8
good thermal stability.
6
dinated nitrate ions. This indicated that there was a close connection
to whether the nitrate ion is coordinated to the terbium(III) ions or
not. Up to 800°C, the complex is completely decomposed and the sta-
ble value of the residual is 24.00%, which is consistent with the theo-
3.5
|
The structure of the ligands and their
terbium(III) complexes
According to the results of elemental analysis, UV, IR and thermal
retical value (24.83%) of the rare earth ions oxide (Tb
4
O
7
). The earlier
analysis, the composition and structure of the terbium(III) complexes
1
1–4
analysis indicated that the ligand L coordinated with the terbium(III)
can be confirmed. The formulas of the complexes are [Tb(NO
3
)
2
L
]
−1
TABLE 3 The IR data of the terbium(III) complexes and corresponding ligands (cm
)
3
−
ν (NO
)
Complex
ν(O‐H)
ν(C=O)
ν(N‐C=O)
ν(C=N)
ν
1
ν
2
ν
3
ν
4
ν
1
L
1693
1653
1684
1653
1693
1647
1697
1655
2351
2359
2363
2359
2355
2372
2361
2356
1599
1576
1599
1562
1601
1577
1601
1576
1
[
Tb(NO
3
3
3
3
)
2
)
2
)
2
)
2
L ]NO
3
·2H
3
·2H
3
·2H
3
·2H
2
2
2
2
O
O
O
O
3525
3520
3523
3495
1456
1456
1458
1458
1041
1050
1059
1050
835
827
837
830
1340
1338
1340
1340
1385
1385
1385
1385
2
L
2
[
Tb(NO
L ]NO
3
L
3
[
Tb(NO
L ]NO
4
L
4
[
Tb(NO
L ]NO

6
XIAO ET AL.
FIGURE 3 The thermogravimetric‐differential thermal analysis (TG‐
1
DTA) curve of [Tb (NO
3
)
2
]L NO
3
·2H
2
O
FIGURE 5 The excitation spectrum (a) and emission spectrum (b) of
4
[
Tb(NO
3
)
2
L ]NO ·2H
3 2
O
3 2
NO ·2H O, and the two‐dimensional structure of the ligands and their
terbium(III) complexes can be deduced and are shown in Figure 4.
5
7
5
7
bands, distributed at 496.0 nm ( D
4
→
F
6
), 543.0 nm ( D
4
→
5
F ),
5
7
5
7
5
85.0 nm ( D
4
→
F
4
) and 622.0 nm ( D
4
→
F
3
). The intensity of
3
.6
|
Fluorescence properties analysis
the fluorescence emission peaks of the magnetic dipole transition
5
7
5
7
(
D
4
→ F
6 4 5
) and the electric dipole transition ( D → F ) are stronger
The excitation spectra of the terbium(III) complexes are determined
under the emission wavelength of 545.0 nm, and their fluorescence
spectra data are listed in Table 5. Since the spectra of complexes
than the other two emission peaks, and the emission peak intensity
5
7
5
7
ratio ( D
4
→
F
5
/ D
4
→
F
6
) is 4.40, indicating that the terbium(III)
4
ion of the complex [Tb(NO
3
)
2
L ]NO
3
·2H
2
O is in the asymmetric cen-
1
–4
[
Tb(NO
3
3
)
2
2
L
]NO
3
·2H
2
O are similar, only the spectra (Figure 5) of
ter. The fluorescence intensity order of the four terbium(III) complexes
4
1
2
3
[
Tb(NO
)
L ]NO
3
·2H
2
O is selected for illustration.
is [Tb(NO
3
)
2
L ]NO
3
·2H
2
3 2 3 2 3 2
O > [Tb(NO ) L ]NO ·2H O > [Tb(NO ) L ]
4
It can be seen from Table 5, the four terbium(III) complexes have
different fluorescence excitation peaks, located at 275 nm, 278 nm,
76 nm, 281 nm, respectively, and present four characteristic fluores-
NO ·2H O > [Tb(NO
3
2
3
)
2
L ]NO
3
·2H
1
2
O. Since the planarity of the ben-
zene ring structure of ligand L is stronger, it can form a better rigid
structure with terbium(III) ions; this is suitable to achieve an efficient
ligand‐to‐metal energy transfer, so the terbium ions can be better sen-
sitized and emit characteristic light. This indicated that the fluores-
cence intensity is determined by the efficiency of the intramolecular
energy transfer. The fluorescence emission (antenna effect) is deter-
mined by the energy difference between the three excited states
2
cence emission peaks. As shown in Figure 5, the emission spectrum of
4
complex [Tb(NO
3
)
2
L ]NO
3
2
·2H O consists of four main characteristic
(
ligand) and the lowest excited state (the central ion), and the emission
efficiency is affected by the efficiency of energy transfer. Hence when
the ligand absorbs light energy, it transitions from the ground state to
the emission state, then the energy is transferred to a triplet state of
the ligand by the intersystem crossing, and then intramolecularly
transferred to the rare earth ions. Finally, the rare earth ions return
back to the ground state from the excited state, and emit characteris-
[
17,18]
tic light.
matched better with the energy gap between the
tion, so the emission peak distributed at 546.0 nm is the highest
Since the energy transferred to the terbium ions is
5
7
1–4
4 5
D → F transi-
FIGURE 4 The two‐dimensional ligands L
(a) and their terbium(III)
complexes (b)
TABLE 5 Fluorescence spectra data of the terbium(III) complexes
5
7
5
7
5
7
5
7
D
4
→
F
6
D
4
→
F
5
D
4
→
F
4
4 3
D → F
Complexes
Λ
ex (nm)
λem (nm)
RLI
λ
em (nm)
RLI
λ
em (nm)
RLI
λ
em (nm)
RLI
1
[Tb(NO
[Tb(NO
[Tb(NO
[Tb(NO
3
3
3
3
)
2
)
2
)
2
)
2
L ]NO
3
·2H
3
·2H
3
·2H
3
·2H
2
2
2
2
O
O
O
O
275.0
278.0
276.0
281.0
496.0
492.0
493.0
496.0
383
377
154
83
546.0
544.0
546.0
543.0
1384
1217
848
583.0
585.0
585.0
585.0
63
80
26
26
622.0
621.0
622.0
622.0
23
24
11
11
2
L ]NO
3
L ]NO
4
L ]NO
365
Note: Λex, exciting wavelength; λem, emission wavelength; RLI, relative fluorescence intensity.

XIAO ET AL.
7
1
among the four peaks. As the terbium(III) complexes with ligand L
withdrawing groups to the ligand can decrease the fluorescence quan-
tum yield of the terbium(III) complexes.
achieved an efficient ligand‐to‐metal energy transfer, its fluorescence
intensity, therefore, is the strongest among them.
|
Electrochemical properties analysis
3
.7
|
Fluorescence quantum yield analysis
3
.8
The highest occupied molecular orbital (HOMO) energy levels of the
terbium(III) complexes are obtained according to the equations
Fluorescence quantum yield is measured according to the measure
[19]
proposed by Yunxiang Ci et al.
The fluorescence quantum yields
EHOMO = −(4.74 eV + EOX), where EOX is the starting value of the oxi-
(
Φfx) are calculated using the following equation:
dation potential peak and is measured with ferrocene as standard. The
lowest occupied molecular orbital (LUMO) energy levels of the
2
n
Fx Astd
· · ∅std
x
∅
fx ¼
·
2
std
n
Fstd Ax
terbium(III)
complexes
, where the energy gap (E
g
= 1240/λonset (eV), and λonset is the value of the largest UV absorp-
are
calculated
by
the
formula
ELUMO = EHOMO + E
g
g
) is calculated as
where nstd (1.337) and n
x
(1.480) are the refractive index of the solu-
E
[
20]
tion used for the standard and sample, respectively; the solvent is
tion peak.
The electrochemical properties of the terbium(III) com-
DMSO; F is the integral area of fluorescence; A is the absorbance
plexes are investigated by means of a cyclic voltammetric technique
in the UV spectrum; Astd/A
x
= 1. The fluorescence quantum yield
in DMSO solution. The electrochemical data are listed in Table 7,
1
of the standard solution is 0.55 (Фfstd = 0.55). The fluorescence quan-
tum yield data of all the terbium(III) complexes are summarized in
Table 6.
and only the cyclic voltammetry curve of complex [Tb(NO
3
)
2
L ]
NO ·2H O is selected and depicted in Figure 6.
3
2
As shown in Table 7 and Figure 6, the order of the oxidation
2
As shown in Table 6, the order of fluorescence quantum yield of
potential (Eox) of the terbium(III) complexes is [Tb(NO
3
)
2
L ]NO
·2H
3 2
O
1
1
4
3
the terbium(III) complexes is as follows: [Tb(NO
3
)
2
L ]NO
3
·2H
2
O >
> [Tb(NO
NO ·2H O, the order of the HOMO energy level (EHOMO
[Tb(NO
NO ·2H
gap (E
NO ·2H
[Tb(NO
3
)
2
L ]NO
3
·2H
2
O > [Tb(NO
3
)
2
L ]NO
3
·2H
2
O > [Tb(NO
3
)
2
L ]
2
3
4
[
Tb(NO
3
)
2
L ]NO
3
·2H
2
O
>
[Tb(NO
3
)
2
L ]NO
3
·2H
2
O > [Tb(NO
3
)
2
L ]
3
2
)
is
3
4
1
NO ·2H
3
2
O. The fluorescence emission (antenna effect) is determined
3
)
2
L ]NO
3
·2H
2
O > [Tb(NO
3
)
2
L ]NO
3
·2H
2
O > [Tb(NO
3
)
2
L ]
2
by the energy difference between the triplet state of the ligand and
the lowest excited state of the central ion. Since the rigidity of the
3
2
O > [Tb(NO
3
)
2
L ]NO
3
·2H
2
O, and the order of the energy
1
g
) and the LUMO energy level (ELOMO) are [Tb(NO
3
)
2
L ]
1
3
2
benzene ring structure of ligand L is strongest among the ligands, it
3
2
O > [Tb(NO
3
)
2
L ]NO
3 2 3 2 3 2
·2H O > [Tb(NO ) L ]NO ·2H O >
4
can form a rigid structure with the terbium ion, so the energy transfer
efficiency is the highest among the terbium(III) complexes. Thus, the
terbium(III) ion can be better sensitized and its fluorescence quantum
yield is the highest. This indicated that the fluorescence quantum yield
is related to the planarity of the molecules. Furthermore, the emission
efficiency is also affected by the substituent group. Compared to the
furan and thiophene, the pyridine ring is an electron deficient hetero-
cyclic compound. Therefore, since the electron‐donating group can
produce a p‐π conjugation with the benzene ring and enhance the π
conjugation, the fluorescence intensity is enhanced and the fluores-
3
)
2
L ]NO
3
·2H
2
O. In the pyridine ring, five carbon atoms and
one nitrogen atom can provide a single electron p orbital, respectively,
and form a conjugated system. However, the electronegativity of the
nitrogen atom is larger than that of the carbon, and nitrogen is
electron‐withdrawing compared to CH. Therefore, the pyridine ring
2
is an electron deficient heterocyclic compound. When ligand L coor-
dinated to terbium ion, the electron cloud density of terbium(III) ion is
small and the complex finds it difficult to lose electrons, the oxidation
potential is increased and the HOMO energy level is decreased. Since
2
the nitrogen and oxygen atoms of furan and thiophene are in the sp
cence quantum yield is increased. Hence the fluorescence quantum
hybrid state, and a five atom or six atom π electron conjugated system
2
yield of the complex [Tb(NO
3
)
2
L ]NO
3
2
·2H O is the second highest
can be formed, respectively, they are electron rich aromatic systems.
3
4
among them. On the contrary, the electron‐withdrawing groups have
π electrons and cannot form a conjugation with the benzene ring,
and the intersystem crossing is increased, so the fluorescence inten-
sity and the fluorescence quantum yield are decreased. The earlier
mentioned results revealed that the introduction of electron‐donating
groups to the ligand can increase the fluorescence quantum yield of
the terbium(III) complexes and the introduction of electron‐
When L or L coordinated to the terbium ion, the electron cloud den-
sity of the terbium ion is increased, and the complex easily loses elec-
trons, so the oxidation potential is decreased and the HOMO energy
level is increased. Therefore, the oxidation potential of complexes
2
[Tb(NO
3
)
2
L ]NO
3
·2H
2
O is the highest and the HOMO energy level
is the lowest. This indicated that the oxidation properties, the HOMO
energy level and the energy gap of the terbium(III) complexes are
TABLE 6 The fluorescence quantum yields of the terbium(III)
TABLE 7 The electrochemical data of the terbium(III) complexes
complexes
Λ
onset
E
ox
E
g
E
HOMO
E
LUMO
Complex
λ (nm)
I (a.u.)
Ф
fx
Complex
(nm)
(eV)
(eV)
(eV)
(eV)
1
1
[Tb(NO
[Tb(NO
[Tb(NO
[Tb(NO
3
3
3
3
)
2
)
2
)
2
)
2
L ]NO
3
·2H
3
·2H
3
·2H
3
·2H
2
2
2
2
O
O
O
O
316.0
311.0
304.0
313.0
186
157
120
108
0.132
0.110
0.084
0.076
[Tb(NO
[Tb(NO
[Tb(NO
[Tb(NO
3
)
3
)
3
)
3
)
2
2
2
2
L ]NO
3
3
3
3
·2H
·2H
·2H
·2H
2
O
2
O
2
O
2
O
278
288
284
304
0.581
0.591
0.564
0.574
4.46
4.30
4.37
4.08
−5.321
−5.331
−5.304
−5.314
−0.861
−1.031
−0.934
−1.234
2
2
L ]NO
L ]NO
3
3
L ]NO
L ]NO
4
4
L ]NO
L ]NO

8
XIAO ET AL.
ACKNOWLEDGEMENTS
The authors are grateful for the financial support of the National Nat-
ural Science Foundation of China (No. J1103312; No.J1210040;
No.21341010), the Natural Science Foundation of Hunan Province
(
(
No.11JJ5005), Hunan Provincial Science and Technology Department
No.2016SK2064), Changsha Science and Technology Bureau (No.
kq1701029; No.kq1701164), the Innovative ResearchTeam in Univer-
sity (No.IRT1238), China Outstanding Engineer Training Plan for Stu-
dents of Chemical Engineering and Technology in Hunan University
(
MOE‐No.2011‐40), and the instrument sharing platform of Hunan
University. The authors also thank Dr William Hickey, the US profes-
sor of HRM, for the English editing on this article.
ORCID
Dongcai Guo https://orcid.org/0000-0001-9975-319X
1
3 2 3 2
FIGURE 6 The cyclic voltammetry curves of [Tb(NO ) L ]NO ·2H O
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13
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[
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L
3 2
]NO ·2H O. The thermal analysis results showed that
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1
showed that the terbium(III) complexes with ligand L possessed the
[
[
[
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How to cite this article: Xiao R, Huang W, Xiao X, Liu Y, Guo
D. Novel salicyloylhydrazone derivatives and corresponding
terbium(III) complexes: synthesis and properties research.
Luminescence. 2018;1–8. https://doi.org/10.1002/bio.3583