Synthesis, characterization and properties of salicylhydrazide-salicylacylhydrazone derivatives and their terbium complexes

Article abstract of DOI:10.1002/bio.2989

A series of terbium complexes with salicylhydrazide-salicylacylhydrazone derivatives were synthesized and characterized by elemental analysis, IR spectra, UV/vis spectra and thermal analysis. The luminescence and electrochemical properties of the terbium complexes were investigated. The results show that all the target complexes exhibited characteristic emissions of terbium ions and the complex substituted by the chlorine has the strongest luminescence intensity with the highest quantum yield at 0.609. The introduction of donating electron groups could increase the oxidation potential and the highest occupied molecular orbital energy level of the terbium complex; however, the introduction of accepting electron groups gave the opposite result.

Full text of DOI:10.1002/bio.2989

Research article
Received: 12 January 2015,
Revised: 02 July 2015,
Accepted: 03 July 2015
Published online in Wiley Online Library: 18 September 2015
(wileyonlinelibrary.com) DOI 10.1002/bio.2989
Synthesis, characterization and properties of
salicylhydrazide–salicylacylhydrazone
derivatives and their terbium complexes
Defen Meng,a Fen Liu,a Yingying Li,a Zehui Yang,b Guizhi Lia
and Dongcai Guoa*
ABSTRACT: A series of terbium complexes with salicylhydrazide–salicylacylhydrazone derivatives were synthesized and charac-
terized by elemental analysis, IR spectra, UV/vis spectra and thermal analysis. The luminescence and electrochemical properties
of the terbium complexes were investigated. The results show that all the target complexes exhibited characteristic emissions of
terbium ions and the complex substituted by the chlorine has the strongest luminescence intensity with the highest quantum
yield at 0.609. The introduction of donating electron groups could increase the oxidation potential and the highest occupied mo-
lecular orbital energy level of the terbium complex; however, the introduction of accepting electron groups gave the opposite
result. Copyright © 2015 John Wiley & Sons, Ltd.
Keywords: terbium complexes; salicylacylhydrazone derivatives; synthesis; luminescence; electrochemical properties
1H NMR spectra were recorded in dimethyl sulfoxide (DMSO)-d6/
deuterated chloroform (CDCl3) on a Bruker AV-400 spectrometer
Introduction
N-Acylhydrazones, which are readily obtained by the condensation
(Bruker Corporation, Germany) with Tetramethylsilane (TMS) as an
of aldehydes or ketones and acylhydrazines in the presence of an
internal standard. Mass spectra (MS) were measured with the
acid catalyst, represent a class of azomethine compounds (1). N-
MAT95XP mass spectrometer. Infrared (IR) spectra (400–4000
cmꢀ1) were obtained in KBr discs using a Perkin–Elmer Spectrum
Acylhydrazones, which include the fragment (–CO–NH–N=CH–),
have been the subject of much interest in recent years because of
One (PerkinElmer Inc, USA). UV/vis spectra (190–450 nm) were
their biological properties as well as their chelating properties
recorded using a LabTech UV-2100 spectrophotometer (LabTech
toward metal ions (2). In addition, acylhydrazones have a number
Company, USA), with DMSO as the solvent and reference. Elemental
of metal-binding sites and can act as neutral or monoanionic
analysis of the complexes was carried out on a VarioEL 111 (Germany)
bidentate or tridentate ligands, depending on the substituents
CHNS analyser. The melting points of all compounds were
and the reaction conditions, making them attractive as ligands (3).
determined on an X-4 binocular microscope. Thermal gravimetric
Investigation of the luminescence enhancement of terbium ions in
analysis was carried out on a NETZSCH STA 409PC thermal
the presence of Schiff bases is of special interest, because terbium
gravimetric analyser (NETZSCH company, Germany). The
complexes with Schiff bases are frequently used as structural and
luminescence spectra were measured by using powder samples
functional probes in biological systems and have technological appli-
cations in lasers, sensors and electroluminescent displays (4–7).
In this study, salicylhydrazide–salicylacylhydrazone derivatives
and their corresponding terbium complexes were synthesized and
on a HIACHI F-2700 luminescence spectrophotometer (HIACHI,
Japan) at room temperature. Molar conductance was measured
by DDS-12A conductivity instrument. The terbium ions were
determined by ethylenediaminetetraacetic acid (EDTA) titration
characterized. The fluorescence properties and fluorescence quan-
using xylenol orange as an indicator. Cyclic voltammetry curves
tum yields of the target complexes were studied. The relationship
were tested using three electrodes including a glassy electrode,
between the structure of the ligands and the electrochemical
properties of the terbium complexes are also discussed in detail.
The synthetic route for salicylhydrazide–salicylacylhydrazone
* Correspondence to: D. Guo, School of Chemistry and Chemical Engineering,
derivatives is shown in Scheme 1.
Hunan University, Changsha 410082, China. E-mail: dcguo2001@hnu.edu.cn
[Corrections added on 2 February 2016, after first online publication: Citations
for Figures 1 to 8 have been corrected throughout the article to match their
Experimental
corresponding Figures.]
Materials and methods
a
School of Chemistry and Chemical Engineering, Hunan University, Changsha
Terbium nitrate was prepared according to the literature (8). Ani-
410082, China
line and its derivatives were of chemical grade. Methyl salicylate
and other reagents were of analytical grade and were purchased
from commercial suppliers.
b
School of Chemical Engineering, Ningbo University of Technology, Ningbo
315016, China
Luminescence 2016; 31: 507–514
Copyright © 2015 John Wiley & Sons, Ltd.

D. Meng et al.
Scheme 1. Synthetic route for salicylhydrazide-salicylacylhydrazone derivatives. [Correction added on 2 February 2016, after first online publication: Figure 9 has been relabeled
as Scheme 1 to match the citation.]
a platinum electrode and a saturated calomel electrode, with
ferrocene as the external standard; nitrite solution was used as
the supporting electrolyte and DMSO as the solvent, the test
scanning speed was 100 mV/s and the sensitivity was 1 mA.
poured into saturated sodium acetate solution (300 mL) to give a
mass of white solid and then filtered. The residue was recrystallized
from the mixed solution of absolute alcohol and water (1: 2, v/v) to
obtain the compound 3a. The synthetic procedures for 3bꢀd are
similar to that of 3a.
2-Chloro-N-phenylacetamide (3a) a white solid. Yield: 68%. 1H NMR
(400 MHz, DMSO-d6), δ/ppm: 10.29 (s, 1H, NH), 7.77–7.47 (m, 2H, ArH),
7.40–7.22 (m, 2H, ArH), 7.18–6.95 (m, 1H, ArH), 4.25 (s, 2H, CH2). MS (EI)
m/z (%): 172 (M+3, 3), 171 (M+2, 25), 169 (M, 80), 121 (3), 120 (40), 106
(7), 94 (10), 93 (100), 77 (22), 65 (28).
Preparation of intermediates
Preparation of compound 2. The preparation of salicylhydrazide–
salicylacylhydrazone was according to the literature (9). To a
solution of methyl salicylate (0.1 mol, 13.81 g) in absolute alcohol
(30 mL) in a 150 mL three-neck flask was added hydrazine hydrate
(30 mL 80%). The reaction mixture was then heated to reflux for 4
h. Next, the excess absolute alcohol was completely removed
under reduced pressure. The residue was recrystallized from water
to give compound 1 and was used for the next reaction directly
without further purification.
A solution of compound 1 (0.02 mol, 3.04 g) in absolute alcohol
(30 mL) was heated to boiling with stirring, then salicylaldehyde
(0.02 mol, 2.12 g) dissolved in absolute alcohol (15 mL) was added
to it dropwise. The reaction mixture was refluxed for 6 h, then
cooled to room temperature and filtered. The residue was recrys-
tallized from absolute alcohol to give a yellow solid.
2-Chloro-N-(4-chlorophenyl)acetamide (3b) a white solid. Yield:
94%. 1H NMR (400 MHz, DMSO-d6), δ/ppm: 7.67–7.57 (m, 2H, ArH),
7.46–7.34 (m, 2H, ArH), 4.26 (s, 2H, CH2). MS (EI) m/z (%): 207
(M+3, 5),205 (M+1, 33), 203 (M–1, 52), 156 (4), 154 (13), 129 (32),
127 (100), 126 (15), 111 (5), 99 (14), 77 (5), 63 (7).
2-Chloro-N-p-tolyacetamide (3c) a faint yellow solid. Yield: 78%.
1H NMR (400 MHz, DMSO-d6), δ/ppm: 10.21 (s, 1H, NH), 7.42–7.46
(m, 2H, ArH), 7.16–7.18 (m, 2H, ArH), 4.22 (s, 2H, CH2), 2.21 (s, 3H,
CH3). MS (EI) m/z (%): 186 (M+3, 3), 185 (M+2, 25), 183 (M, 75), 148
(4), 134 (27), 107 (100), 106 (76), 91 (16),77 (26), 51 (10).
2-Chloro-N-(4-methoxyphenyl)acetamide (3d) a faint purple solid.
Yield: 53%. 1H NMR (400 MHz, DMSO-d6), δ/ppm: 10.18 (s, 1H, NH),
7.54–7.48 (m, 2H, ArH), 6.95–6.87 (m, 2H, ArH), 4.22 (s, 2H, CH2),
3.73 (s, 3H, CH3). MS (EI) m/z (%): 202 (M+3, 3), 201 (M+2, 32), 199
(M, 100), 124 (29), 123 (72), 108 (72), 95 (13), 80 (6).
Salicylhydrazide–salicylacylhydrazone (2) Yield: 96%. 1H NMR
(400 MHz, DMSO-d6), δ/ppm: 6.92–7.01 (m, 4H, ArH), 7.32 (d, 1H,
ArH), 7.46 (d, 1H, ArH), 7.58 (dd, 1H, ArH), 7.90 (dd, 1H, ArH), 8.69
(s, 1H, NH), 11.20 (s, 1H, CH=N), 11.78 (s, 1H, OH), 12.05 (s, 1H, OH).
MS (EI) m/z (%): 264 (M+18, 3), 257 (M:1, 5), 256 (M, 33), 137
(M–119, 36), 121 (M–119–16, 100), 120 (40), 93 (15), 65 (15).
Preparation of La–d
.
To the solution of compound 2 (3 mmol, 0.77 g)
in N,N-dimethylformamide (40 mL) was added sodium hydrate
(6 mmol, 0.24 g). The mixture was heated to 80°C and stirred
for 1.5 h in a 150 mL three-neck flask. A solution of compound
3a (6.6 mmol, 1.12 g) and potassium iodide (3.3 mmol, 0.55 g)
in N,N-dimethylformamide (30 mL) was added dropwise to the
flask. The reaction mixture was stirred for 20 h at 80°C. Next,
the residue was poured into 150 mL of distilled water and
Preparation of compound 3a–d
.
A solution of aniline (0.066 mol,
6.15 g) in glacial acetic acid (40 mL) was added to a 150 mL
three-neck flask. Then 2-chloride-acetyl chloride (0.074 mol, 8.36
g) was added dropwise to the flask in an ice water bath. The
reaction mixture was stirred for 30 min in the ice water bath and
for another 1 h at room temperature. The resulting mixture was
wileyonlinelibrary.com/journal/luminescence
Copyright © 2015 John Wiley & Sons, Ltd.
Luminescence 2016; 31: 507–514

Synthesis and luminescence properties of terbium complexes
stirred for 30 min to give a mass of precipitate. The precipitate
was collected by filtration, washed with water and recrystallized
from a mixed solution of absolute alcohol and chloroform (1: 3,
v/v) to give La. The synthetic procedures for Lbꢀd are similar to
that for La.
A yellow power. Yield: 56%. M.p.: 252 °C. 1H NMR (400 MHz,
DMSO-d6), δ/ppm: 11.34 (s, 1H, CH=N), 8.38 (s, 1H, NH), 7.72 (d, J
= 8.3 Hz, 2H, ArH), 7.43 (dd, J = 15.9, 7.8 Hz, 6H, ArH), 7.34 (dd, J =
15.4, 8.4 Hz, 2H, ArH), 724 (s, 2H, NH), 7.17–7.08 (m, 1H, ArH),
7.04–6.95 (m, 1H, ArH), 6.85 (dt, J = 15.9, 10.5 Hz, 2H, ArH), 6.78 (d,
J = 7.9 Hz, 2H, ArH), 4.63 (s, 4H, CH2), 3.72 (s, 6H, CH3). IR (KBr)
v/cmꢀ1: 3394, 3063, 2911, 2834, 1659, 1602, 1582, 1509, 1454,
1240, 1056, 827. MS (EI) m/z (%): 582 (M, 12), 419 (M–15–16–76–
15, 8), 300 (12), 284 (41), 256 (22), 207 (12), 177 (6), 134 (26), 121
(100), 106 (48), 91 (42), 77 (20). Anal. calcd for C32H30N4O7: C, 65.97;
H, 5.19; N, 9.62; O, 19.22. Found: C, 65.94; H, 5.22; N, 9.67.
(E)-2-(2-((2-(2-(2-Oxo-2-(phenylamino)ethoxy)benzoyl)
hydrazono)methyl)phenoxy)-N-phenylacetamide (La) an earthy
yellow power. Yield: 85%. m.p.: 218°C. 1H NMR (400 MHz,
DMSO-d6), δ/ppm: 11.21 (s, 1H, CH=N), 8.68 (s, 1H, NH), 7.94–
7.87 (m, 4H, ArH), 7.82 (dt, J = 12.8, 6.4 Hz, 2H, ArH), 7.70 (t, J
= 7.8 Hz, 4H, ArH), 7.53 (s, 2H, NH), 7.33 (ddd, J = 16.8, 12.3,
6.2 Hz, 4H, ArH), 7.26–7.10 (m, 4H, ArH), 4.98 (s, 4H, CH2). IR
(KBr) v/cmꢀ1: 3416, 3057, 2920, 2857, 1651, 1605, 1550, 1484,
1446, 1239, 1056, 827, 745, 689. MS (EI) m/z (%): 523 (M+1,
2), 522 (M, 10), 389 (M–77–15–28–13, 10), 270 (11), 254 (17),
226 (20), 177 (8), 134 (22), 121 (100), 106 (50), 93 (45), 77 (18).
Anal. calcd for C30H26N4O5: C, 68.95; H, 5.02; N, 10.72; O,
15.31. Found: C, 68.92; H, 5.06; N, 10.71.
Preparation of terbium complexes. A solution of compound La
(0.5 mmol, 0.26 g) in chloroform (30 mL) was heated to reflux,
and then terbium nitrate in absolute alcohol (5 mL) was added
to produce a precipitate. The reaction mixture was then refluxed
for 4 h. The solid product was filtered, washed with chloroform
several times, and dried under vacuum to give a complex with
ligand La. The synthetic procedures for other complexes with
ligands Lbꢀd are similar to that for complex with ligand La.
(E)-N-(4-Chlorophenyl)2-(2-((2-(2-(2-(4-chlorophenylamino)-2-
oxoethoxy)benzoyl)hydrazono)methyl)phenoxy)acetamide (Lb)
a terreous power. Yield: 89%. m.p.: 235°C. 1H NMR (400 MHz,
DMSO-d6), δ/ppm: 11.34 (s, 1H, CH=N), 8.97 (s, 1H, NH), 8.77 s,
1H, ArH), 8.08 (dd, J = 29.2, 8.3 Hz, 5H, ArH), 7.64–7.53 (m, 8H,
ArH), 7.43 (s, 2H, NH), 7.02 (dd, J = 18.9, 7.9 Hz, 2H, ArH),
4.32 (s, 4H, CH2). IR (KBr) v/cmꢀ1: 3402, 3042, 2918, 2856,
1658, 1604, 1575, 1494, 1453, 1246,1049, 820. MS (EI) m/z (%):
608 (M+18, 1), 591 (M+1, 2), 590 (M, 8), 464 (M–35–76–15, 10),
423 (15), 304 (21), 288 (44), 260 (24), 211 (10), 177 (8), 134 (24),
121 (100), 106 (48), 91 (36), 77 (18). Anal. calcd for
C30H24Cl2N4O5: C, 60.92; H, 4.09; Cl, 11.99; N, 9.47; O, 13.53.
Found: C, 60.95; H, 4.11; Cl, 11.97; N, 9.44.
Results and discussion
Properties of terbium complexes
Analytical data for terbium complexes, presented in Table 1,
indicate that the target complexes conform to a 1: 1 metalto-
ligand stoichiometry [TbLa–d(NO3)2](NO3). Ligands Laꢀd are soluble
in DMSO and N,N-dimethylformamide, slightly soluble in chloro-
form, and insoluble in ethyl ether and benzene, whereas the
terbium complexes are only soluble in DMSO and N,N-
dimethylformamide. The molar conductance data of the target
complexes in acetone solution are in the range of 107ꢀ131
S·cm2/mol, which indicates that the complexes are 1: 1 ionic com-
plexes (10).
(E)-2-(2-((2-(2-(2-Oxo-2-(p-tolylamino)ethoxy)benzoyl)
hydrazono)methyl)phenoxy)-N-p-tolyacetamide (Lc) a brown
power. Yield: 84%. m.p.: 239°C. 1H NMR (400 MHz, CDCl3),
δ/ppm: 11.46 (s, 1H, CH=N), 8.84 (s, 1H, NH), 7.49 (dd, J = 10.0,
3.7 Hz, 4H, ArH), 7.42 (m, 2H, NH), 7.34 (dd, J = 15.0, 8.0 Hz, 4H,
ArH), 7.13 (dd, J = 11.6, 9.1 Hz, 4H, ArH), 7.00 (dd, J = 14.3, 8.4
Hz, 2H, ArH), 6.85 (dd, J = 8.6, 3.3 Hz, 1H, ArH), 6.78 (d, J = 7.9
UV/vis spectra analysis
The UV/vis absorption spectra of the terbium complexes and
corresponding ligands were carried out in DMSO at room tem-
perature. The numerical values of the maximum absorption
wavelength (λmax) are listed in Table 2. Because the UV/vis spec-
tra of all the complexes are similar, only the UV/vis spectra of
[TbLa(NO3)2]NO3 and [TbLc(NO3)2]NO3 and their corresponding
ligands La and Lc are selected, as shown in Figs 1 and 2,
respectively.
Absorption of the terbium complexes and ligands is charac-
terized by two main absorption bands in the region 275–400
nm. The bands at 290 and 285 nm for La and Lc, respectively,
are attributed to the π→π* transitions, and the bands at 326
Hz, 1H, ArH), 4.64 (s, 4H, CH2), 3.49 (s, 6H, CH3). IR (KBr) v/cmꢀ1
:
3421, 3056, 2913, 2866, 1647, 1602, 1541, 1485, 1453, 1246,
1056 816. MS (EI) m/z (%): 568 (M+18, 1), 551 (M+1, 2), 550 (M,
6), 444 (M-15-76-15, 3), 403 (18), 284 (25), 268 (43), 240 (27),
227 (2), 209 (7), 191 (3), 177 (6), 134 (26), 121 (100), 106 (42),
91 (24), 77 (19). Anal. Calcd. for C32H30N4O5: C, 69.80; H, 5.49;
N, 10.18; O, 14.53. Found: C, 69.84; H, 5.51; N, 10.16.
(E)-N-(4-methoxyphenyl)2-(2-((2-(2-(2-(4ꢀmethoxyphenylamino)
-2-oxoethoxy)benzoyl)hydrazono)methyl)phenoxy)acetamide (Ld)
Table 1. Elemental analysis and molar conductance data of terbium complexes
Complex
Found (Calculated) (%)
Λm (acetone)
C
H
N
Tb
(S·cm2/mol)
[TbLa(NO3)2](NO3)
[TbLb(NO3)2](NO3)
[TbLc(NO3)2](NO3)
[TbLd(NO3)2](NO3)
44.69 (44.73)
41.23 (41.21)
46.09 (46.11)
44.38 (44.41)
3.27 (3.25)
2.81 (2.77)
3.64 (3.63)
3.45 (3.49)
10.49 (10.43)
9.66 (9.61)
10.06 (10.08)
9.77 (9.71)
17.96 (17.93)
18.15 (18.18)
18.33 (18.36)
18.34 (18.36)
131
114
107
119
Luminescence 2016; 31: 507–514
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/luminescence

D. Meng et al.
and 318 nm for La and Lc, respectively, are attributed to the
n→π* transitions. The UV/vis spectra of [TbLa(NO3)2]NO3 and
[TbLc(NO3)2]NO3 were similar to those of the free ligands La
and Lc. The only difference is that the first strong absorption
shifted to 292 and 287 nm, and the second strong absorption
shifted to 328 and 321 nm, respectively. This is because the in-
troduction of terbium ions enlarged the ligand’s conjugated sys-
tem, which indicates that the nitrogen atom of the C=N group
and the oxygen atom of the C=O group of La and Lc are coor-
dinated successfully to the central terbium ions (11).
Table 2. UV data of terbium complexes and corresponding
ligands
Complex
λ
max (nm)
Ligand
λmax (nm)
[TbLa(NO3)2]NO3
[TbLb(NO3)2]NO3
[TbLc(NO3)2]NO3
[TbLd(NO3)2]NO3
292, 328
288, 318
287, 321
288, 314
La
Lb
Lc
Ld
290, 326
289, 321
285, 318
289, 316
IR spectra analysis
The most significant frequencies in the IR spectral data of the
ligands and their corresponding terbium complexes are presented
in Table 3. Because the IR spectra of all the complexes are similar,
only the IR spectra of [TbLb(NO3)2]NO3 and [TbLc(NO3)2]NO3 and
their corresponding ligands Lb and Lc are selected (Figs 3 and 4,
respectively) for illustration.
The characteristic absorption bands of the free ligands Lb and Lc
due to ν(C=N) appear at 1604 and 1602 cmꢀ1, respectively, which
shift ~ 9 and 6 cmꢀ1, respectively, to higher wave numbers after
the formation of the complexes, suggesting that the nitrogen
atom of the C=N group participates in coordination to the terbium
ions (12). The characteristic absorption bands of Lb and Lc due to
ν(N–C=O) appear at 1658 and 1647 cmꢀ1, respectively, which is
shifted by ~ 21 and 13 cmꢀ1, respectively, to lower wave numbers
after the formation of the complexes, indicating that the oxygen
atom of the N–C=O group takes part in coordination to the
Figure 1. UV/vis spectra of (a): [TbLa(NO3)2]NO3 and (b): La.
Figure 2. UV/vis spectra of (a) [TbLc(NO3)2]NO3 and (b) Lc.
Figure 3. IR spectra of (a) [TbLb(NO3)2]NO3 and (b) Lb.
Table 3. IR data of terbium complexes and corresponding ligands
–1
Compound
νNH
νAr–H
νAr–C=C
νC=N
νN–C=O
νAr–O–C
ν
NO3
La
3416
3426
3402
3397
3421
3412
3394
3390
3057
3064
3042
3047
3056
3059
3063
3057
1550, 1484
1549, 1485
1575, 1494
1539, 1488
1541, 1485
1542, 1491
1582, 1509
1548 1502
1605
1618
1604
1613
1602
1608
1602
1610
1651
1639
1658
1637
1647
1634
1659
1648
1239
1248
1246
1249
1246
1249
1240
1253
[TbLa(NO3)2]NO3
1479, 1369, 1033, 835
1474, 1350, 1038, 818
1480, 1358, 1013, 826
1477, 1362, 1022, 836
Lb
[TbLb(NO3)2]NO3
Lc
[TbLc(NO3)2]NO3
Ld
[TbLd(NO3)2]NO3
wileyonlinelibrary.com/journal/luminescence
Copyright © 2015 John Wiley & Sons, Ltd.
Luminescence 2016; 31: 507–514

Synthesis and luminescence properties of terbium complexes
Figure 5. TG-DSC curve of [TbLa(NO3)2]NO3.
Figure 4. IR spectra of (a) [TbLc(NO3)2]NO3 and (b) Lc.
Luminescence properties analysis
terbium ions (13). The characteristic absorption bands of Lb and Lc
due to ν(Ar–O–C) both appear at 1246 cmꢀ1, which does not shift
obviously in the complexes, indicating that the oxygen atom of the
Ar–O–C group does not coordinate to the terbium ions.
The characteristic frequencies of the coordinating nitrate groups in
[TbLb(NO3)2]NO3 and [TbLc(NO3)2]NO3 appear at about 1474 (υ1),
1350 (υ4), 1038 (υ2) and 818 cmꢀ1 (υ3), and 1480 (υ1), 1358 (υ4),
1013 (υ2) and 826 cmꢀ1 (υ3), respectively. The difference between
the two highest frequency bands (|υ1–υ4|) of [TbLb(NO3)2]NO3 and
[TbLc(NO3)2]NO3 are ~ 124 and 122 cmꢀ1, respectively, indicating that
the coordinated nitrate groups in the complexes are bidentate (14).
Meanwhile, there is a free nitrate group in the complexes, in agree-
ment with the results of the conductivity experiment.
The luminescence characteristics of terbium complexes in the solid
state were measured at room temperature. The fluorescence spec-
tral data of [TbLa–d(NO3)2]NO3 are listed in Table 5. The excitation
and emission spectra of [TbLb(NO3)2]NO3 are shown in Figs 6 and
7, respectively.
The efficiency of energy transfer from ligand to central ions (the
antenna effect) is a key factor in achieving characteristic rare earth
fluorescence (15). It is shown in Table 5 that all the target com-
plexes present luminescence characteristic of terbium ions. This
indicated that all the ligands were comparatively good organic
chromophores to absorb and transfer energy to the terbium ions.
The relative luminescence intensity of the complexes is related to
the efficiency of intramolecular energy transfer between the triple
levels of the ligand and the emitting level of the rare earth ion,
which depends on the energy gap between the two levels (16).
As is shown in Fig. 7, excited at 368 nm, the characteristic emis-
sion spectra of the complex [TbLb(NO3)2]NO3 consist of four main
bands at ~ 492 nm (5D4→7F6), 545 nm (5D4→7F5), 585 nm
(5D4→7F4) and 623 nm (5D4→7F3). Meanwhile, there is no emission
spectra observed for ligand Lb, which means that the energy trans-
ferred from the excited triplet state of Lb to the vibrational state of
the terbium ions is efficient and ligand Lb is an efficient sensitizer
for the luminescence of terbium ions (17).
Thermal analysis
The thermal behaviour of the terbium complexes was investigated by
thermal analysis (Table 4). Thermogravimetric (TG) curves and Differ-
ential scanning calorimetry (DSC) for the target complexes were ob-
tained in nitrogen atmosphere between 20 and 800°C. Because the
four complexes present similar thermal behaviour, we give only the
TG-DSC curve of [TbLa(NO3)2]NO3 (Fig. 5) as examples for illustration.
As is shown in Fig. 5, there is no loss of mass from 20 to 150°C,
which means that no crystal water molecule exits in the complex
[TbLa(NO3)2]NO3. The appearance of small exothermic peak on
the DSC curve around 295°C corresponds to the loss of the outside
nitrate molecule, and the weight loss percentage at 7.01% is close
to the calculated value of 7.15%. A further increase of temperature
to 417°C leads to decomposition of the organic ligand with a
weight loss of 60.79%, which is consistent with the calculated
value of 60.20%. Further enhancement of the temperature to
591.6°C leads to the decomposition of two internal nitrate mole-
cules with a weight loss of 14.05% (calculated value 14.30%). The
final residue of 22.73% corresponds to Tb2O3.
5
5
The intensity ratio of the D4→7F5 transition to the D4→7F6
transition is widely used as a measure of the coordination state
and the site symmetry of the terbium ion, because the emission
5D4→7F6 is independent of the ligand environment, and primarily
magnetic dipole in character, whereas the emission 5D4→7F5 is es-
sentially purely electric dipole in character, and its intensity is very
sensitive to the crystal field symmetry. In the complex [TbLb(NO3)2]
NO3, the transition 5D4→7F5 is the strongest of all the transitions
and is ~ 2.47 times the strength of the transition of 5D4→7F6. The
results show that the terbium ion has the lower symmetric coordi-
nation environment (18).
Table 4. Thermogravimetric data of terbium complexes
Complex
NO3 (lost)
Ligand (lost) (calcd)(%)
Residue (calcd)(%)
[TbLa(NO3)2]NO3
[TbLb(NO3)2]NO3
[TbLc(NO3)2]NO3
[TbLd(NO3)2]NO3
21.06 (21.45)
19.18 (19.89)
19.98 (20.78)
19.75 (20.06)
60.79 60.20)
63.69 (63.10)
60.15 (61.45)
62.49 (62.80)
22.73 (21.09)
20.82 (19.56)
21.25 (20.44)
20.97 (19.74)
Luminescence 2016; 31: 507–514
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/luminescence

D. Meng et al.
Table 5. Luminescence spectral data of terbium complexes
Complex
λex
(nm)
5D4→7F6
em (nm)
5D4→7F5
em (nm)
5D4→7F4
em (nm)
5D4→7F3
λ
I (a.u.)
λ
I (a.u.)
λ
I (a.u.)
λ
em (nm)
I (a.u.)
[TbLa(NO3)2]NO3
[TbLb(NO3)2]NO3
[TbLc(NO3)2]NO3
[TbLd(NO3)2]NO3
368
368
368
368
491
491
491
837.4
1781
454
544.5
545
545
2709
4405
1218
1389
585.5
586
585
165.6
257
72.06
81.03
625
625
625
625
48.43
79.8
19.07
25.12
491.5
509
545
585.5
state energy level of the ligand and the resonance level of rare
earth cannot be too large or too small. As shown in Table 5, among
the four complexes, the complex substituted by the chlorine (–Cl)
has the strongest luminescence intensity. This may be ascribed to
the triplet level of the ligand Lb being lowered by the accepting
electron group, thus the triplet state energy level of the ligand ap-
proaches the resonance level of the terbium ions, which makes the
energy transition from ligands to terbium ions more easy. The lu-
minescence intensities of the complexes [TbLc,d(NO3)2]NO3 are
weaker than that of the complex [TbLa(NO3)2]NO3. This probably
results from the introduction of donating electron groups (–CH3
and –OCH3, respectively), which increase the triplet energy level
of ligands Lc and Ld, so the triplet energy level is far from the low-
est resonance level of terbium ions and the efficiency of the intra-
molecular energy transfer from the triplet state of the ligand to the
resonance state of terbium ions is decreased.
Figure 6. Excitation spectrum of [TbLb(NO3)2]NO3.
Fluorescence quantum yields analysis
The fluorescence quantum yields (Φfx) of the terbium complexes
were determined using a sulfuric acid solution (0.1 mol/L) of qui-
nine sulfate (1.0 μg/mL) with a known quantum yield (Φfstd
=
0.55) as a standard reference at room temperature because of
the similarly between its absorption and fluorescent spectra and
those of the target complexes. The fluorescence quantum yields
(Φfx) are calculated by a comparative method (19) using the fol-
lowing equation:
n2X FX Astd
ΦfX
¼
ꢁ
ꢁ
ꢁΦfstd
n2std Fstd AX
where nx (1.48) and nstd (1.34) are the refractive indices of solvents
used for the sample and standard. Fx and Fstd are the areas under
the fluorescence curves of the sample and standard. Ax and Astd
are the absorbances of the sample and standard at the excitation
wavelength, respectively. Both the sample and standard are ex-
cited at the same relevant wavelength, so that Astd = Ax. The fluo-
rescence quantum yield data of all the terbium complexes are
summarized in Table 6.
Figure 7. Emission spectrum of [TbLb(NO3)2]NO3.
Intramolecular energy transfer from the triplet state of the li-
gand to the resonance level of the rare earth ion is one of the most
important processes influencing the fluorescence quantum yields
of rare earth complexes. The energy difference between the triplet
As shown in Table 6, the fluorescence quantum yield of the ter-
bium complex [TbLb(NO3)2]NO3 with accepting electron group
Table 6. Fluorescence quantum yields of the teibium complexes
Complex
λ
ex (nm)
I (a.u.)
FX
Fluorescence quantum yield (Фfx)
[TbLa(NO3)2]NO3
[TbLb(NO3)2]NO3
[TbLc(NO3)2]NO3
[TbLd(NO3)2]NO3
316
318
320
314
2184
2806
1809
1927
95987.179
105187.761
89285.866
86737.159
0.563
0.609
0.497
0.522
wileyonlinelibrary.com/journal/luminescence
Copyright © 2015 John Wiley & Sons, Ltd.
Luminescence 2016; 31: 507–514

Synthesis and luminescence properties of terbium complexes
(–Cl) is higher than that of the terbium complexes with donating
electron groups (–CH3 and –OCH3), which is consistent with the
fluorescence data of the terbium complexes measured in the solid
state. The complex [TbLb(NO3)2]NO3 exhibits the highest quantum
yield (0.609), because the triplet level of ligand Lb is lowered by
the accepting electron group (–Cl), thus the triplet state energy
level of the ligand approaches the resonance level of terbium
and the efficiency of the intramolecular energy transfer from the
triplet state of the ligand to the resonance state of terbium ions
is highest in the four terbium complexes.
level of the complex with an accepting electron group are lower
than that of the complex without a substituent. The frontier orbital
theory (22) may provide an explanation for the above phenomena;
the HOMO possesses the priority to provide electrons. For electron
donor compounds, the oxidation process corresponds to the
process of losing electrons in HOMO.
Conclusions
Four salicylaldehyde–salicylhydrazone derivatives and their ter-
bium complexes have been synthesized and characterized. The
fluorescent test results revealed that all the terbium complexes
emitted fluorescence characteristic of terbium ions, and the fluo-
rescence intensity of the complex with ligand substituted by chlo-
rine is the strongest. The electrochemical analysis results showed
that the introduction of donating electron groups can increase
the oxidation potential and the HOMO energy level of the terbium
complex; however, the introduction of accepting electron group
can make the oxidation potential and the HOMO energy level of
the terbium complex decrease.
Electrochemical properties analysis
The electrochemical properties of the terbium complexes were in-
vestigated by means of a cyclic voltammetric technique in DMSO
solution. The highest occupied molecular orbital (HOMO) energy
levels and lowest unoccupied molecular orbital (LUMO) energy
levels of the terbium complexes were estimated according to the
electrochemical performance and the UV absorption spectra (20).
The HOMO and LUMO data for the terbium complexes are ob-
tained using equation EHOMO = 4.74 + eEOX, ELUMO = EHOMO – Eg,
Eg = 1240/λonset (eV), where λonset is the largest UV absorption
spectra peak starting value (21). All cyclic voltammetrics are
depicted in Fig. 8 and their electrochemical data are listed in
Table 7.
As shown in Table 7, the oxidation potentials of all the terbium
complexes occur in the range +0.677 to +0.781 V. The oxidation
potential and HOMO energy level of the complex with the donat-
ing electron group are higher than that of the complex without a
substituent, whereas the oxidation potential and HOMO energy
Acknowledgements
The authors are grateful for the financial support of the National
Natural Science Foundation of China (No. J1103312; No.
J1210040; No. 21341010), the Innovative Research Team in Univer-
sity (No. IRT1238) and excellent chemical engineer training pro-
gram of Hunan University. We also thank Dr William Hickey U.S.
Professor of HRM for the English editing on this paper.
References
1. Masaharu S, Shu K. N-Acylhydrazones as versatile electrophiles for the
synthesis of nitrogen-containing compounds. Angew Chem Int Ed
2005;44:5176–86.
2. Tian BH, He MZ, Tan ZW, Tang SX, Hewlett I, Chen SG, et al. Synthesis
and antiviral evaluation of new N-acylhydrazones containing glycine
residue. Chem Biol Drug Des 2011;77:189–198.
3. Goekce C, Gup R. Copper(II) complexes of acylhydrazones: synthesis,
characterization and DNA interaction. Appl Organometal Chem
2013;27:263–8.
4. Li WX, Zheng YS, Chai WJ, Ren T, Liu Y, Li YJ, et al. Fluorescence emission
mechanism and fluorescence properties of ternary Tb(III) complex with
diphenyl sulphoxide and bipyridine. Luminescence 2011;26:754–61.
5. Liu Q, Wang DM, Li YY, Yan M, Wei Q, Du B. Synthesis and luminescent
properties of Eu(TTA)3·3H2O nanocrystallines. Luminescence 2010;25:307–10.
6. Song XQ, Zheng QF, Wang L, Liu WS. Synthesis and luminescence
properties of lanthanide complexes with a new tripodal ligand featur-
ing N-thenylsalicylamide arms. Luminescence 2012;27:459–65.
7. Feng SY, Li WX, Guo F, Cao XF. Luminescence enhancement of terbium
(III) perchlorate by 2,2′-dipyridyl on bis (benzylsulfinyl)methane com-
plex and luminescence mechanism. Luminescence 2014;29:791–7.
8. Nakagawa K, Amita K, Mizuno H. Preparation of some lanthanoid
picrates and the behavior of their water of hydration. B Chem Soc
Jpn 1987;60:2037–40.
Figure 8. CV curves of (a) [TbLa(NO3)2]NO3, (b) [TbLb(NO3)2]NO3, (c) [TbLc(NO3)2]NO3
and (d) [TbLd(NO3)2]NO3.
9. He SY, Chen YL, Yang R. Synthesis, spectrum study and biological activ-
ity of salicylaldehyde salicylhydrazone complexes with rare earth.
Chinese J Org Chem 2003;23:1387–92.
Table 7. EHOMO, ELUMO and Eg of the terbium complexes
10. Geary WJ. The use of conductivity measurements in organic solvents
for the characterisation of coordination compounds. Coord Chem
Rev 1971;7:81–122.
Complex
λonset
(nm)
Eox (v) EHOMO Eg (ev) ELUMO
(ev)
(ev)
11. Zhang W, He W, Guo XR, Chen YW, Wu LM, Guo DC. Synthesis and
luminescence properties of 1,3,4-oxadiazole acetamide derivatives
and their rare earth complexes. J Alloy Compd 2015;620:383–9.
12. Lv YG, Li G, Shi CH, Yu LS. Synthesis and emission analysis of novel rare
earth complex Eu(TTA)3(2NH2-Phen). Trans Nonferrous Met Soc China
2010;20:2336–9.
[TbLa(NO3)2]NO3 264
[TbLb(NO3)2]NO3 264
[TbLc(NO3)2]NO3 261
[TbLd(NO3)2]NO3 259
0.677
0.663
0.742
0.781
5.517
5.503
5.482
5.521
4.700
4.700
4.751
4.788
0.717
0.703
0.731
0.733
Luminescence 2016; 31: 507–514
Copyright © 2015 John Wiley & Sons, Ltd.
wileyonlinelibrary.com/journal/luminescence

D. Meng et al.
13. Zhang F, Zhu WZ, Lin QY. Synthesis, characterization and DNA
binding of the complexes of rare earth with phenanthroline and
demethylcantharate. J Rare Earth 2011;29:297–302.
14. Curtis NF, Curtis YM. Some nitrato-amine nickel(II) compounds with
monodentate and bidentate nitrate ions. Inorg Chem 1965;4:804–9.
15. Wang W, Huang Y, Tang N. Synthesis and infrared and fluorescence
spectra of rare earth complexes with a novel amide-based ligand.
Spectrochim Acta A 2007;66:1058–62.
16. Guo DC, He W, Liu B, Gou LN. Synthesis and luminescence properties of
2-(benzylcarbamoyl)phenyl derivatives and their europium complexes.
Luminescence 2013;28:280–6.
17. Lekha L, Kanmani Raja K, Rajagopal G, Easwaramoorthy D. Schiff base
complexes of rare earth metal ions: synthesis, characterization and
catalytic activity for the oxidation of aniline and substituted anilines.
J Organomet Chem 2014;753:72–80.
18. Guo YL, Dou W, Wang YJ, Zhou XY, Liu WS. Synthesis, characterization
and luminescence properties of rare earth complexes with a new
biphenylamide. J Lumin 2013;135:84–8.
19. Li LD, Zhang M. Comparative method for determining fluorescence
quantum yield. Anal Chem 1988;16:732–4.
20. Pablo MR, Carmen C, Angel LA. Charge transport and sensitized 1.5 μm
electroluminescence properties of full solution-processed NIR-OLED
based on novel Er(III) fluorinated β-diketonate ternary complex. J Phys
Chem C 2013;117:10020–30.
21. Ding BD, Zhang JM, Zhu WQ. Fast and convenient determination of
HOMO energy level of organic electroluminescent material using
electrochemistry method. Chem Res Appl 2002;14:712–14.
22. Fleming I. Frontier orbitals and organic chemical reactions. Wiley:
London, 1976.
wileyonlinelibrary.com/journal/luminescence
Copyright © 2015 John Wiley & Sons, Ltd.
Luminescence 2016; 31: 507–514