New Zn complexes based on 1,2,4-triazoles: Synthesis, structure and luminescence

Article abstract of DOI:10.1016/j.ica.2011.07.009

The reaction of 3-(pyridin-2-yl)-5-(2-aminophenyl)-1H-1,2,4-triazole and salicylaldehyde or benzaldehyde leads a new type of 1,2,4-triazole's derivats. Reactions of these ligands with zinc acetate in ethanol lead to the formation of two new complexes with

Full text of DOI:10.1016/j.ica.2011.07.009

Inorganica Chimica Acta 376 (2011) 509–514
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Inorganica Chimica Acta
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New Zn complexes based on 1,2,4-triazoles: Synthesis, structure and luminescence
a
a
b
c
Alexey N. Gusev a, , Victor F. Shul’gin , Oleg V. Konnic , Svetlana B. Meshkova , Grygory G. Aleksandrov ,
⇑
Mikhail A. Kiskin c, Igor L. Eremenko c, Wolfgang Linert d,
⇑
a Taurida National V.I. Vernadsky University, Simferopol 95007, Ukraine
b A.V. Bogatsky Physico-Chemical Institute of the National Academy of Sciences of Ukraine, Odessa 65080, Ukraine
c N.S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Moscow 119991, Russia
d Institute for Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9/163, A-1060 Vienna, Austria
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of 3-(pyridin-2-yl)-5-(2-aminophenyl)-1H-1,2,4-triazole and salicylaldehyde or benzalde-
hyde leads a new type of 1,2,4-triazole’s derivats. Reactions of these ligands with zinc acetate in ethanol
lead to the formation of two new complexes with azomethine or dihydrotriazaindolizine form of ligands.
The structures of these complexes were investigated by X-ray analysis. The complexes showed strong
green–blue luminescence in solid state.
Received 18 March 2011
Received in revised form 4 July 2011
Accepted 11 July 2011
Available online 23 July 2011
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
1,2,4-Triazole
Zinc complexes
X-ray study
Luminescence
1. Introduction
in low-polarity solvents, making the production of high-quality thin
films difficult which would be required for the OLED production.
Our investigations on ZnII triazole and tetrazole derivative coor-
dination compounds have been encouraged due to their expected
fluorescence properties. Specific spectroscopic properties of coordi-
nation complexes have made them one of the essential components
in the preparation of new materials to be applied especially in
organic-light-emitting-diods (OLEDs) [1–4].
In this work we report new stable and readily soluble in low-
polarity solvents zinc complexes on 1,2,4-triazoles bases with
strong photo- and electroluminescent activity.
2. Experimental part
1,2,4-Triazole and derivatives are on the one hand a broadly
distributed class of ligands for creation a variety of interesting coor-
dination compounds, on the other hand starting materials for neces-
sary components of OLED devices as substances with the electron
and hole conductivity [5,6]. Therefore, it is exciting to obtain fluores-
cent complexes containing triazole fragment. Quite a number Ir and
Os complexes of 1,2,4-triazole’s derivatives which exhibit intense
photo- and electroluminescence are given in the literature [7,8].
However, there are relatively few reports on the photo- and electro-
luminescent properties of (probably much cheaper) Zn and Cd tria-
zole coordination compounds [9]. Among them, zinc complexes
have received much attention because they exhibit many advanta-
geous electroluminescent properties, such as electron transporting
ability, light emitting efficiency, high thermal stability, ease of sub-
limation, and great diversity of electronic properties tunable by
various ligand substitution. One of the reasons for the limited explo-
ration of Zn and Cd 1,2,4-triazole’s complexes is their low solubility
2.1. Materials and methods
Commercially available solvents, salicylaldehyde, benzaldehyde,
2-cyanopyridine,
hydrazine
hydrate,
isatoic
anhydride,
Zn(OAc)2ꢀ2H2O were used without further purification.
2-Aminobenzoic acid hydrazide was obtained by hydrazinolis
ofisatoic anhydride. 3-(Pyridin-2-yl)-5-(2-aminophenyl)-1H-1,
2,4-triazole was prepared by reacting 2-cyanopyridine with
2-aminobenzoic acids hydrazides according to the literature [10].
IR spectra of the complexes were recorded as KBr pellets in the
range of 4000–400 cmꢁ1 on a Nicolet Nexus 470 FT-IR spectrome-
ter. 1H and 13C NMR spectra were recorded on a Bruker VXR-400
spectrometer at 400 and 75 MHz respectively. NMR spectra were
obtained from solutions in DMSO-d6. Thermogravimetric experi-
ments were performed on a Paulik–Paulik–Erdey Q-derivatograph
under a static air atmosphere. Absorption spectra were recorded on
a Perkin-Elmer Lambda-9 UV–Vis/NIR spectrophotometer. Lumi-
nescence spectra of solid samples were obtained with a LOMO
SDL-1 spectrometer equipped with a FEU-79 photomultiplier. Exci-
tation and luminescence spectra of solutions were recorded on a
⇑
Corresponding authors.
E-mail addresses: galex0330@rambler.ru (A.N. Gusev), wlinert@mail.zserv.tu-
wien.ac.at (W. Linert).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.07.009

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A.N. Gusev et al. / Inorganica Chimica Acta 376 (2011) 509–514
Horiba Jobin-Yvon Fluorolog-FL 3-22 spectrophotometer equipped
with a 450 W Xe lamp.
2.3. X-ray studies
Single crystal structure determination of 1 and 2 by X-ray dif-
fraction was performed on a Bruker Apex-II CCD diffractometer
0
2.2. Synthesis
(Mo Ka radiation, graphite monochromator, k = 0.71073 ÅA) at
298 K. For both complexes semiempirical absorption corrections
were applied [11]. The structures were solved by direct methods
and using Fourier techniques and were refined by the full-matrix
least squares against F2 with anisotropic thermal parameters for
all non-hydrogen atoms. The hydrogen atoms of the carbon-
containing ligands were positioned geometrically and refined
using the riding model. All calculations were carried out with the
use of the SHELX97 program package [12]. The crystallographic
parameters for complexes 1 and 2 are given in Table 1.
2.2.1. Synthesis of ligands (L1 and L2)
A solution of 2.1 mmol of salicylaldehyde (256 mg) or benzalde-
hyde (222 mg) in 10 mL of ethanol was added to a solution of
2 mmol (474 mg) of the 3-(pyridin-2-yl)-5-(2-aminophenyl)-1H-
1,2,4-triazole in 10 mL of ethanol (96%). The resulting reaction
mixture was stirred under heating with a magnetic stirrer for 1 h
until the solid complex precipitated. The precipitate was filtered
off, washed with ethanol and dried in vacuum.
5-(2-Hydroxyphenyl)-2-(20-pyridiyl)-7,8-benzo-6,5-dihydro-1,
3,6-triazaindolizine (L1) – white powder. Yield was 53%. Anal. Calc.
for C20H15N5O: C, 70.38; H, 4.40; N, 20.53. Found: C, 70.22; H,
4.28; N, 20.61%. M.p. = 237 °C (EtOH). 1H NMR (400 MHz, DMSO-
d6, ppm): d = 10.1 (1H, s, OH); 8.65 (1H, d, CHarom); 8.12 (1H, d,
CHarom), 7.90(1H, d-tr, CHarom), 7.80(1H, d, CHarom), 7.40 (2H, mult,
CHarom), 7.27 (1H, tr, CHarom); 7.24–7.19 (2H, mult, CHarom), 6.95–
6.85 (3H, mult, CHarom+N–H), 6.85(1H, tr, CHarom), 6.80 (1H, tr,
CHarom). 13C NMR (75 MHz, DMSO-d6, ppm): d = 161.65, 155.29,
151.19, 150.05, 149.95, 143.73, 137.54, 132.33, 130.65, 127.75,
126.10, 124.60, 124.46, 122.22, 119.56, 118.39, 116.34, 115.05,
3. Results and discussion
3.1. Synthesis, NMR and IR data of L1 and L2
The interaction of aromatic aldehyde with the 3-(pyridin-2-yl)-
5-(2-aminophenyl)-1H-1,2,4-triazole can lead to two isomeric
forms of ligands: azomethine – A and dihydrotriazaindolizine
cyclic form – B (Scheme 1).
NMR and IR data indicate that in a free state L1 and L2 exist in
cyclic form. For the PMR-spectra of the ligands L1 and L2 C6–H pro-
ton group signals were observed in the 7.19–7.44 ppm region,
while the signals of hydrogen atoms of the azomethine groups in
the region 8.7–9.3 ppm (expected as a singlet peak) are missing,
that is a strong argument in favor of the formation of the cyclic
form. It should be noted that the same shift was registered for
the C6–H protons in the related compounds [13] There is no signal
110.04, 67.67. IR (KBr, cmꢁ1):
m = 3270, 1629, 1597, 1523, 1457,
1361, 1292, 1281, 1236, 1159, 742.
5-Phenyl-2-(20-pyridiyl)-7,8-benzo-6,5-dihydro-1,3,6-triaza-
indolizine (L2) – white powder. Yield was 46%. Anal. Calc. for
C20H15N5: C, 73.67; H, 4.65; N, 21.54. Found: C, 73.85; H, 4.62; N,
21.70%. M.p. = 216 °C (EtOH). 1H NMR (400 MHz, DMSO-d6,
ppm): d = 8.62 (1H, d, CHarom); 8.07 (1H, d, CHarom), 7.89 (1H, d-
tr, CHarom), 7.79 (1H, d, CHarom), 7.69 (1H, s, CHarom); 7.44–7.36
(6H, mult, CHarom), 7.29 (1H, d-tr, CHarom), 6.99 (1H, s, NH), 6.92
(H, d, CHarom), 6.86 (1H, tr, CHarom). 13C NMR (75 MHz, DMSO-d6,
ppm): d = 160.93, 154.72, 150.27, 150.01, 149.27, 142.98, 138.32,
132.38, 130.81, 126.24, 126.10, 124.49, 124.46, 122.28, 119.39,
Table 1
Crystal data and structure refinement statistics for 1 and 2.
Parameter
1
2
Formula
C
41H29N10O2.5Zn2
C27H29N5O5Zn
568.92
118.57, 116.31, 114.96, 109.96, 67.65. IR (KBr, cmꢁ1):
1624, 1590, 1528, 1480, 1412, 1356, 1152, 740.
m = 3296,
Formula weight (g molꢁ1
)
832.48
Crystal dimensions (mm)
T (K)
0.20 ꢂ 0.14 ꢂ 0.11 0.35 ꢂ 0.18 ꢂ 0.14
296
296
Crystal system
Space group
monoclinic
C2/c
triclinic
ꢀ
2.2.2. Synthesis of [Zn2(L1)2]ꢀ0.5EtOH (1)
P1
Unit cell parameters
Zinc acetate dihydrate (2 mmol, 438 mg) was added to suspen-
sion of L1 (2 mmol, 682 mg) in 10 mL of ethanol (96%). The mixture
was stirred while heating for 2 h. The formed precipitate was kept
under the mother liquor for 12 h, then filtered off, washed with
alcohol, and dried in air. The procedure yielded 510 mg (61.3%)
of a yellow crystalline substance. Recrystallization from mixture
DMSO–EtOH gave yellow prism crystals suitable for X-ray analysis.
Anal. Calc. for C41H29N10O2.5Zn2: Zn, 15.59; C, 59.13; H, 3.48; N,
16.66. Found: Zn, 15.62; C, 58.91; H, 3.69; N, 16.36%. IR (KBr,
0
25.405(18)
14.938(11)
19.430(14)
9.593(3)
11.080(4)
13.106(4)
a (ÅA)
0
b (AÅ)
0
c (AÅ)
a
(°)
76.641(6)
84.847(7)
80.300(7)
1334.1(8)
b (°)
96.006(10)
7333.9(9)
c
(°)
0
V (AÅ3)
Z
8
2
qcalc. (g cmꢁ3
)
1.508
1.362
3400
30.07
1.416
0.97
592
27.75
cmꢁ1): 1610 (
800, 752.
m
(C@NSchiff)), 1593, 1533, 1457, 1444, 1330, 1147,
l
(mmꢁ1
)
F(0 0 0)
hmax (°)
Index ranges
ꢁ29 6 h 6 35
ꢁ21 6 k 6 20
ꢁ27 6 l 6 25
28343/10636
ꢁ12 6 h 6 10
ꢁ14 6 k 6 14
ꢁ13 6 l 6 16
9264/6194
2.2.3. Synthesis of [Zn(L2)(OAc)2]ꢀi-PrOH (2)
Reflections measured/reflections
independent
Zn(OAc)2ꢀ2H2O (657 mg, 3 mmol) was added to a suspension of
L2 (1.05 g, 3 mmol) in i-PrOH (10 ml), and the mixture was stirred
while heating for 2 h. The formed precipitate was left to stay over-
night under the mother liquor, then filtered off, washed with alco-
hol, and dried in air. The yield of 2 was 1.1 g (65%). Recrystallization
from i-PrOH gave white crystals of prismatic habitus suitable for
X-ray analysis. Anal. Calc. for C27H29N5O5Zn: Zn, 11.52; C, 55.99;
H, 5.10; N, 11.52. Found: Zn ,11.43; C, 55.24; H, 5.77; N, 11.37%.
Rint
0.0328
1.048
0.0149
1.010
Goodness-of-fit (GOF) on F2
R (all data)
R1 = 0.0842
wR2 = 0.1278
R1 = 0.0424
wR2 = 0.1095
0.8646/0.7723
0.664/ꢁ0.254
R1 = 0.1015
wR2 = 0.1503
R1 = 0.0516
wR2 = 0.1221
0.8765/0.7284
0.508/ꢁ0.531
R [I > 2r(I)]
Tmin/Tmax
Residual electron density (max/
min) (e ÅAꢁ3
IR (KBr, cmꢁ1): 3236
s(COOꢁ), 1154, 740.
m(NH), 3052, 1626, 1588 m
as(COOꢁ), 1452
0
)
m

A.N. Gusev et al. / Inorganica Chimica Acta 376 (2011) 509–514
511
N
N
N
N
H
N
H
X
2
O
H
A
N
X
N
+
N
N
H
NH2
X - H, OH
3
N
N
4
N
N
NH
1
5
6
X
B
Scheme 1. Preparative scheme of ligands and numbering of the atoms of cyclic form.
in the PMR spectra of a hydrogen atom associated with triazole’s
ring, usually manifested in the region 13–14 ppm, but the typical
signal of the hydrogen atom of a secondary amine is recorded at
6.95–6.99 ppm. All other signals in the NMR spectra are typical
for related functional groups: OH-group at 10.1 ppm and aromatic
proton at 8.65–6.80 ppm. Cyclic form is also evidenced by the
13C NMR spectroscopy data. The most revealing in terms of evi-
dence of cyclic structure of the ligand is characteristic signal of
the carbon atom C6–H which is observed at 67 ppm. This agrees
with the shift data described for related heterocycles [13]. The pos-
sible signals of the carbon atom of CH@N usually lies in the
57–164 ppm region [14]. The values of chemical shifts for the other
signals are typical of aromatic carbon atoms.
azomethine form of L1 (Fig. 1). The local coordination environ-
ment of the zinc(II) ion can be described as a distorted tetrago-
nal-pyramid completed by four nitrogen atoms in the base of
the pyramid and an oxygen atom in the axial position. The
Zn2N4 central six-membered metal ring has 0a boat conformation.
The intramolecular ZnꢀꢀꢀZn distance is 4.038 ÅA, which is typical for
binuclear complexes of 1,2,4-triazoles [5]. In both L1 ligands tria-
zole and phenyl moieties are nearly coplanar with the pyridyl
plane, and the planar 2-imino(methylphenol) moiety is turned
around the benzene ring plane by 37.9° in the first ligand and
by 52.4° in the second. Hydrogen bonding is present between
the oxygen atoms of the solvate molecule of ethanol and oxygen
0
of L1 (O2ꢀꢀꢀO1S(EtOH) 2.82 ÅA).
The dihydrotriazaindolizine form of the ligand was found for
the crystal structure for complex 2 (Fig. 2). The complex 2 is mono-
nuclear and crystallizes as a solvate with one molecule of propa-
nol-2. The zinc ion coordinates four oxygen atoms of two acetate
anions and two nitrogen atoms of triazole ligand arranged at the
vertices of a strongly distorted octahedron. Both acetate anions
3.2. Synthesis and X-ray studies of the zinc complexes
Interaction of L1 and L2 with zinc acetates leads to two types of
complexes with both the azomethine form (complexes 1) and the
cyclic form (complex 2) (Scheme 2).
are bidentate, but if the bond length of Zn1–O1 and Zn1–O2 are al-
According to X-ray crystallography, the complex 1 has binu-
0
most equal (2.117(3) and 2.205(3) ÅA respectively) then Zn1–O3
clear molecular structure present in
a
double deprotonated
N
N
N
N
N
N
H
.
Zn
N
2
Zn(OAc)2 H2O
O
O
N
N
NH
OH
Zn
N
H
reflux
EtOH
N
N
N
N
L1
1
H3C
O
O
O
CH3
N
Zn
O
N
N
N
N
.
NH
2
Zn(OAc)2 H2O
N
N
N
reflux
i-PrOH
NH
L2
2
Scheme 2. Preparative scheme of complexes.

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A.N. Gusev et al. / Inorganica Chimica Acta 376 (2011) 509–514
Fig. 1. Structure of complex 1 (hydrogen atoms and EtOH are not shown for clarity; thermal ellipsoids are drawn at the 30% probability level). Selected bond lengths (A) and
bond angles (°): Zn1–N1 2.166(2), Zn1–N2 2.097(2), Zn1–N8 2.043(2), Zn1–N10 2.102(2), Zn2–N3 2.053(2), Zn2–N5 2.114(2), Zn2–N6 2.145(2), Zn2–N7 2.072(2), Zn1–O2
1.9270(19), Zn2–O1 1.9229(17), O2Zn1N8 129.74(8), O2Zn1N2 100.15(8), N8–Zn1–N2 89.53(8), O2–Zn1–N10 93.69(7), N8–Zn1–N10 82.96(7), N2–Zn1–N10 166.04(8), O2–
Zn1–N1 100.64(8), N8–Zn1–N1 129.45(8), N2–Zn1–N1 76.09(8), N10–Zn1–N1 99.67(7).
Fig. 2. Structure of complex 2 (molecule of i-PrOH is not shown; thermal ellipsoids are drawn at the 30% probability level). Selected bond lengths (A) and bond angles (°):
Zn1–O3 2.013(3), Zn1–N1 2.106(3), Zn1–O1 2.117(3), Zn1–N5 2.137(3), Zn1–O2 2.205(3), Zn1–O4 2.449(3), O3–Zn1–N1 98.17(12), O3–Zn1–O1 140.92(12), N1–Zn1–O1
117.61(12), O3–Zn1–N5 113.44(13), N1–Zn1–N5 78.93(12), O1–Zn1–N5 89.73(12), O3–Zn1–O2 104.53(14), N1–Zn1–O2 95.06(14), O1–Zn1–O2 59.65(12), N5–Zn1–O2
142.01(13), O3–Zn1–O4 57.22(12), N1–Zn1–O4 149.65(12), O1–Zn1–O4 91.63(12), N5–Zn1–O4 94.20(12), O2–Zn1–O4 107.56(14).
0
and Zn1–O4 are markedly asymmetrical (2.013(3) and 2.449(3) ÅA).
The heterocyclic ligand L2 exists in cyclic form and is coordinated
via a bidentate mode bound to the zinc atom through the N5 atom
of the pyridine ring and the N1 atom of the triazole ring. The bond
Zn1–N5 (2.137(3) ÅA) is slightly longer than Zn1–N1 (2.106(3) ÅA).
The triazole, iminophenyl, and pyridyl cycles lie almost in the same
plane, and the phenyl fragment is turned by 88.22°. Two molecules
in crystal lattice unit exist both in their R and S isomer forms,
molecules of the complex, whose planes are almost parallel and
0
lie at a distance of ꢃ3.5 ÅA (p-stacking interactions).
Thus the studied triazole ligands show diverse coordination
behavior. The formation of the azomethine form of ligand for
complex 1 stabilizes the coordination of phenolic oxygen atom of
the L1. In the absence of stabilizing factors the investigated tria-
zoles are coordinated in a cyclic form (complex 2).
0
0
creating a racemate. The crystalline lattice is stabilized by the sys-
3.3. NMR and IR data of zinc complexes
0
tem of intermolecular hydrogen bonds (N4ꢀꢀꢀO4(x, y + 1, z) 2.90 ÅA,
0
O3ꢀꢀꢀO1S(i-PrOH) 2.92 ÅA) and nonvalent interactions between the
The results of the study of complex 1 by NMR and IR spectros-
copy confirm the azomethine form structure of the ligands. The
conjugated nitrogen-containing heterocycles of the adjacent

A.N. Gusev et al. / Inorganica Chimica Acta 376 (2011) 509–514
513
signals of azomethine protons as singlet peak were found at
8.80 ppm. In addition, the characteristic hydrogen signal of second-
ary amines registered for the free triazole disappeared after com-
plex formation. There are no signals of hydrogen atoms
originating from acidic groups either, confirming the deprotonation
of the ligands upon coordination. In contrast the 1H NMR-spectra of
complex 2 contain several sets of signals, one of which coincides
with the spectrum of the free L2. This suggests equilibrium of partial
dissociation of the complex 2 in solution when recording the
spectrum.
The IR spectrum of complex 1 does not contain bands corre-
sponding to stretching vibrations of NAH and OAH groups. The
coordination of the phenoxyl oxygen atom is accompanied by a
shift of the band of the stretching vibrations of the CphenAO bond
from 1292 cmꢁ1 in the free triazole to 1330 cmꢁ1 in the complex.
A shift of the band of the stretching vibrations of the AHC@NA
bond by 20 cmꢁ1 to the shortwave range from the tabulated values
is indicative of the coordination of the imine nitrogen atom. For the
IR spectrum of complex 2, most bands do not undergo significant
variations compared with free L2. However, two new intense
bands at 1588 and 1452 cmꢁ1 are registered, related to asymmetric
and symmetric stretching vibrations of the carboxyl group of ace-
tate anion, respectively.
3.4. Thermogravimetric analysis of zinc complexes
For creating thin-film devices by vacuum deposition the thermal
stability of the complexes plays a significant role to allow the trans-
port of the stable species in the gas phase [15]. The thermal stability
has been studied by thermogravimetric analysis. The complex 1 is
stable up to a temperature of 100 °C. A further increase of temper-
ature leads to desolvation. Removal of ethanol molecules occurs in
the temperature range 100–350 °C and is not accompanied by
noticeable thermal effects. At a temperature of 410 °C starts the oxi-
dative decomposition of the complex which passes to the process of
burning out the organic ligand. Burnout is accompanied with a ser-
ies of powerful exothermic effects at 600–670 °C. The process of
decomposition is completed at a temperature of 900 °C.
Fig. 3. (i) The emission spectrum of L1 (a) and
temperature, (ii) exciting spectra of complex 1.
1 (b) in solid state at room
Desolvation of complex 2 occurs in one stage: in the tempera-
ture range 100–160 °C molecule of propanol-2 is removed. Desolv-
ation processes are accompanied by minor endothermic effect with
minimum at 140 °C. Further heating leads to thermal oxidative
degradation, transforming into a burnout of the organic part of
the complex. The last stage is accompanied by a series of powerful
exothermic effects with maxima at 480 °C.
Obviously, zinc complex 1 exhibited high thermal stability that
can be used to create thin films by thermal evaporation in vacuum.
Unfortunately, this method is not suitable for the complex 2, due to
its destruction, even at 160 °C.
Table 2
The photoluminescence properties of L1, L2, 1 and 2.
Compound
kmax (nm)
Ilumi, rel. un.
L1
L2
1
459
450
496
450
5
5
152
82
2
UV radiation is more effective than visible light excitation. Photo-
luminescent spectra of complex 1 undergo a bathochromic shift
(36 nm) compared with the spectra of free ligand. Such a shift is
associated with the transition of the ligand in the azomethine
deprotonated form in the coordination and, consequently, increas-
ing the length of conjugated double bonds.
The blue fluorescence of complexes 2 can be observed with the
maximum emission wavelength at 450 nm. There is no consider-
able shift compared to free ligand emission was observed. This is
consistent with the conservation cyclic form of the L2 in complex
2. So, the formation of metal chelates with Zn ions promotes fluo-
rescence by increasing rigidity and minimizing internal vibrations.
The high luminescence efficiency in the green and blue light
region, as well as the high thermally stability, indicates that the
two complexes may be excellent candidates for highly thermally
stable fluorescent materials.
3.5. Photo and electroluminescent properties
From the literature data it is known that the luminescent proper-
ties for thin films and solid samples are close to each other [16]. Since
the complexes of zinc are considered as candidates for thin-film
electroluminescent materials, optophysical characteristics of solid
samples of complexes 1 and 2 have been studied. The luminescence
of the ligands L1 and L2 was not high and therefore was not studied in
detail. In contrast zinc complexes in the solid state showed a strong
luminescence in the visible region. The photoluminescence spectra
of the complex 1 represents a broad band with emission maximum
at 495 nm (Fig. 3i) and at 450 nm for complex 2 (Table 2) when ex-
cited with 350 nm radiation, due to energy transfer between the
highest occupied and lowest unoccupied molecular orbitals.
Exciting spectra of complex 1 contains two peaks at 362 and
447 nm (Fig. 3ii). The spectrum clearly shows that excitation by
Electroluminescent properties were studied for the complex 1.
The current–voltage and current-brightness characteristics of the

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A.N. Gusev et al. / Inorganica Chimica Acta 376 (2011) 509–514
sandwich device ITO/PEDOT/PVC:Zn2(L1)2/LiF/CaMg/Ag (ITO is
indium tin oxide; PEDOT is poly(3,4-ethylenedioxythiophene))
was described in [17]. At 6 V the device generates light with a peak
at 493 nm. It should be noted that the electroluminescence of zinc
complexes with 1,2,4-triazole derivatives have not been described
previously.
Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary
data associated with this article can be found, in the online version,
at doi:10.1016/j.ica.2011.07.009.
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This study was supported by the Ministry of Education and Sci-
ence of the Russian Federation (SC-14.740.11.0363) and the Rus-
sian Academy of Sciences.
Appendix A. Supplementary material
CCDC 733658 and 817001 contain the supplementary crystallo-
graphic data for compounds 1 and 2 respectively. These data can be
obtained free of charge from The Cambridge Crystallographic Data
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