SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES
The study presents the synthesis, characterization, and photophysical investigation of novel Ln(III)complexes with 1,2,4-triazole-based Salen-type ligands, focusing on europium-centered optical properties. An optimized synthetic method for Ln(III) complex formation was developed with the use of var...
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| Дата: | 2024 |
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| Автори: | , , , , , , , |
| Формат: | Стаття |
| Мова: | Англійська |
| Опубліковано: |
V.I.Vernadsky Institute of General and Inorganic Chemistry
2024
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Репозитарії
Ukrainian Chemistry Journal| _version_ | 1871466028848906240 |
|---|---|
| author | Halushchenko, Valeriia Korovin, Oleksandr Smola, Serhii Bibik, Yurii Khomenko, Dmytro Doroshchuk, Roman Lampeka, Rostyslav Rusakova, Natalya |
| author_facet | Halushchenko, Valeriia Korovin, Oleksandr Smola, Serhii Bibik, Yurii Khomenko, Dmytro Doroshchuk, Roman Lampeka, Rostyslav Rusakova, Natalya |
| author_institution_txt_mv | [
{
"author": "Valeriia Halushchenko",
"institution": "A.V. BogatskyPhysico-Chemical Institute of the NAS of Ukraine, Lyustdorfskadoroga, 86,Odesa 65080, Ukraine"
},
{
"author": "Oleksandr Korovin",
"institution": "A.V.Bogatsky Physico-Chemical Institute of the NAS of Ukraine, 86 Lyustdorfska doroga, 65080 Odesa, Ukraine"
},
{
"author": "Serhii Smola",
"institution": "A.V.Bogatsky Physico-Chemical Institute of the NAS of Ukraine, 86 Lyustdorfska doroga, 65080 Odesa, Ukraine"
},
{
"author": "Yurii Bibik",
"institution": "Department of Chemistry, Taras Shevchenko National University of Kyiv, 64 Volodymyrska st., 01601 Kyiv, Ukraine"
},
{
"author": "Dmytro Khomenko",
"institution": "Department of Chemistry, Taras Shevchenko National University of Kyiv, 64 Volodymyrska st., 01601 Kyiv, Ukraine"
},
{
"author": "Roman Doroshchuk",
"institution": "Department of Chemistry, Taras Shevchenko National University of Kyiv, 64 Volodymyrska st., 01601 Kyiv, Ukraine"
},
{
"author": "Rostyslav Lampeka",
"institution": "Department of Chemistry, Taras Shevchenko National University of Kyiv, 64 Volodymyrska st., 01601 Kyiv, Ukraine"
},
{
"author": "Natalya Rusakova",
"institution": "A.V.Bogatsky Physico-Chemical Institute of the NAS of Ukraine, 86 Lyustdorfska doroga, 65080 Odesa, Ukraine"
}
] |
| author_sort | Halushchenko, Valeriia |
| baseUrl_str | https://ucj.org.ua/index.php/journal/oai |
| collection | OJS |
| datestamp_date | 2026-07-22T08:23:54Z |
| description | The study presents the synthesis, characterization, and photophysical investigation of novel Ln(III)complexes with 1,2,4-triazole-based Salen-type ligands, focusing on europium-centered optical properties. An optimized synthetic method for Ln(III) complex formation was developed with the use of various salts, solvents, and deprotonating agents, with methanol, triethylamine, and triethylorthoformate yielding the best results. This approach produced light-yellow crystalline products with a 65–70% yield. Structural characterization through IR spectroscopy and mass spectrometry confirmed coordination by nitrogen and oxygen atoms, as evidenced by shifts in vibrational bands indicative of Eu–N bonds and alterationsin phenolic OH and CO stretching modes. UV-Vis absorption spectra revealed bathochromic shifts, indicating changes in electron density and increased conjugation resulting from complex formation. Upon excitation, the complexes exhibited fluorescence in the 400–500 nm range and phosphorescence in the 450–550 nm range, demonstrating effective energy transfer within the system. The CIE chromaticity coordinates for EuL1 (x=0,631, y=0,368) and EuL2 (x=0,603, y=0,396) denote a deep red emission with color purity and correlated color temperature (CCT) values of 2017,94 K and 1720,92 K, respectively, indicating their potential for high-purity red emissions in optoelectronic applications. Lifetime measurements (0,544 ms at 298 K and 0,706 ms at 77 K) indicate non-radiative relaxation processes that may be modulated by local symmetry, as suggested by the distinctive emission splitting in Eu(III) transitions. Emission spectra revealed prominent transitions typical of Eu(III) ions, with extensive splitting indicative of a low-symmetry environment, likely within C₂ᵥ or Cs point groups. Structural analysis supports a coordination number of 8, suggesting polyhedral arrangements like a bicapped trigonal prism. This synthetic route effectively produces Ln(III) complexes with tunable luminescent properties, revealing key structure-property relationships and enabling tailored red emissions, making these complexes promising precursors for display and lighting technologies. |
| doi_str_mv | 10.33609/2708-129X.90.3.2024.3-17 |
| first_indexed | 2025-09-24T17:43:55Z |
| format | Article |
| fulltext |
3
UDC 541.49:546.65:547.584:547.594.3:535.37 doi: 10.33609/2708-129X.90.3.2024.3-17
SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT
PROPERTIES OF EUROPIUM(III) COMPLEXES WITH
SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES.
Valeriia S. Halushchenko1,2*, Oleksandr Yu. Korovin1, Serhii S. Smola1, Yurii S. Bibik3,
Dmytro M. Khomenko3,4, Roman O. Doroshchuk3,4, Rostyslav D. Lampeka3, Natalya V. Rusakova1
1A.V.Bogatsky Physico-Chemical Institute of the NAS of Ukraine,
86 Lyustdorfska doroga, 65080 Odesa, Ukraine;
2Faculty of Chemistry and Pharmacy, Odesa I.I. Mechnikov National University,
2 Dvoryans'ka St, 65082 Odessa, Ukraine;
3Department of Chemistry, Taras Shevchenko National University of Kyiv,
64 Volodymyrska st., 01601 Kyiv, Ukraine;
4Enamine Ltd. (www.enamine.net),
78 Winston Churchill Street, 02094 Kyiv, Ukraine
*e-mail: valeriia.halushchenko@gmail.com
The study presents the synthesis, characterization, and photophysical investigation of novel Ln(III)
complexes with 1,2,4-triazole-based Salen-type ligands, focusing on europium-centered optical pro
perties. An optimized synthetic method for Ln(III) complex formation was developed with the use
of various salts, solvents, and deprotonating agents, with methanol, triethylamine, and triethyl or-
thoformate yielding the best results. This approach produced light-yellow crystalline products with
a 65–70% yield. Structural characterization through IR spectroscopy and mass spectrometry con-
firmed coordination by nitrogen and oxygen atoms, as evidenced by shifts in vibrational bands in-
dicative of Eu–N bonds and alterationsin phenolic OH and CO stretching modes. UV-Vis absorption
spectra revealed bathochromic shifts, indicating changes in electron density and increased conjuga-
tion resulting from complex formation. Upon excitation, the complexes exhibited fluorescence in the
400–500 nm range and phosphorescence in the 450–550 nm range, demonstrating effective energy
transfer within the system. The CIE chromaticity coordinates for EuL1 (x=0,631, y=0,368) and EuL2
(x=0,603, y=0,396) denote a deep red emission with color purity and correlated color temperature
(CCT) values of 2017,94 K and 1720,92 K, respectively, indicating their potential for high-purity red
emissions in optoelectronic applications. Lifetime measurements (0,544 ms at 298 K and 0,706 ms at
77 K) indicate non-radiative relaxation processes that may be modulated by local symmetry, as sug-
gested by the distinctive emission splitting in Eu(III) transitions. Emission spectra revealed prominent
transitions typical of Eu(III) ions, with extensive splitting indicative of a low-symmetry environment,
likely within C₂ᵥ or Cs point groups. Structural analysis supports a coordination number of 8, suggest-
ing polyhedral arrangements like a bicapped trigonal prism. This synthetic route effectively produces
Ln(III) complexes with tunable luminescent properties, revealing key structure-property relationships
and enabling tailored red emissions, making these complexes promising precursors for display and
lighting technologies.
Keywords: Europium(III), Schiff bases, Salen-type ligands, Complexes, Luminescence.
4 ISSN 2708-129X. Укр. хім. журн., 2024
SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES
WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES.INORGANIC CHEMISTRY
INTRODUCTION. The unique properties
of lanthanide (III) compounds, such as cha
racteristic narrow emission peaks, large Stokes
shifts, high luminescence intensity, long life-
times, and others, provide them advantages
over other light emitters. These benefits make
the study of Ln(III) complexes increasingly
promising with substantial growth in research
over recent decades [1–3].
Developers of highly luminescent lantha-
nide-containing compounds often face the
challenge of optimizing sensitization efficien-
cy while minimizing quenching processes. For
the first aspect, it is crucial to carefully con-
sider the energy levels of ligand states, charge
transfer, and the kinetics of energy migration
among these states. Regarding the second as-
pect, it is essential to avoid energetic vibrations
from groups that are either directly associated
with the emission ion (the inner coordination
sphere) or interact with it at a greater distance
through weak interactions (the outer coordi-
nation sphere). Although suchweak interac-
tions have long often been overlooked, they
constitute a significant portion of all binding
interactions and strongly influence energy
transfer/quenching processes. Applying these
principles is relatively straight forward for lan-
thanide ions that emit visible light (i.e. Eu(I-
II), Tb(III)), which can exhibit quantum yields
exceeding 70%, even in coordination com-
pounds. However, adhering to these principles
in coordination compound design is challeng-
ing, as organic ligands contain not only O–H
and N–H groups, whose vibrations are effec-
tive quenchers, but also C–H, C=O, and C=C
groups which contribute significantly to the
quenching [4–6].
The design of organic ligands is crucial
in creating luminescent coordination com-
pounds of Ln(III) with specific topology and
desired properties. Research on lanthanide
complexes with Schiff bases is motivated by
their applications in luminescent probes [7],
magnetic resonance imaging [8], and magnet-
ic materials [9]. Among the various types of
reagents classified as Schiff bases, compounds
of the Salen-group are of particular interest. By
condensing (1:2) salicylaldehyde or its deriva-
tives with various diamines, tetradentate N2O2
donor Schiff bases are obtained. Consequently,
many other N2O2 donor ligands based on Schiff
bases belonging to the Salen family have been
synthesized and characterized, often referred
to as Salen-type ligands [10]. The use of poly-
dentate ligands, including Schiff bases prevents
the coordination of labile ligand molecules and
solvents, while promoting the saturation of the
high coordination numbers of lanthanide ions.
A new wave of research on Salen complexes is
associated with their potential applications in
photonics, medical diagnostics and treatment,
as well as the development of new functional
materials [9–14]. These complexes are often
immobilized on inorganic or organic polymer
carriers, combined with other materials to en-
hance or complement their properties, or used
as building blocks for creating new supramo-
lecular systems [11–14].
Among organic compounds that serve as
N-donor linkers, 1,2,4-triazole and its deri
vatives attract significant interest due to their
functional properties, including various bridg-
ing modes, the ability to exhibit intrinsic lumi-
nescence, and ease of modification. The intro-
duction of rigid substituents, such as pyridyl
and its derivatives with additional donor atoms,
creates bi- or tridentate binding sites, enhanc-
ing the stability of the resulting complexes
through the chelate effect. One of the simplest
5https://ucj.org.ua
Valeriia S. Halushchenko, Oleksandr Yu. Korovin, Serhii S. Smola, Yurii S. Bibik, Dmytro M. Khomenko,
Roman O. Doroshchuk, Rostyslav D. Lampeka, Natalya V.Rusakova UCJ № 3 / Vol. 90
and most widely used substituents for this pur-
pose is the 2-pyridyl group, while derivatives
of 3- and/or 4-pyridyl have gained researchers'
attention only in the past decade [15, 16].
The aim of this work was to establish con-
ditions for the formation of new luminescent
lanthanide complexes with a series of func-
tionalized Schiff bases – Salen-type ligands,
containing 1,2,4-triazole, and to study their
luminescent properties.
EXPERIMENT OF DISCUSSION OF THE
RESULTS. Samples for physicochemical stu
dies were prepared by grinding the precipitates
of the corresponding compounds, which were
aged at a temperature of 90–95°C until a cons
tant mass was achieved.
Electrospray ionization (ESI) mass spect
ra were recorded using a TSQ Fortis triple
quadrupole mass spectrometer (Thermo Fisher
Scientific, USA). All spectra were measured for
methanol solutions with a complex concen-
tration of approximately 10 μg/cm3. Isotope
distribution patterns were calculated using
the online tool at https://www.sisweb.com/
mstools/isotope.htm
IR absorption spectra (400–4000 cm-1) of
samples pressed with KBr were recorded using
a Spectrum BX II FT-IR System spectropho-
tometer (Perkin – Elmer).
The NMR spectra of the obtained com-
pounds were recorded on a Varian "Mercury
400" instrument in DMSO-d6 solutions.
Elemental analysis was performed using
Perkin – Elmer 2400 CHN Analyzer.
The absorption spectra of the studied com-
plexes were recordedon a ULAB spectrophoto
meter in the wavelength range of 200–400 nm.
Photoluminescence measurements at room
temperature and liquid nitrogen tempera-
ture were carried out using a Fluorolog 3–22
spectrofluorometer (Horiba JobinYvon) with
a 450 W Xe lamp excitation source. The vi
sible region detector used was a PMT R928P
(Hamamatsu, Japan). The excitation and lumi-
nescence spectra were corrected to account for
the emission distribution of the xenon lamp
and the sensitivity of the detectors. The integ
ral luminescence intensity (Il) was calculated
using the Origin Pro 8.5.1 software package.
Oxalohydrazide and salicylic acid imido
ester hydrochloride were synthesized as de-
scribed in [17, 18].
N,N’-dimethyloxalohydrazide was obtained
according to the following procedure (Fig. 1):
Fig. 1. – Synthesis of N, N’-dimethyloxalohydrazide.Fig. 1. – Synthesis of N, N’-dimethyloxalohydrazide.
(I) To a cooled (0°C) solution of methylhydrazine (0.1 mol) in dichloromethane (100 ml), a
solution of di-tert-butyl dicarbonate (Boc anhydride) (0.1 mol) in dichloromethane (100 ml) was
added dropwise. The mixture was stirred for 3 hours at room temperature, the solvent was
evaporated, and the residue was distilled (boiling point = 90°C, 20 mm Hg). Yield: 68%.
(II) In a 500 ml three-neck round-bottom flask equipped with a reflux condenser and
thermometer, 200 ml of dry dichloromethane was added. Then, 0.5 mol of N-BOC-N-
methylhydrazine and 0.5 mol of N,N-diisopropylethylamine (DIPEA, Hunig's base) were added.
The mixture was cooled to 0–5°C. To the mixture, 19 ml (0.22 mol) of freshly distilled oxalyl
chloride solution in 50 ml of dichloromethane was added dropwise while maintaining the
temperature below 5°C. After the addition of oxalyl chloride, the mixture was stirred for 24 hours at
room temperature. The solvent was then evaporated, yielding a colorless oil, which crystallized
upon stirring with water (1 liter). The white crystalline precipitate was filtered, then refluxed in
hexane using a Dean-Stark apparatus for 4 hours and filtered again. Yield: 75%.
(III) To a solution of disubstituted oxalic acid dihydrazide (0.165 mol, 1 eq.) in
dichloromethane, 1.65 mol (10 eq.) of trifluoroacetic acid was added, and the mixture was stirred
and refluxed for 24 hours. After cooling, the precipitate formed was filtered, then refluxed in
ethanol for 4 hours, and filtered again. Yield: 77%.
1,2,4-triazole-based Salen-type compounds, namely H4L12,2'-(1H,1'H-[3,3'-bi(1,2,4-
triazole)]-5,5'-diyl)diphenol (1) and H2L2, 2,2'-(1,1'-dimethyl-1H,1'H-[3,3'-bi(1,2,4-triazole)]-5,5'-
diyl)diphenol (2) were synthesized using a following method (Fig. 2):
In a 100 ml round-bottom flask, 10 mmol (1 eq.) of grinded oxalohydrazide were placed with
50 ml of methanol. To the resulting suspension, 50 mmol (5 eq.) of salicylic acid imido ester
hydrochloride and 50mmol (5 eq.) of triethylamine were added. The reaction mixture was refluxed
6 ISSN 2708-129X. Укр. хім. журн., 2024
SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES
WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES.INORGANIC CHEMISTRY
(I) To a cooled (0°C) solution of methylhy-
drazine (0.1 mol) in dichloromethane (100 ml),
a solution of di-tert-butyl dicarbonate (Boc an
hydride) (0.1 mol) in dichloromethane (100 ml)
was added dropwise. The mixture was stirred
for 3 hours at room temperature, the solvent
was evaporated, and the residue was distilled
(boiling point = 90°C, 20 mm Hg). Yield: 68%.
(II) In a 500 ml three-neck round-bottom
flask equipped with a reflux condenser and ther-
mometer, 200 ml of dry dichloromethane was
added. Then, 0,5 mol of N-BOC-N-methylhy-
drazine and 0,5 mol of N,N-diisopropylethyl-
amine (DIPEA, Hunig's base) were added. The
mixture was cooled to 0–5°C. To the mixture,
19 ml (0,22 mol) of freshly distilled oxalyl chlo-
ride solution in 50 ml of dichloromethane was
added dropwise while maintaining the temper-
ature below 5°C. After the addition of oxalyl
chloride, the mixture was stirred for 24 hours
at room temperature. The solvent was then
evaporated, yielding a colorless oil, which crys-
tallized upon stirring with water (1 liter). The
white crystalline precipitate was filtered, then
refluxed in hexane using a Dean-Stark appara-
tus for 4 hours and filtered again. Yield: 75%.
(III) To a solution of disubstituted oxalic acid
dihydrazide (0,165 mol, 1 eq.) in dichlorome
thane, 1,65 mol (10 eq.) of trifluoroacetic acid
was added, and the mixture was stirred and re-
fluxed for 24 hours. After cooling, the precipi-
tate formed was filtered, then refluxed in etha-
nol for 4 hours, and filtered again. Yield: 77%.
1,2,4-triazole-based Salen-type compounds,
namely H4L
12,2'-(1H,1'H-[3,3'-bi(1,2,4-triazo-
le)]-5,5'-diyl)diphenol (1) and H2L
2, 2,2'-(1,
1'-dimethyl-1H,1'H-[3,3'-bi(1,2,4-triazole)]-
5,5'-diyl)diphenol (2) were synthesized using a
following method (Fig. 2):
In a 100 ml round-bottom flask, 10 mmol
(1 eq.) of grinded oxalohydrazide were placed
with 50 ml of methanol. To the resulting sus-
pension, 50 mmol (5 eq.) of salicylic acid imi-
do ester hydrochloride and 50mmol (5 eq.) of
triethylamine were added. The reaction mix-
ture was refluxed with stirring for 36 hours.
The resulting precipitate of the ligand was fil-
tered and washed with methanol.
For H4L
1, yield 55%; 1НNMR: (400 MHz,
DMSO-d6), δ 14,52 (br, 2Н); 11,24 (br, 2Н);
8,04 (d, 2Н); 7,39 (t, 2Н); 7,06 (d, 2Н); 7,02 (t,
2Н). For С16H12N6O2 (MW = 320,31 g/mol):
Anal. calc.(%):С60,00, Н3,78, N26,24. Found
(%): С59,36, Н3,89, N27,2. Melting point =
286 ºC with decomposition; white powder, so
luble in DMF, poorly soluble in MeOH, insolu-
ble in most organic solvents.
For H2L
2, yield 46%; 1H NMR: (400 MHz,
DMSO-d6), δ 10,48 (s, 2Н); 7,47 (d, 2Н); 7,41
(t, 2Н); 7,06 (d, 2Н); 6,99 (t, 2Н); 3,85 (s, 6Н).
For С18H16N6O2(MW = 348,36 g/mol): Anal.
calc.(%): С62,06, Н4,63, N24,12. Found (%):
С61,74, Н4,29, N23,99. Melting point> 255 ºC
with decomposition; white powder, soluble in
DMF, poorly soluble in MeOH, insoluble in
most organic solvents.
Fig. 2. – General route for the synthesis of the ligands.
with stirring for 36 hours. The resulting precipitate of the ligand was filtered and washed with
methanol.
For H4L1, yield 55%; 1НNMR: (400 MHz, DMSO-d6), δ 14,52 (br, 2Н); 11,24 (br, 2Н); 8,04
(d, 2Н); 7,39 (t, 2Н); 7,06 (d, 2Н); 7,02 (t, 2Н). For С16H12N6O2 (MW = 320,31 g/mol):Anal.
calc.(%):С60,00, Н3,78, N26,24.Found (%):С59,36, Н3,89, N27,2. Melting point = 286ºC with
decomposition; whitepowder, solublein DMF, poorly solublein MeOH, in solublein most organic
solvents.
For H2L2, yield 46%; 1H NMR: (400 MHz, DMSO-d6), δ 10,48 (s, 2Н); 7,47 (d, 2Н); 7,41 (t,
2Н); 7,06 (d, 2Н); 6,99 (t, 2Н); 3,85 (s, 6Н). For С18H16N6O2(MW = 348,36 g/mol): Anal.
calc.(%):С62,06, Н4,63, N24,12. Found (%): С61,74, Н4,29, N23,99. Melting point> 255ºC with
decomposition; whitepowder, solublein DMF, poorly solublein MeOH, in soluble in most organic
solvents.
Fig. 2. – General route for the synthesis of the ligands.
A methodfor the synthesis of Ln(III) complexes was developed, testingvarious Ln(III)
salts(acetates, nitrates, and chlorides), different solvents (alcohols, DMF, DMSO), conditions such
as temperature, reagent ratios, deprotonating agents (triethylamine, ammonia). It was determined
that the complexes are formed effectively through the reaction of lanthanide acetates in methanol in
the presence of triethylamine and triethylorthoformate. Typically,0,5mmolofLn(III) acetateand 0,5
mmol of H4L1 (or H2L2) were placed in a 250 cm³ round-bottom flask with approximately 100 cm³
of MeOH. Then, about 1 cm³ of triethylamine and a few drops of triethyl orthoformate were added.
The mixture was refluxed until there agents were fully dissolved (3–4 hours). Next, the solution was
filtered through filter paper, evaporatedto 1/3 of its volume, and left tocoolinair. The following day,
a light-yellow fine crystalline precipitate was observed, which was separated from the mother liquor
by decantation. Yield was in the range of 65–70%. Thus, Ln1 and Ln2 (Ln = Eu, Lu) were
synthesized.
The isolated compounds were characterized by means of elemental analysis, FTIR
spectroscopy and mass spectrometry methods. In the mass spectrum of theEu(III) complex with
H4L1 (Fig. 3), signalsfor fragmented ion with m/z 563,23 and 561,22 were observed, identified
7https://ucj.org.ua
Valeriia S. Halushchenko, Oleksandr Yu. Korovin, Serhii S. Smola, Yurii S. Bibik, Dmytro M. Khomenko,
Roman O. Doroshchuk, Rostyslav D. Lampeka, Natalya V.Rusakova UCJ № 3 / Vol. 90
A method for the synthesis of Ln(III) com-
plexes was developed, testing various Ln(III)
salts (acetates, nitrates, and chlorides), different
solvents (alcohols, DMF, DMSO), conditions
such as temperature, reagent ratios, deprotonat-
ing agents (triethylamine, ammonia). It was de-
termined that the complexes are formed effec-
tively through the reaction of lanthanide acetates
in methanol in the presence of triethylamine
and triethyl orthoformate. Typically, 0,5 mmol
of Ln(III) acetate and 0,5 mmol of H4L
1 (or
H2L
2) were placed in a 250 cm³ round-bottom
flask with approximately 100 cm³ of MeOH.
Then, about 1 cm³ of triethylamine and a few
drops of triethyl orthoformate were added. The
mixture was refluxed until the reagents were ful-
ly dissolved (3–4 hours). Next, the solution was
filtered through filter paper, evaporated to 1/3
of its volume, and left to cool in air. The follow-
ing day, a light-yellow fine crystalline precipitate
was observed, which was separated from the
mother liquor by decantation. Yield was in the
range of 65–70%. Thus, Ln1 and Ln2 (Ln = Eu,
Lu) were synthesized.
The isolated compounds were characterized
by means of elemental analysis, FTIR spect
roscopy and mass spectrometry methods. In
the mass spectrum of the Eu(III) complex with
H4L
1 (Fig. 3), signals for fragmented ion with
m/z 563,23 and 561,22 were observed, iden-
tified as [Eu(H2L
1)(AcO)(MeOH)]; signals
with m/z 490,17 and 488,18 were identified as
[Eu(H2L
1)(H2O)]. The 2,0 m/z difference be-
tween the described peaks can be attributed to
the presence of Eu(III) isotopes with m = 151
and 153.
as[Eu(H2L1)(AcO)(MeOH)]; signals with m/z 490,17 and 488,18 were identified as
[Eu(H2L1)(H2O)]. The 2,0 m/z difference between the described peaks can be attributed to the
presence of Eu(III) isotopes with m = 151 and 153.
Fig. 3 – ESI mass spectra of Eu(III) complex with H4L1.
The IR spectra analysis for both Eu(III) complexes (Fig. 4) reveals consistent coordination
features and shifts compared to their respective free ligands, providing insights into complexation
behavior. In the spectrum of H4L1, a broad band at 3419 cm-1 is observedcorresponding to O–H
stretching of phenolic groups, involved in hydrogen bonding. In the spectrum of Eu1 multiple
bands appear in the 3500–3400 cm-1 region, suggesting interactions between Eu(III) ion and
coordinated water/methanol molecules. The bands around 1603 cm-1, 1569 cm-1, and 1537 cm-1 in
the spectrum of Eu1 are strong, indicating coordination interactions affecting the C=O/C=N
vibrations and possibly involving acetate. Specifically, the 1569 cm-1 and 1537 cm-1 bands suggest
asymmetric stretching of the C=O groups in the acetate. The presence of these bands close to 1569
cm-1 supports bidentate coordination of the acetate to Eu(III) [19]. Strong bands at 1603 cm-1
(complex) and 1622 cm-1 (free H4L1) region are likely due to C=N stretches of the triazole and
aromatic groups. This slight shift upon complexation indicates Eu(III) coordination affects electron
density in the ligand, altering C=N bonding character. The bands at 1413 cm-1 and 1398 cm-1 in the
spectrum of Eu1 suggest the C–O stretch of the phenolic group, shifting slightly compared to the
free ligand (1410 cm-1, 1399 cm-1). The shift and retention of the intensity suggest the Eu(III)
complexation impacts these bonds, potentially involving O-phenolic coordination.
Fig. 3 – ESI mass spectra of Eu(III) complex with H4L
1.
The IR spectra analysis for both Eu(III) com-
plexes (Fig. 4) reveals consistent coordination
features and shifts compared to their respective
free ligands, providing insights into complexa-
tion behavior. In the spectrum of H4L
1, a broad
band at 3419 cm-1 is observed corresponding to
O–H stretching of phenolic groups, involved
in hydrogen bonding. In the spectrum of Eu1
multiple bands appear in the 3500–3400 cm-1
region, suggesting interactions between Eu(III)
ion and coordinated water/methanol mole
cules. The bands around 1603 cm-1, 1569 cm-1,
and 1537 cm-1 in the spectrum of Eu1 are
strong, indicating coordination interactions af-
8 ISSN 2708-129X. Укр. хім. журн., 2024
SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES
WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES.INORGANIC CHEMISTRY
fecting the C=O/C=N vibrations and possibly
involving acetate. Specifically, the 1569 cm-1
and 1537 cm-1 bands suggest asymmetric
stretching of the C=O groups in the acetate.
The presence of these bands close to 1569 cm-1
supports bidentate coordination of the ace-
tate to Eu(III) [19]. Strong bands at 1603 cm-1
(complex) and 1622 cm-1 (free H4L
1) region are
likely due to C=N stretches of the triazole and
aromatic groups. This slight shift upon comp
lexation indicates Eu(III) coordination affects
electron density in the ligand, altering C=N
bonding character. The bands at 1413 cm-1 and
1398 cm-1 in the spectrum of Eu1 suggest the
C–O stretch of the phenolic group, shifting
slightly compared to the free ligand (1410 cm-1,
1399 cm-1). The shift and retention of the inten-
sity suggest the Eu(III) complexation impacts
these bonds, potentially involving O-phenolic
coordination.
Fig. 4. – IR spectra of compounds (a: 1 – H4L
1, 2 – EuL1, b: 1 – H2L
2, 2 – EuL2)
in comparison with the corresponding free ligands.
Bands around 1481 cm-1 (Eu1) and 1456 cm-1
in both spectra correspond to C=C stretches
of aromatic rings, with no significant shifts,
indicating limited Eu(III) influence on these
bonds. The complex’s additional bands (e.g.,
at 512 cm-1 and 444 cm-1) can be attributed to
Eu–O and Eu–N coordination, which are ab-
sent in the free ligand.
In the spectrum of H2L
2, a medium band
at 3448 cm-1 indicates O–H stretching, likely
from hydrogen-bonded phenolic groups. In
the spectrum of Eu2 complex, a strong band
appears at 3442 cm-1, indicating the presence
of coordinated water and methanol as in the
case of Eu1.
A medium band at 1624 cm-1 in the spec-
trum of H2L
2 can be attributed to C=N stretch-
ing in the triazole or aromatic system. In the
spectrum of the complex, this band shifts to
1604 cm-1 and increases in intensity, suggesting
coordination between Eu(III) ion and nitrogen
atoms, possibly altering the electron density
and stretching mode. In the spectrum of Eu2
complex, the bands at 1558 cm-1 and 1548 cm-1
represent the C=O stretching modes of ace-
tate-ion. The appearance of these two bands
9https://ucj.org.ua
Valeriia S. Halushchenko, Oleksandr Yu. Korovin, Serhii S. Smola, Yurii S. Bibik, Dmytro M. Khomenko,
Roman O. Doroshchuk, Rostyslav D. Lampeka, Natalya V.Rusakova UCJ № 3 / Vol. 90
points to a bidentate coordination of the ace-
tate to Eu (III) ion, as the two C=O bonds are
now involved in binding, altering their stretch-
ing behavior. Additionally, a strong band at
1462 cm-1 in the complex further indicates
asymmetric stretching in the C–O of acetate,
reinforcing the bidentate mode.
The bands in the 1590–1580 cm-1 range
of medium intensity for H2L
2 shift to 1558–
1548 cm-1 in the complex. This shift suggests
that C=N in the triazole ring are impact-
ed by Eu(III) coordination. A strong band
at 1480 cm-1 in both spectra represents C=C
stretching in the aromatic rings, which re-
mains strong, indicating that Eu(III) does not
significantly impact these aromatic bonds.
A medium band at 1403 cm-1 in H2L
2 shifts
to 1420 cm-1 in the complex, suggesting a
C–O stretch, likely from phenolic groups, in-
dicating involvement in coordination with
Eu(III). Bands around 1277 cm-1 and 1257 cm-1
in H2L
2 also shift to 1299 cm-1 and 1274 cm-1
in the complex, suggesting C–O vibrations
affected by complexation. The complex intro-
duces weak bands at 451 cm-1 and 580 cm-1,
likely representing Eu–O and Eu–N vibrations,
which do not appear in the free ligand, as in
the case of Eu1. Thus, the detailed analysis of
the IR spectra indicate the formation of stable
Eu(III) complexes with bidentate acetate co-
ordination, and coordination via triazole nit
rogen and phenolic oxygen atoms, comple-
mented by coordinated water and methanol
molecules.
Based on the obtained experimental data
and considering similar complexes described
in the literature, the structure of the synthe-
sized Eu(III) complexes was proposed (Fig. 5).
A medium band at 1403 cm-1 in H2L2 shifts to 1420 cm-1 in the complex, suggesting a C–O
stretch, likely from phenolic groups, indicating involvement in coordination with Eu(III). Bands
around 1277 cm-1 and 1257 cm-1 in H2L2 also shift to 1299 cm-1 and 1274 cm-1 in the complex,
suggesting C–O vibrations affected by complexation. The complex introduces weak bands at 451
cm-1 and 580 cm-1, likely representing Eu–O and Eu–N vibrations, which do not appear in the free
ligand, as in the case of Eu1. Thus, the detailed analysis of the IR spectra indicate the formation of
stable Eu(III) complexes with bidentate acetate coordination, and coordination via triazole nitrogen
and phenolic oxygen atoms, complemented by coordinated water and methanol molecules.
Based on the obtained experimental data and considering similar complexes described in the
literature, the structure of the synthesized Eu(III) complexes was proposed (Fig. 5).
Fig. 5. – Schematic structure of synthetized complexes (Ln = Eu(III), Lu(III)).
In the complex Ln1, the coordination polyhedron of the central atom includes two nitrogen
atoms from the 1,2,4-triazole groups, two oxygen atoms from the phenolic groups of the ligand, and
one oxygen atom from the acetate ion. The structure of the complexes Ln2 is similar to that of Ln1.
It should be noted that the exact number of coordinated solvent molecules has not been precisely
determined; however, according to mass spectrometry data, one or two labile molecules appear to
becoordinated, which exchange occurring between MeOH and H2O.
The absorption spectra of the compounds H4L1and H2L2 (Fig. 6) were analyzed in methanol
solutions at concentrations ranging from 1×10-4to 10-5 M. These compounds are characterized by
broad doubleb and swith maxima in the range of 265–270nm and 300–330nm, resulting from the
over lap of π→π* and n→π* transitions with in the conjugated systems of the benzene and 1,2,4-
triazole rings [20]. Methylation of the nitrogenatominthe 1,2,4-triazole rings results in a
bathochromic shift (Δλ = 20nm) of the maxima of the first absorption band with minimal change in
its intensity, which may indicate the involvement of the phenolicrings in the formation of in
tramolecular hydrogen bonds, specifically ‒O-H···N. These hydrogen bonds restrict therotation of
the phenolicrings [21]. Furthermore, the compound H2L2exhibits higher extinction than H4L1.
The complexation of Ln(III) with the H4L1and H2L2ligands leads to a slight bathochromic
shift (Δλ = 2–7 nm) of the absorption band maxima in the 300–330 nm region, which can indeed
Fig. 5. – Schematic structure of synthetized complexes (Ln = Eu(III), Lu(III)).
In the complex Ln1, the coordination po
lyhedron of the central atom includes two nit
rogen atoms from the 1,2,4-triazole groups,
two oxygen atoms from the phenolic groups of
the ligand, and one oxygen atom from the ace-
tate ion. The structure of the complexes Ln2 is
similar to that of Ln1. It should be noted that
the exact number of coordinated solvent mole-
cules has not been precisely determined; how-
ever, according to mass spectrometry data, one
or two labile molecules appear to be coordina
ted, which exchange occurring between MeOH
and H2O.
The absorption spectra of the compounds
H4L
1 and H2L
2 (Fig. 6) were analyzed in metha
nol solutions at concentrations ranging from
1×10-4 to 10-5 M. These compounds are cha
racterized by broad double bands with ma
xima in the range of 265–270 nm and 300–
330 nm, resulting from the overlap of π→π*
10 ISSN 2708-129X. Укр. хім. журн., 2024
SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES
WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES.INORGANIC CHEMISTRY
and n→π* transitions within the conjugated
systems of the benzene and 1,2,4-triazole rings
[20]. Methylation of the nitrogen atom in the
1,2,4-triazole rings results in a bathochromic
shift (Δλ = 20 nm) of the maxima of the first
absorption band with minimal change in its in-
tensity, which may indicate the involvement of
the phenolic rings in the formation of intramo-
lecular hydrogen bonds, specifically ‒O-H···N.
These hydrogen bonds restrict the rotation of
the phenolic rings [21]. Furthermore, the com-
pound H2L
2 exhibits higher extinction than
H4L
1.
The complexation of Ln(III) with the H4L1
and H2L
2 ligands leads to a slight bathochro-
mic shift (Δλ = 2–7 nm) of the absorption
band maxima in the 300–330 nm region,
which can indeed indicate coordination of the
nitrogen atoms in the 1,2,4-triazole groups and
the oxygen atoms in the phenolic groups of the
ligand. Such a bathochromic shift is typical for
processes associated with increased conjuga-
tion efficiency or changes in electron density
within the system, which often occur during
the coordination of metals with nitrogen- and
oxygen-containing donors. This effect can be
explained by shifts in the energy levels of the
ligand's electronic orbitals upon coordination,
leading to a change in the position of the ab-
sorption bands in the spectrum [20–24].
indicate coordination of the nitrogen atoms inthe 1,2,4-triazole groups and the oxygen atoms inthe
phenolic groups of the ligand. Such a bathochromic shift is typical for processes associated with
increased conjugation efficiency or changes in electron density within the system, which often
occur during the coordination of metals with nitrogen- and oxygen-containing donors. This effect
can be explained by shifts in the energy levels of the ligand's electronic orbitals upon coordination,
leading to a change in the position of the absorption bands in the spectrum [20–24].
a b
Fig. 6. – Absorption spectra of the compounds (a: 1 – H4L1 2 – Eu1; b: 1 – H2L2 2 – Eu2, DMF, C = 1×10-
4M).
The molecular luminescencespectral profileof Lu(III) complexes is similar acrossall ligands
and features a broad band in the 400–550 nm range, likely attributed to π-π* transitions with in the
ligand structure. Similar bands with a slight blue shift are observed in solutions (Fig. 7).
a b
Fig. 7. – Fluorescence (1) and phosphorescence (2) spectra of Lu1 (a) and Lu2 (b).
The alignment of the energy levels of the ligand (singlet S1 and triplet T1) and the excited
statesof Ln(III) ions is a key factor in ensuring the efficiency of luminescence in lanthanide
Fig. 6. – Absorption spectra of the compounds
(a: 1 – H4L
1 2 – Eu1; b: 1 – H2L
2 2 – Eu2, DMF, C = 1×10-4M).
The molecular luminescence spectral profile
of Lu(III) complexes is similar across all ligands
and features a broad band in the 400–550 nm
range, likely attributed to π-π* transitions with in
the ligand structure. Similar bands with a slight
blue shift are observed in solutions (Fig. 7).
The alignment of the energy levels of the li-
gand (singlet S1 and triplet T1) and the excited
states of Ln(III) ions is a key factor in ensuring
the efficiency of luminescence in lanthanide
complexes [1, 2]. In these complexes the en-
ergy level of the singlet state of the ligands is
22124 cm-1 for Lu1 and 24510 cm-1 for Lu2.
According to the provided data, the energy of
the lowest lying triplet state for both Lu1 and
Lu2 is 21008 cm-1, as determined from the
maximum wavelength of the phosphorescence
band (Fig. 7).
11https://ucj.org.ua
Valeriia S. Halushchenko, Oleksandr Yu. Korovin, Serhii S. Smola, Yurii S. Bibik, Dmytro M. Khomenko,
Roman O. Doroshchuk, Rostyslav D. Lampeka, Natalya V.Rusakova UCJ № 3 / Vol. 90
Fig. 7. – Fluorescence (1) and phosphorescence (2) spectra of Lu1 (a) and Lu2 (b).
indicate coordination of the nitrogen atoms inthe 1,2,4-triazole groups and the oxygen atoms inthe
phenolic groups of the ligand. Such a bathochromic shift is typical for processes associated with
increased conjugation efficiency or changes in electron density within the system, which often
occur during the coordination of metals with nitrogen- and oxygen-containing donors. This effect
can be explained by shifts in the energy levels of the ligand's electronic orbitals upon coordination,
leading to a change in the position of the absorption bands in the spectrum [20–24].
a b
Fig. 6. – Absorption spectra of the compounds (a: 1 – H4L1 2 – Eu1; b: 1 – H2L2 2 – Eu2, DMF, C = 1×10-
4M).
The molecular luminescencespectral profileof Lu(III) complexes is similar acrossall ligands
and features a broad band in the 400–550 nm range, likely attributed to π-π* transitions with in the
ligand structure. Similar bands with a slight blue shift are observed in solutions (Fig. 7).
a b
Fig. 7. – Fluorescence (1) and phosphorescence (2) spectra of Lu1 (a) and Lu2 (b).
The alignment of the energy levels of the ligand (singlet S1 and triplet T1) and the excited
statesof Ln(III) ions is a key factor in ensuring the efficiency of luminescence in lanthanide
Luminescence of the europium complexes
was observed in DMF solutions and in crys-
talline samples at both room temperature and
liquid nitrogen temperature (Fig. 8). Previous
studies indicate that the absorption and ex-
citation spectra of 4f-luminescence coincide,
which is supports the presence of intramolecu-
lar energy transfer from the excited electronic
levels of the ligands to the emitting level of the
Eu(III) ion.
Fig. 8. – 4f-Luminescence spectra of the complex Eu1 at 298 K
(for crystalline samples – 1 and solutions in DMF – 2)(a) and CIE chromaticity diagram 1931 (b).
complexes [1, 2]. In these complexes the energy level of the singlet state of the ligands is 22124 cm-
1 for Lu1 and 24510 cm-1 for Lu2. According to the provided data, the energy of the lowest lying
triplet state for both Lu1 and Lu2 is 21008 cm-1, as determined from the maximum wavelength of
the phosphorescence band (Fig. 7).
Luminescence of the europium complexes was observed in DMF solutions and in crystalline
samples at both room temperature and liquid nitrogen temperature (Fig. 8). Previous studies
indicate that the absorption and excitation spectra of 4f-luminescence coincide, which is supports
the presence of intramolecular energy transfer from the excited electronic levels of the ligands to
the emitting level of the Eu(III) ion.
580 600 620 640 660 680 700
0
200000
400000
600000
800000
1000000
J = 4
J = 3
J = 2
J = 1
Ilum, a.u.
, nm
1
2
J = 0
5D0 -
7FJ
a b
Fig. 8. – 4f-Luminescence spectra of the complex Eu1 at 298 K (for crystalline samples – 1 and solutions in
DMF – 2)(a) and CIE chromaticity diagram 1931 (b).
The CIE coordinates for the Eu-centered emission were calculated,placing both Eu1 and Eu2
in the red region of the CIE 1931 chromaticity diagram [25]. For Eu1, coordinates x=0,631 and y=
0,368 indicate a deep red emission, representinga rich, saturated red light. The coordinates forEu2
arex = 0,603 and y = 0,396, also fall within the red region but are slightly shifted toward a warmer
hue compared to Eu1. This shift may result from differences in the ligand field or subtlevariations
in coordination symmetry, affecting the precise emission profile of the Eu(III) ion and slightly
altering the hue.
Thecorrelated color temperature(CCT) values provide additional context on the warmth of the
emitted light. For Eu1, a CCT of 2017,94 K indicates a warm, intense red light with low color
temperature, consistent with deep red region. Such a CCT is typical for narrow red emissions, often
desirable inapplications like red phosphors for LEDs that require pure red chromaticity. Eu2, with a
slightly lower CCT of 1720,92 K, producesa warmer and deeper red emission than Eu1. The lower
indicate coordination of the nitrogen atoms inthe 1,2,4-triazole groups and the oxygen atoms inthe
phenolic groups of the ligand. Such a bathochromic shift is typical for processes associated with
increased conjugation efficiency or changes in electron density within the system, which often
occur during the coordination of metals with nitrogen- and oxygen-containing donors. This effect
can be explained by shifts in the energy levels of the ligand's electronic orbitals upon coordination,
leading to a change in the position of the absorption bands in the spectrum [20–24].
a b
Fig. 6. – Absorption spectra of the compounds (a: 1 – H4L1 2 – Eu1; b: 1 – H2L2 2 – Eu2, DMF, C = 1×10-
4M).
The molecular luminescencespectral profileof Lu(III) complexes is similar acrossall ligands
and features a broad band in the 400–550 nm range, likely attributed to π-π* transitions with in the
ligand structure. Similar bands with a slight blue shift are observed in solutions (Fig. 7).
a b
Fig. 7. – Fluorescence (1) and phosphorescence (2) spectra of Lu1 (a) and Lu2 (b).
The alignment of the energy levels of the ligand (singlet S1 and triplet T1) and the excited
statesof Ln(III) ions is a key factor in ensuring the efficiency of luminescence in lanthanide
12 ISSN 2708-129X. Укр. хім. журн., 2024
SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES
WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES.INORGANIC CHEMISTRY
The CIE coordinates for the Eu-centered
emission were calculated, placing both Eu1 and
Eu2 in the red region of the CIE 1931 chromatic-
ity diagram [25]. For Eu1, coordinates x=0,631
and y= 0,368 indicate a deep red emission, rep-
resenting a rich, saturated red light. The coordi-
nates for Eu2 are 6x = 0,603 and y = 0,396, also
fall within the red region but are slightly shifted
toward a warmer hue compared to Eu1. This
shift may result from differences in the ligand
field or subtle variations in coordination sym-
metry, affecting the precise emission profile of
the Eu(III) ion and slightly altering the hue.
The correlated color temperature (CCT) va
lues provide additional context on the warmth of
the emitted light. For Eu1, a CCT of 2017,94 K
indicates a warm, intense red light with low
color temperature, consistent with deep red
region. Such a CCT is typical for narrow red
emissions, often desirable in applications like
red phosphors for LEDs that require pure red
chromaticity. Eu2, with a slightly lower CCT of
1720,92 K, produces a warmer and deeper red
emission than Eu1. The lower CCT aligns with
the slight shift in CIE coordinates, indicating
that emission of Eu2 is perceptibly warmer,
likely due to subtle structural differences that
influence the Eu(III) electronic environment.
Table 1.
Luminescent characteristics of Eu(III) complexes.
Complex
η
(5D0-
7F2)/(5D0-
7F1)
τ, ms
φem, Ф, %
DMF solid
DMF solid 298K 77K 298K 77K DMF solid
Eu1 7,6 7,1 0,533 0,549 0,544 0,706 0,023 29,7
Eu2 7,9 7,5 0,563 0,584 0,575 0,685 0,019 26,7
The luminescence decay curves of the com-
plexes were analyzed and fitted with single ex-
ponential decay law (Table 1). The shorter life-
time at room temperature (0,544 ms) suggests
the presence of non-radiative decay pathways,
consistent with a coordination environment
that facilitates vibrational relaxation process-
es. The increase in lifetime at low temperatures
(0,706 ms at 77K) is typical, as non-radiative
processes are suppressed at lower tempera-
tures. This behavior suggests a somewhat open
coordination structure with lower symmetry,
allowing for more vibrational coupling and
therefore non-radiative decay at higher tem-
peratures [26].
The emission spectrum of the Eu(III) com-
plex provides insight into its coordination
environment, revealing information on lo-
cal symmetry, coordination number, and the
point symmetry group of the Eu(III) center
[27]. The luminescent profile of the Eu(III)
complex in the solid state at 77K (Table 2)
shows characteristic emissions in the visible
region, with well-resolved transitions from
the excited 5D0 state to various 7FJ ground-
state levels. Key observed transitions include
the following: 5D0→7F0 as a single, sharp peak
at 580,0 nm; 5D0→7F1 as three peaks at 590,0,
593,2, and 595,8 nm, indicating splitting due
to lower symmetry around the Eu(III) center;
13https://ucj.org.ua
Valeriia S. Halushchenko, Oleksandr Yu. Korovin, Serhii S. Smola, Yurii S. Bibik, Dmytro M. Khomenko,
Roman O. Doroshchuk, Rostyslav D. Lampeka, Natalya V.Rusakova UCJ № 3 / Vol. 90
5D0→7F2 as four distinct peaks at 614,7, 615,4,
616,2, and 619,8 nm, corresponding to the hy-
persensitive electric dipole transition and sug-
gesting a non-centrosymmetric environment.
Higher-order transitions 5D0→7F3 and 5D0→7F4
exhibit even more splitting: the 5D0→7F3 tran-
sition shows five peaks (647,7, 649,6, 650,8,
651,7, and 653,6 nm), and the 5D0→7F4 tran-
sition shows seven peaks (684,8, 686,1, 690,0,
692,6, 694,2, 698,5, and 700,0 nm), indicating
a high degree of asymmetry in the ligand field.
It should be noted that in DMF solutions,
the profile of band splitting is consistent with
that observed in solid state, indicating struc-
tural identity in both crystalline and solution
phases.
Table 2.
Splitting of bands in the emission spectrum of Eu1 complex.
Measurement conditions
λmax, nm
5D0→7F0
5D0→7F1
5D0→7F2
5D0→7F3
5D0→7F4
solution
(DMF)
298K 580,0 590,8
593,9
616,0
620,0
651,0
657,0
687,0
691,1
699,0
77K 579,8
590,0
593,2
595,8
614,7
615,4
616,2
619,8
647,7
649,6
650,8
651,7
653,6
684,8
686,1
690,0
692,6
694,2
698,5
700,0
crystal
298K 580,2
590,0
593,5
596,4
614,3
616,1
620,4
651,0
652,3
685,9
690,5
694,6
698,5
700,2
77K 580,3
590,1
593,6
596,5
614,5
616,2
620,2
620,8
649,1
650,4
651,8
652,4
653,3
685,8
690,5
693,9
694,5
697,1
698,5
700,4
Given the observed high asymmetry and
distinctive splitting patterns, the coordination
polyhedron around Eu(III) likely has a coor-
dination number (CN) of 8 or 9. This CN is
typical for polyhedra with low symmetry such
as a bicapped trigonal prism (CN=8) or tri-
capped trigonal prism (CN=9). The symmetry
type appears to be low, likely Cs or C2v, based
on the pronouncedsplitting and high η intensi-
ty ratio (5D0-
7F2)/(5D0-
7F1). These point groups
lack a center of inversion, which explains the
enhanced electric dipole transitions.
14 ISSN 2708-129X. Укр. хім. журн., 2024
SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES
WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES.INORGANIC CHEMISTRY
CONCLUSIONS. An optimized synthesis
protocol was developed for Ln(III) complexes
with 1,2,4-triazole-based Salen-type ligands
using various salts, solvents, and deprotonating
agents. Through the use of lanthanide acetates
in methanol with triethylamine and triethyl
orthoformate, crystalline Ln(III) complexes
were obtained with high yields (65-70%). Cha
racterization by IR and mass spectrometry
confirmed the formation of specific coordi-
nation structures, including Eu(III)-centered
complexes with triazole and phenolic groups,
involving coordination of multiple N and O do-
nor atoms from the ligand and acetate groups.
The IR and absorption spectra revealed sub-
stantial shifts upon complex formation, con-
sistent with effective coordination of Eu(III)
by nitrogen and oxygen donors, and indicat-
ing changes in electronic conjugation. Eu(III)
complexes exhibited luminescence with in-
tense red emission. The luminescence lifetimes
indicated the presence of non-radiative path-
ways at higher temperatures, which aligns with
an open, lower symmetry coordination envi-
ronment. Emission spectra analysis at low tem-
peratures revealed significant splitting in the
Eu(III) transitions, consistent with a low-sym-
metry coordination polyhedron, likely in a
bicapped or tricapped trigonal prismatic ar-
rangement with Cs or C2v point group sym-
metry. This is supported by the intensity ratio
and emission profile. The study establishes a
foundation for further exploration of these
complexes in applications requiring controlled
luminescence properties. The CIE coordinates
and CCT values highlight their potential as
high-purity red-emitting complexes with de-
sirable color characteristics for optoelectronic
and photonic applications, with Eu2 exhibiting
a slightly redder and warmer tone than Eu1.
AKNOWLEDGEMENT. The work was
carried out with the financial support
of the National Academy of Sciences of
Ukraine within the state budget topic «New
near-infrared luminescent materials based
on modified tetrapyrrole and complex oxide
compounds of d- and f-elements: synthesis,
design, properties». The state registration
number of the work is 0122U000415.
СИНТЕЗ, ХАРАКТЕРИСТИКА ТА ЛЮМІНЕС-
ЦЕНТНІ ВЛАСТИВОСТІ КОМПЛЕКСІВ ЄВРО-
ПІЮ (III) З ЛІГАНДАМИ SALEN-ТИПУ, ЩО
МІСТЯТЬ 1,2,4-ТРИАЗОЛЬНІ ФРАГМЕНТИ
Валерія С. Галущенко1,2, Олександр Ю. Коро-
він1, Сергій С. Смола1, Юрій С. Бібік3, Дмитро
М. Хоменко3,4, Роман О. Дорощук3,4, Ростис-
лав Д. Лампека3, Наталя В. Русакова1
1Фізико-хімічний інститут ім. О. В. Богат-
ського НАН України,
Люстдорфська дорога, 86, 65080 Одеса,
Україна;
2Факультет хімії та фармації Одеського на-
ціонального університету ім. І. І. Мечникова,
вул. Дворянська, 2, Одеса 65026, Україна;
3Хімічний факультет Київського національ-
ного університету імені Тараса Шевченка,
вул. Володимирська, 60, Київ 01601, Україна;
4ТОВ «НВП «Єнамін»(www.enamine.net),
вул. Вінстона Черчилля, 78, Київ 02094,
Україна
*e-mail: valeriia.halushchenko@gmail.com
У роботі представлено синтез, характе-
ристику та фотофізичне дослідження но-
вих комплексів Ln(III)з лігандами Salen-ти-
пу на основі 1,2,4-триазолу, зокрема оптич-
15https://ucj.org.ua
Valeriia S. Halushchenko, Oleksandr Yu. Korovin, Serhii S. Smola, Yurii S. Bibik, Dmytro M. Khomenko,
Roman O. Doroshchuk, Rostyslav D. Lampeka, Natalya V.Rusakova UCJ № 3 / Vol. 90
ні властивості комплексів з європієм. Було
оптимізовано метод синтезу для утворення
комплексів Ln(III) з використанням різ-
них солей, розчинників та депротонуючих
агентів, серед яких найефективнішими
виявилися метанол, триетиламін та трие-
тилортоформіат. Це дозволило отримати
світло-жовті кристалічні продукти з вихо-
дами 65–70%. За допомогою ІЧ-спектроско-
пії та мас-спектрометрії охарактеризовано
координацію через атоми азоту та кисню,
що підтримується зсувами в коливальних
смугах, які вказують на зв’язки Eu–N та
зміни в коливаннях фенольних груп ОН і
С=О. Спектри поглинання в УФ-видимій
області продемонстрували батохромний
зсув, вказуючи на змінену густину електро-
нів і підвищену кон'югацію через комплек-
соутворення. Під час збудження комплекси
проявляли флуоресценцію в діапазоні 400–
450 нм і фосфоресценцію в діапазоні 450–
550нм, що вказує на ефективну передачу
енергії в системі. Кольорові координати CIE
для Eu1 (x=0,631, y=0,368) та Eu2 (x=0,603,
y=0,396) вказують на насичене червоне ви-
промінювання з високою чистотою кольо-
ру та значеннями корельованої колірної
температури (CCT) 2017,94K та 1720,92K
відповідно, що робить їх придатними для
чисто-червоного випромінювання в опто-
електронних засобах. Вимірювання часу
життя (0,544 мс при 298 K та 0,706 мс при
77 K) вказують на наявність безвипроміню-
вальних релаксаційних процесів, які потен-
ційно модулюються локальною симетрією,
що підтверджується характерним розще-
пленням ліній випромінювання переходів
Eu(III). Спектри випромінювання проде-
монстрували виразні переходи, типові для
іонів Eu(III), з інтенсивним розщепленням,
що вказує на низькосиметричне середови-
ще, ймовірно, у точкових групах C₂ᵥ або Cs.
Структурний аналіз вказує на координа-
ційне число 8, припускаючи поліедральні
конфігурації, такі як дво- або тришапкову
тригональну призму. Цей метод синтезу
ефективно дозволяє отримати комплек-
си Ln(III) з керованими люмінесцентними
властивостями, виявляючи ключові залеж-
ності структура – властивість і забезпечу-
ючи спрямоване червоне випромінювання,
що робить ці комплекси перспективними
для застосування в дисплеях та освітлю-
вальних технологіях.
Ключові слова: європій(III), основи
Шиффа, ліганди Salen-типу, комплекси, лю-
мінесценція.
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Cтаття надійшла 20.01.2024.
|
| id | oai:ojs2.1444248.nisspano.web.hosting-test.net:article-647 |
| institution | Ukrainian Chemistry Journal |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2026-07-23T01:11:25Z |
| publishDate | 2024 |
| publisher | V.I.Vernadsky Institute of General and Inorganic Chemistry |
| record_format | ojs |
| resource_txt_mv | ucjorgua/62/f10e499e805b259b6f79ece29c805162.pdf |
| spelling | oai:ojs2.1444248.nisspano.web.hosting-test.net:article-6472026-07-22T08:23:54Z SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES Halushchenko, Valeriia Korovin, Oleksandr Smola, Serhii Bibik, Yurii Khomenko, Dmytro Doroshchuk, Roman Lampeka, Rostyslav Rusakova, Natalya Europium(III), Schiff bases, Salen-type ligands, Complexes, Luminescence. The study presents the synthesis, characterization, and photophysical investigation of novel Ln(III)complexes with 1,2,4-triazole-based Salen-type ligands, focusing on europium-centered optical properties. An optimized synthetic method for Ln(III) complex formation was developed with the use of various salts, solvents, and deprotonating agents, with methanol, triethylamine, and triethylorthoformate yielding the best results. This approach produced light-yellow crystalline products with a 65–70% yield. Structural characterization through IR spectroscopy and mass spectrometry confirmed coordination by nitrogen and oxygen atoms, as evidenced by shifts in vibrational bands indicative of Eu–N bonds and alterationsin phenolic OH and CO stretching modes. UV-Vis absorption spectra revealed bathochromic shifts, indicating changes in electron density and increased conjugation resulting from complex formation. Upon excitation, the complexes exhibited fluorescence in the 400–500 nm range and phosphorescence in the 450–550 nm range, demonstrating effective energy transfer within the system. The CIE chromaticity coordinates for EuL1 (x=0,631, y=0,368) and EuL2 (x=0,603, y=0,396) denote a deep red emission with color purity and correlated color temperature (CCT) values of 2017,94 K and 1720,92 K, respectively, indicating their potential for high-purity red emissions in optoelectronic applications. Lifetime measurements (0,544 ms at 298 K and 0,706 ms at 77 K) indicate non-radiative relaxation processes that may be modulated by local symmetry, as suggested by the distinctive emission splitting in Eu(III) transitions. Emission spectra revealed prominent transitions typical of Eu(III) ions, with extensive splitting indicative of a low-symmetry environment, likely within C₂ᵥ or Cs point groups. Structural analysis supports a coordination number of 8, suggesting polyhedral arrangements like a bicapped trigonal prism. This synthetic route effectively produces Ln(III) complexes with tunable luminescent properties, revealing key structure-property relationships and enabling tailored red emissions, making these complexes promising precursors for display and lighting technologies. V.I.Vernadsky Institute of General and Inorganic Chemistry 2024-04-29 Article Article Inorganic Chemistry Неорганическая химия Неорганічна хімія application/pdf https://ucj.org.ua/index.php/journal/article/view/647 10.33609/2708-129X.90.3.2024.3-17 Ukrainian Chemistry Journal; Vol. 90 No. 3 (2024): Ukrainian Chemistry Journal; 3-17 Украинский химический журнал; ##issue.vol## 90 ##issue.no## 3 (2024): Ukrainian Chemistry Journal; 3-17 Український хімічний журнал; Том 90 № 3 (2024): Ukrainian Chemistry Journal; 3-17 2708-129X 2708-1281 en https://ucj.org.ua/index.php/journal/article/view/647/323 Copyright (c) 2024 Valeriia Halushchenko, Oleksandr Korovin, Serhii Smola, Yurii Bibik, Dmytro Khomenko, Roman Doroshchuk, Rostyslav Lampeka, Natalya Rusakova https://creativecommons.org/licenses/by-nc/4.0 |
| spellingShingle | Halushchenko, Valeriia Korovin, Oleksandr Smola, Serhii Bibik, Yurii Khomenko, Dmytro Doroshchuk, Roman Lampeka, Rostyslav Rusakova, Natalya SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES |
| title | SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES |
| title_full | SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES |
| title_fullStr | SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES |
| title_full_unstemmed | SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES |
| title_short | SYNTHESIS, CHARACTERIZATION, AND LUMINESCENT PROPERTIES OF EUROPIUM(III) COMPLEXES WITH SALEN-TYPE LIGANDS CONTAINING 1,2,4-TRIAZOLE MOIETIES |
| title_sort | synthesis, characterization, and luminescent properties of europium(iii) complexes with salen-type ligands containing 1,2,4-triazole moieties |
| topic_facet | Europium(III) Schiff bases Salen-type ligands Complexes Luminescence. |
| url | https://ucj.org.ua/index.php/journal/article/view/647 |
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