New rare-earth metal acyl pyrazolonates: Synthesis, crystals structures, and luminescence properties

Article abstract of DOI:10.1134/S1070328414090024

Ligand 3-methyl-1-phenyl-4-stearoylpyrazol-5-one (HQ) is synthesized and used to obtain new complexes of rare-earth metals (Eu, Gd, and Tb) of the composition [Ln(Q)₃(H₂O)(EtOH)]. The crystal structure of the terbium complex is determined by X-ray diffraction analysis (CIF file CCDC 975286). In a molecule of the complex, three aliphatic fragments n-C ₁₇H₃₅ are codirected, which results in the formation of layers bound according to the fastener-sticker principle. The molecules of the complex are joined by a hydrogen bond network involving the pyrazolone rings and oxygen atoms of the inner-sphere solvent molecules (H₂O and EtOH). The terbium complex is luminescent at room temperature, whereas the luminescence of the europium complex is very weak at room temperature and increases by 60 times at lowered temperatures. This makes it possible to consider these compounds as a new class of luminescent thermometers.

Full text of DOI:10.1134/S1070328414090024

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2014, Vol. 40, No. 9, pp. 627–633. © Pleiades Publishing, Ltd., 2014.
Original Russian Text © Yu.A. Belousov, V.V. Utochnikova, S.S. Kuznetsov, M.N. Andreev, V.D. Dolzhenko, A.A. Drozdov, 2014, published in Koordinatsionnaya Khimiya, 2014,
Vol. 40, No. 9, pp. 543–549.
New RareꢀEarth Metal Acyl Pyrazolonates: Synthesis, Crystals
Structures, and Luminescence Properties
Yu. A. Belousova, *, V. V. Utochnikovaa, b, S. S. Kuznetsova, M. N. Andreeva,
V. D. Dolzhenkoa, and A. A. Drozdova
a Moscow State University, Moscow, 119899 Russia
b Lebedev Physical Institute, Russian Academy of Sciences, Leninskii pr. 53, Moscow, 119991 Russia
*eꢀmail: belousov@gmail.com
Received December 4, 2013
Abstract—Ligand 3ꢀmethylꢀ1ꢀphenylꢀ4ꢀstearoylpyrazolꢀ5ꢀone (HQ) is synthesized and used to obtain new
complexes of rareꢀearth metals (Eu, Gd, and Tb) of the composition [Ln(Q)3(H2O)(EtOH)]. The crystal
structure of the terbium complex is determined by Xꢀray diffraction analysis (CIF file CCDC 975286). In a
molecule of the complex, three aliphatic fragments nꢀC17H35 are codirected, which results in the formation
of layers bound according to the fastenerꢀsticker principle. The molecules of the complex are joined by a
hydrogen bond network involving the pyrazolone rings and oxygen atoms of the innerꢀsphere solvent moleꢀ
cules (H2O and EtOH). The terbium complex is luminescent at room temperature, whereas the luminescence
of the europium complex is very weak at room temperature and increases by 60 times at lowered temperatures.
This makes it possible to consider these compounds as a new class of “luminescent thermometers.”
DOI: 10.1134/S1070328414090024
INTRODUCTION
Ligand HQ and some other acylpyrazolones formꢀ
ing complexes [Ln(L)3(H2O)(EtOH)] are shown in the
scheme.
Permanent interest in luminescent complexes of
lanthanides, first of all, terbium and europium comꢀ
plexes, is due to the possibility of their practical use in
OLED devices [1] and luminescent sensors [2] and as
biological labels [3]. The lanthanide complexes with
3ꢀmethylꢀ1ꢀphenylpyrazolꢀ5ꢀones are characterized
by the simple synthesis, good luminescence characterꢀ
istics, and the possibility of controlling the luminesꢀ
cence properties by the variation of the radical at the
carbonyl group [4–9]. Interest in compounds containꢀ
ing the extended aliphatic chain is related to the possiꢀ
bility of their use for the deposition of Langmuir–
Blodgett films and immobilization on the nanoparticle
surface. It is also interesting to study processes of
vibrational luminescence quenching from the viewꢀ
point of the development of materials for luminescent
thermometers.
O
O
R'
Ph
N
N
R
HQ: R = Me, R' = nꢀC17H35
HL1: R = Me, R' = CH2CH2
HL2: R = Ph, R' = CH2Ph
HL3: R = Me, R' =
S
The structures of the rareꢀearth metal complexes
with ligand HQ were not studied. At the same time,
three extended nꢀC17H35 fragments assume two possiꢀ
Ligand HQ [10] was earlier studied for the purpose
of possible applications in the extraction separation of
rareꢀearth metals [11, 12]. However, the task of the
synthesis and isolation of individual complexes was
ble structures of the complex: with differently directed
aliphatic fragments to form a 2D network as in the case
of [Cd(Q)2(EtOH)2] and with codirected aliphatic
not stated and their luminescence properties were not fragments.
studied. The synthesis of the cadmium complex
We synthesized ligand HQ and complexes
Ln(Q)3(H2O)(EtOH)], where Ln is Eu ( ), Gd (II),
and Tb (III). The crystal structure of complex III was
determined and demonstrated the codirected arrangeꢀ
ment of the aliphatic fragments. The photophysical
[
Cd(Q)2(EtOH)2] was described in which individual
[
I
molecules are linked into infinite chains through
hydrogen bonds between the N(2) atom of each
acylpyrazolone and ethanol molecule of the adjacent
fragment [13]. In each molecule, the aliphatic residues
C17H35 are linear and antiparallel to each other.
properties of complexes I–III were studied.
627

628
BELOUSOV et al.
Table 1. Elemental analysis results for HQ and
compounds III
acted SOCl2. The reaction product was purified by
recrystallization from ꢀhexane. The yield was 76%.
I–
n
1H NMR (CDCl3),
, ppm: 0.86–0.89 (3H, m,
CH3–C16H32), 1.26–1.41 (28H, m, (CH2)14–CH3),
.70–1.78 (2H, m, CH2–C15H31), 2), 2.47 (3H, s.,
CH3–Рz), 2.71–2.75 (2H, t, CH2ꢀC16H33), 7.54–7.29
(3H, m, pꢀ and ꢀHꢀAr), 7.82–7.84 (2H, d, ꢀHꢀAr).
δ
Content (found/calculated), %
Compound
C
H
N
1
HQ
76.1/76.32
67.1/67.29
67.3/67.06
66.7/66.99
10.2/10.06
9.1/9.00
9.3/8.97
9.1/8.96
6.2/6.36
5.3/5.47
5.2/5.46
5.3/5.45
m
o
I
The syntheses of I–III were carried out by dropping
an alcohol solution of the corresponding rareꢀearth
metal (70 mmol, 5 mL) to an alcohol solution of the in
situ obtained KQ (210 mmol, 10 mL). The reaction
mixture was refluxed for 20–30 min and cooled, chloꢀ
roform (5 mL) was added, and potassium nitrate preꢀ
cipitated from the solution was filtered off. Solutions
of compounds I–III in an ethanol–chloroform mixꢀ
ture were evaporated to 2 mL and cooled, and the
crystallized reaction mixture was filtered off. The preꢀ
cipitates were washed on the filter with diethyl ether
and dried in a vacuum drying box over P2O5 for 48 h.
The yield was ~70%. The elemental analysis results for
compounds I–III are given in Table 1.
II
III
EXPERIMENTAL
The following commercially available reagents and
solvents were used without additional purification:
stearic acid, SOCl2, 3ꢀmethylꢀ1ꢀphenylpyrazolꢀ5ꢀ
one, potassium hydroxide, acetonitrile, and ethanol.
Dioxane was dehydrated by storage above molecular
sieves (4 Å) followed by distillation under argon. Terꢀ
bium, gadolinium, and europium nitrates were
obtained by the dissolution of the corresponding
oxides (reagent grade) in nitric acid (special purity
grade).
Complex
I
: IR,
ν
, cm–1: 3739 (OH), 3573, 2931–
2856 (CH), 1941, 1868, 1740, 1636, 1508
ν(С=С,
С=О), 1470, 1151, 1083, 996, 760, 630, 496, 483.
IR spectra in the attenuated total internal reflecꢀ
tance mode were recorded on a SpectrumOne specꢀ
trophotometer (PerkinElmer) in the range from 650 to
4000 cm–1. A small amount of the triturated sample
was placed in a cell and pressed to a diamond crystal,
and the spectrum was recorded.
MALDI: 592 (EuQ), 1031, 1259 (EuQ2), 1493
(EuQ3 + C2H5), 1593 (Eu2Q2(Q–C2H5)), 1621
(Eu2Q2(Q–C17H35))
Complex II: IR,
2859 (CH), 1944, 1871, 1786, 1740, 1560, 1491
(С=С, С=О), 1364, 1210, 1151, 1082, 984, 906, 758,
642, 509.
Complex III: IR,
2854 (CH), 1941, 1859, 1652, 1549, 1527
.
ν
, cm–1: 3667 (OH), 3317, 2952–
ν
Matrixꢀassisted
laser
desorption/ionization
(MALDI) mass spectrometry was carried out on an
Autoflex II instrument with a timeꢀofꢀflight detector
(Bruker Daltonics, Germany).
The photoluminescence spectra of powdered samꢀ
ples was measured using an S2000 multichannel specꢀ
trometer (Ocean Optics, US) and an LGIꢀ21 nitrogen
ν
, cm–1: 3662 (OH), 3318, 2926–
(С=С,
ν
С=О), 1467, 1343, 1205, 1151, 1064, 962, 803, 746,
652, 526, 450.
Single crystals of complex III were obtained as colꢀ
orless needles at the slow evaporation of a solution of
the complex in ethanol.
laser (λexc = 337 nm) as an excitation source. The
measurements were carried out at 300 and 77 K. All
luminescence and excitation spectra were measured
with a correction to instrumental functions.
The Xꢀray diffraction analysis of complex III was
carried out on a Bruker SMART APEX2 automated
The lifetimes of the excited state were determined
from the spectra recorded using an EG&G system
(Princeton applied research) containing the averaging
scheme with a narrowꢀband filter (model 162). The
system included a gated oscillator (model 164) and a
broadꢀband preamplifier (model 115) with the excitaꢀ
tion of the organic ligands (λexc = 337 nm) and detecꢀ
diffractometer (λMoKα, graphite monochromator) at
160 K. The structure was solved by a direct method.
The positions of hydrogen atoms were found in differꢀ
ence Fourier syntheses. Nonꢀhydrogen atoms were
refined by least squares in the anisotropic approximaꢀ
tion, and all hydrogen atoms were determined in
the isotropic approximation. The APEX2, SAINT,
SADABS, and XPRE programs were used for the colꢀ
tion of the transitions 5D4
→ →
7F5 and 5D0 7F2 of terꢀ
bium and europium ions, respectively. The lifetimes
were averaged by three independent measurements.
lection and processing of the
I(hkl) array [15]. The
calculations were performed using the SHELX97 proꢀ
The synthesis of HQ was carried out according to a gram package [16]. The crystallographic parameters
modified standard procedure for the synthesis of for structure III are given in Table 2. The coordinates
acylpyrazolones [14], replacing calcium hydroxide by of atoms and other parameters for structure III were
freshly calcined CaO. Stearyl chloride was preliminarꢀ deposited with the Cambridge Crystallographic Data
ily obtained by the reaction of stearic acid with an Centre (CCDC 975286; deposit@ccdc.cam.ac.uk or
excess of SOCl2 followed by the distillation of unreꢀ http://www.ccdc.cam.ac.uk/data_request/cif).
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NEW RAREꢀEARTH METAL ACYL PYRAZOLONATES
629
Table 2. Crystallographic data and the experimental and reꢀ
finement parameters for structure III
RESULTS AND DISCUSSION
Structure III is built of Tb(Q)3(H2O)(EtOH) molꢀ
ecules (Fig. 1). The coordination polyhedron of the
central atom can be described as a strongly distorted
square antiprism with the bases O(1), O(2), O(6),
O(7)(H2O) and O(3), O(4), O(5), O(8)(EtOH). The
L–O distances in structure III and in complexes
Parameter
Value
M
1535.89
Triclinic
Crystal system
Space group
P
1
[
Ln(Q)3(H2O)(EtOH)] are presented in Table 3.
a
, Å
, Å
14.871(4)
15.311(4)
20.446(5)
82.410(4)
73.482(3)
66.011(3)
4076.9(17)
1.251
The Tb–O(Q) bonds in complex III are shorter, on
b
the average, than those in other studied complexes by
1.5–2%. This is due to the fact that the С17H35 group
occupies a smaller volume near the central atom than
the cyclic substituents in the complexes described earꢀ
lier. For the same reason, the Tb–О(H2O) and Tb–
O(EtOH) bonds in complex III are shorter than those
in other similar complexes by 2–4% on the average.
c
, Å
, deg
, deg
, deg
, Å3
α
β
γ
V
ρcalcd, g/cm3
Molecules of complex III are packed in infinite
planar layers formed by a hydrogen bond network
between the oxygen atoms of the solvents and unsubꢀ
stituted nitrogen atoms of ligands Q of three adjacent
molecules of the complex. The O(7)(H2O)–N(6),
O(7)(H2O)–N(2), and O(8)(EtOH)–N(4) distances
are 2.832(13), 2.874(12), and 2.748 Å, respectively.
The shortest Tb–Tb distance in the layer is 9.357 Å.
Z
2
Scan range,
θ, deg
2.07–26.37
Index range
–18
≤
h
≤
17, –19
≤ l ≤
≤ k ≤ 19,
–24 25
Goodnessꢀofꢀfit for F2
2.110
Number of measured/indepenꢀ
dent reflections
31248/14791
Individual layers (Fig. 2) in structure III are surꢀ
rounded from two sides by extended fragments C17H35
Number of refined parameters
910
.
The aliphatic residue of the first acylpyrazolone moleꢀ
cule (C(12)–C(28)) exists in the conformation similar
to an ideal one for the untwisted aliphatic chain. The
R
R
factors (
factors (all reflections)
Δρmin
Å–3
I
> 2
σ
(
I
))
R
R
1 = 0.1088, wR2 = 0.3247
1 = 0.1411, wR2 = 0.3323
3.244/–2.742
Δρmax
/
, e
residue of the second molecule (C(12А)–C(28А)) is
turned after the C(15
(C(13 )C(15 )C(17 ) 134.42
(C(24 )C(26 )C(28 ) 102.87
atom. Finally, the residue of the third molecule
С(12 )–C(28 ) is turned by 52° after the C(14
A
)
atom by 46
°
°
A
A
A
A
A
A
°) and then by 77
atom (C(12B)C(14B)C(16B) 127.92°)). Due to these
bents, all three residues become codirected and have
approximately the same extension (the Tb–C(28),
°) after the C(26A)
(
B
B)
B)
C(13)
C(15)
C(17)
C(19)
C(23)
C(12)
C(21)
C(25)
C(26)
C(27)
C(28)
N(2)
C(14)
C(16)
C(28)
C(18)
C(20)
C(22)
C(24)
N(3)
O(3)
O(6)
O(2)
O(1)
N(4)
N(1)
Tb(1)
O(4)
O(7)
O(8)
O(5)
N(6)
C(28A)
N(5)
Fig. 1. Molecular structure of complex III. The phenyl groups at the N(1), N(3), and N(5) atoms and hydrogen atoms are omitted.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40 No. 9 2014

630
BELOUSOV et al.
Table 3. Comparison of the Ln–O bond lengths in structure III and in some other terbium and europium acyl pyraꢀ
zolonates
d
, Å
Bond
III
Tb(L1)3(H2O)(EtOH) [7] Tb(L2)3(H2O)(EtOH) [17] Eu(L3)3(H2O)(EtOH) [18]
Ln–O(1)
Ln–O(2)
Ln–O(3)
Ln–O(4)
Ln–O(5)
Ln–O(6)
2.276
2.364
2.325
2.341
2.398
2.303
2.3345
2.410
2.404
2.347
2.349
2.301
2.324
2.369
2.353
2.3590
2.470
2.391
2.356
2.362
2.396
2.357
2.412
2.352
2.391
2.382
2.3816
2.497
2.514
2.363
2.352
2.331
2.341
2.456
2.430
Av. Ln–O(L)
Ln–O(7)(H2O)
Ln–O(8)(EtOH)
Tb–C(28A), and Tb–C(28B) distances are 20.213, according to the fastenerꢀsticker principle (Fig. 3).
19.681, and 21.145 Å, respectively). The layers are The Tb–Tb distance between the nearest terbium
linked by the interpenetration of these fragments atoms of two adjacent layers is 30.336 Å.
(a)
(b)
Fig. 2. Layer of molecules III bound by hydrogen bonds: along the (a)
x and (b) y axes.
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NEW RAREꢀEARTH METAL ACYL PYRAZOLONATES
631
Fig. 3. Packing of the layers in structure III according to the fastenerꢀsticker principle (along the x axis).
The sizes of thermal ellipsoids of atoms in the molꢀ the characteristic narrow intense bands with maxima
ecule are not uniformly distributed: they increase sigꢀ at 490, 545, 583, and 621 nm and the unresolved
nificantly on going from the nearest coordination broadened peak with a maximum at 651 nm correꢀ
sphere of the metal (3ꢀmethylꢀ1ꢀphenylacypyraꢀ sponding to the electron transitions 5D4
→
7FJ
(J = 6,
zolone ring) to less structurally rigid aliphatic chains.
5, 4, 3, 2–0) inside the f shell of the terbium ion. Both
the intensity and character of the luminescence specꢀ
trum of complex III remains almost unchanged as the
temperature decreases (Fig. 5a). The absence of a
temperature dependence of the luminescence is conꢀ
firmed by the data of measurements of the lifetime
The space between the layers linked by hydrogen
bonds contain cavities infinite along the
having linear sizes of 2.7 11.5 Å. Similar cavities are
also arranged along the axis but their sizes are smaller
(1.7 11 Å). We believe that these cavities can be filled
x axis and
×
y
×
with various molecules of an appropriate size to
approach the synthesized complex to materials of the
class of metalꢀorganic framework (MOF) structures.
The photoluminescence spectrum of gadolinium
complex II was recorded at 77 K (Fig. 4) to estimate
the position of the triplet level of ligand HQ. The specꢀ
trum exhibits three bands with maxima at 21800,
19200, and 16300 cm–1, i.e., they differ by ~2800–
3000 cm–1. These values correspond to the frequencies
of intense vibrations of the OH and CH groups of the
complex, which allows us to ascribe the corresponding
bands to the transitions from the excited triplet state to
different vibrational levels of the ground singlet state
and to estimate the position of the triplet level of the
acylpyrazolone ligand as Т1 = 21800 cm–1. This value
corresponds to the efficient energy transfer to the
1.0
0.8
0.6
0.4
0.2
0
excited 5D4 level of the terbium ion ( 5D4
ΔЕ(T1 → ) =
1400 cm–1), whereas the gap between the Т1 and
5D0 levels of the europium ion is too large, being
4400 cm–1.
400
500
600
Wavelength, nm
700
800
In fact, the study of the photoluminescence spectra
of complexes I and III shows that at room temperature
only complex III exhibits an intense luminescence
Fig. 4. Normalized photoluminescence spectrum of comꢀ
plex II at 77 K ( = 337 nm).
(Fig. 5a). The luminescence of the Tb3+ ion appears as
λ
exc
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
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632
BELOUSOV et al.
(а)
(b)
2000
1500
1000
500
0
2000
1500
1000
500
0
300 К
77 К
77 К
300 К
400
600
Wavelength, nm
800
560
640
Wavelength, nm
720
Fig. 5. Normalized photoluminescence spectra of complexes (a) III and (b)
peratures.
I
(λ
= 337 nm) at room and lowered (77 K) temꢀ
exc
(τ, µs) of the excited state (λexc = 337 nm), which is substantially change the nearest coordination enviꢀ
also temperatureꢀindependent:
ronment of the central atom compared to the earlier
known acyl pyrazolonates. Three aliphatic fragments
of ligand HQ are codirected. The intense luminesꢀ
cence of the terbium ion in complex III makes it posꢀ
sible to consider complex III and related structures as
promising for problems of modifying the surfaces of
hydrophobic particles and preparing porous frameꢀ
work structures of the MOF class. At the same time,
the temperature dependence of the luminescence
77 К
300 К
Compound
I
332(13)
610(10)
No data
610(10)
III
The luminescence of complex
I
at room temperaꢀ
ture is very lowꢀintensity but is significantly enhanced
at a lowered temperature (to 77 K) and appears as four
peaks with maxima at 590, 613, 650, and 697 nm corꢀ
intensity in complex I is interesting from the viewpoint
of developing “luminescent thermometers.”
responding to the electron transitions 5 5D0
→ (J =
7FJ
1, 2, 3, 4) inside the
(Fig. 5b). The ratio of luminescence intensities
I77 I300) was chosen as a parameter characterizing the
temperature dependence of the luminescence properꢀ
ties. This ratio for complex is 60. This value is high:
for example, in [19] the record value for the studied
terbium compounds was I77 I300 = 80. This allows one
to ascribe complex to the class of “luminescent therꢀ
mometers” [19–23].
The reason for the temperature dependence of the
luminescence of complex is too high position of the
Т1 level and the presence of the long alkyl substituent
in the acylpyrazolone ligand. This results in the nonraꢀ
diative vibrational relaxation of the excited state at
room temperature and luminescence at a lowered
temperature, when the vibrational levels are “frozen
out.” The phenomenon is also confirmed by the fact
f shell of the europium ion
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Translated by E. Yablonskaya
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 40
No. 9
2014