Influence of the nature of carboxylic acid on the luminescence and spectral properties of (carboxylato)bis(dibenzoylmethanato)europium(III) complexes

Article abstract of DOI:10.1023/A:1012318729308

A series of (carboxylato)bis(dibenzoylmethanato)europium(III) complexes containing anions of both saturated and unsaturated carboxylic acids were synthesized to compare the luminescence and spectral properties of heteroligand Eu(III) complexes. (Carboxylato)bis(dibenzoylmethanato)europium(III) complexes with unsaturated acid anions were synthesized for the first time. The compounds obtained were characterized using elemental analysis and luminescence and IR spectroscopy. These studies revealed two types of influence of the nature of an acid substituent on the luminescence spectra of (carboxylato)bis(dibenzoylmethanato)europium(III) complexes. The anomalous Stark structure of the luminescence spectra of one group of compounds is attributed to the charge transfer state at 77 K.

Full text of DOI:10.1023/A:1012318729308

Russian Journal of Coordination Chemistry, Vol. 27, No. 10, 2001, pp. 746–750. Translated from Koordinatsionnaya Khimiya, Vol. 27, No. 10, 2001, pp. 790–794.
Original Russian Text Copyright © 2001 by Karasev, Petrochenkova, Mirochnik, Petukhova, Lifar.
Influence of the Nature of Carboxylic Acid
on the Luminescence and Spectral Properties
of (Carboxylato)bis(dibenzoylmethanato)europium(III) Complexes
V. E. Karasev, N. V. Petrochenkova, A. G. Mirochnik, M. V. Petukhova, and L. I. Lifar
Institute of Chemistry, Far East Division, Russian Academy of Sciences,
pr. Stoletiya Vladivostoka 159, Vladivostok, 690022 Russia
Received August 21, 2000
Abstract—A series of (carboxylato)bis(dibenzoylmethanato)europium(III) complexes containing anions of
both saturated and unsaturated carboxylic acids were synthesized to compare the luminescence and spectral
properties of heteroligand Eu(III) complexes. (Carboxylato)bis(dibenzoylmethanato)europium(III) complexes
with unsaturated acid anions were synthesized for the first time. The compounds obtained were characterized
using elemental analysis and luminescence and IR spectroscopy. These studies revealed two types of influence
of the nature of an acid substituent on the luminescence spectra of (carboxylato)bis(dibenzoylmetha-
nato)europium(III) complexes. The anomalous Stark structure of the luminescence spectra of one group of
compounds is attributed to the charge transfer state at 77 K.
The creation of light-collecting and light-transform- methanato)europium(III) complexes with the unsatur-
–
–
ing composite materials, including those produced ated acid anions TFAc and Form were obtained for
from macromolecular complexes (MMCs), is of topical the first time.
interest. Metal-containing polymers with various chro-
mophores can be prepared, e.g., through polymeriza-
EXPERIMENTAL
tion and copolymerization of metal-containing mono-
mers [1, 2].
Unlike (carboxylato)(β-diketonato)europium(III)
complexes [5], the Eu(Dbm) Acid · nH O complexes
Previously [3, 4], we studied the luminescence and
2
2
(
n = 0, 0.5, and 1) were synthesized in one step by
reacting stoichiometric amounts of Eu(NO ) · 6H O,
spectral properties and polymerization transformations
of Ln(III) salts with unsaturated acids and of the
derived heteroligand complexes. Insofar as the fluores-
cence intensity of the lanthanide ions in MMC is low,
study of the energy migration in lanthanide-containing
monomers and in MMCs and the search for methods of
3 3
2
the corresponding acid, and HDbm in a small amount
of ethanol with continuous stirring. The reaction mix-
ture was neutralized with ethanolic ammonia, and the
resulting precipitate was filtered off, washed with etha-
nol, and dried in air and in vacuo. For example,
3
+
sensitizing the fluorescence of Ln are topical prob-
lems. Dibenzoylmethane C H CO(CH )COC H
Eu(Dbm) Acr · 0.5H O was prepared as follows.
2
2
6
5
2
6
5
Eu(NO) · 6H O (0.0024 mol) was dissolved under
(
HDbm) is known to possess a branched π electron sys-
3
2
heating in 20 ml of ethanol, and HDbm (0.0012 mol)
was added. Then, HAcr (0.0012 mol) was added drop-
wise with continuous stirring. The reaction mixture was
neutralized by adding a concentrated solution of
ammonia in drops with stirring until a voluminous pow-
dery precipitate of Eu(Dbm) Acr · 0.5H O was formed.
tem, which can favor fluorescence sensitization.
In continuation of the studies into the influence of
the composition and structure of starting metal-contain-
ing monomers on the fluorescence of MMC, as well as
for the purpose of comparing the luminescence and
spectral properties of heteroligand complexes contain-
ing saturated [5, 6] and unsaturated carboxylic acids,
we investigated the luminescence and spectral proper-
ties of some (carboxylato)bis(dibenzoylmetha-
nato)europium(III) complexes Eu(Dbm) Acid· nH O
2
2
The precipitate was filtered off, washed repeatedly with
ethanol, and dried in air and then in vacuo at 60°ë.
All of the (carboxylato)bis(dibenzoylmetha-
nato)europium(III) complexes are yellow powders and
are insoluble in water and nonpolar organic solvents but
soluble in hot DMF, DMSO, dioxane, and cyclohex-
anone under heating.
2
2
–
–
(
whereAcid is the acrylate (Acr ), methacrylate (Macr ),
–
–
cinnamate (Cin ), α-cyano-β-phenylacrylate (CN-Cin ),
–
–
β-piperanylacrylate (β-Pipacr ), formate (Form ), ace-
–
–
–
tate (Ac ), trifluoroacetate (TFAc ), propionate (Prop ),
The compounds obtained were characterized using
–
–
–
butyrate (But ), valerate (Val ), isovalerate (Isoval ), elemental analysis (Table 1) and IR and luminescence
–
–
caproate (Hex ), and caprylate (Oct ) anions, and n = 0, spectroscopy. IR spectra were recorded on a Perkin-
.5, and 1). Note that the (carboxylato)bis(dibenzoyl- Elmer Spectrum-1000 spectrophotometer (KBr) in the
0
1
070-3284/01/2710-0746$25.00 © 2001 åÄIä “Nauka /Interperiodica”

INFLUENCE OF THE NATURE OF CARBOXYLIC ACID
Table 1. Elemental analysis data for the Eu(Dbm) RCOO · nH O complexes
747
2
2
Content (found/calculated), %
No.
R
n
Empirical formula
C
H
N
Eu
I
CH =CH
(Acr)
(Macr)
(Cin)
0.5 Eu C H O
57.94/58.04 4.06/3.83
58.72/58.87 4.00/3.89
61.86/61.99 4.21/4.10
22.33/22.41
22.00/21.93
20.01/20.13
2
33 26 6.5
II
CH =C(CH )
0.5 Eu C H O
2
3
34 28 6.5
III
Ph–CH=CH
0.5 Eu C H O
30 6.5
3
9
IV
CO CH CH (β-Pipacr)
Eu C H O
9
61.70/61.65 4.11/4.01
19.80/19.05
4
1
30
O
O
V
Ph–CH=C(CN)
(CN-Cin)
(Form)
(TFAc)
(Ac)
0.5 Eu C H O N
61.84/61.53 4.05/3.84 1.80/1.79 19.70/19.48
4
0
29
6
VI
H
Eu C H O
57.89/57.85 3.56/3.42
52.52/52.60 3.39/3.56
58.46/58.44 3.78/3.81
58.46/59.02 3.99/4.02
59.53/59.56 4.59/4.23
61.75/61.80 4.50/4.43
61.98/61.80 4.64/4.43
60.23/60.59 4.60/4.63
61.56/61.54 4.91/4.99
23.80/23.64
20.47/20.82
23.00/23.14
22.48/22.65
22.30/22.16
21.98/21.75
22.00/21.75
21.03/21.32
20.38/20.51
3
1
23
6
VII
VIII
IX
CF3
CH3
C H
1
Eu C H O F
32
24
7
6
6
6
6
6
6
6
3
Eu C H O
32
25
(Prop)
(But)
Eu C H O
2
5
7
9
33 27
X
C H
Eu C H O
3
34 29
XI
C H
(Val)
Eu C H O
4
35 31
XII
XIII
XIV
i-C H
(Isoval)
(Hex)
Eu C H O
4
9
35 31
C H
Eu C H O
5
11
36 33
C H
(Oct)
Eu C H O
7
15
38 37
–
1
–
–
range 400–4000 cm . Luminescence spectra were ν (COO ). The difference between the ν (COO ) and
s
as
–
–1
recorded on a SDL-1 spectrometer with a DRSh-250 ν (COO ) frequencies (~130 cm ) suggests a bridging
s
mercury lamp as an excitation source. Luminescence bidentate coordination of the carboxyl groups by the
excitation spectra were recorded on a setup based on europium atom [8].
the SDL-1 spectrometer and an MRD-23 monochroma-
The IR spectra of I–III, V, and VII show bands at
tor with a Tungsram xenon lamp (2500 W) as an exci-
–1
3
300–3400 cm from the stretching vibrations of
tation source. Measurements were carried out at 300
and 77 K.
water. The presence of crystallization water in these
compounds is also confirmed by thermogravimetric
measurements (elimination of the water molecules
occurs below 100°ë).
RESULTS AND DISCUSSION
The IR spectra of the (carboxylato)bis(dibenzoyl-
The antisymmetrical and symmetrical CH and CH
3
2
–
1
methanato)europium(III) complexes obtained are alike. stretching vibrations give bands at 2850–2950 cm .
They all show a set of intense absorption bands at 550– Their intensities in the spectra of compounds VIII–
–1
9
00 and 1380–1597 cm . These bands cannot be pre- XIV depend on the number of skeletal carbon atoms in
cisely assigned because the CO and phenyl stretching the corresponding acid. The intensities of the ν (CH )
as
2
–
–1
vibrations in dibenzoylmethane, as well as ν (COO ) and ν (CH ) bands (at 2926 and 2850 cm , respec-
as
s
2
–
and ν (COO ) in the acid, overlap.
tively) increase when passing from (acetato)bis(diben-
zoylmethanato)europium(III) to (caprylato)bis(diben-
zoylmethanato)europium(III).
s
–
1
The intense band at 1552 cm corresponds to
–
–
ν(C=O) of Dbm [7]. The benzene rings of Dbm give
–
1
bands at 1480 and 1597 (ν(C=C)) and 1070 cm (in-
plane deformation vibrations) and medium-intensity
The IR spectra of I–V and VII contain bands char-
acteristic of the corresponding substituents in R. Thus,
the spectra of Eu(Dbm) Cin · 0.5H O, Eu(Dbm) (CN-
–
1
bands at 686, 720, 750, and 784 (out-of-plane defor-
mation vibrations). The positions and intensities of
these bands in the spectra of (carboxylato)bis(diben-
zoylmethanato)europium(III) complexes are very close
to those in the IR spectrum of dibenzoylmethana-
toeuropium(III).
2
2
2
Cin) · 0.5H O, and Eu(Dbm) (β-Pipacr) show broad-
2
2
ened bands from the benzene ν(C=C) vibrations; in
–1
addition, bands at 1070, 784, and 750 cm correspond-
ing to the benzene δ(CH) vibrations become more
intense and split into two components. The intensity of
–
1
The carboxylate anions in complexes I–XIV give a the band at 3060 cm (the ν(CH) vibrations of the ben-
–
1
–
new band at 1520 cm (ν (COO )) and a doublet at zene ring) also increases. The spectrum
as
–1
1
380–1400 cm , a component of which is due to ofEu(Dbm) (CN-Cin) · 0.5H O contains a weak ν(CN)
2
2
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 10 2001

7
48
KARASEV et al.
5
7
D → F
0
2
(
a)
(b)
CTS
π* ← n
5
7
D → F
0
1
4
CTS
3
2
CTS
CTS
1
'
1
3
00
400
500
580
600
620
λ, nm
Fig. 1. (a) Luminescence excitation spectra (λlum = 615 nm, 77 K) and (b) luminescence spectra (77 K) of (1, 1' (300 K))
Eu(Dbm) Acr · 0.5H O, (2) Eu(Dbm) å‡cr · 0.5H O, (3) Eu(Dbm) Cin · 0.5H O, and (4) Eu(Dbm) Oct.
2
2
2
2
2
2
2
band at 2222 cm–1 [8]. The IR spectrum of groups. The first group includes complexes I–IV and
Eu(Dbm) (β-Pipacr) exhibits additional bands at VIII–XIV, whose luminescence spectra (Fig. 1b) differ
2
–1
1
252 (s) and 1041 cm (m) attributable to the ν(=C–O–) significantly in band splitting and intensity distribution
and ν(C–O–C) vibrations of the piperanyl group. In the from those of most of the known Eu(III) complexes and
IR spectrum of Eu(Dbm) (TFAc) · H O, a ν(CF ) band are similar to the spectra of the previously studied (car-
appears at 1200 cm . The spectra of complexes I–V boxylato)(dibenzoylmethanato)europium(III)
2
2
3
–1
com-
that contain an unsaturated acid anion show a band at plexes [5].
–
1
1
640 cm corresponding to the ν(C=C) vibrations of
5
7
In the spectra of these compounds, the D – F sin-
0
0
the acid. The deformation and stretching vibrations of
the chelating M–O bond give bands in the range below
5
7
glet-singlet transition is more intense than the D – F
0
1
5
7
–
1
one. The Stark components of the D – F transition are
0 1
6
50 cm .
spaced apart at a long distance; the splitting value ∆F1
The
(carboxylato)bis(dibenzoylmetha- is nearly the same for all complexes of this group
5
7
nato)europium(III) complexes obtained exhibit bright (17.3–18.8 nm). The D − F transition band contains
0
2
luminescence at 77 K. Based on their luminescence up to seven components, which can be subdivided into
spectra, one can divide these compounds into two three groups depending on their intensities. Note that
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 10 2001

INFLUENCE OF THE NATURE OF CARBOXYLIC ACID
749
5
7
the acid structure (the presence of substituents and the
hydrocarbon radical length) most strongly influences
D → F
0 2
(a)
(b)
5
7
the redistribution of the intensities of the D – F tran-
π* ← n
0
2
sition bands in the range 607–612 nm, in which two to
four bands of different intensity can appear (Fig. 1b)
5
7
D → F
0
1
The luminescence spectra of the complexes belong-
ing to the second group (V–VII) are close to those of
5
7
3
2
most Eu(III) chelate complexes [9]. The D – F transi-
0
2
tion accounts for the major fraction of emission energy,
5
7
the intensity of the D – F transition being insignifi-
0
0
cant (Fig. 2b). The ∆F value is nearly constant for the
compounds of this group (7.9–8.4 nm).
1
The relative luminescence intensities I for the
fl
obtained Eu(III) complexes at 77 and 300 K are pre-
sented in Table 2. The I value for Eu(Dbm) Hex at
fl
2
3
00 K was taken as an arbitrary unit. It can be seen that
Eu(Dbm) Oct (77 K) has the highest I value among the
2
fl
compounds under study. The intensity I increases with
fl
the carbon chain length in the order VIII–XI and then
from XIII to XIV.
The changes in the luminescence and spectral prop-
erties of the compounds under discussion are most
probably associated with the nature of substituents R in
1
'
–
RCOO . The electron influence of the substituents on
the reaction centers in like organic ligands can be char-
1
acterized by an inductive constant of substituents σ*
(the Taft constant) [10]. It is known that σ* serves as a
measure of the inductive effect, as it is proportional to
the electron density redistribution on a reaction center
caused by substituents [11]. The second group includes
3
00 400 500
580
600
620
λ, nm
–
Fig. 2. (a) Luminescence excitation spectra (λlum = 615 nm,
7 K) and (b) luminescence spectra (77 K) of (1, 1' (300 K))
Eu(Dbm) (CN-Cin) · 0.5ç é, (2) Eu(Dbm) Form, and (3)
the Eu(Dbm) Acid · nH O complexes in which Acid
2
2
7
has substituents with a strong negative inductive effect
2
2
2
(
CN, CF , and H). In the diffuse luminescence spectra
3
Eu(Dbm) (TFAÒ) · H O.
2
2
of these compounds (V–VII), I decreases with an
fl
increase in σ* (Table 2), while the spectra of the com-
plexes with a weak negative (CH=CH, C H , and
6
5
alous Stark structures characterized by an unusually
CH=CH ) or positive inductive effect (CH , C H , etc.)
2
3
2
5
5
high luminescence intensity of the singlet-singlet D –
of the acid substituent have a discrete character. In the
0
7
7
series of compounds VIII–XIV, I increases with a
F transition and by a large Stark splitting ∆ F . Such
0
1
fl
decrease in σ*.
a distribution of the luminescence intensity cannot be
explained by the Judd–Ofelt theory and seems to be due
The luminescence spectra of the complexes belong-
ing to the first group (I–IV and VIII–XIV) have anom- to a partially borrowed intensity from the charge trans-
Table 2. Relative luminescence intensity of the (carboxylato)bis(dibenzoylmethanato)europium(III) complexes at 77 and
3
00 K and the Taft constants σ* for the acid substituents
Ifl, arbitrary units
Ifl, arbitrary units
77 K 300 K
Compound
σ* [10]
+0.40
+0.41
Compound
σ* [10]
7
7 K
300 K
I
3876
4926
6922
2667
2774
4334
4489
34
48
VIII
IX
3957
5634
6346
7370
5664
6662
7385
2
4
0.00
II
–0.100
–0.115
–0.130
–0.125
–0.162
III
IV
V
4
X
19
2
1
XI
132
363
609
XII
XIII
XIV
37
1
VI
VII
+0.49
+2.60
1
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 10 2001

7
50
KARASEV et al.
fer band [9]. The formation of charge transfer com-
plexes at 77 K for the compounds of the first group is
indicated by the presence of a long-wave component at
ACKNOWLEDGMENTS
This work was supported by the Russian Foundation
for Basic Research, project no. 98-03-32472a.
4
20–460 nm in their luminescence excitation spectra
(
Fig. 1a). This band is absent from the luminescence
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positive inductive effect in the latter complexes.
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pletely (the intensity decreases by more than a hundred
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VII (the second group) and of most Eu(III) chelates.
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This study revealed two types of influence of the
nature of a substituent in a carboxylic acid on the lumi-
nescence spectra of (carboxylato)bis(dibenzoylmetha-
nato)europium(III) complexes. The anomalous Stark
structure of the luminescence spectra of the compounds
belonging to the first group is attributed to the charge
transfer complexes formed at 77 K.
1
1
1. Vereshchagin, A.N., Induktivnyi effekt (Inductive
Effect), Moscow: Nauka, 1987.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 27 No. 10 2001