Effect of heptadentate (N4O3) tripodal Schiff base ligand and its yttrium(III) complex on the luminescence and extraction of tris(β-diketonato)europium(III)

Article abstract of DOI:10.1016/j.jallcom.2007.04.152

In order to learn the effect of a Schiff base and the complex of Y^III on the extraction of Eu^III with β-diketones and on the luminescence of the extracted species, the extraction of Eu^III with 2-thenoyltrifluoroacetone (Htta) and/or these Schiff bases, tris(5-t-butyl)salicylidenaminoethyl amine (H₃L¹), and its Y^III complex ([YL¹]) prepared, into CHCl₃ was examined. Further, the luminescence and excited spectra of CHCl₃ phases extracted Eu^III complexes and the solutions containing tris(β-diketonato)Eu^III and/or the Schiff bases were measured. On the measurement of the luminescence spectra, tris(pivaloyltrifluoroacetonato)Eu^III (Eu(pta)₃) as well as Eu(tta)₃ was used. Synergistic effect with Htta and these Schiff bases was observed. However, proper effect of Y^III was not observed. The luminescence intensity of Eu(tta)₃ at 613 nm decreased with increasing concentration of H₃L¹ or [YL¹], whereas that of Eu(pta)₃ increased with increasing concentration of the ligands, but no difference between both Schiff bases was observed, because of picking up of Y^III from [YL¹] with the interaction between [YL¹] and water.

Full text of DOI:10.1016/j.jallcom.2007.04.152

Journal of Alloys and Compounds 451 (2008) 320–324
Effect of heptadentate (N4O3) tripodal Schiff base ligand and its
yttrium(III) complex on the luminescence and extraction
of tris(␤-diketonato)europium(III)
Y. Hasegawaa,∗, S. Saitoua, D. Nagaokaa, H. Yajimaa, M. Kanesatob
a Department of Chemistry, Faculty of Science, Science University of Tokyo, Tokyo 162-8601, Japan
b National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8562, Japan
Available online 19 April 2007
Abstract
In order to learn the effect of a Schiff base and the complex of YIII on the extraction of EuIII with ␤-diketones and on the luminescence of
the extracted species, the extraction of EuIII with 2-thenoyltrifluoroacetone (Htta) and/or these Schiff bases, tris(5-t-butyl)salicylidenaminoethyl
amine (H3L1), and its YIII complex ([YL1]) prepared, into CHCl3 was examined. Further, the luminescence and excited spectra of CHCl3 phases
extracted EuIII complexes and the solutions containing tris(␤-diketonato)EuIII and/or the Schiff bases were measured. On the measurement of the
luminescence spectra, tris(pivaloyltrifluoroacetonato)EuIII (Eu(pta)3) as well as Eu(tta)3 was used. Synergistic effect with Htta and these Schiff
bases was observed. However, proper effect of YIII was not observed. The luminescence intensity of Eu(tta)3 at 613 nm decreased with increasing
concentration of H3L1 or [YL1], whereas that of Eu(pta)3 increased with increasing concentration of the ligands, but no difference between both
Schiff bases was observed, because of picking up of YIII from [YL1] with the interaction between [YL1] and water.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Europium(III); 2-Thenoyltrifluoroacetone; Pivaloyltrifluoroacetone; Tris(5-t-butyl)salicylidenaminoethyl amine; Luminescence enhancement
expected to obtain the dinuclear complexes consisting of EuIII
and YIII as the extracted species in the synergistic extraction of
EuIII with ␤-diketone and the Lewis base [4].
1. Introduction
Since lanthanoid(III) complexes with ␤-diketone and Lewis
base such as 1,10-phenanthroline show much stronger lumines-
cence than the tris(␤-diketonato)Ln itself, the ternary complexes
can be used for micro-analysis [1]. The ternary complexes con-
sisting of lanthanoids(III), ␤-diketones, and Lewis bases are
mostlyacceptedastheextractedspeciesinthesynergisticextrac-
tion of lanthanoids(III) with ␤-diketones and Lewis bases.
In the present paper, the effect of a Schiff base and the com-
plex of YIII on the luminescence of tris(␤-diketonato)EuIII and
the extraction of EuIII with ␤-diketone into CHCl3 has been
examined. As a Schiff base, tris(5-t-butyl)salicylidenaminoethyl
amine was used to neutralize the charge of YIII. Yttrium(III) was
chosen because YIII would be expected to function as sensitizer,
since luminescence enhancement is observed in aqueous solu-
tions, e.g., theluminescenceofEuIII ␤-diketonateinthepresence
of YIII was enhanced in the micellar environment [2,3]. It was
2. Experimental
Reagents: The ␤-diketones and the Schiff bases used in the present work
are shown in Scheme 1. Tris(␤-diketonato)EuIII was prepared in a similar way
described elsewhere [5]. The purity was checked with elemental analysis—For
C
24H30F9EuO6 (Eu(pta)3): Anal. Calcd. C 39.1, H 4.10; found: C 37.1, H 4.20.
C24H12S3F9EuO6 (Eu(tta)3·H2O): Anal. Calcd. C 34.6, H 1.69; found: C 37.0,
H 1.62.
Tris[4-(2-hydroxy-5-tert-butylphenyl)-3-aza-3-butenyl]amine (H3L1):
A
solution of 5-tert-butylsalicylaldehyde (2.68 g, 15.0 mmol) in methanol (20 cm3)
was added to a hot solution of tris(2-aminoethyl)amine (tren) (0.73 g, 5.0 mmol)
in methanol (40 cm3). The solution was stirred at 50–60 ◦C for 10 min. After
cooling, the precipitate was filtered and dried in vacuo to leave a yellow powder
(2.44 g, 78%). Anal. Calcd. for C39H54N4O3: C, 74.72%; H, 8.68%; N, 8.94%;
found: C, 75.06%; H, 8.72%; N, 8.89%.
[YL1]: A solution of tren (1.46 g, 10.0 mmol) in methanol (5 cm3) was added
to a hot solution of Y(CF3SO3)3 (2.68 g, 5.0 mmol) in methanol (40 cm3). The
reaction solution was stirred at 50–60 ◦C for 2 min. Then, a solution of 5-
tert-butylsalicylaldehyde (2.68 g, 15.0 mmol) in methanol (5 cm3) was added
and stirred at 50–60 ◦C for 2 min. After cooling, the precipitate was filtered
and dried in vacuo to leave a yellow powder (3.01 g, 83%). Anal. Calcd. for
∗
Corresponding author. Tel.: +81 3 3260 4271; fax: +81 332352214.
E-mail address: yhasegaw@rs.kagu.tus.ac.jp (Y. Hasegawa).
0925-8388/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jallcom.2007.04.152

Y. Hasegawa et al. / Journal of Alloys and Compounds 451 (2008) 320–324
321
Scheme 1.
C
39H51N4O3Y·0.5H2O: C, 64.90%; H, 7.26%; N, 7.76%; found: C, 65.00%; H,
of the tert-butyl group of the salicylidene group of the lig-
ands.
7.19%; N, 7.73%. ESI-MS: m/z (%): 735 (100) [YL1 + Na+]. IR: νC (cm−1
)
N
(KBr): 1630.
Europium(III) aqueous solution was prepared by dissolving the oxide
into perchloric acid. The total ionic solution was adjusted to 0.10 M
(1 M = 1 mol dm−3) with sodium perchlorate. The hydrogen ion concentration
was measured potentiometrically using 0.0100 M perchloric acid and 0.09 M
sodium perchlorate as a standard of pCH = 2.00 (pCH = −log[H+]).
Procedures: Tris(␤-diketonato)EuIII chloroform solution and a Lewis base
solution were mixed at different molar ratio. The excitation and emission spectra
were measured with a Hitachi-F4500 spectrofluorometer. Synergistic extraction
of EuIII was performed by using Htta and the Lewis bases according to the proce-
duresreportedpreviously[6]. TheconcentrationofEuIII andYIII wasdetermined
by ICP/AES (inductively coupled plasma atomic emission spectrometry; Hitachi
P-4000).
3.2. Photochemical properties of EuIII complexes
Fig. 1 shows the excitation and emission spectra of [Eu(tta)3]
(a) and [Eu(pta)3] (b). The shape of the emission spectrum of
[Eu(tta)3] is quite similar to that of [Eu(pta)3], although the
intensity is quite different, that is, the former is much larger
by a factor of 160 times than that of the latter; both spectra
show a sharp peak at 613 nm. However, the excitation spectra
are different to each other; at around 394 nm the intensity of
[Eu(tta)3] is larger than that of [Eu(pta)3] (the intensity of the
former is by a factor of 130 than the latter at the same concen-
tration. In Figs. 1–3, the initial concentration of Eu(tta)3 was
used 5 × 10−5 M while that of Eu(pta)3 was 1 × 10−4 M. The
intensity of Eu(pta)3 was linear to the concentration at least
till 5 × 10−4 M. The UV spectra of [Eu(pta)3] and [Eu(tta)3]
show the peak at 290 and 350 nm, respectively, and at longer
than 340 nm, [Eu(pta)3] slightly shows absorbance (the molar
absorptivity is 20 at 394 nm), but [Eu(tta)3] still shows some-
what absorbance (the molar absorptivity is 600 at 394 nm). The
much smaller absorbance of [Eu(pta)3] than that of [Eu(tta)3]
at 394 nm would give rise to the much weaker luminescence of
[Eu(pta)3].
3. Results and discussion
3.1. Preparation and properties of [YL1]
The complex of [YL1] prepared exhibited an IR band at
1630 cm−1 due to C N stretching vibration, but the IR bands
correspondingtoaprimaryamineoratrifluoromethanesulfonate
anion were not observed. Since the complex does not contain
a counter anion, it is concluded that the ligand (H3L1) forms
an inner-complex in which it functions as a trivalent anionic
heptadentate ligand.
Concerning the complexes with tripodal heptadentate lig-
ands, one of the authors (M.K.) reported the syntheses and
crystallographic studies of yttrium(III) and lanthanoid(III)
complexes of tris[4-(2-hydroxy-3-tert-butylphenyl)-3-aza-3-
butenyl]amine (H3L2) [7]. Although attempts to obtain a single
crystalof[YL1]suitableforX-raystructureanalysiswereunsuc-
cessful, the tripodal heptadentate Schiff-base ligand H3L1 seems
to effectively encapsulate the metal ion and enforce a seven-
coordinate geometry in the same manner as H3L2 because
the difference between [YL1] and [YL2] is the only position
In spite of low excitation intensity and molar absorptivity at
394 nm, EuIII was excited at 394 nm in the present work. The
reason is as follows: it has been reported that the excitation to
5L6 electronic level resulted mainly in emission from the first
5
excited energy level of D0 situated at ∼17300 cm−1 (around
578 nm) above the ground level 7F0 [8,9]. For the fluorescence
spectra measured in all cases, the intense peak was observed
at 613 nm. Due to the large Stokes shift, the fluorescence of
EuIII was measured without the influence of ligands. Further, it
has been reported that since the energy gap between Htta sin-

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Y. Hasegawa et al. / Journal of Alloys and Compounds 451 (2008) 320–324
Fig. 2. Effect of concentration of [YL1] on the luminescence spectra of
tris(␤-diketonato)EuIII in CHCl3 at the excited wavelength 394 nm and
excited spectra at the emission wavelength 613 nm. (a) Eu(tta)3: (– – –)
[Eu(tta)3]T = 5.0 × 10−5 M, (– · –) [YL1]T = 5.0 × 10−5 M, (—) mixed solu-
tion [Eu(tta)3]T (5.0 × 10−5 M), [YL1]T (5.0 × 10−5 M). (b) Eu(pta)3: (– – –)
[Eu(pta)3]T = 1.0 × 10−4 M, (– · –) [YL1]T = 1.0 × 10−4 M, (—) mixed solution
[Eu(pta)3]T (1.0 × 10−4 M) and [YL1]T (1.0 × 10−4 M).
Fig. 1. Excitation and emission spectra of tris(␤-diketonato)EuIII in CHCl3:
(– – –) excitation spectra at emission wavelength, 613 nm; (—) emission spectra
at excitation wavelength, 394 nm ((a) Eu(tta)3 and (b) Eu(pta)3).
5
glet (26107 cm−1) and L6 (25300 cm−1) is small, the energy
transfer from tta to EuIII is efficient [10].
Fig. 2 shows the effect of [YL1] on the excitation and emis-
sion spectra of [Eu(tta)3] (a) and [Eu(pta)3] (b). The spectrum of
[YL1] itself (chain curve) shows a strong peak at around 470 nm,
although it is not sharp as shown in Fig. 2(a). The intensity at
613 nm and at 470 nm in the solution containing [Eu(tta)3] and
[YL1] (solid curve) is remarkably smaller than that observed in
the spectra of the respective solution of [Eu(tta)3] and [YL1],
though their concentration is similar to each other. On the other
hand, as shown in Fig. 2(b), in the solution containing [YL1]
and Eu(pta)3 (solid curve), the intensity at 613 nm is enhanced
to that of [Eu(pta)3] itself (broken curve) and the intensity at
470 nm assigned to [YL1] decreases to that of [YL1] itself
(chain curve).
the spectra in Fig. 2, it was found that the luminescence inten-
sity ratio at 613 nm between [Eu(tta)3] and [Eu(pta)3] is almost
equivalent to that of the excitation intensity ratio at 394 nm (for
the former the ratio is 80 and for the latter it is 70), and also the
luminescence intensity ratio in the solution containing [YL1]
complex and [Eu(tta)3] to that containing [YL1] and [Eu(pta)3]
is almost equivalent to that of the excitation intensity ratio (the
ratio for the former 7.0 and also that for the latter 6.6), that is,
the intensity ratio, either in luminescence or in the excitation,
of the [YL1] complex with the tris(␤-diketonato)EuIII is almost
one tenth smaller than that of tris(␤-diketonato)EuIII themselves.
However, the result of UV spectra which was separately mea-
sured showed that the ratio of the absorbance at 394 nm between
the solution containing the [YL1] complex and [Eu(tta)3] and
that containing the [YL1] complex and [Eu(pta)3] (the value
is almost 1) is much smaller compared to the intensity ratio
between [Eu(tta)3] and [Eu(pta)3] (20). It may suggest that the
energy absorbed at 394 nm would be much smaller in [Eu(tta)3]
complex with [YL1] than the pta complex. Accordingly, it would
Fig. 3 shows the emission intensity at 613 nm against [H3L1]
or [YL1] concentration at a given EuIII concentration and at
λex 394 nm. As seen from Fig. 3(a), the intensity of [Eu(tta)3]
decreases with increase in the Schiff base concentration, while
that of [Eu(pta)3], as shown in Fig. 3(b), increases along with the
increasing concentration. We cannot explain the different behav-
ior with these ␤-diketones up to now. From the comparison of

Y. Hasegawa et al. / Journal of Alloys and Compounds 451 (2008) 320–324
323
Fig. 4. Change in the distribution ratio of EuIII as a function of concentration of
YL1 and H3L1 when EuIII was extracted with Htta and YL1 (ꢀ) and H3L1 (᭹).
are the ternary complexes consisting of [EuA3] and H3L1 or
[EuA3] and [YL1] in addition to EuA3, and the species of EuIII
in aqueous phase is only Eu3+, the distribution ratio (D) defined
by the total concentration ratio of EuIII between the organic and
aqueous phases is represented as
[EuA3]o + [EuA3B]o + · · ·
D =
[Eu3+
]
The extraction equilibria can be represented as
Eu3+ + 3HA(o) + nB(o) ꢀ EuA3 · nB(o) + 3H+
or
Fig. 3. Emission intensity at 613 nm (λex = 394 nm) of tris(␤-diketonato)EuIII in
CHCl3 asafunctionof[YL1]T (ꢀ)or[H3L1]T (᭹):(a)Eu(tta)3 (6.25 × 10−5 M)
and (b) Eu(pta)3 (1.25 × 10−4 M).
Eu3+ + 3HA(o) ꢀ EuA3(o) + 3H+
(Kex0 = [EuA3]o[H+]3[Eu3+
]
−1[HA]−o 3);
EuA3(o) + nB(o) ꢀ EuA3 · nB(o)
(βn = [EuA3 · nB]o[EuA3]−o 1[B]o−n
be related that the energy absorbed with the complex between
[Eu(tta)3] and [YL1] is reduced.
)
As seen from Fig. 3, any different effect is not recognized
between H3L1 and [YL1]. Although the structural interaction
between [YL1] and Eu(pta)3 or [YL1] and Eu(tta)3 is still uncer-
tain, YIII encapsulated into H3L1 through the bonding to three
hydroxyl groups and the coordination with four N donor atoms
would not be involved in the photochemical process to EuIII.
Tris(␤-diketonato) EuIII seems to be influenced to the lumi-
nescence of YIII in [YL1], that is, as seen in Fig. 2, in the mixed
solution of [Eu(pta)3] or [Eu(tta)3] with [YL1], the intensity
derived from YIII at around 470 nm decreases with the presence
of tris(␤-diketonato)EuIII. It is suggested that [YL1] forms din-
uclear complex with EuIII like as [Eu(pta)3·YL1] but the YIII in
[YL1] does not influence to the luminescence of EuIII.
Then D is rewritten as
D = Kex0[HA]3o[H+]−3(1 + Σβn[B]no)
where log Kex0 was −8.28 0.05.
Fig. 4 shows the plot of log D − 3 log [HA]o − 3pCH against
the total concentration of [YL1] (ꢀ) and H3L1 (᭹) (log [B]T).
Although the reproducibility is not good, the value at Y-axis
approaches to log Kex0 along with decreasing Schiff base con-
centration, and also any difference is not observed between both
Schiff bases. When the concentration of YIII in the organic and
the aqueous phases was measured, it was found that most YIII
was in aqueous phases. This result suggests that [YL1] easily
interacts with water to be YIII and H3L1. The H3L1 forms a
complex with tris(␤-diketonato)EuIII and the complex makes
better extraction of EuIII. Since Y ion as well as lanthanoid ions
is typical Lewis hard acid, Y ion has strong affinity to O donor
atoms so that water interacts with [YL1] and pulls out YIII of
[YL1].
3.3. Synergistic extraction of EuIII with Htta and H3L1 or
[YL1] and the emission intensity of the organic phases
When Eu ion is extracted with Htta and H3L1 or [YL1] (in
this section, to simplify, Htta is described as HA and H3L1 or
[YL1], Lewis base, is represented as B), the extracted species

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Y. Hasegawa et al. / Journal of Alloys and Compounds 451 (2008) 320–324
The co-luminescence is also observed in a dinuclear com-
plexes consisting of EuIII and YIII with salicylic acid and 1,
10-phenanthroline [11] or the EuIII and LnIII such as Nd3+,
Gd3+ and Tb3+ with dibenzoylmethide and phenanthroline [12].
However, the presence of YIII in CHCl3 does not show the
co-luminescence.
4. Conclusion
In CHCl3, the luminescence of EuIII was enhanced with the
interactionbetweentris(pivaloyltrifluoroacetonato)EuandH3L1
or [Eu(pta)3] and [YL1], while that of [Eu(tta)3] decreased in the
presence of H3L1 or [YL1]. The difference between H3L1and
[YL1] was not observed. This is due to YIII encapsulated into
the Schiff base. The extraction of Eu ion with Htta and H3L1 or
[YL1] increased with increasing ligand concentration, whereas
the luminescence intensity decreased with increasing YIII con-
centration in organic phases. The co-luminescence with EuIII
and YIII can not be observed.
Fig. 5. Luminescence intensity at 613 nm in the CHCl3 into which EuIII was
extracted with 0.10 M Htta and 1.25 × 10−3 M [YL1] (ꢀ) or H3L1 in the pres-
ence of YIII in aqueous phase (᭹) as a function of YIII concentration in the
CHCl3 at equilibrium.
References
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also measured. The luminescence intensity at 613 nm in the
CHCl3 phase into which EuIII was extracted with 0.10 M Htta
and 1.25 × 10−3 M [YL1] was measured and compared with
the luminescence in the CHCl3 into which EuIII was extracted
with 0.10 M Htta and 1.25 × 10−3 M H3L1 from the aque-
ous solution containing EuIII and 1.25 × 10−3 M YIII. Fig. 5
shows the intensity as a function of YIII concentration in the
CHCl3 at equilibrium. Either in the extraction with [YL1] and
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be log Kex = −8.12 0.05. Strong luminescence is generally
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