The role of copper ions in Tb(III) luminescence sensitization in heterometallic complexes with podands

Article abstract of DOI:10.1134/S0036023616070068

It has been demonstrated that copper-induced terbium(III) luminescence sensitization in heterometallic complexes with hydrazine-containing podands is caused by the ligand ring closure and joint coordination of both metal ions to the carbonyl oxygen atoms

Full text of DOI:10.1134/S0036023616070068

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2016, Vol. 61, No. 7, pp. 872–876. © Pleiades Publishing, Ltd., 2016.
Original Russian Text © Yu.P. Golovach, A.V. Kiriyak, L.N. Ognichenko, S.S. Basok, I.P. Kovalevskaya, I.M. Rakipov, V.E. Kuz’min, S.B. Meshkova, 2016, published in Zhur-
nal Neorganicheskoi Khimii, 2016, Vol. 61, No. 7, pp. 912–916.
PHYSICAL METHODS
OF INVESTIGATION
The Role of Copper Ions in Tb(III) Luminescence Sensitization
in Heterometallic Complexes with Podands
Yu. P. Golovach, A. V. Kiriyak, L. N. Ognichenko, S. S. Basok, I. P. Kovalevskaya, I. M. Rakipov,
V. E. Kuz’min, and S. B. Meshkova
Bogatskii Physicochemical Institute, National Academy of Sciences of Ukraine,
Lyustdorfskaya doroga 86, Odessa, 65080 Ukraine
e-mail: s_meshkova@ukr.net
Received July 9, 2015
Abstract—It has been demonstrated that copper-induced terbium(III) luminescence sensitization in hetero-
metallic complexes with hydrazine-containing podands is caused by the ligand ring closure and joint coordi-
nation of both metal ions to the carbonyl oxygen atoms as well as, mainly, by the reduction with the hydrazine
substituents of Cu(II) to Cu(I), which is able to sensitize terbium luminescence.
DOI: 10.1134/S0036023616070068
–1
Copper(II) ions are known to be strong quenchers energy inputs ΔE(ds). The ΔE(ds) value (kJ mol ) for
of lanthanide luminescence in solutions of their com- copper is the lowest one in the series Cu (34.4)–Ag
plexes with diverse organic reagents [1–4]. This is a (91.8)–Au (40.2) [7]. The Cu(I) luminescence in
serious hindrance to the determination of lanthanides
in the presence of copper. The quenching effect of
Cu(II), Ni(II), and Fe(II) ions on the Eu(III) lumi-
nescence in heterometallic complexes has been
described in [5, 6].
complexes with halide ions and pyridine derivatives
has been reported [8]. In the Cu(dmp)BH complex
4
with 2,9-dimethyl-1,10-phenanthroline (dmp) and
borohydride (reducing agent), Cu(I) luminescence is
observed in solution as well as in the solid state [9].
As distinct from Cu(II), the Cu(I) ions exhibit Efficient copper-induced Tb(III) luminescence sensi-
2
6
10
intrinsic luminescence caused by the 1s …3p 3d
tization has been observed for the first time in a solu-
electronic structure inherent in noble metal ions, tion of a heterometallic complex with a podand con-
namely, in silver(I) and gold(I). Formation of the taining hydrazine substituents and oxygen atoms coor-
9
2
nd (n + 1)s electronic configuration requires different dinated to the terbium and copper ions [10, 11]:
O
O
O
Cl
O
O
O
O
O
O
TbCl3
CuCl2
Tb
pH 6.3
Cl
O
O
OHHO
O
Cu
NH HN
N
N
N
N
NH H N
2
2
H N
2
H N
2
NH2
NH2
(L1)
Copper(II) ions form two five-membered rings Zn(II), Cd(II), Pb(II), Ni(II), and Co(II)—does not
with hydrazine substituents and hydroxyl oxygen induce luminescence. In addition, being coordinated
atoms, thus closing the chain, which makes the ligand to hydrazine substituents, Cu(II) ions are able to be
structure more rigid. Under these conditions, sensi- reduced to Cu(I) and exhibit broadband luminescence
tized Tb(III) luminescence is observed, while the with a maximum at 440 nm. The broad Cu(I) lumi-
introduction of other d metals into the solution— nescence band overlaps the Tb(III) absorption band,
872

THE ROLE OF COPPER IONS IN Tb(III) LUMINESCENCE
873
which is responsible for the possible energy transfer Under these conditions, the Tb(III) ion is coordinated
and sensitization of terbium 4f luminescence by the to all oxygen atoms of the podand and the Cu(II) ion
copper(I) ions in the heterometallic complex.
is bound only to the enol oxygen atoms and the nitro-
The aim of this study is to elucidate the cause of the gen atoms of the hydrazine NH groups to give two
2
Tb(III) luminescence sensitization effect of copper
five-membered rings [12]. The structure of the heter-
ions and assess the contributions of the ligand rigidity
ometallic complex is more rigid than that of the
in going from the podand to the macroheterocycle and
monometallic complex TbL1. A question arises
excitation energy transfer to the central ion when cop-
whether the copper-induced Tb(III) luminescence
per ions are reduced to Cu(I).
will be observed if the ligand chain is closed with some
moiety rather than with the copper ion. To answer this
question, we synthesized ligand L2 in which the
EXPERIMENTAL
The weak luminescence of Tb(III) ions in a solu- hydrazine moieties are replaced by an oxyethylene
tion of the complex with podand L1 (pH 3) revealed in
bridge closing a ring.
[
10, 11] sharply increases (up to 30 times) when a
CuCl solution is added but only in an acid medium
6,7,9,10,18,19-Hexahydro-16Н,21Н-dibenzo[h,p]
2
(
pH 6.1) optimal for the formation of both the CuL1 [1, 4, 7, 11,14]pentaoxacycloheptadecane-16,21-dione
complex and the heterometallic complex CuTbL1. (4) was synthesized by Scheme 1:
OH HO
OH
OH
KOH
TsO-CH2CH2OTs
MeOH
COOH
COOK
O
O
O
O
(1)
(2)
(3)
O
O
O
O
TsO-CH2CH2OCH2CH2OTs
K2CO3
DMFA
L2
O
O
O
(4)
Scheme 1.
The reaction of salicylic acid (1) with КОН gave and the solid residue was dissolved in ethanol. An
–
2
potassium salicylate (2). The latter was alkylated with ethanol solution of copper chloride (1 × 10 mol/L)
ethylene glycol ditosylate (or 1,2-dibromoethane) in was prepared from CuCl ⋅ 2H O (pure for analysis
2
2
DMF in the presence of К СО to give podand 3, and
2
3
grade). An acetonitrile solution of neocuproine (1 ×
its reaction with diethylene glycol ditosylate under the
above conditions (Scheme 1) led to its macrocycliza-
tion to give the target macrocycle (4). Yield, 5.80 g
–2
10
mol/L) was prepared using an exact weighed
portion of the compound. Working solutions were
prepared by dilution of the stock solutions.
(
78%); mp = 152–153°С.
Solutions of the complexes were prepared by mixing
solutions of the metal chlorides, the reagent, and an
1
Н NMR (CDCl , δ, ppm): 4.01 (s, 4Н, ArОСН ),
3
2
4
6
.22 (s, 4Н, ОСН ), 4.64 (s, 4Н, СОСН ), 6.92– ammonium acetate buffer with pH 5.5–6.8 (pH 6.2).
opt
2
2
.94 (d, 2Н, ArH), 7.00 (s, 2Н, ArH), 7.45 (t, 2H, The luminescence spectral characteristics of the solu-
ArH), 7.86–7.88 (d, 2Н, ArH). Mass spectrum: tions were measured within 30 min after preparation.
+
m/z 372 (М ).
Acetonitrile solutions of ligands L1 and L2 (1 × luminescence lifetimes, were recorded on a Horiba
The excitation and luminescence spectra, as well as
–
2
10
mol/L) were prepared using exact weighed por- Jobin Yvon Fluorolog FL3-22 spectrofluorimeter with
tions of solid compounds. They maximally absorb light a dual light source (continuous and pulsed xenon lamp
in the range 260–370 nm. A stock ethanol solution of 450 W). All measurements were carried out at room
–1
TbCl (1 × 10 mol/L) was prepared by dissolving ter- temperature (21–23°С). The triplet energies of the
3
–1
bium oxide (99.99%) in HCl; then, an acid excess was ligands (ET1, cm ) were determined from the lumi-
removed, and the solution was evaporated to dryness, nescence spectra of their Gd(III) complexes at 77 K.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 61 No. 7 2016

8
74
GOLOVACH et al.
6
5
4
3
2
1
× 105
4
3
× 107
(
а)
(b)
× 105
1
2
× 107
× 105
× 105
× 105
× 105
0
2 × 107
1
1
× 107
2
0
2
75 300 325350 375 450 500 550 600 650
2
75 300 325350 375 450 500 550 600 650
λ, nm
λ, nm
Fig. 1. (a) Excitation (λ
= 545 nm) and (b) lumines-
lum
cence (λ : (1) 285 and (2) 345 nm) spectra of a solution
Fig. 2. (1) Excitation (λ
= 545 nm) and (2) lumines-
exc
lum
of TbL2 (c
= 1 × 10–4 mol/L).
cence (λ = 350 nm) spectra of solid TbL2.
exc
TbL2
The terbium(III) luminescence spectra were recorded mixing an ethanol solution of TbCl with an acetoni-
3
in the range 450–650 nm. The IR absorption spectra
of samples as KBr pellets were recorded in the range
trile solution of L2, and acetonitrile was added to a
volume of 10 mL. The component ratio in the complex
–1
4
00–4000 cm on a Shimadzu FTIR-8400S spectro- was found to be Tb : L2 = 1 : 1.
photometer. The X-ray powder diffraction patterns
The luminescence spectrum of TbL2 (Fig. 1)
were recorded on a DRON diffractometer (CuK radi-
α
shows the bands corresponding to the transitions from
ation, nickel filter. The mass spectra were recorded on
МХ-1321 and VG 7070 instruments with an ionizing
5
the Tb(III) emitting level D to the sublevels of the
4
7
electron energy of 70 eV and an argon atom beam ground level F (where j = 6, 5, 4, 3, 2). Splitting of the
j
energy of 8 keV, respectively.
As an additional tool, MM+ calculations were
Table 1. X-ray powder diffraction data for ligand L2 and its
used. Unfortunately, it is difficult to use more precise
Tb(III) complex
quantum-chemical calculations for lanthanide com-
plexes. Molecular mechanics calculations, rough as
they are, make it possible to evaluate the ligand strain
energy caused by complexation, which is an essential
factor determining the complex stability.
L2
TbL2
L2
TbL2
I/I0,
I/I0,
I/I0,
I/I0,
d, Å
d, Å
d, Å
d, Å
%
%
%
%
To evaluate the complex strain energy, the energies
1
8
6
5
3.200 100 12.900 20
.320 25 10.600 100
.490 72 7.740 20
.880 24 6.310 20
5.510 20 5.880 20
.970 14 4.910 20
3.000
2.789 15
2.551
2.391 10
2.258 12
2.226 18
8
3.133 15
3.929 16
2.922 16
2.614 15
2.760 100
2.448 10
of the complexes (Е ) and the ligands in the complex
c
conformation (E ) were calculated. The strain energy
l
3
is the energy difference ΔE = E – E , which character-
c
l
izes the change in the strain energy in the course of
complexation. The E and E energies for each of the
c
l
complexes were calculated by the molecular mechan-
ics method (MMFF force field) with the HyperChem
4
4
4
.610
.218
5
6
4.650 90
4.258 30
2.184
2.079 12
7
2.343
5
software.1
3
3
3
3
.960 10 3.950 42
.822 3.637 25
.608 21 3.551 15
2.025
1.891
1.774
1.648
1.556
7
3
2
5
3
RESULTS AND DISCUSSION
Since the Tb(III) complex with L2 is poorly soluble
in water, the complexation reaction was carried out by
7
.366
8
6
3.540 30
3.125 80
1
Here, an available trial version of HyperChem 7.01 was used.
3.245
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2016

THE ROLE OF COPPER IONS IN Tb(III) LUMINESCENCE
875
A
0.14
(а)
(b)
70
60
50
40
30
20
0
.12
.10
0
0.08
0
.06
.04
0
0.02
0
1
2
3
4
5
Extraction number
10
0
1
2
3
4
5
Extraction number
Fig. 3. (1) Luminescence intensity of the TbCuL1 complex before and after extraction of Cu(I) ions with neocuproine (a) and
= 1 × 10– mol/L) (b).
4
(2) the change in the absorbance of Cu(I) neocuproinate solutions (c
Tb, Cu, L1
bands at 490, 588, and 620 nm is poorly pronounced. heterocycle results in a 115-fold rise of the lumines-
The luminescence of the solid TbL2 complex is stron- cence of TbCuL1 as compared with TbL1, which is
ger about half an order of magnitude stronger than in due to both the more rigid ligand structure and
solution, but the band pattern persists (Fig. 2). The Tb(III) luminescence sensitization by reduced Cu(I)
X-ray powder diffraction data in Table 2 confirm the ions. The closure of the podand with an ethylene
formation of the TbL2 complex.
bridge (L2) leads to a 49-fold rise of the luminescence
of TbL2 as compared with TbL1 caused by the forma-
tion of a more rigid ligand structure.
Comparison of the IR spectra of L2 and TbL2
shows that there is a sharp decrease in the intensity of
–1
the C=O (ν = 1693 cm ) and aromatic С–С groups
The reduction of Cu(II) to Cu(I) by the hydrazine
substituents in the TbCuL1 complex has been proven
by the fourfold Cu(I) extraction with a neocuproine
–
1
(
ν = 1604 cm ) bands. In the spectrum of the com-
plex, the –O–CH –CH —O– band (doublet, ν =
2
2
–
1
1
303 and 1249 cm ) and the bands of the ring C–H solution (Fig. 3). As copper ions are removed from the
–1
groups and C=O (ν = 748 cm ) become weaker. The heterometallic complex, the Tb(III) luminescence is
–
1
reduced.
absorption band at (ν = 550 cm ) in the spectrum of
TbL2 can be assigned to Tb–O bond vibrations.
The introduction of a CuCl solution into a solu-
2
The heterometallic complex with podand L1 has
two coordination sites formed by the Tb(III) and
Cu(II) ions, which are both coordinated to the car-
bonyl oxygen atoms [10], whereas there is no such
compound in the case of L2. The cyclic ligand forms a
complex with the Tb(III) ion, while the effect of the
copper ions can only be outer-sphere as a result of dif-
fusion.
tion of TbL2 reduces the Tb(III) luminescence by a
factor of 4.2 (Table 2). In this case, the Cu(II) ions
quench the TbL2 luminescence, as is observed in solu-
tions of complexes with other ligands as well. Reduc-
tion of Cu(II) to Cu(I) by introducing hydrazine
hydrate into the solution leads only to a further
decrease (by a more than one order of magnitude) in
Tb(III) luminescence intensity. This behavior can be
Comparison of the luminescence intensities of explained by that the hydrazine-reduced Cu(I) ions in
Tb(III) complexes (Table 2) demonstrates that the the heterometallic complex TbCuL1 exhibit intrinsic
closure of podand L1 with the Cu(II) ion to form a luminescence and, owing to joint coordination to the
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 61 No. 7 2016

8
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GOLOVACH et al.
Table 2. Luminescence intensity of solutions of the Tb(III) complexes with ligands L1 and L2 in the absence and presence
= 1 × 10–4 mol/L (ethanol), c
= 1 × 10 mol/L (acetonitrile), c
–4
= 1 × 10 mol/L
–4
of Cu(II) ions (c
Tb, Cu
L1, L2
hydrazine hydrate
(
ethanol))
∆
E = E – E ,
kcal/mol
c
l
No.
Solution composition
Ilum, rel. units
Intensity ratio
1
2
3
4
5
TbL1
4 (I0)
460 (I)
196 (I1)
47 (I2)
17 (I3)
I/I = 115
–183.1
–215.2
–103.2
–
0
TbCuL1
TbL2
I /I = 4.2
1
2
I /I = 11.5
TbL2 + CuCl (1 : 1)
1
3
2
TbL2 + CuCl + hydrazine hydrate (1 : 1 : 1)
–
2
The Ilum values are reduced to the common recording conditions.
oxygen atoms, sensitize the Tb(III) luminescence. As
distinct from this pattern, the Cu(I) ions reduced by
hydrazine hydrate quench the TbL2 luminescence
more strongly than Cu(II), presumably because of the
more efficient excitation energy transfer to Cu(I) than
to Cu(II).
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Translated by G. Kirakosyan
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY
Vol. 61
No. 7
2016