N -aryl chromophore ligands for bright europium luminescence

Article abstract of DOI:10.1021/ic100129r

Sterically hindered N-aryl-benzimidazole pyridine-2-carboxylic acids (aryl = phenyl, 4-biphenyl, 2-naphthyl) readily form homoleptic, neutral, nine-coordinate europium complexes which display efficient sensitized luminescence in solid state and in dichloromethane solution with quantum yields reaching 59% and have monoexponential and nearly temperature-independent lifetimes as long as 2.7 ms. The ligand-centered absorption band with a maximum at 321-342 nm and intensity (50-56) - 10³ M^-1cm ^-1 ensures efficient harvesting of excitation light by the complexes. Variation of N-aryl chromophore enhances the ligand absorption at 250-350 nm without changing its triplet state energy which amounts to (19.2-21.3) × 10³ cm^-1. Photophysical properties of europium complexes benefit from adequate protection of the metal by the ligands against non-radiative deactivation and efficient ligand-to-metal energy transfer exceeding 70%. A correlation is observed between the sensitized luminescence quantum yields of europium and the ligand triplet state energy; in certain cases it points to the presence of a second-sphere quenching of Eu^III by co-crystallized water in the solid state.

Full text of DOI:10.1021/ic100129r

Inorg. Chem. 2010, 49, 3927–3936 3927
DOI: 10.1021/ic100129r
N-Aryl Chromophore Ligands for Bright Europium Luminescence
†
†
†
,†,‡
€
Nail M. Shavaleev, Svetlana V. Eliseeva, Rosario Scopelliti, and Jean-Claude G. Bunzli*
† ꢀ
ꢀ ꢀ
Ecole Polytechnique Federale de Lausanne, Laboratory of Lanthanide Supramolecular Chemistry, BCH 1405,
CH-1015 Lausanne, Switzerland, and ‡World Class University (WCU) Professor, Department of Advanced
Materials Chemistry, Center for Next Generation Photovoltaic Systems, Korea University, 208 Seochang,
Jochiwon, ChungNam 339-700, South Korea
Received January 22, 2010
Sterically hindered N-aryl-benzimidazole pyridine-2-carboxylic acids (aryl = phenyl, 4-biphenyl, 2-naphthyl) readily
form homoleptic, neutral, nine-coordinate europium complexes which display efficient sensitized luminescence in solid
state and in dichloromethane solution with quantum yields reaching 59% and have monoexponential and nearly
temperature-independent lifetimes as long as 2.7 ms. The ligand-centered absorption band with a maximum at
321-342 nm and intensity (50-56) ꢀ 103 M-1cm-1 ensures efficient harvesting of excitation light by the complexes.
Variation of N-aryl chromophore enhances the ligand absorption at 250-350 nm without changing its triplet state
energy which amounts to (19.2-21.3) ꢀ 103 cm-1. Photophysical properties of europium complexes benefit from
adequate protection of the metal by the ligands against non-radiative deactivation and efficient ligand-to-metal energy
transfer exceeding 70%. A correlation is observed between the sensitized luminescence quantum yields of europium
and the ligand triplet state energy; in certain cases it points to the presence of a second-sphere quenching of EuIII by
co-crystallized water in the solid state.
Introduction
to transfer energy to the EuIII ion; its first triplet state is
generally responsible for most of the energy transfer,11,12
but singlet-state excitation may also play a non-negligible
role.13 It is also desirable that the ligand saturates the
coordination sphere of europium, therefore protecting it
from water molecules which strongly coordinate to the
Trivalent europium ion displays orange or red lumin-
escence prompting the use of its inorganic and organic com-
pounds in display, lighting (including OLED), and sensor
applications.1-4 Although europium luminescence is long-
lived, in the μs-ms time scale, it is not quenched by oxygen, as
the excited state is located on the shielded f-orbitals of the ion
which advantageously distinguishes it from brightly phos-
phorescent transition metal complexes with charge-transfer
(MLCT, LLCT) or ligand-centered emissive states.5-9
“hard” EuIII cation and quench its excited state.14
A
number of ligands have been developed to achieve bright
luminescence of europium,15-27 the most studied ones
being bidentate β-diketonates.28
Weak absorption transitions of EuIII necessitates the use
of chromophore ligands to achieve efficient harvesting of
excitation light.10 The ligand must have suitable excited states
(11) Sato, S.; Wada, M. Bull. Chem. Soc. Jpn. 1970, 43, 1955.
(12) Latva, M.; Takalo, H.; Mukkala, V. M.; Matachescu, C.; Rodriguez-
Ubis, J.-C.; Kankare, J. J. Lumin. 1997, 75, 149.
(13) Ha-Thi, M. H.; Delaire, J. A.; Michelet, V.; Leray, I. J. Phys. Chem. A
2010, 114, 3264.
(14) Beeby, A.; Clarkson, I. M.; Dickins, R. S.; Faulkner, S.; Parker, D.;
Royle, L.; de Sousa, A. S.; Williams, J. A. G.; Woods, M. J. Chem. Soc.,
Perkin Trans. 2 1999, 493.
*To whom correspondence should be addressed. E-mail: jean-claude.
bunzli@epfl.ch.
€
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Cavazzini, M.; Tondello, E. Coord. Chem. Rev. 2010, 254, 487.
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r
2010 American Chemical Society
Published on Web 03/19/2010
pubs.acs.org/IC

3928 Inorganic Chemistry, Vol. 49, No. 8, 2010
Shavaleev et al.
Chart 1. Previously Reported N-Alkyl-Benzimidazole Pyridine-2-
Scheme 1. Synthesis of N-Aryl-Benzimidazole Pyridine-2-Carboxylic
Carboxylic Acids30,31
Acids and Their Lanthanide Complexesa,b
We have recently reported that tridentate N-alkyl-benzi-
midazole-pyridine carboxylates29 (Chart 1) form neutral
homoleptic complexes with europium and sensitize its emis-
sion with quantum yields reaching 71%.30,31 To modulate the
light-harvesting properties of the ligands we set out to modify
them with a strongly absorbing aryl chromophore at the N(1)
atomof benzimidazole instead of a “transparent” alkyl group
(Scheme 1 and Chart 2; compare with Chart 1). It should be
noted that N-aryl benzimidazole-pyridines have been rarely
used in coordination chemistry32,33 likely because of the anti-
cipated steric hindrance to metal binding. Herein we demon-
strate that these ligands are easily accessible, readily coordi-
nate to europium, and efficiently sensitize its luminescence.
a Benzimidazole ring numbering is indicated in the structure of the
complex. b Reaction conditions: (a) Na2S2O4, [2-methoxyethanol and/
or DMF]/H2O, under N2, 110 °C; (b) SeO2, dioxane, under N2, 110 °C;
(c) H2O2, formic acid, under air, 0 °C; (d) LnCl3 nH2O, NaOH, ethanol/
3
H2O, under air, heating.
Chart 2. N-Aryl-Benzimidazole Pyridine-2-Carboxylic Acidsa
Results and Discussion
Synthesis. Six new ligands havebeen prepared (Chart 2);
the formation of benzimidazole ring34 was followed by
stepwise oxidation of pyridine-2-methanol first to carbox-
aldehyde with SeO2, and then to carboxylic acid with
H2O2/formic acid35 (Scheme 1). The cyclization of N-aryl
benzimidazoles was less efficient compared to N-alkyl
ones31 as a result of steric hindrance, while both oxidation
steps were high-yielding.
N-Aryl-2-nitroanilines (key precursors) were obtained
by reaction of 2-fluoronitrobenzenes with arylamines
(used as a reagent and a base) in dimethyl sulfoxide
(22) Pavithran, R.; Saleesh Kumar, N. S.; Biju, S.; Reddy, M. L. P.;
Junior, S. A.; Freire, R. O. Inorg. Chem. 2006, 45, 2184.
(23) Teotonio, E. E. S.; Brito, H. F.; Viertler, H.; Faustino, W. M.; Malta,
a Ligand HLPh has been reported;30 other ligands are new.
ꢀ
O. L.; de Sa, G. F.; Felinto, M. C.; Santos, R. H. A.; Cremona, M.
Polyhedron 2006, 25, 3488.
(24) Wilkinson, A. J.; Maffeo, D.; Beeby, A.; Foster, C. E.; Williams,
J. A. G. Inorg. Chem. 2007, 46, 9438.
(25) Zebret, S.; Dupont, N.; Bernardinelli, G.; Hamacek, J. Chem.;Eur.
J. 2009, 15, 3355.
(26) Zhang, F. L.; Hou, Y. H.; Du, C. X.; Wu, Y. J. Dalton Trans. 2009,
7359.
(DMSO) at 100 °C for 24-48 h (Scheme 2). The reaction
did not require external base or a catalyst; however, in the
case of electron-deficient 4-bromoaniline, it was sluggish
and had to be carried out for 72 h. A facile multigram-
scale synthesis of another precursor, 2-pyridinecarbox-
aldehyde-6-methanol, has been previously described.36
(27) Sivakumar, S.; Reddy, M. L. P.; Cowley, A. H.; Vasudevan, K. V.
Dalton Trans. 2010, 39, 776.
The complexes [Ln(Ligand)3] nH2O, denoted as LnLi-
3
ꢀ
(28) de Sa, G. F.; Malta, O. L.; Donega, C. D.; Simas, A. M.; Longo,
gand, have been obtained as air- and moisture-stable white
solids from hot ethanol/water solutions starting with a
stoichiometric 3:3:1 molar ratio of ligand, NaOH (base),
R. L.; Santa-Cruz, P. A.; da Silva, E. F. Coord. Chem. Rev. 2000, 196, 165.
(29) Piguet, C.; Bocquet, B.; Hopfgartner, G. Helv. Chim. Acta 1994, 77,
931.
(30) Shavaleev, N. M.; Scopelliti, R.; Gumy, F.; Bunzli, J.-C. G. Inorg.
Chem. 2009, 48, 5611.
(31) Shavaleev, N. M.; Eliseeva, S. V.; Scopelliti, R.; Bunzli, J.-C. G.
Chem.;Eur. J. 2009, 15, 10790.
(32) Jia, W. L.; McCormick, T.; Tao, Y.; Lu, J. P.; Wang, S. Inorg. Chem.
2005, 44, 5706.
(33) He, L.; Qiao, J.; Duan, L.; Dong, G.; Zhang, D.; Wang, L.; Qiu, Y.
Adv. Funct. Mater. 2009, 19, 2950.
€
and LnCl3 nH2O (Scheme 1 and Chart 2). They are soluble
3
€
in DMSO, and the ones containing tert-butyl or n-octyloxy
groups are also soluble in CH2Cl2. All new compounds have
been identified by C, H, N elemental analysis; X-ray crystallo-
graphy; 1H and 13C NMR spectroscopy; and ESIþ MS.
(34) Yang, D. L.; Fokas, D.; Li, J. Z.; Yu, L. B.; Baldino, C. M. Synthesis
2005, 47.
(35) Dodd, R.; Le Hyaric, M. Synthesis 1993, 295.
€
(36) Shavaleev, N. M.; Scopelliti, R.; Gumy, F.; Bunzli, J.-C. G. Inorg.
Chem. 2009, 48, 6178.

Article
Inorganic Chemistry, Vol. 49, No. 8, 2010 3929
Scheme 2. Synthesis of Precursorsa
Table 1. Selected Structural Parameters of the Complexesa
b
angle (deg)c
˚
bond lengths (A)
Ln-Ln
(A)
d
˚
complex
Ln-O Ln-N(py) Ln-N(b) py-b ph-b
[La(LPhBr)3] 2.422(5) 2.638(6) 2.761(5) 28.75 61.57 9.663
2.453(5) 2.655(6) 2.709(5) 23.53 57.56
2.465(5) 2.676(6) 2.778(6) 25.90 60.85
2.447(44) 2.656(38) 2.749(72) 26(5) 60(4)
0.043
0.038
0.069
5
4
[Eu(LPhBr)3] 2.339(4) 2.535(5) 2.681(5) 27.00 61.17 9.665
2.358(4) 2.553(5) 2.630(5) 24.86 55.71
2.389(4) 2.571(5) 2.688(5) 24.31 60.49
2.362(50) 2.553(36) 2.666(63) 25(3) 59(6)
5
0.050
0.036
0.058
3
a Each row corresponds to one and the same ligand in the complex.
Numbers in bold are for averaged data (with standard deviations 2σ in
parentheses); numbers in bold and in italic are differences between the
minimum and the maximumvalues. b N(py)and N(b) are nitrogen atoms
of pyridine and benzimidazole rings, respectively. c Dihedral angles
between the planes of pyridine and benzimidazole, or benzimidazole
and phenyl (ph) rings. The planes were defined by C and N atoms of core
rings. d Shortest Ln-Ln distance in the structure.
a Reaction conditions: (a) arylamine (excess, used as a reagent and as
a base), DMSO, under N2, 24-72 h, 100 °C.
Structural Characterization. Single crystals suitable
for X-ray analysis could be obtained for [Ln(LPhBr)3]
(Ln = La, Eu); their molecular structures are shown in
Figure 1, and selected parameters are collected in Table 1.
The complexes share similar structural properties. The
lanthanide ion is 9-coordinate by three ligands, and its
coordination polyhedron can be described as a distorted
tricapped trigonal prism (TCTP, Figure 2), with N(py =
pyridine) atoms in capping positions and forming a plane
with Ln. Two triangular faces of the prism are defined by
O-N(b)-N(b) and O-O-N(b) atoms (b =benzimidazole).
Each of the three ligands spans both triangular faces
of the TCTP via a capping position. The ligands are
arranged in up-up-down fashion around the metal result-
ing in low symmetry (C1) of the complex.
The coordinated ligands are not planar, with dihedral
angles between pyridine and benzimidazole in the range
24-29°, while the angles between phenyl and benzimida-
zole are 56-62°. The three ligands in the complex are not
equally strongly bonded to the metal as reflected in
the different respective sets of bond lengths. The metal
is preferentially bound to the pyridine-2-carboxylate
moiety, while bonding to the benzimidazole is weaker,
which is reflected in longer bond lengths and in their wider
variation. The bond lengths decrease as La>Eu because
of lanthanide contraction.
Each ligand of the complex is hydrogen bonded to
co-crystallized ethanol or water molecules via carbo-
nyl oxygen of a carboxylate group with O O(water
Figure 1. Molecular structures of the complexes [Ln(LPhBr)3] (Ln =
La, Eu) viewed down the triangular face of the tricapped trigonal prism
(50% probability ellipsoids, H atoms, and co-crystallized solvent mole-
cules omitted). Heteroatoms: O, red; N, blue; Br, brown; Ln, black.
3 3 3
˚
or ethanol) distances in the range 2.704-2.952 A. Both
structures contain eight Ln
O(7 water þ 1 ethanol)
3 3 3
˚
The following N-aryl groups have been chosen as chro-
mophores: phenyl (Ph), 4-biphenyl (Biph), or 2-naphthyl
(Nap). The presence of bromine in ligand HLPhBr and its
precursors opens the way for coupling reactions as means
of further modification. The n-octyloxy group at N-phenyl
(HLPhO8) or at benzimidazole (HLRX), apart from
providing solubility, demonstrates a facile attachment of
a functional group to the ligand via ether linkage starting
from a suitable phenol precursor. It should be noted that
the parent ligand HLPh and its complexes have been
reported previously.30
distances in the range 6.0-8.0 A which may result in
second-sphere interaction between metal ion and O-H
oscillators. Intermetallic communication in the structures
is likely to be negligible as the Ln-Ln distances are >9.6 A,
a favorable condition for efficient luminescence.
˚
The structures of the N-aryl complexes are very similar
to the previously reported N-alkyl complexes.31 The only
notable difference is that the angles between pyridine and
benzimidazole show very small variation in N-aryl com-
plexes with average and (2σ) values of 26(4) for LnLPhBr,
while in N-alkyl complexes they vary as 2-40°.31

3930 Inorganic Chemistry, Vol. 49, No. 8, 2010
Shavaleev et al.
Table 2. Calculated Bond Valence Parametersa
νLn, j(N)
complex
VLn
νLn, j(O)
N(py)
N(b)
N(av.)
[La(LPhBr)3]
[Eu(LPhBr)3]
[Eu(LPh)3]b
all data
3.18
3.06
2.94
0.45(5)
0.42(6)
0.40(8)
0.42(7)
0.34(4)
0.35(3)
0.33(3)
0.34(4)
0.27(5)
0.26(4)
0.26(10)
0.26(6)
0.31(9)
0.30(11)
0.29(10)
0.30(9)
aAveraged bond-valence contribution is listed with standard devia-
tion (2σ) in parentheses. b From ref 30.
Figure 3. Absorption spectra of europium complexes [Eu(LRX)3]
3
nH2O (R = Ph, Biph, Nap) at (4.22-5.24) ꢀ 10-5 M in CH2Cl2.
Additional absorption spectra are provided in the Supporting Infor-
mation.
series, v(O), 0.42(7) >v(N-py), 0.34(4) > v(N-b), 0.26(6)
(Table 2), and similar to the ones previously reported for
complexes with N-alkyl substituted ligands.31
Figure 2. Coordination environments of LnIII in [Ln(LPhBr)3] (Ln =
La, Eu) viewed down the square face of the tricapped trigonal prism.
Heteroatoms: O, red; N, blue; Ln, black.
Electronic States of the Ligands. UV-vis absorption
spectra have been recorded in DMSO for the ligands,
and in non-coordinating CH2Cl2 for the complexes (the
ligands themselves are insoluble in CH2Cl2). Representa-
tive spectra for EuIII complexes are shown in Figure 3 while
spectra for all ligands and their complexes with LaIII
and EuIII are displayed on Figures S1-S6 (Supporting
Information). The main spectral features are presented in
Table 3 and Table S1 (Supporting Information).
The ligands display a composite broad band in the
UV corresponding to π f π* transitions with a lowest-
energy maximum at 303-324 nm and molar absorp-
tion coefficients of (17-20) ꢀ 103 M-1cm-1 assigned
to the benzimidazole chromophore. Its position does
not depend on the identity of N-aryl chromophore
at benzimidazole indicating lack of electronic commu-
nication between the two aromatic moieties. Introduc-
tion of an electron-donor n-octyloxy group at the C(6)-
atom of benzimidazole red-shifts this absorption by
20 nm which can be explained by a contribution of
a benzimidazole-localized charge-transfer transition
wherein the imine group acts as an acceptor. The varia-
tion of N-aryl from phenyl via naphthyl to biphenyl
enhances the absorption of the ligand at 250-350 nm
because of a contribution of the corresponding chromo-
phore (Figure 3).
The relative bonding strengths of the ligands have been
quantified with the bond-valence method37 wherein a
donor atom j at a distance dLn,j from the metal ion is
characterized by a bond-valence contribution νLn,j
:
j - dLn jÞ=b
νLn,j ¼ eðR
Ln
ð1Þ
where RLn,j are the bond-valence parameters for the pair
,
,
of interacting atoms (Ln-O38 or Ln-N39), and b is a
constant equal to 0.37 A. The bond valence sum (BVS) of
˚
the metal ion VLn defined by eq 2 is supposed to match its
formal oxidation state if average bond distances are
standard:
X
VLn
¼
νLn,j
ð2Þ
j
The BVS for LnLPhBr (Ln = La, Eu) and EuLPh30 are
in the range 2.94-3.18, and match the expected value for
LnIII (3.00) within the variability of the method, accepted
to be (0.25 valence units, and confirm the good quality of
the crystallographic data (Table 2). The average contri-
butions from the coordinating groups are in the expected
Upon complex formation, the lowest-energy band of
the ligand is red-shifted by ≈20 nm, and its intensity
increases to (50-56) ꢀ 103 M-1cm-1 reflecting the pre-
sence of three ligands in the complex. The trends in the
absorption spectra of the complexes are identical to the
ones observed for the free ligands.
(37) Brown, I. D.; Altermatt, D. Acta Crystallogr., Sect. B 1985, 41, 244.
(38) Trzesowska, A.; Kruszynski, R.; Bartczak, T. J. Acta Crystallogr.,
Sect. B 2004, 60, 174.
(39) Trzesowska, A.; Kruszynski, R.; Bartczak, T. J. Acta Crystallogr.,
Sect. B 2005, 61, 429.

Article
Inorganic Chemistry, Vol. 49, No. 8, 2010 3931
Table 3. Absorption Spectra of the Ligands in DMSO and of the Europium
Complexes in CH2Cl2
Table 4. Energies of the Phonon Transitions in the Phosphorescence Spectra of
Lanthanum Complexes in Solid State at 77 Ka
a
E/103 cm-1
λ
max/nm (ε/103 M-1 cm-1
)
complex
0-0
0-1
Δ
HLPh
HLPhBr
HLPhBu 0.5H2O
HLPhO8
HLPhX
HLBiphX
304 (18)
305 (18)
304 (17)
303 (17)
325 (19)
324 (20)
267 (27)
324 (20)
[Eu(LPh)3] 1.5H2Ob
322 (53)
321 (53)
321 (53)
322 (55)
342 (51)
342 (53)
258 (82)
342 (53)
295 (37)
282 (36)
3
[Eu(LPhBr)3] 2.5H2Ob
[Eu(LPhBu)3] 1.5H2O
3
[La(LPh)3] 3H2O
3
19.8
21.3
20.2
20.9
19.3
19.2
19.2
18.5
19.8
18.6
19.5
18.0
18.0
17.8
1.3
1.5
1.6
1.4
1.3
1.2
1.4
3
3
3
[La(LPhBr)3] 3H2O
[La(LPhBu)3] 2H2O
3
[Eu(LPhO8)3] 2H2O
[Eu(LPhX)3] 1.5H2O
3
3
3
[La(LPhO8)3] 2H2O
[La(LPhX)3] 2H2O
[Eu(LBiphX)3]
3
[La(LBiphX)3] H2O
3
HLNapX
[Eu(LNapX)3] H2O
3
[La(LNapX)3] H2O
3
a Estimated error on the energy is (200 cm-1
.
a Spectra were recorded at room temperature in the range 250-
500 nm. Estimated errors are (1 nm for λmax and (5% for ε. Absorption
data for LaIII complexes are similar and are provided in Table S1
(Supporting Information). Concentration of EuIII complexes was
(4.22-5.78) ꢀ 10-5 M. b Recorded in DMSO. The complex is insoluble
in CH2Cl2; its ε has been calculated by assuming that it remains
undissociated in DMSO.
Figure 5. Luminescence spectra (corrected and normalized) of euro-
pium complexes in solid state at room temperature displaying the
5D0f7FJ, J = 0-4, transitions; λexc = 355 nm; emission slit: 0.2 nm.
Figure 4. Phosphorescence spectra (corrected and normalized; emission
slit: 5 nm) of lanthanum complexes in solid state at 77 K.
For a ligand to be a good sensitizer, its donor state,
usually the first triplet state, should be situated sufficiently
in solid state and in CH2Cl2 (Figures 5 and 6). The
corresponding excitation spectra display ligand bands
below 425 nm which confirms sensitization of EuIII emis-
sion by the ligands (Figure S7 in the Supporting Infor-
mation).
5
above the emitting D0 level of EuIII to allow efficient
energy transfer to higher excited states of the metal and to
prevent quenching by back energy transfer.11,12 The triplet
energies of the ligands, ET, have been determined to be
(19.2-21.3) ꢀ 103 cm-1 from the zerophonon transition in
the phosphorescence spectra of the lanthanum complexes
which display vibrational progression with a spacing of
(1.2-1.6) ꢀ 103 cm-1 attributable to ring-breathing modes
(Figure 4, Table 4). Changing the 4-substituent on the
N-phenyl ring results in variation of ET within 1500 cm-1
in the series Br > OC8H17 > tert-butyl > H. Replacement
of the C(6)-substituent in the benzimidazole ring from H to
OC8H17 (LaLPh versus LaLPhX) lowers ET by 500 cm-1
while variation of the N-aryl group in the LaLRX series
(R = Ph, Biph, Nap) has no effect on ET. Overall, the
energygapbetween ET and 5D0 statesinthe newcomplexes
is in the range 1950-4050 cm-1, which is suitable for
sensitization of EuIII luminescence.11,12
In the solid state, the emission spectra consist of sharp
bands due to 5D0f7FJ transitions (denoted as 0fJ) with
their fine structure depending on the complex (Figure 5).
For EuLPhBr, the 0f1 transition features three equally
spaced components of similar intensity which is charac-
teristic of EuIII ion in a low symmetry environment and is
in line with the results of crystal structure analysis; similar
patterns are observed for EuLPhBu, EuLPhX, and Eu-
LNapX. In contrast, the 0f1 transition for EuLPh,30
EuLBiphX, and EuLPhO8 with two more closely spaced
higher-energy components reflects a distorted pseudo-C3
symmetry around the metal ion. In solution, the spectra
are broader and are nearly identical for all the complexes
(Figure 6), with the splitting pattern of the 0f1 transition
pointing to EuIII environments derived from a distorted
pseudo-C3 symmetry. Luminescence spectra in all media
are independent of excitation wavelength. The emission
Europium-Centered Luminescence. All new europium
complexes emit characteristic metal-centered luminescence

3932 Inorganic Chemistry, Vol. 49, No. 8, 2010
Shavaleev et al.
The intrinsic quantum yields of europium could not
be determined experimentally upon direct f-f excitation
because of very low absorption intensity. Therefore,
radiative lifetimes of Eu(5D0) have been calculated from
eq 4,40 where n is the refractive index (1.5 for solid state
metal-organic complexes; 1.4242 for CH2Cl2), AMD,0 is
5
the spontaneous emission probability for the D0f7F1
transition in vacuo (14.65 s-1), and Itot/IMD is the ratio of
the total integrated intensity of the corrected EuIII emis-
sion spectrum to the integrated intensity of the magnetic
5
dipole D0f7F1 transition (Table S2 in the Supporting
Information):
1=τrad ¼ AMD,0 ꢀ n3 ꢀ ðItot=IMD
Þ
ð4Þ
The calculated radiative lifetimes are long: 3.2-4.3 ms in
solid state, increasing to 3.9-4.2 ms in CH2Cl2 (Table 5).
The intrinsic quantum yields of europium estimated from
Figure 6. Luminescence spectra (corrected and normalized) of euro-
pium complexes in (5.86-7.75) ꢀ 10-4 M solution in CH2Cl2 at room
the ratio τobs/τrad are high: 49-65% in all media (Table 5).
Eu
The relatively small variations of τrad and Q are an
temperature displaying the 5D0f7FJ, J = 0-4, transitions; λexc
355 nm; emission slit: 0.2 nm.
=
Eu
outcome of the similar N6O3-coordination environment
for all the complexes.
intensity is fairly equally distributed in the range 575-
720 nm with the hypersensitive 0f2 transition dominat-
ing the spectrum. The 0f0 and 0f3 transitions are weak,
representing <0.6% and <3% of the total emission,
respectively (Table S2 in the Supporting Information).
The contributions of the 0f1, 0f2, and 0f4 transitions
to the total emission are nearly constant in solution, with
averages of 17(1), 50(2), and 30(1)%, respectively; in the
solid state, these values display larger variation being
equal to 19(3), 46(8), and 32(5)%, respectively (Table S2
in the Supporting Information).
The sensitization efficiencies calculated from the ratio
Eu
Eu
QELu/Q are nearly quantitative (>90%) in solid state,
except for EuLNapX (77%) (Table 5). In solution, they
become smaller, 70-80%, which probably reflects energy
losses within the ligands by collisional deactivation with
solvent molecules and via labile ligand-lanthanide bond-
ing; as a result, QELu is lower in solution compared to solid
state samples.
Conclusions
We have developed a facile approach to N-aryl chromo-
phore substituted benzimidazole pyridine-2-carboxylic acids.
Despite steric hindrance, these ligands form 9-coordinate
The emission of europium complexes can be analyzed
Eu
in terms of eq 3 where QELu and Q are ligand-sensitized
Eu
and intrinsic luminescence quantum yields of EuIII; ηsens
is the efficiency of the ligand-to-metal energy transfer;
τobs and τrad are the observed and radiative lifetimes of
Eu(5D0):
lanthanide complexes [Ln(Ligand)3] nH2O. The europium
3
complexes are highly luminescent in solid state and in solu-
tion with ligand-sensitized quantum yields and observed
lifetimes reaching 59% and 2.7 ms, respectively, and ligand-
to-EuIII energy-transfer efficiencies exceeding 70%.
QELu ¼ ηsens ꢀ QEEuu ¼ ηsens ꢀ ðτobs=τrad
To achieve bright luminescence, the ligands must protect
Þ
ð3Þ
The sensitized quantum yields of europium complexes,
QELu, decrease as the energy gap between the ligand triplet
5
state and the emissive D0 level of EuIII becomes smaller
EuIII from non-radiative deactivation (term Q ), and
Eu
Eu
(Figure 7) which facilitates quenching by back energy transfer
from metal to ligand.11,12 The correlation is applicable to both
the N-aryl complexes and to the previously reported31 N-alkyl
complexes with the optimum energy gap being >2000 cm-1
(ET > 19300 cm-1), providing QELu > 50%. For the “solution
data”, the correlation is smooth, reflecting only the variation
of ET. The relatively large scattering of the “solid state data”
in Figure 7 is likely to reflect the effect of second sphere
quenching of EuIII by co-crystallized water:
provide efficient light harvesting and energy transfer
(term ηsens).
The observed luminescence decays (τobs) are single
exponential functions for all europium complexes in all
media at 298 and 10 K indicating the presence of only one
emissive EuIII center. They are long, 1.8-2.6 ms in solid
state and 2.2-2.7 ms in solution and vary by less than
20% in solid state between 298 and 10 K which points to
the absence of significant thermally activated deactiva-
tion pathways (Table 5, Table S3 in the Supporting
Information). They are consistent with the absence of
water in the inner coordination sphere of europium and
suggest that the metal ion is well shielded from non-
radiative deactivation by the ligands.
The quantum yields of ligand-sensitized europium
luminescence (QELu) are large: 43-59% in solid state and
38-49% in CH2Cl2 (Table 5) and are independent of λexc
within experimental error (Table S3 in the Supporting
Information).
(i) In the complexes containing co-crystallized water,
τobs increases by up to 25% when going from the
solid state to CH2Cl2 while τobs of the anhydrous
complex EuLBiphX is nearly independent of the
medium (Table 5). We suggest that co-crystallized
water in the former compounds contributes to
the quenching of the emissive state of EuIII via
(40) Werts, M. H. V.; Jukes, R. T. F.; Verhoeven, J. W. Phys. Chem.
Chem. Phys. 2002, 4, 1542.

Article
Inorganic Chemistry, Vol. 49, No. 8, 2010 3933
Table 5. Photophysical Properties of EuIII Complexesa
τ
obs/msb
Eu
complex
QELu/%
298 K
10 K
τrad/ms
Q
/%
ηsens/%
Eu
[Eu(LPh)3] 1.5H2O
3
solid
solid
solid
CH2Cl2
solid
CH2Cl2
solid
CH2Cl2
solid
54(2)
59(2)
57(2)
49(3)
57(2)
47(1)
46(2)
40(1)
58(2)
42(1)
43(2)
38(1)
2.02(1)
2.64(3)
2.19(1)
2.70(3)
2.24(1)
2.76(1)
2.02(2)
2.51(4)
2.24(2)
2.36(1)
1.84(2)
2.24(2)
2.12(2)
2.58(2)
2.23(2)
4.12
4.28
3.87
4.19
3.84
4.22
3.95
4.19
3.64
3.92
3.22
3.91
49
≈100
[Eu(LPhBr)3] 2.5H2O
3
62
57
64
58
65
51
60
62
60
57
57
95(14)
100(15)
77(12)
98(15)
72(11)
90(14)
67(10)
94(14)
70(11)
77(12)
67(10)
[Eu(LPhBu)3] 1.5H2O
3
[Eu(LPhO8)3] 2H2O
3
2.32(1)
2.39(1)
2.25(1)
2.06(2)
[Eu(LPhX)3] 1.5H2O
3
[Eu(LBiphX)3]
CH2Cl2
solid
CH2Cl2
[Eu(LNapX)3] H2O
3
a At 298 K, unless stated otherwise. In solid state or (5.86-7.75) ꢀ 10-4 M in CH2Cl2 at λexc = 355 nm. Standard deviations (2σ) are given between
parentheses; estimated relative errors: τobs, (2%; QLEu, (10%; τrad, (10%; Q , (12%; ηsens, (22%. Photophysical parameters at other excitation
Eu
Eu
wavelengths are collected in Table S3 in the Supporting Information. b In solid state, τobs may show variation by ≈10% when λexc is changed between
320 and 527 nm; in CH2Cl2, τobs are independent of λexc (Table S3 in the Supporting Information).
complexes with similar ET, that is, EuLPhX and
EuLNapX. On the other hand, these three com-
plexes have comparable QELu in CH2Cl2, again
because of the dissociation of co-crystallized
water (Table 5, Figure 7A).41
(iii) The N-aryl complexes EuLPhBr and EuLPhO8
containing 2-2.5 co-crystallized water mole-
cules display lower QELu = 57-59% compared
to QELu = 68-71% for the “anhydrous’ N-alkyl
complexes31 with similar ET (Figure 7B).
With regard to the influence of ligand structure on the
luminescence efficiency of europium we notice that the
introduction of a para-substituent at the N-phenyl ring in
going from H (EuLPh) to Br (EuLPhBr), tert-butyl
(EuLPhBu) or OC8H17 (EuLPhO8) has no effect on QLEu
even though the triplet states of the corresponding ligands
vary up to 1500 cm-1. In contrast, the grafting of a OC8H17
substituent on the C(6) atom of benzimidazole lowers QLEu
from 54% (EuLPh) to 46% (EuLPhX) reflecting a small
decrease in ET by 500 cm-1. Therefore, synthetic modifica-
tion of the ligands at the N-aryl group might be preferred to
that at benzimidazole, as it appears to have less negative
influence on the luminescence of europium. In fact, even the
variation of the N-aryl group in the EuLRX series with
R = Ph, Nap, Biph, has little influence on QELu; however,
this trend is likely to change for N-aryl chromophores with
lower energies of electronic states compared to that of
benzimidazole.
Therefore, the replacement of the N-alkyl substituent31
at benzimidazole with N-aryl (aryl = phenyl, 4-biphenyl,
2-naphthyl) provides enhanced absorption to the lanthanide
complexes, but it does not significantly alter either their
Figure 7. Dependence of the sensitized luminescence quantum yield of
structural parameters, or the intrinsic photophysical proper-
EuIII on the energy gap between the triplet state of the ligand (zero
Eu
ties of europium (τrad and Q ), or the ligand-to-metal
phonon) and EuIII(5D0=17260cm-1) state in the solid (9) and in CH2Cl2
Eu
energy transfer efficiency. This study demonstrates the
amenability of tridentate benzimidazole-pyridine 2-car-
boxylates to modification, and points to these ligands
as promising candidates for the development of brightly
emissive europium compounds for display and lighting
applications.
solution (0) at room temperature. A: N-Aryl complexes; 1: EuLPhBr; 2:
EuLPhO8; 3: EuLPhBu; 4: EuLPh; 5: EuLBiphX; 6: EuLPhX; 7: Eu-
LNapX. B: N-Aryl complexes (in red) are presented together with the
previously reported31 N-alkyl complexes (in black).
second-sphere interaction in the solid state, while
in CH2Cl2, water dissociates, which eliminates
41
.
quenching and increases τobs
(ii) In solid state, the anhydrous complex EuLBiphX
€
(41) Shavaleev, N. M.; Scopelliti, R.; Gumy, F.; Bunzli, J.-C. G. Inorg.
Chem. 2009, 48, 7937.
displays a higher QELucompared to the “hydrated”

3934 Inorganic Chemistry, Vol. 49, No. 8, 2010
Shavaleev et al.
Table 6. Crystal Data and Structure Refinementa
[La(LPhBr)3]
[Eu(LPhBr)3]
C57H33Br3EuN9O6 4C2H5OH 3H2O
empirical formula
fw
cryst syst
space group
unit cell dimensions
C57H33Br3LaN9O6 4C2H5OH 3H2O
3
3
3
3
1556.88
triclinic
P1
1569.93
triclinic
P1
˚
˚
a = 12.3326(7) A
a = 12.2911(6) A
˚
b = 15.8747(9) A
˚
b = 15.8191(7) A
˚
˚
c = 17.5508(8) A
c = 17.8434(11) A
R = 71.845(5)°
β = 75.155(5)°
γ = 89.695(5)°
3198.0(3)
R = 72.415(4)°
β = 75.272(4)°
γ = 89.408(4)°
3137.9(3)
3
vol [A ]
˚
Z
2
1.617
2.613
1564
0.34 ꢀ 0.30 ꢀ 0.25
2.99 - 27.48°
-16 e h e 16
-19 e k e 20
-22 e l e 23
14575
2
1.662
2.982
1576
0.28 ꢀ 0.20 ꢀ 0.13
2.99 - 26.02°
-14 e h e 15
-19 e k e 19
-21 e l e 18
24585
F (calc) [Mg/m3]
μ [mm-1
F(000)
]
cryst size [mm3]
θ range
index ranges
reflns collected
independent reflns
completeness to θ
max/min transm
data/restraints/params
GOF on F2
14575 [R(int) = 0.0000]
27.48° - 99.3%
1.00000/0.76643
14575/48/822
1.036
12322 [R(int) = 0.0444]
26.02° - 99.6%
1.00000/0.51159
12322/66/820
0.977
final R indices [I > 2σ(I)]
R1 = 0.0646
wR2 = 0.1509
R1 = 0.1149
wR2 = 0.1674
2.142/-1.099
R1 = 0.0560
wR2 = 0.1399
R1 = 0.0810
wR2 = 0.1482
2.974/-1.708
R indices (all data)
3
largest diff. peak/hole [e/A ]
˚
a
2
Data in common: Temperature, 140(2) K. Wavelength, 0.71073 A. Refinement method, full-matrix least-squares on F . Absorption correction:
˚
semiempirical from equivalents.
Experimental Section
Data collections for both structures were performed at 140 K
using Mo KR radiation on an Oxford Diffraction Sapphire/
KM4 CCD with a kappa geometry goniometer. Data were
reduced by means of CrysAlis PRO43 and then corrected for
absorption.44 Solutions and refinements were carried by
SHELX.45 The structures were refined using full-matrix least-
squares on F2 with all non hydrogen atoms anisotropically
defined. Hydrogen atoms were placed in calculated positions
by means of the “riding” model (apart from the ones belonging
to water molecules).
Solvent molecules in both structures were clearly disordered;
however, disorder was not modeled and restraints (SIMU and
ISOR cards) were applied to displacement parameters of the
C2H5OH and H2O molecules. A twinning problem was discov-
ered during the refinement of [La(LPhBr)3] and treated by
means of the TWINROTMAT routine in PLATON.46 A new
data set was then created and used in the final stages of
refinement with cards HKLF 5, MERG 0, and two refined
BASF parameters [0.096(1); 0.080(4)].
General Methods, Equipment, and Chemicals Used. Elemental
analyses were performed by Dr. E. Solari, Service for Elemental
Analysis, Institute of Chemical Sciences and Engineering
(EPFL). 1H and 13C NMR spectra (presented as δ in ppm and
J in Hz) were recorded on a Bruker Avance DRX 400 MHz
and Bruker Avance II 800 MHz spectrometers, respectively. ESI
MS were recorded on a Q-TOF Ultima (Waters) or TSQ7000
(Thermo Fisher) spectrometers at the Mass Spectrometry Ser-
vice of the Institute of Chemical Sciences and Engineering
(EPFL). Absorption spectra were measured on a Perkin-Elmer
Lambda 900 UV/vis/NIR spectrometer at room temperature in
the spectral range 250-500 nm. Estimated errors are (1 nm for
λmax and (5% for ε. Luminescence spectra were measured on a
Fluorolog FL 3-22 spectrometer from Horiba-Jobin Yvon and
were corrected for the instrumental function. Quantum yields
were determined on the same instrument through an absolute
method using a home-modified integrating sphere.42 Lumines-
cence lifetimes were measured with a previously described instru-
mental setup.31 Spectroscopic studies were conducted in optical
cells of 2 mm path length or 2 mm i.d. quartz capillaries under air
with the samples of lanthanide complexes obtained directly from
the synthesis and used without further purification. The solutions
of the complexes in CH2Cl2 (Fisher Scientific, analytical reagent
grade) were freshly prepared before each experiment.
Synthesis of Benzimidazole-Substituted Pyridine-2-Carboxylic
Acids. The synthesis of the precursors is described in the Support-
ing Information. The reactions were performed under air. Sub-
stituted pyridine-2-carboxaldehyde was dissolved in formic acid
(Merck, 98-100%) at room temp. to give a yellow solution which
sometimes appeared as being cloudy because of the presence of a
red solid, probably, residual Se from the previous synthetic step.
The amount of formic acid was chosen to correspond either to a
minimum of 3-5 mol equiv relative to aldehyde or to the
minimum volume necessary to dissolve the aldehyde at 0 °C.
X-ray Crystallography. The crystal data and structure refine-
ment parameters are presented in Table 6. Single crystals were
grown by dissolving a small sample (1-2 mg) of the complex in
boiling C2H5OH for [La(LPhBr)3] or C2H5OH/CH3CN for
[Eu(LPhBr)3] followed by cooling to room temp. and slow
evaporation (1-4 weeks).
(43) CrysAlis PRO; Oxford Diffraction Ltd.: Yarnton, Oxfordshire, U.K.,
2009.
(44) Blessing, R. H. Acta Crystallogr., Sect. A 1995, 51, 33.
(45) Sheldrick, G. Acta Crystallogr., Sect. A 2008, 64, 112.
(46) Spek, A. L. PLATON. A Multipurpose Crystallographic Tool; Utrecht
University: Utrecht, The Netherlands, 2008.
€
(42) Aebischer, A.; Gumy, F.; Bunzli, J.-C. G. Phys. Chem. Chem. Phys.
2009, 11, 1346.

Article
Inorganic Chemistry, Vol. 49, No. 8, 2010 3935
This solution was cooled to 0 °C, stirred for 10 min, and cold
H2O2 (30% wt. aq. solution) was added in excess. The solution
was stirred at 0 °C for 4-6 h, and kept overnight at 0 °C. Addition
of ice-cold water (20 mL) precipitated the product. In the case of
HLPhO8 and HLRX (R = Ph, Biph, Nap) the product separates
as sticky oil which solidifies on stirring and sonication. The
resulting suspension was stirred at 0 °C for 1 h and filtered to
give a solid. It was washed with water, ether (25 mL), and hexane
for HLPhBr or with water and hexane in all other cases, and was
dried under vacuum. Synthesis of HLPh has been described
elsewhere.30 Further specific synthetic details are provided below.
HLPhBr. The reaction was performed with LPhBr-CHO
(269 mg, 0.71 mmol), formic acid (4 mL, 4.88 g, 0.11 mol),
and H2O2 (0.45 mL of 30% wt. aq. solution, containing 150 mg
of H2O2, 4.41 mmol). White solid: 216 mg (0.55 mmol, 77%).
Anal. Calcd for C19H12BrN3O2 (MW 394.22): C, 57.89; H, 3.07;
N, 10.66. Found: C, 57.63; H, 3.07; N, 10.44. 1H NMR(400 MHz,
DMSO-d6): 8.35 (d, J 7.2, 1H), 8.11 (t, J 7.6, 1H), 8.00 (d, J 7.6,
1H), 7.85 (dd, J 6.8, J 2.0, 1H), 7.71-7.65 (m, 2H), 7.42-7.31 (m,
H2O2 (0.45 mL of 30% wt. aq. solution, containing 150 mg of
H2O2, 4.41 mmol). Off-white solid: 239 mg (0.46 mmol, 61%).
Anal. Calcd for C33H33N3O3 (MW 519.63): C, 76.28; H, 6.40; N,
1
8.09. Found: C, 76.53; H, 6.35; N, 8.24. H NMR (400 MHz,
DMSO-d6): 8.28 (d, J 7.6, 1H), 8.08 (t, J 7.6, 1H), 7.96 (d, J 8.0,
1H), 7.82-7.70 (m, 5H), 7.55-7.46 (m, 4H), 7.41 (t, J 7.6, 1H),
6.99 (dd, J 8.8, J 2.4, 1H), 6.68 (d, J 2.0, 1H), 3.93 (t, J 6.4, 2H),
1.73-1.64 (m, 2H), 1.44-1.17 (m, 10H), 0.83 (t, J 7.2, 3H),
CO2H proton not observed. 13C NMR (200 MHz, DMSO-
d6):165.94, 157.19, 149.28, 149.06, 147.91, 140.30, 139.81,
138.89, 138.52, 137.07, 136.73, 129.45, 128.35, 128.20, 127.92,
127.45, 127.31, 124.80, 121.08, 113.79, 94.75, 68.45, 31.68, 29.22,
29.16, 29.11, 25.98, 22.54, 14.41. ESIþ MS: m/z 520.7 {M þ H}þ.
HLNapX. The reaction was performed with LNapX-CHO
(520 mg, 1.09 mmol), formic acid (5 mL, 6.1 g, 0.13 mol), and
H2O2 (0.75 mL of 30% wt. aq. solution, containing 250 mg of
H2O2, 7.34 mmol). Dull yellow solid: 246 mg (0.50 mmol, 46%,
non-optimized yield). Anal. Calcd for C31H31N3O3 (MW
493.60): C, 75.43; H, 6.33; N, 8.51. Found: C, 75.44; H, 6.28;
N, 8.55. 1H NMR (400 MHz, DMSO-d6): 8.28 (dd, J 8.0, J 0.8,
1H), 8.09-7.96 (m, 4H), 7.95 (dd, J 7.2, J 1.6, 1H), 7.91 (dd,
J 7.6, J 0.8, 1H), 7.74 (d, J 8.8, 1H), 7.61-7.52 (m, 2H), 7.47 (dd,
J 8.8, J 2.0, 1H), 6.97 (dd, J 8.8, J 2.4, 1H), 6.63 (d, J 2.4, 1H),
3.87 (t, J 6.4, 2H), 1.69-1.58 (m, 2H), 1.38-1.12 (m, 10H), 0.81
(t, J 6.8, 3H), CO2H proton not observed. 13C NMR (200 MHz,
DMSO-d6): 165.78, 157.18, 149.29, 147.91, 138.86, 138.75,
137.07, 134.93, 133.53, 132.77, 129.47, 128.61, 128.19, 127.48,
127.13, 127.04, 126.28, 126.15, 124.80, 121.08, 113.80, 94.82,
68.39, 31.65, 29.19, 29.11, 29.08, 25.95, 22.52, 14.39, one of the
aromaticcarbons is not observed. ESIþ MS: m/z 494.7 {M þ H}þ.
Synthesis of the Complexes. The reactions were performed
under air using 3:3:1 molar ratio of the ligand, NaOH, and
4H), 7.23 (dd, J 6.8, J 2.0, 1H), CO2H proton not observed. 13
C
NMR (200 MHz, DMSO-d6): 165.97, 149.75, 149.00, 148.09,
142.66, 139.01, 137.67, 136.84, 132.61, 130.10, 127.71, 125.29,
124.82, 123.70, 121.64, 120.39, 111.37. ESIþ MS: m/z 394.1, 396.1
{M þ H}þ.
HLPhBu. The reaction was performed with LPhBu-CHO
(366 mg, 1.03 mmol), formic acid (4 mL, 4.9 g, 0.11 mol), and
H2O2 (0.55 mL of 30% wt. aq. solution, containing 183 mg
of H2O2, 5.39 mmol). White solid: 337 mg (0.91 mmol, 88%).
Anal. Calcd for C23H21N3O2 0.5H2O (MW 380.44): C, 72.61;
3
H, 5.83; N, 11.05. Found: C, 72.44; H, 5.88; N, 10.86. 1H NMR
(400 MHz, DMSO-d6): 8.29 (d, J 7.6, 1H), 8.09 (t, J 7.6, 1H),
7.99 (d, J 7.6, 1H), 7.85 (dd, 1H), 7.51 (d, J 8.4, 2H), 7.39-7.29
(m, 4H), 7.23 (dd, 1H), 1.33 (s, 9H), CO2H proton not observed.
13C NMR (200 MHz, DMSO-d6): 165.87, 151.19, 149.91, 149.20,
147.96, 142.61, 138.97, 137.78, 134.60, 127.92, 127.32, 126.47,
125.09, 124.64, 123.50, 120.32, 111.52, 34.95, 31.56. ESIþ MS: m/z
372.7 {M þ H}þ.
LnCl3 nH2O. The ligand was suspended in hot ethanol (70-
3
80 °C, 5 mL; the same temperature was kept throughout the
reaction), followed by addition of NaOH dissolved in water
(0.5-1 mL, used as a stock solution with approximately 100 mg
of NaOH per 10 mL of water) and stirring for 10 min to give
colorless solution. A solution of LnCl3 nH2O (n = 6 or 7;
HLPhO8. The reaction was performed with LPhO8-CHO
(432 mg, 1.01 mmol), formic acid (4 mL, 4.9 g, 0.11 mol), and
H2O2 (0.52 mL of 30% wt. aq. solution, containing 173 mg of
H2O2, 5.09 mmol). White solid: 295 mg (0.67 mmol, 66%). Anal.
Calcd for C27H29N3O3 (MW 443.54): C, 73.11; H, 6.59; N, 9.47.
Found: C, 72.86; H, 6.72; N, 9.35. 1H NMR (400 MHz, DMSO-
d6): 8.24 (d, J 7.6, 1H), 8.09 (t, J 7.6, 1H), 8.01 (d, J 7.6, 1H), 7.83
(dd, 1H), 7.39-7.28 (m, 4H), 7.19 (dd, 1H), 7.01 (d, J 8.8, 2H),
4.00 (t, J 6.8, 2H), 1.79-1.68 (m, 2H), 1.48-1.22 (m, 10H), 0.87
(t, J 6.8, 3H), CO2H proton not observed. 13C NMR (200 MHz,
DMSO-d6): 165.98, 158.81, 150.22, 149.33, 148.11, 142.55,
138.88, 138.08, 129.60, 129.15, 128.00, 125.06, 124.51, 123.42,
120.28, 115.34, 111.45, 68.25, 31.73, 29.25, 29.16 (two over-
lapping resonances), 26.01, 22.58, 14.45. ESIþ MS: m/z 444.7
{M þ H}þ.
3
99.9%, Aldrich) in water (2 mL) was added dropwise over 5 min
and stirred for further 5 min. A white precipitate of the complex
may form on addition. If necessary, an additional volume of
water (as specified below) was added to complete the precipita-
tion of the complex. The resulting suspension was stirred for
5 min at 70-80 °C, allowed to cool to 40-50 °C while stirring,
and filtered while warm. The product was washed with ethanol/
water (1:1) followed by ether for LnLPhBr; with ethanol/water
(1:4) and hexane for LnLPhBu; or with ethanol/water (1:1)
followed by hexane in all other cases, and was dried under
vacuum at room temperature. The complexes are white solids
that are soluble in DMSO, boiling ethanol and are insoluble in
hexane and water; the complexes with tert-butyl or n-octyloxy
groups are also soluble in CH2Cl2. Further synthetic details and
analytical data are provided below. Synthesis of LnLPh has been
described elsewhere.30
HLPhX. The reaction was performed with LPhX-CHO
(203 mg, 0.47 mmol), formic acid (3 mL, 3.66 g, 0.08 mol) and
H2O2 (0.3 mL of 30% wt. aq. solution, containing 100 mg of
H2O2, 2.93 mmol). Cream solid: 71 mg (0.16 mmol, 34%).
Anal. Calcd for C27H29N3O3 (MW 443.54): C, 73.11; H, 6.59;
N, 9.47. Found: C, 73.17; H, 6.62; N, 9.40. 1H NMR (400 MHz,
DMSO-d6):8.20-8.13 (br, 1H), 8.03 (t, J 7.6, 1H), 7.94 (d, J 8.0,
1H), 7.72 (d, J 8.8, 1H), 7.54-7.36 (m, 5H), 6.97 (dd, J 8.8, J 2.4,
1H), 6.60 (d, J 2.4, 1H), 3.91 (t, J 6.4, 2H), 1.73-1.63 (m, 2H),
1.43-1.20 (m, 10H), 0.85 (t, J 7.2, 3H), CO2H proton not
observed. 13C NMR (200 MHz, DMSO-d6): 165.96, 157.11,
149.22, 148.24, 138.80, 138.46, 137.36, 137.03, 129.80, 128.68,
127.80, 127.43, 124.72, 121.05, 113.71, 94.68, 68.41, 31.68, 29.21,
29.15, 29.11, 25.98, 22.55, 14.43, one of the aromatic carbons is
not observed. ESIþ MS: m/z 444.7 {M þ H}þ.
[La(LPhBr)3] 3H2O. The complex precipitated on mixing of
3
reagents: 48 mg (0.035 mmol, 83%) from HLPhBr (50 mg, 0.127
mmol), NaOH (5.1 mg, 0.127 mmol), and LaCl3 7H2O (15.7 mg,
3
0.042 mmol). Anal. Calcd for C57H33Br3LaN9O6 3H2O (MW
1372.59): C, 49.88; H, 2.86; N, 9.18. Found: C, 50.14; H, 2.81; N,
3
8.72. ESIþ MS: m/z 1342.4 {M þ Na}þ, 682.7 {M þ 2Na}2þ
.
[La(LPhBu)3] 2H2O. The complex was precipitated with
3
water (8 mL): 45 mg (0.035 mmol, 80%) from HLPhBu 0.5H2O
(50 mg, 0.131 mmol), NaOH (5.25 mg, 0.131 mmol), and
3
LaCl3 7H2O (16.3 mg, 0.044 mmol). Anal. Calcd for C69H60La-
3
N9O6 2H2O (MW 1286.21): C, 64.43; H, 5.02; N, 9.80. Found:
3
C, 64.26; H, 4.93; N, 9.77. ESIþ MS: m/z 1250.8 {M þ H}þ,
625.9 {M þ 2H}2þ
.
[La(LPhO8)3] 2H2O. The complex was precipitated with
water (2.5 mL): 43 mg (0.029 mmol, 75%) from HLPhO8 (50 mg,
HLBiphX. The reaction was performed with LBiphX-CHO
(376 mg, 0.75 mmol), formic acid (4 mL, 4.88 g, 0.11 mol), and
3

3936 Inorganic Chemistry, Vol. 49, No. 8, 2010
Shavaleev et al.
0.113 mmol), NaOH (4.51 mg, 0.113 mmol), and LaCl3 7H2O
(13.95 mg, 0.038 mmol). Anal. Calcd for C81H84LaN9O9 2H2O
(MW 1502.52): C, 64.75; H, 5.90; N, 8.39. Found: C, 64.84; H, 5.96;
[Eu(LPhO8)3] 2H2O. The complex was precipitated with
water (2.5 mL): 41 mg (0.027 mmol, 71%) from HLPhO8
3
3
3
(50 mg, 0.113 mmol), NaOH (4.51 mg, 0.113 mmol), and EuCl3
6H2O (13.77 mg, 0.038 mmol). Anal. Calcd for C81H84Eu-
3
N, 8.26. ESIþ MS: m/z 756.0 {M þ 2Na}2þ
.
[La(LPhX)3] 2H2O. The complex was precipitated with
N9O9 2H2O (MW 1515.58): C, 64.19; H, 5.85; N, 8.32.
3
3
Found: C, 64.05; H, 5.96; N, 8.22. ESIþ MS: m/z 763.0
water (1 mL): 25 mg (0.017 mmol, 88%) from HLPhX (25 mg,
0.056 mmol), NaOH (2.25 mg, 0.056 mmol), and LaCl3 7H2O
{M þ 2Na}2þ
.
[Eu(LPhX)3] 1.5H2O. The complex was precipitated with
3
3
(7.0 mg, 0.019 mmol). Anal. Calcd for C81H84LaN9O9 2H2O
(MW 1502.52): C, 64.75; H, 5.90; N, 8.39. Found: C, 64.64; H,
3
water (3 mL): 25 mg (0.017 mmol, 73%) from HLPhX (30 mg,
0.068 mmol), NaOH (2.71 mg, 0.068 mmol), and EuCl3 6H2O
1
5.92; N, 8.23. ESIþ MS: m/z 756.1 {M þ 2Na}2þ. H NMR
3
(400 MHz, CD2Cl2) of the complex indicates the presence of
several interconverting species in solution (Figure NMR-25 in
the Supporting Information).
(8.3 mg, 0.0227 mmol). Anal. Calcd for C81H84EuN9O9 1.5H2O
3
(MW 1506.58): C, 64.57; H, 5.82; N, 8.37. Found: C, 64.74; H,
5.92; N, 8.37. ESIþ MS: m/z 763.0 {M þ 2Na}2þ
.
[Eu(LBiphX)3]. The complex precipitated on mixing of reagents:
[La(LBiphX)3] H2O. The complex precipitated on mixing of
reagents: 47 mg (0.029 mmol, 91%) from HLBiphX (50 mg,
3
46 mg (0.027 mmol, 84%) from HLBiphX (50 mg, 0.096 mmol),
NaOH (3.85 mg, 0.096 mmol), and EuCl3 6H2O (11.8 mg, 0.032
mmol). Anal. Calcd for C99H96EuN9O9 (MW 1707.84): C, 69.62;
0.096 mmol), NaOH (3.85 mg, 0.096 mmol), and LaCl3 7H2O
(11.9 mg, 0.032 mmol). Anal. Calcd for C99H96LaN9O9 H2O
3
3
3
H, 5.67; N, 7.38. Found: C, 69.49; H, 5.89; N, 7.37. ESIþ MS: m/z
(MW 1712.80): C, 69.42; H, 5.77; N, 7.36. Found: C, 69.27; H,
5.73; N, 7.35. ESIþ MS: m/z 870.6 {M þ 2Na}2þ
877.1 {M þ 2Na}2þ
.
[Eu(LNapX)3] H2O. The complex was precipitated with water
.
[La(LNapX)3] H2O. The complex was precipitated with
3
3
(1 mL): 46 mg (0.028 mmol, 82%) from HLNapX (50 mg, 0.10
mmol), NaOH (4.05 mg, 0.10 mmol), and EuCl3 6H2O (12.4 mg,
0.034 mmol). Anal. Calcd for C93H90EuN9O9 H2O (MW 1647.74):
water (1 mL): 46 mg (0.28 mmol, 83%) from HLNapX (50
mg, 0.10 mmol), NaOH (4.05 mg, 0.10 mmol), and LaCl3 7H2O
3
3
(12.5 mg, 0.034 mmol). Anal. Calcd for C93H90LaN9O9 H2O
(MW 1634.69): C, 68.33; H, 5.67; N, 7.71. Found: C, 68.07; H,
3
3
C, 67.79; H, 5.63; N, 7.65. Found: C, 67.85; H, 5.85; N, 7.62. ESIþ
MS: m/z 1631.1 {M þ H}þ, 816.1 {M þ 2H}2þ
.
5.75; N, 7.71. ESIþ MS: m/z 831.6 {M þ 2Na}2þ
.
[Eu(LPhBr)3] 2.5H2O. The complex precipitated on mixing of
3
reagents: 51 mg (0.037 mmol, 88%) from HLPhBr (50 mg, 0.127
mmol), NaOH (5.1 mg, 0.127 mmol), and EuCl3 6H2O (15.5 mg,
Acknowledgment. This research is supported by a grant from
the Swiss National Science Foundation (No. 200020_119866/1).
J.C.B. thanks the WCU (World Class University) program from
the National Science Foundation of Korea (Ministry of Education,
Science, and Technology) for Grant R31-10035.
3
0.042 mmol). Anal. Calcd for C57H33Br3EuN9O6 2.5H2O (MW
3
1376.64): C, 49.73; H, 2.78; N, 9.16. Found: C, 49.85; H, 2.74; N,
.
[Eu(LPhBu)3] 1.5H2O. The complex was precipitated with water
8.75. ESIþ MS: m/z 1354.4 {M þ Na}þ, 688.7 {M þ 2Na}2þ
3
(8 mL): 45 mg (0.035 mmol, 79%) from HLPhBu 0.5H2O (50 mg,
0.131 mmol), NaOH (5.25 mg, 0.131 mmol), and EuCl3 6H2O(16.05
Supporting Information Available: Synthesis of the ligand
3
1
precursors; absorption and luminescence spectra; H and 13C
3
mg, 0.044 mmol). Anal. Calcd for C69H60EuN9O6 1.5H2O (MW
3
NMR spectra; CIF files of the crystal structures, CCDC 762688
and 762689. This material is available free of charge via the
Internet at http://pubs.acs.org.
1290.26): C, 64.23; H, 4.92; N, 9.77. Found: C, 64.18; H, 4.83; N, 9.65.
ESIþ MS: m/z 1264.8 {M þ H}þ, 632.4 {M þ 2H}2þ
.