Sensitized luminescence in dinuclear lanthanide(iii) complexes of bridging 8-hydroxyquinoline derivatives with different electronic properties

Article abstract of DOI:10.1039/c0dt01663b

Three new dinuclear lanthanide(iii) complexes {Eu(hfac)₃(H ₂O)}₂(μ-HPhMq)₂ (2) and {Ln(hfac) ₃(H₂O)}₂(μ-HMe₂NC ₆H₄Mq)₂ (Ln = Eu, 3; Nd, 4) with 8-hydroxylquinoline derivatives in μ-phenol mode were synthesized and characterized, where hfac^- = hexafluoroacetylacetonate, HPhMq = 2-methyl-5-phenylquinolin-8-ol, and HMe₂C₆H₄Mq = 5-(4-(dimethylamino)phenyl)-2-methylquinolin-8-ol. Compared with that (400 nm) for {Eu(hfac)₃}₂(μ-HMq)₂ (1, HMq = 2-methy-8-hydroxylquinoline), the excitation wavelength for sensitized lanthanide luminescence is extended to ca. 420 nm for 2, and 500 nm for 4 by introducing a phenyl or 4-(dimethylamino)phenyl to 8-hydroxylquinoline. These dinuclear lanthanide(iii) complexes exhibit distinctly fluoride-induced lanthanide(iii) emission enhancement in both intensity and lifetime due to replacing coordination water molecules or formation of strong O-H...F hydrogen bonds with coordinated H₂O and μ-phenol, thus suppressing significantly the non-radiative O-H oscillators. The Royal Society of Chemistry.

Full text of DOI:10.1039/c0dt01663b

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PAPER
Sensitized luminescence in dinuclear lanthanide(III) complexes of bridging
8-hydroxyquinoline derivatives with different electronic properties†
Hai-Bing Xu,*a,b Jia Li,a Lin-Xi Shia and Zhong-Ning Chen*a
Received 30th November 2010, Accepted 21st March 2011
DOI: 10.1039/c0dt01663b
Three new dinuclear lanthanide(III) complexes {Eu(hfac)3(H2O)}2(m-HPhMq)2 (2) and
{Ln(hfac)3(H2O)}2(m-HMe2NC6H4Mq)2 (Ln = Eu, 3; Nd, 4) with 8-hydroxylquinoline derivatives in
m-phenol mode were synthesized and characterized, where hfac- = hexafluoroacetylacetonate,
HPhMq = 2-methyl-5-phenylquinolin-8-ol, and HMe2C6H4Mq = 5-(4-(dimethylamino)phenyl)-2-
methylquinolin-8-ol. Compared with that (400 nm) for {Eu(hfac)3}2(m-HMq)2 (1, HMq =
2-methy-8-hydroxylquinoline), the excitation wavelength for sensitized lanthanide luminescence is
extended to ca. 420 nm for 2, and 500 nm for 4 by introducing a phenyl or 4-(dimethylamino)phenyl to
8-hydroxylquinoline. These dinuclear lanthanide(III) complexes exhibit distinctly fluoride-induced
lanthanide(III) emission enhancement in both intensity and lifetime due to replacing coordination water
molecules or formation of strong O–H ◊ ◊ ◊ F hydrogen bonds with coordinated H2O and m-phenol, thus
suppressing significantly the non-radiative O–H oscillators.
properties with a triplet state located around 17 100 cm-1 (585 nm),
Introduction
making it suitable for the sensitization of NdIII luminescence. In
Due to the forbidden Laporte rule for the lanthanide(III) f–f
fact, lanthanide(III) complexes of 8-hydroxyquinolinates have been
transitions, it is inefficient to populate lanthanide energy levels
considered as one of the most promising materials for the design
of electroluminescent devices.9–13
directly. A typical strategy to circumvent this predicament is to
increase the luminescence excitation by coordinating lanthanide
ions to organic ligands which act as antennae to transfer energy
to the lanthanide ions.1 In order to favour energy transfer from
antenna to lanthanide(III) ions effectively, the excited state of
the ligand should be higher than the lowest excited state of
the lanthanide(III) ion, within an appropriate range.1 Among
the efforts to further optimize the luminescent properties of
lanthanide(III) complexes, a particular trend is aimed at shifting
the excitation domain toward the visible region.2–5 In fact, organic
ligands suitable for sensitizing visible and NIR (near-infrared)
emission from lanthanide(III) ions by excitation with visible light
have been less explored.6–8
As shown in Scheme 1, Hq and its derivatives exhibit versatile
coordination modes including chelating,9–11 chelating-bridging in
m- and m3-phenoxo coordination modes,14,15 and bridging in m-
phenol modes.15–17 The former three modes occur frequently, while
the latter one has been rarely reported in literature.15–17 Tradition-
ally, sensitized lanthanide luminescence is tunable by modifying
the electronic properties of peripheral ligands.1,9 Nevertheless,
modification of the electronic properties of bridging ligands to
modulate sensitizing lanthanide luminescence have not yet been
explored.
As the emission of the Hq derivatives originates primarily
from the electronic transitions in the quinoline rings, modifi-
cation of the substituents is one of the feasible approaches to
tune the emission properties.18 Taking advantage of Hq or its
derivatives as bridging ligands, we describe herein the prepara-
tion, structures and fluoride-enhanced lanthanide(III) lumines-
cence of dimeric lanthanide(III) complexes {Eu(hfac)3(H2O)}2(m-
HPhMq)2 (2) and {Ln(hfac)3(H2O)}2(m-HMe2NC6H4Mq)2 (Ln =
Eu, 3; Nd, 4) with 8-hydroxylquinoline derivatives in m-phenol
mode, where hfac- = hexafluoroacetylacetonate, HPhMq =
8-Hydroxyquinoline (Hq) and its derivatives are versatile co-
ordination ligands towards a wide range of metal ions, including
lanthanide(III) ions. These ligands possess useful photophysical
aState Key Laboratory of Structural Chemistry, Fujian Institute of Research
on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian,
350002, China. E-mail: haibingxu@fjirsm.ac.cn, czn@fjirsm.ac.cn; Fax: 86-
591-8379-2346
bNew Materials R&D Center, Institute of Chemical Materials, China
Academy of Engineering Physics, Chendu, 621900, China
2-methyl-5-phenylquinolin-8-ol, and HMe2C6H4Mq
= 5-(4-
(dimethylamino)phenyl)-2-methylquinolin-8-ol (Scheme 2). Sen-
sitized lanthanide(III) luminescence is indeed achieved in these
dinuclear complexes upon irradiation with visible light, suggesting
an effective energy transfer from the bridging ligands to lan-
thanide(III) centres.
† Electronic supplementary information (ESI) available: UV-vis absorp-
tion, excitation and emission spectra of titration, lifetime decay curves and
X-ray crystallographic files in CIF format for the structure determination
of compounds 2·H2O and 4·H2O. CCDC reference numbers 803484 and
803485. For ESI and crystallographic data in CIF or other electronic
format see DOI: 10.1039/c0dt01663b
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Scheme 1 The bonding modes of HMq.
Scheme 2 The structures of dinuclear lanthanide(III) complexes.
˚
Table 1 Selected interatomic distances (A) and bond angles (deg) of 1, 2
and 4
Results and discussion
Syntheses and characterisation
117
2
4
Complexes 2–4 were by-products from the reactions of
O7–Ln1
Ln1–O7–Ln1A
Ln ◊ ◊ ◊ Ln1A
2.411(3)
110.56(10)
3.9292(11)
2.447(6)
112.6(2)
4.0851(12)
2.462(3)
113.05(12)
4.1088(8)
Al(L¢)2(OC6H4CN-4)18 (L¢
=
PhMq, Me2NC6H4Mq) with
Ln(hfac)3(H2O)2 (Ln
= Eu and Nd) in dichloromethane,
in which the main products are [Al3(L)4(HL)(m3-OH)2(m-
OH)3{Ln(hfac)3}2].15 The IR spectra of complexes 2–4 show
characteristic n(OH) bands at 2920 and 3440 cm-1, and n(C O)
bands at ca. 1665 cm-1. The structures of 2 and 4 were determined
by X-ray crystallography.
Photophysical properties
The absorption and emission data of 1–4 are summarized in
Table 2. The UV-Vis spectra of 1, 2 and 4 in dichloromethane
solutions are depicted in Fig. 3. In the UV-Vis spectra of 1, 2, and
4, there are mainly three sets of absorption bands. The high-energy
band at < 300 nm is from the Hq derivative ligands (ca. 260 nm for
HMq, 267 nm for HPhMq, and 275 nm for HMe2NC6H4Mq),18
and the absorption at ca. 300 nm results from the intraligand
p–p* transition of hfac-.2–4,14–15,17 A broad, low-energy absorption
trailing to the visible light region arises probably from the n→p*
transitions of Hq derivative ligands (centred at ca. 385 nm for
HMq, 410 nm for HPhMq, and 470 nm for HMe2NC6H4Mq
(Fig. 3, inset)).10b,13b,14c As depicted in Fig. 3 (inset), the broad low-
energy band is distinctly red-shifted in the order 1 (385 nm) →
2 (410 nm) → 4 (470 nm), demonstrating that introducing an
aromatic group or electron-donating substituent favors achieving a
red-shift of the absorption spectrum. Ln(hfac)3(H2O)2 has almost
no absorption above 350 nm,2,14,15,17,25 while 1–4 exhibit distinct
absorption bands above 350 nm, ascribed most likely to the
extended n→p* transitions in Hq derivative ligands bound to
the lanthanide(III) ions.10b,13b,14c
The structure of 2 was depicted in Fig. 1. The EuIII ions
are coordinated by nine oxygen atoms with two from the m-
phenol of HPhMq, one from a coordinated H2O, and six from
three hfac-, forming a capped square antiprism geometry. The
dinuclear lanthanide(III) centres are bridged by HPhMq through
m-phenol in a symmetric fashion with Eu–L–Eu distance being
˚
4.0851(12) A. The bond lengths of O7–Eu1 and O7–C15 are ca.
˚
2.447(6) and 1.317(10) A, and the bond angle of Eu1–O7–Eu1A is
112.6(2)◦.
The crystal structure of 4 is similar to that of 2 (Fig. 2), except
that two of the nine oxygen atoms around the NdIII ion are from
the m-phenol of HMe2NC6H4Mq to furnish a capped distorted
square-antiprism. The bridging HMe2NC6H4Mq is featured with
a m-phenol mode to link two NdIII ions in a symmetric fashion
˚
with the Nd–L–Nd distance being 4.1088(8) A. The bond lengths
˚
of O7–Nd1 and O7–C15 are ca. 2.462(3) and 1.343(6) A, and the
bond angle of Nd1–O7–Nd1A is 113.05(12)◦. It is interesting to
note that the O–Ln length and Ln–L–Ln separation together with
the Ln–O–Ln angle increase with the bulk of the bridging ligands
in the order: HMq17 < HPhMq < HMe2C6H4Mq as indicated in
Table 1.
Excitation of the ligand-centred charge-transfer band in the
UV region for 1–4 (Fig. 5) gives rise to typical luminescence from
the corresponding lanthanide(III) ions with microsecond range of
5550 | Dalton Trans., 2011, 40, 5549–5556
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Fig. 1 ORTEP drawing (30% thermal ellipsoid) of 2. The F atoms on the trifluoromethyl, the disorder and the hydrogen atoms or solvent water are
omitted for clarity.
Fig. 2 ORTEP drawing (30% thermal ellipsoid) of 4. The F atoms on the trifluoromethyl, the disorder, and the hydrogen atoms or solvent water are
omitted for clarity.
Table 2 Absorption and Emission Data of Compounds 1–4 at 298 K
Compounds
Medium
l
abs /nm (e/dm3mol-1cm-1)
l
em/nm (tem/ms)a
Uem (%)
1
powder
CH2Cl2
1-Fd
powder
CH2Cl2
2-Fd
powder
CH2Cl2
3-Fd
powder
CH2Cl2
4-Fd
614 (318)
614 (269)
614 (488)
614 (112)
614 (99)
614 (447)
614 (151)
614 (350)
614 (544)
1064 (––b)
1061 (—b)
1061 (—b)
245 (49 500), 260 (61– 600), 300 (53 100), 380 (2500)
265 (36 800), 300 (27 500), 406 (2000)
1.9c
2
3
4
2.2e
1.3e
275 (33 500), 300 (38 900), 363 (3900), 480 (800)
275 (32400), 302 (38800), 367 (3700), 475 (800)
a Excitation wavelength in the lifetime measurement is 335 nm. b Due to the instrument limitation, we could not give the accurate lifetime shorter than
10 ms c Reference 17 d This represents the samples in dichloromethane solution upon addition of 2 equivalents of F- for 2–4. e The quantum yields of
Eu-based emission in dichlorormethane solutions with lex = 335 nm were determined relative to that of Ru(bpy)3Cl2 (Uem = 0.028) in ambient water.
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Fig. 5 Excitation spectra and fluoride-induced lanthanide(III) emission
enhancement for 3 (red) and 4 (blue) in dichloromethane solutions before
(short dash) and after (solid) addition of 2 equiv. [Bu4N]F at ambient
temperature. Inset: Excitation spectra of 3 (red) and 4 (blue) at long
wavelength region (350 nm < lex < 500 nm) in dichloromethane solution
at 298 K.
Fig. 3 The UV-vis absorption spectra of 1 (blue), 2 (black) and 4 (red) in
dichloromethane at ambient temperature.
lifetimes both in solid states and dichloromethane solutions at
ambient temperature (Table 2). The emission band ascribed to the
p→p* excited state of the ligand in the UV region, however, are
remarkably attenuated due to energy transfer from the ligands to
lanthanide centres. The longer Eu-based lifetime for 1 (t = 318 ms)
than that for 2 (t = 122 ms) and 3 (t = 151 ms) in the solid state is
attributable to exclusion of the solvent molecules coordinating to
the EuIII ions for 1.19
hydroxyquinolinates, attributed to the low-lying excited states of
the quinoline derivatives and their inability to transfer energy to
the lanthanide(III) centres.1a,9 Nevertheless, dimeric europium(III)
complexes 2 and 3 display bright red luminescence from eu-
ropium(III) centres. This may be induced due to two reasons.
One is that the peripheral ligands around the europium(III) ions
include not only Hq derivatives, but also the chelating ligand hfac-.
The other is that the Hq derivative is not chelating but bridging
the europium(III) ions in m-phenol mode. Excitation at the low-
energy absorbing region of Hq derivatives, sensitized europium(III)
emission could be detected at 350 nm < lex < 400 nm for 1,17 and
350 nm < lex < 420 nm for 2 (Fig. 4). This suggests that the
excitation domain for sensitized lanthanide(III) luminescence is
extended to the visible light region by introducing a phenyl to 8-
hydroxyquinoline ligands, in which substantial energy transfer is
most likely operating from Hq derivative ligands to the lanthanide
centres in these dimeric lanthanide(III) complexes.
As the emission of 8-hydroxyquinoline derivatives originates
from the electronic transitions in the quinolinolate ligands,
the substituent attached to the quinolinolate could be used to
tune the emission color.18 Thus, introducing a phenyl or 5-(4-
(dimethylamino)phenyl to the quinolinolate causes a red shift
in the emission band ascribed to the p→p* excited state from
460 nm (21 000 cm-1) to 510 nm (20 000 cm-1) (Figure S6,
ESI†). Additionally, hfac- only acts as antenna chromophore
for sensitized lanthanide emission within 350 nm,22 whereas
lanthanide emission obtained beyond 350 nm was achieved by
the 8-hydroxyquinoline derivatives as antennae to transfer energy
to the lanthanide ions.9–11
On the one hand, as both hfac- and 8-hydroxyquinoline
derivatives exist as the ligands in these lanthanide(III) compounds,
both ligands have absorption within 350 nm and could act as
antennae to transfer energy to the lanthanide ions, achieving
sensitized lanthanide emission.10b,13b,14c,20 So, the lifetimes of these
complexes are much longer than the corresponding values of the
precursors Ln(hfac)3(H2O)2 and Lnq3(H2O)n.21,22,27 On the other
hand, although the precursor Ln(hfac)3(H2O)2 has no absorption
above 350 nm,2–4,14–15,17 the lanthanide(III) luminescence in these
complexes could also be sensitized by energy transfer from Hq
derivative ligands upon excitation at 350–500 nm (Fig. 4 and
5). The luminescence of these lanthanide(III) complexes is thus
improved compared with the precursor Ln(hfac)3(H2O)2.22,27
As indicated in Table 2, the quantum yield of 2 (Uem = 2.2%)
is higher than that of 1 (Uem = 1.9%)17 in dichloromethane
solution, which is due likely to the much more matched energy
level for HPhMq (21 000 cm-1)→Eu energy transfer than that for
HMq (25 000 cm-1)→Eu,1,14b although there exists an additional
quenching pathway from the two coordination water molecules in
2 to quench the Eu-centred emission through O–H non-radiative
oscillator. Furthermore, the quantum yield of 3 (Uem = 1.3%) is
much lower than those of 1 and 2. As the p→p* excited-state
energy of HMe2C6H4Mq in 3 is about 20 000 cm-1, it is too close to
Fig. 4 Excitation spectra (lem = 610 nm) of 1 (black), 2 (red), and 3 (blue)
at long wavelength region. Inset: emission spectra of 2 with excitation at
400 nm (black) and 420 nm (red) in dichloromethane solution at 298 K.
It has been demonstrated that europium(III) emission is usually
undetectable for most of the lanthanide(III) complexes with 8-
5552 | Dalton Trans., 2011, 40, 5549–5556
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that of emissive state of EuIII ions at 5D1 (19 000 cm-1) level. Thus,
energy transfer from the excited-state energy of HMe2C6H4Mq
to EuIII ions is less efficient than that for HMq (1) or HPhMq
(2).1,14b Nevertheless, the electronic features of HMe2NC6H4Mq
are better suitable for populating NIR emitting excited states of
the neodymium(III) ions. As expected, excitation at the absorbing
region of HMe2C6H4Mq (270 nm < lex < 540 nm), three NIR
emission bands were observed for NdIIIcomplex 4 at ca. 865, 1064,
phenol mode have been isolated and the corresponding structures
established by X-ray crystallography. The luminescence of these
complexes is improved due to both hfac- and 8-hydroxyquinoline
derivatives as antennae to sensitize lanthanide(III) emissions.
Additionally, modification of the electronic properties of the
bridging 8-hydroxyquinoline ligands, the excitation domain for
achieving sensitized lanthanide luminescence, shifts to a longer
wavelength visible light region. Moreover, remarkable fluoride-
induced enhancement in emission intensity and lifetime for
both visible and NIR lanthanide(III) luminescence are observed
upon addition a small amount of [Bu4N]F to the corresponding
solutions.
4
4
and 1330 nm due to F3/2→ I9/2,4I11/2, and4I13/2 transitions in the
solid state, respectively (Figure S4, ESI†).
Fluoride-induced luminescence enhancement
Due to the direct linkage of m-phenol to the lanthanide(III)
ions and the presence of an additional two coordinated wa-
ters around the lanthanide(III) ions in 2–4, the emissive states
of lanthanide(III) would be partially deactivated through non-
radiative O–H vibration excitation, so as to severely quench
the lanthanide(III) luminescence.23–24 One feasible approach to
suppress the O–H oscillators so as to increase the emissive
efficiency is the use of fluoride to replace coordination water
molecules or form strong O–H ◊ ◊ ◊ F interactions so as to suppress
the O–H oscillators, thus minimizing the vibrational radiationless
processes and improving the lanthanide(III) luminescence from f–f
transitions.15,19,24–26 As anticipated, titration of 1–4 with [Bu4N]F
in aerated dichloromethane solutions induced remarkable en-
hancement of lanthanide(III) luminescent intensity and lifetime.
As shown in Fig. 5 and Fig. S1, ESI,† addition of 2 equivalents
of F- to the dichloromethane solutions of 2–4 caused 7, 6 or
3-fold enhancement in emissive intensity, respectively, and the
lifetimes were increased from 99 to 447 ms for 2, and 350 to
544 ms for 3 (Table 2; Figure S5, ESI†). The significant emission
enhancement both in intensity and lifetime in the presence of a
small amount of F- suggests that 2–4 could be served as potential
luminescence probes for F- detection. As there exists an additional
two coordinated water molecules, except for two bridging ligands
in the m-phenol mode for 2 and 3, a larger amount of F- for the
maximum luminescent enhancement for 2 and 3 (2 equivalents)
is needed than that for 1 (0.2 equivalents),17 leading to more
remarkably enhanced emissive intensity (> 6-fold) in comparison
with 1 (4-fold). However, if more than 2 equivalents of F- are used,
the lanthanide(III) emission is gradually attenuated (Fig. S2, ESI†).
This is because the lanthanide(III) ions would gradually be ligated
by excess fluoride so as to destroy the original structures.15,17 This
variation process was monitored by UV-vis absorption titration.
By successive addition of fluoride to the dichloromethane solution
of 2 (Figure S3, ESI†), the absorption band at ca. 250 nm is
shifted to 225 nm when 100 equiv. of fluoride is used. Similarly,
EuIII-centred emission is gradually attenuated so as to disappear
entirely when excess fluoride is added to the dichloromethane of
2. The ligand-based emission, however, is significantly enhanced
with a blue shift (Figure S2, ESI†).15,17 This phenomenon further
suggests that the structures of the complexes could be destroyed
by excess fluoride.
Experimental section
General procedures
All manipulations were performed under a dry argon atmosphere
using Schlenk techniques and a vacuum-line system. The solvents
were dried, distilled, and degassed prior to use, except for those for
spectroscopic measurements which were of spectroscopic grade.
Aluminium isopropoxide, 2-Methyl-8-hydroxylquinoline (HMq),
hexafluoroacetylacetone (Hhfac), and 4-hydroxybenzonitrile (4-
HOC6H4CN) were commercially available. Ln(hfac)3(H2O)2 were
prepared by the literature procedures.2c,2d,22,27 Phenylboronic acid,
4-(dimethylamino) phenylboronic acid 95%, 48% hydrogen bro-
mide solution, tri-o-tolylphosphine were purchased from Alfa
Aesar. 2-Methyl-5-phenyl-8-hydroxylquinoline and 8-hydroxy-5-
(4-dimethylaminophenyl) quinoline were preparedby the synthetic
routes below.
Preparations
2-Methyl-8-methoxylquinoline. Sodium hydroxide solution
(0.47 M, 100 mL) and methyliodide (10.30 g, 72.53 mmol) were
added to a dichloromethane solution (100 mL) of 2-methyl-8-
hydroxyquinoline (5.00 g, 31.4 mmol) and tetrabutylammonium-
bromide (1.01 g, 3.01 mmol). The reaction mixture was stirred
overnight. The organic layer was collected and the aqueous layer
was extracted with dichloromethane (2 ¥ 30 mL). The organic layer
was dried over magnesium sulfate and the solvent was removed
on a rotary evaporator. The product was purified by silica column
chromatography using dichloromethane as the eluent. Yield: 3.56 g
(65.3%). MS: m/z 174 (M+H)+.1H NMR (CDCl3), d (ppm): 8.01
(d, J = 8.40 Hz, 1H), 7.42–7.27 (m, 3H), 7.03 (dd, J = 7.30, 1.45 Hz,
1H), 4.08 (s, 3H), 2.80 (s, 3H).
2-Methyl-5-bromo-8-methoxylquinoline. N-bromo-succini-
mide (10.68 g, 60 mmol) in 15 mL of methanol was added to 60 mL
of methanol solution (100 mL) of 2-methyl-8-methoxylquinoline
(3.48 g, 20 mmol) and NaHCO3 (5.88 g, 70 mmol). The mixture
was stirred for 10 min at room temperature, then 3 mL water was
added, which was stirred for another 5 min. A solution of Na2SO3
(0.32 g, 10 mmol) in 30 mL water was added to the mixture. The
aqueous layer was extracted with dichloromethane (3 ¥ 50 mL),
the organic layer was washed with NaCl solution, then dried over
Na2SO4 and the solvent was removed on a rotary evaporator.
The product was purified by silica column chromatography using
1 : 1 dichloromethane : petroleum ether as the eluent. The purified
product was obtained as a white solid. Yield: 20% (1.05 g). MS:
Conclusions
Three new dimeric lanthaninde(III) complexes {(Ln(hfac)3H2O}2-
(m-L)2 with bridging HPhMq or/and HMe2NC6H4Mq) in m-
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m/z 252 (M+H)+, 254.1H NMR (CDCl3), d (ppm): 8.31 (d, J =
8.64 Hz, 1H), 7.59 (d, J = 8.37 Hz, 1H), 7.36 (d, J = 12.04 Hz,
1H), 6.86 (d, J = 9.57, 1H), 4.04 (s, 3H), 2.80 (s, 3H).
filtrate was rotary evaporated to give the dry product and
then dissolved in dichloromethane. Layering n-hexane onto the
concentrated dichloromethane solution gave 2 as yellow crystals.
Yield: 23%. Anal. Calcd for C62H36Eu2F36N2O16·2H2O: C, 35.65;
H, 1.93; N, 1.34. Found: C, 35.79; H, 1.82; N, 1.35. IR (KBr, cm-1):
1654 s (C O), 2922 w (OH), 3427 w (OH).
2-Methyl-5-phenyl-8-methoxylquinoline.
A
mixture of 2-
methyl-5-bromo-8-methoxylquinoline (3.011 g, 11.95 mmol), pal-
ladium(II) acetate (0.141 g, 0.624 mmol), tri-o-tolylphosphine
(0.363 g, 1.19 mmol) and potassium carbonate solution (2 M,
40 mL) in toluene (200 mL) was heated to 80 ◦C in a two-necked
round bottom flask (500 mL) under nitrogen. Phenylboronic acid
(1.52 g, 12.6 mmol) dissolved in methanol (5 mL) was then added
to the reaction mixture using a syringe. The mixture was heated at
{Ln(hfac)3(H2O)}2(l-HMe2NC6H4Mq)2 (Ln = Eu, 3; Nd, 4).
HMe2NC6H4Mq (556 mg, 2 mmol), aluminium isopropox-
ide (204 mg, 1 mmol), and 4-hydroxybenzonitrile (238 mg,
2 mmol) were added to absolute ethanol (60 mL) with stirring
at 85 ◦C for 6 h, producing Al(Me2NC6H4Mq)2(OC6H4CN-4)
as a precipitate.18 Al(Me2NC6H4Mq)2(OC6H4CN-4) (0.3 mmol,
◦
80 C under nitrogen overnight. After cooling, the toluene layer
210 mg) and Ln(hfac)3(H2O)2 (0.2 mmol; Ln
162 mg; Ln = Nd, 160 mg) were added to dichloromethane
(30 mL) with stirring for h. The concentrated solu-
tion was precipitated by addition of Et2O to give the
main product [Al3Me2NC6H4Mq)4(HMe2NC6H4Mq)(m3-OH)2(m-
OH)3-{Ln(hfac)3}2].15 The filtrate was rotary evaporated to
give the dry product and then dissolved in dichloromethane.
Crystallization by layering n-hexane onto the concentrated
dichloromethane solution afforded red crystals of 3 or 4.
=
Eu,
was washed with water, dried over anhydrous magnesium sulfate
and the extract was concentrated on a rotary evaporator. The
residue was purified via chromatography on a silica gel column
using dichloromethane as the eluent to give a white solid. Yield:
85.4% (2.46 g). MS: m/z 250 (M+H)+.1H NMR (CDCl3), d (ppm):
8.11 (d, J = 8.68 Hz, 1H), 7.50–7.41 (m, 5H), 7.36 (d, J = 7.57 Hz,
1H), 7.26 (d, J = 8.68 Hz, 1H), 7.03 (d, J = 7.53 Hz, 1H), 4.12 (s,
3H), 2.80 (s, 3H).
1
8-Hydroxy-5-(phenyl)-2-methyl-quinoline (HPhMq). A 48%
hydrogen bromide solution (30 mL) and 2-methyl-5-phenyl-8-
methoxyl quinoline (1.02 g, 4.10 mmol) was refluxed overnight.
The resultant solution was set to pH = 7 by addition of sodium
hydroxide solution and extracted with dichloromethane (3 ¥
50 mL). The organic layer was dried over magnesium sulfate and
the solvent was removed on a rotary evaporator. The product was
purified by silica column chromatography using dichloromethane
as the eluent. The purified product was obtained as a yellow
powder. Yield: 57.9% (0.547 g). mp: 102–103 ◦C. MS: m/z 236
(M+H)+. 1H NMR (CDCl3), d (ppm): 8.14 (d, J = 8.67 Hz, 1H),
7.48–7.40 (m, 5H), 7.35 (d, J = 7.86, 1H), 7.26 (d, J = 8.66 Hz,
1H), 7.19 (d, J = 7.83 Hz, 1H), 2.73 (s, 3H). 13C NMR (CDCl3),
d (ppm): 156.67 C, 139.40 C, 137.89 C, 134.72 CH, 130.07 CH,
128.42 CH, 127.21 C, 127.08 CH, 122.65 CH, 109.29 CH, 24.89
CH3.
3
(Ln
=
Eu). Yield: 25%. Anal. Calcd for
C66H46F36N4Eu2O16·2H2O: C, 36.45; H, 2.32; N, 2.58. Found: C,
36.81; H, 2.27; N, 2.58. IR (KBr, cm-1): 1654 s (C O), 2928 w
(OH), 3432 w (OH).
4
(Ln
=
Nd). Yield: 20%. Anal. Calcd for
C66H46F36N4Nd2O16·2H2O: C, 36.71; H, 2.33; N, 2.59. Found: C,
37.16; H, 2.27; N, 2.62. IR (KBr, cm-1): 1654 s (C O), 2929 w
(OH), 3430 w (OH).
Physical measurements
Elemental analyses (C, H, N) were carried out on a Perkin–
Elmer model 240 C automatic instrument. Electrospray mass
spectra (ES-MS) were recorded on a Finnigan LCQ mass spec-
trometer using dichloromethane–methanol as the mobile phase.
UV-vis absorption spectra were measured on a Perkin-Elmer
Lambda25 UV-Vis spectrometer. Infrared spectra were recorded
on a Magna750 FT-IR spectrophotometer with a KBr pellet.
Emission and excitation spectra in the UV-vis region were recorded
on a Perkin–Elmer LS 55 luminescence spectrometer with a
red-sensitive photomultiplier type R928. The steady-state near-
infrared (NIR) emission spectra were measured on an Edinburgh
FLS920 fluorescence spectrometer equipped with a Hamamatsu
R5509-72 super cooled photomultiplier tube at 193 K and a
TM300 emission monochromator with NIR grating blazed at
1000 nm. Corrected spectra were obtained via a calibration curve
supplied with the instrument. The emission lifetimes were obtained
by using an Edinburgh Xe900 450 W pulse xenon lamp as the
excitation light source. The calculations of the quantum yields
of 2 and 3 in degassed dichloromethane solutions at 298 K of
Eu3+ were based on the lex = 335 nm and estimated relative to
Ru(bpy)3Cl2 in water as the standard (Uem = 0.028) and calculated
by Us = Ur(Br/Bs)(ns/nr)2(Ds/Dr), where the subscripts s and r
refer to the sample and reference standard solution, respectively, n
is the refractive index of the solvents, d is the integrated intensity,
and U is the luminescence quantum yield.28 The quantity B is
calculated by B = 1–10-AL, where A is the absorbance at the
excitation wavelength and L is the optical path length.
8-Hydroxy-5-(4-dimethyl-amino-phenyl)-2-methyl-quinoline
(HMe2NC6H4Mq). The synthesis procedure was similar
to that of 2-methyl-5-phenyl-8-hydroxylquinoline using 4-
(dimethylamino)phenyl-boronic acid instead of phenylboronic
acid. The resulting compound was recrystallized from iso-
propanol. Yield: 87% (0.230 g). mp: 160–162 ◦C. MS: m/z 278
[M]+. 1H NMR (CDCl3), d (ppm): 8.22 (d, 1H, J = 8.85 Hz), 7.32
(d, 3H, J = 8.30 Hz), 7.27 (d, 1H, J = 7.16 Hz), 7.16 (d, 1H, J =
7.53 Hz), 6.84 (d, 2H, J = 9.23 Hz), 3.02 (s, 6H), 2.72 (s, 3H).
13C NMR (CDCl3), d (ppm): 130.74 CH, 126.77 CH, 122.44 CH,
122.31 CH, 40.62 CH3, 24.65 CH3.
{Eu(hfac)3(H2O)}2(l-HPhMq)2 (2). HPhMq (470 mg,
2
mmol), aluminium isopropoxide (204 mg, 1 mmol),
and 4-hydroxybenzonitrile (238 mg, 2 mmol) were added
to absolute ethanol (60 mL) with stirring at 85 ◦C for
6 h, producing Al(PhMq)2(OC6H4CN-4) as a precipitate.18
Al(PhMq)2(OC6H4CN-4) (0.3 mmol, 184 mg) and Eu(hfac)3-
(H2O)2 (0.2 mmol, 162 mg) were added to dichloromethane
(30 mL) with stirring for 1 h. The concentrated solution was
precipitated by addition of Et2O to give the main product
[Al3(PhMq)4(HPhMq)(m3-OH)2(m-OH)3{Eu(hfac)3}2].15
The
5554 | Dalton Trans., 2011, 40, 5549–5556
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©

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Crystal structural determination
(c) R. Ziessel, S. Diring, P. Kadjane, L. Charbonnie`re, P. Retailleau and
C. Philouze, Chem.–Asian J., 2007, 2, 975.
5 (a) M. Mehlsta¨ubl, G. S. Kottas, S. Colella and L. De Cola, Dalton
Trans., 2008, 2385; (b) G. S. Kottas, M. Mehlsta¨ubl, R. Fro¨hlich
and L. De Cola, Eur. J. Inorg. Chem., 2007, 3465; (c) P. Kadjane, L.
Charbonnie`re, F. Camerel, P. P. Laine´ and R. Ziessel, J. Fluoresc., 2008,
18, 119.
6 (a) P. A. Vigato, V. Peruzzo and S. Tamburini, Coord. Chem. Rev., 2009,
253, 1099; (b) S. Swavey and R. Swavey, Coord. Chem. Rev., 2009, 253,
2627.
7 (a) A. Fratini, G. Richards, E. Larder and S. Swavey, Inorg. Chem.,
2008, 47, 1030; (b) T.-S. Kang, B. S. Harrison, M. Bouguettaya, T. J.
Foley, J. M. Boncella, K. S. Schanze and J. R. Reynold, Adv. Funct.
Mater., 2003, 13, 205.
8 M. Albrecht, M. Fiege and O. Osetska, Coord. Chem. Rev., 2008, 252,
812.
9 (a) D. Imbert, S. Comby, A.-S. Chauvin and J.-C. G. Bu¨nzli, Chem.
Commun., 2005, 1432; (b) S. Comby, D. Imbert, A.-S. Chauvin and J.-
C. G. Bu¨nzli, Inorg. Chem., 2006, 45, 732; (c) M. Albrecht, R. Fro¨hlich,
J.-C. G. Bu¨nzli, A. Aebischer, F. Gumy and J. Hamacek, J. Am. Chem.
Soc., 2007, 129, 14178; (d) N. M. Shavaleev, R. Scopelliti, F. Gumy and
J.-C. G. Bu¨nzli, Inorg. Chem., 2008, 47, 9055; (e) N. M. Shavaleev, R.
Scopelliti, F. Gumy and J.-C. G. Bu¨nzli, Inorg. Chem., 2009, 48, 2908.
10 (a) R. Van Deun, P. Fias, P. Nockemann, A. Schepers, T. N. Parac-
Vogt, K. Van Hecke, L. van Meervelt and K. Binnemans, Inorg. Chem.,
2004, 43, 8461; (b) F. Artizzu, P. Deplano, L. Marchio`, M. L. Mercuri,
L. Pilia, A. Serpe, F. Quochi, R. Orru`, F. Cordella, F. Meinardi, R.
Tubino, A. Mura and G. Bongiovanni, Inorg. Chem., 2005, 44, 840.
11 (a) G. B. Deacon, C. M. Forsyth, P. C. Junk, U. Kynast, G. Meyer, J.
Moore, J. Sierau and A. Urbatsch, J. Alloys Compd., 2008, 451, 436;
(b) M. Iwamuro, T. Adachi, Y. Wada, T. Kitamura, N. Nakashima and
S. Yanagida, Bull. Chem. Soc. Jpn., 2000, 73, 1359; (c) A. Meyers, A.
Kimyonok and M. Weck, Macromolecules, 2005, 38, 8671.
12 (a) L.-N. Sun, H.-J. Zhang, J.-B. Yu, S.-Y. Yu, C.-Y. Peng, S. Dang,
X.-M. Guo and J. Feng, Langmuir, 2008, 24, 5500; (b) L. Ning, M. I.
Trioni and G. P. Brivio, J. Mater. Chem., 2007, 17, 4464; (c) R. Kikkeri,
L. H. Hossain and P. H. Seeberger, Chem. Commun., 2008, 2127; (d) A.
Nonat, D. Imbert, J. Pe´caut, M. Giraud and M. Mazzanti, Inorg. Chem.,
2009, 48, 4207.
Single crystals of 2·H2O and 4·H2O suitable for X-ray diffrac-
tion were grown by layering n-hexane onto the corresponding
dichloromethane solutions, respectively. Data collection was per-
formed on Rigaku Mercury CCD diffractometer for 2·H2O, and
SATURN70 CCD diffractometer for 4·H2O by scan technique at
room temperature using graphite-monochromated Mo–K (l =
˚
0.71073 A) radiation. The Lp corrections were carried out
in the reflection reduction process. The structures were solved
by direct methods. The remaining non-hydrogen atoms were
determined from the successive difference Fourier syntheses. The
non-hydrogen atoms were refined anisotropically except for the
F atoms, and the hydrogen atoms were generated geometrically
with isotropic thermal parameters. The structures were refined on
F2 by full-matrix least-squares methods using the SHELXTL-97
program package.29 The refinements were carried out by fixing the
˚
C–F distances (1.32 0.01 A) with the occupancy factors of F and
F¢ being 0.50, respectively. Crystallographic data are summarized
◦
˚
below. Selected bond distances (A) and angles ( ) for 2·H2O and
4·H2O were presented in Table 1.
Crystal Data for 2·2H2O (CCDC 803484): C62H36Eu2F36-
N2O16·2H2O, Mr = 2088.88, monoclinic, space group P21/n, a =
◦
˚
3
˚
˚
13.951(5) A, b = 18.353(5) A, c = 15.516(5) A, b = 106.683(5) ; V =
-1
-1
˚
3806(2) A , Z = 2, rc = 1.823 g cm , m(Mo–Ka) = 1.788 mm , T =
293(2) K, 25 742 reflections collected, 5474 unique (Rint = 0.066),
R1 = 0.0618, wR2 = 0.1626 for 6560 reflections with I > 2s(I),
GOF = 1.167.
Crystal Data for 4·2H2O (CCDC 803485): C66H46F36N4O16-
Nd2·2H2O, Mr = 2159.58, monoclinic, space group C2/c, a =
◦
˚
˚
˚
27.259(7) A, b = 14.464(3) A, c = 23.046(5) A, b = 105.126(5) ,
3
-1
-1
˚
13 (a) S. Comby, and J.-C. G. Bu¨nzli, Handbook on the Physics and
Chemistry of Rare Earths, Vol. 37 (ed.: K. A. Gschneidner, J.-
C. G. Bu¨nzli and V. K. Pecharsky), Elsevier, 2007, p.217; (b) S. Comby,
D. Imbert, C. Vandevyver and J.-C. G. Bu¨nzli, Chem.–Eur. J., 2007, 13,
936.
V = 8771(4) A , Z = 4, rc = 1.635 g cm , m(Mo–Ka) = 1.309 mm ,
T = 293(2) K, 24 726 reflections collected, 6286 unique (Rint
=
0.028), R1 = 0.0578, wR2 = 0.1525 for 7207 reflections with I >
2s(I), GOF = 1.103.
14 (a) H.-B. Xu, H.-M. Wen, Z.-H. Chen, J. Li, L.-X. Shi and Z.-N. Chen,
Dalton Trans., 2010, 39, 1948; (b) H.-B. Xu, Y.-T. Zhong, W.-X. Zhang,
Z.-N. Chen and X.-M. Chen, Dalton Trans., 2010, 39, 5676; (c) R. V.
Deun, P. Fias, P. Nockemann, A. Schepers, T. N. Parac-Vogt, K. V.
Hecke, L. V. Meervelt and K. Binnemans, Inorg. Chem., 2004, 43, 8461.
15 H.-B. Xu, X.-M. Chen, Q.-S. Zhang, L.-Y. Zhang and Z.-N. Chen,
Chem. Commun., 2009, 7318.
Acknowledgements
This work was financially supported by the NSFC (20901077),
the 973 project (2007CB815304) from MSTC, and NSF of Fujian
Province (2008I0027 and 2008F3117).
16 H. He, X. Zhu, A. Hou, J. Guo, W.-K. Wong, W.-Y. Wong, K.-F. Li
and K.-W. Cheah, Dalton Trans., 2004, 4064.
17 H.-B. Xu, J. Li, L.-Y. Zhang, X. Huang, B. Li and Z. N. Chen, Cryst.
Growth Des., 2010, 10, 4101.
18 (a) V. A. Montes, R. Pohl, J. Shinar and P. Jr. Anzenbacher, Chem.–
Eur. J., 2006, 12, 4523; (b) C. Pe´rez-Bolivar, V. A. Montes and P. Jr.
Anzenbacher, Inorg. Chem., 2006, 45, 9610.
19 (a) B. Chen, L. Wang, F. Zapata, G. Qian and E. B. Lobkovsky, J. Am.
Chem. Soc., 2008, 130, 6718; (b) H. Tsukube, A. Onimaru and S.
Shinoda, Bull. Chem. Soc. Jpn., 2006, 79, 725.
20 G. F. de Sa´, O. L. Malta, C. de Mello Donega´, A. M. Simas, R. L.
Longo, P. A. Santa-Cruz and E. F. da Silva Jr, Coord. Chem. Rev.,
2000, 196, 165.
21 (a) N. M. Shavaleev, S. J. A. Pope, Z. R. Bell, S. Faulkner and M. D.
Ward, Dalton Trans., 2003, 808; (b) H.-B. Xu and H.-Y. Chao, Inorg.
Chem. Commun., 2007, 10, 1129.
22 Y. Hasegawa, Y. Kimura, K. Murakoshi, Y. Wada, J.-H. Kim, N.
Nakashima, T. Yamanaka and S. Yanagida, J. Phys. Chem., 1996, 100,
10201.
23 (a) G. E. Buono-Core, H. Li and B. Marciniak, Coord. Chem. Rev.,
1990, 99, 55; (b) S. W. Magennis, A. J. Ferguson, T. Bryden, T. S. Jones,
A. Beeby and I. D. W. Samuel, Synth. Met., 2003, 138, 463.
24 (a) M. D. Ward, Coord. Chem. Rev., 2007, 251, 1663; (b) C. M. G. dos
Santos, A. J. Harte, S. J. Quinn and T. Gunnlaugsson, Coord. Chem.
References
1 (a) J.-C. G. Bu¨nzli and C. Piguet, Chem. Soc. Rev., 2005, 34, 1048;
(b) S. V. Eliseeva and J.-C. G. Bu¨nzli, Chem. Soc. Rev., 2010, 39, 189;
(c) F.-F. Chen, Z.-Q. Chen, Z.-Q. Bian and C.-H. Huang, Coord. Chem.
Rev., 2010, 254, 991.
2 (a) H.-B. Xu, L.-X. Shi, E. Ma, L.-Y. Zhang, Q.-H. Wei and Z.-N.
Chen, Chem. Commun., 2006, 1601; (b) H.-B. Xu, L.-Y. Zhang, Z.-L.
Xie, E. Ma and Z.-N. Chen, Chem. Commun., 2007, 2744; (c) H.-B. Xu,
L.-Y. Zhang, Z.-H. Chen, L.-X. Shi and Z.-N. Chen, Dalton Trans.,
2008, 4664; (d) H.-B. Xu, X.-M. Chen, X.-L. Li, L.-Y. Zhang and Z.-N.
Chen, Cryst. Growth Des., 2009, 9, 569.
3 (a) D. Guo, C.-Y. Duan, F. Lu, Y. Hasegawa, Q.-J. Meng and S.
Yanagida, Chem. Commun., 2004, 1486; (b) Z. N. Chen, H.-B. Xu,
Rare Earth Coordination: Fundamentals and Application, Chap. 12 (ed.:
C. H. Huang), Wiley, 2010, p.473.
4 (a) S. I. Klink, H. Keizer and F. C. J. M. van Veggle, Angew. Chem., Int.
Ed., 2000, 39, 4319; (b) T. K. Ronson, T. Lazarides, H. Adams, S. J. A.
Pope, D. Sykes, S. Faulkner, S. J. Coles, M. B. Hursthouse, W. Clegg,
R. W. Harrington and M. D. Ward, Chem.–Eur. J., 2006, 12, 9299;
This journal is
The Royal Society of Chemistry 2011
Dalton Trans., 2011, 40, 5549–5556 | 5555
©

View Article Online
Rev., 2008, 252, 2512; (c) K. Kuriki, Y. Koike and Y. Okamoto, Chem.
Rev., 2002, 102, 2347; (d) S. Faulkner, S. J. A. Pope and B. P. Burton-
Pye, Appl. Spectrosc. Rev., 2005, 40, 1; (e) S. Yanagida, Y. Hasegawa, K.
Murakoshi, Y. Wada, N. Nakashima and T. Yamanaka, Coord. Chem.
Rev., 1998, 171, 461.
and H. Zhang, J. Mater. Chem., 2001, 11, 2615; (d) G. Mancino, A. J.
Ferguson, A. Beeby, N. J. Long and T. S. Jones, J. Am. Chem. Soc.,
2005, 127, 524; (e) K. Kuriki, Y. Koike and Y. Okamoto, Chem. Rev.,
2002, 102, 2347.
27 (a) H.-B. Xu, J. Ni, K.-J. Chen, L.-Y. Zhang and Z.-N. Chen,
Organometallics, 2008, 27, 5665; (b) E. C. Constable and M. D. Ward,
J. Chem. Soc., Dalton Trans., 1990, 1405; (c) T Kido, Y Ikuta, Y
Sunatsuki, Y Ogawa and N Matsumoto, Inorg. Chem., 2003, 42, 398;
(d) M. F. Richardson, W. F. Wagner and D. E. Sands, J. Inorg. Nucl.
Chem., 1968, 30, 1275.
28 J. N. Demas and G. A. Crosby, J. Phys. Chem., 1971, 75, 991.
29 SHELXTL 6.10, Bruker Analytical Instrumentation, Madison, Wis-
consin, USA, 2000.
25 (a) G. Stein, J. Chem. Phys., 1975, 62, 208; (b) N. Sabbatini, S.
Perathoner, G. Lattanzi, S. Dellonte and V. Balzani, J. Phys. Chem.,
1987, 91, 6136.
26 (a) Y. Hasegawa, T. Ohkubo, K. Sogabe, Y. Kawamura, Y. Wada, N.
Nakashima and S. Yanagida, Angew. Chem., Int. Ed., 2000, 39, 357;
(b) S. Yanagida, Y. Hasegawa, K. Murakoshi, Y. Wada, N. Nakashima
and T. Yamanaka, Coord. Chem. Rev., 1998, 171, 461; (c) Y. Zheng, J.
Lin, Y. Liang, Q. Lin, Y. Yu, Q. Meng, Y. Zhou, S. Wang, H. Wang
5556 | Dalton Trans., 2011, 40, 5549–5556
This journal is
The Royal Society of Chemistry 2011
©