Near-infrared photoluminescence of lanthanide complexes containing the hemicyanine chromophore

Article abstract of DOI:10.1016/j.poly.2007.08.005

The near-infrared luminescence properties of three (E)-N-hexadecyl-N′,N′-dimethylamino-stilbazolium tetrakis(1-phenyl-3-methyl-4-benzoyl-5-pyrazolonato) lanthanide(III) complexes are described. These three complexes, containing trivalent neodymium, erbium and ytterbium, respectively, show near-infrared luminescence in acetonitrile solution upon UV irradiation. Luminescence decay times have been measured. The complexes consist of a positively charged hemicyanine chromophore with a long alkyl chain and a tetrakis(pyrazolonato) lanthanide(III) anion. Because of the absence of an α-hydrogen atom in the pyrazolonato ligands, and because of the saturation of the coordination sphere by four bidentate ligands, the luminescence properties are enhanced when compared to, e.g. quinolinate complexes.

Full text of DOI:10.1016/j.poly.2007.08.005

Available online at www.sciencedirect.com
Polyhedron 26 (2007) 5441–5447
www.elsevier.com/locate/poly
Near-infrared photoluminescence of lanthanide complexes
containing the hemicyanine chromophore
*
Rik Van Deun , Peter Nockemann, Tatjana N. Parac-Vogt, Kristof Van Hecke,
Luc Van Meervelt, Christiane Gorller-Walrand, Koen Binnemans
¨
Katholieke Universiteit Leuven, Department of Chemistry, Celestijnenlaan 200F, B-3001 Leuven, Belgium
Received 20 July 2007; accepted 8 August 2007
Available online 17 September 2007
Abstract
The near-infrared luminescence properties of three (E)-N-hexadecyl-N0,N0-dimethylamino-stilbazolium tetrakis(1-phenyl-3-methyl-4-
benzoyl-5-pyrazolonato) lanthanide(III) complexes are described. These three complexes, containing trivalent neodymium, erbium and
ytterbium, respectively, show near-infrared luminescence in acetonitrile solution upon UV irradiation. Luminescence decay times have
been measured. The complexes consist of a positively charged hemicyanine chromophore with a long alkyl chain and a tetrakis(pyraz-
olonato) lanthanide(III) anion. Because of the absence of an a-hydrogen atom in the pyrazolonato ligands, and because of the saturation
of the coordination sphere by four bidentate ligands, the luminescence properties are enhanced when compared to, e.g. quinolinate
complexes.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: Rare earths; Near-infrared luminescence; Chelates; Hemicyanine; NLO materials
1. Introduction
tric dipole (ED) transitions [13]. One of the consequences
of the forbidden nature of these transitions is the relatively
long lifetimes of the excited states. This, together with the
high colorimetric purity of the emitted light (narrow lumi-
nescence bands), are the main advantages of lanthanides as
luminophores. One way to overcome the disadvantage of
the low molar absorptivities of the lanthanide ions
(e 6 10 L molꢀ1 cmꢀ1) is using ligands that can operate as
antennas [14]. In this case, the light that is absorbed by
the ligand is transferred to the lanthanide’s excited states
and thus enhances the luminescence. Because the electronic
transitions of the ligand absorption are allowed, much
more energy can be transferred to the lanthanide. Second,
one should prevent radiationless deactivation of the excited
states of the rare-earth ion, by dissipation of heat to the
environment. Especially the presence of O–H, N–H and
C–H groups in close proximity to the rare-earth ion should
be avoided [15]. In the case of b-diketones, the presence of
an a-hydrogen atom can be detrimental to the lumines-
cence yield of the resulting complex. Third, the design of
The design of photoluminescent lanthanide-containing
materials continues to be an active area of research,
because of the possible application of these materials in dif-
ferent kinds of light-conversion and light-amplification
devices [1–3]. Visible photoluminescence, emitted by lan-
thanide ions, plays a fundamental role not only in fluores-
cent lamps and cathode-ray tubes (both divalent and
trivalent europium and trivalent terbium), its role in immu-
noassays is ever increasing [4–6]. But also lanthanide ions
emitting in the near-infrared region (NIR) are getting more
and more attention because of possible use in optical
amplifiers and datacom applications [7–12].
The lanthanide ions’ f–f transitions are parity forbidden
and the observed transitions are therefore very weak and
consist mainly of magnetic dipole (MD) and induced elec-
*
Corresponding author. Tel.: +32 16 32 73 36; fax: +32 16 32 79 92.
E-mail address: rik.vandeun@chem.kuleuven.be (R. Van Deun).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.08.005

5442
R. Van Deun et al. / Polyhedron 26 (2007) 5441–5447
a protective ‘shell’ around the rare-earth ion can lead to
significant enhancement of the luminescent properties of
the complex: avoiding the coordination of small but
strongly quenching solvent molecules can be done by
designing very bulky ligands, or by opting for a tetrakis
stoichiometry instead of a tris stoichiometry [16–19].
Complexes of lanthanide ions with a hemicyanine unit
have only been scarcely investigated [20–25]. Compounds
with a hemicyanine chromophore are well known as dyes
[26–29]. Hemicyanine dyes, having a large energy gap
between the ground state and the excited states, which is
beneficial for high polarisability, have been studied for
their nonlinear optical (NLO) properties, e.g. in Lang-
muir–Blodgett films [30–32]. It was shown that combining
a lanthanide complex with a hemicyanine compound
enhances the film-forming properties and at the same time
increases the charge separation in the chromophore, thus
improving the NLO properties [33].
In this paper, we show that the hemicyanine unit in com-
bination with the pyrazolone groups in the lanthanide com-
plexes provide a suitable basis for sensitized near-infrared
luminescence. We describe the synthesis of the hemicyanine
bromide precursor as well as the final lanthanide com-
plexes. The absorption spectrum of the complexes, as well
as the luminescence spectra of the trivalent neodymium,
erbium and ytterbium ions are discussed.
C16H33Br, EtOH
CH3
N
CH3
N C16H33
reflux, 24h
Br
1
CH3
CH3
CH3
piperidine
N
N
CHO
1
2
+
EtOH, reflux, 4h
CH3
N
C16H33
Br
2
CH3
N
O
N
LnCl3.xH2O
4
+
+
O
NaOH 4eq.
EtOH
-
CH3
O
O
N
CH3
CH3
Ln
N
C16H33
N
N
4
3
4
5
Ln = Nd (yield: 20%)
Ln = Er (yield: 63%)
Ln = Yb (yield: 52%)
Scheme 1. Synthetic procedure towards the hemicyanine counterion and the final lanthanide complexes.

R. Van Deun et al. / Polyhedron 26 (2007) 5441–5447
5443
2. Results and discussion
cules with slightly different conformations. The coordina-
tion number of the lanthanum ion is eight and the
coordination polyeder of the lanthanum ion can be
regarded as a slightly distorted square antiprism. No evi-
dence of solvent coordination to the central lanthanum
ion was found in the crystal structure.
To tackle the limitations described in the introduction,
we have chosen the b-diketone 1-phenyl-3-methyl-4-ben-
zoyl-5-pyrazolone (see Scheme 1) as ligand. This molecule
does not have an a-hydrogen atom, so no C–H vibrational
quenching at that site is expected. At the same time, the
phenyl groups provide a means of light harvesting. Finally,
b-diketones are well known as ligands for rare-earth ions
and easy synthetic procedures towards tetrakis complexes
(with a metal-to-ligand ratio of 1:4) are available [34,35].
The synthetic procedure towards the hemicyanine coun-
terion and the final lanthanide complexes is displayed in
Scheme 1. The hemicyanine bromide was prepared in a
two-step reaction: first, 4-picoline was reacted with
1-bromohexadecane. Second, the resulting 1-hexadecyl-4-
methylpyridinium bromide 1 was condensed with 4-dim-
ethylaminobenzaldehyde via a Knoevenagel-type reaction,
yielding the hemicyanine bromide 2. The lanthanide com-
plexes 3–5 were synthesised by reaction of the hemicyanine
bromide 2 with the b-diketone 4-benzoyl-3-methyl-1-phe-
nyl-2-pyrazolin-5-one and the appropriate lanthanide salt.
The complexes were obtained in good yields. See Section
4 for more details.
Single crystals, suitable for X-ray structure determination,
were obtained of the (E)-N-dodecyl-N0,N0-dimethylamino-
stilbazolium tetrakis(1-phenyl-3-methyl-4-benzoyl-5-pyraz-
olonato) lanthanum(III) complex. The crystal structure of
the complex consists of the anionic complex molecule with
four pyrazolonato ligands, a hemicyanine counterion and
some water of crystallization. Fig. 1 shows the complex
without the large hemicyanine counterion. The asymmetric
unit contains two crystallographically independent mole-
Each two of the 1-phenyl pyrazolonato parts of the
ligands are oriented almost parallel to each other, but with
an antipodal orientation with respect to each other. The
cations are situated in the cavity between two neighboring
pyrazolonato ligands and exhibit weak p–p stacking inter-
actions between the 4-benzoyl groups of the ligands and the
pyridinium part of the cation (centroid-to-centroid dis-
˚
tances range from 4.13 to 4.39 A). This is shown in
Fig. 2. Hydrogen bonding was found from the nitrogen
atom of some of the pyrazolonato ligands to water mole-
cules of crystallization with Nꢁ ꢁ ꢁO distances in the range
˚
of 2.92–2.97A. The crystal structure data are summarised
in Table 1, whereas the crystal packing is shown in Fig. 3.
The complexes exhibit a strong orange-red colour, due
to the charge-transfer band in the hemicyanine chromo-
phore unit. The absorption spectrum of the neodymium
complex 3 is given in Fig. 4. The peak maxima have been
indicated. Whereas the maxima located at 238 and
276 nm are due to the singlet-to-singlet transitions in the
pyrazolonate ligands, the broad band at 475 nm is due to
the charge-transfer transition in the hemicyanine chromo-
phore. This band is responsible for the intense orange-red
colour of the complexes. Since visible excitation is a much
sought-after property in NIR emitting rare-earth
complexes, it was our hope that excitation of the pyrazol-
onato complexes in the hemicyanine band would result in
Fig. 2. Detail of the crystal structure of the (E)-N-dodecyl-N0,N0-
dimethylamino-stilbazolium tetrakis(1-phenyl-3-methyl-4-benzoyl-5-pyr-
azolonato) lanthanum(III) complex, showing the four pyrazolonato
ligands as well as the hemicyanine chromophore counterions. Hydrogen
atoms have been omitted for clarity.
Fig. 1. Detail of the crystal structure of the (E)-N-dodecyl-N0,N0-
dimethylamino-stilbazolium tetrakis(1-phenyl-3-methyl-4-benzoyl-5-pyr-
azolonato) lanthanum(III) complex, showing the local surrounding of
the lanthanum(III) ion.

5444
R. Van Deun et al. / Polyhedron 26 (2007) 5441–5447
Table 1
Crystal structure data for the (E)-N-dodecyl-N0,N0-dimethylamino-stil-
bazolium tetrakis(1-phenyl-3-methyl-4-benzoyl-5-pyrazolonato) lantha-
num(III) complex shown in Figs. 1–3
Formula
C380H372La4N40O41
6710.83
0.3 · 0.2 · 0.1
triclinic
Molecular weight (g molꢀ1
Crystal dimensions (mm)
Crystal system
)
ꢀ
Space group
P1
˚
a (A)
15.545(2)
21.453(2)
28.586(2)
68.636(4)
75.054(4)
80.336(5)
8548.4(11)
1
˚
b (A)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
3
˚
V (A )
Z
Dcalc (g cmꢀ3
)
1.304
4.387
l (Cu Ka) (mmꢀ1
)
Fig. 4. Absorption spectrum of complex 3 in acetonitrile (c = 10ꢀ5
mol Lꢀ1).
Absorption correction
F(000)
Measured reflections
Unique reflections
refined from delta-F
3488
78888
31779
Observed reflections [Io > 2r(Io)]
Parameters refined
Goodness-of-fit
R1a
22774
2317
1.003
0.0653
0.1680
0.0950
0.1931
or to the central neodymium ion. On the contrary, excita-
tion of 3 at 276 nm resulted also in the appearance of this
band at 630 nm, albeit less intense (about 5 times less
intense) then upon excitation at 475 nm. Of course, also
the neodymium(III)-centered NIR emission could be easily
detected. This indicates that part of the excitation energy in
the pyrazolonato ligands is transferred to the neodym-
ium(III) ion, but another part is also transferred to the
hemicyanine chromophore, which emits it as red light.
In Fig. 5, the combined emission spectra are shown of
complexes 3, 4 and 5 in acetonitrile upon excitation at
276 nm. Complex 3 shows the typical emission bands at
875 nm, 1060 nm and 1330 nm, corresponding to the
wRb2
R1 (all data)
wR2 (all data)
P
P
a
R1 = iFoj ꢀ jFci/ jFoj.
P
P
wR2 = [ w(Fo ꢀ Fc2)2/ w(Fo2)2]1/2
.
b
2
4
4F3/2 ! IJ lines (J = 9/2, 11/2 and 13/2). The emission
spectrum of 4 is shown as the dashed line and exhibits
Fig. 3. Molecular crystal packing of the (E)-N-dodecyl-N0,N0-dimethyl-
amino-stilbazolium tetrakis(1-phenyl-3-methyl-4-benzoyl-5-pyrazolonato)
lanthanum(III) complex.
rare-earth centered NIR luminescence. Unfortunately, this
did not turn out to be the case. Moreover, excitation of 3 in
the hemicyanine chromophore at 475 nm resulted in the
appearance of a strong red fluorescence band with a max-
imum at 630 nm. This shows that no energy is transferred
from the hemicyanine moiety to the pyrazolonato ligands
Fig. 5. Combined emission spectra of neodymium complex 3 (solid line),
erbium complex 4 (dashed line) and ytterbium complex 5 (dotted line) in
acetonitrile (c = 10ꢀ5 mol Lꢀ1, kexc = 276 nm, emission intensities are not
to scale).

R. Van Deun et al. / Polyhedron 26 (2007) 5441–5447
5445
Table 2
of developing NIR-emitting thin films based on pyrazolo-
nato rare-earth complexes.
Luminescence decay times of the Nd3+ (4F3/2), Er3+ (4I13/2) and Yb3+ (2F5/2
levels in complexes 3, 4 and 5, respectivelya
)
Complex
Rare-earth ion
Decay time (ls)
4. Experimental
3
4
5
a
Nd3+
Er3+
Yb3+
1.0
3.2
46.4
4.1. Equipment and techniques
Lifetimes measured at room temperature; kexc = 266 nm; c = 10ꢀ5
Absorption spectra were recorded on a Varian Cary
5000 spectrophotometer. Visible luminescence spectra were
obtained with an Edinburgh Instruments F900 spectrome-
ter, equipped with a 1800 lines/mm grating excitation
monochromator and a 1800 lines/mm grating emission
monochromator. A 450 W xenon lamp is used as the exci-
tation source and a red-sensitive photomultiplier tube type
S900-R is used as the detector. The steady state near-infra-
red luminescence spectra and the lifetime measurements
were done on an Edinburgh Instruments FS920P near
infrared spectrometer, with a 450 W xenon lamp as the
steady state excitation source, a double excitation mono-
chromator with 1800 lines/mm, an emission monochroma-
tor with 600 lines/mm, and a liquid nitrogen cooled
Hamamatsu R5509-72 near infrared photomultiplier tube.
For luminescence decay time measurements, the setup
includes a Continuum Minilite Nd:YAG laser, equipped
with 2nd, 3rd and 4th harmonic crystals, allowing excita-
tion at 1064, 532, 355 and 266 nm. Repetition rate is
10 Hz, pulse width is 3–5 ns. Standard quartz 1 cm fluores-
cence cuvets (Hellma type QS-111) were used. Lumines-
cence lifetime data were extracted from the decay curves
using the program Originꢂ.
mol Lꢀ1; solutions in acetonitrile.
one characteristic band at 1530 nm, corresponding to the
4
4I13/2 ! I15/2 line. Finally, the spectrum of complex 5,
drawn as the dotted line, exhibits one emission band at
2
2
975 nm, corresponding to the F5/2 ! F7/2 line.
In Table 2, the luminescence decay times of the
Nd3+ (4F3/2), Er3+ (4I13/2) and Yb3+ (2F5/2) levels in (E)-
N-hexadecyl-N0,N0-dimethylamino-stilbazolium tetrakis(1-
phenyl-3-methyl-4-benzoyl-5-pyrazolonato) rare-earth(III)
complexes are given. These decay times compare well to
decay times of other NIR-emitting rare-earth complexes
in organic solution. For example, a tetrakis (5,7-dichloro-
8-oxyquinolinato) lanthanide(III) complex with a tetraeth-
yl ammonium counterion dissolved in THF has decay time
values of 0.95 ls for the neodymium(III) sample, 2.2 ls for
the erbium(III) ion and 11.6 ls for the ytterbium(III) sam-
ple [36]. The hemicyanine materials presented here have
comparable (neodymium(III) complex), slightly longer
(erbium(III) complex) or even significantly longer (ytter-
bium(III) complex) luminescence decay times. On the other
hand, they are not as good as the values obtained by Bas-
sett et al. for the tetraphenylimidophosphinate complexes
of NIR-emitting rare-earth ions in dry acetonitrile solution
(2.6 ls for the Nd(III) complex, 6.5 ls for the Er(III) com-
plex and 52.8 ls for the Yb(III) complex) [18]. It has to be
added that the ytterbium(III) ion can be excited through an
alternative redox mechanism [37]. A detailed photophysical
study of the materials under investigation, however, falls
outside the scope of this paper.
1H NMR spectra have been recorded on a Bruker WM
250 spectrometer, operating at 250 MHz or a Bruker AMX
400 spectrometer, operating at 400 MHz, using deuterated
chloroform (CDCl3) as the solvent and tetramethylsilane
(TMS) as internal standard. 13C NMR spectra have been
recorded on a Bruker AMX 400 spectrometer, operating
at 100.6 MHz, using deuterated chloroform (CDCl3) as
the solvent and tetramethylsilane (TMS) as internal
standard.
3. Conclusions
EI mass spectra have been obtained on a Hewlett–Pack-
ard 5989A mass spectrometer.
In conclusion, we have shown that NIR luminescence
can be obtained from (E)-N-hexadecyl-N0,N0-dimethyl-
amino-stilbazolium tetrakis(1-phenyl-3-methyl-4-benzoyl-
5-pyrazolonato) rare-earth(III) complexes in acetonitrile
solution. Because of the absence of the a-hydrogen atom
on the pyrazolonato ligand and because of the shielding
provided by the tetrakis stoichiometry of the complex,
luminescence decay times could be obtained that compare
well to the better behaving rare-earth complexes in solu-
tion. Nevertheless, the incorporation of the hemicyanine
chromophore in the complexes did not lead to enhanced
emission properties, nor did it allow visible light sensitisat-
ion of the NIR-luminescence. However, it is known from
the literature that the combination of hemicyanine units
with rare-earth complexes increases the film-forming proper-
ties of the hemicyanine compound, creating the possibility
CHN elemental analyses have been performed on a Per-
kin–Elmer 2400 elemental analyser, operated by the univer-
sity of Exeter (School of Chemistry) or on a CE
Instruments EA-1110 elemental analyser (K.U.Leuven,
Chemistry Department).
IR spectra have been recorded on a Bruker FT-IR
IFS66 spectrometer, using KBr pellets.
4.2. Synthesis
The hemicyanine bromide was synthesized by a two-step
reaction (Scheme 1). During the first step, 4-picoline was
refluxed with n-bromohexadecane in ethanol. The crude
1-hexadecyl-4-methylpyridinium bromide 1 was recrystal-
lized twice from a diethyl ether:ethanol mixture. Yield:
1
85% (67.8 g). H NMR (dH, CDCl3, 250 MHz): 0.89 (3H,

5446
R. Van Deun et al. / Polyhedron 26 (2007) 5441–5447
t, CH3); 1.26 (26H, m, CH2); 2.04 (2H, m, CH2); 2.69 (3H,
s, CH3-aryl); 4.92 (2H, t, N+-CH2); 7.94 (2H, d, H-aryl,
the hydrated nitrate or chloride salt. All the reactions were
carried out in ethanol. The complexes were recrystallized
from ethanol:water (1:1). Analysis results for neodymium
complex 3: yield 20% (0.33 g). IR (cmꢀ1, KBr): 3059 (w),
2932 (m), 2849 (m), 1640 (sh, alkene C@C), 1612
(s, C@O stretching), 1595 (s, C@N), 1573 (s, aryl C@C),
1530 (m, C@C stretching), 1491 (s, C@O stretching and
CH bending), 1434 (m), 1396 (m), 1361 (m), 1322 (m),
1231 (w), 1162 (m), 1053 (m), 945 (m), 837 (m), 759 (m),
703 (m), 607 (m). CHN Elemental Anal. Calc. for
C99H101N10O8Nd (1703.19 g molꢀ1): C, 69.82; H, 5.98; N,
8.22. Found: C, 69.44; H, 5.91; N, 8.20%. Analysis results
for erbium complex 4: yield 63% (2.16 g). IR (cmꢀ1, KBr):
3049 (w), 2916 (m), 2847 (m), 1642 (sh, alkene C@C), 1616
(s, C@O stretching), 1593 (s, C@N), 1577 (s, aryl C@C),
1528 (m, C@C stretching), 1500 (s, C@O stretching and
CH bending), 1436 (s), 1394 (m), 1371 (s), 1325 (m), 1233
(w), 1160 (s), 1057 (m), 942 (m), 835 (m), 766 (s), 694
(m), 609 (m). CHN Elemental Anal. Calc. for
C99H101N10O8Er (1726.21 g molꢀ1): C, 68.88; H, 5.90; N,
8.11. Found: C, 69.02; H, 5.77; N, 8.05%. Analysis results
J0 = 6 Hz); 9.39 (2H, d, H-aryl, J0 = 6 Hz). IR (cmꢀ1
,
KBr): 3009 (m), 2913 (s), 2846 (s), 1639 (s), 1568 (w),
1519 (m), 1470 (s), 1383 (w), 1322 (w), 1176 (m), 1045
(w), 974 (w), 821 (m), 713 (m), 555 (w). Mass (m/z, EI,
70 eV): M+ = C22H40N+; 319 ([M+1]+, 4); 318 (M+, 25);
317 (M+ꢀ1H, 97); 316 (M+ꢀ2H, 44); 288 (M+ꢀC2H6,
42); 274 (M+ꢀC3H8, 48); 260 (M+ꢀC4H10, 55); 246
(M+ꢀC5H12, 55); 232 (M+ꢀC6H14, 51); 218 (M+ꢀC7H16,
42); 190 (M+ꢀC9H20, 40); 162 (M+ꢀC11H24, 40); 134
(M+ꢀC13H28, 72); 121 (M+ꢀC14H29, 53); 120 (M+ꢀ
C14H30, 61); 107 (M+ꢀC15H31, 100); 94 (M+ꢀC16H32,
52); 93 (M+ꢀC16H33, 36). CHN Elemental Anal. Calc.
for C22H40BrN (398.47 g molꢀ1): C, 66.31; H, 10.12; N,
3.52. Found: C, 66.20; H, 10.32; N, 3.37%.
The 1-hexadecyl-4-methylpyridinium bromide 1 was
then condensed with 4-dimethylaminobenzaldehyde via a
Knoevenagel-type reaction. The reagents were heated in
absolute ethanol with piperidine as the catalyst. The crude
hemicyanine bromide 2 was recrystallized twice from an
ethanol:hexane mixture. Yield: 71% (18.8 g). 1H NMR
(dH, CDCl3, 400 MHz): 0.87 (3H, t, CH3); 1.26 (26H, m,
CH2); 1.93 (2H, quintet, CH2); 3.06 (6H, s, (CH3)2N);
4.64 (2H, t, N+-CH2); 6.68 (2H, d, H-aryl, J0 = 9 Hz);
6.86 (1H, –CH@, Jtrans = 16 Hz); 7.52 (2H, d, H-aryl,
J0 = 9 Hz); 7.62 (1H, –CH@, Jtrans = 16 Hz); 7.88 (2H, d,
H-aryl, J0 = 7 Hz); 8.94 (2H, d, H-aryl, J0 = 7 Hz).13C
NMR (dC, CDCl3, 100.6 MHz): 14.1 (CH3); 22.6 (CH2);
26.1 (CH2); 29.05 (CH2); 29.30 (CH2); 29.35 (CH2); 29.50
(CH2); 29.55 (CH2); 29.60 (CH2); 29.65 (CH2); 31.6
(CH2); 31.9 (CH2); 40.1 ((CH3)2N); 60.2 (N+-CH2);
111.9; 116.3; 122.2 (quaternary C); 122.7 (alkene C);
130.6; 142.9; 152.2 (quaternary C); 154.0 (quaternary C).
IR (cmꢀ1, KBr): 3000 (w), 2912 (s), 2852 (m), 1641 (m,
alkene C@C), 1591 (s, aryl C@C), 1526 (s, aryl C@C),
1467 (m), 1430 (m), 1362 (m), 1330 (m), 1161 (s), 827
(w), 717 (w), 518 (w). Mass (m/z, EI, 70 eV):
Mþ ¼ C31H49N2þ; 451 ([M+1]+, 7); 450 (M+, 5); 448
(M+ꢀ2H, 2); 225 (M+ꢀC16H32, 18); 224 (M+ꢀC16H33,
100); 223 (M+ꢀC16H34, 52). CHN Elemental Anal. Calc.
for C31H49BrN2 (529.65 g molꢀ1): C, 70.30; H, 9.32; N,
5.29. Found: C, 69.94; H, 9.75; N, 4.88%.
for ytterbium complex 5: yield 52% (1.80 g). IR (cmꢀ1
,
KBr): 3432 (w), 3061 (m), 2928 (w), 1644 (sh, alkene
C@C), 1617 (s, C@O stretching), 1591 (s, C@N), 1573 (s,
aryl C@C), 1529 (m, C@C stretching), 1498 (s, C@O
stretching and CH bending), 1432 (m), 1400 (w), 1365
(m), 1321 (w), 1233 (w), 1162 (m), 1056 (w), 950 (m), 840
(m), 760 (m), 694 (m), 614 (m). CHN Elemental Anal. Calc.
for C99H101N10O8Yb (1731.99 g molꢀ1): C, 68.65; H, 5.88;
N, 8.09. Found: C, 68.33; H, 5.96; N, 8.00%.
4.3. Crystallography
Red single crystals of the (E)-N-dodecyl-N0,N0-dimethyl-
amino-stilbazolium tetrakis(1-phenyl-3-methyl-4-benzoyl-
5-pyrazolonato) lanthanum(III) complex were obtained
by slow evaporation of diethylether into a solution of the
compound in dimethylformamide. X-ray intensity data
were collected on a SMART 6000 diffractometer equipped
˚
with CCD detector using Cu Ka radiation (k = 1.54178 A).
The images were interpreted and integrated with the pro-
gram SAINT from Bruker [38]. Crystal data can be found
in Table 1.
Only the trans-product (E) is formed. There was no evi-
dence for the formation of the cis-isomer, probably because
of steric hindrance by the aromatic groups. The 1-hexade-
The structure was solved by direct methods and refined
by full-matrix least-squares on F2 using the SHELXTL pro-
gram package [39]. Non-hydrogen atoms were anisotropi-
cally refined and the hydrogen atoms in the riding mode
with isotropic temperature factors fixed at 1.2 times Ueq
of the parent atoms (1.5 times for methyl groups).
cyl-4-methylpyridinium bromide is
a white powder,
whereas the hemicyanine bromide has a very intense
orange-red colour.
The lanthanide complexes 3–5 were formed by reaction
of the hemicyanine bromide 2 with the b-diketone 4-ben-
zoyl-3-methyl-1-phenyl-2-pyrazolin-5-one and the appro-
priate lanthanide salt. First, the b-diketone was
deprotonated by an equivalent amount of NaOH, then,
the hemicyanine bromide and a lanthanide salt were added.
The molar ratio b-diketone:hemicyanine bromide:lantha-
nide salt was 4:1:1. For the lanthanide salt, one can use
Acknowledgements
R.V.D. and T.N.P.-V. are Postdoctoral Fellows of the
Fund for Scientific Research
(F.W.O. – Vlaanderen). Financial support by the F.W.O.
– Flanders (G.0117.03) and by the K.U.Leuven (GOA
03/03) is gratefully acknowledged. R.V.D. thanks the
– Flanders (Belgium)

R. Van Deun et al. / Polyhedron 26 (2007) 5441–5447
5447
Earths, vol. 25, North-Holland, Amsterdam, 1998, p. 101 (Chapter
167).
[14] N. Sabbatini, M. Guardigli, I. Manet, in: K.A. GschneidnerJr., L.
Eyring (Eds.), Handbook on the Physics and Chemistry of Rare
Earths, vol. 23, North-Holland, Amsterdam, 1996, p. 70 (Chapter
154).
FWO-Flanders for a Research Grant of the Fund for Sci-
entific Research – Flanders (FWO) (Project 1.5.099.06).
The authors thank Prof. C. Go¨rller-Walrand for providing
laboratory facilities. CHN microanalyses were done by
Mrs. P. Bloemen (K.U.Leuven).
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Appendix A. Supplementary material
[17] S.W. Magennis, S. Parsons, Z. Pikramenou, Chem. Eur. J. 8 (2002)
5761.
[18] A.P. Bassett, R. Van Deun, P. Nockemann, P.B. Glover, B.M.
Kariuki, K. Van Hecke, L. Van Meervelt, Z. Pikramenou, Inorg.
Chem. 44 (2005) 6140.
CCDC
crystallographic data for the (E)-N-dodecyl-N0,N0-dimeth-
ylamino-stilbazolium tetrakis(1-phenyl-3-methyl-4-ben-
623073
contains
the
supplementary
zoyl-5-pyrazolonato) lanthanum(III) complex. These data
can be obtained free of charge via http://www.ccdc.cam.a-
c.uk/conts/retrieving.html, or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit
@ccdc.cam.ac.uk. Supplementary data associated with this
article can be found, in the online version, at doi:10.1016/
j.poly.2007.08.005.
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