Two Luminescent Complexes Alq3
and Eu(tta)3(phen)
Laboratory report on Experiment 8 for Chemistry 261
John Stephenson (8js5@qlink.queensu.ca)
Prepared for Pat Causey, Frost 405 (patrick@chem.queensu.ca)
April 4, 2002
Introduction
Luminescent compounds have important applications in a number of commercial
products. They are used in flat-panel displays based on electroluminescence (such as
night lights, laptop computer displays and indiglo watch faces), sensor technologies and
the dyes present in glow-sticks. The goal of this laboratory project is to prepare and
analyze two of the most well-known coordination complexes used in electroluminescent
displays, Alq3 and Eu(tta)3(phen).
Alq3 is formed by complexing Al(III) in an octahedral (sp3d2) arrangement with 8hydroxyquinoline (qH) in the presence of base as shown in Scheme 1. Three 8hydroquinolinolato (q) groups coordinate to the Al(III) ion due to a chelating effect.
Since aluminum nitrate has a highly ionic nature this salt is dissolved in water. 8hydroxyquinoline is a organic compound with an ionic nature and a less polar solvent,
methanol, is used to dissolve the 8-hydroxyquinoline. Sodium carbonate is used to
neutralize the acidic protons that are released as qH forms q to push the equilibrium to the
right.
2 Al(NO3)3.9H2O + 3 Na2CO3 + 6 qH  2 Alq3 + 6 NaNO3 + 21 H2O + 3 CO2
Scheme 1: Formation of Alq3 from Al(NO3)3, Na2CO3 and 8-hydroxyquinoline
Similarly Eu(tta)3(phen) is formed by complexing Eu(III) with thenoyltrifluoroacetone
(ttaH) in the presence of base, followed by precipitating it by further complexing it with
1,10-phenanthroline (phen) to form Eu(tta)3(phen) as shown in Scheme 2. The ligands are
all organic compounds with ionic natures. Europium chloride is not a purely ionic species
and exhibits good solubility in methanol. There is need to use water to get the europium
chloride to dissolve, so the reaction is carried out in methanol. Sodium hydroxide is used
to mop up the acidic protons from ttaH as it forms tta to push the equilibrium to the right.
EuCl3.6H2O + 3 ttaH + 3 NaOH + phen  Eu(tta)3(phen) + 3 NaCl + 9 H2O
Scheme 2: Formation of Eu(tta)3(phen) from EuCl3, NaOH, ttaH and phen.
Experimental
Preparation of Alq3
In a 250ml Erlenmeyer flask 1.0g of 8-hydroxyquinoline was dissolved in 30ml of
methanol and a stir-bar added. In a separate flask, 0.5g of Al(NO3)3.9H2O was dissolved
in 70mL of water. Magnetic stirring was started and the methanol solution was added to
the aqueous solution. An already made solution of 4g of Na2CO3 in 60ml of water was
added drop-wise until the pH of 8 was obtained according to pH paper, this took only a
fraction of the alkaline solution. The mixture was then stirred for 30 minutes longer. The
solution was suction filtered and the yellow solid thus obtained was washed with a small
amount of methanol, suction-dried then air-dried. 0.6640g (1.45mmol, 109% yield) of
product was obtained. Under 365nm wavelength from a hand-held UV lamp the product
glowed green. At a shorter wavelength of 254nm the product did not glow. Analytical
work was then conducted on the solid.
Preparation of Eu(tta)3(phen)
0.50g of EuCl3.6H2O was dissolved in a minimum amount of methanol. In a separate
flask 0.85g of thenoyltrifluoroacetone was dissolved in a minimum amount of methanol.
The two solutions were added together, a magnetic stir bar added, and the solution stirred
for 30 minutes. An already prepared saturated solution of NaOH in methanol with 5%
water was added drop-wise to the solution until the pH reached 8 according to pH paper.
The solution was then allowed to stir an additional 30 minutes. 0.22g of 1,10phenanthroline was added to the europium solution and the white product precipitated.
The solution was allowed to stir an extra 30 minutes and the white solid suction filtered
and washed with a small amount of methanol. The solid was allowed to suction-dry and
then air-dry. 0.975g (0.979mmol, 72% yield) of product was obtained. Under 365nm
wavelength from a hand-held UV lamp the product glowed a bright red, and under a
shorter wavelength of 254nm the product glowed a dull red. Analytical work was then
conducted on the solid.
Analytical work
Infrared spectra were prepared by weighing approximately 20mg of sample and 200mg of
KBr weighed. The samples were intimately ground together with a polished ceramic
mortar and pestle, pressed at 10 tonnes of pressure. The KBr disks were analyzed with a
Bomem Hartmann & Braun MB-series infrared spectrophotometer with PC interface.
UV-VIS spectra were obtained for both samples by preparing a solution of approximately
10mg in 10mL of dichloromethane. The samples were analyzed with a UV-VIS apparatus
with PC interface by first calibrating with a cuvet of DCM to get a baseline, then running
a cuvet filled with each of the solutions.
Fluorescent spectra of both the ligands and the complexes and IR spectra of the ligands
were not taken in this lab, rather they were obtained under the CHEM261 course reserve
from the Douglas Library at Queen’s University.
Results
Table 1: Physical data on the luminescent complexes Alq3 and Eu(tta)3(phen)
Product
Yield
Physical
Luminescent Properties
Appearance
Alq3
0.6640g
Yellow powder Glows yellow-green under 365nm
1.45mmol
No emission under 254nm
109% yield (*)
Eu(tta)3(phen) 0.975g
White powder
Glows bright red under 365nm
0.979mmol
Glows dull red under 254nm
72% yield
(*)Note that the yield exceeds this value, indicating that the sample still contained some solvent
MW of phen is 180.21 g/mol, ttaH is 221.18 g/mol, tta is 221.17 g/mol, qH is 145.15 g/mol, q is
144.15 g/mol, Eu is 151.96 g/mol, Al is 26.98 g/mol, aluminum (III) nitrate nonahydrate is 375.13
g/mol, europium (III) chloride hexahydrate is 366.41 g/mol.
Table 2: UV-Vis data on the luminescent complexes
Compound
Absorbance, A
Wavelength,  (nm)
Alq3
214 (likely Al(III))
1.05
318 (likely Al(III))
1.28
334 (likely q)
1.39
388 (likely Al(III))
2.50
Eu(tta)3(phen) 322 (likely phen)
3.02
366 (likely ttfa)
2.65
UV-Vis, IR, Fluorescent and NMR spectra is attached at the end of this document in the
“Spectra” section.
Discussion
The 109% yield of Alq3 indicates that the sample was still wet with solvent. The sample
appeared to be dry before weighing, so it can be assumed that the yield of this compound
was nearly quantitative. The role of the solvents and of the base used in this reaction has
been discussed in the introduction, including the overall reaction. However, what was not
mentioned was that Alq3 is able to form four possible isomers depending on how the
hydroquinolinolato (q) groups co-ordinate to the aluminum ion as shown in Figure 1.
Either the ligands, which are in hard ionic bonding mode, could arrange to the facial
arrangement, fac-Alq3, in two chiral forms or to the meridonal arrangement, mer-Alq3
again in two chiral forms. X-ray crystallography could be used to determine which
structural isomers were formed in this lab.
Uv-vis spectra reveals to us that 8-hydroxyquinoline absorbs at 338nm and that Alq3
absorbs at four wavelengths shown in Table 2. This leaves the three peaks, 214, 318 and
334nm attributed to the Al(III) ion. Since Alq3 does not produce a glow around 254nm it
shows that the absorption of the light by the 8-hydroxyquinolo ligand is crucial (close to
the light source which peaks at 365nm) to the excitation stage of the fluorescence and the
interaction between the ligand followed by a relaxation between the metal center and the
ligand and emission of a lower energy, visible yellow light. The fluorescence spectra
shows a similar excitation profile to the absorption profile that is seen in the UV-Vis
spectroscopy for Alq3, and the emission spectra is shifted to a lower energy wavelength
around 450-600nm corresponding to the yellow light that Alq3 emits. As Alq3 still
absorbs a significant amount of radiation around 400nm (in the visible region), it only
reflects the light seen as the color yellow, corresponding to the qualitative observation
made in Table 1.
The 72% yield of Eu(tta)3(phen) is fairly nice yield. Methanol was chosen for this step
because all reagents other than the complex would dissolve in it as explained in the
introduction--also explained was the role of the sodium hydroxide. Unlike Alq3
Eu(tta)3(phen) is able to form many different isomers. Eu(III) adopts a high coordination
number of 8 in a square antiprismatic (sp3d4) arrangement. This coordination number is
not unusual for a lanthanide as coordination numbers up to 12 are known for certain
elements this series. Eu(tta)3(phen) could form many possible isomers, one possibility is
shown in Figure 2.
It appears that the purpose of phen is to merely get the Eu(tta)3 to precipitate, the
important ligand in producing the brilliant red light emitted by Eu(tta)3(phen) lies in the
tta ligands. Uv-vis spectra shows us that phen 328nm and tta around 342, 366 and 378nm.
Of the two peaks observed for the Eu(tta)3(phen) the higher energy peak, 322nm is
attributed to phen and the lower energy 366nm is attributed to tta. Since Eu(tta)3(phen)
does not produce a bright glow around 254nm it shows that the absorption of the light by
the tta ligand is crucial (close to 365nm) to the excitation stage of the fluorescence and
the interaction between the ligand followed by a relaxation between the metal centre and
the ligand and emission of a lower energy, visible red light. The fluorescence spectra
shows a similar excitation profile to the absorption profile that is seen in the UV-Vis
spectroscopy for Eu(tta)3(phen), and the emission spectra is shifted to a lower energy
narrow wavelength around 600-625nm corresponding to the light red that Eu(tta)3(phen)
emits. As Eu(tta)3(phen) does not absorb a significant amount of radiation around 380750nm it appears as a white solid, corresponding to the qualitative observation made in
Table 1.
NMR spectras for these compounds were likely not provided because a high-resolution
scanner (>250MHz) is needed due to the magnetic properties of the metal centre.
IR was not examined because a) it’s boring and gives only crumbs of structural data, b)
it’s 12:53pm and this report is due sometime in the near future. :-)
N
N
O
Al
N
O
N
O
O
N
O
Al
N
O
N
O
O
N
N
Al
N
O
O
Figure 1: Four structural isomers of Alq3 (left is facial, right is meridonal)
CF3
N
CF3
O
O
H
N
Eu
O
S
H
S
O
O
O
S
CF3
H
Figure 2: One possible structure of Eu(tta)3(phen)
References
Housecroft and Sharpe, 2001. Inorganic Chemistry, Prentice-Hall: Harlow, England.
p. 625-626.
Wang, S. 2002. “Chem 261 Course Material” Queen’s University: Douglas Library
XE5.E05
Wang, S. 2002. “Chem 261: Laboratory Material” p 17-18.
N
Al
N
O
O