Synthesis, characterization, and properties of three europium 2-propoxides: [Eu4(OPri)10 (HOPri)3]*2HOPri, Eu5O(OPri)13, and EuAl3(OPr

Article abstract of DOI:10.1021/ic010745l

The reaction of Eu metal with HOPrⁱ/toluene solutions yielded the mixed Eu²⁺/Eu³⁺ alkoxide [Eu₄(OPrⁱ)₁₀ (HOPrⁱ)₃]· 2HOPrⁱ(1), in contrast to the other lanth

Full text of DOI:10.1021/ic010745l

Inorg. Chem. 2002, 41, 3249−3258
Synthesis, Characterization, and Properties of Three Europium
2-Propoxides: [Eu4(OPri)10(HOPri)3]*2HOPri, Eu5O(OPri)13, and
EuAl3(OPri)12
,†
G. Westin,* M. Moustiakimov,‡ and M. Kritikos‡
Department of Materials Chemistry, A° ngstro¨m Laboratory, Uppsala UniVersity,
SE-751 21 Uppsala, Sweden, and Department of Structural Chemistry,
Arrhenius Laboratory, Stockholm UniVersity, SE-106 91 Stockholm, Sweden
Received July 12, 2001
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The reaction of Eu metal with HOPr/toluene solutions yielded the mixed Eu2+/Eu3+ alkoxide [Eu4(OPr)10(HOPr)3]‚
i
2HOPr (1), in contrast to the other lanthanide metals, which exclusively yield trivalent lanthanide ions in the alkoxides
formed. Metathesis between EuCl3 and 3KOPr and stoichiometric hydrolysis yielded the square-pyramidal Eu O(OPr)13
(2), and metathesis with EuCl3 and 3KAl(OPr)4 gave EuAl3(OPr)12 (3). The structures of these compounds were
determined by single-crystal X-ray diffraction. IR spectroscopic studies showed that the solid-state molecular structure
of the three alkoxides remained close to intact in solution. Further characterizations were made with UV−vis
spectroscopy, differential scanning calorimetry, and solubility studies. It was also found that 1 can be converted to
2 by oxidation with dioxygen, but 2 was not reduced by Eu metal to 1. The reactions of 2 and 1 with Al4(OPr)12
in toluene/HOPr solvent were studied by IR and UV−vis spectroscopy; 2 reacted completely to form 3 in 2 h at 75
°C, while 1 reacted to yield 3 and other unidentified Eu2+ containing product(s) in the same time.
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1. Introduction
or ether-oxygen containing alkyl-alkoxides, in many cases
also containing oxo-ligands, but the number of such Eu
alkoxides whose structures have been determined is, as far
In the organic sol-gel processing of high-tech ceramic
materials, alkoxides are the most important precursors.1
Knowledge about their structures is important for the
understanding of the sol-gel process itself and for giving
increased possibilities of tailoring the product content and
morphology. An area that has received considerable interest
in recent time is the sol-gel processing of rare-earth doped
glasses and ceramics as bulk, waveguide, and finely pow-
dered material. In these materials, lanthanide ion doping
produces ceramics that can be used in a number of applica-
tions, for example, for laser amplification and frequency up-
conversion in the near-IR region, for signal enhancement in
integrated optic devices, and in various types of fluorescent
lamps and displays.2,3 In the latter application, Eu doping is
of great importance.
4
as we can find, limited to EuNa8(OH)(OBut)10 and EuSn2-
(OBut)6.5 In the 1970s, Mazdiyasni et al. reported the
formation of Eu 2-propoxide by dissolution of the metal with
a mercury salt as catalyst in 2-propanol containing solvents
at reflux.6 The Eu alkoxide was assumed to have the formula
Eu(OPri)2, on the basis of IR and elemental analysis data.6
During the course of our studies, Evans et al. reported that
a divalent Eu 2-propoxide formed by dissolution of metal
(2) Weber, M. J. J. Non-Cryst. Solids 1990, 123, 208. Westin, G.; Ekstrand,
A° ; Zanghellini, E.; Bo¨rjesson, L. J. Phys. Chem. Solids 2000, 61, 67.
Yeh, D. C.; Sibley, W. A.; Suscavage, M.; Drexhage, M. G. J. Appl.
Phys. 1987, 62, 266. Shinn, M. D.; Sobley, W. A.; Drexhage, M. G.;
Brown, R. N. Phys. ReV. 1983, 27, 6635. Desurvire, E. Phys Today
1994, 20.
(3) Nageno, Y.; Takebe, H.; Morinaga, K.; Izumitani, T. J. Non-Cryst.
Solids 1994, 169, 288. Piriou, B.; Chen, Y. F.; Vilminot, S. Eur. J.
Solid State Inorg. Chem. 1998, 35, 341. Pillonet-Minardi, A.; Marty,
O.; Bovier, C.; Carapon, C.; Mugnier, J. Opt. Mater. (Amsterdam)
2001, 16, 9.
The purest materials and lowest preparation temperatures
are normally obtained with the very reactive alkyl-alkoxides
* To whom correspondence should be addressed. E-mail:
Gunnar.Westin@mkem.uu.se.
† Uppsala University.
(4) Evans, W. J.; Sollenberger, M. S.; Ziller, J. W. J. Am. Chem. Soc.
1993, 115, 4120.
‡ Stockholm University.
(1) Chandler, C. D.; Rogers, C.; Hampden-Smith, M. J. Chem. ReV. 1993,
93, 1205. Brinker, C. J.; Scherer, G. W. The Physics and Chemistry
of Sol-Gel Processing; Academic Press: London, 1990.
(5) Veith, M.; Hans, J.; Stahl, L.; May, P.; Huch, V.; Sebald, A. Z.
Naturforsch., B: Chem. Sci. 1991, 46, 403.
(6) Brown, L. M.; Mazdiyasni, K. S. Inorg. Chem. 1970, 9, 2783.
10.1021/ic010745l CCC: $22.00 © 2002 American Chemical Society
Published on Web 05/14/2002
Inorganic Chemistry, Vol. 41, No. 12, 2002 3249

Westin et al.
solid materials, in transmittance mode, placed in quartz cuvettes
in front of a 60 mm integrated reflectance sphere. Up to 50 scans
were collected to obtain sufficiently good average signal-to-noise
ratio. The behavior on heating in the range 25-250 °C, at a rate of
5 °C min-1, was studied with a differential scanning calorimeter
(DSC, Perkin-Elmer DSC-2), using airtight steel compartments.
Crystals in sealed glass capillaries were visually studied during
heating, using a solid-block melting-point apparatus at temperatures
up to 300 °C.
The syntheses and recrystallizations, as well as the preparations
of samples for DSC, IR and UV-vis spectroscopic, and visual
studies during heating, and the mounting of crystals for single-
crystal X-ray data collection, were performed in a glovebox
containing dry, oxygen-free argon atmosphere. The europium metal
was dissolved outside the glovebox, in closed vessels connected to
an isopiestic nitrogen atmosphere dried with P2O5. The oxygen gas
used in the oxidation experiments was dried with P2O5. The
glassware was dried at 150 °C for more than 30 min before being
inserted into the glovebox. The toluene and the 2-propanol (HOPri)
were dried by distillation over CaH2. Eu metal (99.9% Strem
Chemicals) and anhydrous EuCl3 (99.9% Strem Chemicals) were
used as purchased. Commercial Al4(OPri)12 (Aldrich or Sigma) was
recrystallized before use.
2.2. Synthesis. [Eu4(OPri)10(HOPri)3]*2HOPri (1). Typically,
13.61 mmol (2.000 g) of Eu metal was added a 1:1 mixture (vol/
vol) of 40 mL of toluene and HOPri. A small amount (∼1 mg,
0.004 mmol) of HgCl2 was added as catalyst. This mixture was
heated to 65-70 °C and reacted for 24 h to dissolve the metal.
The dark yellow solution was transferred to another beaker, leaving
behind a very small amount of black powder. Slow evaporation of
the solvent produced an orange-yellow mass of small crystals of
1, in a yield of 98% based on Eu. SEM-EDS studies showed no
impurities of Hg and Cl in the product. Larger crystals for X-ray
determination were prepared by dissolving the crystal mass in HOPri
and very slowly evaporating the solvent. IR and UV-vis spectra
of the compound are given in Figures 1 and 2, respectively. Selected
peaks for identification: IR(KBr) 1174sh, 1165, 1132, 1000, 970,
832sh, 822, 520, 484, 444, 413, 398 cm-1; and UV-vis(HOPri)
526.3, 530.9, 539.8, 578.7, 584 nm. Compound 1 is very soluble
in HOPri and rather soluble in toluene and hexane, which is rather
unusual for alkoxides. It is stable for long times in HOPri and in
the solid state.
Eu5O(OPri)13 (2). Typically, 12.8 mmol (0.500 g) of K was
dissolved in 20 mL of 1:1 (vol/vol) toluene/HOPri, and 0.85 mL
of 1 M H2O in toluene/HOPri was added. Then, 4.263 mmol (1.101
g) of EuCl3 was added, and after 48 h at room temperature, the
mixture was centrifuged to separate the white precipitate of KCl
formed in the reaction. The very pale yellow solution part was
evaporated to dryness, and just enough toluene was added to
dissolve it, and then, crystallization was achieved by slow evapora-
tion. The yield of the off-white, transparent crystals of 2 was 90%.
SEM-EDS analyses showed no signals from K or Cl. IR and UV-
vis spectra of the compound are shown in Figures 5 and 6,
respectively. Selected peaks for identification: IR(KBr) 1164,
1151sh, 1130, 1125, 1001, 975, 970sh, 957sh, 953, 837, 829sh,
824, 526, 490, 446, 435sh, 417sh, 409, 396sh, 389sh, 384, 380
cm-1; and UV-vis(toluene/HOPri 1:2) 376.4, 378.1, 381, 384.8,
390.8, 399.5, 401.4, 411, 412.9, 462.4, 464.4, 524.8, 532.8, 576.5,
583.2, 587 nm. Compound 2 is very soluble in toluene and hexane
but is only slightly soluble in HOPri. The compound is stable for
long times in any of these solvents or in the solid state.
without catalyst at temperatures up to 45 °C which, after
dissolution in THF and crystallization, yielded a product
formulated as Eu(OPri)2(THF)x. Refluxing in HOPri yielded
instead mixed Eu2+/Eu3+ compounds.7 Evans et al. also
reported the synthesis of a methoxy-ethoxide formulated as
Eu(OC2H4OCH3)2 by dissolution of Eu metal in methoxy-
ethanol.8 Unfortunately, it has proven difficult to obtain the
crystal structures of the homometallic Eu alkoxides, and so
far, no structure has been reported for any of these
compounds.
In the present work, which is part of a larger study on
homo- and heterometallic Ln alkoxides,9-16 we obtained as
the product of metal dissolution in HOPri the mixed-valence
alkoxide 1, rather than the expected trivalent Eu alkoxide 2.
The latter compound can be however obtained by metathesis
of EuCl3 and KOPri, combined with stoichiometric hydroly-
sis. Compound 1 could also be converted to 2 by oxidation
with O2, while we failed to reduce 2 by Eu metal to 1.
Furthermore, the reaction in solution of both these 2-pro-
poxides with Al4(OPri)12 to yield 3 was studied. This reaction
is intriguing since it has been reported by several groups
not to occur with Ln ) Sc, Y, and Nd17-19 even under reflux,
but has worked in our hands with Ln ) Y, Er, Gd, and Nd.9,10
The structures of the three mentioned Eu alkoxides were
determined by single-crystal X-ray techniques, and they were
characterized by differential scanning calorimetry, IR and
UV-vis spectroscopy, and solubility studies.
2. Experimental Section
2.1. Equipment and Chemicals. The elemental ratios (Eu, K,
Cl, and Hg) were obtained from samples hydrolyzed in air and
gently dried, using a scanning electron microscope (SEM, JEOL
820) equipped for analysis of energy-dispersive X-ray spectra (EDS,
LINK AN 10000). The presence of these elements can normally
be detected down to ∼0.3 at. %. FT-IR spectra, in the range 5000-
370 cm-1, were recorded with a Bruker IFS-55 spectrometer, with
solid samples as KBr tablets and paraffin mulls and dissolved
samples in a 0.1 mm path-length KBr cell. UV-vis spectra, in the
range 300-800 nm, were obtained at ambient temperature with a
Perkin-Elmer Lambda 19 dispersive spectrometer with a <0.3 nm
slit. The solutions were analyzed in sealed quartz cuvettes, and the
(7) Evans, W. J.; Greci, M. A.; Ziller, J. W. Inorg. Chem. 2000, 39, 3213.
(8) Evans, W. J.; Greci, M. A.; Ziller, J. W. Inorg. Chem. 1998, 37, 5221.
(9) Westin, G.; Kritikos, M.; Wijk, M. J. Solid State Chem. 1998, 141,
168.
(10) Kritikos, M.; Moustiakimov, M.; Wijk, M.; Westin, G. J. Chem. Soc.,
Dalton Trans. 2001, 13, 1931.
(11) Wijk, M.; Norrestam R.; Nygren, M.; Westin, G. Inorg. Chem. 1996,
35, 1077.
(12) Westin, G.; Wijk, M.; Moustiakimov, M.; Kritikos, M. J. Sol-Gel Sci.
Technol. 1998, 13, 125.
(13) Moustiakimov, M.; Kritikos, M.; Westin, G., Acta Crystallogr. 2001,
C57, 515.
(14) Wijk, M.; Kritikos, M.; Westin, G. Acta Crystallogr. 1998, C54, 576.
(15) Westin, G.; Norrestam, R.; Nygren, M.; Wijk, M. J. Solid State Chem.
1998, 135, 149.
(16) Moustiakimov, M.; Kritikos, M.; Westin, G. Acta Crystallogr. 1998,
C54, 29.
(17) Turevskaya, E. P.; Belokon, A. I.; Starikova, Z. A.; Yanovsky, A. I.;
Kiruschenkov, E. N.; Turova, N. Ya. Polyhedron 2000, 19, 705.
(18) Poncelet, O.; Sartain, W. J.; Hubert-Pfalzgraf, L. G.; Folting, K.;
Caulton, K. G. Inorg. Chem. 1989, 28, 263.
EuAl3(OPri)12 (3). Typically, 12.8 mmol (0.500 g) of K was
dissolved in 35 mL of 1:2 (vol/vol) toluene/HOPri, followed by
(19) Helgesson, G.; Jagner, S.; Poncelet, O.; Hubert-Pfalzgraf, L. G.
Polyhedron 1991, 10, 1559.
3250 Inorganic Chemistry, Vol. 41, No. 12, 2002

Europium 2-Propoxides
Table 1. Selected Crystal Data for Eu4(OPri)10(HOPri)3·2(HOPri) (1),
Eu5O(OPri)13 (2), and EuAl3(OPri)12 (3)
The twin fraction was refined to 0.497 and subsequently fixed at
0.5. A number of 2-propyl groups in all three structures appeared
to be disordered. Further details on the refinement are provided as
Supporting Information.
1
2
3
empirical formula
C45H110O15Eu4 C39H91O14Eu5 C36H84O12Al3Eu
fw
1499.17
monoclinic
1543.92
monoclinic
941.93
monoclinic
3. Results and Discussion
cryst syst
space group
a, Å
b, Å
c, Å
â, deg
V, Å3
Z
P21/n (No. 14) P21/n (No. 14) P21 (No. 4)
3.1. [Eu4(OPri)10(HOPri)3]*2HOPri (1). Synthesis. The
europium metal was dissolved in toluene/HOPri (1:1) in close
accordance with the synthesis routes reported by Brown and
Mazdiyasni et al.6 and by Evans et al.7 The former group
obtained a product formulated as Eu(OPri)2, while the latter
group reported the formation of a divalent Eu 2-propoxide
when using temperatures up to 45 °C without catalysis, and
mixed Eu2+/Eu3+ products when using reflux temperature.
The product of our synthesis was the same with or without
Hg catalyst and regardless of temperature in the studied
interval 25-70 °C. It is possible that our Eu 2-propoxide is
identical with that reported by Evans et al., but more data
are needed for a safe conclusion. The structural determination
showed that the mixed Eu2+/Eu3+ valence alkoxide 1 formed,
and IR spectroscopic studies, as well as the homogeneous
color and shape of the small crystals, indicated that the
compound was highly pure and monophasic. The isolated
yield was 98%, which is much higher than that for dissolution
of the other lanthanide metals under the same conditions;
the normal yield is some 45%-75% of isolated alkox-
ide.6,9,10,18,23,24 After dissolution of the Eu metal, a very small
amount of a black, insoluble material remained, which might
come from some parts of the Eu metal pieces where the oxide
layer was not entirely removed, or from Hg/Eu/Cl residues.
In contrast, a large amount of very fine olive-green particles,
shown to be Ln hydride, formed in an amount of ∼50 mol
% with the other lanthanide metals.9,23 The difference
between Eu and the other Ln metals is that the dissolution
proceeds through a divalent state for Eu, which seems to
prevent hydride formation, whereas no divalent alkoxides
of the other lanthanide elements (Lu-Sm, Pr-La) have been
observed under similar conditions.
IR Spectroscopy. The IR spectrum of 1 is shown in Figure
1. The peak maxima in the fingerprint region, 1200-370
cm-1, are assigned to 1200-800 cm-1 C-O and C-C
stretch; 850-800 cm-1 C-O and C-C bend; and 550-370
cm-1 Eu-O stretch. A hydroxyl stretch band with a
maximum at 3210 and a shoulder at 3340 cm-1, tailing down
to ∼2100 cm-1, indicated a variety of hydrogen bonds
ranging from strong to weak, which is consistent with the
structure determination. The IR spectra of solid and dissolved
1 are quite similar, indicating that the molecular entities
remain almost unchanged in solution. In the hexane solution,
the OH stretch maximum was found at 3350 cm-1 which
fits the shoulder of the solid-state compound well, but the
peak at 3210 cm-1 was much reduced in intensity, and the
long tail to 2100 cm-1 was missing. This indicates that the
stronger hydrogen bonds had been destroyed, perhaps the
bonds between HOPri molecules binding the Eu complexes
23.246(5)
22.372(5)
27.466(6)
108.30(2)
13562(5)
8
1.469(1)
150(2)
3.697
12.846(17)
21.54(3)
21.65(2)
91.49(10)°
5990(12)
4
2.112(1)
170(1)
5.206
13.146(2)
22.738(2)
16.971(3)
90.00(0)°
5072.8(13)
4
1.233(1)
120(2)
1.336
F
calc, g cm-3
temp, K
µ(Mo KR), (mm-1
F(000)
)
6016.0
3008.0
3888/325/29
1992.0
10401/925/7
N(obs)/N(par)/N(res) 7833/855/32
R1, wR2, (I > 2σ(I))a 0.0611, 0.1441 0.0797, 0.2171 0.0336, 0.0924
∆Fmax, ∆Fmin (e/Å3)
1.04, -1.17
1.55, -1.14
0.45, -0.88
a R1 ) ∑||Fo| - |Fc||/∑|Fo|; wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]]1/2
.
2
2
2
addition of 12.8 mmol of (2.612 g) Al(OPri)3. Two hours later,
4.263 mmol (1.101 g) of EuCl3 was added. After another 48 h at
room temperature, the mixture was centrifuged to separate the white
precipitate of KCl formed in the reaction. The solution part was
evaporated to dryness, and just enough toluene was added to
dissolve it, before crystallization was achieved by slow evaporation.
The off-white crystals formed were then washed with a small
amount of HOPri. The yield of 3 was ∼90%. The SEM-EDS
analyses showed that the Eu/Al ratio was correct and no K or Cl
was present within the expected error. IR spectra and UV-vis
spectra of the compound are shown in Figures 8 and 9, respectively.
Selected peaks for identification: IR(KBr) 1200sh, 1185, 1171,
1159sh, 1138, 1126, 1120sh, 1042sh, 1034, 958sh, 954, 862, 856,
830, 730, 669, 608, 587sh, 573, 539, 477, 461sh, 448, 430sh, 401
cm-1; and UV-vis(hexane) 362.4, 375.0, 376.9, 378.6, 381.3,
383.5, 391.8, 393.9, 396.1, 401.0, 402.3, 410.7, 417.4, 419.0, 460.8,
463.5, 466.0, 524.0sh, 525.8, 528.2sh, 529.5, 532.3, 537.1, 574.6,
576.5, 583.7, 593.4 nm. Compound 3 is very soluble in toluene
and hexane but is only slightly soluble in HOPri. The compound is
stable for long times in any of these solvents or in the solid state.
2.3. Structure Determinations. Suitable single crystals of 1, 2,
and 3 were selected and glued with a very small amount of paraffin
in glass capillaries that were subsequently melt sealed. Single-crystal
X-ray diffraction data were collected on a Stoe image-plate
diffractometer at low temperature. Selected crystallographic and
experimental data for 1, 2, and 3, together with the refinement
details, are given in Table 1. Systematic absences in the collected
diffraction data were consistent with space groups P21/n (No. 14)
for 1 and 2 and P21 (No. 4) for 3. The data were corrected for
absorption effects using the X-Shape program package.20 The
structures were solved with direct methods and refined against F2
with the computer programs SHELXS9721 and SHELXL97,22
respectively. Hydrogen atoms were added at ideal positions and
refined using a riding model with thermal displacement parameters
1.2 times the Uiso of their respective pivot carbons. The absolute
configuration for noncentrosymmetric 3 was chosen according to
the Flack parameter (-0.049). The investigated crystal was
pseudomerohedrally twinned with the twin law: 100, 01h0, 001h.
(20) STOE, X-SHAPE reVision 1.09. Crystal Optimisation for Numerical
Absorption Correction; Darmstadt, 1997.
(21) Sheldrick, G. M. Acta Crystallogr. 1994, A46, 467.
(22) Sheldrick, G. M. SHELX97. Computer Program for the Refinement
of Crystal Structures, Release 97-2; Sheldrick, G. M., Ed.; University
of Go¨ttingen: Go¨ttingen, Germany, 1997.
(23) Westin, G.; Moustiakimov, M.; Kritikos, M. Unpublished results.
(24) Bradley, D. C.; Chudzynska, H.; Frigo, D. M.; Hammond, M. E.;
Hursthouse, M. B.; Mazid, M. A. Polyhedron 1990, 9, 719.
Inorganic Chemistry, Vol. 41, No. 12, 2002 3251

Westin et al.
Figure 1. IR spectra of 1 as solid in KBr (A), hexane solution (B), and
Figure 3. DSC graphs of 1 as a fresh sample (A) and a sample reheated,
after first being heated to 220 °C and cooled (B), 2 (C), and 3 (D).
toluene/HOPri (1:2) solution (C).
spectrum, but it was not possible to obtain well-defined peaks
from the solid material.
Behavior on Heating. Inspection of crystals in sealed
glass capillaries showed that the compound melted to a clear
yellow liquid at 55-58 °C, followed by some bubbling in
the range 80-130 °C, leaving a solid yellow material. No
major changes were observed on further heating to about
250 °C where the material darkened. In the DSC graph,
shown in Figure 3, a composite endothermic peak is observed
in the interval 52-74 °C which coincides with the observed
melting of the compound. This shape of this composite peak
differed much more between different samples than is usual,
but the distribution of enthalpies of it was found to be normal,
∼40-50 kJ mol-1. The composite negative peaks observed
in four runs of samples, kept at ambient temperature before
the runs, always had a main peak with an onset of 53-57
°C and a minimum of 59-61 °C, as that observed in Figure
3. In addition to this peak, a shoulder on the low-temperature
side starting at ∼40 °C and/or a shoulder on the high-
temperature side ending at ∼75 °C was observed in some
runs. A sample kept at -30 °C before the run had even
stronger peaks before and after the main peak. This endo-
therm coincides with the observed melting of the compound,
but the negative enthalpy is somewhat higher than is normal
for melting alone, which is normally found around 5-20 kJ
mol-1,9,10 and the number of closely spaced peaks indicate
a more complex process. It might be speculated that the peaks
stem from a melting occurring after the intermolecular
hydrogen bonds have been broken up and followed by some
rearrangements of the HOPri molecules. This might be
similar to what happens on dissolution of 1, where the IR
study indicated changes mainly in the hydrogen bonds and
virtually unchanged Eu-O bonds within the complex
clusters. It is also possible that some of the HOPri molecules
are released even at this low temperature and contribute by
dissolving the complexes. The bubbling observed following
Figure 2. Electronic spectra of 1 as solid (A) and HOPri solution (B).
(The insert picture spectrum of the of the 5D1
baseline corrected with a straight line.)
r
7F0 transition has been
together. In addition, a sharp peak at 3637 cm-1 was
observed, indicating isolated HOPri molecules.
UV-Vis Spectroscopy. The electronic transition spectra
of solid and dissolved 1 are shown in Figure 2. The spectra
contain a very strong band stretching from the UV region to
∼550-600 nm, causing the strong orange-yellow color of
the compound. We have earlier shown that the fine structure
of the absorptions in the UV-vis-NIR region can be used
to study even very subtle changes in the coordination
geometry of Ln3+ ions, making it possible to separate
different Ln3+ ion sites, even with the same coordination
number and only oxygen donor ligands.9,10,15 Also, Eu3+ is
suitable for such studies, and the assignments have been
made according to the scheme reported by Yatsimirskii et
al.33 Five weak peaks, assigned as due to f-f transitions
within the Eu3+ ions, can be observed in the solution
(25) Sirio, C.; Hubert-Pfalzgraf, L. G.; Bois, C. Polyhedron 1997, 16, 1129.
(26) Clegg, W.; Drummond, A. M.; Liddle, S. T.; Mulvey, R. E.; Robertson,
A. Chem. Commun. 1999, 1569.
(27) Turevskaya, E. P.; Turova, N. Ya.; Kessler, V. G.; Yanovsky, A. I.;
Struchkov, Yu. T. Zh. Neorg. Khim. 1993, 38, 928.
(28) Evans, W. J.; Golden, R. E.; Ziller, J. W. Inorg. Chem. 1993, 32,
3041.
(30) Yunlu, K.; Gradeff, P. S.; Edelstein, N.; Kot, W.; Shalimoff, G.; Streib,
W. E.; Vaarstra, B. A.; Caulton, K. G. Inorg. Chem. 1991, 30, 2317.
(31) Mehrotra, R. C.; Batwara, M. J. Inorg. Chem. 1970, 9, 2505.
(32) Veith, M.; Mathur, S.; Leclerf, N.; Bartz, K.; Heinz, M.; Huch, V.
Chem. Mater. 2000, 12, 271.
(33) Yatsimirskii, K. B.; Davidenko, N. K. Coord. Chem. ReV. 1979, 27,
(29) Brown, I. D.; Altermatt, D. Acta Crystallogr. 1985, B41, 244.
223.
3252 Inorganic Chemistry, Vol. 41, No. 12, 2002

Europium 2-Propoxides
Table 2. Selected Interatomic Distances (Å) for
Eu4(OPri)10(HOPri)3·2(HOPri) (1)
terminal M-O
µ3 M-O
Eu(2)-O(11)
Eu(3)-O(11)
Eu(4)-O(11)
Eu(1)-O(12)
Eu(3)-O(12)
Eu(4)-O(12)
Eu(1)-O(1)
Eu(1)-O(2)
Eu(2)-O(3)
Eu(2)-O(4)
Eu(3)-O(5)
Eu(4)-O(6)
2.595(10)
2.569(12)
2.500(12)
2.554(13)
2.103(11)
2.100(13)
2.595(11)
2.369(12)
2.408(10)
2.538(11)
2.466(11)
2.428(10)
µ2 M-O
µ4 M-O
Eu(1)-O(7)
Eu(1)-O(8)
Eu(2)-O(9)
Eu(2)-O(10)
Eu(3)-O(7)
Eu(3)-O(10)
Eu(4)-O(8)
Eu(4)-O(9)
2.452(12)
2.464(12)
2.450(12)
2.503(13)
2.282(10)
2.297(11)
2.283(11)
2.270(11)
Eu(1)-O(13)
Eu(2)-O(13)
Eu(3)-O(13)
Eu(4)-O(13)
2.813(11)
2.801(11)
2.496(10)
2.493(12)
The four metal atoms form a butterfly conformation in
which the metal atoms are connected to each other by two
bridging µ3-OR and four µ2-OR units in addition to the
central µ4-OR moiety. This µ4-OR unit is displaced in the
opposite direction compared to the hinge atoms; that is, the
Eu(1)-O(13)-Eu(2) angle is 169.5(4)°, which makes the
Eu4(µ4-O) unit convex, in contrast to, for example, Ce4(µ4-
O) in Ce4O(OPri)14,25 where it is concave. The two hinge
atoms, Eu(3) and Eu(4), are separated by 3.632(2) Å, while
the wingtip atoms, Eu(1) and Eu(2), are separated by 5.591(2)
Å. The two distant metal atoms bind two terminal OPri
groups each, while the two other metal atoms bind one
terminal OPri group each.
Quite remarkably, one µ4-OPri group connects all four
metal atoms through the O atom. In contrast, the related
Ce4O(OPri)14 molecule contains a µ4-O oxo-oxygen atom in
a similar structural position. To our knowledge, this is the
first example of a structurally characterized µ4-OPri group.
There are, however, known examples of µ4-OBut 26 and µ4-
OEt27 groups in alkyl-type metal alkoxides and of µ4-OpTol28
in the phenoxo ligand group.
Figure 4. ORTEP view (30% probability displacement ellipsoids) of 1,
showing the molecular structure of the metal-oxygen core. Only one
molecule from the asymmetric unit is shown. Note that O13 belongs to a
µ4-OR group.
the melting above 80 °C is probably due to boiling of the
HOPri. The origins of the low energy transfer ripples around
140 °C are not clearly understood but are possibly due to
some sintering of the material observed in some of the visual
inspections. The retained yellow color indicates that Eu2+
ions remain also after heating to higher temperatures. In a
study where the compound had first been heated to 90 or
220 °C, then cooled to room temperature, and then heated
again, one could observe that the endotherm was not
reproducible, which has been the case also for other solvated
alkoxides.15,9
Repeated dissolution of 1 in toluene or hexane fol-
lowed by evaporation removed the solvating HOPri mol-
ecules according to the IR spectroscopic studies and left a
yellowish brown powder different also from 2. The dark
yellow color indicated that the compound still contained Eu2+
ions.
The Eu-O bond lengths are in the range 2.45-2.81 Å
for the Eu(1) and Eu(2) atoms and between 2.10 and 2.50 Å
for Eu(3) and Eu(4). Moreover, there are significant differ-
ences between the hinge and wingtip Eu atoms when
comparing Eu-OR, Eu-µ2-OR, Eu-µ3-OR, and Eu-µ4-
OR distances. The Eu-O bond distance distributions and
calculated bond valence sums29 show that the two hinge
atoms have oxidation state +3 while the two wingtip atoms
are divalent. The presence of Eu2+ is also confirmed by the
strong yellow color of the solid compound.
The molecular structure of 1 is closely related to several
tetranuclear oxo-alkoxides, for example, Ce4O(OPri)13-
(HOPri),30 Ce4O(OPri)14,25 and Er2Zr2O(OPri)12(HOPri)3,12 but
also to the phenoxides, for example, [La2Na2(µ4-OpTol)(µ3-
OpTol)2(µ2-OpTol)4(OpTol)2(OC4H4)5]1-.28
Structure. The molecular structure of 1 is shown in Figure
4. Selected bond lengths for 1 are given in Table 2. The
asymmetric unit content of this alkoxide consists of two
crystallographically independent [Eu4(OPri)10(HOPri)3] mol-
ecules and four HOPri solvent molecules. The solid-state
structure is built up of chains consisting of tetranuclear units
that are interconnected with HOPri molecules. The complexes
and the alcohol molecules are connected to each other by
hydrogen bonds, resulting in two polymer strands. The two
[Eu4(OPri)10(HOPri)3] molecules have almost identical M4O13
geometries, and because each of them has two hydrogen-
bonded HOPri solvent molecules in similar arrangements,
only one of the tetranuclear molecules will be described here.
Further geometrical details for the other molecule can be
found in the Supporting Information.
As mentioned previously, intermolecular hydrogen bonds
are present in compound 1. The 2-propoxo groups involved
in hydrogen bonding are located at the wingtip Eu atoms in
the butterfly complexes. These terminally bonded 2-propoxo
groups have Eu-O-C angles in the range 123°-141°, which
are characteristic for 2-propoxo groups participating in
Inorganic Chemistry, Vol. 41, No. 12, 2002 3253

Westin et al.
Figure 5. IR spectra of 2 as solid in KBr (A), hexane solution (B), and
toluene/HOPri (2:1) solution (C).
hydrogen bonding. The equivalent angles in the other strand
are in the range 134°-140°. Adjacent complexes in both
strands are connected to each other through two HOPri
groups. The distances between oxygen atoms involved in
hydrogen bonding are slightly different between the two
chains, ranging from 2.50(2) to 2.78(2) Å and from 2.53(2)
to 2.70(2) Å, respectively. The hydroxylic H atoms necessary
for charge balance were not located by the X-ray experiment.
The presence of hydrogen bonds ranging from weak to strong
was also corroborated by the IR study.
Figure 6. Electronic spectra of 2 as solid (transmittance) (A), hexane
solution (B), and toluene/HOPri (2:1) solution (C).
solid and in solution, which corroborates the indication from
the IR spectra of retained structure in solution.
Behavior on Heating. Visual inspection of crystals in
melt-sealed glass capillaries showed no changes up to 174
°C, where the crystals became slightly matt. On further
heating, no changes were observable up to ∼260 °C, where
the crystal surfaces started to darken, indicating charring by
decomposition of the 2-propyl groups. The DSC graph of 2,
given in Figure 3, shows an endothermic peak with an onset
at 168 °C and a minimum at 172 °C, corresponding to an
energy of ∼10 kJ mol-1. This endotherm is probably due
solely to melting, because it could be reproduced after
cooling from 180 °C, although melting was not visually
observed in glass capillaries. Hence, the behavior of this
alkoxide is consistent with the findings on Ln5O(OPri)13 (Ln
) Er, Nd, Gd).9,10
Structure. Crystallographic data are represented in Table
1. Selected bond lengths and angles are given in Table 3,
and the molecular structure is shown in Figure 7. The metal-
oxygen M5O14 fragment of the molecular structure consists
of five metal atoms, each of them six-coordinated by oxygen
atoms. The five metal atoms form a highly regular square
pyramidal polyhedron with the µ5-O(14) atom displaced
0.22(2) Å above the basal plane. The Eu-O bond distances
follow the trend terminal Eu-OR < Eu-µ2-OR < Eu-µ3-
OR < Eu-µ5-O. Calculated bond valence sums indicate that
the Eu atoms are all trivalent. The Eu-O-C angles are
largest for the terminal OR groups (164°-177°); the Eu-
O-C angles for the µ2-OR and µ3-OR groups are comparable
in magnitude to each other (120°-142° and 114°-135°,
respectively). The trends seen in bond lengths and angles
for 2 are consistent with what is found for other M5O(OPri)13
compounds containing the square pyramidal M5O structure
fragment, for example, M ) Y,18 In,24 Yb,24 Er,9,10 Gd,10
Nd.10 Because the structures of these molecules have been
described in detail elsewhere, we omit a more thorough
discussion here.
3.2. Eu5O(OPri)13 (2). Synthesis. After structure deter-
mination of the Y and Yb 2-propoxides formed by dissolution
of Ln metal, given the formula Ln(OPri)3,18,24 it was often
believed that all isolated Ln 2-propoxides had the Ln5O-
(OPri)13 or Nd5O(OPri)13(HOPri)2 composition.19 However,
the products of Eu metal dissolution in HOPri containing
solvents have been formulated as Eu(OPri)2.6,7 The IR
spectroscopy data given in the literature for the orange
“Eu(OPri)2” product reported by Mazdiyasni et al.6 fit most
closely to the data of our compound 2, but in our case,
oxidation was necessary to avoid formation of 1. The orange
color reported indicates the presence of at least some Eu2+
in the sample, however, but it might also be that the
compound was affected differently when subjected to various
studies. To get a facile formation of Ln5O(OPri)13 (Ln )
Er,9 Gd,10 and Nd10), we have previously used a combination
of metathesis and stoichiometric hydrolysis. Using this route
to access the pure Eu3+ alkoxide, the structure determination
of the product showed that 2 was obtained, and IR spectro-
scopic studies and the homogeneous habit and color of the
crystals showed that the compound was highly pure.
IR Spectroscopy. The IR spectrum of the alkoxide is
shown in Figure 5; it is consistent with the IR spectra of the
other M5O(OPri)13 with M ) Y, La-Pr, Sm-Lu.23 The peaks
are assigned in the same way as for 1. The great similarity
of the IR spectra of the solid and dissolved compound shows
that the molecular structure is retained on dissolution in
toluene/HOPri or hexane solvent.
UV-Vis Spectroscopy. The UV-vis spectra of solid and
dissolved 2 are shown in Figure 6. The many weak peaks
are assigned as due to transitions between f-orbital levels of
Eu3+. The peak shapes and positions are very similar in the
3254 Inorganic Chemistry, Vol. 41, No. 12, 2002

Europium 2-Propoxides
Figure 7. ORTEP view of the metal-oxygen framework of 2 showing
30% probability displacement ellipsoids.
Figure 8. FT-IR spectra of 3 as solid in KBr (A), hexane solution (B),
and toluene/HOPri (2:1) solution (C).
Table 3. Selected Interatomic Distances (Å) for Eu5O(OPri)13 (2)
Further oxidation to decompose 2 did not occur even with a
large excess of oxygen.
Reduction of 2. An attempt to convert 2 to 1 by reduction
and O2- abstraction according to the formula
terminal M-O
Eu(1)-O(13)
Eu(2)-O(9)
Eu(3)-O(11)
Eu(4)-O(12)
Eu(5)-O(10)
µ5 M-O
Eu(1)-O(14)
Eu(2)-O(14)
Eu(3)-O(14)
Eu(4)-O(14)
Eu(5)-O(14)
2.08(2)
2.06(2)
2.13(3)
2.07(2)
2.07(2)
2.43(2)
2.42(2)
2.41(2)
2.48(2)
2.39(2)
i
2Eu5O(OPri)13 + 4Eu(s) + 4HOPri HOPr 8
µ2 M-O
µ3 M-O
3Eu4(OPri)10(HOPri)3 + 2EuO(s) + 2H2
Eu(1)-O(7)
Eu(1)-O(8)
Eu(2)-O(5)
Eu(2)-O(6)
Eu(3)-O(5)
Eu(3)-O(7)
Eu(4)-O(6)
Eu(4)-O(8)
2.27(2)
2.28(2)
2.28(2)
2.31(2)
2.30(2)
2.28(2)
2.28(2)
2.28(2)
Eu(1)-O(1)
Eu(1)-O(2)
Eu(2)-O(3)
Eu(2)-O(4)
Eu(3)-O(2)
Eu(3)-O(3)
Eu(4)-O(1)
Eu(4)-O(4)
2.45(2)
2.48(2)
2.50(2)
2.47(2)
2.46(2)
2.45(2)
2.46(2)
2.42(2)
was made by adding 2 mol of Eu to 1 mol of 2 in toluene/
HOPri (1:1). Within 4 h after mixing the starting compounds,
the almost non-colored solution had turned strongly yellow,
and some grayish red insoluble material formed. The UV-
vis and IR spectra of the evaporated solution part showed
that the product was similar to 2, but not identical, and that
it was different from 1, and thus, the reaction did not proceed
as intended.
3.4. EuAl3(OPri)12 (3). Compound 3 was prepared by
metathesis in the same way as we prepared LnAl3(OPri)12
(Ln ) Er,11 Gd,10 and Nd10,13). The method is also in close
accordance with the method given by Mehrotra et al. for
the synthesis of several LnAl3(OPri)12, among which the Eu-
Al 2-propoxide was reported.31 The structures of these
molecules were not determined, but mass spectroscopy
indicated the formula LnAl3(OPri)12.
The structural determination showed that 3 had formed,
and the IR spectroscopic studies and the homogeneous color,
shape, and Eu/Al ratio of the crystals indicated that the
material was pure.
IR Spectroscopy. The IR spectrum of the alkoxide is
shown in Figure 8; it is completely consistent with the IR
spectra of other LnAl3(OPri)12 with Ln ) Er,11 Gd, and Nd.13
The great similarity of the IR spectra of the solid and the
dissolved compound suggest that the molecular structure is
retained to a large extent on dissolution in toluene/HOPri or
hexane solvent.
µ3 M-O
Eu(5)-O(1)
Eu(5)-O(2)
Eu(5)-O(3)
Eu(5)-O(4)
2.40(2)
2.38(2)
2.36(2)
2.34(2)
3.3. Redox Reactions of [Eu4(OPri)10(HOPri)3]*2HOPri
(1) and Eu5O(OPri)13 (2). Oxidation of 1. The mixed-
valence alkoxide, 1, formed spontaneously when the metal
was dissolved under inert atmosphere. Addition of dry
oxygen gas to a toluene/HOPri (1:2) solution or a pure HOPri
solution containing 1 generated a great deal of heat, and the
strong yellow color indicating the presence of Eu2+ weakened
to a very pale yellow tint. The UV-vis and IR spectra
showed that the product was almost exclusively 2. Thus, the
Eu2+ ions can be oxidized by oxygen gas to yield the
exclusively Eu3+ containing compound 2. Two reaction
formulas that seem plausible are
5Eu4(OPri)10(HOPri)3 + 2.5O2 f
4Eu5O(OPri)13 + H2O + 13HOPri
5Eu4(OPri)10(HOPri)3 + 2O2 f
4Eu5O(OPri)13 + H2 + 13HOPri
UV-Vis Spectroscopy. The UV-vis spectra of the off-
white solid and dissolved 2 are shown in Figure 9. The solid-
state and hexane solution spectra are very similar, but
differences, especially in the intensities, are shown for the
HOPri-containing solution. This might indicate some changes
The very small amount of byproduct formed indicates that
the second formula is a better description of the reactions,
which then should occur under relatively reducing conditions.
Inorganic Chemistry, Vol. 41, No. 12, 2002 3255

Westin et al.
Figure 10. ORTEP view of the metal-oxygen framework of 3 showing
Figure 9. Electronic spectra of 3 as solid (A), hexane solution (B), and
30% probability displacement ellipsoids.
hexane/HOPri (1:1) solution (C).
Table 4. Selected Interatomic Distances (Å) for EuAl3(OPri)12 (2)
in structure in the presence of the O-donor 2-propanol. The
changes are probably small, because the peaks are found
close to the hexane spectrum positions, while the other Eu
2-propoxides have quite different positions and intensities
of the electronic transitions. A possible change could be that
the Eu3+ ion coordinates an HOPri adduct and adopts seven-
coordination. Such a structure was recently obtained by
single-crystal X-ray determination for NdAl3(OPri)12(HOPri)
by Veith et al, after crystallization from HOPri-containing
solvent.32 On the other hand, we have obtained the non-
solvated NdAl3(OPri)12 by crystallization from hexane/
toluene.13 With the smaller radius of the Eu3+ ion, solvation
should be more difficult than for the Nd3+ ion, but there is
probably at least some tendency for adduct formation in these
molecules in the presence of HOPri. Thus, it might be that
a weak Eu3+‚‚‚HOPri interaction influences the very sensitive
Eu3+ probe.
Behavior on Heating. Visual inspection of crystals in
melt-sealed glass capillaries showed no changes up to 104-
105 °C, where they melted to yield a clear liquid. No further
changes could be observed up to 300 °C. The DSC curve of
3 in Figure 3 shows an endothermic peak with onset at 102
°C and a minimum at 105 °C, fitting the melting point and
corresponding to an energy of ∼31 kJ mol-1. This is in line
with what was found for ErAl3(OPri)12 with a reproducible
melting point at 120-122 °C.11
Eu(1)-O(1)
Eu(1)-O(2)
Eu(1)-O(3)
Eu(1)-O(4)
Eu(1)-O(5)
Eu(1)-O(6)
Al(1)-O(1)
Al(1)-O(2)
Al(1)-O(7)
2.315(9)
2.335(7)
2.307(7)
2.342(9)
2.305(8)
2.318(7)
1.823(11)
1.787(8)
1.684(8)
Al(1)-O(8)
Al(2)-O(3)
Al(2)-O(4)
Al(2)-O(9)
Al(3)-O(10)
Al(3)-O(5)
Al(3)-O(6)
Al(3)-O(11)
Al(3)-O(11)
1.691(9)
1.833(9)
1.783(8)
1.693(10)
1.708(10)
1.803(8)
1.801(8)
1.700(11)
1.712(9)
M-O-C angles found in f-element 2-propoxides, for
example, 1 and 2. The M-O bond distance distributions and
calculated bond valence sum values indicate that the euro-
pium and aluminum atoms are all trivalent.
3.5 Reaction of Eu5O(OPri)13 (2) and [Eu4(OPri)10-
(HOPri)3]*2HOPri (1) with Al4(OPri)12. Reactivity of 2
with Al4(OPri)12. We have studied the reaction of 2 and
Al4(OPri)12 with a Eu/Al 1:3 ratio in toluene/HOPri (2:1 vol/
vol) by UV-vis spectroscopy. In earlier articles, we have
used the absorptions in the UV-vis-NIR region to follow
alkoxide reactions in solution.9,10,15 Studies of the 5D2 r 7F0,
5D1 r 7F0, and 5D0 r 7F0 transitions showed that the reaction
was very slow at room temperature, and only small changes
in the fine structure of 2 could be observed even after 24 h.
At 75 °C, the reaction became much more rapid, and after 2
h, the fine structures of the peaks completely coincided with
those of 3, as shown in Figure 11. Evaporation of the solvent
from this solution yielded a material homogeneous in Eu/Al
ratio, according to SEM-EDS studies, and the IR spectrum
was almost identical to that of 3, as seen in Figure 12. Only
one additional weak peak was found in the IR spectrum at
1005 cm-1, whose origin is not known. Possibly, they might
stem from a slightly erroneous Eu/Al ratio or the presence
of small amounts of oxo or hydroxo groups. The latter might
thus be an indication of where the oxo-oxygen of 2 ends up.
At 90 °C, the reaction was even faster, being finished in
about 1 h.
Structure. In the solid state, 3 is isostructural with NdAl3-
13
(OPri)12 and can be considered as a monoclinic deviation
of the orthorhombic ErAl3(OPri)12.11 The metal-oxygen
framework of the molecular structure is shown in Figure 10,
and selected bond distances are given in Table 4. The
coordination polyhedron of the Eu atom can be described
as twisted octahedral, that is, one triangular face of the
octahedron is rotated through 28° around the 3-fold axis.
The Eu-µ2-O distances are narrowly distributed around 2.32
Å. The Eu and Al atoms are connected through µ2-O bridges.
Each Al atom has two additional terminal 2-propoxo oxygens
completing the distorted tetrahedral coordination sphere. The
Al-µ2-O distances are approximately 0.10 Å longer than
the terminal Al-O bonds. Furthermore, the Al-O-C angles
at terminal O atoms are significantly smaller than the
We have earlier studied the reactivity of Er5O(OPri)13,
Nd5O(OPri)13, and Y5(OPri)13 with Al4(OPri)12 in the same
way and obtained similar results, with times ranging from 2
to 3 h for complete conversion into MAl3(OPri)12 at 80 °C.9,10
Reactivity of [Eu4(OPri)10(HOPri)3]*2HOPri (1) with
Al4(OPri)12. In the studies of the reaction between 1 and
3256 Inorganic Chemistry, Vol. 41, No. 12, 2002

Europium 2-Propoxides
7
5
7
5
7
Figure 11. 5D2 r F0, D1 r F0, and D0 r F0 transitions of Eu3+ in
toluene/HOPri (2:1) solutions of 2 (A); 2 and Al4(OPri)12 (Eu/Al 1:3) after
24 h at room temperature (B), 30 min at 75 °C (C), 60 min at 75 °C (D),
80 min at 75 °C (E), 120 min at 75 °C (F); and 3 (G).
Figure 13. Electronic spectra of Eu3+ obtained of 1 (in HOPri) (A); 2 (in
toluene) (B); a mixture of 1 and Al4(OPri)12 (Eu/Al 1:3) after 24 h at room
temperature (C), 120 min at 75 °C (D); and 3 (E), all in toluene/HOPri
(2:1).
which off-white crystals were obtained in about 50% yield,
which showed an IR spectrum very similar to that of 3; only
a small additional shoulder was found at ∼970 cm-1, which
might stem from the other part of the material which was a
bright, yellow, viscous liquid. There seemed to be no
Al4(OPri)12 left according to the IR spectrum, which suggests
that the viscous liquid was essentially a Eu2+-Al alkoxide.
At 90 °C, the reaction was complete with the same results
as for the 75 °C study after 1 h, similar to the 2-Al4(OPri)12
mixture. A possible interpretation of these results is then that
first the Eu2+ ions react to form an Eu2+-Al alkoxide, and
then the remaining Eu3+ ions yield 2. The latter alkoxide
then reacts with Al4(OPri)12 within 2 h, following the results
reported for 2.
Figure 12. IR spectra of Al4(OPri)12 (A); a mixture 1 and Al4(OPri)12
with an Eu/Al ratio of (1:3) after heating in toluene/HOPri (2:1) at 75 °C
for 2 h and evaporation of solvent, the bright yellow, viscous liquid (B),
and the off-white crystals (C); 3 (D); and the solid obtained after heating
in toluene/HOPri (2:1) of a mixture of 2 and Al4(OPri)12 (Eu/Al 1:3) at 75
°C for 2 h, after evaporation of solvent (E).
4. Conclusions
Al4(OPri)12 with a Eu/Al ratio of 1:3 in toluene/HOPri solvent,
only the D1 r F0 and D0 r F0 transitions of the Eu3+
ion could be observed because of the low intensity of the
peaks. At room temperature, some reaction took place,
causing changes in the peaks due to Eu3+, while the solution
clearly still contained a large amount of Eu2+, observable as
the strong band tailing in from shorter wavelengths, yielding
the strong yellow color. The new peaks corresponded better
to 2 than to 3, as can be seen in Figure 13. If 2 is formed,
it might be because the Eu2+ ions react to form a new
compound, possibly with Al4(OPri)12, leaving the Eu3+ ions
to form the more stable compound 2. The IR spectrum
showed peaks mainly from Al4(OPri)12 which gives rise to
strong peaks in the IR spectrum, and the remaining peaks
could not be identified. At 75 °C, the reaction proceeded to
a steady state after 2 h, with peaks in the UV-vis region of
the same shape and position as for dissolved 3. From the
remaining strong yellow color, it seems that the Eu2+ ions
introduced through 1 remained in the solution. Evaporation
of the solution yielded an inhomogeneous material, from
5
7
5
7
Three Eu 2-propoxides have been prepared, their structures
determined, and their reactivities studied. [Eu4(OPri)10-
(HOPri)3]*2HOPri (1) was obtained by dissolution of Eu
metal at temperatures from 25 to 70 °C in toluene/HOPri
solvent. It turned out to be a mixed Eu2+/Eu3+ compound,
contrary to what has been believed. The butterfly-shaped
tetranuclear molecular units contained a very rare example
of µ4-OR groups, which is also the first such group with R
) OPri.
Combined metathesis with EuCl3 and KOPri and stoichio-
metric hydrolysis produced the exclusively Eu3+ ion contain-
ing alkoxide, Eu5O(OPri)13 (2), which has the same square
pyramidal molecular structure as the other M5O(OPri)13
compounds reported, with the oxo-oxygen atom slightly
above the basal plane.
Conversion of 1 to 2 was possible by oxidation of 1 with
oxygen gas, while reduction with Eu metal of 2 did not yield
1.
Inorganic Chemistry, Vol. 41, No. 12, 2002 3257

Westin et al.
Metathesis with EuCl3 and 3KAl(OPri)4 yielded EuAl3-
(OPri)12 (3), which has the same structure as the earlier
determined LnAl3(OPri)12 (Ln ) Er, Nd). Compound 3 can
also be obtained by reaction of 2 and Al4(OPri)12 at 75 °C.
This is in accordance with our previous results with Ln )
Y, Er, Gd, and Nd but contradicts the reports on this reaction
with Ln ) Y, Nd, and Sc from other groups. This reaction
is of importance, not only for the understanding of alkoxide
chemistry, but also because LnAl3(OPri)12 is a very good
precursor to Ln-doped lasing waveguides via sol-gel or
CVD processing, because clustering of Ln ions in the oxide
matrix severely reduces the optical yield in the important
laser applications.
Acknowledgment. The natural science research council
(NFR) has financed this work. Dr. K. Jansson, Stockholm
University, is thanked for performing the DSC measure-
ments.
Supporting Information Available: X-ray crystallographic files
in CIF format for complexes 1, 2, and 3. This material is available
free of charge via the Internet at http://pubs.acs.org.
IC010745L
3258 Inorganic Chemistry, Vol. 41, No. 12, 2002