Direct Synthesis of Heterometallic Europium/Barium Complexes: H2[Eu2Ba6O2(OiPr)16(THF)4] and EuBa2(OC6H4Me-4)7(diglyme)2(DME)

Article abstract of DOI:10.1002/1099-0682(20022)2002:2<453::AID-EJIC453>3.0.CO;2-4

Convenient syntheses of mixed-metal Eu/Ba complexes starting from the elemental metals have been explored. A mixture of europium and barium ingots reacts in boiling 2-propanol to form a product which crystallizes from THF as the heterometallic complex for

Full text of DOI:10.1002/1099-0682(20022)2002:2<453::AID-EJIC453>3.0.CO;2-4

FULL PAPER
Direct Synthesis of Heterometallic Europium/Barium Complexes:
H2[Eu2Ba6O2(OiPr)16(THF)4] and EuBa2(OC6H4Me-4)7(diglyme)2(DME)
William J. Evans,*[a] Dimitrios G. Giarikos,[a] Michael A. Greci,[a] and Joseph W. Ziller[a]
Keywords: Europium / Barium / Heterometallic complexes / Isopropoxide complexes
Convenient syntheses of mixed-metal Eu/Ba complexes
an octametallic geometry comprised of two square pyramids
starting from the elemental metals have been explored. A with coplanar bases which share a basal edge and have
mixture of europium and barium ingots reacts in boiling
2-propanol to form a product which crystallizes from THF as
the heterometallic complex formulated as H2[Eu2Ba6O2-
(OiPr)16(THF)4] (1). An analogous reaction in the presence of
apices on opposite sides. The six barium atoms occupy the
basal positions and the two europium atoms are at the apices.
Complex 2 exhibits a triangular arrangement of metal atoms
with both terminal and bridging aryloxide ligands coordi-
p-cresol (HOC6H4Me-4) forms trimetallic EuBa2(OC6H4Me4)7- nated to the europium atom and bridging aryloxide and ter-
(diglyme)2(DME) (2), after recrystallization from THF/DME/
diglyme (DME = 1,2-dimethoxyethane). Complex 1 exhibits
minal ether ligands coordinated to the barium atoms.
Introduction
Results and Discussion
Synthesis
One approach to improve the performance of multi-me-
tallic solid-state materials is to construct them from mo-
lecular precursors which have the metal components mixed
with a predetermined stoichiometry at the molecular
level.[1] To use this method to improve phosphors[2,3] that
depend on the special fluorescent properties of europium,[4]
convenient syntheses of heterometallic europium complexes
are needed. Alkoxide or aryloxide complexes are desirable
since they could be converted into oxide materials by sol-
gel and thermal methods.[5] Preparation of such complexes
directly from the metals is preferable, since it avoids the
problems of drying and potential anion contamination
which accompany the use of metal salts as precursors.
Although several routes to well-defined homometallic
europium alkoxide complexes have been reported,[6Ϫ15] het-
erometallic species have remained elusive. For example, at-
tempts to produce heterometallic Eu/alkaline earth species
by direct reaction of the metal ingots with aryl alcohols
in liquid ammonia were unsuccessful and produced only
mixtures of homometallic species.[16]
Mixtures of metallic europium and barium react with 2-
propanol at reflux to form an ether-soluble product. Struc-
tural details could not be elucidated from the NMR spectra
of the product due to the broadness and shifts in resonances
caused by the paramagnetism of europium in this product.
To unambiguously determine the nature of reaction prod-
ucts, crystallization was attempted from a variety of coordi-
nating solvents and mixtures of solvents.
Single crystals of 1 could only be obtained from THF.
Crystallization of the europium/barium/2-propanol reac-
tion product from THF yielded single crystals which were
found by X-ray diffraction to be H2[Eu2Ba6O2-
(OiPr)16(THF)4] (1), see Figure 1. The magnetic moment of
We report here the direct synthesis of well-defined hetero-
metallic europium alkoxide complexes by reaction of mix-
tures of europium and barium metal ingots with 2-propanol
at reflux. Barium was chosen since it is a frequent hetero-
component in europium-based phosphors.[17Ϫ19] We also
describe the variation in structure and metal stoichiometry
induced in the isolated products by addition of p-cresol to
the reaction mixture.
[a]
Department of Chemistry, University of California,
Irvine, California 92697-2025, USA
Figure 1. Ball-and-stick diagram of H2[Eu2Ba6O2(OiPr)16(THF)4]
(1); hydrogen atoms are omitted for the sake of clarity
Eur. J. Inorg. Chem. 2002, 453Ϫ456
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453

W. J. Evans, D. G. Giarikos, M. A. Greci, J. W. Ziller
FULL PAPER
this complex was consistent with the presence of trivalent, is not unique to
1
and has been observed in
rather than divalent, europium.[20]
H2[Ba8O2(OC6H5)14(HMPA)6] (3), and H2[Ba2Sr6O2-
Reactions containing aryl alcohols were also examined, (OC6H5)14(HMPA)6] (4), both of which have the same gen-
since they had previously been shown to be effective in gen- eral formula as 1, namely H2[M8O2(ligand)20].[22]
erating
crystalline
polymetallic
lanthanide
The two apical positions of the square pyramids in 1 are
complexes.[6,7,11Ϫ13,21] After heating a mixture of p-cresol occupied by europium atoms and the six basal positions are
and europium and barium metals in 2-propanol at reflux, occupied by barium atoms. Complex 4 also has a 3:1 ratio
removal of solvent resulted in a yellow solid. The solid of metals (Sr/Ba) in the same geometry as 1, but the set of
failed to crystallize from THF, diglyme, diethyl ether, and two Ba atoms occupy the shared basal edge positions in 4
DME, but formed crystals from a mixture of ethers (THF, instead of the apical positions occupied by the set of two
DME, diglyme, 6:1:1). The fact that 2 crystallized only from europium atoms in 1. Both square-pyramidal units in 1 are
a mixture of ethers, but not from any single ether suggested symmetry-related due to a center of symmetry located be-
that there may be more than one type of ether in the prod- tween the two europium atoms. The metal···metal distances
uct. IR data indicated that the product contained arlyoxide are given in Table 1.
ligands. The effective magnetic moment of 2 was also con-
˚
Table 1. MetalϪmetal bond lengths [A] in H2[Eu2-
Ba6O2(OiPr)16(THF)4] (1)
sistent with the presence of EuIII [20]
Elemental analysis was
.
consistent with a 2:1 ratio of Ba/Eu. The structure was de-
termined by X-ray diffraction to be EuBa2(OC6H4Me-4)7-
(diglyme)2(DME) (2), Figure 2.
Bond
1
Eu(1)···Ba(3)
Eu(1)···Ba(2)
Eu(1)···Ba(4A)
Eu(1)···Ba(4)
Ba(2)···Ba(3)
Ba(2)···Ba(4)
Ba(3)···Ba(4A)
Ba(4)···Ba(3A)
Ba(4)···Eu(1A)
3.737(1)
3.738(1)
3.895(1)
3.896(1)
3.836(1)
3.892(1)
3.886(1)
3.886(1)
3.895(1)
The five metal atoms of each square pyramid are con-
nected by one µ5-oxygen, four µ3-OiPr ligands bridging the
triangular faces, and three µ-OiPr ligands bridging the un-
shared basal edges of the square pyramid. In addition, there
is one terminal isopropoxide ligand on each of the two
europium atoms and there is one THF ligand attached to
each of the four unshared basal corners of the square pyr-
amids. This generates a six-coordinate europium atom and
six- and eight-coordinate barium atoms. Two THF ligands
also co-crystallize with each molecule of 1, but do not inter-
act with the metal centers. In addition to the components
described so far, the presence of two protons is required to
balance the charge between the observed cations and an-
ions. Hydrogen atoms were not located in the X-ray study
and there are no structural anomalies in 1 that would indic-
ate their exact position, in contrast to the situation in 3
and 4.[22]
Figure 2. ORTEP diagram of the molecular structure of EuBa2-
(OC6H4Me-4)7(diglyme)2(DME) (2); thermal ellipsoids are drawn
at the 30% probability level; hydrogen atoms are omitted for the
sake of clarity
Structure of H2[Eu2Ba6O2(OiPr)16(THF)4] (1)
Due to the limited quality of the data, only the atomic
connectivity in this structure can be described. The metal
atoms in 1 do not adopt a conventional eight-coordinate
geometry, but rather form the vertices of two square pyr-
amids which share an edge and have their apices on the
opposite sides of the basal plane (Figure 3). This geometry
Structure of EuBa2(OC6H4Me-4)7(diglyme)2(DME) (2)
The three metal atoms in 2 occupy a triangular arrange-
˚
ment with 4.1316(14) A Ba(1)···Ba(2) nonbonding distances
˚
and 3.8440(13) and 3.8934(13) A Eu(1)···Ba nonbonding
distances. The metal atoms in 2 are connected by two µ3-
aryloxide ligands above and below the triangular plane and
three µ2-aryloxide ligands, each bridging one edge of the
triangle. The europium atom has two additional terminal
aryloxide ligands, which lead to a formal coordination
number of six. The barium atoms have dissimilar coordina-
tion environments: each atom has one tridentate diglyme
coordinated to it, but Ba(2) also has a bidentate DME. This
Figure 3. Metal framework in H2[Eu2Ba6O2(OiPr)16(THF)4] (1)
454
Eur. J. Inorg. Chem. 2002, 453Ϫ456

Direct Synthesis of Heterometallic Europium/Barium Complexes
FULL PAPER
gives a formal coordination number of seven for Ba(1) and The BaϪOϪC (Ar) angles in 2 involving these two ligands
nine for Ba(2), with respect to the oxygen donor atoms, but also suggest that both phenyl rings are canted towards Ba(1):
further ligation is present, as described below. Bond lengths the angles involving Ba(1) [97.0(7) and 98.7(8)°] are more
in 2 are shown in Table 2.
acute than those involving Ba(2) [127.5(8) and 128.3(8)]. Con-
sideration of these two interactions increases the coordination
number of Ba(1) to nine, the same as Ba(2).
˚
Table 2. Bond lengths [A] in EuBa2(OC6H4Me-4)7(diglyme)2-
(DME) (2)
Conclusion
Eu(1)ϪO(1)
Eu(1)ϪO(2)
Eu(1)ϪO(3)
Eu(1)ϪO(5)
Eu(1)ϪO(6)
Eu(1)ϪO(7)
Ba(1)ϪO(1)
Ba(1)ϪO(2)
Ba(1)ϪO(4)
Ba(1)ϪO(5)
Ba(1)ϪO(13)
Ba(1)ϪO(14)
2.432(9)
2.412(9)
2.299(10)
2.343(9)
2.161(10)
2.193(9)
2.770(9)
2.780(9)
2.630(10)
2.672(9)
2.849(10)
2.837(10)
Ba(1)ϪO(15)
Ba(2)ϪO(1)
Ba(2)ϪO(2)
Ba(2)ϪO(3)
Ba(2)ϪO(4)
Ba(2)ϪO(8)
Ba(2)ϪO(9)
Ba(2)ϪO(10)
Ba(2)ϪO(11)
Ba(2)ϪO(12)
Eu(1)···Ba(1)
Eu(1)···Ba(2)
2.815(10)
2.822(9)
2.829(9)
2.751(9)
2.675(9)
2.918(11)
2.909(11)
2.893(12)
2.943(11)
Mixed metal complexes of europium and barium can be
readily synthesized directly from the metals in 2-propanol
at reflux. Varying Eu/Ba stoichiometries have been identi-
fied in crystalline systems depending on the crystallization
conditions.
2.815(11) Experimental Section
3.844(1)
3.893(1)
General: All reactions were performed in a glovebox under nitrogen
or by using standard Schlenk and vacuum line techniques under
nitrogen. Europium and barium ingots were washed with hexanes,
dried, and cut to appropriate size before use. 2-Propanol was dried
by addition of 0.02 equiv. of sodium per equivalent of 2-propanol
at 20° C, followed by vacuum transfer of the alcohol from this
mixture into the reaction flasks. 4-Methylphenol (Aldrich) was
˚
The 2.412(9) and 2.432(9) A EuϪµ3-O (OAr) (OAr ϭ
˚
OC6H4Me-4) distances and the 2.161(10) and 2.193(9) A
EuϪO (terminal OAr) distances in 2 are in the range of
those in the trivalent lanthanum 4-methylphenoxide com-
˚
plex
[Me4N][La2Na2(µ4-OAr)(µ3-OAr)2(µ-OAr)4(OAr)2-
dried and vacuum-distilled from molecular sieves (3 A). Other solv-
(THF)5] [2.284(3) and 2.296(3) A],[21] considering the differ-
˚
ents were dried and physical measurements were made as previ-
ously described.[15] Magnetic moments were measured by the
method of Evans[30] with a General Electric QE300 NMR spectro-
meter. Elemental analyses were performed by Desert Analytics,
Tucson, AZ with metal analyses done by atomic absorption spec-
troscopy.
ences in Shannon radii,[23] but they are shorter than the
˚
corresponding 2.350(5)
A distance in divalent Eu2-
(OC6H3Me2-2,6)4(DME)3.[6] The 2.299(10) and 2.343(9) A
˚
EuϪµ-O (OAr) distances in 2 are also reasonable compared
[24]
to those in trivalent K3Nd2(µ-OAr)6(µ4-OAr)3(THF)7
and {[La2Na2(µ4-OAr)3(µ-OAr)6(dioxane)5](dioxane)}n,[17]
but they are shorter than the 2.479(3)Ϫ2.632(3),
H2[Eu2Ba6O2(OiPr)16(THF)4] (1): Mixtures of europium (0.166 g,
1.1 mmol) and barium (0.408 g, 3 mmol) ingots, typically 0.5 mm
in diameter, were combined in a round-bottom flask equipped with
a stir bar and a Schlenk adapter. 2-Propanol (25 mL) was vacuum-
transferred into the flask. The mixture was heated at reflux for 4 h
and the solvent was removed under vacuum with slight heating to
give an orange-brown solid (0.51 g, 50% yield based on Eu). A
portion of this material (110 mg) was then dissolved in hot THF
and centrifuged. Yellow crystals formed overnight at Ϫ31 °C
(75 mg, 68%). C64H146Ba6Eu2O22 (2395.74): calcd. C 32.08, H 6.14,
˚
2.447(5)Ϫ2.597(5), and 2.444(13)Ϫ2.581(12) A EuϪO (µ-
OC6H3Me2-2,6) distances in the divalent complexes Eu2-
(OC6H3Me2-2,6)4(N-methylimidazole)5,[12]
Eu2(OC6H3Me2-2,6)4(DME)3,[6] and Eu3(OC6H3Me2-
2,6)6(THF)6,[14] respectively. In general, the differences in
EuϪO bond lengths between 2 and divalent europium ary-
loxides in the literature correspond to the difference in
Shannon radii between EuIII and EuII.[23] This is in agree-
ment with the magnetic data on 2 which indicate that the
Ba 34.39, Eu 12.69; found C 31.86, H 6.28, Ba 34.25, Eu 12.45.
Magnetic susceptibility: χg298K ϭ 5.4 ϫ 10Ϫ6, µ
ϭ 4.2 µB. IR
298K
eff
˜
(KBr): ν ϭ 2948 s, 2858 m, 2770 m, 2670 w, 2581 m, 2353 w, 2104
w, 1933 w, 1731 w, 1457 m, 1368 m, 1348 m, 1239 w, 1150 s, 1040
w, 966 s, 902 w, 812 m, 763 w, 728 w, 510 m cmϪ1. Space group:
europium atom is trivalent.
˚
The 2.630(10)Ϫ2.751(9)
A
BaϪO (µ-OAr) and
˚
2.770(9)Ϫ2.829(9) A BaϪO (µ3-OAr) distances in 2 are also
similar to the corresponding average distances in
HBa5(O)(OC6H5)9(THF)8 [2.65(3) and 2.75(2) A],
˚
C2/c. Unit cell: a ϭ 27.853(5), b ϭ 24.263(3), c ϭ 17.097(4) A, β ϭ
3
˚
108.496(12)°, V ϭ 10958(4) A , Z ϭ 4.
[25]
˚
3
[22]
˚
[2.65(6) and 2.76(9) A],
and those in Ba5(OH)-
X-ray Data Collection and Solution and Refinement for H2[Eu2-
[2.61(5) and 2.70(3) A]. The Ba6O2(OiPr)16(THF)4] (1): A yellow crystal of approximate dimen-
[26]
˚
(OC6H3Me2-3,5)9(THF)5
˚
sions 0.30 ϫ 0.23 ϫ 0.23 mm was mounted on a glass fiber and
transferred to the Siemens P4 diffractometer. The determination
of symmetry, crystal class, unit cell parameters and the crystal’s
orientation matrix were carried out according to standard proced-
ures.[31] Intensity data were collected at 163 K using the 2θ/ω scan
technique with Mo-Kα radiation. The raw data were processed with
a local version of CARESS[32] which employs a modified version of
the LehmanϪLarsen algorithm to obtain intensities and standard
deviations from the measured 96-step peak profiles. All 7818 data
were corrected for absorption and Lorentz and polarization effects
2.815(11)Ϫ2.943(11) A BaϪO (ether) distances in 2 are in
good agreement with the 2.814(6)Ϫ2.900(6)
˚
A
and
˚
2.826(7)Ϫ2.919(8) A distances in Ba(tetramethylheptane-
dionate)2(triglyme)[27] and KBa2(OSiPh3)5(DME)2.[28]
In addition to coordination from oxygen atoms, Ba(1)
exhibits close contacts with the ipso-carbon atoms, C(8) and
C(1), from both µ3-aryloxide ligands, with 3.229(13) and
˚
3.254(14) A BaϪC (ipso-Ar) distances, respectively. These
distances are in the range of similar 2.981(6)Ϫ3.193(7) A
˚
BaϪC (Ar) contacts in [Ph2P(4-methylbenzylide)2]2Ba.[29] and were placed on an approximately absolute scale. The diffrac-
Eur. J. Inorg. Chem. 2002, 453Ϫ456
455

W. J. Evans, D. G. Giarikos, M. A. Greci, J. W. Ziller
FULL PAPER
[2]
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tion symmetry was 2/m and the systematic absences were consistent
with the centrosymmetric monoclinic space group C2/c. All calcu-
lations were carried out using the SHELXL program.[33] The ana-
lytical scattering factors for neutral atoms were used throughout
the analysis.[34] The structure was solved by direct methods and
refined on F2 by full-matrix least-squares techniques. Hydrogen
atoms were included using a riding model. Two molecules of THF
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[3]
[4]
EuBa2(OC6H4Me-4)7(diglyme)2(DME) (2): Europium (117 mg,
0.77 mmol) and barium (210 mg, 1.53 mmol) ingots and p-cresol
(592 mg, 5.47 mmol) were combined in a round-bottom flask
equipped with a stir bar and a Schlenk adapter. 2-Propanol
(15 mL) was vacuum-transferred into the flask and the mixture was
heated at reflux for 24 h. After the solvent was removed under va-
cuum with slight heating, 30 mL of THF, 5 mL of DME, and 5 mL
of diglyme were added to the flask. After heating for 30 min, the
entire product was soluble. Reduction of the solution volume to
5 mL by rotary evaporation led, over a period of 12 h, to the forma-
tion of crystals of 2 suitable for single-crystal X-ray diffraction
(910 mg, 80%). C65H87Ba2EuO15 (1534.99): calcd. C 50.9, H 5.7,
[5]
[6]
[7]
[8]
[9]
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275Ϫ277, 841.
[11]
Eu 9.9; found C 50.8, H 5.9, Eu 10.4. Magnetic susceptibility:
χg298K ϭ 3.5 ϫ 10Ϫ6, µ
298K
˜
ϭ 3.5 µB. IR (KBr): ν ϭ 3010 w, 2916
eff
[12]
[13]
[14]
[15]
[16]
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w, 1167 m, 1097 w, 1065 m, 1013 m, 933 w, 858 m, 824 s, 753 m,
580 w cmϪ1. Temperature: 163 K. Crystal system: monoclinic.
5221.
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Am. Chem. Soc. 1988, 110, 6423.
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XSCANS Software Users Guide, Version 2.1, Siemens Indus-
trial Automation, Inc., Madison, WI, 1994.
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Space group: P21/n. Unit cell: a ϭ 12.269(3), b ϭ 24.750(5), c ϭ
3
˚
˚
23.570(4) A, β ϭ 98.685(10)°, V ϭ 7076(2) A , Z ϭ 4, ρcalcd.
ϭ
1.441 Mg/m3, µ ϭ 2.035 mmϪ1
.
X-ray Data Collection and Solution and Refinement for 2: A yellow
crystal of approximate dimensions 0.20 ϫ 0.10 ϫ 0.10 mm was
handled and raw data were processed as described above for 1. All
9756 data were corrected for absorption and Lorentz and polariza-
tion effects and were placed on an approximately absolute scale.
The diffraction symmetry was 2/m and the systematic absences were
consistent with the centrosymmetric monoclinic space group P21/
n. All calculations were as described for 1 above. The structure was
solved by direct methods and refined on F2 by full-matrix least-
squares techniques. Minor disorder in the diglyme molecules was
modeled by assigning partial occupancy to components of the dis-
ordered groups. Hydrogen atoms were included using a riding
model. At convergence, wR2 ϭ 0.1705 and GOF ϭ 1.066 for 748
variables refined against all 9248 unique data [for refinement on F,
R1 ϭ 0.0631 for those 5757 data with F Ͼ 4.0σ(F)].
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
[28]
Crystallographic data (excluding structure factors) for the struc-
tures reported in this paper have been deposited with the Cam-
bridge Crystallographic Data Centre as supplementary publication
no. CCDC-171956 (1) and -171957 (2). Copies of the data can be
obtained free of charge on application to CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK [Fax: (internat.) ϩ 44-1223/336-033;
E-mail: deposit@ccdc.cam.ac.uk].
[29]
[30]
[31]
Acknowledgments
For support of this research, we thank the Division of Chemical
Sciences of the Office of Basic Energy Sciences of the Department
of Energy.
[32]
[33]
[34]
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Eur. J. Inorg. Chem. 2002, 453Ϫ456