Europium(II) and ytterbium(II) aryloxide chemistry: Synthesis and crystal structure of [Eu(OC6H3Bu2t-2,6) 2(THF)3]·0.75C7H8 and [Yb(OC6H3Bu2

Article abstract of DOI:10.1016/S0277-5387(03)00193-1

The reactions of europium and ytterbium with 2,6-di-tert-butylphenol were studied by the metal vapour synthesis technique and by dissolution in liquid ammonia. The lanthanide complexes [Eu(OC₆H₃Bu₂^t-2,6)₂

Full text of DOI:10.1016/S0277-5387(03)00193-1

Polyhedron 22 (2003) 1425Á1429
/
www.elsevier.com/locate/poly
Europium(II) and ytterbium(II) aryloxide chemistry: synthesis and
crystal structure of [Eu(OC6H3But2-2,6)2(THF)3]×
/
0.75C7H8 and
[Yb(OC6H3But2-2,6)2(NCMe)4]
ˆ
Jose´ Carretas *, Joaquim Branco, Joaquim Marcalo, Angela Domingos,
¸
Anto´nio Pires de Matos
Departamento de Qu´ımica, Instituto Tecnolo´gico e Nuclear, Estrada Nacional 10, P-2686-953 Sacave´m, Portugal
Received 19 December 2002; accepted 21 February 2003
Abstract
The reactions of europium and ytterbium with 2,6-di-tert-butylphenol were studied by the metal vapour synthesis technique and
by dissolution in liquid ammonia. The lanthanide complexes [Eu(OC6H3But2-2,6)2(THF)3]×0.75C7H8 1 and [Yb(OC6H3Bu2t -
2,6)2(NCMe)4] 2 were synthesized and characterized by X-ray diffraction studies.
/
# 2003 Elsevier Science Ltd. All rights reserved.
Keywords: Europium; Ytterbium; MVS; Dissolution in ammonia; Aryloxides
1. Introduction
2. Experimental
Lanthanide alkoxides and aryloxides have been
extensively studied due to the applicability of these
complexes as precursors to high purity oxides [1,2] and
catalysts for organic reactions [3]. The reactions with the
elemental metal are the most convenient routes to
lanthanide alkoxides and aryloxides, since the presence
of undesirable ligands can be avoided, as they can
contaminate the final product. In our laboratories we
have studied the reactions of lanthanide metals with
alcohols and phenols using the metal vapour synthesis
technique (MVS) [4], the direct metal-alcohol reaction
[5] and metal dissolution in liquid ammonia [5,6], having
in mind the preparation of very pure aryloxides as
precursors of catalysts supported on silica substrates.
In this work we studied the reactions of europium and
ytterbium with 2,6-di-tert-butylphenol by the MVS
technique and by dissolution in liquid ammonia. We
report here the characterization of the compounds
obtained, including the crystal and molecular structures.
2.1. Materials and instrumentation
All manipulations were routinely performed under N2
using glove-box and Schlenk techniques. MVS experi-
ments were made in a Planer products plant VPS 500.
Solvents were purified by standard methods [7]. Euro-
pium and ytterbium ingots were obtained commercially
from the Baotou Research Institute of Rare Earth. 2,6-
Di-tert-butylphenol was sublimed before use. C, H and
N analyses were performed in a CE instruments EA1110
automatic analyser. Eu and Yb analyses were performed
according to a standard gravimetric method [8]. IR
spectra were registered in a 577 PerkinÁElmer spectro-
/
1
meter with samples prepared as Nujol mulls. H NMR
spectra were recorded using a Varian Unity Inova 300
MHz spectrometer.
2.2. Preparation of complexes
* Corresponding author. Tel.: ꢀ
994-1455.
E-mail address: carretas@itn.mces.pt (J. Carretas).
/
351-211-994-6218; fax: ꢀ351-211-
/
[Eu(OC6H3But2-2,6)2(THF)3]×
C6H3But2-2,6)2(NCMe)4] 2.
/
0.75C7H8 1 and [Yb(O-
0277-5387/03/$ - see front matter # 2003 Elsevier Science Ltd. All rights reserved.
doi:10.1016/S0277-5387(03)00193-1

1426
J. Carretas et al. / Polyhedron 22 (2003) 1425Á1429
/
2.2.1. Dissolution in liquid ammonia
reaction, and the characterization of the ytterbium
compound gave similar results as in (yieldꢂ40%).
Europium (2.50 g, 16.45 mmol) was added to a
solution of 2,6-di-tert-butylphenol (6.7 g, 32.47 mmol)
in THF (100 ml), in a 250 ml Schlenk flask. The flask
was connected to a vacuum line and liquid ammonia
/
2.3. X-ray structure determination
was condensed into the reaction vessel at ꢁ78 8C. After
/
Very air sensitive yellow and red crystals of 1 and 2
were mounted under nujol in thin-walled glass capil-
laries, with atmosphere of solvent of crystallization, in a
nitrogen-filled glove-box. Data were collected at room
temperature on an Enraf-Nonius CAD4-diffractometer
with graphite-monochromatized Mo Ka radiation,
3 h the reaction mixture was allowed to slowly warm to
room temperature and was purged with N2. This
mixture was then filtered through a Celite bed and the
solution evaporated. The product was washed several
times with pentane and a yellow solid formulated as
[Eu(OC6H3But2-2,6)2(THF)3] was obtained after drying
using a vꢁ
/
2u scan mode. The value umax
ꢂ238 was
/
under vacuum (yieldꢂ76%). Analysis found (%): Eu,
/
imposed by the expected decay and the quality of the
crystals. A summary of the crystallographic data is given
in Table 1. Data were corrected [9] for Lorentz and
polarization effects, for linear decay and for absorption
by empirical corrections based on C scans. The
structures were solved by Patterson methods [10] and
19.10; C, 59.91; H, 9.00. Calculated for EuO5C40H66:
Eu, 19.51; C, 61.67; H, 8.56. IR (cmꢁ1): 3620w, 3040w,
2700w, 2660w, 2515w, 1570m, 1450s, 1400s, 1370s,
1360w, 1340w, 1330w, 1270s, 1250w, 1190m, 1170w,
1140w, 1130w, 1110w, 1100s, 1020s, 935w, 930w, 910w,
870s, 850s, 810m, 740m, 730m, 660w, 630m, 535m,
460w, 440m. X-ray quality crystals of 1 were grown
from a solution of the yellow solid in toluene at room
temperature.
The procedure for the reaction of ytterbium (2.89 g,
16.70 mmol) with 2,6-di-tert-butylphenol (6.9 g, 33.44
mmol) was identical to that for the europium reaction.
A red solid formulated as [Yb(OC6H3But2-2,6)2(THF)3]
refined by full matrix least-squares on F2 using SHELXL
-
93 [11]. For 1 there are two crystallographically
independent molecules and one and a half molecules
of toluene of crystallization per asymmetric unity. All
the non-hydrogen atoms were refined with anisotropic
thermal motion parameters except those of the solvent,
which were severely disordered, and were refined with
positional restraints and so the corresponding hydrogen
atoms were neglected. In compound 1, the carbon atoms
was obtained (yieldꢂ73%). Analysis found (%): Yb,
/
21.24; C, 58.55; H, 7.54. Calculated for YbO5C40H66:
Yb, 21.63; C, 60.04; H, 8.33. IR (cmꢁ1): 3610w, 3140w,
2700w, 1570m, 1450s, 1400s, 1370s, 1355w, 1345w,
1335w, 1330w, 1310w, 1270s, 1250w, 1220w, 1200w,
1190m, 1160w, 1140w, 1130w, 1090m, 1030w, 1010m,
950w, 930w, 910w, 900w, 870w, 860s, 840s, 830s, 810w,
800w, 790w, 735s, 725w, 715w, 660w, 640m, 540w,
440w. 1H NMR (298 K; C7D8; d; ppm/TMS): 7.42 (4 H
m-H), 6.84 (2 H p-H), 3.80 {12 H CH2 (THF)}, 1.75 (36
H But), 1.36 {12 H CH2 (THF)}. X-ray quality crystals
of 2 were grown from a solution of the red solid in
acetonitrile at room temperature.
Table 1
Crystallographic data for complexes 1 and 2
1
2
Formula
C
40H66O5Eu×/0.75C7H8
C36H54N4O2Yb
747.87
Molecular weight
Crystal size (mm)
Crystal system
Space group
847.99
0.23ꢃ
triclinic
/0.18ꢃ/0.13
0.65ꢃ
monoclinic
/
0.23ꢃ0.16
/
¯
P1
/
P21/c
˚
a (A)
13.422(2)
18.864(3)
19.732(2)
111.76(1)
99.63(1)
92.28(1)
4546.3(11)
4
11.833(2)
17.691(1)
18.073(1)
˚
b (A)
˚
c (A)
a (8)
b (8)
g (8)
91.123(13)
2.2.2. Metal vapour synthesis
Europium atoms (1.50 g, 9.87 mmol) were vaporized
with a resistance heating furnace (432 W) and were co-
condensed with 2,6-di-tert-butylphenol (32 g, 15.51
mmol) onto a liquid nitrogen-cooled surface over a
period of 2 h. The resultant mixture was allowed to
warm slowly to room temperature under a nitrogen
atmosphere. The product was washed out with THF and
filtered through a Celite bed. Volatile components were
removed under vacuum to give a yellow solid formu-
lated as [Eu(OC6H3Bu2t -2,6)2(THF)3]. The characteriza-
tion of the europium compound gave similar results as
3
˚
V (A )
3782.6(7)
4
Z
Dcalc (g cmꢁ3
)
1.239
0.0988
1.313
0.0889
0.1658
5454
a
R1
b
wR2
0.2083
13069
Reflections
collected
Reflections
12615 (0.0623)
5259 (0.0662)
2965
independent (Rint
Reflections
)
6169
873
observed [Iꢀ/2s(I)]
Parameters varied
388
in (yieldꢂ42%).
/
The values were calculated for data with I ꢀ
/
2s(I).
a
The procedure for the reaction of ytterbium (1.74 g,
10.06 mmol) with 2,6-di-tert-butylphenol (35 g, 16.96
mmol) by MVS was identical to that for the europium
R1ꢂ
/
ajjFojꢁ
wR2ꢂ
[a(w(F2oꢁ
(F2oꢀ2F2c)/3.
/
jFcjj/ajFoj.
b
/
/
F2c)2)/a(w(F2o)2)]1/2
;
wꢂ
/
1/[s2(F2o)ꢀ
/
(aP)2ꢀ
bP],
/
where Pꢂ
/
/

J. Carretas et al. / Polyhedron 22 (2003) 1425Á
/1429
1427
Fig. 1. ORTEP diagram of 1, using 20% probability ellipsoids.
of one of the THF molecules (O11) show exceptionally
high displacement parameters. The contribution of the
hydrogen atoms were included in calculated positions.
Atomic scattering factors and anomalous dispersion
terms were taken as in Ref. [11]. The drawings were
made with ORTEP-3 [12] and all the calculations were
performed on a DECa 3000 computer.
but no crystal structures were reported. Only the crystal
structure of the complex [Eu(OC6H3But2-2,6)2(NCMe)4]
has been determined [16].
Crystallization of [Eu(OC6H3But2-2,6)2(THF)3] in the
presence of toluene at room temperature forms
[Eu(OC6H3But2-2,6)2(THF)3]×
/
0.75C7H8 1, whereas crys-
tallization of [Yb(OC6H3But2-2,6)2(THF)3] in the pre-
sence of acetonitrile at room temperature forms
[Yb(OC6H3But2-2,6)2(NCMe)4] 2.
The crystal structure of 1 consists of discrete mole-
cular units, with two independent but chemically
identical molecules per asymmetric unit. For both
molecules the coordination geometry around the euro-
3. Results and discussion
Metallic europium and ytterbium react with a solu-
tion of 2,6-di-tert-butylphenol in liquid ammonia to
produce, respectively, a yellow and a red solid, soluble in
tetrahydrofuran, dichloromethane and acetonitrile.
These compounds were formulated by elemental analy-
Table 2
˚
Selected bond lengths (A) and angles (8) for 1
sis as Ln(OC6H3But2-2,6)2(THF)3 (Lnꢂ
Eu, Yb). The
/
Bond lengths
Eu(1)ꢀ
Eu(1)ꢀ
Eu(1)ꢀ
Eu(1)ꢀ
Eu(1)ꢀ
/
O(1)
2.313(12) Eu(2)ꢀ
2.309(14) Eu(2)ꢀ
2.57(2)
Eu(2)ꢀ
2.530(14) Eu(2)ꢀ
2.564(12) Eu(2)ꢀ
/
O(3)
O(4)
2.302(12)
2.352(12)
2.579(13)
2.553(13)
2.53(2)
IR spectra were consistent with the presence of aryloxide
and tetrahydrofuran ligands. The 1H NMR spectrum of
the ytterbium compound confirmed the formulation
suggested. These reactions were also studied by the
MVS and gave similar results as above. These MVS
experiments involving europium and ytterbium con-
firmed the higher stability of the divalent state of these
elements, comparing to the analogous reaction with
samarium using the same synthetic method, where only
a trivalent samarium aryloxide was obtained [4].
/O(2)
/
/
O(11)
O(12)
O(13)
/
O(21)
O(22)
O(23)
/
/
/
/
Bond angles
O(1)ꢀEu(1)ꢀ
O(1)ꢀEu(1)ꢀ
O(1)ꢀEu(1)ꢀ
O(1)ꢀEu(1)ꢀ
O(2)ꢀEu(1)ꢀ
O(2)ꢀEu(1)ꢀ
O(2)ꢀEu(1)ꢀ
O(11)ꢀEu(1)ꢀ
O(11)ꢀEu(1)ꢀ
O(12)ꢀEu(1)ꢀ
Eu(1)ꢀ
Eu(1)ꢀ
/
/
O(2)
143.6(5)
91.1(5)
90.3(4)
106.4(5)
86.2(6)
91.2(5)
109.9(5)
177.2(6)
97.0(6)
84.9(5)
O(3)ꢀ
O(3)ꢀ
O(3)ꢀ
O(3)ꢀ
O(4)ꢀ
O(4)ꢀ
O(4)ꢀ
O(21)ꢀ
O(21)ꢀ
O(22)ꢀ
/
Eu(2)ꢀ
Eu(2)ꢀ
Eu(2)ꢀ
Eu(2)ꢀ
Eu(2)ꢀ
Eu(2)ꢀ
Eu(2)ꢀ
Eu(2)ꢀ
Eu(2)ꢀ
Eu(2)ꢀ
/
O(4)
146.2(5)
88.1(5)
91.3(5)
/
/
O(11)
O(12)
O(13)
O(11)
O(12)
O(13)
/
/
O(21)
O(22)
O(23)
O(21)
O(22)
O(23)
/
/
/
/
/
/
/
/
108.3(5)
86.3(4)
/
/
/
/
/
/
/
/
93.6(4)
Lnꢀ2C6H3But2-2; 6-OH
/
/
/
/
105.4(5)
178.8(5)
98.5(5)
/
/
O(12)
O(13)
O(13)
/
/
O(22)
O(23)
O(23)
NH3 or MVS [Ln(OC6H3But2-2; 6)2(THF)3]ꢀH2
The compounds [Eu(OC6H3But2-2,6)2(THF)3] [13] and
[Yb(OC6H3But2-2,6)2(THF)3] [13Á
synthesized by several authors using other methods,
/
/
/
/
/
/
/
/
82.7(5)
/
O(1)ꢀ
/
C(10)
C(20)
177.6(12) Eu(2)ꢀ
178.6(14) Eu(2)ꢀ
/
O(3)ꢀ
O(4)ꢀ
/
C(30)
176.3(13)
176.5(12)
/
15] were previously
/
O(2)ꢀ
/
/
/C(40)

1428
J. Carretas et al. / Polyhedron 22 (2003) 1425Á1429
/
Fig. 2. ORTEP diagram of 2, using 20% probability ellipsoids.
pium atom is best described as distorted trigonal-
bipyramidal, with two aryloxide groups and one THF
molecule in the equatorial plane and two THF mole-
cules in the axial positions. The ORTEP diagram for one
of the molecules can be seen in Fig. 1. Selected bond
distances and angles for the molecule 1 and 2 are given
in Table 2.
2,6)2(NCMe)4] can be seen in Fig. 2. Selected bond
distances and angles are given in Table 3. The Ybꢀ
bond lengths for the aryloxide groups are 2.204(12) and
/O
˚
2.245(10) A, which are comparable with analogue values
in the complex [Yb(OC6H2But2-2,6-Me-4)2(THF)3],
˚
2.217(12) and 2.196(18) A [17]. The average values of
the Ybꢀ
/
O bonds in the aryloxide groups and the Ybꢀ
/
N
˚
bonds, respectively, 2.22(2) and 2.61(2) A, can be
The distances Euꢀ
/
O to the aryloxide groups are for
˚
molecule 1, 2.313(12) and 2.309(14) A, and for molecule
compared with analogue values in the complex
[Eu(OC6H3But2-2,6)2(NCMe)4]: Euꢀ
˚
2.33(2) A and
˚
/
Oꢂ
/
2, 2.302(12) and 2.352(12) A, which are comparable to
analogue distances in the complex [Eu(OC6H3But2-
˚
Euꢀ
/
Nꢂ2.74(2) A [16]. The observed differences can be
/
explained considering the different ionic radius of Eu2ꢀ
˚
2,6)2(NCMe)4] [16], 2.313(12) and 2.35(2) A. Compar-
2ꢀ
˚
(1.17 A) and Yb
˚
(1.02 A) in complexes with a
ison can also be made with the Euꢀ
/
O bond distances in
the aryloxide groups of the complex [Eu(OC6H2But2-2,6-
coordination number of 6. The bond angle between
the two aryloxide groups is 108.2(4)8, which is compar-
˚
Me-4)2(THF)3].THF: 2.321(5) and 2.337(5) A [15]. The
average value for the Euꢀ
/
O distance to the THF groups,
˚
2.55(2) A for both molecules is also comparable with the
analogue average value in the latter complex: 2.559(5)
Table 3
˚
Selected bond lengths (A) and angles (8) for 2
˚
A. The bond angles between the two aryloxide groups
Bond lengths
are for molecule 1, 143.6(5)8 and for molecule 2,
146.2(5)8, which are comparable with the analogue
bond angle in the complex [Eu(OC6H2But2-2,6-Me-
4)2(THF)3].THF: 150.3(2)8 [15]. In this complex the
bond angle between the two THF molecules in axial
positions is 178.6(2)8, whereas for complex 1 the bond
angles are 177.2(6)8 and 178.8(5)8, respectively, for
molecule 1 and 2.
Ybꢀ
Ybꢀ
Ybꢀ
/
O(1)
O(2)
N(1)
2.204(12)
2.245(10)
2.62(2)
Ybꢀ
Ybꢀ
Ybꢀ
/
N(2)
N(3)
N(4)
2.52(2)
2.63(2)
2.66(2)
/
/
/
/
Bond angles
O(1)ꢀYbꢀ
O(1)ꢀYbꢀ
O(1)ꢀYbꢀ
O(1)ꢀYbꢀ
O(1)ꢀYbꢀ
O(2)ꢀYbꢀ
O(2)ꢀYbꢀ
O(2)ꢀYbꢀ
O(2)ꢀYbꢀ
N(1)ꢀYbꢀ
N(1)ꢀYbꢀ
/
/
O(2)
N(1)
N(2)
N(3)
N(4)
N(1)
N(2)
N(3)
N(4)
108.2(4)
158.0(5)
102.5(5)
101.9(5)
84.8(5)
93.7(5)
95.5(5)
101.6(5)
164.3(5)
76.9(5)
70.5(5)
N(1)ꢀ
N(2)ꢀ
N(2)ꢀ
N(3)ꢀ
YbꢀO(1)ꢀ
YbꢀO(2)ꢀ
YbꢀN(1)ꢀ
YbꢀN(2)ꢀ
YbꢀN(3)ꢀ
YbꢀN(4)ꢀ
/
Ybꢀ
Ybꢀ
Ybꢀ
Ybꢀ
/
N(4)
N(3)
N(4)
N(4)
74.1(6)
143.9(6)
72.5(5)
/
/
/
/
/
/
/
/
/
/
/
/
83.8(6)
/
/
/
/C(10)
175.7(11)
175.5(10)
/
/
/
/C(20)
The monomeric complex 2 has a distorted octahedral
geometry with one acetonitrile molecule and one aryl-
/
/
/
/
C(1)
C(2)
C(3)
C(4)
172(2)
/
/
/
/
173(2)
177(2)
174(2)
oxide ligand in axial positions {O(2)ꢀ
/
Ybꢀ
/
N(4):
/
/
/
/
164.3(5)8}. The equatorial plane is defined by an
aryloxide ligand and three acetonitrile molecules. The
ORTEP diagram for the complex [Yb(OC6H3But2-
/
/
N(2)
/
/
/
/
N(3)

J. Carretas et al. / Polyhedron 22 (2003) 1425Á
/1429
1429
[2] L.G. Hubert-Pfalzgraf, New J. Chem. 11 (1987) 663.
[3] I. Tsuneo, Lanthanides in Organic Synthesis, Academic Press,
able with the analogue bond angle 105.2(4)8 in the
complex [Eu(OC6H3Bu2t -2,6)2(NCMe)4] [16]. These two
complexes can be considered as isostructural.
London, 1994.
[4] J.M. Carretas, A. Pires de Matos, Mater. Chem. Phys. 31 (1992)
123.
[5] J.M. Carretas, J. Branco, J. Marcalo, J.C. Waerenborgh, N.
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Marques, A. Pires de Matos, J. Alloys Comp. 275Á
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/
277 (1998)
4. Conclusion
¸
The reactions of the europium and ytterbium metals
with 2,6-di-tert-butylphenol in liquid ammonia and by
the MVS technique proved to be convenient routes to
synthesize monomeric divalent aryloxides. The new
crystallographic structures 1 and 2 were determined.
Pires de Matos, J. Alloys Comp. 322Á324 (2001) 169.
/
[7] D.D. Perrin, W.L.F. Armarego, Purification of Laboratory
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387.
5. Supplementary material
Supplementary data are available from the Cam-
bridge Crystallographic Data Center, CCDC, 12 Union
Road, Cambridge CB2 1EZ, UK (fax: ꢀ44-1223-
336033; e-mail: deposit@ccdc:cam:ac:uk) on request,
quoting the deposition numbers 198682 for compound
1 and 198683 for compound 2.
/
[14] G.B. Deacon, C.M. Forsyth, R.H. Newham, Polyhedron 6 (1987)
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