Two new benzoate-di(methylcyclopentadienyl)ytterbium(III) complexes: [Yb(MeCp)2(O2CC6F5)]2 and [Yb(MeCp)2(O2C-o-HC6F 4)]2

Article abstract of DOI:10.1002/zaac.200390098

Transparent orange crystals of [Yb(MeCp)₂(O₂CC₆F₅)]₂ and [Yb(MeCp)₂(O₂C-o-HC₆F ₄)]₂ were obtained by oxidation of Yb(MeCp)₂ with M(O₂CR) (M = 1/2 Hg, T1; R = C₆F₅, o-HC₆F₄) in tetrahydrofuran. They have a dimeric structure with bridging bidentate (O,O')-benzoate groups and eight coordinated ytterbium. Both crystallise isotypic in the orthorhombic space group Pbca. Room temperature as well as low temperature single crystal X-ray investigations show the o-H/F positions in [Yb(MeCp)₂(O₂C-o-HC₆F ₄)]₂ not to be ordered.

Full text of DOI:10.1002/zaac.200390098

Two New Benzoate-di(methylcyclopentadienyl)ytterbium(III) Complexes:
[Yb(MeCp)2(O2CC6F5)]2 and [Yb(MeCp)2(O2C-o-HC6F4)]2
Glen B. Deacona, Catharina C. Quitmanna,b, Klaus Müller-Buschbaumb, Gerd Meyerb*
a Clayton/Australia, School of Chemistry, Monash University
b Köln, Institut für Anorganische Chemie, Universität zu Köln
Received December 18th, 2002.
Abstract. Transparent orange crystals of [Yb(MeCp)2(O2CC6F5)]2
and [Yb(MeCp)2(O2C-o-HC6F4)]2 were obtained by oxidation of
Yb(MeCp)2 with M(O2CR) (M ϭ 1/2 Hg, Tl; R ϭ C6F5, o-HC6F4)
in tetrahydrofuran. They have a dimeric structure with bridging
bidentate (O,O’)-benzoate groups and eight coordinated ytterbium.
Both crystallise isotypic in the orthorhombic space group Pbca.
Room temperature as well as low temperature single crystal X-ray
investigations show the o-H/F positions in [Yb(MeCp)2(O2C-o-
HC6F4)]2 not to be ordered.
Keywords: Lanthanides; Benzoate; Crystal structure; Ytterbium;
Methylcyclopentadienyl
Carboxylatobis(cyclopentadienyl)lanthanide(III) complexes display
a considerable variety in carboxylate coordination ranging from
O,O’-chelation (η2) in monomeric complexes [1Ϫ3] to bridging tri-
dentate (µ3-η2(O,O), η1(O’)) [4, 5] and bridging bidentate (µ-
η1(O),η1(O’)) [4, 6, 7] in dimeric complexes. The nature of the re-
spective type of coordination seems to be mostly dependant on the
steric demand of the carboxylate group. The previously reported
structures of [Yb(MeCp)2(O2CPh)]2 with the unsubstituted benzo-
ate [8] and the substituted [Yb(Cp)2(O2CC6F5)]2 [6] showed them
to be dimeric with bridging bidentate groups. In
[Yb(Cp)2(O2CC6F5)]2 the ortho-fluorine atoms of the carboxylate
groups show close non-bonding contacts with ring carbon atoms
of one cyclopentadienyl group, that could be minimized by an in-
creased dihedral angle between the planes of the pentafluorophenyl
groups and the plane formed by the ytterbium and oxygen atoms.
From this it was of interest to investigate the coordination behav-
iour of the substituted benzoates [Yb(MeCp)2(O2CR)]2 (R ϭ C6F5,
o-HC6F4) to determine the degree of substitution of a benzoate
ligand needed to obtain a monomeric structure as well as to elimin-
ate disorder problems observed for [Yb(MeCp)2(O2CPh)]2 by sub-
stitution with fluorine atoms.
improve the crystal quality of both complexes the crystals and their
mother liquor were sealed in ampoules under vacuum and heated
to 50 °C for of three months (Yields: (1) 0.34 g (72%);(2) 0.17
g (64%)).
thf
ᎏ
n[(MeCp)2Yb(THF)]ϩM(O2CR)n Ǟ n[(MeCp) Yb(O CR)]ϩM
2
2
(M ϭ Hg, n ϭ 2, R ϭ o-HC6F4; M ϭ Tl, n ϭ 1, R ϭ C6F5)
The data collections for the single crystal X-ray structure determi-
nations were carried out on a IPDS-II diffractometer (STOE).
Crystallographic data for C38H28O4F10Yb2: orthorhombic, Pbca,
Z ϭ 8, T ϭ 173(2) K, a ϭ 1293.2(3), b ϭ 2340.3(5) c ϭ 2305.8(5)
pm, µ ϭ 5.422 cm-1, MoKα, 3.48 Յ 2θ Յ 50.68°, -27 Յ h Յ 27,
-15 Յ k Յ 15, -27 Յ l Յ 27, F(000) ϭ 4144, R1 ϭ 0.0613 for 3350
reflections [I>2sigma(I)], R1 ϭ 0.1104 and wR2 ϭ 0.1579 for all
6194 unique reflections, GOOF on F2 ϭ 0.880. Structure resolu-
tion: SHELXS-86 [10], structure refinement: SHELXL-97 [11].
IR (Nujol): 3075 w (ν(CH) MeCp), 1651 s and 1626 s (νas(CO2)),
1423 vs (νs(CO2)), 1236 m (ν(CC)), 1001 m (β(CH) MeCp), 772 s
(γ(CH) MeCp), 744 s (ring def.) cm-1.
UV/VIS/near IR (thf/dme): λmax (E) 980(8) nm.
Crystallographic data for C38H30O4F8Yb2: orthorhombic, Pbca,
Z ϭ 8, T ϭ 173(2) K, a ϭ 1280.72(13), b ϭ 2343.47(9), c ϭ
2327.94(9) pm, µ ϭ 5.404 cm-1, MoKα, 3.90° Յ 2θ Յ 50.68°, -14
Experimental
[Yb(MeCp)2(O2CC6F5)]2 (1) and [Yb(MeCp)2(O2C-o-HC6F4)]2 (2):
Under an argon atmosphere Yb(MeCp)2 ((1): 0.36 g, 0.89 mmol;
(2): 0.2 g, 0.5 mmol) and M(O2CR) (M ϭ ‰ Hg, Tl; R ϭ C6F5,
o-HC6F4; (1):0.28 g, 0.45 mmol; (2): 0.2 g, 0.5 mmol) were reacted
in tetrahydrofuran (20 ml) to give an orange solution and a precipi-
tate of thallium/mercury, which was removed by filtration. Small
air-sensitive orange plates of 1 and 2 were obtained from a mixture
of dme/thf ((1): 4:1; (2): 3:1) by cooling ((1): 6-8 h; (2): 2 days). To
Յ h Յ 14, -25 Յ k Յ 24, -26 Յ l Յ 26, F(000) ϭ 4000, R1
ϭ
0.0616 for 1900 reflections [I>2sigma(I)], R1 ϭ 0.1833 and wR2 ϭ
0.1233 for all 5242 unique reflections, GOOF on F2 ϭ 0.766. Struc-
ture resolution: SHELXS-86 [10], structure refinement: SHELXL-
97 [11].
IR (Nujol): 3070 w (ν(CH) MeCp), 1622 vs and 1593 vs (νas(CO2)),
1405 m (νs(CO2)), 1260 m (ν(CC)), 1037 m (β(CH) MeCp), 756 s
(γ(CH) MeCp), 722 m (ring def.) cm-1.
UV/VIS/near IR (thf/dme): λmax (E) 982(13) nm.
* Prof. Dr. G. Meyer
Institut für Anorganische Chemie
Universität zu Köln
Results and Discussion
Greinstraße 6
[Yb(MeCp)2(O2CC6F5)]2 (1) and [Yb(MeCp)2(O2C-o-HC6F4)]2 (2)
are isotypic and crystallise in the orthorhombic crystal system in
the space group Pbca with two crystallographically independent
D-50939 Köln
Fax: 0221 4705083
E-mail: gerd.meyer@uni-koeln.de
Z. Anorg. Allg. Chem. 2003, 629, 589Ϫ591  2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 0044Ϫ2313/03/629/589Ϫ591 $ 20.00ϩ.50/0
589

G. B. Deacon, C. C. Quitmann, K. Müller-Buschbaum, G. Meyer
Fig. 2 Twist angles between planes made up of the polyfluorophe-
nyl groups and the Yb2O2 plane in (2).
Fig. 1 The dimeric molecule of [Yb(MeCp)2(O2CC6F5)]2 1. The
thermal ellipsoids are scaled to a probability density of 30%. Selec-
ted distances/pm and angles/°:
Yb1-O1 222(1), Yb1-O2 220(1), Yb2-O3 221(1), Yb2-O4 220(1), O1-C1
122(2), O2-C1 124(2), O3-C8 123(2), O4-C8 124(2); O2-Yb1-O3 97(1), O4-
Yb2-O1 92(1), C1-O1-Yb2 175(1), C1-O2-Yb1 146(1), C8-O3-Yb1 167(1),
C8-O4-Yb2 152(1), O4-C8-O3 124(1), O1-C1-O2 124(1), O2-Yb1-(centroid
C27-C31) 104, O2-Yb1-(C33-C37) 107, O3-Yb1-(C27-C31) 107, O3-Yb1-
(C33-C37) 105, O1-Yb2-(centroid C15-C19) 107, O1-Yb2-(C21-C25) 108,
O4-Yb2-(C15-C19) 104, O4-Yb2-(C21-C25) 106, (C21-C25)-Yb2-(C15-C19)
132.
In the isotypic dimeric molecule of [Yb(MeCp)2(O2C-o-HC6F4)]2
2, the ortho positions of the (O2C-o-HC6F4) ligands are half-occu-
pied by F and H. Selected distances/pm and angles/°:
Yb1-O1 219(2), Yb1-O2 212(2), Yb2-O3 223(2), Yb2-O4 216(2), O1-C25
128(2), O2-C32 124(2), O3-C32 128(2), O4-C25 122(2); O2-Yb1-O1 93(5),
O4-Yb2-O3 97(5), C32-O2-Yb1 171(2), C32-O3-Yb2 145(2), C25-O1-Yb1
150(2), C25-O4-Yb2 165(2), O4-C25-O1 127(2), O2-C32-O3 127(2), O1-Yb1-
(centroid C1-C5) 105, O1-Yb1-(C7-C11) 110, O2-Yb1-(C1-C5) 105, O2-
Yb1-(C7-C11) 105, O3-Yb2-(centroid C13-C17) 105, O3-Yb2-(C19-C23)
106, O4-Yb2-(C13-C17) 105, O4-Yb2-(C19-C23) 107, (C13-C17)-Yb2-(C19-
C23) 132.
Yb positions. The structures consist of dimeric molecules. The co-
ordination spheres of both ytterbium atoms consist of two (η5-
MeCp) and two (µ-O2CR) (R ϭ C6F5, o-HC6F4) ligands giving a
coordination number of eight (Fig. 1). This is similar to the struc-
tures of [YbCp2(O2CC6F5)]2 [6] and [Yb(MeCp)2(O2CPh)]2 [8]. Evi-
dently the steric demand of the methyl group on the cyclopen-
tadienyl ligand does not suffice to cause the formation of mono-
meric carboxylates with these substituting arrangements in the ben-
zoates. The bridging carboxylate groups (µ-O2CR) (R ϭ C6F5, o-
HC6F4) are twisted, resulting in a considerable dihedral angle be-
tween the planes of one of the polyfluorophenyl groups and the
Yb2O2 plane, as opposed to the unsubstituted benzoate groups of
[Yb(MeCp)2(O2CPh)]2 that lie in the Yb2O2 plane. This distortion
constitutes the essential difference between the two molecular
structures 1 and 2 and other comparable benzoates [6, 8]. The re-
sulting mean angle between the carboxylate groups amounts to 35°
in 1 and 32° in 2. It is made up from the two different angles that
the two carboxylate groups form with the Yb2O2 plane. In both
complexes the twist of one of the ligands is substantially bigger
than that of the opposed ligand, 28° and 7° in 1 and 26° and 6° in
2 (Fig. 2). Thus they are in good accordance with [YbCp2-
(O2CC6F5)]2 [6], whereas the unsubstituted benzoate [Yb(MeCp)2-
(O2CPh)]2 [8] shows almost no twisting of the phenyl rings. The Yb-
C distances average to 258 pm in 1 and 256 pm in 2. Subtraction of
Fig. 3 The crystal structure of [Yb(MeCp)2(O2CC6F5)]2 along
[001].
the ionic radius of eight co-ordinate Yb(III) [12] results in a radius
of the Cp anion of 162 pm corresponding to the value derived
from [YbCp2(O2CC6F5)]2 [6] and being in the usual range [9]. The
bonding of the benzoate ligands to the metal centres is unsym-
metrical (for distances and angles between atoms, see legend of
590
Z. Anorg. Allg. Chem. 2003, 629, 589Ϫ591

New Benzoate-di(methylcyclopentadienyl)ytterbium(III) Complexes
Fig. 1), the differences between corresponding C-O-Yb angles are
substantial (15-28°) but less than those (14-34°) found in
[YbCp2(O2CC6F5)]2 [6]. The methyl groups of the MeCp ligands
point in the direction opposite to the polyfluorophenyl groups.
[3] M. A. St. Clair, B. D. Santarsiero, Acta Crystallogr. 1989,
C45, 850.
[4] H. Schumann, K. Zietzke, R. Weimann, Eur. J. Solid State
Inorg. Chem. 1996, 32, 121.
[5] G. B. Deacon, G. D. Fallon, B. M. Gatehouse, A. Rabinovich,
B. W. Skelton, A. H. White, J. Organomet. Chem. 1995, 501,
23.
[6] G. B. Deacon, G. D. Fallon, P. I. MacKinnon, R. H. Newn-
ham, G. N. Pain, T. D. Tuong, D. L. Wilkinson, J. Organomet.
Chem. 1984, 277, C21.
[7] B. K. Campion, R. H. Heyn, T. D. Tilley, Inorg. Chem. 1990,
29, 4356.
[8] G. B. Deacon, C. C. Quitmann, K. Müller-Buschbaum, G.
Meyer, Z. Anorg. Allg. Chem. 2001, 627, 1431.
[9] K. N. Raymond, C. W. Eigenbrot, Jr., Acc. Chem. Res. 1981,
20, 4115.
Due to the long period of time the crystals were treated in the
mother liquor, crystals of 1 and 2 did not show the same disorder
problems for the methyl groups or even half dimers as observed
in [Yb(MeCp)2(O2CPh)]2 [8]. Independent from the temperature at
which the data collection for the crystal structure determination
was carried out the o-H/F of the (O2C-o-HC6F4) ligands are not
ordered in the crystal structure of 2. The crystal structure of 1
arranged in π-stacking pillars is shown in Fig. 3. It can be con-
cluded that a dimer is the most stable structure of Cp2-Yb-benzo-
ates and that either bulkier substitution or metals with smaller ionic
radii, e.g. Sc, are necessary in order to obtain a monomeric struc-
ture.
[10] G. M. Sheldrick, SHELXS-86, Program for the solution of
crystal structures, Göttingen 1986.
[11] G. M. Sheldrick, SHELXL-97, Program for the refinement of
crystal structures, Göttingen 1997.
We thank the Deutsche Forschungsgemeinschaft, the Studienstif-
tung des Deutschen Volkes and the Australian Research Council
for supporting this work.
[12] R. D. Shannon, Acta Crystallogr. 1976, A32, 751.
[13] Further information about the crystal structure determination
is deposited at the Cambridge data base and can be requested
by citing the names of the authors and the deposition number
CCDC-199472, 199473, 199474, for (1) and (2) and the room
temperature investigation of (2).
[1] H. Schumann, J. A. Meese-Marktscheffel, A. Dietrich, F. H.
Görlitz, J. Organomet. Chem. 1992, 430, 299.
[2] H. Schumann, K. Zietzke, F. Erbstein, R. Weimann, J. Or-
ganomet. Chem. 1996, 520, 265.
Z. Anorg. Allg. Chem. 2003, 629, 589Ϫ591
591