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Synthesis and Structural Characterization of Several Ytterbium Bis(trimethylsilyl)amides Including Base-free [Yb{N(SiMe
3
)
2
}
2
(µ-Cl)]
2
Figure 1 Molecular structure of 1a, showing thermal ellipsoids (at
the 30 % probability level) and the numbering scheme. Hydrogen
atoms have been omitted for clarity. Atoms marked by primes are
generated by the symmetry operation 22x,12y, 2z.
Selected bond lengths/pm and angles/°:Yb2Cl 268.37(11), Yb2Cl9
268.20(11), Yb2N(1) 217.5(3), Yb2N(2) 219.5(3), Yb2O(51) 235.3(3), av.
Si2N 172.9, av. Si2C 187.8, Cl2Yb2Cl9 74.79(4), Yb2Cl2Yb9 105.21(4),
N(1)2Yb2N(2) 115.74(13), Si(1)2N(1)2Si(2), 119.4(2), Si(3)2N(2)2Si(4)
119.2(2), Si(1)2N(1)2Yb 122.7(2), Si(2)2N(1)2Yb 117.8(2),
Si(3)2N(2)2Yb 122.9(2), Si(4)2N(2)2Yb 117.8(2), N(1)2Yb2O(51)
108.22(12), N(2)2Yb2O(51) 86.96(12), N(1)2Yb2Cl9 94.90(10),
N(2)2Yb2Cl9 100.24(9), O(51)2Yb2Cl9 149.99(8), N(1)2Yb2Cl
111.29(9), N(2)2Yb2Cl 132.97(10), O(51)2Yb2Cl 79.03(8).
(7412760 cm
21
) are found in some µ-η
2
:η
2
-peroxo copper
complexes which are of great interest as model compounds
for certain copper containing enzymes [22].
Solid-State Structures
The compounds 125 have been characterized by X-ray cry-
stallography. Oddly, complex 1 could be crystallized in two
different monoclinic forms, designated as compound 1a
(β 5 114.1°) and 1b (β 5 91.4°). The former is identical to
the modification described earlier by Bradley and co-wor-
kers [4]. However, their dataset was obtained at room tem-
perature, which results in significantly larger standard devi-
ations. Crystals of 1a and 1b can be distinguished by their
different habitus. 1b crystallizes in yellow rods, whereas 1a
forms well-shaped yellow prisms. The molecular structures
of both compounds revealed differences of up to ca. 2pm
(Yb2Cl) and ca. 5° (Cl2Yb2N) in corresponding bond
distances and angles. Curiously, the slightly more dense
form 1b features a disordered coordinated thf molecule,
which is strictly ordered in the less dense modification 1a.
The following discussion is restricted to the more accurate
structure determination of the latter.
Compound 1a crystallizes as a centrosymmetric dimer,
and its molecular structure is shown in Figure 1. The dime-
ric units are associated through bridging chlorine atoms. In
addition, each Yb atom is bonded to the N atoms of two
terminal amido ligands and the O atom of a thf molecule.
Z. Anorg. Allg. Chem. 2002, 628, 6472657 649
Figure 2 Molecular structure of 2, showing thermal ellipsoids (at
the 30 % probability level) and the numbering scheme. Hydrogen
atoms and minor parts of the disordered thf ligand have been omit-
ted for clarity.
Selected bond lengths/pm: Yb(1)2Cl(3) 265.4(3), Yb(1)2Cl(1) 266.6(3),
Yb(1)2Cl(4) 286.4(3), Yb(2)2Cl(1) 268.2(3), Yb(2)2Cl(2) 270.1(3),
Yb(2)2Cl(4) 283.1(3), Yb(3)2Cl(2) 266.3(3), Yb(3)2Cl(3) 267.2(3),
Yb(3)2Cl(4) 294.2(3), Yb(1)2N(1) 218.0(9), Yb(2)2N(2) 216.5(10),
Yb(3)2N(3) 218.3(11), Yb(1)2O(1) 219.6(9), Yb(2)2O(1) 221.7(8),
Yb(3)2O(1) 218.3(9), Yb(1)2O(71) 229.2(8), Yb(2)2O(81) 230.8(8),
Yb(3)2O(91) 230.5(9), av. Si2N 172.5, av. Si2C 186.8.
The coordination sphere of the metal atom can be described
as a very distorted trigonal bipyramid where the equatorial
plane is defined by N1, N2 and Cl. Nevertheless, the equa-
torial and axial ytterbium-chlorine distances of 268.4(1) pm
(Yb2Cl) and 268.2(1) pm (Yb2Cl9) are practically identi-
cal. The axial Cl92Yb2O51 angle is 149.99(8)° and the in-
terligand angles between the equatorial (111.29(9)2
133.0(1)°) and axial/equatorial (79.03(8)2108.2(1)°) groups
vary considerably. With 235.3(3) pm the Yb2O51 bond
length is in the upper range of known Yb2O(thf) distances
[23], which feature a five-coordinate metal atom. The relati-
vely long value may be rationalized by the trans influence
of the stronger chlorine ligand.
The solid-state structure of the trinuclear cluster 2 is
shown in Figure 2. Each Yb atoms is octahedrally sur-
rounded by the nitrogen atom of a terminal bis(trimethylsi-
lyl)amido group, the oxygen atom of a terminal thf ligand,
two µ
2
-bridging chlorine atoms and one µ
3
-coordinate chlo-
rine (Cl4) and oxygen (O1) atom, respectively. Three di-
storted YbCl
3
NO
2
octahedra are connected by sharing two
adjacent faces and one edge (O12Cl4) in such a way that
the amido ligands point to one side and the thf ligands
point to the other side of the Yb
3
Cl
3
six-membered ring.
The central Yb
3
Cl
4
O
4
N
3
unit resembles the structural motif
which is found in the solid-state structures of Cs
11
O
3
[24]