Chemistry Reference
In-Depth Information
Figure 5.6
Structure of [Gd
6
4
-
O
3
,
2
-OR
4
,
2
-OR
6
-
OR
2
O
R
4
](RD C
2
H
4
OMe;
ž
D
4
-oxo, D O, D Gd; H atoms
omitted).
molecule (Fig. 5.6) is composed of a central Gd
4
4
-O
OC
2
H
4
OMe
10
tetra-
hedron containing 2 seven-coordinate and 2 eight-coordinate gadoliniums with two
edges
capped
by
Gd
OC
2
H
4
OMe
3
units
containing
eight-coordinated
Gd.
The
methoxyethoxo ligands exhibit four different modes of bonding.
The cerium(
IV
) isopropoxide [Ce
2
-OPr
i
2
OPr
i
6
Pr
i
OH
] underwent photoreduc-
iontotheCe(
III
)Ce
3
(
IV
) tetranuclear oxo-isopropoxide [Ce
4
4
-O
3
-OPr
i
2
-
OPr
i
4
OPr
i
7
Pr
i
OH
] which has a “butterfly” structure
42
whereas thermal desolva-
tion gave the Ce(
IV
) complex [Ce
4
4
-O
3
-OPr
i
2
-OPr
i
4
OPr
i
8
] which has a
flattened tetrahedral Ce
4
O core with 2 six-coordinated and 2 seven-coordinated cerium
atoms.
67
Treatment of [Pr
5
5
-O
OPr
i
13
] with 2-methoxyethanol in the presence of Me
3
PO
gave rise to the octanuclear species [Pr
8
4
-O
4
3
-OC
2
H
4
OMe
4
-
OC
2
H
4
OMe
10
OC
2
H
4
OMe
2
OPMe
3
2
]. In this centrosymmetrical molecule all of the
metal atoms are eight-coordinated, 2 of the
4
-oxo atoms are tetrahedrally coordinated
and the other 2 are in an irregular four-coordination.
63
Another interesting pentanuclear heterometallic oxo-alkoxide is [Sm
4
Ti
5
-O
3
-
OPr
i
2
-OPr
i
6
OPr
i
6
]inwhichthe
5
-oxo ligand is encapsulated in a trigonal
bipyramid of metal atoms with Ti an equatorial position.
113
The giant molecule
[Li
8
Y
8
4
-O
2
3
-OBu
t
4
-OBu
t
12
-Cl
4
OBu
t
8
] is composed of two outer
[Y
4
4
-O
3
-OBu
t
2
-OBu
t
4
-Cl
2
OBu
t
4
]
2
anions joined by chloride bridges
to a central [Li
6
3
-OBu
t
4
]
2C
unit with two additional lithium ions in the lattice. The
yttriums are all six-coordinated and the lithiums two- and three-coordinated.
114
It is
fascinating to see covalently bonded lithium chloride built into this structure. Since
the Y
4
unit has a “butterfly” configuration the
4
-oxo ligand is linearly bonded to the
wing-tip metals and makes an angle of 96
.
5
Ž
with the backbone metals.
In the mixed ligand octanuclear heterometallic compound [Gd
2
Zr
6
4
-O
2
-
OPr
i
10
-OAc
6
OPr
i
10
] the molecule may be viewed as two halves [GdZr
3
4
-O
-
OPr
i
5
-OAc
2
OPr
i
5
] joined by two acetate bridges at the Gd atoms. The
configuration at the
4
-oxo ligand is like a trigonal pyramid with Gd at the apex; the
zirconiums are six-coordinated and the gadoliniums seven-coordinated.
115
