2 Homometallic Alkoxides

X-Ray Crystal Structures of Alkoxo Metal Compounds 231
Figure 4.2 M2O10 core structure
of [M2( -OR)2(OR)8].
Figure 4.3 M3O12 core structure
of [M3( -OR)6(OR)6].
Figure 4.4 M4O16 core
structure of [M4( 3-
OR)2( -OR)4(OR)10].
Cotton et al. 11 found that face-sharing octahedra are involved in the mixed valency compound
[U2⊲ -OBu t ⊳3⊲OBu t ⊳6] in contrast to uranium pentaisopropoxide which has edgesharing
octahedra [U2⊲ -OPr i ⊳2⊲OPr i ⊳8]. The face-sharing bi-octahedral unit was also
found in [KU2⊲OBu t ⊳9], 11 [NaCe2⊲OBu t ⊳9], 12 [NaTh2⊲OBu t ⊳9] 13 and [KZr2⊲OBu t ⊳9]. 14
Another structural motif is present in the trinuclear species [La3⊲ 3-OBu t ⊳2⊲ -
OBu t ⊳3⊲OBu t ⊳4⊲Bu t OH⊳2] 6 and [Y3⊲ 3-Cl⊳⊲ 3-OBu t ⊳⊲ -OBu t ⊳3⊲OBu t ⊳4⊲thf⊳2] 15
(Fig. 4.5). The same framework is present in [W3⊲ 3-X⊳⊲ 3-OR⊳⊲ -OR⊳3⊲OR⊳6]
(where X D O or NH). 16