2 Homometallic Alkoxides

X-Ray Crystal Structures of Alkoxo Metal Compounds 259
Figure 4.26 Structure of [La4( -
OCH2Bu t )8(OCH2Bu t )4 ( D La;
D O; H atoms and CH3 groups
omitted).
Figure 4.27 Structure of
[La⊲hftb⊳3⊲thf⊳3] ⊲hftb D
OCCH3⊲CF3⊳2; D O; H
and F atoms omitted).
Ce(IV) organometallic alkoxide was the mononuclear tris-cyclopentadienyl cerium
tert-butoxide [⊲C5H5⊳3Ce⊲OBu t ⊳] which has a pseudo-tetrahedral configuration (data
in Table 4.7). 119 The first homoleptic alkoxo cerium(III) compound characterized
structurally was the dimeric [Ce2⊲ -OCHBu t 2 ⊳2⊲OCHBu t 2 ⊳4] obtained by thermolysis
of the monomeric [Ce(OCBu t 3 ⊳3]. 120 The dimer exhibits the familiar pseudotetrahedral
structure (Fig. 4.1). The remarkable mixed ligand Ce(IV) complex
[Ce(OBu t ⊳2⊲NO3⊳2⊲Bu t OH⊳2] has bidentate nitrato ligands giving a formal eightcoordination
configuration to the cerium (Fig. 4.28). 121 The coordinated Bu t OH
ligands are clearly distinguishable from the Ce–OBu t groups by their longer
Ce–O bond lengths (av. 2.525 ˚A vs av. 2.025 ˚A) and more acute Ce � OC angles
(av. 138.2 Ž vs av. 169.5 Ž ). The dimeric [Ce2⊲ -OPr i ⊳2⊲OPr i ⊳6⊲Pr i OH⊳2] has the
expected structure based on the familiar edge-sharing bi-octahedral configuration
(Fig. 4.2). 122 The coordinated Pr i OH ligands were identified by longer Ce–O bonds