2 Homometallic Alkoxides

Figure 5.13 Structure of [Ti18⊲ 4-
O⊳4⊲ 3-O⊳20⊲ -O⊳4H⊲OBu t ⊳17]( D
Ti; H atoms omitted).
Metal Oxo-alkoxides 411
The 5 capping five-coordinated titaniums adopt distorted trigonal bipyramidal (TBP)
configurations.
The structures of some heterometallic titanium-containing molecules have been
reported. In the tetranuclear compound [Ti2Pb2⊲ 4-O⊳⊲ 3-OPr i ⊳2⊲ -OPr i ⊳4⊲OPr i ⊳4] the
4-oxo ligand has an irregular configuration (Ti � OTi, 163 Ž ; Pb � OPb, 99.6 Ž ; Pb � OTi,
95.0 Ž and 95.4 Ž ), the titaniums are octahedrally coordinated and the lead atoms fivecoordinated
(distorted square pyramidal with the vacant octahedral site occupied by a
lone electron pair). 18
The presence of -acetato ligands in [Ti2Pb2⊲ 4-O⊳⊲ -OPr i ⊳5⊲ -OAc⊳2⊲OPr i ⊳3]
generates a different structure with one lead atom four-coordinated and the
other five-coordinated together with distorted octahedral titaniums. 121 In the
novel complex [TiPb4⊲ 4-O⊳⊲ 3-NBu t ⊳3⊲OPr i ⊳4] the oxo ligand in the cubanelike
Pb4⊲ 3-O⊳⊲ 3-NBu t ⊳3 unit coordinates to a TBP titanium through an axial
position. 122
In the methoxo titanotungstate anion [⊲MeO⊳TiW5O18] 3 the M6O19 framework is
retained with a central 6-oxo, twelve -oxo and five terminal oxo ligands with the
methoxo ligand bound terminally to the titanium atom. 81
5.4.2 Zirconium
The first zirconium oxo-alkoxide structure reported was the tridecanuclear
[Zr13⊲ 4-O⊳8⊲ -OMe⊳24⊲OMe⊳12] which contains a central eight-coordinated (almost
cubic) zirconium connected by 4-oxo ligands to 12 seven-coordinated metals
which are linked by bridging methoxo groups. Each of the exterior zirconiums
is bonded to a terminal methoxo ligand. 123 Recently the trinuclear compounds
[Zr3⊲ 3-O⊳⊲ 3-Cl⊳⊲ -OCH2Bu t ⊳3⊲OCH2Bu t ⊳6] and [Zr3⊲ 3-O⊳⊲ 3-OBu t ⊳⊲ -OH⊳