2 Homometallic Alkoxides

408 Alkoxo and Aryloxo Derivatives of Metals
The compound [Ti16⊲ 4-O⊳4⊲ 3-O⊳8⊲ -O⊳4⊲ -OEt⊳16⊲OEt⊳16] was obtained in two
forms, I (stable in air, monoclinic) and II (sensitive to moisture, tetragonal) due to
different packings of the hexadecanuclear molecules in the crystals. The Ti16O48 core in
each form is built up of two orthogonal blocks of eight TiO6 octahedra. In each block six
octahedra form a layer structure (NiAs-type) with the seventh and eighth being on either
side (Fig. 5.8). The coordination around the 4-oxo atoms is unsymmetrical (Ti2O
angles, 94.4–150.3 Ž ) whilst some 3-O are pyramidal and others trigonal planar. 118
In the decanuclear molecule [Ti10⊲ 4-O⊳4⊲ 3-O⊳2⊲ -O⊳2⊲ -OEt⊳10⊲OEt⊳14] (Fig. 5.9)
it can be seen how three more octahedra have been attached to the Ti7O4⊲OEt⊳20
structure. 9
The hydrolysis of Ti⊲OCH2Ph⊳4⊲PhCH2OH⊳ gave rise to the crystalline octanuclear
compound [Ti8⊲ 3-O⊳4⊲ -O⊳2⊲ -OCH2Ph⊳8⊲OCH2Ph⊳12] (Fig. 5.10) 9 which contains
4 octahedral and 4 five-coordinated titanium atoms presumably due to the greater steric
effect of the benzyloxo ligand compared to the ethoxide. In solution there was 17 O
Figure 5.8 Ti16O48 core structure
of [Ti16⊲ 4-O⊳4⊲ 3-O⊳8⊲ -
O⊳4⊲ -OEt⊳16⊲OEt⊳16].
Figure 5.9 Ti10O32 core structure
of [Ti10⊲ 4-O⊳4⊲ 3-O⊳2⊲ -O⊳2⊲ -
OEt⊳10⊲OEt⊳14] (ž D Ti; Et groups
omitted).