2 Homometallic Alkoxides

416 Alkoxo and Aryloxo Derivatives of Metals
Some vanadium(IV) oxo-alkoxides have also been studied. In ⊲PPh4⊳2[V2⊲O⊳2⊲ -
OR⊳2Cl4] (R D Me, Et) the vanadium atoms are in edge-shared square pyramids
with the oxo ligands occupying the apical sites. 136 The centrosymmetric
tetranuclear V(V) complex [V4⊲O⊳4⊲ -O⊳⊲ 3-OMe⊳2⊲OMe⊳2⊲bpy⊳2] has an interesting
structure involving edge-sharing octahedra (Fig. 5.14). 137 The two outer vanadiums
each have terminal VDO bonds, and a chelating bipy ligand and are
bonded by two -O ligands and one 3-OMe ligand to the central dimeric
V2⊲O⊳2⊲OMe⊳2⊲ -O⊳4⊲ 3-OMe⊳2 moiety. 137 In the vanadium(IV) tetranuclear anion
[V4⊲O⊳4f⊲ 3, , -OCH2⊳3CEtg2⊲ -O2SO2⊳2⊲H2O⊳2] 2 one type of V atom is bonded
terminally to an oxo ligand and an aqua ligand and bridged by a sulphato and three
oxygens from the organic (alkoxo) ligands. The other type is bonded terminally to an
oxo ligand and by bridging to a sulphato and four oxygens from the organic ligands.
All of the vanadiums are in distorted octahedral configurations. 60
A neutral mixed-valence complex [V4⊲O⊳4⊲ -O⊳2⊲ -OEt⊳2⊲OEt⊳4⊲phen⊳2] was
shown to involve two outer OV⊲OEt⊳2⊲ -O⊳ four-coordinated vanadium(V) moieties
bridged to a central dinuclear V2⊲O⊳2⊲ -OEt⊳2⊲phen⊳2⊲ -O⊳2 unit containing
octahedral V(IV) atoms. 138
Some structures of hexanuclear and decanuclear vanadium oxo-alkoxides have been
reported. The hexavanadate anion [V6O13f⊲OCH2⊳3CNO2g2] 2 has the 6-oxo centred
cubic V6O19 core with the two tridentate alkoxo ligands clamped on opposite faces of
the V6 octahedron. 56 In the vanadium(IV) complex [V6O7⊲OH⊳3f⊲OCH2⊳3CMeg3] 2
there are three symmetrically placed tridentate alkoxide ligands and in
[V6O7f⊲OCH2⊳3CEtg4] 2 there are four alkoxides completely replacing all twelve -
oxo atoms of the V6O19 core. 55 The [V6O7⊲OH⊳3f⊲OCH2⊳3CMeg3] anion contains
one V(V) andfiveV(IV) atoms whilst in [V6O6⊲ 3-F⊳⊲OH⊳3f⊲OCH2⊳3CMeg3] a 6oxo
ligand has been replaced by a 3-fluoride with consequent distortion of the
structure (Fig. 5.15). 55 The 3-fluoride also interacts significantly with the other
three vanadiums (V-F, 2.245 (6) ˚A and 2.522 (6) ˚A). In the V(V) complex anion
[V6⊲O⊳6⊲ 6-O⊳⊲ -O⊳5⊲ -OMe⊳7] the monodentate methoxide ligands occupy seven
of the twelve -oxo positions. 57
The tridentate alkoxo ligand ⊲OCH2⊳3CEt has also been attached to the decavanadate
core [V10O28] in the decanuclear V(IV) complexes [V10⊲O⊳8⊲ 6-O⊳2⊲ 3-O⊳2⊲ -
O⊳4f⊲OCH2⊳3CEtg4] 4 and [V10⊲O⊳8⊲ 6-O⊳2⊲ 3-O⊳⊲ -O⊳2f⊲OCH2⊳3CEtg5] . In
addition to the all V(IV) complex [V10⊲O⊳8⊲ 6-O⊳2⊲ 3-O⊳2⊲ -O⊳2⊲ -
OH⊳2f⊲OCH2⊳3C⊲CH2OH⊳g4] 2 the mixed valence complexes (VIVVV) [V10⊲O⊳8⊲ 6-
O⊳2⊲ 3-O⊳2⊲ -O⊳4f⊲OCH2⊳3CRg4] 2 (R D Me, Et) have also been characterized. 54
Figure 5.14 Structure of [V4⊲O⊳4⊲ -
O⊳4⊲ 3-OMe⊳2⊲OMe⊳2⊲bpy⊳2] (ž D
V; H atoms omitted).