2 Homometallic Alkoxides

X-Ray Crystal Structures of Alkoxo Metal Compounds 357
The trinuclear [ClCufZr2⊲OPr i ⊳9g]hasthe[CuZr⊲ 3-OPr i ⊳2⊲ -OPr i ⊳3] core similar to
the analogous titanium complex. 512 The homoleptic Cu(I)Zr(IV) complex has a different
structure [Cu2Zr2⊲OPr i ⊳10] containing the confacial bi-octahedral Zr2⊲OPr i ⊳9 unit into
which the Cu2⊲ -OPr i ⊳ group is inserted by the copper atoms bridging with terminal
isopropoxo ligands on each Zr. The ( -OPr i )Cu( -OPr i ) system has a linear O–Cu–O
arrangement. 512
The centrosymmetric dimer [fCd[Zr2⊲OPr i ⊳9]⊲ -Cl⊳g2] is interesting compared to
the monomeric [ClCufZr2⊲OPr i ⊳9g] because the bridging chlorides give the Cd
atoms a distorted octahedral configuration. 513 Interestingly in the dimeric complexes
[fM2⊲OPr i ⊳9gSn⊲ -Cl⊳]2 (M D Zr, Hf) the M2⊲OPr i ⊳9 moieties act as bidentate bridging
ligands towards the Sn(II) atoms, which are joined by an unsymmetrical ⊲ -Cl⊳2
bridge. 522 On the other hand in the dimeric [fZr2⊲OPr i ⊳9gSn⊲ -I⊳]2 the Zr2⊲OPr i ⊳9 unit
acts as a tridentate ligand towards the Sn(II) atom which is thus five-coordinated. 525
The Zr2⊲OPr i ⊳9 unit is also present in the centrosymmetric hexanuclear complex
[fZr2⊲OPr i ⊳9gPb⊲ -OPr i ⊳2PbfZr2⊲OPr i ⊳9g] in which the Pb(II) atoms are 4-coordinated
or pseudo-trigonal bipyramidal, assuming the presence of the lone pair of electrons occupying
the vacant equatorial site. 514 The centrosymmetric [⊲Pr i O⊳3Zr⊲ -OPr i ⊳3Pb⊲ -
OPr i ⊳Pb⊲ -OPr i ⊳2Pb⊲ -OPr i ⊳Pb⊲ -OPr i ⊳3Zr⊲OPr i ⊳3] has a zig-zag chain structure with
two pyramidal three-coordinated Pb(II) atoms and two pseudo-trigonal bipyramidal fivecoordinated.
514
The trinuclear [Tl⊲ -hfip⊳3Zr⊲ -hfip⊳3Tl] ⊲hfip D OCH⊲CF3⊳2⊳ is also centrosymmetric
with octahedral Zr and three-coordinated Tl(I) which also have six Tl....F
contacts. 515
3.4.3 Hafnium
The hafnium cadmium complex [ICdfHf2⊲OPr i ⊳9g] has a similar trinuclear structure to that
of the previously described titanium cadmium analogue, 495 as does the hafnium copper(II)
complex [ClCufHf2⊲OPr i ⊳9g]. 200 The trinuclear [⊲Pr i O⊳2Hf⊲ -OPr i ⊳4fAl⊲OPr i ⊳2g2]hasa
cis-octahedral Hf chelated by two bidentate bridging ⊲ -OPr i ⊳2Al⊲OPr i ⊳2 tetrahedra. 516
3.5 Vanadium Group Heterometallic Alkoxides
The trinuclear niobium(V) cadmium mixed ligand complex [⊲Pr i O⊳3Nb⊲ -OPr i ⊳2⊲ , 2 -
O2CMe⊳Cd⊲ -OPr i ⊳2⊲ , 2 -O2CMe⊳Nb⊲OPr i ⊳3] has a central six-coordinated (trigonal
prismatic) Cd atom which is bridged to two -OPr i ligands and one bridging ( 2 )
acetate to each octahedral Nb atom (Table 4.21, pp. 362–363). 517 Other heterometallic
alkoxides involving niobium or tantalum have been dealt with in earlier sections.
3.6 Chromium Group Heterometallic Alkoxides
In the tetranuclear homoleptic dimeric complex [⊲Bu t O⊳Sn⊲ -OBu t ⊳2Cr⊲ -OBu t ⊳]2
the inner Cr(II) atoms are four-coordinated and the outer Sn(II) atoms are threecoordinated
(pyramidal) (Table 4.21). 523 In the mixed ligand tetranuclear complex