2 Homometallic Alkoxides

X-Ray Crystal Structures of Alkoxo Metal Compounds 353
other five-coordinated (distorted square pyramid) (Table 4.19, pp. 354–355). The yttrium
is chelated by two hfd ligands, and the copper(II) atoms are each chelated by one thd
ligand. 504 In the tetranuclear complex [YCu3⊲ 3, 2 -OC2H4OMe⊳2⊲ , 2 -OC2H4OMe⊳⊲ -
OC2H4OMe⊳2⊲thd⊳4] each metal is chelated by one thd ligand and the Y atom is eightcoordinated
and the Cu atoms five-coordinated (square pyramid). 504 Another tetranuclear
species [Y2Cu2⊲ 3, 2 -OC2H4OMe⊳2⊲ , 2 -OC2H4OMe⊳2⊲ -OC2H4OMe⊳2⊲hfd⊳4] has
2 eight-coordinated Y atoms which are each chelated by two hfd ligands, a 3, 2 -
OC2H4OMe ligand, a , 2 -OC2H4OMe ligand and a -OC2H4OMe ligand. The two
Cu atoms are five-coordinated (square pyramidal) in a centrosymmetrical molecule. 504
Yttrium titanium chloride isopropoxide [YTi2⊲ 3-OPr i ⊳2⊲ -OPr i ⊳3⊲OPr i ⊳4Cl2]hasan
isosceles triangle of octahedral metals with 3-OPr i ligands capping above and below
the YTi2 plane which is girdled by three -OPr i ligands in the plane. The Y atom has
two terminal chlorides and the Ti atoms each have two terminal isopropoxo ligands.
The YTi2O9Cl2 framework is related to the M3⊲ 3-OR⊳2⊲ -OR⊳3⊲OR⊳4L2 structures
(Figs 4.5 and 4.25). 493
Some novel yttrium organoaluminium complexes have been reported. In the trinuclear
complex [⊲thf⊳⊲Bu t O⊳Yf⊲ -OBu t ⊳⊲ -CH3⊳AlMe2g2]theYatomiscis-octahedrally
coordinated and the aluminiums are four-coordinated (distorted tetrahedral). 505 In the
tetranuclear [Yf⊲ -OBu t ⊳⊲ -CH3⊳AlMe2g3] the yttrium is tris-chelated by the bridging
⊲ -OBu t ⊳⊲ -CH3⊳AlMe2 ligands in the facial configuration. A related complex is the
trinuclear organo-yttrium compound [⊲C5H4SiMe3⊳Yf⊲ -OBu t ⊳⊲ -CH3⊳AlMe2g2]. 506
3.3.2 Lanthanides
The tetranuclear [Laf⊲OC2H4⊳3Ng2fNb⊲OPr i ⊳4g3] contains eight-coordinated (bicapped
trigonal antiprism) La and distorted octahedral niobium (Fig. 4.62). 506 A homoleptic trinuclear
lanthanum niobium complex [⊲Pr i O⊳3Nb⊲ -OPr i ⊳3La⊲OPr i ⊳⊲ -OPr i ⊳2Nb⊲OPr i ⊳4]
has also been established. The distorted octahedral La is triple-bridged to one Nb and
double-bridged to the other, generating a bent ⊲136.2 Ž ⊳ Nb�LaNb axis. 497
In the centrosymmetrical hexanuclear complex [f⊲Pr i O⊳2Al⊲ -OPr i ⊳2g2Pr⊲Pr i OH⊳⊲ -
Cl⊳2Pr⊲Pr i OH⊳f⊲ -OPr i ⊳2Al⊲OPr i ⊳2g2] the praseodymium is seven-coordinated (distorted
capped trigonal prism) and the aluminiums are in typical distorted tetrahedral coordination.
507 The trinuclear [Ge⊲ -OBu t ⊳3Eu⊲ -OBu t ⊳3Ge] contains six-coordinated Eu(II)
and three-coordinated Ge(II). 487
3.4 Titanium Group Heterometallic Alkoxides
In addition to the previously mentioned heterometallic species formed by alkali metal,
alkaline earth, or yttrium and lanthanide ions with titanium, zirconium, or hafnium, a
number of other heterometallic complexes of the latter elements with transition and
nontransition metals have been reported.
3.4.1 Titanium
A novel example formally involving a Ti Rh triple bond (Ti–Rh, 2.214 ˚A) is
[Ti⊲ , 2 -OCMe2CH2PPh2⊳3Rh] containing a pseudo-tetrahedral Ti(III) atom (Table 4.20,