Chemistry Reference
In-Depth Information
was determined,
136
which not only confirmed its existence, but also revealed a
spontaneous
change
in
its
composition
from
the
expected
(on
the
basis
of
the
route) fBa
OPr
i
3
gCdfZr
2
OPr
i
9
g to
synthetic
the
thermodyamically
more
stable
form fCd
OPr
i
3
gBafZr
2
OPr
i
9
g.Mehrotra
234
immediately
drew
attention
to
this
achievement
in
the
field
of
heterometal
alkoxides.
This
has
been
followed
by
crystal
structure
characterization
of
several
other
similar
derivatives,
such
as
[fCd
OPr
i
3
gBafM
2
OPr
i
9
g](MD Ti, Hf)
160
and [fCd
OPr
i
3
gSrfZr
2
OPr
i
9
g]
.
235
As heteroleptic halide heterometal alkoxides remain as starting materials for the
higher heterometallic derivatives as discussed in Section 2.3, these are receiving
renewed attention:
e.g.
by the synthesis of [I
2
SnfAl
OPr
i
4
g
2
], [I
2
SnfTi
OPr
i
5
g
2
],
[I
3
SnfZr
OPr
i
5
g
Pr
i
OH
], and [I
2
SnfMo
C
5
H
5
CO
3
g
2
].
236
Work on the isolation
of this last interesting cyclopentadienyl framework, had been preceded by the
synthesis
142
of [
C
5
H
5
SnfZr
2
OPr
i
9
g] from [ClSnfZr
2
OPr
i
9
g]
2
, which had been
reported earlier.
141
It may be relevant to recall that Veith
et al
.
83
have evinced interest in attempting
to tune metal stoichiometry in heterometal alkoxide systems and have been successful
in the synthesis of [BaZr
OH
OPr
i
5
Pr
i
OH
3
]and[BaZr
OBu
t
6
thf
2
], which they
have described as the first structurally characterized molecular precursor leading to the
important ceramic material BaZrO
3
.
It might be appropriate to conclude this brief account of heterometallic alkoxide
systems by mentioning [
Bu
t
O
8
Li
4
K
4
], prepared by Clegg
et al
.
237
in their continuing
efforts to develop hetero-s-block metal chemistry.
4
FUTURE OUTLOOK
Although it is gratifying that the X-ray structural elucidation of several heterometallic
alkoxides has in general confirmed the plausible frameworks suggested for them on
the basis of simpler physico-chemical techniques, yet the emergence of an interesting
variety of actual structural patterns is playing a vital role in a much better understanding
of the factors responsible for the extraordinary stability of this fascinating group of
heterometallic coordination systems.
In addition to these academic developments, the synthesis of single-source
heteropolymetallic alkoxide precursors for high-purity mixed metal - oxide ceramic
materials, including superconductors, is becoming a possibility, for which more
penetrating investigations on novel alkoxometallate systems and their hydrolytic and
pyrolytic behaviour are required.
REFERENCES
1.
H. Meerwein and T. Bersin,
Ann.
,
476
, 113 (1929).
2.
W.G. Bartley and W. Wardlaw,
J. Chem. Soc.
, 421 (1958);
see also
W.G. Bartley,
Ph.D.
Thesis
London University (1953).
3.
R.C. Mehrotra and A. Mehrotra,
Inorg. Chim. Acta. Rev.
,
5
, 127 (1971).
4.
D.C. Bradley, R.C. Mehrotra, and D.P. Gaur,
Metal Alkoxides
, Academic Press, London
(1978).
