Chemistry Reference
In-Depth Information
benzene
! [fAl
OPr
i
2
g
2
fM
0
tea
2
g] C 2Pr
i
OH "
(
V
), (
W
) Soluble, monomeric solids
T
,
U
C 2Al
OPr
i
3
3
.
114
benzene
! [fNb
OPr
i
4
g
2
fM
0
tea
2
g] C 2Pr
i
OH "
(
X
), (
Y
) Soluble, monomeric solids
T
,
U
C 2Nb
OPr
i
5
3
.
115
All the products (
V
), (
W
), (
X
), and (
Y
) are white crystalline solids, soluble in hydro-
carbon solvents, out of which the titanium - niobium product fNb
OPr
i
4
g
2
fTi
tea
2
g
could be distilled
175
unchanged at 205
Ž
C/0.05 mm.
A survey of the literature has revealed
176
that the triethanolaminate lanthanum deriva-
tive, La
H
2
tea
Htea
reacts with 3 moles of Nb
OPr
i
5
to give a heterobimetallic
derivative (Eqs 3.116 and 3.117), which has been characterized by X-ray crystallog-
raphy:
room temp
.
! La
H
2
tea
Htea
Insoluble
La
OPr
i
3
C 2H
3
tea
C 3Pr
i
OH "
3
.
116
dissolution
!
r
.
t
.
La
H
2
tea
Htea
C 3Nb
OPr
i
5
C3Pr
i
OH "
3
.
117
fLa
tea
2
gfNb
OPr
i
4
g
3
Soluble
The heterobimetallic La-Nb product is readily soluble in hydrocarbons and sublimes
at 180 - 250
Ž
C under 0.1 mm pressure.
3
PROPERTIES OF HETEROMETALLIC ALKOXIDES
3.1
Introduction
A close parallelism in the properties of homo- and heterometal alkoxides has been
elucidated by Mehrotra and Singh.
47
The role of mainly steric (coupled with inductive)
factors was established in the homometal species since the early 1950s by a systematic
study of the oligomerization and volatility of the alkoxides of metals (groupwise) in a
number of publications from the research school of Bradley.
177
Two interesting publica-
tions emphasizing the similarity of the neopentyloxides of titanium and zirconium
178
to
their secondary amyloxides, followed by a similar conclusion for aluminium
179
tended
to indicate the more significant role of steric factors. Bradley
180
made a highly signifi-
cant contribution in 1958 by his conclusion that metals in homometal alkoxides gener-
ally tend to attain the higher (preferred) coordination number by the lowest possible
degree of oligomerization through alkoxo(
2
-/
3
-) bridges between similar metals. A
similar generalization was arrived at by Caulton
et al
.
181
that the ratio of
m
/
a
C
b
in
closed polyhedral structures of heterobimetallic alkoxides, [M
a
M
0
b
OR
m
] tends to be
typically low. All the M and M
0
metal atoms are enclosed in a closed polyhedron by
2
-and
3
-OR-type bridging to yield a compact structural unit; the heterometal atoms
try to fit themselves in convenient geometries: the metal atoms in [KZr
2
OPr
i
9
]
64
and [BaZr
2
OPr
i
10
]
131
arrange themselves in a triangular pattern whereas the metal
atoms of [K
2
Zr
2
OPr
i
10
]
131
and [K
4
Zr
2
O
OPr
i
10
]
64
are arranged respectively in tetra-
hedral and octahedral geometries. The last example, [K
4
Zr
2
O
OPr
i
10
], depicts the
