Chemistry Reference
In-Depth Information
this should cause a lowering of symmetry from D
3h
to the C
2v
local symmetry point
group with splitting of the
2
E
0
and
2
E
00
states.
The electronic spectra
589
of pure liquid and benzene solution of vanadium tetra-
tert
-
butoxide were quite similar and the intense absorption band observed at 28 000 cm
1
was assumed to be due to charge-transfer whereas the sharp weak band at 5920 cm
1
was ascribed to an infrared overtone (C-H stretching). The spectrum also contained
a broad asymmetric band which was resolved by Gaussian analysis into two d-d
transitions at 13 900 and 10 930 cm
1
for a distorted tetrahedral species. The ESR
spectrum of liquid vanadium tetra-
tert
-butoxide at 30
Ž
C shows signals, h
g
iD1
.
964 š
0
.
005 cm
1
and h
a
iD0
.
006 4 š 0
.
000 2 cm
1
with eight
51
V(
I
D 7
/
2) hyperfine
splitting.
590
It was observed that below 5
Ž
C, the ESR spectrum of 1 - 2% V
OBu
t
4
in Ti
OR
4
was anisotropic which did not change appreciably up to 120
Ž
C, but
above 120
Ž
C the spectrum becomes isotropic. The ESR spectrum of frozen solid
vanadium tetra-
tert
-butoxide at 196
Ž
C showed more resolution and the values
g
jj
D 1
.
940 š 0
.
005,
g
?
D 1
.
984 š 0
.
005,
A
jj
D 0
.
0125 š 0
.
005 and
A
?
D 0
.
0036 š
0
.
004 cm
1
were obtained. The application of the molecular orbital treatment gave
a low value of the spin - orbit coupling constant
D 156 cm
1
and the covalency
due to involvement of the d orbitals in bond formation.
590
Bradley
et al
.
588
also
studied the ESR spectrum of vanadium tetra-
tert
-butoxide and found a similar value
of h
g
iD1
.
962, as had been observed earlier by Kokoszka
et al
.,
590
for the distorted
tetrahedral configuration (D
2
symmetry) with a
2
B
1
d
x
2
y
2
orbital) ground state. On this
basis, the d-d transitions were assigned to
2
B
2
2
B
1
and
2
E
2
B
1
corresponding
to the values 10 930 and 13 900 cm
1
, respectively. The distortion of the tetrahedral
structure for the d
1
system (
2
E ground state) of vanadium tetra-
tert
-butoxide might be
ascribed to the Jahn - Teller effect, but it is not necessarily so because the d
2
Cr(
IV
)
system also shows distortion from regular tetrahedral and the result was explained by
Bradley and Chisholm
591
on the basis of covalent bonding in the tetra-
tert
-butoxide.
The electronic spectrum of the blue d
2
chromium tetra-
tert
- butoxide was measured
471
in the region 5000 - 40 000 cm
1
to show bands at 9100, 15 200, 25 000 and 41 000 cm
1
whichwereassignedtod-d transitions (first three bands)
1
D
2
T
2
F
2
A
2
F
;
2
D
3
T
1
F
3
A
2
F
;
3
D
3
T
1
P
3
A
2
F
(with 10 Dq D 9430 cm
1
and
B
D
795 cm
1
) and charge-transfer transitions (latter band), respectively assuming that it
was tetrahedral. The blue colour of chromium tetra-
tert
-butoxide is due to the presence
of the band around 15 000 cm
1
.The
1
and
2
transitions were split into two doublets
at 8700, 9500 and 13 700, 15 750 cm
1
and this was attributed to distortion from T
d
to
D
2d
symmetry. During the study of the ESR spectrum for chromium tetra-
tert
-butoxide
in toluene, Alyea
et al
.
471
did not observe any signal below 175
Ž
C. However, in
frozen toluene at 263
Ž
C, the signals were observed over a range of 120 000 G. The
broad absorption band at
g
¾ 4 and a sharp band at
g
D 1
.
962 were consistent with
the distorted tetrahedral symmetry having an orbital singlet ground state (
3
B
1
in D
2d
symmetry) with a zero-field splitting. The reflectance spectrum of polymeric chromium
dimethoxide shows transitions at 18 200 and 22 200 cm
1
which suggested a tetragonally
distorted octahedral geometry
219
for this compound.
Dubicki
et al
.
592
measured the diffuse reflectance spectra of chromium dichloride
monomethoxide monomethanolate and dimethanolate which gave bands at around
15 000 cm
1
21 000 cm
1
37 500 cm
1
1
,
2
and
3
,
which
were assigned
4
T
2g
4
A
2g
,
4
T
1g
4
A
2g
F
and
4
T
1g
P
4
A
2g
transitions, respectively. The
to
