Chemistry Reference
In-Depth Information
Fig. 6.5
-enantiomer of tris-chelate octahedral complex of
D
3
symmetry. The
xyz
-coordinate
system passes through the ligator atoms; the primed coordinate system has the
z
-direction along
the threefold axis, and
x
on a twofold axis through ligand
A
. The ligand orbital shown on the right
is of
ψ
-type: it is antisymmetric under a rotation about the twofold axis through the ligator bridge.
The
ψ
orbital on ligand
A
interacts with the
1
√
2
(d
xz
−
d
yz
)
-combination on the metal
Ta b l e 6 . 4
Symmetry-adapted zeroth-order metal and ligand orbital functions
t
2
g
-orbitals
dipole moments
1
√
3
(d
xy
|
a
1
=
+
d
xz
+
d
yz
)
a
2
:
μ
z
1
√
6
(
|
e
θ
=
−
2
d
xy
+
d
xz
+
d
yz
)
e
θ
:
μ
x
1
√
2
(d
xz
−
d
yz
)
|
e
=
e
:
μ
y
ψ
-orbitals
χ
-orbitals
1
√
3
(
1
√
3
(
|
a
2
=
|
ψ
A
+|
ψ
B
+|
ψ
C
)
|
a
1
=
|
χ
A
+|
χ
B
+|
χ
C
)
1
√
2
(
|
ψ
C
−|
ψ
B
)
1
√
6
(
2
|
e
θ
=
|
e
θ
=
|
χ
A
−|
χ
B
−|
χ
C
)
1
√
6
(
2
|
ψ
A
−|
ψ
B
−|
ψ
C
)
1
√
2
(
|
χ
B
−|
χ
C
)
|
e
=
|
e
=
Linear Dichroism
The linear dichroism is associated with the metal-to-ligand charge-transfer (CT)
transitions [
16
]. Dipole-allowed transitions between the orbitals are governed by the
appropriate
D
3
coupling coefficients. However, since both donor and acceptor or-
bitals, as well as the transition operators, each involve two irreps, several symmetry-
independent coupling channels are possible. As is often the case in transition-metal
spectroscopy, it is not sufficient to identify the reduced matrix elements; for a deeper
understanding a further development of the model is often required to compare the
reduced matrix elements. In the case of the CT bands the model of Day and Sanders
offers just that little extra [
17
]. According to this simple model, a charge-transfer
