g zz
g xx
g yy
2:00
3:26
1:88
ð1:87Þ ð3:24Þ ð2:05Þ
c 1
c 2
c 3
c 4
c 5
À0:2064
À0:0359 À0:0664
À0:0035
0:9556
E yz À E z 2
E yz À E zz E yz À E xy E yz À E x 2 Ày 2
ðca: 1700Þ
8000
5000
ð57:000Þ
ðca: 6000Þ ð3000Þ
Ground configuration (xz)
2 (xy)
2 (yz)
2 (z
2 )
g zz ¼ 2b
2
3 À 2b
2
2 À 2b
2
1 þ 4Kb 1 b 2
g xx ¼ 2b
2
1 À 2b
2
2 þ 2b
2
3 À 4
ffiffi ffi
3
p
Kb 1 b 3
g yy ¼ 2b
2
3 þ 2b
2
2 À 2b
2
1 À 4
ffiffi ffi
3
p
Kb 2 b 3
g zz
g xx
g yy
2:00
3:26
1:88
ð1:89Þ
ð3:21Þ
ð2:12Þ
b 1
b 2
b 3
À0:1803 À0:0380 0:9829
E z 2 À E yz E z 2 À E xz
ð1900Þ
8000
ðca: 9000Þ
The research pathway consists in calculating the g component values by a
second-order approximation, using the g expressions above reported and the crystal
field energy differences derived from the electronic absorption spectra of planar
CoAcacen and pentacoordinated CoAcacen pyridine (Fig. 5.6, the energies are in
cm−1) and then in comparing the calculated g values with the experimental ones
(reported in parentheses).
It can be observed that whatever is the ground state configuration, the experimental values of g zz and g yy cannot be satisfactorily reproduced. Moreover, the
experimental crystal field energies fit with both the ground state configurations. For
these reasons, it is not possible to unambiguously assign the ground state configuration, and a large mixing between the states (xz)
2 (xy)
2 (yz)(z
2 )
2 and
(xz)
2 (xy)
2 (yz)
2 (z
2 ) seems to occur. The relative distance is less than 2000 cm
−1 .
In any case, the unpaired electron lies out of the molecular plane and can be
easily transferred to the p
* molecular orbitals of the coordinated oxygen. Even a
feeble axial perturbation along the z-axis could stabilize the (xz)
2 (xy)
2 (yz)
2 (z
2 )
ground configuration, which becomes really very suitable to react with oxygen, due
to the location of the unpaired electron in the d
2
z orbital. This happens in [Co(II)
Acacen py] where the absorption at about 8000 cm
−1 shifts to about 12,000
(Fig. 5.6).
5.5 Discussion of the Case
91
g xx
g yy
2:00
3:26
1:88
ð1:87Þ ð3:24Þ ð2:05Þ
c 1
c 2
c 3
c 4
c 5
À0:2064
À0:0359 À0:0664
À0:0035
0:9556
E yz À E z 2
E yz À E zz E yz À E xy E yz À E x 2 Ày 2
ðca: 1700Þ
8000
5000
ð57:000Þ
ðca: 6000Þ ð3000Þ
Ground configuration (xz)
2 (xy)
2 (yz)
2 (z
2 )
g zz ¼ 2b
2
3 À 2b
2
2 À 2b
2
1 þ 4Kb 1 b 2
g xx ¼ 2b
2
1 À 2b
2
2 þ 2b
2
3 À 4
ffiffi ffi
3
p
Kb 1 b 3
g yy ¼ 2b
2
3 þ 2b
2
2 À 2b
2
1 À 4
ffiffi ffi
3
p
Kb 2 b 3
g zz
g xx
g yy
2:00
3:26
1:88
ð1:89Þ
ð3:21Þ
ð2:12Þ
b 1
b 2
b 3
À0:1803 À0:0380 0:9829
E z 2 À E yz E z 2 À E xz
ð1900Þ
8000
ðca: 9000Þ
The research pathway consists in calculating the g component values by a
second-order approximation, using the g expressions above reported and the crystal
field energy differences derived from the electronic absorption spectra of planar
CoAcacen and pentacoordinated CoAcacen pyridine (Fig. 5.6, the energies are in
cm−1) and then in comparing the calculated g values with the experimental ones
(reported in parentheses).
It can be observed that whatever is the ground state configuration, the experimental values of g zz and g yy cannot be satisfactorily reproduced. Moreover, the
experimental crystal field energies fit with both the ground state configurations. For
these reasons, it is not possible to unambiguously assign the ground state configuration, and a large mixing between the states (xz)
2 (xy)
2 (yz)(z
2 )
2 and
(xz)
2 (xy)
2 (yz)
2 (z
2 ) seems to occur. The relative distance is less than 2000 cm
−1 .
In any case, the unpaired electron lies out of the molecular plane and can be
easily transferred to the p
* molecular orbitals of the coordinated oxygen. Even a
feeble axial perturbation along the z-axis could stabilize the (xz)
2 (xy)
2 (yz)
2 (z
2 )
ground configuration, which becomes really very suitable to react with oxygen, due
to the location of the unpaired electron in the d
2
z orbital. This happens in [Co(II)
Acacen py] where the absorption at about 8000 cm
−1 shifts to about 12,000
(Fig. 5.6).
5.5 Discussion of the Case
91