Chemistry Reference
In-Depth Information
dx
2
- y
2
dx
2
- y
2
(eg)
dx
2
- y
2
, dz
2
(t
2
)
dxy
d
xy
, d
xz
, d
yz
E
dz
2
d
∆o
∆T
d
xy
d
z
2
dx
2
- y
2
, dz
2
d
xz
, d
yz
(e)
d
xy
, d
xz
, d
yz
(t
2g
)
d
xz
, d
yz
Metal ion
in a spherical
negative eld
Octahedral
Tetragonal
Square planar
Tetrahedral
FIGURE 3.9
Crystal field splitting of
d
orbitals of central ion in complexes with geometries:
tetrahedral, octahedral, tetragonal, and square-planar.
3.3.2.4 Size of Transition 3d-Metal Ions
Variation with Z of the size of di- and trivalent 3
d
cations in MO oxides of an
NaCl-type lattice presents a maximum for the
d
5
configuration and two minimums
for the
d
3
configurations (V
2+
, Cr
3+
), and
d
8
configurations (Ni
2+
).
In a weak field and for a given oxidation state, the ionic radius decreases when
going from left to right in a transition series. The magnitude of this decrease is not uni-
form, being greater for
d
4
,
d
5
,
d
9
, and
d
10
. That is explained by differences in repulsion
between the distinctive electron and the anionic ligands. Thus, for ions with configura-
tions d
1
≡ t
2g
1
, d
2
≡ t
2g
2
, d
3
≡ t
2g
3
, d
6
≡ t
2g
4
e
g
2
, d
7
≡ t
2g
5
eg
2
, d
8
≡ t
2g
6
e
g
2
, the distinctive elec-
tron that occupies the t
2g
orbitals is more weakly repulsed by the negative charges of
anionic ligands. As a consequence, it is subjected only to the influence of the increasing
nuclear effective charge. Ions with configurations d
4
≡ t
2g
3
e
g
1
, d
5
≡ t
2g
3
eg
2
, d
9
≡ t
2g
6
e
g
3
,
and d
10
≡ t
2g
6
e
g
4
have the distinctive electron in the e
g
orbitals and more interaction with
anionic ligands, resulting in the electron being more weakly attracted by the nucleus.
In a strong field, the radii of M
2+
and M
3+
ions decreases with Z up to the configu-
ration t
2g
6
. At that configuration, there is an increase with stepwise occupation of e
g
orbitals being more influenced by the repulsing interaction with the anionic ligands.
Figure 3.10
represents the variation of divalent transition metal ions in combina-
tion with anions generating a weak and a strong field, respectively.
3.3.2.5 Hydration Enthalpy of Transition Metal Ions
Hydration enthalpy is extrapolated to infinite dilution when a metal ion coordi-
nates only six water molecules forming hexaaquacomplexes of type [M(H
2
O)
6
]
2+,3+
.
