Chemistry Reference
In-Depth Information
Fig. 2.8 Mössbauer spectra
of three selected Fe
II
compounds. The occurrence
of quadrupole splitting in
[Fe(H
2
O)
6
]SO
4
H
2
O(A) and
Na
2
[Fe(CN)
5
NO]
2H
2
O
(C) and the absence of it in
K
4
[Fe(CN)
6
](B) are
explained in the text in
connection with Figs.
2.9
and
2.10
occupying them. There is also no lattice contribution to the EFG arising from the
coordination sphere of six identical H
2
O ligands arranged with O
h
symmetry.
Thus, there is no quadrupole splitting expected under O
h
symmetry. [Fe(H
2
O)
6
]
2+
,
however, is a ''Jahn-Teller-active'' complex ion. It is unstable under O
h
symmetry.
It undergoes axial distortion with symmetry lowering to (e.g.) D
4h
as schematized
in Fig.
2.9
(right), either compressing or elongating the octahedron in z-direction.
