Chemistry Reference
In-Depth Information
hydrolyzes to Mn(OH)
2
in alkaline solutions, where it easily oxidizes to
Mn(III) and Mn(IV) species. The Mn(III) species could be stabilized by
forming their complexes. In alkaline solutions, Mn
2
O
3
and MnOOH are known
compounds of Mn(III). Examples of Mn(IV) compounds include MnO
2
,
Mn(SO
4
)
2
, and MnF
4
. MnO
2
is the only species stable in water. Hypomanga-
nate (
MnO
3−
), manganate (
MnO
2−
), and permanganate (
MnO
−
) are oxo com-
pounds of Mn(V), Mn(VI), and Mn(VII), respectively.
In the solid state, Mn(V) compounds in the tetrahedral oxo coordination
in host compounds Ca
2
(MO
4
)Cl (M=As(V), V(V), and P(V)) have been syn-
thesized to obtain their single-crystal EPR spectra [175]. The EPR spectra of
Mn(VI) have also been determined by stabilizing the +6 oxidation state of Mn
in numerous host compounds possessing the β-K
2
SO
4
structure. The crystalline
oxo compounds of Mn(V) and Mn(VI) with low doping concentrations could
be distinguished using their EPR spectra. However, at high concentrations of
Mn, it was difficult to distinguish between the two oxidation states [175]. The
low-temperature absorption and luminescence spectra of
MnO
2−
-doped crys-
tals of CsBr, CsI, SrCrO
4
, and Cs
2
CrO
4
are also known [176].
In aqueous solution, various oxidation states of manganese have distinct
colors:
MnO
−
—purple,
MnO
2−
—dark green,
MnO
3−
—light blue, and finally
MnO
2
—brown precipitate. The uV-vis spectra of the different species are
shown in Figure 6.13. The spectra of Mn(V) and Mn(VI), shown in Figure 6.13,
5.0
10.0
MnO
2
4.0
8.0
3.0
6.0
MnO
4
-
4.0
2.0
MnO
4
2-
M
n
O
4
3-
1.0
2.0
0.0
0.0
200
300
400
500
600
700
800
λ
(nm)
Figure 6.13.
ultraviolet and visible spectra of the
MnO
−
,
MnO
2−
,
MnO
3−
, and MnO
2
.
Data were taken from References 179 and 216.
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