Chemistry Reference
In-Depth Information
Molecular cluster compounds are particularly interesting as they might be
considered the smallest structural units of a bulk solid, yet are not a classical
solid-state material and as such are analysed using techniques usually
associated with pure inorganic chemistry, such as single-crystal XRD. As
mentioned above, they can be e
ective precursors, yet clusters such as [(
N
,
N
0
-
(CH
3
)
2
NCH
2
CH
2
N(CH
3
)
2
)
5
Zn
5
Cd
11
E
13
(EPh)
6
(tetrahydrofuran)
n
](E
¼
Se,
d
n
1
y
4
n
g
|
4
n
¼
2; E
¼
Te,
n
¼
1) exhibit optical properties consistent with quantum-
con
Se).
91,92
In this case, the cluster can be envisaged as
aCd
11
Se
13
core with a (
N
,
N
0
-(CH
3
)
2
NCH
2
CH
2
N(CH
3
)
2
)ZnSe
2
shell. This
should not be too surprising, as the clusters are prepared using silylated
chalcogenides, metal salts and phosphines
ned CdSe (when E
¼
—
-
VI
nanomaterials, with the reaction proceeding at much lower temperatures
(room temperature or lower). The
similar precursors to II
rst excitonic transition in [(
N
,
N
0
-
(CH
3
)
2
NCH
2
CH
2
N(CH
3
)
2
)
5
Zn
5
Cd
11
Se
13
(SePh)
6
(tetrahydrofuran)
2
] is found at
379 nm, with broad
emission visible at room temperature.
Thermolysing related precursors such as [Zn
x
Cd
10
x
E
4
(EPh)
12
(R)
y
](E
'
band edge
'
¼
Se,
Te; R
5) in HDA resulted in
the formation of alloyed particles of Zn
x
Cd
1
x
E, up to 5 nm in diameter. The
emission spectra showed some evidence of trap emission when E
¼
propyl,
y
¼
4; R
¼
(CH
3
)
2
NCH
2
CH
2
N(CH
3
)
2
,
y
¼
¼
Te, yet
appeared band edge when E
Se. Thermolysis of [Zn
5
Cd
11
Se
4
(-
SePh)
6
((CH
3
)
2
NCH
2
CH
2
N(CH
3
)
2
)
5
] in the long-chain amine resulted in
a material consistent with a CdSe/ZnSe core/shell structure (or a highly
graded alloy structure).
93
Other materials used as single-source precursor
include
¼
the polysul
de
N
-methylimidazole
complexes
[M(
N
-methyl-
.
imidazole)
6
]S
8
(M
Fe, Ni) and ZnS
6
(
N
-methylimidazole)
2
, which have been
used in the synthesis of spherical or irregular NiS
2
particles, Fe
3
S
4
particles
and nanorods of ZnS respectively when decomposed in OAm at 300
C.
94
The single-source route to HgE (E
¼
chalcogen) nanoparticles has also
been examined; Hg(TeCH
2
CH
2
NMe
2
)
2
has been thermolysed in a toluene
solution of HDA at 80
C yielding HgTe particles with a cubic crystalline core,
ca.
6 nm in diameter. Introducing Mn(OAc)
2
$
¼
4H
2
O into the reaction resulted
in the formation of ferromagnetic Hg
0.973
Mn
0.027
Te particles.
95
Likewise,
HgSe particles have been prepared by
the thermolysis of
[Hg(Se-
¼
Ph, C
6
H
4
-
p
-CH
3
) in HDA although few
COR)
2
(Me
2
NCH
2
CH
2
NMe
2
)] (R
properties were provided.
96
7.6 Single-Source Precursors to Other
Semiconducting Systems
There are semiconducting systems, other than cadmium and zinc chalco-
genides, where the use of single-source precursors provided more obvious
bene
ts. Lead chalcogenide QDs are of immense interest due to their
emission in the infrared region, but early studies (before the use of metal
carboxylate salts) were hindered by the lack of a convenient metal precursor:
whereas group II metal alkyls were routinely used, lead alkyls were avoided
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