Chemistry Reference
In-Depth Information
design covers numerous issues such as volatility, design of simple organic
leaving groups, stoichiometry control and programmed orientation of the
deposited crystalline phase.
3
Despite the fact that single-source precursors are o
en viewed as a later
development in the
eld of nanoparticle preparation, much of the initial
work in the synthesis of nanomaterials by organometallics was in fact single-
source based. Early work on alternative routes for the preparation of CdTe
and HgTe thin
d
n
1
y
4
n
g
|
4
lms utilised bis(organotelluro)cadmium and bis(organo-
telluro)mercury compounds as precursors.
4
This methodology was used in
the synthesis of a range of nanomaterials using complexes of M(ER)
2
(M
¼
¼
¼
Cd, Zn, Hg; E
organic group) which were thermolysed in
4-ethylpyridine (except Hg(TeBu)
2
, which decomposed photolytically).
5,6
This
showed that single molecular precursors could be thermolysed in Lewis base
solvents to give nanomaterials, although few investigations were carried out
into the optical properties or the nature of the surface capping agents. The
particles produced were ill-de
S, Se, Te; R
ned, yet clearly crystalline and displayed
evidence of the size quantisation e
ects. The relatively poor quality of these
materials can in part be attributed to the low boiling point of 4-ethylpyridine
(167
C) and the tendency for pyridines to tar and cross-link upon prolonged
heating.
7,8
The use of single-source precursors is not con
ned to high-
temperature routes with coordinating solvents; [(
t
Bu)GaSe]
4
and [(EtMe
2
C)
InSe]
4
have been used to prepare GaSe and InSe nanoparticles respectively,
9
and (X
2
GaP(SiMe
3
)
2
)
2
(X
Br, I) and (Cl
3
Ga
2
P)
n
have both been used to
prepare GaP nanoparticles
10
although these reactions are not solution-based.
Thermolysis of a related compound, [H
2
GaE(SiMe
3
)
2
]
3
,(E
¼
.
¼
P, As), in xylenes
yielded 5 nm GaP or GaAs nanoparticles.
11
7.2 Dithio- and Diselenocarbamates
The advent of high-temperature solution routes based on trioctylphosphine
oxide (TOPO) allowed single-source precursors to be used in reaction
conditions that favoured the growth of high-quality particles. The single-
source route to TOPO-capped nanoparticles was pioneered by O
'
Brien,
12,13
who utilised dithio- and diselenocarbamates on the basis of their successful
use in the formation of metal sul
lms. The dimeric
complexes can in most cases be prepared from readily available starting
material. This route relies on the availability of the sodium (or ammonium)
salt of the carbamate ligand, which is only commercially available with
symmetrical alkyl groups such as ethyl. A more useful route involves the
reaction between the metal salts, CS
2
and the required, o
de/selenide thin
en asymmetrical,
secondary amine. The range of alkyl groups available on secondary amines
allows a wide range of symmetrical and asymmetrical precursors to be
prepared. It is worth noting that although carbon disul
de is commercially
available, carbon diselenide is not; it is toxic and di
cult to prepare.
14
In this
case, preparing nanoparticles by the green routes described by Peng is
simpler, although single-source precursors have distinct bene
ts.
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