Chemistry Reference
In-Depth Information
other phases (Fe
2
P and Fe
3
P) are better known for their magnetic properties.
Chemical routes to FeP have been reported
via
the reduction of the phos-
phate on a surface,
78
although few details have been reported for this
method. This material obviously lends itself to the desilylation reaction,
similar to the synthetic processes described for III
V materials in Chapter 2.
An early report
79
on the synthesis of FeP described the desilylation reaction,
where iron(
III
) acetylacetonate, Fe(C
5
H
7
O
2
)
3
, was dissolved in a mixture of
TOPO, myristic acid and DDA, followed by the injection of P(SiMe
3
)
3
and the
subsequent heating of the reaction to 240
-
d
n
1
y
4
n
g
|
2
320
C for 2
3 days. The reaction
was then cooled, the materials dispersed in pyridine, and puri
-
-
ed by size-
selective precipitation using hexane as a non-solvent. The presence of the
long-chain amine and the carboxylic acid were found to be essential: their
absence resulted in the formation of precipitates due to the weak binding of
TOPO. Interestingly, phosphonic acids were found to bind too strongly. The
resulting particles,
ca.
4.6 nm diameter, were determined to be pure-phase
FeP, with antiferromagnetic order observed below 124 K.
The desilylation reaction was found to be unsuitable for the synthesis of
MnP, a related magnetic material of some interest. However, the expansion
of this method to the use of zero-valent carbonyl complexes, such as
Mn
2
(CO)
10
, Fe(CO)
5
and Co
2
(CO)
8
as cation precursors in a similar reaction
resulted in the formation of MnP, FeP and CoP respectively.
80
This route
highlights the suitability of the carbonyl complexes as e
cient precursors,
which can be traced back to the earliest organometallic synthetic routes to
compound semiconductors
81
and metal particles.
82
In these reactions, the
injection of P(SiMe
3
)
3
into a hot solution of TOPO, myristic acid and the
metal carbonyl complex at 100
C, followed by heating for 1 day at 220
C,
resulted in the formation of the metal phosphide particles. The particles were
isolated into pyridine, and hexane was again used as a non-solvent. The MnP
particles prepared by this route were
ca.
5.1 nm
.
0.48 nm in diameter and
exhibited superparamagnetism when below the Curie temperature. The FeP
particles (
ca
. 3.1 nm) required a higher synthesis temperature of 270
C, and
CoP particles required a still higher temperature of 320
C.
The formation of MnP nanoparticles using the carbonyl complex could
also be achieved using simple alkylphosphines as a precursor. These are
usually used as capping agents, notably TOP, which highlights the transition
from inert capping ligand to labile precursor when used at an elevated
temperature (>300
C). TOP has now emerged as a standard synthetic
precursor for phosphorus, and has been used to prepare Ni
2
P, PtP
2
,Rh
2
P,
Au
2
P
3
,Pd
5
P
2
and PdP
2
,
83
Ni
5
P
4
,Zn
3
P
2
,Cu
3
P, CuP
2
, InP and GaP
84
by the
reaction of TOP with preformed metal nanoparticles, the formation of which
was suggested to occur
via
adi
usion mechanism. The synthesis of FeP from
preformed iron metal particles using TOP as a precursor has been explored in
some depth by Muthuswamy
et al.
who explored the e
ering
reaction times, precursor concentrations and temperatures on particle
formation.
85
It was found that higher reaction temperatures resulted in FeP,
with lower temperatures favouring Fe
2
P. Short reaction times and excess iron
ect of di
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