Synthesis, structural characterisation and thermal decomposition of [{Pt(dppf)(2-SPy)}{BF4}] (dppf=1, 1′- bisdiphenylphosfinoferrocene and 2-SPy=2-mercaptopyridine) - A source for a Fe-Pt containing alloy

Article abstract of DOI:10.1016/j.poly.2003.09.017

The reaction of 2-PySK with [Pt(dppf)Cl₂] [dppf=1,1′- bis(diphenylphosfinoferrocene and 2-PyS=2-mercaptopyridine] produced Pt(dppf)(2-SPy)₂ (1) and its subsequent reaction with SnBu ₂(BF₄)₂ or SnBu₃(BF₄) yielded [{Pt(dppf)(2-SPy)}{BF₄}] (2). Compounds 1 and 2 were fully characterised by multinuclear NMR [¹H, ¹³C{¹H}, ³¹P{¹H} and ¹⁹⁵Pt{¹H}] and ⁵⁷Fe M?ssbauer spectroscopies. In addition the structure of 2 was determined by X-ray crystallographic studies, which can be summarised as follows: monoclinic P2₁/c, a=9.9291(9) ?, b=22.270(4) ?, c=16.919(2) ?, γ=103.6(9)°, V=3636.2(8) ?³ and Z=4. Finally, a thermal decomposition study was carried out with 2 in three different atmosphere: oxygen, nitrogen or hydrogen. The residues were characterised by X-ray powder diffraction (XRD), X-ray electron probe microanalysis (EPMA), scanning electron microscopy (SEM) and ⁵⁷Fe M?ssbauer spectroscopy. The results have shown the formation of a disordered Pt_1-xFe_x based alloy when the pyrolysis process was performed in H₂, simultaneously with small amount of Fe(II) and Fe(III) phosphides. Furthermore, in oxygen and nitrogen the thermal decomposition of 2 produced metallic agglomerates of Pt dispersed in a combination of Fe(II) and Fe(III) phosphates in O₂, and an intricate mixture of sulphides and phosphides in N₂.

Full text of DOI:10.1016/j.poly.2003.09.017

Polyhedron 23 (2004) 63–69
www.elsevier.com/locate/poly
Synthesis, structural characterisation and thermal
decomposition of [{Pt(dppf)(2-SPy)}{BF4}](dppf ¼ 1,10-
bisdiphenylphosfinoferrocene and 2-SPy ¼ 2-mercaptopyridine)
– a source for a Fe–Pt containing alloy
a
a,
a,
a
V.D. de Castro , Geraldo M. de Lima *, Arilza O. Porto *, Helmuth G.L. Siebald ,
a
Jose D. de Souza Filho , J.D. Ardisson , Jose D. Ayala , Gabriella Bombieri
b
a
c
ꢀ
ꢀ
a
Departamento de Quꢀımica, Universidade Federal de Minas Gerais – UFMG, Avenida Antonio Carlos 6627, Belo Horizonte MG 31270-901, Brazil
b
CDTN, Belo Horizonte MG 31270-901, Brazil
Istituto di Chimica Farmaceutica della Universitaꢁ di Milano, Milano, Italy
c
Received 28 May 2003; accepted 8 September 2003
Abstract
The reaction of 2-PySK with [Pt(dppf)Cl2] [dppf ¼ 1,10-bis(diphenylphosfinoferrocene and 2-PyS ¼ 2-mercaptopyridine] pro-
duced Pt(dppf)(2-SPy)2 (1) and its subsequent reaction with SnBu2(BF4)2 or SnBu3(BF4) yielded [{Pt(dppf)(2-SPy)}{BF4}] (2).
57
Compounds 1 and 2 were fully characterised by multinuclear NMR [1H, 13C{1H}, 31P{1H} and 195Pt{1H}] and Fe Mossbauer
spectroscopies. In addition the structure of 2 was determined by X-ray crystallographic studies, which can be summarised as follows:
€
3
ꢂ
ꢂ
ꢂ
ꢂ
monoclinic P21=c, a ¼ 9:9291ð9Þ A, b ¼ 22:270ð4Þ A, c ¼ 16:919ð2Þ A, c ¼ 103:6ð9Þ°, V ¼ 3636:2ð8Þ A and Z ¼ 4. Finally, a
thermal decomposition study was carried out with 2 in three different atmosphere: oxygen, nitrogen or hydrogen. The residues were
characterised by X-ray powder diffraction (XRD), X-ray electron probe microanalysis (EPMA), scanning electron microscopy
57
€
(SEM) and Fe Mossbauer spectroscopy. The results have shown the formation of a disordered Pt1 ꢀ xFex based alloy when the
pyrolysis process was performed in H2, simultaneously with small amount of Fe(II) and Fe(III) phosphides. Furthermore, in oxygen
and nitrogen the thermal decomposition of 2 produced metallic agglomerates of Pt dispersed in a combination of Fe(II) and Fe(III)
phosphates in O2, and an intricate mixture of sulphides and phosphides in N2.
Ó 2003 Elsevier Ltd. All rights reserved.
Keywords: Pyrolysis; Organometallic compounds; Iron–platinum compounds
1. Introduction
taining the dppf fragment, have been deposited at
CCDC (version 5.24 of April 2003).
The compound [Fe(g5-C5H4PPh2)2], dppf, still plays
an important role in organometallic chemistry [1]. The
coordination versatility of this metalloligand is highly
remarkable. Actually, the various coordinating modes
of dppf just reflect its ability to change conformation in
order to match the steric demands of the surrounding
molecular environment. However, in most examples it is
g2 bonded to metal centres. So far more than 250
structures determined by X-ray crystallography, con-
The considerable research attention granted to dppf
relates to: (i) the various coordination modes towards
metallic anions [2], (ii) the catalytic activity of the
complexes [3] and (iii) the chemotherapeutic potential
for cancer treatment of some derivatives [4].
Our research interest towards dppf concerns the
preparation of well characterised Pt(II) [5], Ru(II), and
its Sn(II)-containing heterometallic derivatives in order
to obtain oxides and Fe/Pt/Sn or Fe/Ru/Sn containing
alloys. For that, thermal decomposition of single source
organometallic precursors has received special attention
from us in the last two years [6]. Heterometallic
* Corresponding authors. Tel.: +553134995744; fax: +553134995720.
E-mail address: gmlima@dedalus.lcc.ufmg.br (G.M. de Lima).
0277-5387/$ - see front matter Ó 2003 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2003.09.017

64
V.D. de Castro et al. / Polyhedron 23 (2004) 63–69
derivatives of dppf seems to be attractive since it pos-
sesses different metallic species close enough to interact
and produce synergetic effects which can result in inter-
esting properties. Therefore, this work reports the ther-
mal decomposition of [{Pt(dppf)(SPy)}{BF4}] (2) carried
out in oxygen, nitrogen and hydrogen. The residues were
studied by X-ray powder diffraction (XRD), scanning
electron microscopy (SEM), X-ray electron probe mi-
The clear solution remained stirring for 30 mim in dark.
The AgCl formed was filtered off by cannula and the
solution transferred to another Schlenk-flask containing
210 mg (0.22 mmol) of Pt(dppf)(2-SPy)2 in thf (20 ml).
After 15 h of stirring the solvent was removed and the
residue was washed with n-hexane, extracting SnBu3-
SPy. The resultant golden-yellow solid was re-crystal-
lised in toluene (30 ml) affording X-ray quality crystals.
1
croanalysis (EPMA) and 57Fe Mossbauer spectroscopy.
Yield 69% (144 mg, 0.150 mmol). Mp 215(d) °C. H
€
NMR d 7.9–6.6 (m) (Py and Ph), 4.9(s) and 4.4(s) (Cp);
13C{1H} NMR d 166, 145, 136, 125, 119 (Py), d 134–128
1
2. Experimental
(Ph and Cp); 31P{1H} d 17.27 J(31P–195Pt) ¼ 3162 Hz
and d 11.56 1J(31P–195Pt) ¼ 3609 Hz; 195Pt{1H} d )3500.
Elemental analysis for C39H32BF4FeP2PtS, found(calc):
C, 49.78(49.49); H, 2.81(2.78); N, 1.39(1.38)%. The same
product was obtained using SnBu2Cl2 (50 mg, 0.16
mmol).
2.1. Synthesis and characterisation of metal complexes
The synthetic work was conducted in an atmosphere
of dry N2. All solvents were treated by the appropriate
method in order to remove moisture and oxygen, prior
to use. All chemicals unless stated were obtained from
Aldrich or Strem Co. NMR spectra were recorded in
2.4. X-ray structure determination of 2
1
CDCl3, at 400 MHz, H, 100.62 MHz; 13C{1H}, 50.29
The structure was solved by direct methods with SIR-
92 [7] and the refinements were carried out using SHELXL
97 [8], minimising on the weighted R factor wR2. Further
details are given in Table 1. All non-H atoms are an-
isotropic. The ORTEP drawing shows the non-H atoms
as 50% thermal vibration ellipsoids. The crystals were
obtained by slow evaporation of a toluene solution of 2.
The BFꢀ4 group showed to be very disordered.
MHz; 31P{1H}, 161.92 MHz; 195Pt{1H}, 86.00 MHz
using a Bruker DPX-400 spectrometer equipped with an
89 mm wide-bore magnet. 13C and 1H shifts are reported
relative to SiMe4, 31P to H3PO4 and 195Pt to K2PtCl4.
Carbon and hydrogen elemental analyses were per-
formed on a Perkin–Elmer PE-2400 CHN-analyses us-
ing tin sample-tubes. The X-ray diffraction data were
collected using a Enraf Nonius FR590 with SMART
CCD area detector and graphite–graphite-monochro-
mated Mo Ka.
Table 1
Crystal data and structure refinement for 2
2
2.2. Synthesis of Pt(dppf)(2-SPy)2 (1)
Empirical formula
Formula weight
Temperature (K)
Wavelength
C39H32BF4FeP2PtS
946.41
263(2)
To a Schlenk-flask containing a suspension of 0.88 g
(5.90 mmol) of 2-PySK and 20 ml of thf, was slowly
added a thf solution of [Pt(dppf)Cl2], 2.42 g (2.95 mmol
in 15 ml). Within 4 h of stirring the thf was removed in
vacuum and CH2Cl2 (30 ml) was added in order to ex-
tract the product, originating an orange solution and
KCl which was separated by filtration. A yellow solid
was obtained after removing the solvent and re-crystal-
lisation in CH2Cl2/toluene (1:1, 30 ml). Yield based in
[Pt(dppf)Cl2]: 70% (2.00 g, 2.07 mmol). Mp 180(d) °C.
1H NMR d 6.2–7.5(m) (Py and Ph), 4.4(s) and 4.2(s)
(Cp); 13C{1H} NMR d 168, 147, 137, 125, 115 (Py), d
134–127 (Ph and Cp); 31P{1H} d 16.87 1J(31P–
195Pt) ¼ 3139 Hz; 195Pt{1H} d )4684 1J(31P–195Pt) ¼ 3195
Hz. Elemental analysis for C44H38FeP2PtN2S2, found
(calc): C, 57.41(58.35); H, 3.99(4.01); N, 2.99(3.09)%.
0.71073
monoclinic
P21=c
Crystal system
Space group
Unit cell dimensions
ꢂ
a (A)
9.9291(9)
22.270(4)
103.605(9)
16.919(2)
3636.2(8)
2.298
ꢂ
b (A)
c (°)
ꢂ
c (A)
Volume (A )
3
ꢂ
Calculated density (g cmꢀ3
)
Z
4
4.438
Absorption coefficient
F ð000Þ
1856
0.45 ꢁ 0.25ꢁ 0.08
2.48–28.54
Crystal size (mm)
Theta range for data
collection
Limiting indices
h ¼ 0–13; k ¼ ꢀ29–0;
l ¼ ꢀ22–22
Reflections collected/unique
Refinement method
9260/6317
Full-matrix least-squares on
F 2
2.3. Synthesis of [{Fe(g5-C5H4PPh2)2Pt(SPy)}{BF4}]
(2)
Final R indices ½I > 2rðIÞꢂ
R indices (all data)
CCDC reference
R1 ¼ 0:032, wR2 ¼ 0:066
R
1¼0:078, wR2 ¼ 0:076
To a solution of AgBF4, 42 mg (0.22 mmol) in thf (20
ml), was added 70 mg (0.22 mmol) of SnBu3Cl in thf.
192715

V.D. de Castro et al. / Polyhedron 23 (2004) 63–69
65
2.5. Thermal analysis of 2
In order to determine the range of temperature of
degradation of 2, thermogravimetric analysis (TG) with
simultaneous differential thermal analysis (DTA) ex-
periments were performed in a TA Instruments SDT
2960 with a heating rate of 5 °C/min until 900 °C in
oxygen.
2.6. Pyrolysis of 2, chemical, structural and morpholog-
ical characterisation of the residue
Thermal decomposition of 2 was carried out in a tube
furnace in N2, O2 and H2, using a heating rate of 5 °C/
min until a final temperature of 900 °C employing a gas
flux of 100 ml/min. The decomposed products were
57
€
characterised by XRD, SEM, Fe Mossbauer spec-
troscopy and EPMA.
X-ray powder diffraction was executed in a Rigaku
Scheme 1. Pathway of the preparation of compound 1.
ꢂ
simple coordination reaction, it was observed an ex-
change of 2-PySꢀ ligand between Pt(II) and Sn(IV)
atoms.
Similar interchange was also detected when the re-
action of [SnPh3SPy] with [Pt(PPh3)2Cl2] was performed
in order to obtain a bimetallic complex where Pt(II) was
coordinated through the S donor centre. However, two
separated compounds SnPh3Cl and [Pt(PPh3)2(SPy)2]
[10] were isolated and identified.
Geigerflex using a Cu Ka radiation (k ¼ 1:54178 A). A
scan rate of 4°/min in the 2h range from 4° to 100° was
used. In those samples containing platinum its main
diffraction line at 39.76° (1 1 1) was used as internal
standard for angle calibration.
The scanning electron micrographs was recorded in
a JEOL JSM-840A equipment and the electron probe
X-ray microanalysis were carried out in a JXA 89000
RL wavelength dispersive/energy dispersive combined
microanalyser. For the SEM images and X-ray mi-
croanalysis the samples were recovered with a thin
film of gold and carbon, respectively, deposited by
Compounds 1 and 2 are air and moisture stable
golden-yellow products, readily soluble in CH2Cl2 and
toluene, and they showed satisfactory results of ele-
mental analysis. NMR spectroscopic measurements
were carried out using a CHCl3/CDCl3 solutions. For
both compounds the 13C and 1H NMR spectra exhibited
the expected resonances for Cp, Ph and Py groups.
Compound 1 displayed a single signal at d 16.9 [1J(31P–
195Pt) ¼ 3139 Hz] in the 31P NMR spectrum, and a peak
at d )4684 [1J(31P–195Pt) ¼ 3195 Hz] in the 195Pt NMR
spectrum. It possesses a smaller 31P–195Pt coupling
constant, 3195Hz compared to the starting material
[Pt(dppf)Cl2], 3768 Hz. The latter is a consequence of
the better p-acceptor character of S compared to Cl
which causes a decrease in the Pt–P bond strength.
The 31P NMR spectrum of 2 revealed two signals at d
17.3 [1J(31P–195Pt) ¼ 3162 Hz] and 11.6 [1J(31P–
195Pt) ¼ 3609 Hz]. Moreover, it was detected a coupling
constant between the two non-equivalent phosphorus at
17 Hz. The first set of chemical shifts and coupling
constants are similar to the signals displayed by 1.
Therefore, it might be assigned to the P atom trans to S
of the –SPy moiety and the remaining signal can be at-
tributed the other P atom trans to N. A broad resonance
centred at d )3500 was detected in the 195Pt NMR
spectrum, resulting from a complicated coupling pattern
of 195Pt with the non-equivalent 31P nuclei.
sputtering.
57
€
Fe Mossbauer measurements were obtained in or-
der to identify the Fe oxidation states and number of
different sites in the decomposed materials by using a
conventional apparatus with 57Co as source of c-radia-
tion, kept at room temperature.
3. Results and discussion
Organometallic compounds are good candidates for
single source precursors for thermal decomposition
because they decompose at low temperature, produc-
ing metallic oxides, metallic particles or inorganic
salts. Following our interest in this research area, we
have attempted to prepare a Pt/Fe/Sn derivative, as
described in Scheme 1, to be employed as an source
for the trimetallic containing materials. Firstly, the
reaction of [Pt(dppf)Cl2] with 2-PySK produced the
bimetallic derivative [Pt(dppf)(SPy)2] (1) (see Scheme
1) that was used as a S and N electron donor ligand
towards another metal centre. Organotin(IV) Lewis
acid were chosen due to the great Sn–N affinity ob-
served in other complexes [9]. However, instead of a

66
V.D. de Castro et al. / Polyhedron 23 (2004) 63–69
at 60 °C was subtracted from the curve in order to
disregard the loss of solvent. In this step the complex
loses 54.2% of the weight. After 400 °C, the material
continues to decompose losing at the end, 800 °C, 47%
of mass, leaving a final residue containing 7.2% of the
initial amount, which suggests that an appreciable
amount of material was lost to the gas phase.
3.2. X-ray electron probe microanalysis
The chemical composition of the residues was deter-
mined by EPMA in different regions of the samples in
order to evaluate their level of homogeneity. The pres-
ence of carbon peaks in all residues is a consequence of
the deposit of graphite at the sampleÕs surface.
Two different regions were identified in the residues
obtained in oxygen: a bright one, formed by agglom-
erates of metallic platinum (approximately 10 lm in
size) dispersed in an amorphous media, dark region,
constituted basically of P, Fe and O, Fig. 2. No sul-
phur was identified in this sample. A similar situation
was revealed for the residue obtained in N2, Fig. 3(b),
however, the particles of platinum are much smaller
than the previous one. Moreover, in this case it was
noticed only a trace of oxygen, and the major com-
ponents were Fe, P and S. The residue from decom-
position of 2 in H2 has not shown oxygen or sulphur,
but only Pt, P and Fe, Fig. 3(c). The nature of
Fig. 1. Molecular structure of 2 determined by X-ray crystallography.
Table 2
ꢂ
Selected bond lengths (A) and angles (°) for 2
Bond lengths
Pt–N
2.1160(4)
2.2521(11)
2.2910(11)
1.7470(5)
2.3635(12)
Pt–P(1)
Pt–P(2)
S–C(1)
Pt–S
the species formed could only be tentatively identi-
57
Bond angles
N–Pt–P(1)
P(1)–Pt–P(2)
P(1)–Pt–S
S–C(1)–N
N–Pt–P(2)
N–Pt–S
€
fied with the support of XRD and Fe Mossbauer
spectroscopies.
164.07(14)
99.09(5)
95.09(6)
110.00(3)
96.82(14)
69.00(14)
165.81(6)
P(2)–Pt–S
A single-crystal X-ray experiment confirmed the
structure of 2 to be composed of Pt(dppf)(SPy)þ cations
and BFꢀ4 anions, with no direct contact between the two
fragments, Fig. 1. The Pt(II) atom lies in the centre of a
distorted square where it is bonded to both S {Pt–S,
ꢂ
ꢂ
2.3641(15) A} and N {Pt– N, 2.113(5) A} of the pyridyl
group. These bondlengthandangles {N–Pt–S69.00(14)°,
P(1)–Pt–P(2) 99.09(5)°, S–C(1)–N 110.00(3)°} are very
close to the ones observed for [{Pt(PPh3)2(SPy)}{PF6}]
[11] (Table 2).
The coordination position of the fluorine atoms in the
BFꢀ4 group was very disordered, similarly to other re-
ported results [11].
3.1. Thermal analysis
Compound 2 displayed a highly exothermic decom-
position process in a pseudo single step, which started at
300 °C and finished at 800 °C. The initial loss of weight
Fig. 2. The image and the dispersive energy X-ray microanalysis
(EPMA) of 2 decomposed in O2.

V.D. de Castro et al. / Polyhedron 23 (2004) 63–69
67
Fig. 4(a) revealed lines at 2h ¼ 39°, 46°, 67° and 81°;
corresponding, as indicated by the Miller index to the
diffraction planes (1 1 1), (2 0 0), (2 2 0) and (3 1 1) to
ꢂ
metallic platinum (Cubic, Fm3m, a ¼ 3:923 A) {04-0802}
[12]. The high intensity of the Pt diffraction lines sug-
gests the production of large and well formed particles
of platinum as observed in the electron backscaterred
image. The other diffraction lines can be clearly attrib-
uted to the formation of FePO4 and Fe3(PO4)2 [13] and
57
€
it is in accordance to the EPMA and Fe Mossbauer
spectroscopic results.
Much more broader Pt diffraction lines (1 1 1),
(2 0 0), (2 2 0) and (3 1 1) were revealed for the residue
prepared in N2, in consequence of the lower crystal-
linity of the decomposed material. The much less in-
tense lines at approximately 2h ¼ 28°, 47° and 56°
might be attributed to the cubic FeS [14a] {pyrite form
– 06-0710} and those at 2h ¼ 32° and 53° which are
also observed in the diffractogram of the sample de-
composed in H2, can be associated to the orthorhombic
FeP4 [14b] {34-0996i}, Fig. 4(b). On the basis of the
EPMA analysis there is no oxygen in the sample which
frustrate the presence of phosphate anions. Therefore,
it is reasonable to assume that Fe(II) and Fe(III) are in
the form of sulphide and phosphide. The diffraction
pattern of the product obtained in H2 has shown lines,
at 2h ¼ 25°, 31°, 32° and 53°, corresponding to ortho-
rhombic FeP4, as before, and the diffractions at
2h ¼ 41° and 46°, may be associated to the planes
(1 0 0) and (2 0 0) of the Pt–Fe alloy (cubic – 29-0718).
The intense line at 2h ¼ 24° is probably related to the
alloy as well since other similar materials with different
stoichiometry present diffraction lines at angles smaller
than 30° [12].
Fig. 3. (a) The image and the EPMA of 2 decomposed in N2 (b) and
H2 (c).
3.3. X-ray powder diffraction
X-ray diffraction measurements were executed in or-
der to identify the pyrolysis residues of 2, Fig. 4. The
diffractogram of the decomposed material in oxygen,
3.4. 57Fe M€ossbauer experiments
57
€
The room temperature Fe Mossbauer spectroscopy
experiments supported the identification of iron com-
pounds and its oxidation state, Fig. 5 and Table 3.
For the starting material, 2, it was observed the
presence of Fe(II) to which the parameters d ¼ 0:40ð2Þ
mm sꢀ1 and D ¼ 2:25ð3Þ mm sꢀ1 relates very well with
the classical values reported for ferrocene, [FeCp2],
d ¼ 0:44ð2Þ mm sꢀ1 and D ¼ 2:38ð3Þ mm sꢀ1 and the
dppf d ¼ 0:42ð2Þ mm sꢀ1 and D ¼ 2:30ð3Þ mm sꢀ1 [15],
57
€
Fig. 5(a). The Fe Mossbauer spectrum of the residue
prepared in O2, Fig. 5(b) displayed two signals with the
corresponding parameters, d ¼ 0:30ð2Þ mm sꢀ1, D ¼
0:44ð3Þ mm sꢀ1 and d ¼ 0:37ð2Þ mm sꢀ1, D ¼ 0:98ð3Þ
mm sꢀ1 assigned to the presence of Fe(III), 63%, and
Fe(II), 37%, respectively, that are in the form of phos-
phates [13]. Two sites of Fe(II), d ¼ 0:25ð2Þ mm sꢀ1
,
,
D ¼ 1:49ð3Þ mm sꢀ1 (14%) and d ¼ 0:37ð2Þ mm sꢀ1
D ¼ 0:80ð3Þ mm sꢀ1 (43%) and one site of Fe(III)
Fig. 4. XRD pattern of 2 decomposed in O2 (a), N2 (b) and H2 (c).
d ¼ 0:29ð2Þ mm sꢀ1, D ¼ 0:23ð3Þ mm sꢀ1 (43%) were

68
V.D. de Castro et al. / Polyhedron 23 (2004) 63–69
Table 3
57
€
Fe Mossbauer parameters for the complex 2 and the residue of de-
composition of 2 under O2 (a), N2 (b) and H2 (d)
Sample
Fe oxidation
state
IS
(mm sꢀ1
QS
(mm sꢀ1
)
Area
(%)
)
2
Fe(II)
0.40
2.25
100
O2
Fe(III)
Fe(II)
0.30
0.37
0.44
0.98
63
37
N2
H2
Fe(III)
Fe(II)
Fe(II)
0.30
0.25
0.37
0.44
1.49
0.80
43
14
43
Fe
Fe(III)
Fe(II)
0.26
0.26
0.36
0.19
0.12
0.83
77
11
12
The experimental errors associated to IS and QS are 0.02, 0.03,
respectively.
57
€
Fig. 5. Fe Mossbauer spectra of 2 and the corresponding residues
obtained in O2 (a), N2 (b), and H2(c).
other Fe/Pt alloys [16] and the data of metallic iron
d ¼ 0:29ð2Þ mm sꢀ1, D ¼ 0:14ð3Þ mm sꢀ1 and Bhf ¼ 28
57
€
T. The experiments of Fe Mossbauer have shown the
found in the material obtained in N2, Fig. 5(c). The iron
species are associated to the sulphide and phosphide, as
attested by the other results. Finally, the sample ob-
tained in H2 presents signals related to Fe(II),
d ¼ 0:36ð2Þ mm sꢀ1, D ¼ 0:83ð3Þ mm sꢀ1 (12%), and
Fe(III) with d ¼ 0:26ð2Þ mm sꢀ1, D ¼ 0:12ð3Þ mm sꢀ1
(11%). These cations are in the form of orthorhombic
phosphide FeP4 as the XRD pointed out. The more
formation of different sites of iron which can not be
directly attributed to any particular compound without
the help of other techniques. However, it is clear that a
very different iron phase is formed in the sample de-
composed in H2, that is very similar to the pattern ex-
hibited for iron containing alloys. No further evidence
was found for the formation of iron carbides, carbon-
ates or oxides, at least as major products.
remarkable is the sextet with d ¼ 0:26ð2Þ mm sꢀ1
,
D ¼ 0:19ð3Þ mm sꢀ1 and a hyperfine field (Bhf ) ¼ 27 T
(77%), which indicates some form of metallic iron,
Fig. 5(e). It was attributed to a disordered Pt1 ꢀ xFex
3.5. Scanning electron microscopy
The SEM images, Fig. 6, were obtained for each
residue in order to investigate the level of homogeneity
phase on the basis of the 57Fe Mossbauer parameters of
€
Fig. 6. Electron scanning micrographs of 2 decomposed in O2 (a), N2 (b) and H2 (c).

V.D. de Castro et al. / Polyhedron 23 (2004) 63–69
69
ꢀ
was partially developed at the Laboratorio de Micros-
and the presence of metallic agglomerates. No consid-
erable difference is observed for the decomposed mate-
rial in O2, Fig. 6(a), or N2, Fig. 6(b). It is obvious since
the grains correspond to the presence of metallic plati-
num. The major difference consists in the nature of the
dark and amorphous material that in the first case
consists of a mixture of Fe(II) and Fe(III) phosphates
and in the second product it is associated to a complex
combination of Fe(II) and Fe(III) phosphides or sulp-
hides. Also, the size of the particles obtained in oxygen
vary from 40 to 70 lm whist in nitrogen it is much
smaller. In the case of 2 decomposed in H2 a more
compact and homogenous material was obtained and
seems to be formed by very big grains (100–200 lm).
^
copia Eletronica e Microanalise (LMA) – Fısica,
Quımica, Geologia-UFMG and CDTN-CNEN financed
ꢀ
ꢀ
ꢀ
by FAPEMIG (Project CEX 1074/95).
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We thank TWAS – Third World Academy of Science
(Research Grant Agreement 00-229 RG/CHE/LA) and
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