Double complex salts [Pt(NH3)5Cl][M(C 2O4)3] ? nH2O (M = Fe, Co, Cr): Synthesis and study

Article abstract of DOI:10.1134/S0036023607100014

Double complexes [Pt(NH₃)₅Cl][Fe(C₂O ₄)₃] ? 4H₂O, [Pt(NH₃) ₅Cl][Co(C₂O₄)₃] ? 2H ₂O, and [Pt(NH₃)₅Cl][Cr(C₂O ₄)₃] ? 4H₂O were synthesized and studied by single-crystal X-ray diffraction, X-ray phase analysis, differential thermal analysis, elemental analysis, and IR spectroscopy. The crystal structures of the compounds were examined from the viewpoint of the close packing of coordination polyhedra. The thermal properties of the synthesized complexes and K ₃[M(C₂O₄)₃] salts (M = Fe, Co, Cr) were compared. A procedure for the synthesis of the FePt, CoPt, and CrPt intermetallic compounds through the thermolysis of the obtained complexes was developed.

Full text of DOI:10.1134/S0036023607100014

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2007, Vol. 52, No. 10, pp. 1487–1491. © Pleiades Publishing, Inc., 2007.
Original Russian Text © K.V. Yusenko, D.B. Vasil’chenko, A.V. Zadesenets, I.A. Baidina, Yu.V. Shubin, S.V. Korenev, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007,
Vol. 52, No. 10, pp. 1589–1593.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Double Complex Salts [Pt(NH3)5Cl][M(C2O4)3] · nH2O
(M = Fe, Co, Cr): Synthesis and Study
K. V. Yusenkoa, D. B. Vasil’chenkob, A. V. Zadesenetsa, I. A. Baidinaa,
Yu. V. Shubina, and S. V. Koreneva
a Nikolaev Institute of Inorganic Chemistry, Siberian Branch, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 3, Novosibirsk, 630090 Russia
b Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090 Russia
Received January 26, 2006
Abstract—Double complexes [Pt(NH3)5Cl][Fe(C2O4)3] · 4H2O, [Pt(NH3)5Cl][Co(C2O4)3] · 2H2O, and
[Pt(NH3)5Cl][Cr(C2O4)3] · 4H2O were synthesized and studied by single-crystal X-ray diffraction, X-ray phase
analysis, differential thermal analysis, elemental analysis, and IR spectroscopy. The crystal structures of the
compounds were examined from the viewpoint of the close packing of coordination polyhedra. The thermal
properties of the synthesized complexes and K3[M(C2O4)3] salts (M = Fe, Co, Cr) were compared. A procedure
for the synthesis of the FePt, CoPt, and CrPt intermetallic compounds through the thermolysis of the obtained
complexes was developed.
DOI: 10.1134/S0036023607100014
The synthesis of new double complex salts (DCS) solution of K3[Fe(C2O4)3] was poured with stirring to a
using an ion containing a platinum-group metal and a
counterion containing a base metal is of great interest
for researchers, because these compounds can serve as
precursors of various bimetallic materials. One exam-
ple of using similar systems is the preparation of finely
dispersed particles of solid solutions of metals or inter-
metallic compounds on various supports for the pro-
duction of highly efficient catalysts [1] with a lowered
content of noble metals.
solution of Tschugaeff’s salt. A fine precipitate of the
light green salt immediately appeared. After 1 h, the
precipitate was filtered through a preliminarily weighed
glass filter, washed with a minimum amount of ice-cold
water and a minor amount of acetone, and dried in air.
The yield was 90–97%.
Syntheses of complexes II and III were carried out
similarly. In both cases, the yield was 90–95%. These
complexes were green and blue colored, respectively.
Here, we describe the synthesis and properties
of three new DCS: [Pt(NH3)5Cl][Fe(C2O4)3] ·
4H2O (I), [Pt(NH3)5Cl][Co(C2O4)3] · 2H2O (II), and
[Pt(NH3)5Cl][Cr(C2O4)3] · 4H2O (III). In addition, we
prepared the corresponding bimetallic powders and
developed a procedure for the synthesis of the FePt,
CoPt, and CrPt intermetallic compounds.
The following method was used to obtain single
crystals of the DCS. A U-shaped tube was half-filled
with a hot 3% solution of agarose, and the solution was
let to congeal. A solution of Tschugaeff’s salt was
poured into one column of the tube, and the other col-
umn was filled with a solution of the salt of the corre-
sponding oxalate complex. The open ends of the tube
were sealed, and the tube was left in the dark for
1 week. As a result of diffusion of the solution, trans-
parent crystals of the DCS were formed as orthorhomic
plates with a size to 0.1 mm in the middle of the tube.
EXPERIMENTAL
The initial [Pt(NH3)5Cl]Cl3, K3[Fe(C2O4)3] · 3H2O,
K3[Co(C2O4)3] · 3H2O, and K3[Cr(C2O4)3] were syn-
thesized according to described procedures [2, 3]. To
increase the yield of [Pt(NH3)5Cl]Cl3 · H2O (Tschuga-
The thermal properties of the compounds were stud-
ied on a Q-1000 derivatograph modified for operating
under various gaseous atmospheres. A ~100-mg test
eff’s salt), excess hydrochloric acid was added to the sample was placed in a quartz crucible without a cover
mother solution obtained after the main portion of the and heated with a rate of 7–10 K/min under helium
salt was filtered, and the mixture was left for a week. As flowing at a rate of 150 mL/min.
a result, an additional portion of the product was
X-ray diffraction analysis of polycrystalline sam-
obtained as large needle-like crystals.
ples was carried out on a DRON-SEIFERT-RM4 dif-
Synthesis of complex I. Equimolar amounts of fractometer (CuKα radiation, graphite monochromator
[Pt(NH3)5Cl]Cl3 and K3[Fe(C2O4)3] were dissolved in
minimum amounts of water in two beakers, and then a discrimination). Samples were prepared by spreading
on reflected beam, scintillation detector with amplitude
1487

1488
YUSENKO et al.
Table 1. Crystal data and experimental details for DCS
from 5° to 60°; for thermolysis products, from 5° to
135°).
Parameter
I
II
III
The diffraction patterns of the prepared compounds
were completely indexed using single-crystal data,
which indicates that the samples were single phases
identical to the single crystal. X-ray diffraction analysis
of thermolysis products was carried out by analogy to
the diffraction patterns of the pure metals and interme-
tallic compounds presented in the PDF file [4]. The
parameters of the metal phases were refined for the
whole data body using the PowderCell 2.3 applied pro-
gram [5].
FW
575.39
571.54
542.48
Space group
a, Å
Pccn
P21
Pccn
39.0123(2) 8.5158(2) 38.901(2)
13.7232(7) 12.6409(4) 13.7267(7)
14.8990(8) 8.5726(3) 14.9141(8)
b, Å
c, Å
β, deg
V, Å3
90
105.000(3)
90
7976.5(4) 891.38(24) 7963.9(7)
calcd, g/cm3
2.33
16
2.50
2
2.30
16
X-ray structure analysis of compounds I–III (the
refinement of unit cell parameters and the measurement
of diffraction refection intensities determining crystal
structures) was carried out on a Bruker AXS P4 auto-
mated diffractometer (MoKα radiation, graphite mono-
chromator, θ/2θ scan mode, room temperature). The
crystallographic parameters and details of the experi-
ment and structure refinement for complexes I–III are
presented in Table 1. The structures were solved by the
heavy atom method and refined in the anisotropic
approximation. All calculations were performed using
the SHELX97 program package [6].
ρ
Z
θ range, deg
2.31–30.47 2.46–32.58 2.08–27.48
Number of reflec- 11093/6104 8310/5898 9118/5958
tions: total/inde-
pendent
Index range
–51 < h < 55, –12 < h < 9, –50 < h < 40,
–19 < k < 9, –17 < k < 19, –8 < k < 17,
–19 < l < 12 –12 < l < 10 –19 < l < 15
Goodness-of-fit
1.117
0.771
1.072
(for F2)
The coordinates of atoms, bond angles, and inter-
atomic distances are available from the authors.
∆ρmax, ∆ρmin
,
2.545, –6.542 2.072, –0.993 2.037, –3.172
e Å–3
Number of re-
fined parameters
554
258
553
RESULTS AND DISCUSSION
The crystals of complexes I and III are isostructural
to each other and are not isostructural to the monoclinic
crystals of complex II. The crystal structure of
K3[M(C2O4)3] · 3H2O (M = Fe, Cr) differs from that of
K3[Co(C2O4)3] · 3H2O [7].
R1 and wR2
for I > 2σ(I)
R1 and wR2
for all reflections
0.0509,
0.1093
0.0218,
0.0460
0.0511,
0.1184
0.0817,
0.1589
0.0260,
0.0471
0.0896,
0.1326
The unit cell of complex I is shown in Fig. 1. The
FeO6 octahedron around the complex anion is less dis-
torted than that in the precursor K3[Fe(C2O4)3] · 3H2O.
The minimum and maximum “right” OFeO angles in
the FeO6 octahedra are 79.4° and 105.8° in the precursor
an alcohol suspension on the polished side of a fused
quartz cell. A sample of polycrystalline silicon (a =
5.4309 Å) prepared similarly was used as an external
standard. Diffraction patterns were detected in the step-
to-step mode (for the complex salts, in the 2θ range salt and 80.4° and 96.4° in complex I. For the
Fig. 1. Unit cell of [Pt(NH ) Cl][Fe(C O ) ] · 4H O. The oxygen atoms of the water molecules are shaded.
3 5
2
4 3
2
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 10 2007

DOUBLE COMPLEX SALTS [Pt(NH3)5Cl][M(C2O4)3] · nH2O
1489
Fig. 2. Mutual arrangement of cationic and anionic layers in [Pt(NH ) Cl][Fe(C O ) ] · 4H O and [Pt(NH ) Cl][CrOx ] · 4H O
3 5
2
4 3
2
3 5
3
2
(positions of the Fe (Cr) atoms are gray, and those of the Pt atoms are white).
[Pt(NH3)5Cl]3+ complex cation, this distortion is notice-
ably weaker: the deviations of the angles from ideal val-
ues are within 1°. The metal–ligand distances also
change insignificantly and fall within the experimental
error.
ments on the decomposition of [Pt(NH3)5Cl][Fe(C2O4)3]
made it possible to optimize the thermolysis of the
oxalate DCS to increase the yield of the intermetallic
compounds. A weighed boat with the compound under
study was placed in a quartz tubular reactor through
which hydrogen was passed. The reactor was first heated
to 400°C using a split tubular oven. The sample was stored
at this temperature for 0.5 h, then the temperature was
increased to 700°C, and the sample was stored for 2 h
more. Then, the reactor was filled with helium, and the
sample was stored for 0.5 h under these conditions.
Due to a comparatively low symmetry and large
sizes of the complex ions, the structures of crystals
I−III are rather loosen. Large channels 4.5–5.5 Å in
diameter allow crystallization water molecules to
incorporate into the structures.
In the crystals of complexes I–III, the complex cat- Then, the reactor with the boat was cooled to room tem-
perature, and the boat with the product was weighed.
The annealing in helium is necessary to prevent hydro-
gen absorption by metal products: the samples can
ignite on contact with atmospheric oxygen. A charac-
teristic feature of the decomposition in hydrogen of all
the synthesized DCS is that the complexes change to
black in the temperature interval from 100 to 150°C,
and the change itself takes ~5 s and is well visualized.
The data obtained are presented below.
ions and anions form separate layers at distances of
4.8–4.9 Å. In a crystal of complex I (Fig. 2), the dis-
tances are as follows: Pt···Fe 5.48–5.88Å, Fe···Fe
6.28−7.78 Å, and Pt···Pt 7.20−7.78 Å. In the structure of
complex II, layers are also formed but they are built
according to another principle. The Pt and Co atoms
form common layers between which crystal-water mol-
ecules are arranged also as layers (Fig. 3).
The presence of crystal water is also confirmed by
the IR spectra of the synthesized DCS (absorption
bands at 3600–3400 cm–1).
Found ΣFW,
Calcd,
wt %
Complex
wt %
All compounds synthesized were subjected to ther-
mal decomposition in a hydrogen atmosphere for the
following two purposes: carrying out the elemental anal-
ysis of the DCS to the sum of the metals formed upon
decomposition and obtaining PtM (M = Fe, Co, Cr)
intermetallic compounds. Thermolysis in a hydrogen
I
II
III
37.44
37.65
35.92
32.18
37.64
31.84
This divergence between the experimental and cal-
atmosphere yields metal powders. Their phase composi- culated data is due to the fact that the DCS powders
tion depends on the heating conditions. A set of experi- were taken for elemental analysis while the number of
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 10 2007

1490
YUSENKO et al.
Fig. 3. Mutual arrangement of cationic and anionic layers in the crystal of [Pt(NH ) Cl][Co(C O ) ] · 2H O (positions of the central
3 5
2
4 3
2
Pt atoms are white, and those of Co are gray) between which layers of water molecules are arranged. The Pt···Co distances are
5.14−6.00 Å.
water molecules in the structure was determined for metal powder obtained by the thermolysis of compound
single crystals. Evidently, the evaporation of weakly I using this method contains Pt (~30 wt %), Pt3Fe
bound water occurred more rapidly in the powders and,
hence, the results were underestimated.
(~40 wt %), and Fe3O4 (~20 wt %). Iron oxide is
formed due to contact with air oxygen after the sample
was taken from the reactor.
The final thermolysis products of compounds I and
III are the corresponding intermetallic compounds. The
diffraction pattern of the sample of complex II contains
broadened low-intensity superstructural peaks. A solid
solution with a low degree of ordering is formed,
because CoPt begins to decompose at ~800°C [8]. The
unit cell parameters of the metallic thermolysis prod-
ucts are given in Table 2.
The decomposition of the DCS in a hydrogen atmo-
sphere at a constant rate without stopping at certain
temperature yields polyphase systems containing
phases of pure metals and their partially ordered solid
solutions rather than intermetallic compounds. The
Thermal curves for DCS I–III and initial Tschuga-
eff’s salt are shown in Fig. 4. The results can conve-
niently be analyzed using published data [9] on the
thermal stability of oxalate complexes of various tran-
sition metals. Potassium trioxalatoferrate(III) decom-
poses at 230–265°C to evolve CO2. Tschugaeff’s salt
starts to decompose with ammonia evolution at
~150°C, and the main step of decomposition begins at
250–260°C and ends the formation of metallic plati-
num. The superposition of these thermal curves gives
an approximate image of the thermal curve for salt I.
The first step is the dehydration of the complex, and the
second step corresponds (by its weight loss) to the elim-
ination of two CO2 molecules. This step coincides in
temperature with the transformation of the complex
into a black intermediate upon decomposition in hydro-
gen. Then, the decomposition of the coordination
sphere of chloropentaammineplatinum occurs. The
thermal curve for salt III can be characterized using the
thermal curves for potassium trioxalatochromate(III)
and Tschugaeff’s salt. The first step represents the
dehydration of the complex, and three water molecules
fall per formula unit. Then, a prolong step of complete
Table 2. Phase compositions of the degradation products of
DCS I–III in hydrogen
Composition
Com-
of degradation
product
a, Å
c, Å
CSR, Å
plex
I
II
III
PtFe
3.860(2) 3.732(2) 200–300
3.760(5) 3.750(5) 250–350
3.837(2) 3.825(5) 250–350
Pt0.5Co0.5
PtCr
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 10 2007

DOUBLE COMPLEX SALTS [Pt(NH3)5Cl][M(C2O4)3] · nH2O
1491
tochromium There is an analogy with an increase in the
oxidation potential for the three-charged ions in the
m, %
100
165°C,
84.0%
series Cr3+
Fe3+
Co3+, as for the oxalate com-
(d)
(c)
(b)
50°C,
250°C,
64.7%
80
60
100.0%
plexes [8]. The decomposition ends at 305°C for com-
plexes I and II and at 425°C for salt III.
305°C,
49.0%
The final products of DCS decomposition in an inert
atmosphere contain metallic platinum and oxide phases
of base metals, whereas the decomposition product of
complex I also contains an insignificant amount of a
solid solution of Pt0.5Fe0.5.
40
100
225°C,
66.6%
110°C,
92.5%
80
60
305°C,
46.0%
ACKNOWLEDGMENTS
40
100
The authors are grateful to N.I. Alferova for help in
recording IR spectra.
138°C,
92.5%
80
60
250°C,
87.0%
This work was financially supported by the Presid-
ium of the Russian Academy of Sciences in the frame-
work of the Program “Development of Methods for
Synthesis of New Chemical Substances and Creation
of New Materials Design” (project no. 8-17) and the
Russian Foundation for Basic Research (project
nos. 07-03-01038-a and 00-15-97448).
250°C,
42.0%
40
100
(‡)
275°C,
94.6%
200°C,
97.3%
80
60
40
410°C,
44.3%
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3
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 10 2007