Synthesis and some properties of Heteronuclear platinum and palladium carbonyl clusters

Article abstract of DOI:10.1134/S0036023610020087

Heteronuclear clusters of general formula [Pt_xPd _y(CO)_z] were synthesized by reaction of CO with PtCl ₄ + PdCl₂ solutions in 95% ethanol at room temperature and atmospheric pressure. The products isol

Full text of DOI:10.1134/S0036023610020087

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2010, Vol. 55, No. 2, pp. 186–189. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © I.V. Fedoseev, N.S. Gerasimova, A.Yu. Loginova, 2010, published in Zhurnal Neorganicheskoi Khimii, 2010, Vol. 55, No. 2, pp. 191–194.
SYNTHESIS AND PROPERTIES
OF INORGANIC COMPOUNDS
Synthesis and Some Properties of Heteronuclear Platinum
and Palladium Carbonyl Clusters
I. V. Fedoseev, N. S. Gerasimova, and A. Yu. Loginova
Moscow State Technical University, Kaluga Branch, Kaluga, Russia
Eꢀmail: fn6ꢀkf@bmstuꢀkaluga.ru
Received October 30, 2007
Abstract—Heteronuclear clusters of general formula [PtxPdy(CO)z] were synthesized by reaction of CO with
PtCl4 + PdCl2 solutions in 95% ethanol at room temperature and atmospheric pressure. The products isoꢀ
lated were analyzed by IR spectroscopy, thermogravimetry, and Xꢀray powder diffraction.
DOI: 10.1134/S0036023610020087
A platinum(0) carbonyl complex of general forꢀ are readily subject to hydrolysis, which excludes
mula [Pt(CO)2]n, where n is multiple of three, is known potential isolation of any heteronuclear complexes.
for a rather long time. This product in the form of dark
cherry films was observed, in particular, by Gel’man in
reaction of CO with Na2PtCl4 solution [1]. Synthesis
and some properties of this cluster were described
in [2, 3].
Earlier [12] we reported that after the reaction of
CO with H2PtCl6–H2PdCl4–HCl solutions it was
impossible to separate platinum from palladium,
which was always coprecipitated with platinum, and
the Pt : Pd ratio in the precipitate did not virtually
depend on this ratio in the initial solution.
We know a series of palladium carbonyl derivatives:
palladium(II) and palladium(I) carbonyl halides, carꢀ
bonyl hydrides, and organocarbonyls [4]. However,
palladium(0) carbonyl was synthesized only at cryoꢀ
genic temperatures (4.2 to 20 K) by cocondensation of
palladium atoms and CO (from mixture with Ar).
Pt : Pd in solution
,
1.85;
0.57.
moles
:
Pt : Pd in precipitate
moles
0.054;
0.047.
:
Thus, Pd(CO)n carbonyls, where
n = 1–4, were synꢀ
thesized and characterized by IR spectroscopy [5, 6].
This enabled us to assume the redox hydrolysis of
some heteronuclear Pt–Pd carbonyl chloride taking
place in this case.
In the spectra of these compounds, νСО is observed
in the range from 2070 to 2016 cm–1, evidencing weak
Pd–CO bond that is responsible for the thermal instaꢀ
We isolated the compound in question as follows.
bility of palladium carbonyls. However, Pd–CO bondꢀ Through H2PtCl6–H2PdCl4–HCl solution, CO was
ing is essentially strengthened by addition of neutral passed at room temperature under atmospheric presꢀ
ligands such as alkyl and aryl to the inner sphere. For sure until the start of decomposition (darkening), then
example, in the case of Pd23(CO)20(PЕt3)8 νСО is 1865, the solution was rapidly cooled and CsCl crystals were
1839, and 1815 cm–1 [7]. A similar pattern is observed added. Almost immediately, we observed formation of
for other clusters of this type [8].
small dirty yellow crystals, which were filtered off and
washed with acetone. According to chemical analysis,
this product contained platinum and palladium in a
1 : 1 molar ratio, and its IR spectrum showed νСО of
1955, 1920, and 1880 cm–1.
The redox hydrolysis can be decelerated by
decreasing water concentration, i. e., using aqueous
organic solutions.
There are known heteronuclear carbonyl clusters
of platinum and other platinumꢀgroup metals (e.g.,
[
Rh5Pt(CO)15] [9]), with the exception of palladium.
Earlier [10], we found that interaction of CO and
hydrochloric acid solutions of H2PtCl6 + H2PdCl4
which results in the recovery of these metals in the
form of [Pt(CO)2]n and Pd, respectively, involves forꢀ
mation of platinum and palladium heteronuclear carꢀ
bonyl chlorides as intermediates. We isolated a cesium
salt containing platinum and palladium in the ratio
,
We carried out a series of experiments with such
solutions.
For their preparation, we used PtCl4 and PdCl2 and
1 : 1 (mol/mol) with νСО of 1955, 1920, and 1880 cm–1 95% ethanol as solvent. Carbonylation was provided
[10], while Cs2[Pd2(CO)2Cl4] salt showed νСО of 1916 by bubbling carbon monoxide (CO flow was 1 volume
and 1873 cm–1 [11]. However, in aqueous hydrochloꢀ of gas per 1 volume of solution per minute) at room
ric acid solutions, all newly formed carbonyl chlorides temperature and vigorous stirring.
186

SYNTHESIS AND SOME PROPERTIES
Table 1. Characteristics of Pt–Pd heteronuclear carbonyl clusters
187
Composition of clusters for formula
PtxPdy(CO)z, where the sum
is multiple of three
Pt : Pd : CO
ratio in clusters
Composition of clusters
for formula [M3]n(CO)z
x
+
y
ν
, cm–1
CO
Pt7Pd2(CO)15
Pt7Pd2(CO)14
Pt4Pd5(CO)14
Pt5Pd(CO)11
Pt7Pd3(CO)12
Pt11Pd2(CO)19
Pt13Pd(CO)30
Pt13Pd2(CO)23
Pt17Pd4(CO)41
Pt7Pd2(CO)15
Pt7Pd2(CO)14
Pt4Pd5(CO)14
Pt5Pd(CO)11
Pt21Pd9(CO)36
Pt33Pd6(CO)57
Pt39Pd3(CO)90
Pt13Pd2(CO)23
Pt17Pd4(CO)41
[M3]3(CO)15
[M3]3(CO)14
[M3]3(CO)14
[M3]2(CO)11
[M3]10(CO)36
[M3]13(CO)57
[M3]14(CO)90
[M3]5(CO)23
[M3]7(CO)47
2060, 1880
–
–
–
2067, 1887
2100, 1920
2067, 1880
2067, 1880
2067, 1883
In all our experiments, the same qualitative nature water resulted in precipitation of dark cherry flakes
of carbonylation was as follows.
also containing platinum and palladium.
(1) The color of the initial solution, which conꢀ
tained in some cases a small quantity of a solid phase
in the form of nondissolved chlorides, quickly changed
from mahogany to peach. At the same time, the solid
phase dissolved.
(2) After carbonylation for 5 to 15 min (depending
on the solution contents), the color sharply changed
into dirty green with simultaneous precipitation of
more or less niello.
(3) Further treatment for 1 to 2 h resulted in stabiꢀ
lization of the system consisting of a green grass soluꢀ
tion and some niello.
(4) Exposure of the green solution (filtrate) in a CO
atmosphere for 24 to 72 h resulted in precipitation of a
lot of crystals of blackꢀandꢀblueꢀandꢀviolet color.
Studying metal distribution of metals between
products at various stages of synthesis, we found the
following.
The niello residue was 80 to 90% palladium, but in
all cases some contained platinum as well as carbon
monoxide. The degree of palladium recovery to niello
depended primarily on the contents of the initial soluꢀ
tion and decreased at higher palladium/platinum
ratios in the latter.
Therefore, all intermediates and final products of
the synthesis contained both metals.
The resulting precipitates were analyzed for Pt, Pd,
and CO. We also recorded IR spectra, which did not
show any absorption bands in the ranges from 3600 to
2500 and from 420 to 200 cm–1, evidencing no organic
substances and metal–chlorine bonds in the test samꢀ
ples. The results are summarized in Table 1.
Longoni and Chini [13] described the chemical
characteristics of platinum dianion oligomers
[Pt3(CO)6]2n−
(
n
is 1 to 6 and ~10) recovered as salts of
alkali metals and quaternary ammonium bases. At
higher , the degree of reduction of oligomers
decreases and at > 6 they turn into nonionic species.
n
n
A similar effect is provided by an acid medium.
Structurally these clusters represent triangles of Pt
atoms arranged one over another. The distances
between Pt atoms in these triangles are 2.66 Å and the
distances between triangles are 3.04 Å. Here every
other CO ligand is terminal and the others are bridgꢀ
2−
ing. The IR spectra of
show a systematic
[Pt3(CO)6]n
change in the major νСО frequencies along with growꢀ
ing
n.
The green solution got absolutely dry upon evapoꢀ
ration of alcohol and yielded a dark cherry dry residue,
which was stable to water. Palladium was detected in
all analyzed solutions, while the platinum/palladium
ratio varied depending on this ratio in the initial soluꢀ
tions. In particular, we determined Pt : Pd molar ratios
of 2 : 1 and 7 : 2.
n
1
2
3
4
5
6
ν
СО, cm–1 1945 1995 2030 2040 2055 2065
1740 1795 1840 1860 1870 1875
Our synthesized heteronuclear Pt–Pd carbonyl
clusters may be considered as derivatives from
[Pt3(CO)6]n oligomers, where some Pt atoms are subꢀ
All crystalline precipitates contained platinum and
palladium in various ratios. The yield of precipitates
ranged from 35 to 65% of the total quantity of both
metals in the initial solutions.
According to qualitative analysis, all filtrates resultꢀ
ing from isolation of crystalline precipitates contained
stituted with Pd atoms and
spectra of clusters of both types) of general formula
[PtxPdy]n(CO)z, where the sum is multiple of three
and < 6
The smaller number of CO ligands in heteronuꢀ
n
≥
6 (if we compare the IR
x+ y
z
n.
platinum and palladium. Dilution of the filtrates with clear Pt–Pd clusters compared to [Pt3(CO)6]n clusters
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 2 2010

188
FEDOSEEV et al.
Table 2. Powder diffraction data
Pt : Pd ratio in initial solution, mol/mol
ν
in products, cm–1
d, Å
CO
2 : 1
5 : 1
2060, 1880
2054, 1870
–
4.292; 2.477; 1.648; 1.289; 1.244
4.267; 2.479; 1.652; 1.283
4.295; 2.471; 1.649; 1.284
11 : 1
is probably because Pd–CO bonds are weaker than some series of carbonyl clusters with general formula
Pt–CO bonds.
[
PtxPdy(CO)z], where the
x + y sum is multiple of three.
The figure shows the results of thermogravimetric
analysis for one sample of our synthesized Pt–Pd carꢀ
bonyl clusters in helium and air.
The thermal curves recorded in helium atmosphere
show two decomposition stages in the samples. The
first stage, which accounts for 65.8 to 73.3% of the
total weight loss, ends at 130°С, and the second stage
begins at 130°С and ends at 230–240°С. Both decomꢀ
position stages are endothermic.
For some crystalline precipitates, we calculated
interplanar spacings (Table 2).
As we see in Table 2, the studied samples have difꢀ
ferent νСО frequencies and different interplanar spacꢀ
ings though there are some common features. The
studied samples contain no free Pt or Pd.
The results given in Tables 1 and 2 enable us to
suggest that our synthesized products belong to
In the case of decomposition in air (figure, b), the
second stage is far faster, takes place within the range
from 140 to 160°C, and is exothermic probably, due to
the direct oxidation of CO to СО2 in the complex.
Δ
m, mg
T, °C
(а)
0
The powder diffraction patterns of the thermolysis
TG
products showed crystalline platinum (
palladium ( = 2.24 Å), and their solid solution.
Longoni and Chini [13] reported that the thermal
decomposition of [NВu4]2[Pt3(CO)6]n, where is 4 to
d = 2.26 Å),
4
d
T
500
300
n
8
DTA
6, takes place within the range from 120 to 150°C and
involves other carbonyl derivatives as intermediates in
agreement with the results of our thermogravimetric
analysis of Pt–Pd carbonyl clusters in air.
12
Therefore, the results of our studies evidence synꢀ
thesis of a new type of heteronuclear cluster as prodꢀ
ucts of partial substitution of Pd atoms for Pt atoms in
[Pt3(CO)6]n oligomers.
Taking into account the properties of our syntheꢀ
sized products, we should suggest that they can be used
for the preparation of platinum–palladium solid soluꢀ
tion powders, platinum–palladium supported cataꢀ
lysts, and composite materials based on platinum–
palladium alloys, in particular, dispersionꢀstrengthꢀ
ened alloys containing refractory oxides.
16
100
T, °C
Δ
m
, mg
(b)
0
4
TG
500
300
8
12
16
T
DTA
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100
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RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 2 2010

SYNTHESIS AND SOME PROPERTIES
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