Synthesis, crystal structure, and thermal properties of [Pd(NH 3)4][AuCl4]2

Article abstract of DOI:10.1134/S0036023607030138

The double complex salt [Pd(NH₃)₄][AuCl ₄]₂ was synthesized and studied by X-ray diffraction: a = 7.5234(6) ?, b = 7.7909(5) ?, c = 8.0247(6) ?, α = 108.483(2)°, β = 106.497(2)°, γ = 99.972(3)°, V = 409.43(5) ?³, space group P1?, Z = 1, ρ _calod = 3.456 g/cm³, R = 0.0267. The compound was characterized by powder X-ray diffraction, thermal analysis, and IR and Raman spectroscopy. The metal products of thermolysis of the complex were studied by powder X-ray diffraction. Nauka/Interperiodica 2007.

Full text of DOI:10.1134/S0036023607030138

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2007, Vol. 52, No. 3, pp. 371–377. © Pleiades Publishing, Inc., 2007.
Original Russian Text © P.E. Plyusnin, I.A. Baidina, Yu.V. Shubin, S.V. Korenev, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 3, pp. 421–427.
COORDINATION COMPOUNDS
Synthesis, Crystal Structure, and Thermal Properties
of [Pd(NH ) ][AuCl ]
3
4
4 2
P. E. Plyusnin, I. A. Baidina, Yu. V. Shubin, and S. V. Korenev
Institute of Inorganic Chemistry, Siberian Division, Russian Academy of Sciences,
pr. Akademika Lavrent’eva 3, Novosibirsk, 630090 Russia
E-mail: plus@che.nsk.ru
Received January 26, 2006
Abstract—The double complex salt [Pd(NH ) ][AuCl ] was synthesized and studied by X-ray diffraction:
3
4
4 2
a = 7.5234(6) Å, b = 7.7909(5) Å, c = 8.0247(6) Å, α= 108.483(2)°, β = 106.497(2)°, γ = 99.972(3)°, V =
3
3
4
09.43(5) Å , space group P1 , Z = 1, ρcalcd = 3.456 g/cm , R = 0.0267. The compound was characterized
by powder X-ray diffraction, thermal analysis, and IR and Raman spectroscopy. The metal products of ther-
molysis of the complex were studied by powder X-ray diffraction.
DOI: 10.1134/S0036023607030138
Double complex salts (DCSs) [1, 2] are used as pre-
The required amount of H[AuCl ] (c ~ mol/L) was
4 Au
cursors of various functional materials in many fields of added to
a
saturated aqueous solution of
technology. One of the applications of DCS is the [Pd(NH ) ](NO ) (c ~ 0.3 mol/L). Yellow-colored thin-
3
4
3 2 Pd
development of bimetallic heterogeneous catalysts for
various processes. Previously [3], it was shown that
needle crystals precipitated immediately from the reac-
tion mixture. The precipitate was filtered off in vacuum,
washed with a minimum amount of water and ethanol,
bimetallic AuPd catalysts are active in H oxidation
2
reactions in membrane fuel cells [3]. The compound and dried in air. The yield was ~ 90%.
synthesized and studied here is among the first exam-
The experiments showed that with reactant molar
ples of a precursor containing both gold and palladium.
ratios of 2 : 1 to 5 : 1, the reaction yields the double
complex salt [Pd(NH ) ][AuCl ] , which is due to its
3
4
4 2
low solubility.
EXPERIMENTAL
The single crystal for X-ray diffraction was pre-
The initial compounds used were [Pd(NH ) ]Cl , pared by slow crystallization of the reaction mixture
3
4
2
from highly dilute solutions of the starting compounds.
[
Pd(NH ) ](NO ) , and H[AuCl ]. The [Pd(NH ) ]Cl
3 4 3 2 4 3 4 2
was prepared by a procedure known from work [4] and
Estimation of the solubility gives ~0.7 g per 100 g of
then converted into [Pd(NH ) ](NO ) by replacing the water. The DCS is also poorly soluble in ethanol but is
3
4
3 2
chloride ion by the nitrate ion through the reaction with quite soluble in acetone (~10 g per 100 g of water),
silver nitrate. Solutions of H[AuCl ] of a specified con- which allows impregnation of catalyst supports by
4
rather concentrated solutions of DCS.
centration were prepared by dissolving gold (99.99%)
in aqua regia followed by concentrating with hydro-
chloric acid and water.
The sum of the metals was determined by reducing
the sample in a silica boat in a flow of hydrogen in a
reactor.
Anal. calcd. (%): Au + Pd, 58.72.
Found (%): Au + Pd, 58.72 ± 0.3.
According to powder X-ray diffraction, the product
of DCS recrystallization from acetone was fully identi-
cal to the starting compound obtained from an aqueous
[
Pd(NH ) [AuCl ] was first synthesized from
3 4 4 2
[
Pd(NH ) ]Cl ; however, according to powder X-ray
3 4 2
diffraction and IR spectroscopy, the product always
contained minor amounts (~1–3%) of palladosamine
Pd(NH ) Cl . Palladosamine was formed during the
3
2
2
synthesis upon the replacement of inner-sphere NH
3
–
molecules by Cl ions. Subsequently, the syntheses solution.
were carried out starting from [Pd(NH ) ](NO ) thus
3
4
3 2
The IR spectra of the samples as KBr pellets were
avoiding this side reaction. However, the presence of recorded on a Scimitar FTS 2000 FT IR spectropho-
–
1
excess HCl in the solution H[AuCl ] gives rise to
4
tometer in the range 400–4000 cm . The thermo-
Pd(NH ) Cl even when the nitrate [Pd(NH ] (NO ) is gravimeric measurements were carried out on a Q-1000
3
2
2
3 4
3 2
used as the starting reactant.
derivatograph modified for measurements in various
3
71

3
72
PLYUSNIN et al.
Table 1. Crystal data and X-ray experiment details for gas atmospheres (air, helium). A sample (~100 mg)
[
Pd(NH ) ][AuCl ]
3 4 4 2
was placed in a silica crucible and heated at a rate of
0 K/min in a helium flow (150 mL/min). Calorimetric
1
Molecular formula
H Au Cl N Pd
12 2 8 4
measurements were performed on an STA 409 PC
Luxx® derivatograph (Netzsch) (heating rate 5 K/min,
helium, g-Al O crucible).
M
852.07
293(2)
2
3
Recording temperature, K
Powder X-ray diffraction experiment was carried
λ, Å
0.71073
Triclinic
out on a DRON-Sefert-RM4 diffractometer (CuK radi-
α
System
ation, reflected-beam graphite monochromator, scintil-
lation detector with amplitude discrimination). The
samples were prepared by applying an ethanol suspen-
sion to the polished side of a standard silica cell. A
polycrystalline silicon sample (a = 5.4309 Å) prepared
in a similar way was used as the external standard. The
X-ray diffraction patterns of the complex salts were
recorded in a step-by-step mode in the 2θ range from 5°
to 60°, and those of thermolysis products were mea-
sured in the 2θ range from 5° to 135°.
Space group
P1
Unit cell parameters
a, Å
7.5234(6)
7.7909(5)
8.0247(6)
b, Å
c, Å
α, deg
β, deg
γ, deg
V, Å3
108.483(2)
106.497(2)
99.972(3)
409.43(5)
1
The powder X-ray diffraction patterns of the ther-
molysis products were indexed using data for pure met-
als and compounds found in the PDF database [5]. The
unit cell parameters for metallic phases were refined by
the least-squares method for the whole data array using
the PowderCell 2.4 program [6].
Z
ρcalcd, g/cm–3
µ, mm–1
X-Ray crystallography. The unit cell parameters
and the experimental intensities for crystal structure
solution for the DCS were measured at room tempera-
ture on a Bruker-Nonius X8Apex four-circle automated
diffractometer equipped with an xy-detector (MoKα
radiation, graphite monochromator). The crystal data
and the details of the X-ray experiment are summarized
in Table 1. The structure was solved by the direct
3.456
20.240
F(000)
380
Crystal size (mm3)
Data collection range over θ, deg
Ranges of indices
0.12 × 0.04 × 0.01
2.87–25.34
–8 ≤ h ≤ 9
2
method and refined by least squares for F in the aniso-
8
≤ k ≤ 9
tropic approximation; the hydrogen atoms were speci-
fied geometrically. The coordinates of basis atoms are
presented in Table 2; selected interatomic distances and
bond angles are in Table 3.All calculations were carried
out by the SHELX97 program package [7]. The X-ray
–
9 ≤ l ≤ 9
The number of measured reflections
2686
The number of independent reflec- 1436 [R(int) = 0.0222]
tions
diffraction pattern of [Pd(NH ) ][AuCl ] was indexed
3 4
4 2
using single-crystal data; the results indicate the single-
phase nature of the product.
Data collection completeness for θ,
%
96.0
Transmission (max and min)
0.8232 and 0.1950
1436, 73
RESULTS AND DISCUSSION
The number of reflections/refined
parameters
The structural units of the compound are
2
+
–
[
Pd(NH ) ] complex cations and [AuCl ] complex
3 4 4
GOOF
1.183
anions present in a 1 : 2 ratio. The structure of the
complex species with atom numbering and the extra
coordination of the central metal atoms are shown in
Fig. 1. The palladium atom is located in the center of
symmetry and has a square-planar coordination
formed by the four nitrogen atoms of ammonia mole-
cules. The average Pd–N distance is 2.043 Å, and the
bond angles are nearly 90°. The square coordination
of the Pd atom is completed to bipyramidal by con-
tacts with the Cl atoms of the gold complex anions at
R-factor (I > 2σ (I))
R1 = 0.0267
wR = 0.0867
2
R-factor (all data)
R1 = 0.0294
wR = 0.0879
2
Extinction coefficient
0.0017(7)
The residual electron density (max
1.676 and –1.031
–
3
and min), e Å
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 3 2007

SYNTHESIS, CRYSTAL STRUCTURE, AND THERMAL PROPERTIES
373
Table 2. Atom coordinates and thermal parameters for the structure of [Pd(NH ) ][AuCl ]
4 2
3
4
2
Atom
x
y
z
U , Å
eq
Au(1)
Pd(1)
Cl(1)
Cl(2)
Cl(3)
Cl(4)
N(1)
0.04106(5)
0.5
0.57981(5)
0
0.27564(5)
0
0.02682(19)
0.0260(3)
0.0460(7)
0.0417(6)
0.0480(7)
0.0530(8)
0.040(2)
–0.0087(4)
0.3662(4)
0.0888(5)
–0.2823(4)
0.3467(13)
0.4232(15)
0.2827(4)
0.6347(4)
0.8813(4)
0.5219(4)
0.1672(13)
0.0617(13)
0.2742(5)
0.4091(4)
0.2846(5)
0.1327(5)
0.1114(13)
N(2)
–0.2344(13)
0.042(2)
Pd...Cl distances of 3.584 Å; the Pd...Au distance is
.904 Å.
Decomposition of the double complex salt
4
[Pd(NH ) ][AuCl ] occurs in the same way in air and
3
4
4 2
under helium. The thermoanalytical curves obtained in
a helium atmosphere at a heating rate of 10 K/min are
shown in Fig. 4. Thermal decomposition occurs in three
stages. The first stage takes place at 115–160°ë and is
accompanied by an endotherm with a change in color
from yellow to dark brown without losing mass. The
–
The [AuCl ] complex anion also has a square-pla-
4
nar configuration; the atom deviations from the mean-
square coordination plane do not exceed 0.03 Å. The
Au–Cl distances are in the range of 2.268–2.288 Å
cf. 2.277 Å), the bond angles are 90° to within 0.34°.
These geometric characteristics are consistent with
(
the data reported for the salt [Ir(NH ) Cl][AuCl ]Cl in
3
5
4
work [2], in which the range of Au–Cl bond lengths is
.263–2.280 Å. The square coordination of the gold
Table 3. Selected interatomic distances (d) and bond angles
2
(
ω) in the structure of [Pd(NH ) ][AuCl ]
3
4
4 2
atom in the structure is completed to (4 + 1) by the
chlorine atom of the neighboring complex anion at an
Au–Cl distance of 3.52 Å (Au···Au, 4.328 Å). The
sixth position at 4.024 Å is occupied by the Au atom
Bond
d, Å
Angle
ω, deg
of the other complex anion. Thus, the complex anions Au(1)–Cl(4) 2.268(3) Cl(4)Au(1)Cl(2) 178.04(11)
are stacked along the z axis. The angle between the
normals to the planes of the Pd and Au coordination
squares is 83.5°.
Au(1)–Cl(2) 2.275(3) Cl(4)Au(1)Cl(1)
Au(1)–Cl(1) 2.276(3) Cl(2)Au(1)Cl(1)
Au(1)–Cl(3) 2.288(3) Cl(4)Au(1)Cl(3)
Pd(1)–N(2) 2.038(9) Cl(2)Au(1)Cl(3)
90.09(11)
90.00(10)
89.66(11)
90.31(10)
The packing of structural units in the crystal is
shown in Fig. 2. Apart from the additional contacts of
the central ions, the complex ions are linked by weak
hydrogen bonds Cl···H–N (Cl···N, 3.43–3.55 Å; Fig. 3).
The shortest Cl···Cl interatomic contacts between the
anions (3.25 and 3.36 Å) are also noteworthy. Each Pd
complex cation is surrounded in the structure by ten
Au complex anions (Pd···Au, 4.904–6.374 Å).
Pd(1)–N(1) 2.048(8) Cl(1)Au(1)Cl(3) 178.36(11)
N(2)Pd(1)N(1)
89.9(4)
Generally, the structure of the compound can be
classified as layered, which is also indicated by the
crystal shape.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 3 2007

3
74
PLYUSNIN et al.
Cl(1C)
.584
Cl(3)
Cl(2)
3
4
.02
N(2)
Au(1B)
N(1A)
Au(1)
3
.52
Pd(1)
N(1)
Cl(1A)
N(2A)
Cl(4)
Cl(1)
Cl(1D)
Fig. 1. Structure of the complex species with atom numbering and additional contacts of the central metal atoms.
X-ray diffraction pattern of the thermolysis product
[
AuCl4]–
(
A) exhibits no reflections corresponding to the DCS;
however, it contains several broad diffuse peaks and
narrow low-intensity reflections, some of which were
assigned to the Pd(NH ) Cl phase. This implies that
2
+
[
Pd(NH ) ]
3 4
3
2
2
the thermolysis product has a defective structure or
has been poorly crystallized. Table 4 presents the IR
vibration frequencies for [Pd(NH ) ][AuCl ] ,
3
4
4 2
Pd(NH ) Cl , [Au(NH )Cl ], [PdNH ) ]Cl · H O, and
3
2
2
3
3
3 4
2
2
thermolysis product A formed at 150°C. The thermoly-
sis product is partly soluble in water to give a yellow-
brown solution and a gray-yellow precipitate. Accord-
ing to the electronic spectra of the solution and the
results of thermal analysis and X-ray diffraction of the
insoluble product, both the solid phase and the solution
contain palladium and gold compounds.
Comparison of these results indicates that the inter-
mediate thermolysis product A is mainly a mixture of
Fig. 2. General packing of the structural units in the crystal
along the z axis.
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SYNTHESIS, CRYSTAL STRUCTURE, AND THERMAL PROPERTIES
375
a
c
0
Fig. 3. H-bond system in the structure of [Pd(NH ) ][AuCl ] .
3
4
4 2
X-ray amorphous Pd(NH ) Cl and Au(NH )Cl . The the lattice parameters of metallic gold and palladium:
3
2
2
3
3
presence of Au(NH )Cl is in good agreement with pub- 4.079 and 3.890 Å, respectively.
3
3
lished data [9]. However, the authors of work [9] con-
cede that the product of thermolysis can also contain
other gold and palladium compounds, including poly-
meric phases which cannot be identified by the methods
we used.
The product II of the DCS reduction in a hydrogen
atmosphere at 400°ë is a Pd Au solid solution
0
.3
0.7
(
~90 wt %) and palladium metal (~10 wt %). The
composition of the solid solution was calculated using
the Vegard’s rule whose validity for the given system is
in good agreement with published data [10]. On keep-
The second and third stages of the thermal decom-
position are poorly resolved. They occur at 200–290°C
and 290–330°C, respectively, both being accompanied
by endotherms. The total weight loss is 42.73%, which
m, %
TG
1
00
90
80
corresponds to the Au Pd stoichiometry. Attempts to
2
resolve the stages by decreasing the heating rate were
unsuccessful.
7
6
0
0
In order to estimate the heat absorbed in the first
stage, an additional calorimetric study of a DCS sample
was performed. For this purpose, an aliquot of the salt
50
40
DTA
(20 mg) was heated under helium to 180°ë at a rate of
5
K/min. The curve showed a single peak with the peak
3
2
0
0
temperature of 138°ë. The heat of reaction was –20 J/g.
According to powder X-ray diffraction, the nature of
thermal decomposition products is largely determined
by the process conditions: the atmosphere, temperature,
and heating rate (Table 5, Fig. 5).
10
0
5
0
100
150
200
250
300
350
T, °C
The product I formed upon thermolysis of the DCS
in a helium atmosphere consists of two face-centered
cubic phases whose lattice parameters coincide with
Fig. 4. Thermoanalytical curves for [Pd(NH ) ][AuCl ]
4 2
recorded in a helium atmosphere at a heating rate of
10 K/min.
3
4
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 3 2007

3
76
PLYUSNIN et al.
–
1
Table 4. Vibration frequencies (cm ) in the IR spectra of Pd and Au compounds according to published data
Compound
ν(NH3)
δas(HNH)
δs(HNH)
ρ (NH )
ν(PdN)
r
3
[
Pd(NH ) ][AuCl ]
3321
1613
1291
1248
760
480
3
4
4 2
3
3
252
187
Au(NH )Cl
3240
170
3270
170
3296
1540
1630
1604
1280
825
3
3
3
[
Pd(NH ) ]Cl · H O
1279
1260
1252
849
802
756
495
3
4
2
2
3
trans-[Pd(NH ) Cl ]
490
496
3
2
2
3
3
220
140
(
A)
Thermolysis product of
Pd(NH ) ][AuCl ]
3315
1599
1553
1496
1248
753
494
3
3
238
175
[
3
4
4 2
Table 5. Characteristics of metallic phases depending on the thermolysis conditions
Heating rate,
Apparent
Phase
Atmosphere
He
Phase composition Unit cell parameter, Å
final temperature
crystallite size, Å
I
~10 K/min, 450°C
Au
Pd
4.079(2)
.890(2)
200–300
150–250
3
II
H2
H2
~15 K/min, 400°C
Pd Au
4.010(3)
.890(2)
100–150
200–250
0.3
0.7
3
Pd
III
IV
~30 K/min, 700°C
~20°C
Pd0.33Au0.66
4.002(2)
–
200–300
–
Reduction with
A series of solid solu-
tions Pd1 – xAux
a hydrazine hydrate
N H · H O solution
2
4
2
Note: The unit cell parameters for pure metals according to work [5]: Au, 4.0786 Å; Pd, 3.890(2) Å.
ing product II for 2 h in a hydrogen atmosphere (at uct contains irregularly shaped reflections. Unambigu-
00°C), solid solution III is formed (a = 4.002 Å) with ous interpretation of X-ray diffraction data is difficult in
an apparant crystallite size of 200–300 Å and the com- this case, but it can be stated with confidence that the
4
position Pd Au .
sample contains a set of solid solutions of different
compositions.
0
.4
0.6
It is of interest that the reduction of a solid polycrys-
talline DCS sample with a solution of hydrazine
In summary, the double complex salt
hydrate N H · H O yields product IV even at room [Pd(NH ) ][AuCl ] was synthesized for the first time
2
4
2
3 4
4 2
temperature; the X-ray diffraction pattern of this prod- and its crystal structure and thermal properties were
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 3 2007

SYNTHESIS, CRYSTAL STRUCTURE, AND THERMAL PROPERTIES
377
IV
III
II
I
4
0
50
60
70
80
90
θ, deg
2
Fig. 5. X-ray diffraction patterns of thermolysis products obtained under various conditions.
studied. The possibility of preparing phases of solid
solutions in the Pd–Au system upon the heterogeneous
reduction of the DCS at room temperature was demon-
strated.
4. Synthesis of Complexes of the Platinum-Group Metals,
Ed. by I. I. Chernyaev (Nauka, Moscow, 1964), p. 199
[in Russian].
5
6
7
. PDF Database, PCPDFWIN v. 2.02 (JCPDS-ICDD,
999).
. W. Kraus and G. Nolze, J. Appl. Crystallogr. 29 (3), 301
1996).
. G. M. Sheldrick, SHELX97. Release 97-1 (Univ. of Göt-
tingen, Göttingen, 1997).
1
(
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