Double complex salts of Pt and Pd ammines with Zn and Ni oxalates - promising precursors of nanosized alloys

Article abstract of DOI:10.1016/j.ica.2007.07.006

Double complex salts [M(NH₃)₄][M′(Ox)₂(H₂O)₂] · 2H₂O (M = Pd, Pt, M′ = Ni, Zn) were synthesized by combination of solutions containing corresponding cations [M(NH₃)₄]²⁺ and anions [M′(Ox)₂(H₂O)₂]^2-. The salts obtained were characterized by IR spectroscopy, thermal analysis, powder and single crystal X-ray diffraction. The prepared compounds are isostructural and crystallize in the orthorhombic crystal system (space group I222, Z = 2). Thermal decomposition of the salts in helium or hydrogen atmosphere at 200-400 °C results in formation of nano-sized bimetallic powders. Depending on the phase diagram of the respective bimetallic system and temperature conditions, they can be single phase or multiphase products. In particular, thermal decomposition of double complex salts [M(NH₃)₄][Zn(Ox)₂(H₂O)₂] · 2H₂O (M = Pd, Pt) results in formation of PdZn and PtZn intermetallic compounds, correspondingly. Decomposition of [Pd(NH₃)₄][Ni(Ox)₂(H₂O)₂] · 2H₂O affords a disordered solid solution Pd_0.5Ni_0.5. Disordered Pt_0.5Ni_0.5 was obtained from [Pt(NH₃)₄][Ni(Ox)₂(H₂O)₂] · 2H₂O in helium atmosphere, while in hydrogen atmosphere - a two-phase mixture of disordered Pt_0.5Ni_0.5 and ordered PtNi. In all cases crystallite sizes of bimetallic particles varied within 50-250 A?.

Full text of DOI:10.1016/j.ica.2007.07.006

Available online at www.sciencedirect.com
Inorganica Chimica Acta 361 (2008) 199–207
www.elsevier.com/locate/ica
Double complex salts of Pt and Pd ammines with Zn and Ni
oxalates – promising precursors of nanosized alloys
*
A.V. Zadesenets, E.Yu. Filatov , K.V. Yusenko, Yu.V. Shubin, S.V. Korenev, I.A. Baidina
Nikolaev Institute of Inorganic Chemistry SB RAS, 630090 Novosibirsk, Lavrentyev Avenue 3, Russia
Received 18 April 2007; received in revised form 6 July 2007; accepted 9 July 2007
Available online 14 July 2007
Abstract
Double complex salts [M(NH3)4][M0(Ox)2(H2O)2] Æ 2H2O (M = Pd, Pt, M0 = Ni, Zn) were synthesized by combination of solutions
containing corresponding cations [M(NH3)4]2+ and anions [M0(Ox)2(H2O)2]2ꢀ. The salts obtained were characterized by IR spectros-
copy, thermal analysis, powder and single crystal X-ray diffraction. The prepared compounds are isostructural and crystallize in the
orthorhombic crystal system (space group I222, Z = 2). Thermal decomposition of the salts in helium or hydrogen atmosphere at
200–400 °C results in formation of nano-sized bimetallic powders. Depending on the phase diagram of the respective bimetallic system
and temperature conditions, they can be single phase or multiphase products. In particular, thermal decomposition of double complex
salts [M(NH3)4][Zn(Ox)2(H2O)2] Æ 2H2O (M = Pd, Pt) results in formation of PdZn and PtZn intermetallic compounds, correspondingly.
Decomposition of [Pd(NH3)4][Ni(Ox)2(H2O)2] Æ 2H2O affords a disordered solid solution Pd0.5Ni0.5. Disordered Pt0.5Ni0.5 was obtained
from [Pt(NH3)4][Ni(Ox)2(H2O)2] Æ 2H2O in helium atmosphere, while in hydrogen atmosphere – a two-phase mixture of disordered
˚
Pt0.5Ni0.5 and ordered PtNi. In all cases crystallite sizes of bimetallic particles varied within 50–250 A.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Singe-source precursor; X-ray analysis; Thermal analysis; Nanoalloys; Platinum; Palladium; Zinc; Nickel; Oxalato complexes; Ammine
complexes
1. Introduction
system is simultaneous decomposition or reduction of
two precursor compounds. However, this widely used
approach suffers serious drawbacks, such as radial compo-
sition heterogeneity of the developing particles (core-shell
particles) or aggregation of atoms of different types into
separate phases. The technique utilizing single-component
precursor compounds, in particular, double complex salts
containing one of the metals in the complex cation, and
the other – in the complex anion, suggests a number of
advantages for the following reasons.
First, in the complex precursor the metals are uniformly
distributed (‘‘mixed’’) at the molecular level, making the
preparation of a single-phase solid solution much easier.
Second, the stoichiometry of the precursor complex
strictly determines the composition of the bimetallic phase
being formed. Thus, decomposition of double complex
salts (DCS) [Ir(NH3)5Cl]2[ReCl6]Cl2, [Ir(NH3)5Cl][ReCl6],
Development of new approaches to preparation of
nano-sized particles is highly topical for the systems based
on such particles gain increasing role in fundamental
research and applications [1–6]. Nano-sized materials com-
prising bimetallic particles often exhibit very intriguing
optical, magnetic, electric and chemical properties [7]. A
particularly characteristic feature of the particles of this
type is the synergetic effect of atoms of different types in
catalysts.
There are several methods of preparation of such pow-
ders, refer, for example, to [8–11]. One of the most com-
mon approaches to the synthesis of the desired metallic
*
Corresponding author. Tel.: +7 383 330 9904; fax: +7 383 330 9489.
E-mail address: decan@che.nsk.su (E.Yu. Filatov).
0020-1693/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.07.006

200
A.V. Zadesenets et al. / Inorganica Chimica Acta 361 (2008) 199–207
[Ir(NH3)5Cl](ReO4)2 yields solid solutions IrxRe1ꢀx
with component ratios 2:1, 1:1, 1:2, respectively [12,13].
Moreover, the accessible compositions of bimetallic parti-
cles are not just limited to stoichiometrical ratios of the
components. For example, earlier we have prepared a series
of mutual solid solutions of DCS [Ir(NH3)5Cl][ReCl6] and
[Ir(NH3)5Cl][IrCl6] having the following compositions –
[Ir(NH3)5Cl][IrCl6]x[ReCl6](1ꢀx) (x = 0, 0.4, 0.8) [12,14].
On decomposition of these compounds there are formed
solid solutions Ir(1+x)/2Re(1ꢀx)/2 corresponding to the pre-
determined metal ratio in the complex.
8.39; H, 3.52; N, 9.63%. Selected IR spectral data (KBr,
cmꢀ1): 3269 vb, 1651 s, 1435 m, 1350 s, 1300 s, 904 m,
787 m, 717 m, 516 w, 487 m, 389 w.
2.1.2. [Pd(NH3)4][Ni(Ox)2(H2O)2] Æ 2H2O ([Pd–Ni])
Yield: 39%. Anal. Calc. for C4H20N4O12PdNi: (Pd+Ni),
34.30; C, 9.98; H, 4.19; N, 11.64. Found: (Pt+Zn), 45.1; C,
10.39; H, 4.38; N, 11.44%. Selected IR spectral data (KBr,
cmꢀ1): 3283 vb, 1648 s, 1433 m, 1301 s, 850 m, 789 m, 718
m, 505 sh, 483 m, 384 w.
Furthermore, due to comparatively low thermolysis
temperatures, the powders being formed have a high degree
of dispersion (50–250 A). Because of the small size, the
developed bimetallic particles reveal high activity in diverse
chemical reactions.
Finally, synthesis of the precursor compounds can be
carried out directly on the surface of various porous mate-
rials, thus opening prospects for preparation of novel cata-
lysts [15]. When preparing supported bimetallic catalysts,
the lowering of thermolysis temperature of the precursor
compound, achieved by selection of proper ligands, is a
major concern. Besides, DCS must be free from halogens,
sulfur, and other catalytic poisons. Therefore, ammonia
molecules and oxalate ions are the most preferable and
handy ligands for these purposes.
2.1.3. [Pt(NH3)4][Zn(Ox)2(H2O)2] Æ 2H2O ([Pt–Zn])
Yield: 82%. Anal. Calc. for C4H20N4O12PtZn: (Pt+Zn),
45.17; C, 8.62; H, 3.27; N, 9.61. Found: (Pt+Zn), 45.1; C,
8.33; H, 3.50; N, 9.72%. Selected IR spectral data (KBr,
cmꢀ1): 3273 vb, 1650 s, 1432 m, 1351 s, 1301 s, 902 m,
784 m, 714 m, 514 w, 491 m, 392 w.
˚
2.1.4. [Pd(NH3)4][Zn(Ox)2(H2O)2] Æ 2H2O ([Pd-Zn])
Yield: 72%. Anal. Calc. for C4H20N4O12PdZn: (Pd+Zn),
35.21; C, 9.84; H, 4.13; N, 11.48. Found: (Pd+Zn), 35.5; C,
10.11; H, 4.24; N, 11.32%. Selected IR spectral data (KBr,
cmꢀ1): 3286 vb, 1651 s, 1432 m, 1302 s, 851 m, 789 m, 723
m, 514 w, 487 m, 392 w.
2.2. Single crystal and powder X-ray diffraction analysis
2. Experimental
Blue (M0 = Ni) and white (M0 = Zn) needle crystals of
the DCS were grown by slow evaporation of their mother
liquors. Single crystal X-ray diffraction study was carried
out on a BRUKER X8 APEX CCD diffractometer at room
temperature using graphite-monochromated Mo Ka radia-
2.1. Syntheses
All compounds were prepared with the same technique
described in detail below for [Pt(NH3)4][Ni(Ox)2
(H2O)2] Æ 2H2O.
˚
tion (k = 0.7107 A). The structures were solved by the stan-
dard heavy atom method and refined in anisotropic
approximation. All calculations were performed with
SHELX97 program package [17]. Crystal data and experi-
mental details are given in Table 1, selected bond lengths
and angles are listed in Table 2.
2.1.1. [Pt(NH3)4][Ni(Ox)2(H2O)2] Æ 2H2O, (hereafter
abbreviated as [Pt–Ni] for the sake of brevity)
The starting [Pt(NH3)4]Cl2 was prepared from platinum
metal by the standard technique [16]. Anionic complex
(NH4)2[Ni(Ox)2(H2O)2] Æ 2H2O was not isolated as a solid.
A solution of NiSO4 was treated with an equimolar
amount of aqueous (NH4)2Ox to yield NiOx precipitate.
The precipitate was collected on a filter, washed, and dis-
solved in twofold excess of aqueous (NH4)2Ox, the result-
ing solution of (NH4)2[Ni(Ox)2(H2O)2] Æ 2H2O being
further used for the synthesis of DCS. To prepare [Pt–
Ni], a solution of [Pt(NH3)4]Cl2 (1 mmol) in a minimal
amount of water was mixed with the solution of
(NH4)2[Ni(Ox)2(H2O)2] Æ 2H2O (10% molar excess). The
precipitate resulted from the reaction was filtered off,
washed with ethanol and dried in air. The product obtained
was characterized with a number of physical chemical
methods. CHN analyses was carried out in Laboratory of
Microanalysis of Vorozhtsov Institute of Organic Chemis-
try SB RAS, Novosibirsk, Russia.
Polycrystalline samples were studied on a DRON-
RM4 powder diffractometer equipped with a Cu Ka
source (k = 1.5418 A) and graphite monochromator at
˚
the diffracted beam in 2h range 5–120°. Indexing of the
diffraction patterns was carried out using data for pure
metals and compounds reported in the PDF database
[18]. Unit cell parameters were refined by the full-profile
technique within the whole diffraction range with the
POWDERCELL 2.4 program [19]. Crystallite sizes in the pre-
pared bimetallic powders were determined by Fourier
analysis of single diffraction peaks (the program WINFIT
1.2.1 [20]).
2.3. Scanning electron microscopy
Scanning electron microscopy study of the samples was
made on a JEOL JSM 6700F device equipped with a dis-
persive X-ray analyzer EX-23000BU (EDS) operating
15 kV.
Yield: 68%. Anal. Calc. for C4H20N4O12PtNi: (Pt+Ni),
44.53; C, 8.43; H, 3.54; N, 9.83. Found: (Pt+Ni), 44.5; C,

A.V. Zadesenets et al. / Inorganica Chimica Acta 361 (2008) 199–207
201
Table 1
Selected distances and angles for [M(NH3)4][M0(Ox)2(H2O)2] Æ 2H2O
Double complex salt
[Pt–Ni]
[Pt–Zn]
[Pd–Ni]
[Pd–Zn]
Empirical formula
Formula weight
Crystal system
Space group
C4H20N4NiO12Pt
570.00
orthorhombic
I222
7.162(1)
7.182(1)
15.037(2)
2
773.58(3)
2.447
C4H20N4O12PtZn
576.69
orthorhombic
I222
7.237(7)
7.177(0)
15.083(1)
2
783.43(5)
2.445
C4H20N4NiO12Pd
481.34
orthorhombic
I222
7.154(1)
7.204(1)
15.014(1)
2
773.88(2)
2.066
C4H20N4O12PdZn
488.03
orthorhombic
I222
7.214(1)
7.214(1)
15.070(3)
2
784.44(3)
2.066
˚
a (A)
˚
b (A)
˚
c (A)
Z
3
˚
V (A )
Dcalc (g cmꢀ3
)
l (mmꢀ1
F(000)
)
10.315
548
10.514
552
2.444
484
2.740
488
H range
3–35
3–38
3–37
5–30
Reflections collected
Independent reflections
Parameters
3845
1644
63
2648
1019
66
1795
1566
74
754
752
62
Goodness-of-fit
1.035
1.111
1.090
1.048
R1, wR[I > 2r(I)]
R1, wR (all data)
0.0193, 0.0461
0.0193, 0.0461
1.784, ꢀ2.867
0.0153, 0.0392
0.0153, 0.0392
1.361, ꢀ0.737
0.0274, 0.0572
0.0335, 0.0601
1.086, ꢀ1.255
0.0199, 0.0587
0.0200, 0.0588
0.510, ꢀ0.649
ꢀ3
˚
(e A )
Dqmin and
max
The salts are denoted as [M–M0].
Table 2
Crystal data and experimental characteristics for [M(NH3)4][M0(Ox)2(H2O)2] Æ 2H2O
˚
Distances (A)
Angles (°)
Angles (°)
[Pt–Ni]
Pt–N1
2.0460(22)
2.0141(36)
2.0390(18)
1.2669(30)
1.2317(31)
1.5600(31)
N100–Pt–N1
N1–Pt–N10
N100–Pt–N10
O1W–Ni–O1W0
O1W–Ni–O1
O1W0–Ni–O1
O1–Ni–O100
179.879(87)
91.321(87)
88.679(87)
179.983(83)
89.577(261)
90.423(261)
179.155(67)
O1–Ni–O1000
97.976(69)
82.031(69)
112.845(160)
126.660(232)
117.202(217)
116.138(188)
Ni–O1W
Ni–O1
O1–C1
O2–C1
C1–C10
O1–Ni–O10
C1–O1–Ni
O2–C1–O1
O2–C1–C10
O1–C1–C10
[Pt–Zn]
Pt–N1
2.0457(25)
2.0672(40)
2.0683(28)
1.2695(39)
1.2307(46)
1.5681(66)
N100–Pt–N1
179.986(121)
91.635(106)
88.365(106)
180.000(225)
88.439(67)
O1–Zn–O0001
O1–Zn–O10
C1–O1–Zn
O2–C1–O1
O2–C1–C10
O1–C1–C10
98.623(82)
81.377(82)
112.911(170)
127.103(246)
116.510(296)
116.387(261)
Zn–O1W
Zn–O1
O1–C1
O2–C1
C1–C10
N1–Pt–N10
N100–Pt–N10
O1W–Zn–O1W0
O1W–Zn–O1
O1W0–Zn–O1
O1–Zn–O100
91.561(67)
180.000(104)
[Pd–Ni]
Pd–N1
Ni–O1W
Ni–O1
O1–C1
O2–C1
C1–C10
2.0427(21)
2.0160(29)
2.0341(13)
1.2641(21)
1.2287(21)
1.5564(21)
N100–Pd–N1
N1–Pd–N10
N100–Pd–N10
O1W–Ni–O1W0
O1W–Ni–O1
O1W0–Ni–O1
O1–Ni–O100
178.626(81)
91.619(81)
88.397(81)
179.982(66)
88.972(220)
91.028(220)
177.944(50)
O1–Ni–O1000
O1–Ni–O10
C1–O1–Ni
O2–C1–O1
O2–C1–C10
O1–C1–C10
98.264(50)
81.774(50)
113.100(105)
126.595(157)
117.254(137)
115.891(133)
[Pd–Zn]
Pd–N1
Zn–O1W
Zn–O1
O1–C1
O2–C1
C1–C10
2.046(3)
2.062(4)
2.070(2)
1.262(4)
1.229(4)
1.558(6)
N100–Pd–N1
N1–Pd–N10
N100–Pd–N10
O1W–Zn–O1W0
O1W–Zn–O1
O1W0–Zn–O1
O1–Zn–O100
179.4(7)
91.55(16)
88.45(16)
180.000
87.8(4)
O1–Zn–O1000
O1–Zn–O10
C1–O1–Zn
O2–C1–O1
O2–C1–C10
O1–C1–C10
99.22(14)
80.95(13)
112.9(2)
125.8(3)
117.2(3)
92.2(4)
175.7(8)
116.58(18)
The salts are denoted as [M–M0].

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A.V. Zadesenets et al. / Inorganica Chimica Acta 361 (2008) 199–207
Table 3
Phase composition, heating temperatures and crystallite size of thermolysis products of [M(NH3)4][M0(Ox)2(H2O) 2] Æ 2H2O
˚
˚
Precursor salt
Atmosphere
Tmax (°C)
Phase
Space group
a (A)
c (A)
Crystallite size (nm)
[Pt–Ni]
He
H2
400
475
Pt0.5Ni0.5
Pt0.5Ni0.5
PtNi
Fm-3m
Fm-3m
P4/mmm
3.760(4)
3.753(3)
2.705(2)
6–8
10–14
10–14
+
3.620(3)
[Pd–Ni]
[Pt–Zn]
[Pd–Zn]
He
H2
400
250
Pd0.5Ni0.5
Pd0.5Ni0.5
Fm-3m
Fm-3m
3.754(4)
3.745(3)
6–8
7–10
He
H2
450
300
PtZn
PtZn
P4/mmm
P4/mmm
2.848(3)
2.858(2)
3.516(4)
3.465(3)
5–8
9–13
He
H2
360
300
PdZn
PdZn
P4/mmm
P4/mmm
2.908(3)
2.897(2)
3.318(4)
3.343(3)
5–8
11–24
The salts are denoted as [M–M0].
2.4. Thermal analysis
was allowed to cool to ambient temperature in continuous
helium stream.
Prepared DCS were studied on a Paulic-Erdey Q-1000 der-
ivatograph equipped with digital output, Al2O3 powder being
used as the standard. The experiments were run in an open
silica crucible in helium stream at heating rate 10 °C/min.
The final temperatures of the experiments are reported in
Table 3.
3. Results and discussion
3.1. Crystal structure
X-ray diffraction study of the crystals revealed that all
new compounds are isostructural. Fig. 1 schematically
illustrates the general view of the unit cell. The crystals of
DCS are built from isolated complex ions shown in Fig. 2.
The atoms of nickel (zinc) have octahedral environment
of six oxygen atoms. The distances M0–Oox and M0–Ow are
2.5. Decomposition in hydrogen atmosphere
To synthesize bimetallic powders in hydrogen atmo-
sphere weighted samples of DCS (ꢁ50 mg) were placed in
a silica boat and put in a tubular silica reactor. Heating
was performed in a split furnace at the rate of 20 °C/min.
After reaching the final temperature (Table 3), samples
were kept for 1 h, and then the hydrogen stream was
switched off and the system was purged with helium during
30 min. Afterwards the heater was removed and the reactor
˚
almost identical differing at most by 0.02 A (Table 2).
Because of the rigidity of the chelate ligands the octahedral
[M0O6] lack symmetry – in the equatorial plane the trans-
angles deviate from 90 and make 82.03(7)° and 97.97(7)°.
The atoms of platinum (palladium) are square-coordinated
with four nitrogen atoms. The adjacent angles between the
Fig. 1. Common view of the unit cell of DCS. Complex cations [M(NH3)4]2+ are shown as dark squares, chelate planes [M0Ox2]2ꢀ are shown as light
rectangles with two coordinated molecules of water.

A.V. Zadesenets et al. / Inorganica Chimica Acta 361 (2008) 199–207
203
Fig. 2. The detailed structure of complex ions.
M–N bonds are different from 90° resulting in a slight dis-
tortion of the planar-square cations.
As evident from Fig. 1, there are two types of water mol-
ecules in the structure. Each atom of nickel (zinc) coordi-
nates two water molecules in the trans-positions. Besides,
a pair of crystallization water molecules is present at each
ac and bc faces of the unit cell. The molecules of the water
of crystallization lie in the plane of the chelate ligands of
the complex anions and make hydrogen bonds to the termi-
nal oxygen atoms (O2). The distances H(W)cryst–O2 are
Fig. 3. The illustration of hydrogen bonds between structural units in DCS.

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A.V. Zadesenets et al. / Inorganica Chimica Acta 361 (2008) 199–207
Table 4
3.2. Thermal properties
Hydrogen bonds by example of interatomic distances A . . . B in D–H . . . B
system
In inert atmosphere the thermal behavior of all new
DCS is similar. The overall thermogram is shown in
Fig. 5. As one can see, all compounds decompose in two
major stages. The first one corresponds to the complete loss
of water. Weight loss (72–75 Da) is in a good accordance
with the calculated value for four water molecules
(72 Da). Above, we have noted that one half of water mol-
ecules are coordinated by nickel (zinc) atoms, while the
other is linked with the complex anions only with hydrogen
bonds. One could suppose that the coordinated water mol-
ecule and the crystallization water molecule would evolve
in separate steps, but this resolution into two stages is
observed only for [Pd–Ni]. The heated products, according
to IR spectroscopy data, do not contain water, but retain
the bands corresponding to the vibrations of the ammonia
and oxalate ligands. We did not succeed in identifying these
phases because these products are being amorphous.
The temperatures of decomposition onset for the DCS
and the corresponding dehydrated products are shown in
Fig. 6. It also presents the temperatures of decomposition
onset of diaqua oxalates of nickel and zinc M0Ox Æ 2H2O,
as well as of tetraammineplatinum and tetraamminepalla-
dium perrhenates [M(NH3)4](ReO4)2 (M = Pt, Pd)
[21,22]. On the basis of the data obtained, three regularities
can be derived. First, as evident from the plot, zinc DCS
begin to loose water at lower temperatures than nickel
DCS. This correlates with available data on the thermal
stability of M0Ox Æ 2H2O undergoing dehydration in the
same priority due to the differences in the strength of the
bonds Zn–OH2 and Ni–OH2.
Salt
Contacts
[Pt–Ni]
[Pd–Ni]
[Pt–Zn]
[Pd–Zn]
Crystal water stabilization
O1W. . .O2W
O2. . .O2W
2.750(3)
2.696(3)
2.743(2)
2.706(2)
2.748(3)
2.698(3)
2.706(3)
2.738(3)
Cation stabilization
N1. . .O1
N1. . .O10
3.106(9)
3.082(9)
3.052(7)
3.111(9)
3.097(9)
3.030(6)
3.121(1)
3.110(1)
3.052(7)
3.182(13)
3.058(13)
3.088(10)
N1. . .O2
˚
within 1.85–2.00 A. In turn, the coordinated water mole-
cules are joined by hydrogen bonds with the crystallization
water molecules, the distances H(W)coord–O(W)cryst being
1.95–2.20 A. Thus, crystallization water molecules and
the complex cations are stabilized by the complex anions
˚
by virtue of hydrogen bonding. Average distances O. . .O
and O. . .N are 2.7 and 3.1 A, what is characteristic of
˚
strong bonding in such systems. Fig. 3 and Table 4, listing
the distances between the atoms A and B in the D–H . . . B
system, illustrate the situation.
Mutual arrangement of the complex anions, as deter-
mined using the central atoms (Fig. 4), indicates that each
complex ion is surrounded by six complex counter ions.
Therefore, the DCS crystallize in the distorted structural
type of NaCl.
As found with powder X-ray diffraction, all precipitates
of the compounds obtained are single-phase. Experimental
diffraction patterns of the polycrystalline samples coincide
with theoretical ones and do not have additional
reflections.
The second stage corresponds to complete decomposition
of the complexes to the bimetallic products. One can con-
clude that the thermal stability of the anhydrous products
is primarily governed by the thermal stability of the complex
cation, as DCS comprising the cation [Pd(NH3)4]2+ begin to
decompose earlier than DCS containing the cation
Fig. 4. The mutual arrangement of central atoms in DCS. The unit cell is
drawn with dotted line.
Fig. 5. Combined TG-pattern for [M(NH3)4][M0(Ox)2(H2O)2] Æ 2H2O
(M = Pt, Pd, M0 = Zn, Ni). The complex salts are denoted as [M–M0].

A.V. Zadesenets et al. / Inorganica Chimica Acta 361 (2008) 199–207
205
Fig. 6. Temperatures of thermal stability for [M(NH3)4][M0(Ox)2(H2O)2] Æ 2H2O (M = Pt, Pd, M0 = Zn, Ni), M0Ox Æ 2H2O (M0=Zn, Ni), anhydrous
products of corresponding salts and [M(NH3)4](ReO4)2 (M = Pt, Pd). The complex salts are denoted as [M–M0]. White symbols represent the temperatures
of dehydration beginning; black symbols represent the temperatures of the beginning of further full decomposition.
[Pt(NH3)4]2+. This agrees with the fact that platinum(II)
complexes are generally more stable than corresponding pal-
ladium(II) complexes. This fact is illustrated by the example
of [M(NH3)4](ReO4)2, which begin to degrade from decom-
below 650 °C. As a consequence, the alloy obtained has
undergone partial ordering to yield the intermetallic com-
pound. The final product is two-phased and comprises
˚
the disordered solid solution (a = 3.753(3) A) and the inter-
position of the [M(NH3)4]2+ cations while ReO4 anions
metallic PtNi (space group P4/mmm, a = 2.705(2) A,
ꢀ
˚
˚
remain intact [21,22], and the palladium salt also being
decomposed first.
c = 3.620(3) A). As reported in Ref. [27], unit cell parame-
˚
ters of the intermetallic compound are a = 2.711(2) A,
˚
˚
˚
However, the nature of the complex anion is also of
importance. Among the prepared DCS containing the
same cation, the salts involving nickel are less stable due
to its higher oxidative potential. Lower decomposition
temperatures of the dehydrated nickel oxalates support this
fact.
c = 3.602(2) A, and Ref. [28] gives a = 2.698(2) A,
c = 3.582(2) A. Powder diffraction pattern of the sample
is illustrated in Fig. 8. The composition of the sample
was confirmed by energy dispersive X-ray spectroscopy
(EDS).
It is noteworthy that the shape of metallic particles
inherits the habitus of the original crystals of DCS. How-
ever, subsequent scans with growing resolution reveal that
the particles are built from smaller blocks with the sizes of
ꢁ10 nm (see Fig. 9).
3.3. Products of thermolysis
All synthesized DCS were subjected to heating in helium
and hydrogen atmospheres. Heating in hydrogen was car-
ried out at 20 K/min rate, after the target temperature
had been reached; the sample was kept in the gas stream
for another hour. Heating in helium atmosphere was per-
formed 7 K/min rate. After achieving the desired tempera-
ture, the sample was cooled to ambient temperature in a
helium stream during 1 h. The products were examined
with powder XRD and EDS. Annealing temperatures,
phase composition and crystal chemical data for the sam-
ples are given in Table 3.
a
The product obtained by thermal decomposition of the
DCS [Pt–Ni] in helium at 400 °C is a single-phase fine black
powder of the solid solution Pt0.5Ni0.5, which has the FCC
b
˚
unit cell parameter a = 3.760(3) A. The value of the unit
cell parameter found for this solid solution is in a good
agreement with that determined from the experimental
dependence of the unit cell parameter of the solid solution
on its composition derived from the data of [23–25]
(Fig. 7a).
During reductive thermolysis of the DCS [Pt–Ni] in
hydrogen atmosphere the final temperature was raised to
475 °C. According to the phase diagram of the platinum–
nickel system [26], a field of an ordered solid solution exists
Fig. 7. Experimental dependence of atomic volume vs solid solution
composition for system Ni–Pt (a) Ni–Pd (b). Literature date are marked
by black points, data of this work are marked by light one’s.

206
A.V. Zadesenets et al. / Inorganica Chimica Acta 361 (2008) 199–207
25 nm. Longer exposure of samples to a preset temperature
also promotes the growth of the particles: when the sample
prepared at 400 °C (25 nm) was kept in a sealed quartz
ampoule for another 12 h, particle size increased to 40 nm.
PtNi, PdNi and Pd–Zn samples manifest the same
tendencies.
High chemical activity of bimetallic particles prepared
by DCS decomposition also has a negative aspect. The sur-
face of the particles is partially oxidized by atmospheric
oxygen as evidenced by EDS data. However, the amount
of the adsorbed oxygen is negligible. When exposed to air
for several weeks, the products do not show any changes
in weight.
4. Conclusion
Novel double complex salts combining a platinum metal
in the cation and base transition metal in the anion have
been prepared. The synthesized complexes have been
shown to be isostructural. It has been demonstrated that
the compounds can be used as single-source precursors of
nano-sized alloys: thermal decomposition of the com-
pounds in helium and hydrogen results in formation of
ultrafine bimetallic powders with varying metal ratios.
It is noteworthy that during thermolysis of a double
complex salt comprising a platinum metal, zinc can be
reduced to yield the intermetallic compound, while com-
mon zinc salts do not afford metal even under reduction
in hydrogen atmosphere.
Fig. 8. XRD pattern of PtNi intermetallic and Pt0.5Ni0.5 solid solution
mixture, – peaks of PtNi intermetallic, – peaks of Pt0.5Ni0.5 solid
*
solution.
Ù
Thermolysis of the [Pd–Ni] DCS, both in helium and in
hydrogen, afforded single-phase samples of the disordered
solid solution palladium–nickel. The values of the unit cell
parameter of the FCC cell, found for these solid solutions,
˚
are slightly above the value a = 3.741 A derived for the sol-
ids solution Pd0.5Ni0.5 from experimental dependence of
the unit cell parameter on the composition of the solid
solution [29,18,30–32] (Fig. 7b, Table 3).
For the systems Pt–Zn and Pd–Zn, the thermolysis of
starting DCS both in helium and in hydrogen gave sin-
gle-phase samples of intermetallic compounds PtZn and
PdZn, respectively, which have the tetragonal crystal lattice
of the CuAu type, space group P4/mmm (Table 3).
This method of preparation of nano-sized particles
enables to control the sizes of the developing particles by
proper tuning of the thermolysis conditions (temperature,
duration, and heating rate). Thus, the intermetallic PtZn
can be obtained as particles of average size 10 nm
(300 °C, 10 E/min, exposure 1 h). When decomposition
temperature is raised to 400 °C, the particle size reaches
Acknowledgements
We express gratitude to the Haldor Topsoe foundation
for supporting this work.
Appendix A. Supplementary material
Crystallographic data from the structural analyses have
been deposited with the Fachinformationszentrum Kar-
lsruhe, D-76344 Eggenstein-Leopoldshafen, Germany
(fax: (+49)7247-808-666; e-mail crysdata@fiz-karlsruhe.de)
Fig. 9. Microphotographs of obtained PtNi particles was to carried out by SEM. (a) Shows that shape of metal particles inherits a habitus of initial
crystals of DSC [Pt–Ni]. But if to increase the resolution it can be see that bulk particles consist of smaller blocks which are about 100 nm in size (b).

A.V. Zadesenets et al. / Inorganica Chimica Acta 361 (2008) 199–207
207
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