Novel heterometallic palladium-silver complex

Article abstract of DOI:10.1016/j.ica.2011.02.003

The reaction between Pd₃(OOCMe)₆ and Ag ₂(OOCMe)₂ afforded the first palladium-silver heterometallic acetate-bridged complex Pd^II[(μ-OOCMe) ₂Ag^I(HOOCMe)₂]₂ (1). The molecular geometry and electronic structure of 1 were studied by single-crystal XRD and quantum-chemical DFT calculations. Thermal transformations of 1 in vacuo and under Ar, H₂ produced PdAg alloy nanoparticles characterized with powder XRD and EXAFS.

Full text of DOI:10.1016/j.ica.2011.02.003

Inorganica Chimica Acta 370 (2011) 382–387
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Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Novel heterometallic palladium–silver complex
a
a
a
Natalia Yu. Kozitsyna a, , Sergei E. Nefedov , Alla P. Klyagina , Alexander A. Markov ,
Zhanna V. Dobrokhotova a, Yuri A. Velikodny b, Dmitry I. Kochubey c, Tatiana S. Zyubina d,
Alexander E. Gekhman a, Michael N. Vargaftik a, Ilya I. Moiseev a
⇑
a N.S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, 119991 Moscow, Russian Federation
b M.V. Lomonosov Moscow State University, 119991 Moscow, Russian Federation
c G.K. Boreskov Institute of Catalysis, Siberian Branch of Russian Academy of Sciences, 630090 Novosibirsk, Russian Federation
d Institute for New Chemical Problems, Russian Academy of Sciences, 142432 Moscow Region, Chernogolovka, Russian Federation
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction between Pd3(OOCMe)6 and Ag2(OOCMe)2 afforded the first palladium–silver heterometallic
acetate-bridged complex PdII[( -OOCMe)2AgI(HOOCMe)2]2 (1). The molecular geometry and electronic
l
Received 22 December 2010
Received in revised form 28 January 2011
Accepted 1 February 2011
Available online 5 March 2011
structure of 1 were studied by single-crystal XRD and quantum-chemical DFT calculations. Thermal
transformations of 1 in vacuo and under Ar, H2 produced PdAg alloy nanoparticles characterized with
powder XRD and EXAFS.
Ó 2011 Elsevier B.V. All rights reserved.
Keywords:
Palladium
Silver
Heterometallic complexes
X-ray structure
Quantum-chemical analysis
Thermal decomposition
1. Introduction
2. Results and discussion
Silver(I) acetate is still not clearly understood complex of this
metal. Particularly, its XRD crystal structure was properly docu-
mented just recently [1]. Meanwhile, the transition and precious
metal carboxylates become a challenge of current coordination
chemistry [2–4]. Both monometallic and particularly heterometal-
lic carboxylates are valuable precursors for molecular magnets
[2,5], catalysts [6–9] and other nanostructural materials.
2.1. Synthesis and structure
By analogy with the previous syntheses [10,11] we found that
the reaction of Pd3(OOCMe)6 with Ag2(
acid produces the crystalline heterobimetallic complex
PdII[( -OOCMe)2AgI(HOOCMe)2]2 (1, Fig. 1).
l-OOCMe)2 (2) in hot acetic
l
X-ray diffraction study showed that the Pd atom in molecule 1
is square-plane coordinated to four oxygen atoms of four bridging
acetate ligands (Pd–O 2.0062(9)–2.0063(9) Å, Ag–O 2.3535(12),
2.3535(12) Å) (Table 1).
Recently we synthesised and structurally characterized the
paddlewheel tetra(acetate)-bridged PdII( -OOCMe)4CuII(OH2)-
l
(HOOCMe)2 [10] and trinuclear palladium–copper bis(acetate)-
bridged Pd2
similar synthetic approach, we prepared the first acetate-bridged
palladium–silver complex PdII[( -OOCMe)2AgI(HOOCMe)2]2 (1)
(
l
-OOCMe)6CuII [11] complexes. In this work, using
The PdAg2 metal core of 1 is a linear metal chain (Ag–Pd–Ag an-
gle is 180°), the Ag–Pd distances are fairly short (PdꢀꢀꢀAg 2.9194(2),
2.9195(2) Å). Slightly distorted tetrahedral coordination of each Ag
atom is complemented with two terminal acetic acid ligands (Ag–
O 2.4118(12), 2.4118(12) Å). The H atoms of the coordinated AcOH
molecules are H-bonded to O atoms of the bridging acetate ligands
of the adjacent molecules 1 (OꢀꢀꢀO 2.608(1) Å), forming in the crys-
II
l
and studied its structure and thermal transformations into Pd–Ag
nanoparticles. A comparative quantum-chemical DFT study of
complex 1, its virtual formate (1f) and trifluoroacetate (1tf)
analogs as well as the homonuclear silver(I) carboxylates Ag2(
OOCR)2 (R = Me (2), H (2f) and CF3 (2tf)) and hypothetical complex
Pd( -OOCMe)2Ag (3) revealed conditions for the metal–metal
l-
tal the linear polymer {Ag2Pd(l-OOCMe)4(HOOCMe)4}n (Fig. 2)
l
with close intermolecular AgꢀꢀꢀAg contacts 3.7641(2) Å and AgꢀꢀꢀO
bonding in these molecular systems.
3.1102(9), 3.1102(9) Å).
Chemical reactivity studies showed that two-bridged molecule
1 is less chemically stable compared to the tetrabridged Pd com-
plexes Pd(OOCMe)4MLn (M = NiII, CoII, ZnII and MnII) with rather
short metal–metal distances (2.55–2.65 Å) [11]. For example, the
⇑
Corresponding author.
E-mail address: nkoz2009@gmail.com (N.Yu. Kozitsyna).
0020-1693/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2011.02.003

N.Yu. Kozitsyna et al. / Inorganica Chimica Acta 370 (2011) 382–387
383
Fig. 1. Molecular structure of the formula unit of the complex PdII[(
l
-OOCMe)2AgI(HOOCMe)2]2 (1) with thermal ellipsoids drawn at 50% probability level.
Table 1
2.2. Quantum chemical analysis of 1 and 2
Selected bond lengths (Å) and angles (°) for Complex 1.
The well known Cotton scheme of ‘‘metallic’’ MOs [14a–c] sug-
gests the absence of the direct M–M0 bonding in binuclear late
transition metal complexes. Meanwhile, the possibility of bonding
M–M0 interactions in polynuclear late metal compounds is now ar-
gued [1,13a,b,14c,15a,b].
Bond lengths (Å)
Ag(1)–Pd(1)
Pd(1)–O(1)
Pd(1)–O(1)#2
Ag(1)–O(2)
2.9195(2)
2.0063(9)
2.0062(9)
2.3535(12) Ag(1)–O(2)#1
2.4118(12) Ag(1)–O(3)#1
Pd(1)–Ag(1)#3
Pd(1)–O(1)#1
Pd(1)–O(1)#3
2.9194(2)
2.0063(9)
2.0063(9)
2.3535(12)
2.4118(12)
Ag(1)–O(3)
In this work we carried out a DFT study of the electronic struc-
ture and chemical bonding in molecules 1 and 2, as well as in the
formate (1f and 2f) and trifluoroacetate analogs (1tf, 2tf) and
Bond angles (°)
Ag(1)#3–Pd(1)–
Ag(1)
O(1)#1–Pd(1)–Ag(1)
O(1)#3–Pd(1)–Ag(1)
O(1)#1–Pd(1)–
Ag(1)#3
O(1)#3–Pd(1)–
Ag(1)#3
O(2)#1–Ag(1)–Pd(1)
O(3)#1–Ag(1)–Pd(1)
O(1)#2–Pd(1)–O(1)
180.0
O(1)–Pd(1)–Ag(1)
86.81(4)
86.81(4)
93.19(4)
93.19(4)
O(1)#2–Pd(1)–Ag(1)
O(1)–Pd(1)–Ag(1)#3
O(1)#2–Pd(1)–
Ag(1)#3
93.19(4)
93.19(4)
86.81(4)
hypothetical complex Pd(l-OOCMe)2Ag (3) with B3LYP functional
[17a,b] using the CEP-121G basis set and GAUSSIAN 03 program [18].
The geometry optimization for complexes 1 and 2 gave quite
reasonable agreement between the calculated and experimental
values (Tables 2 and 3).
86.81(4)
O(2)–Ag(1)–Pd(1)
69.84(3)
69.84(3)
123.56(3)
90.179(5)
O(3)–Ag(1)–Pd(1)
O(1)–Pd(1)–O(1)#1
O(1)#2–Pd(1)–
O(1)#3
O(1)#2–Pd(1)–
O(1)#1
123.56(3)
173.62(9)
173.62(9)
As seen in Tables 2 and 3, the singlet states are much more
favorable than the triplet ones for all the complexes. The calculated
geometry of 1 and 2 well agree with experimental data for the sin-
glet states. The interatomic distances D(Pd–Ag) in 1 and D(Ag–Ag)
in 2 and their analogs are shortened upon excitation to the triplet
state, which can be an indication on M–M0 bonding in this state,
whereas the bonding is absent in the singlet state. This is in agree-
ment with the antibonding character of the HOMO in 1 and 2 and
nonbonding and bonding character of LUMO in 1 (Fig. 3) and 2,
respectively (see Fig. 6 in [1] for 2; similar frontal MOs were found
in our calculations). The overlap populations P(Ag–Ag) data in Ta-
ble 3 confirm these conclusions.
O(1)–Pd(1)–O(1)#3
90.178(5)
90.176(5)
90.177(5)
108.80(4)
O(1)#3–Pd(1)–
O(1)#1
O(2)–Ag(1)–O(3)#1
O(2)#1–Ag(1)–O(3)
O(2)–Ag(1)–O(3)
93.37(4)
93.37(4)
O(2)#1–Ag(1)–O(2)
O(2)#1–Ag(1)–
O(3)#1
139.68(6)
108.80(4)
O(3)–Ag(1)–O(3)#1
112.88(7)
Symmetry transformations used to generate equivalent atoms: #1 ꢁx,ꢁy,z #2
ꢁy,x,ꢁz #3 y,ꢁx,ꢁz.
NBO analysis showed that complexes 2 have no bonding natural
reaction of the latter complexes with Phen and pivalic acid does
not violate the acetate-bridged heterometallic core [12a,b]. Unlike
this, complex 1 is decomposed by Phen or PivH into the monome-
tallic Ag carboxylates and complexes PhenPd(OOCMe)2 or Pd(OOC-
But)2, respectively.
Nevertheless, the relatively short Ag–M distance in molecules 1
(2.919 Å, M = Pd) and 2 (2.852 Å, M = Ag) could suggest some
metal–metal bonding. For instance, direct Ag–Ag bonding was
recently proposed [1] on the basis of Bader’s AIM analysis of mol-
ecule 2 and the band at 80–85 cmꢁ1 found in its Raman spectrum.
The bond order of 0.2 in the fluorinated silver(I) acetates was cal-
culated in works [15a,b]. Meanwhile, the Ag–Ag bond was not
found in the Ag2(NO3)2 fragment of the supramolecular silver(I)
complex with trans-1,2-bis(4-piridyl)ethylene [16]. Hence, it was
of interest to analyze the electron interaction in molecules 1 and 2.
orbitals (NO) in the M–M0 fragment in singlet state, whereas the
triplet state has a bonding NO in
a-representation, providing a
bond order of 0.5. Similar trends in geometric and electronic struc-
ture were found for complexes 2f and 2tf.
The heterometallic complex 3 is isoelectronic to cation 2+, which
contains only one electron at the antibonding MO. This fact can be
responsible for shorter interatomic distances D(Ag–Ag) in 2+ and
D(Pd–Ag) in 3 compared to D(Ag–Ag) in 2 (Table 2). The HOMO in
a- and LUMO in b-representation for 3 have the same antibonding
character as the HOMO in 2. Taking into account these results to-
gether with the overlap populations P(Pd–Ag), we can suggest some
Pd–Ag bonding in the B doublet ground state of 3(D) and its further
increase on going to 3+ and quartet state of 3(Q) (Table 3).
A change in D(Pd–Ag) (Table 2) observed in the cation 1+ and
triplet state of molecule 1 well agree with the expected effect of

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N.Yu. Kozitsyna et al. / Inorganica Chimica Acta 370 (2011) 382–387
Fig. 2. Fragment of the polymer chain {PdII[( -OOCMe)2AgI(HOOCMe)2]2}n of 1 in the crystal.
l
In the case of formate complex 1fꢁ no change in the geometry
Table 2
Interatomic distances (D, Å) in the complexes PdII[( -OOCX)2AgI(HOOCX)2]2 (1, 1+, 1ꢁ
l
was found. The OH groups in the coordinated HCOOH molecules
are arranged in the same way as in 1f (s and t) and 1f+, and the
and 1f) and the energy differences ((
states calculated by DFT (B3LYP) with CEP-121G basis.
DE(SꢁT), kcal/mol) between the singlet and triplet
0
O–H bond length is 0.986 ÅA in all the formate species. The rest
trends in the electronic state and geometry in the series 1f(s)
1f(t), 1f+ and 1fꢁ are the same as those in the acetate analogs
(Table 2).
Hence, we can draw a conclusion that molecules 1 and 2 in the
singlet ground states have no Ag–M (M = Pd, Ag) direct electron
interaction, whereas excitation to the triplet (1T, 1fT, 2T, 2fT and
2tfT) states gives rise to the metal–metal bonding.
Complex
D(Pd–Ag) D(Pd–O) D(Ag–O) D(Ag–O0)
DE(SꢁT)
1, X = CH3, S
1, X = CH3, T
Experiment
2.991
2.740
2.919
2.061
2.217
2.006
2.338
2.206
2.354
2.462
2.513
2.412
ꢁ23.6
ꢁ38.9
1+ cation, X = CH3, D 2.736
2.035
2.256
2.225
2.331
2.435
2.599
1ꢁ anion, X = CH3
2.931
1f, X = H, S
1f, X = H, T
3.076
3.058
2.060
2.169
2.360
2.332
2.450
2.466
1f+ cation, X = H, D
1fꢁ anion, X = H
2.750
2.895
2.037
2.283
2.236
2.240
2.424
2.786
2.3. Thermal transformations of 1
2.3.1. Thermolysis in inert atmosphere
Thermal transformations of complex 1 under Ar occur in two
clear-cut stages (Fig. 5). The first stage, in the interval 75.5–
117 °C ( 1.5 °C), is accompanied with a mass loss of 29.1 1.0 %
and a strong composite endotherm of 224.8 5.5 kJ/mol (including
three close overlapping endotherms with maxima at 92.4, 101.4
and 109.7 °C). The found mass loss is close to the calculated value
for complete removal of four coordinated acetic acid molecules
(30.08%).
Since the intermediate formed at the first stage does not change
during further heating within 117–150 °C, it would seem that the
removal of the coordinated acetic acid ligands produced a new, suf-
ficiently stable metal complex. However, XRD analysis showed that
the intermediate product (prepared in separate experiment by
heating to 120 °C with a rate of 10°/min followed by fast quenching
under Ar) consists of several distinctive phases, Pd(II) and Ag(I)
acetates and small admixtures with unidentified XRD peaks. IR
spectrum of the intermediate product revealed only bridging ace-
tate groups. Hence, the intermediate Pd–Ag complex, if formed,
easily decomposes into monometallic components.
The second stage of thermolysis (150–260 °C) is accompanied
with a weight loss of 28.9 1.0% and a small exotherm (Fig. 5). To-
tal weight loss in two stages is 58.0% ( 1.0%). XRD analysis showed
that the final solid product is a mixture of the PdO, Ag and PdAg
alloy phases. The formation of PdO and Ag is in agreement with
known data on the thermolysis of Pd(II) acetate [19a] and Ag(I)
acetate [19b], respectively. The PdAg alloy seems to form from
an unstable heterometallic intermediate. In a separate experiment,
when thermolysis process was driven to 450 °C, our XRD data
revealed two different PdAg phases in the final product.
Table 3
Interatomic distances (D, Å), overlap populations P(Ag–Ag) in the complexes
Ag2(OOCX)2 and the energy differences (( E(SꢁT), kcal/mol) between the singlet and
triplet states calculated by DFT (B3LYP) with CEP-121G basis.
D
Complex
D(Ag–Ag) P(Ag–Ag) D(Ag–O) P(Ag–O)
DE(SꢁT)
2, X = CH3, S
2, X = CH3, T
Experimenta
2.852
2.741
2.803
0.003
0.116
2.146
2.168
2.200
2.101
2.142
2.153
2.176
2.161
2.191
2.232
0.128
0.123
ꢁ77.1
2+, cation, X = CH3, D 2.655
0.058
0.078
0.020
0.131
0.014
0.132
0.140
0.138
0.127
0.122
0.111
0.123
2ꢁ, anion, X = CH3, D 2.977
2f, X = H, S
2f, X = H, T
2tf, X = CF3, S
2tf, X = CF3, T
Experimentb
2.876
2.736
2.962
2.732
2.967
ꢁ81.1
–84.5
D(Pd–Ag) P(Pd–Ag)
D
E(DꢁQ)
3, X = CH3, D
3, X = CH3, Q
3+, X = CH3
2.730
2.659
2.593
0.009
0.129
0.066
2.142
2.401
2.105
0.132
0.073
0.141
ꢁ72.5
a
Ref. [1].
Ref. [18].
b
electron removal from the strongly antibonding HOMO (Table 2).
On going to anion 1ꢁ, the addition of electron to the nonbonding
LUMO results in minor variation of D(Pd–Ag). Interestingly that
the terminal HO–(COMe) groups in the optimized geometry of an-
ion 1ꢁ are noticeably approached to the O atoms of bridging Me-
COO groups compared to those in 1 (Fig. 4) and 1+, whereas the
0
0
O–H bonds lengthen from 0.985 ÅA in 1 (s and t) and 1+ to 1.06 ÅA
0
in 1ꢁ and the distance between H and O in CH3COO group is 1.43 ÅA.

N.Yu. Kozitsyna et al. / Inorganica Chimica Acta 370 (2011) 382–387
385
Fig. 3. HOMO (a) and LUMO (b) of molecule 1.
Fig. 4. Optimized geometry of the molecule 1 (a) and anion 1ꢁ (b).
of the PdAg alloy (a = 4.0100(24) Å), Pd metal (a ꢂ 3.91 Å) and Ag
metal (a = 4.079 Å) nanoparticles. The mean sizes of the crystallites
estimated by the Scherrer formula are 13 nm for PdAg and 67 nm
for Ag.
The EXAFS study (Fig. 6) revealed the main observable product
of 1 reduction with H2 at 300 °C as a PdAg alloy with the shortest
metal–metal distance 2.82 Å, but with smaller (65 nm) particle
mean size. The inconsistency in the particle size estimates is most
likely due to the fact that XRD is mainly sensitive to particles with
mean size >5 nm, while a substantial fraction of the alloy particles
seems to be smaller in size.
It is known that the palladium–silver solid alloy system is con-
tinuous and has no singularities or intermetallides [20]. Hence, dif-
ferent PdAg alloys could form depending on the experimental
conditions. We estimated the composition of the solid PdAg alloys
obtained in the above experiments, using the known empirical
dependence [21a,b] for the Ag[Pd1ꢁ[ solid alloys:
120
100
80
60
40
20
0
3.0
1.5
0.0
-1.5
-3.0
-4.5
-6.0
1
2
100
200
300
400
t, oC
Fig. 5. TGA–DSC data for thermal decomposition of 1 (Ar flow, heating rate 10 deg/
min): 1 – TGA curve; 2 – DSC curve.
aðxÞ; a ¼ 3:88635 þ 0:1959x:
The H2-reduced product turned to be a single-phase alloy of the
composition Ag0.63Pd0.37. The product of 1 thermolysis under Ar at
2.3.2. Thermolysis in vacuo
When complex 1 was heated in vacuo to 500 °C, the reaction
product was found by powder XRD to consist of PdAg alloy
nanoparticles with a small admixture (ꢂ5%) of Ag nanophase.
The crystallite sizes of PdAg and Ag were estimated by the Scherrer
formula b = Kk/Lcosh, where b is the integrated peak width, K is the
shape factor, k is the wavelength and L is the volume (corrected for
450 °C consists of two phases: Ag0.75Pd0.25 and Ag0.65Pd0.35
.
3. Experimental
3.1. Reagents and physical measurements
the instrumental broadening). The average crystallite size is 13
2
and 67 5 nm for PdAg and for Ag, respectively. Mass spectral
analysis of the volatile reaction products revealed CO2, CO, acetic
acid, CH4 and no acetone.
3.1.1. Reagents and solvents
Silver(I) acetate AgOOCMe, pivalic acid and solvents (acetic
acid, benzene, acetonitrile and THF), all reagent grade were pur-
chased from Acros Organics and used as received. Palladium(II)
acetate Pd3(OOCMe)6 was prepared from PdCl2 (Reakhim, Russia)
by reduction with NaBH4 followed by the oxidation of the Pd black
with concentrated HNO3 in glacial acetic acid according to a
2.3.3. Thermolysis under H2
Reduction of 1 with H2 (1 atm of 10%H2/90%He) at 250 °C pro-
duced a three-phase solid, which according to power XRD consists

386
N.Yu. Kozitsyna et al. / Inorganica Chimica Acta 370 (2011) 382–387
Ag-Ag(Pd)
a
b
Pd-Pd(Ag)
2.0
1.5
1.0
0.5
0.0
2.0
1.5
1.0
0.5
0.0
1
1
2
2
0
2
4
6
8
0
2
4
6
8
R-δ. Å
R-δ. Å
Fig. 6. Radial distribution function obtained from EXAFS data for the product of 1 reduction with H2 at 300 °C: (a) PdK edge, (b) AgK edge; 1 – Fourier transform modulus; 2 –
model for PdAg alloy.
procedure [22] and purified by repetitive recrystallisation from hot
acetic acid.
(graphite monochromator, Mo Ka radiation, k = 0.71073 Å, x-
scans, 2hmax = 60°). For complex 2: C16H28Ag2O16Pd, M = 798.52,
tetragonal, space group I-4, a = b = 11.4895(7) Å, c = 9.5453(7) Å,
V = 1260.06(14) Å3 (100 K), Z = 2, Dcalc = 2.105 g/cm3, 5962 mea-
3.1.2. Physical measurements
sured reflections, 1625 independent reflections with F2 > 2
r
(I),
The elemental C,H,N analysis was performed on an automated
C,H,N-analyzer (Carlo Erba Strumentazione, Italy). The IR spectra
were recorded on a Nicolet Nexus spectrometer with a Pike
micro-ATR accessory.
Thermoanalytic measurements were carried out on NETZSCH TG
209 F1 and NETZSCH DSC 204 F1 instruments in an Ar flow (20 ml/
min) (Ar, >99.998%; O2, 0.0002%; N2, <0.001%; water vapor,
<0.0003%; CH4, <0.0001%). Samples were weighted on a SARTORIUS
RESEARCH R 160P analytical balance with an accuracy of 1 ꢃ
10ꢁ2 mg. The calorimeter was calibrated by an ISO 11357-1
standard.
l
= 2.318 cmꢁ1
, R1 = 0.0114,, wR2 = 0.0285. The semi-empirical
method SADABS [23] was applied for the absorption correction. The
structures were solved by direct methods and refined by the
full-matrix least-squares technique against F2 with the anisotropic
displacement parameters for all nonhydrogen atoms. All the
hydrogen atoms in the complexes were placed geometrically and
included in the structure factors calculation in the riding motion
approximation. All the data reduction and further calculations
were performed using the SAINT [24] and SHELXTL-97 [25] program
packages.
The thermal decomposition of 1 was studied by differential
scanning calorimetry (DSC) and thermogravimetry (TGA). The
thermogravimetric measurements were performed in alundum
crucibles at a heating rate of 10 °C/min. The composition of the
gas phase was studied on a QMS 403C Aëolos mass-spectrometric
unit under TGA conditions. The ionizing electron energy was
70 eV; the highest determined mass number (mass-to-charge ra-
tio) was 300 amu. The weight of the samples was 0.5–3 mg. The
DSC study was carried out in aluminum cells at a heating rate of
10 °C/min. The weight of samples was 4–10 mg. Each experiment
was repeated at least three times. The TGA–DSC data were pro-
cessed by the ISO 11357-1, ISO 11357-2, ISO 11358, ASTM E
1269-95 standards with the use of the NETZSCH Proteus Thermal
Analysis program package.
3.3. Synthesis and reactions
3.3.1. Pd[(l-OOCMe)2Ag(HOOCMe)2]2 (1)
A slurry of Pd3(OCOMe)6 (400 mg, 1.78 mmol based on Pd) and
Ag2(OCOMe)2 (400 mg, 2.4 mmol based on Ag) in 35 ml of glacial
acetic acid was stirred in a shadowed flask at 100 °C for 2 h. The
reaction mixture was cooled ꢂ50 °C and filtered from a dark-gray
solid (unreacted and partially decomposed silver acetate). The
mother liquid was stayed for 12 h in the dark at room temperature
to produce a dark-yellow crystalline precipitate of 1 (277 mg). To
the filtered mother liquid was added a new portion of 1 (300 mg,
1.8 mmol) followed by stirring at 100 °C for 2 h. Cooling and filtra-
tion gave an additional amount of 1 (201 mg). Then the third por-
tion of Ag2(OCOMe)2 (200 mg, 1.2 mmol) was added to the mother
liquid to afford additional amount of 1 (176 mg). Finally, the
mother liquid was concentrated to the half of volume and gave a
new portion of 1 (50 mg). Total yield of 1 was 704 mg (50% based
on Pd). Complex 1 is soluble in acetic acid and water, insoluble in
benzene and slightly soluble with fast decomposition in CHCl3,
CH3CN, acetone and THF; it should be stored in the dark. Anal. Calc.
for PdAg2C16O16H28: C, 24.07; H, 3.53. Found: C, 24.03; H, 3.48%. IR
The X-ray powder diffraction analysis of the solid decomposi-
tion products was carried out on a G670 (HUBER) Guinier camera
using CuK radiation and on an FR-552 monochromator chamber
a
1
(CuK 1 radiation) using germanium as the internal standard (X-ray
a
diffraction patterns were processed on an IZA-2 comparator with
an accuracy of 0.01 mm).
The volatile products of 1 decomposition were detected by GC/
MS on an Agilent 6890 Gas Chromatograph equipped with an Agi-
lent 5973 mass-selective detector and 0.2 mm ꢃ 25 m capillary
column.
spectrum (ATR, m
/cmꢁ1): 1684s, 1603w, 1521vs, 1399vs,br, 1368w,
1374w, 1273s, 1016m, 946w, 890m, 696s, 673w, 619m.
3.2. X-ray diffraction analysis
3.3.2. Intermediate product of 1 thermolysis
Complex 1 (100 mg, 0.13 mmol) was heated in Ar flow (20 ml/
min) to 120 °C with a rate of 5 °C/min and the residue was cooled
under Ar to give 79.9 mg of the thermolysis product whose weight
Single-crystal X-ray diffraction experiments were carried out on
a Bruker SMART APEX II diffractometer with a CCD area detector

N.Yu. Kozitsyna et al. / Inorganica Chimica Acta 370 (2011) 382–387
387
corresponds to the loss of four molecules of acetic acid. Anal. Calc.
chemical bonding and mechanisms of important reactions and
processes’’).
for PdAg2C8O8H12: C, 17.26; H, 2.11. Found: C, 17.21; H, 2.17%. IR
spectrum (ATR,
m
/cmꢁ1): 1602m, 1558w, 1518vs, 11435w,
1396vs, 1345w, 1033m, 931w, 695m, 672s, 618m.
Appendix A. Supplementary material
3.3.3. Reaction of 1 with 1,10-phenanthroline
CCDC 802579 contains the supplementary crystallographic data
for this paper. These data can be obtained free of charge from The
Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/j.ica.2011.
02.003.
A solution of PhenꢀH2O (12.5 mg, 0.06 mmol) in 1 ml of benzene
was added rapidly under stirring to a suspension of 1 (50 mg,
0.06 mmol based on Pd) in 1 ml of benzene. The reaction mixture
was stirred at room temperature for 0.5 h until the initial com-
plexes 1 completely dissolved. White floccular precipitate of Ag
acetate was removed by filtration, washed with heptane and dried.
Anal. Calc. for AgC2O2H3: C, 14.39; H, 1.81. Found C, 14.63; H,
1.93%. Yield 12.6 mg (62%).The mother liquor was concentrated
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Acknowledgements
We thank for financial support the Russian Foundation for Basic
Research (projects Nos. 09-03-00514, 09-03-12114, 10-03-90420
and 11-03-01157), the Foundation of President of the Russian Fed-
eration (program for support of leading Russian scientific schools
NSh-65264.2010.3) and the Foundation of the Russian Academy
of Sciences (programs for Basic Research ‘‘Purposeful synthesis of
inorganic substances and creation of related functional materials’’
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