The unique bis-(disulfato)-aurate anion [Au(S2O 7)2]-: Synthesis and characterization of Li[Au(S2O7)2] and Na[Au(S2O 7)2]

Article abstract of DOI:10.1021/ic201671w

The reaction of Au(OH)₃ and oleum (65% SO₃) in the presence of M₂SO₄ (M = Li, Na) afforded yellow single crystals of Li[Au(S₂O₇)₂] (triclinic, P1, Z = 1, a = 532.20(3), b = 649.69(4), c = 836.72(5) pm, α = 107.982(2)°, β = 90.171(2)°, γ = 102.583(2)°, V = 267.80(3) A³) and Na[Au(S₂O₇) ₂] (monoclinic, P2₁/n, Z = 2, a = 533.31(3), b = 1193.38(7), c = 907.67(5) pm, β = 98.548(3)°, V = 571.26(6) A³). Both compounds exhibit the unprecedented [Au(S ₂O₇)₂]^- anion in which a square planar coordination of the central gold atom is achieved by the chelating attachment of two disulfate groups. The disulfates were characterized by means of IR spectroscopy and DTA/TG measurements. For both compounds, the decomposition occurs via several steps and is finished at about 450 °C at the stage of elemental gold and the sulfates M₂SO₄ (M = Li, Na), as revealed by X-ray powder diffraction of the residues.

Full text of DOI:10.1021/ic201671w

ARTICLE
pubs.acs.org/IC
The Unique bis-(Disulfato)-aurate Anion [Au(S2O7)2]ꢀ: Synthesis and
Characterization of Li[Au(S2O7)2] and Na[Au(S2O7)2]
Christian Logemann* and Mathias S. Wickleder*
Institute of Pure and Applied Chemistry, Carl von Ossietzky University of Oldenburg, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg,
Germany
S Supporting Information
b
ABSTRACT: The reaction of Au(OH)3 and oleum (65% SO3) in the presence of M2SO4
(M = Li, Na) afforded yellow single crystals of Li[Au(S2O7)2] (triclinic, P1, Z = 1, a =
532.20(3), b = 649.69(4), c = 836.72(5) pm, α = 107.982(2)°, β = 90.171(2)°, γ =
102.583(2)°, V = 267.80(3) Å3) and Na[Au(S2O7)2] (monoclinic, P21/n, Z = 2, a =
533.31(3), b = 1193.38(7), c = 907.67(5) pm, β = 98.548(3)°, V = 571.26(6) Å3). Both
compounds exhibit the unprecedented [Au(S2O7)2]ꢀ anion in which a square planar
coordination of the central gold atom is achieved by the chelating attachment of two
disulfate groups. The disulfates were characterized by means of IR spectroscopy and
DTA/TG measurements. For both compounds, the decomposition occurs via several
steps and is finished at about 450 °C at the stage of elemental gold and the sulfates M2SO4 (M = Li, Na), as revealed by X-ray powder
diffraction of the residues.
noble metals. While for the refractory metals, especially reactions
with fuming sulfuric acid (25ꢀ65% SO3) turned out to be very
useful;13 the preparation of platinum sulfates worked especially
well with concentrated sulfuric acid.14 Also, selenic acid
has been used successfully, e.g., for the preparation of
Au2(SeO3)2(SeO4),15 which exhibits puckered layers according
1. INTRODUCTION
The first systematic investigations of gold compounds con-
taining complex oxoanions can be traced back to 1827 when
Mitscherlich reported that elemental gold dissolves in concen-
trated selenic acid.1 Later on, this reaction was studied further by
Lenher,2 and finally Caldwell and Eddy claimed that the product
of the reaction can be used for glass coloring purposes.3 How-
ever, it was only in the early 1980s when the first structure
elucidations revealed the nature of the reaction products,4 which
turned out to be gold oxoselenates(IV). A similar story can be
told for sulfates of gold, which were also investigated a long time
ago by Schottl€ander,5 but which lacked characterization even
until 2001, when we were able to prepare the binary gold(II)-
sulfate Au2(SO4)2 that shows a metalꢀmetal bonded [Au2]4+
dumbbell, which is coordinated by two chelating and two
mondentate sulfate groups.6 In the course of these investiga-
tions, also a number of ternary gold(III)-sulfates showing
2
to ∞[Au(SeO3)3/3(SeO4)1/2] and the palladium compounds
Pd(SeO4), Pd(SeO3), and Pd(Se2O5).16 The latter two have been
obtained independently also by Albrecht-Schmitt and Ling.17 As
part of our investigations, we took also closer look at the system of
gold/oleum, with the gold usually applied in the form of its
hydroxide. Interestingly, the reaction of Au(OH)3 with SO3-rich
oleum led again to Au2(SO4)2.6 However, if additionally alkaline
metal ions are present, the formation of bis-(disulfato)-aurate
anions is observed, which are described here for the first time. It is
worthwhile to mention that this type of compound is not only of
academic interest but has gained severe attention since the catalytic
abilities of gold and gold compounds have contributed significantly
to the observed renaissance of gold chemistry.18
1
∞[Au(SO4)4/2] anionic chains connected via alkaline metal
ions could be gained,7 but binary Au2(SO4)3 is still elusive. Thus,
besides the above-mentioned Au2(SO4)2, the fluorosulfate
Au(SO3F)3,8 which forms [Au(SO3F)3]2 dimers, and the phosphate
AuPO49 are the only binary gold compounds with complex oxoanions
known so far. Also, for other common oxoanions, only polynary
compounds were described until now, e.g., the unprecedented
perchlorate (ClO2)[Au(ClO4)4],10 various nitrates containing the
[Au(NO3)4]ꢀ anion,11 and the iodate(V) K[Au(IO3)4].12 These
compounds exhibit discrete anionic complexes with the gold
atoms in square planar coordination of four monodentate oxo-
anions which are linked by the respective counter cations.
In recent years, we have considerably extended our investiga-
tions on the preparative potential of highly concentrated acids
toward various metals, with special emphasis on refractory and
2. EXPERIMENTAL SECTION
2.1. Synthesis. Au(OH)3 was prepared starting from elemental
gold according to a literature procedure.19 A total of 50 mg (0.2 mmol)
of Au(OH)3, 1 mL of oleum (65% SO3), 22 mg (0.2 mmol) of Li2SO4,
and 28 mg (0.2 mmol) of Na2SO4, respectively, were filled in glass tubes
(d = 16 mm; l = 300 mm). The tubes were torch-sealed under a vacuum,
placed in a resistance furnace, and heated up to 250 °C. The temperature
was maintained for 24 h. Upon slow cooling (1.8 °C/h), a large number
of yellow colored and extremely moisture sensitive single crystals were
Received: August 2, 2011
Published: September 29, 2011
r
2011 American Chemical Society
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Inorganic Chemistry
ARTICLE
obtained. They were collected by decantation of the mother liquor under
inert conditions. The yield was approximately 80% with respect to the
initial gold hydroxide.
It seems to be worthwhile to mention that the application of gold
hydroxide is mandatory for the reaction. Analogous reactions starting
with tetrachloroauric acid or its salts failed.
The single crystals of M[Au(S2O7)2] (M = Li, Na) are extremely
hygroscopic and have to be handled under strict exclusion of moisture.
Hydrolysis leads to a brownish residue, most probably Au(OH)3.
Treatment with organic solvents like absolute THF or ethyl acetate
for the removal of adhering fuming sulfuric acid resulted in decomposi-
tion of the compounds under the formation of elemental gold. Thus,
removal of the acid is best done mechanically.
Caution! During the reaction and even after cooling down to room
temperature, the glass tubes might be under pressure. The tubes have to be
protected with an explosion shield during reaction and should be cooled with
liquid nitrogen before they are opened.
2.2. X-Ray Crystallography. Several single crystals of
Li[Au(S2O7)2] and Na[Au(S2O7)2] were selected under protecting
oil with the help of a polarization microscope and directly transferred
into the cool nitrogen stream (153 K) of a single-crystal diffractometer
(BRUKER APEX II and Stoe IPDS I, respectively). For the lithium
compound, a triclinic unit cell could be determined, while the sodium
compound exhibits monoclinic symmetry. The intensities of the respective
best specimens were collected.
Li[Au(S2O7)2]. Assuming the space group P1 for Li[Au(S2O7)2]
application of the direct methods as provided by SHELXS-9720 revealed
the position of the gold and sulfur atoms, as well as those of some oxygen
atoms. Further oxygen atoms and the sodium atom could be successively
located in the course of difference Fourier syntheses during the refinement
with SHELXL-97.21 A numerical absorption correction was applied to the
data using the programs X-RED 1.2222 and XSHAPE 1.06,23 and all
atoms were refined anisotropically. Finally, the structure model refined to
R1 = 0.0206 and wR2 = 0.0475 for all data.
Na[Au(S2O7)2]. The observed systematic absences led unambigu-
ously to the space group P21/n. The structure solution in that space
group was successful using the direct methods of SHELXS-9720 and gave
the positions of the gold and sulfur atoms. Further oxygen atoms could
be successively located in the course of difference Fourier syntheses
during the refinement with SHELXL-97.21 Anisotropic temperature
factors were introduced for all atoms after a numerical absorption
correction was applied to the data using the programs X-RED 1.2222
and X-SHAPE 1.06.23 The structure model converged at residuals of
R1 = 0.0140 and wR2 = 0.0291 for all data.
2.3. Thermal Analysis. The investigation of the thermal behavior
of both compounds was performed using the thermoanalyzers TGA/
SDTA851e and TGA/DSC1 (both Mettler-Toledo GmbH, Schwerzen-
bach, Switzerland) for Na[Au(S2O7)2] and Li[Au(S2O7)2], respectively.
In a flow of dry nitrogen, about 11 mg of each compound was placed in a
corundum crucible and heated at a rate of 10 K/min up to 1050 °C. The
collected data were processed using the software of the analyzers
(Mettler-Toledo STARe V9.3).24
Table 1. Crystallographic Data for Li[Au(S2O7)2] and
Na[Au(S2O7)2]
chemical formula
crystal size
Li[Au(S2O7)2]
Na[Au(S2O7)2]
0.24 ꢁ 0.30 ꢁ 0.39 mm 0.08 ꢁ 0.10 ꢁ 0.82 mm
556.15 g/mol
triclinic
molar mass
572.20 g/mol
crystal system
space group
monoclinic
P1 (No. 2)
P21/n (No. 14)
a = 533.31(3) pm
b = 1193.38(7) pm
c = 907.67(5) pm
lattice parameters
a = 532.20(3) pm
b = 649.69(4) pm
c = 836.72(5) pm
α = 107.982(2)°
β = 90.171(2)°
γ = 102.583(2)
V = 267.80(2) Å3
1
β = 98.548(3)°
cell volume
no. of formula units
temperature
radiation
V = 571.26(6) Å3
2
153 K
153 K
MoꢀKα, λ = 71.07 pm MoꢀKα, λ = 71.07 pm
μ
14.595 mmꢀ1
0.095(3)
16679
13.724 mmꢀ1
0.0083(3)
9067
extinction coeff
measured reflns
unique reflns
with Io > 2σ(I)
Rint
3377
1406
3377
1296
0.0818
0.0240
a
Rσ
0.0389
0.0140
R1;b wR2c (Io > 2 σ (I)) 0.0202; 0.0487
0.0123; 0.0280
0.0140; 0.0291
1406/95
R1;b wR2c (all data)
0.0202; 0.0487
3377/95
data/parameter
a Rσ is defined as ∑[σ(Fo )]/∑[Fo ]. b R1 is defined as ∑ Fo| ꢀ |Fc /
2
2
∑|Fo|. c wR2 is defined as {∑ w(Fo ꢀ Fc2)2/∑ w(Fo ) }
.
2
2 2 1/2
data were processed with the OPUS 2.0.5 program.26 We also attempted to
gain Raman spectra of Li[Au(S2O7)2] and Na[Au(S2O7)2] (spectrometer
FRA106, Bruker, Karlsruhe, Germany, excitation: 1064 nm radiation of a
Nd:YAG laser), but in both cases the compounds changed color upon
irradiation, probably due to decomposition in the laser beam.
3. RESULTS AND DISCUSSION
3.1. Crystal Structures. Although Li[Au(S2O7)2] and
Na[Au(S2O7)2] crystallize with different symmetries, their crys-
tal structures are very similar. Both contain the [Au(S2O7)2]ꢀ
anion, showing the gold atom situated at crystallographic sites
bearing inversion symmetry (Li[Au(S2O7)2], 1h of space group
P1; Na[Au(S2O7)2], 2a of space group P21/n; Table 1). In
accordance with their trivalent oxidation state, the coordination
of the gold atoms is square planar. If AuꢀO distances above 300
pm are taken into account, the observed AuꢀO contacts (327
pm for the lithium and 310 pm for the sodium compound) would
lead to a pseudo-octahedral coordination sphere of the central
gold atom. However, a rationalization of the coordination con-
tributions of these oxygen atoms, e.g., with the help of the ECoN
concept (effective coordination number) as implemented in the
program MAPLE,27 shows that only very weak interactions can
be assumed.
2.4. X-Ray Powder Diffraction. The residues of the thermal
decomposition of Li[Au(S2O7)2] and Na[Au(S2O7)2] have been char-
acterized by means of X-ray powder diffraction with a STADI P powder
diffractometer (Stoe + Cie, Darmstadt, Germany) using Cu Kα radia-
tion and a flat sample holder. The intermediate phase observed during
the decomposition of Na[Au(S2O7)2] at 280 °C was measured with the
same diffractometer, but the sample was prepared in a glass capillary.
The diffraction data were processed with the WinXPow 2007 program
package (Stoe, V. 2.20).25
The [AuO4] squares are nearly undistorted and show OꢀAuꢀO
angles close to 90° and AuꢀO distances in the range from
196.7(2) to 198.3(2) pm. These observations match pretty well
the findings for gold(III) compounds with oxoanions up to
now.4,6ꢀ12 However, the new feature of the compounds under
2.5. IR Spectroscopy. IR spectra data were collected with a Bruker
Tensor 27 Spectrometer using the ATR method (attenuated total reflec-
tion). Spectra were collected within a range of 6500 to 550 cmꢀ1. The IR
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Table 2. Selected Bond Length and Angles for Li[Au(S2O7)2]
and Na[Au(S2O7)2]
M = Li
M = Na
bond lengths/pm
Au1ꢀO11 (2ꢁ)
Au1ꢀO21 (2ꢁ)
S1ꢀO12
196.7(2)
197.9(1)
141.1(2)
141.8(2)
151.9(2)
160.7(2)
141.2(2)
141.9(2)
152.4(2)
163.7(2)
207.1(2)
219.8(2)
205.4(2)
197.7(2)
198.3(2)
141.9(2)
141.8(2)
152.4(2)
161.0(2)
141.2(2)
141.3(2)
152.4(2)
164.1(2)
235.6(2)
233.6(2)
232.3(2)
S1ꢀO13
S1ꢀO11
S1ꢀO121
S2ꢀO22
S2ꢀO23
S2ꢀO21
S2ꢀO121
M1-O12 (2ꢁ)
M1-O13 (2ꢁ)
M1-O23 (2ꢁ)
Figure 1. The Ci symmetric bis-(disulfato)-aurate anions in the crystal
bond angles/deg
structures of Na[Au(S2O7)2] (on top) and Li[Au(S2O7)2] (at bottom).
2ꢀ
O11ꢀAu1ꢀO21 (2ꢁ)
O11ꢀAu1ꢀO21 (2ꢁ)
O12ꢀS1ꢀO13
O12ꢀS1ꢀO11
O13ꢀS1ꢀO11
O12ꢀS1ꢀO121
O13ꢀS1ꢀO121
O11ꢀS1ꢀO121
O22ꢀS2ꢀO23
O22ꢀS2ꢀO21
O23ꢀS2ꢀO21
O22ꢀS2ꢀO121
O23ꢀS2ꢀO121
O21ꢀS2ꢀO121
S1ꢀO121ꢀS2
88.99(6)
89.29(7)
90.71(7)
120.0(1)
107.5(1)
112.8(1)
103.19(9)
108.3(1)
103.49(9)
121.7(1)
112.7(1)
107.7(1)
108.2(1)
102.3(1)
102.01(9)
122.7(1)
In the sodium compound, the S2O7 groups exhibit nearly C2v
symmetry with respect to the alignment of the two [SO3] moieties.
The latter are twisted with respect to each other in Li[Au(S2O7)2],
leading to nearly Cs symmetry. The thermal ellipsoids are drawn at a 50%
probability level; the labeling scheme is in accordance with Table 2.
91.01(6)
119.9(1)
112.3(1)
107.73(9)
107.9(1)
103.63(9)
104.0(1)
121.2(1)
113.3(1)
107.8(1)
105.5(1)
103.9(1)
103.29(9)
124.7(1)
discussion is the coordination of the gold atoms by two chelating
inorganic ligands (Figure 1). Up to now, this motif has only been
realized with organic ligands.28 With respect to the observed
distances and angles within the disulfate groups, this anion seems
to be particularly suitable for such a type of coordination.
Especially the angles within the bridge SꢀOꢀS (124.7(1)° for
M = Li and 122.7(1)° for M = Na, respectively) exhibit no
significant deviations from the (unfortunately few) values re-
ported so far.29 The distances SꢀO can be divided into three
groups: The terminal oxygen atoms that are only coordinated to
M+ cations show short bond lengths around 142 pm. Those
distances of oxygen atoms bonded to the gold atoms are about
10 pm larger, and the SꢀO values within the SꢀOꢀS bridge are
found between 161 and 164 pm (Table 2). According to
these bond length variations, the disulfate groups have only
C1 symmetry in both compounds. Neglecting these altera-
tions, C2v symmetry would be found for the S2O72ꢀ ions in
Na[Au(S2O7)2] and Cs symmetry for those in Li[Au(S2O7)2].
The difference arises from the orientation of both [SO3] moieties
in the anions with respect to each other. If viewed along the SꢀS
direction, they are ecliptic in the sodium compound with a
O13ꢀS1ꢀS2ꢀO22 torsion angle of only 3.8° and twisted with
an O22ꢀS2ꢀS1ꢀO12 angle of 161.5° in the lithium compound
(Figure 1). Charge compensation for the [Au(S2O7)2]ꢀ anions
is achieved by Li+ and Na+ ions, respectively. They are also
located on special sites with Ci symmetry and have an octahedral
surrounding of six monodentate disulfate groups (Figure 2).
Within the [NaO6] octahedron, the NaꢀO distances fall in a
narrow range between 232.3(2) and 235.6(2) pm, while for
[LiO6], LiꢀO bond lengths from 205.4(2) up to 219.8(2) pm are
found. On the other hand, with respect to the OꢀMꢀO angles,
the [NaO6] octahedra are more strongly distorted (83.24(7)ꢀ
96.76(7)°) than the lithium analogues (89.38(6)ꢀ90.62(6)°).
In the crystal structures of Li[Au(S2O7)2] and Na[Au(S2O7)2],
the [Au(S2O7)2]ꢀ anions and the [MO6] octahedra are arranged
on chains running along the a axis of the unit cells, which is
almost identical for both compounds (M = Li, 532.20(3) pm;
M = Na, 533.31(3) pm; Figure 3).
3.2. IR Spectroscopy. The S2O72ꢀ group may adopt different
symmetries depending on the orientation of the [SO3] moieties
with respect to each other, and on the nature (symmetric or
asymmetric) of the SꢀOꢀS bridge. In most cases, C2v symmetry
is observed with ecliptic arranged [SO3] fragments. If the
fragments are in opposite orientation with respect to each other,
the anion exhibits Cs symmetry. In the first case, 21 normal
modes are expected representing the symmetry classes A1 (7ꢁ),
A2 (4ꢁ), B1 (6ꢁ), and B2 (4ꢁ), of which 17 are IR-active. The
normal modes considering Cs symmetry with the classes A0
(11ꢁ) and A00 (10ꢁ) are all IR-active. However, with respect
to the crystal structures discussed above in both compounds, the
disulfate groups display Ci symmetry, and 21 vibrations should be
observable on IR excitation, if further factor group splitting is
neglected. Indeed, both spectra show numerous bands which
are, however, not completely resolved (Figure 4). An assignment
of the observed frequencies was done based on literature data
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Figure 4. IR spectra of Li[Au(S2O7)2 (red) and Na[Au(S2O7)2]
(black).
Table 3. IR Spectra of Li[Au(S2O7)2] and Na[Au(S2O7)2]a
Figure 2. Coordination of the alkaline cations in Li[Au(S2O7)2] (on
top) and Na[Au(S2O7)2] (at bottom). Both cations are located on
crystallographic sites with inversion symmetry and show quite regular
coordination. The labeling is according to the entries in Table 2.
Li[Au(S2O7)2]
energy/cmꢀ1
Na[Au(S2O7)2]
energy/cmꢀ1
assignment27
560
s
δsSO3
601
w
603
m
s
658
δas SO3
672
725
760
w
w
m
686
s
755
s
νasSOS
νsSOS
780
s
800
s
893
s
895
w
m
s
941
s
974
1054
1164
1213
m
s
1003
1116
1207
1220
1239
1289
1387
w
s
νs SO3
w
w
w
w
s
1334
1380
m
w
νas SO3
a s = strong; m = medium; w = weak.
(Table 3).30 The latter were obtained for K2S2O7 and Na2S2O7.
Compared to these data, severe splitting of bands is observed
especially for the stretching vibrations ν(SꢀO), in accordance
2ꢀ
with the different SꢀO distances within the S2O7 ions. It
seems that a reliable assignment can only be done on detailed
quantum mechanical calculations, favorably taking into account
the entire [Au(S2O7)2]ꢀ anion.
3.3. Thermal Decomposition. The thermal decomposition of
Li[Au(S2O7)2] and Na[Au(S2O7)2] occurs in three steps, of
which the first two between 150 and 350 °C are not well
separated (Figures 5 and 6). The last step is found at about
400 °C and leads finally to elemental gold and the respective
sulfates M2SO4 (M = Li, Na). This could be unambiguously
proved by the X-ray powder pattern of the residues (Figure 5 and 6)
and is furthermore confirmed by the observed melting points of
the sulfates in the DTA curve at 849 °C for Li2SO4 (Lit: 845 °C)
Figure 3. Crystal structures of Na[Au(S2O7)2] (on top) and
Li[Au(S2O7)2] (at bottom) shown as a projection on the respective
(100) planes. Both the square planar [AuO4] units as well as the [MO6]
octahedra (drawn in yellow) are aligned in the [100] direction.
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Figure 6. Thermal decomposition of Li[Au(S2O7)2]. The DSC/TG
diagram on top shows a three step decomposition similar to those of its
Na congener, however, with different heights of the first two steps. In
analogy to the sodium compound, the final decomposition step leads to
Li2SO4 and elemental gold, as indicated by the XRD pattern of the
residue (at bottom). The asterisk in the upper diagram indicates the
melting point of Li2SO4, the double asterisk, its phase transition.
not.7a Indeed, the presence of NaAu(SO4)2 is clearly seen in the
diffractogram. Additionally, several reflections occur which can-
not be assigned as of now. Most likely, the decomposition of
Na[Au(S2O7)2] to NaAu(SO4)2 is not completely finished at
280 °C, and in the XRD pattern, a SO3 richer phase is present.
The third decomposition step for both compounds is in very
good accordance with the findings for the decomposition of
MAu(SO4)2 (M = Li, Na) that have been reported by Donova
and Siftar.32 On the basis of our present knowledge, we pro-
pose that the decomposition of the disulfates occurs according
to the following reaction sequence (compounds in italics not
identified):
Figure 5. Thermal decomposition of Na[Au(S2O7)2]. On top, the
DTA/TG diagram is shown, which shows essentially three decomposi-
tion steps. Steps I and II are in close proximity and are attributed to the
successive loss of SO3, leading to NaAu(SO4)2 at the end of step II. The
occurrence of the latter is proved by the XRD pattern gained from the
280 °C intermediate (middle diagram), which also shows a yet uni-
dentified product. According to the XRD diffractogram of the final
residue (at bottom), the third step leads to Na2SO4 and elemental gold.
The asterisk in the upper diagram indicates the melting point of Na2SO4.
M½AuðS2O7Þ2ꢂ f M½AuðS2O7Þ2ꢀxðSO4Þxꢂ þ xSO3
M½AuðS2O7Þ2ꢀxðSO4Þxꢂ f MAuðSO4Þ2 þ xSO3
ðIÞ
ðIIÞ
and 894 °C for Na2SO4 (Lit: 888 °C). For Li2SO4 also, the
known phase transition from the monoclinic to the cubic
modification is seen at 568 °C (Lit: 577 °C).31 It seems to be
likely that the decomposition is driven by the successive release
of SO3. In order to prove that assumption, we stopped the
decomposition of Na[Au(S2O7)2] at T = 280 °C and performed
an XRD powder measurement of the intermediate (Figure 5,
middle). We chose the sodium compound because the crystal-
lographic data of NaAu(SO4)2 as a possible intermediate are
available for comparison, while those of the lithium phase are
1
3
3
MAuðSO4Þ2 f M2SO4 þ Au þ SO3 þ O2 ðIIIÞ
2
2
4
4. CONCLUSION
The present paper offers further support that reactions with
and in highly concentrated mineralic acids provide efficient
routes to sulfates and polysulfates. Using SO3-rich oleum, we
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dx.doi.org/10.1021/ic201671w |Inorg. Chem. 2011, 50, 11111–11116

Inorganic Chemistry
ARTICLE
were able to prepare the first disulfates of gold in the form of
compounds Li[Au(S2O7)2] and Na[Au(S2O7)2]. Both exhibit
the hitherto unknown [Au(S2O7)2]ꢀ anion consisting of gold
atoms in square planar coordination of two chelating disulfate
groups. Upon thermal decomposition, the disulfates yield ele-
mental gold and the respective alkaline metal sulfates. Additional
investigations must show whether this complex can be stabilized
also in solution so that its catalytic potential can be elucidated.
Furthermore, the redox properties of the system Au/oleum need
special attention. We just started to perform theoretical calcula-
tions in order to shed some light on the stability of different
oxidation states of gold in oleum under various conditions.
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S
Supporting Information. Crystallographic information
b
files (CIF) containing the complete crystallographic data are
available and can also be obtained from the Fachinformations-
zentrum Karlsruhe, 76344 Eggenstein-Leopoldshafen, Germany
(fax: (+49)7247ꢀ808ꢀ666; e-mail: crysdata@FIZ-Karlsruhe.
de, http://fiz-karlsruhe.de/request_for_deposited_data.html)
on quoting the deposition numbers 422909 (Li[Au(S2O7)2])
and 422910 (Na[Au(S2O7)2]), respectively. This material is
available free of charge via the Internet at http://pubs.acs.org.
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Corresponding Author
*E-mail: christian.logemann@uni-oldenburg.de, mathias.wickleder@
uni-oldenburg.de.
’ ACKNOWLEDGMENT
The authors are grateful to Wolfgang Saak for collecting the
X-ray data.
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