SUPPLEMENTARY INFORMATION
Unusual thermal decomposition of Ag(II)SO4 yielding Ag(I)2S2O7: bending the
Hammond’s rule
P. J. Malinowski, M. Derzsi, A. Budzianowski, P. J. Leszczyński, B. Gaweł, Z. Mazej, W. Grochala*
S1. Synthesis (AgSO4, Ag2S2O7).
S2. Thermal decomposition & EGA analysis.
S3. Analysis of TGA and DSC results using Kissinger equation and isoconversional method.
S4. Data on thermal decomposition of +50 sulphates and oxo-sulphates: summary of literature data.
S5. Determination of the crystal structure of Ag2S2O7.
S6. Description of the crystal structure of Ag2S2O7.
S7. DFT calculations.
S8. Projections emphasizing relationship between the crystal structures of AgSO4 and Ag2S2O7.
S9. References.
S1. Synthesis (AgSO4, Ag2S2O7).
AgSO4: AgSO4 has been synthesized according to the published procedure [1]; the reaction equation:
AgF2 + H2SO4 → AgSO4 + 2 HF.
(1)
Ag2S2O7: Silver(I) hydrogen sulfate precursor has been obtained from solution of Ag2SO4 in concentrated
H2SO4 as described in the literature [2] (trifluoroacetic acid was used instead of Me2SO4 to rinse the
product). Ag2S2O7 has been obtained by thermal decomposition (at 503 K) of AgHSO4 (for 10 min)
according to reaction equation:
2 AgHSO4 → Ag2S2O7 + H2O.
(2)
The product has been spontaneously cooled to room temperature by removing the sample from the heater.
The chemical identity of the reaction product (white powder) as Ag2S2O7 has been further confirmed by
Fourier transform infrared (FT-IR) spectroscopy.
Silver(I) disulfate(VI) decomposes endothermally in two steps. The first step 443–593 K is connected
with a ca. 6.6 % mass loss, and a heat of 102 J/g; the second step 593–643 K results in additional 13.3 %
mass loss, and a heat of 202 J/g (the values of heat and mass losses refer to the Ag2S2O7 substrate). The
two-step character of thermal decomposition is connected with gradual elimination of 1/3 SO3 and 2/3
SO3, respectively, from one mole of Ag2S2O7, suggesting Ag6S5O18 (= 2 Ag2S2O7 x Ag2SO4) as an
intermediate. As confirmed by XRDP and FT-IR, Ag(I)2SO4 is the final product of thermal decomposition
at 503 K according to a simplified reaction equation:
Ag2S2O7 → Ag2SO4 + SO3.
(3)
Thermal decomposition of Ag2S2O7 is apparently not preceded by any structural phase transition.
All samples studied were stored in the Ar-filled glovebox (< 0.1 ppm O2, < 1 ppm H2O) while preventing
their exposure to sunlight.
S1
S2. Thermal decomposition & EGA analysis.
The setup for thermal analysis has been described elsewhere [1]. Various heating rates were applied.
The sample of AgSO4 (5-9 mg) in a form of a fine black powder was placed inside a small alumina
crucible with a lid having a small pin hole in the centre. The powder was spread evenly on the bottom of
the crucible using the PTFE tamper. After closing the lid, the crucible was quickly loaded into furnace of
TGA/DSC analyzer, which was then evacuated and filled with Ar (6.6 purity, also used as a carrier gas).
Such procedure minimized the effect of moisture from the air for the sample.
The EGA analysis (i.e. combined Q-MS and FT-IR) has confirmed that the evolved gas consisted of highpurity oxygen.
S3. Analysis of TGA and DSC results using Kissinger equation and isoconversional method.
Activation energy (Edec#) was determined using Kissinger’s equation:
(4)
We used temperatures at the DSC peak for 5 different heating rates (β): 1, 2.5, 5, 10 and 15 K/min. The
linear fit for the DSC maxima yields Edec# = 125.8 kJ/mol. Application of a isoconversional method by
Coats and Redfern [3] at three different stages of decomposition α1 = 0.25, α2 = 0.5 and α3 = 0.75 (Fig.1)
gives the following values: Edec#(α1) = 128.9 kJ/mol, Edec#(α2) = 128.3 kJ/mol and Edec#(α3) = 126.6
kJ/mol. Due to small differences of Edec# determined from the isoconversional method (taken from TG
curves), we may assume that Edec# does not depend on α, which is the precondition for validity of
Kissinger’s equation [4]. As the obtained values does not differ significantly, we take the activation
energy as the average of these four values, Edec# =127.4 kJ/mol.
Figure 1. Abscissa: reciprocal temperature, T–1 [ K–1]; ordinate: ln(T2/Tr) where T is temperature [K] at
which a given α is obtained, while Tr is a heating rate [K min–1].
S2
S4. Data on thermal decomposition of +50 sulphates and oxo-sulphates: summary of literature data.
Substrate
Reductive deoxygenation
AgSO4
Na2SO4
Li2SO4
K2SO4
Cs2SO4
Rb2SO4
Non-redox desulphation
Ti(SO4)2
Sn2(SO4)4
Ce(SO4)2
Th(SO4)2
Fe2(SO4)3*
PbO6Fe6(SO4)4
Zr(SO4)2
Zr(SO4)2
CuSO4
TiOSO4
BeSO4
HgSO4
Sc2(SO4)3
ZnSO4
Tl2SO4
Al2(SO4)3
Cu2O(SO4)
Pb0.5Fe3O3(SO4)6
AgFe3O3(SO4)6
KAl3O3(SO4)2
Ga2(SO4)3
Hf(SO4)2
La2(SO4)3
Ce3O2(SO4)4
Tl2(SO4)3
Cr2(SO4)3
In2(SO4)3
NiSO4
PbSO4
PbSO4
Sm2(SO4)3
5MgO x MgSO4
MgSO4
CdSO4
SrSO4
CaSO4
BaSO4
Products
Tonset [oC]
References
½ Ag2S2O7, ¼ O2
2 Na, SO2, O2
2 Li, SO2, O2
2 K, SO2, O2
2Cs, SO2, O2
2Rb, SO2, O2
110
1200
1400
1400
1500
~1700
[1]
[5],[6]
[5]
[5]
[5]
[5]
TiOSO4, SO3
2 SnO2, 4 SO3
½ Ce2O(SO4)3, ½ SO3
ThO2, 2 SO3
Fe2O3, 3 SO3
PbSO4, 3 SO3, 3 Fe2O3
ZrO2, 2 SO3
ZrO2, 2 SO3
CuO, SO3
TiO2, SO3
BeO, SO3
mostly gaseous products (Hg, O2, SO3),
traces of Hg3O2(SO4) (solid residue)
Sc2O3, 3 SO3
0.33 ZnO x ZnSO4, 0.33 SO3
Tl2O, SO3
Al2O3, 3 SO3
CuO, SO3
½ PbSO4 x Fe2O3, Fe2O3, 3/2 SO3
½ Ag2SO4 x Fe2O3, Fe2O3, 3/2 SO3
½ K2SO4 + 1.5 SO3 +1.5 Al2O3
Ga2O3, 3 SO3
HfO2, 2 SO3
La2O2SO4
3 CeO2, 4 SO3
Tl2O3, SO3
Cr2O3, 3 SO3
In2O3, 3 SO3
NiO, SO2, ½ O2**
1/3 α–Pb3O2(SO4), 2/3 SO3
PbO, SO3
Sm2O2SO4, 2 SO3
6 MgO, SO3
MgO, SO2, ½ O2
CdO, SO3
SrO, SO2, ½ O2
CaO, SO3
BaO, SO2, ½ O2
200
~330
380
500-600
500-510
531
540, 710
~550
572
600
600
600
[7]
[8]
[9]
[10]
[11],[12],[13]
[14]
[15],[16]
[7]
[17]
[7]
[18]
[19]
600
~630
~650
655, 692
660
667
673
680
690
~700
700, 725
720
~750
750
810
819
895
~900
900
910
1100
~1200
1200
1240
~1400
[7]
[7]
[8]
[20],[21]
[17]
[22]
[22]
[23]
[24]
[7]
[25],[26]
[9]
[8]
[7]
[27]
[28]
[19]
[29]
[25]
[30]
[31],[32],[33]
[7]
[32], [33]
[34]
[32], [33]
S3
Oxidative desulphation
(VO2)2SO4
V2O5, SO3
100
[7]
Cu2SO4
2/3 CuSO4, 2/3 Cu2O, 1/3 SO2
400
[35]
SnSO4
SnO2, SO2
400
[36]
VOSO4
V2O5, SO3, SO2
430
[7]
V2(SO4)3
V2O5, 3 SO2, ½ O2
500
[7]
Pb(Fe,Cu)3O3(SO4)2
Pb(Fe,Cu)3O7, 2 SO2
539
[37]
FeSO4
½ Fe2O3, SO2, ¼ O2
550
[38]
Ce2(SO4)3
CeOSO4, CeO2
550
[25]
β–CoSO4
1/3 Co3O4, SO2, 1/6 O2
556, 620
[39], [40]
β–MnSO4
1/2 Mn2O3, SO2, 1/4 O2
600
[41]
Deammoniation***
(NH4)2SO4
NH4HSO4, (NH4)3[H(SO4)2]
238
[42]
Disproportionation****
Cu2SO4
Cu, CuSO4
400
[35]
Unknown pathway
Au2(SO4)3
----[43]
AuSO4
----[44]
* all reports agree except one, which suggests decomposition to Fe2O(SO4)2 & SO3 at a temperature as
low as 30 oC [45].
** at this temperature entropy drives partial decomposition of SO3 to SO2 and ½ O2.
*** elimination of a volatile Lewis base, NH3.
**** concurrent with oxidative desulphation.
S5. Determination of the crystal structure of Ag2S2O7.
Although silver(I) disulfate(VI) was first described over 40 years ago [46], its crystal structure has not yet
been determined. Knowledge of the crystal structure of Ag2S2O7 is obviously needed to get insight into
structural transformations (migrations of both light and heavy atoms) associated with the thermal
decomposition of Ag(II)SO4.
The as-prepared white sample of Ag2S2O7 has been ground to fine powder and loaded into a quartz
capillary of 0.3mm diameter and 30 mm length. Microcrystallites showed a tendency to stick to each other
and to the capillary wall, making loading difficult. The synthesis of Ag2S2O7 has been repeated several
times, but the product was always a mixture of silver(I) disulfate(VI) (main phase) and silver (I) sulphate
(impurity phase) and a multi-phase Rietveld refinement was needed.
X-ray diffraction data have been collected using CuKα radiation in transmission mode on a rotating
capillary under a parallel X-ray beam obtained by Goebel mirror.
S4
Figure 2. The measured diffraction pattern (black), the final calculated profile (red), the 30th order
polynomial of the Chebychev background function (blue) and the difference between the measured and
the calculated profile (grey) of mixture of Ag2S2O7 (green bars and calculated diffractogram from the
structure) and Ag2SO4 (violet bars and calculated diffractogram from the structure).
Powder diffraction pattern was indexed using the X-Cell software [47] in Material Studio interface [48]. It
was found that Ag2S2O7 compound crystallizes in triclinic unit cell. The obtained cell parameters were
refined in TOPAS 4.2 [49]. Structure determination from powder data has been carried out using TOPAS
4.2. The amorphous pattern due to the capillary was modeled by 30th order polynomial of the Chebychev
background function. This is actually the third component in the powder diffraction diagram (Fig. 3). The
unit cell of Na2S2O7 transformed using the (0 1 0, 1 0 0, 0 0 -1) matrix has been used as a starting model
for the refinement. The rigid body approximation for two SO42– tetrahedra has been applied with (S-O =
1.42 Å). During refinement the restraints have been made progressively softer, and ultimately they were
eliminated. Also constrains of isotermal elipsoids of Beq values has been applied; one value of Beq was
allowed for each type of atom (i.e. Ag, S, O). The anti-bumping penalty function has been used for and SO (1.42 Å) contacts to facilitate the refinement. The constraints for atomic displacement parameters were
necessary because the data range was limited to relatively low sin(τ)/λ values. Fundamental Parameters
Approach [50] was utilized during the refinement. Analyzed sample consisted of two phases: 95.9 (1)%
Ag2S2O7 (RBragg=0.97%) and 4.1 (1)% Ag2SO4 (RBragg= 1.19%). Atomic positions of the minority phase
were fixed at the values given by Mehrotra et al. [51] but the cell parameters were refined to improve the
fit. The correction for the preferred orientation of the main phase was described using the 4th order
spherical harmonics [52]. The final Rietveld refinement plots are shown in Fig. 2.
Data collection: XRD Commander [53]; cell refinement: TOPAS 4.2 [49]; data reduction: TOPAS 4.2;
program(s) used to solve structure: TOPAS 4.2; program(s) used to refine structure: TOPAS 4.2;
molecular graphics: TOPAS Rigid-body editor & Mercury 1.4 [54]; software used to prepare material for
publication: PLATON [55], publCIF [56], CrimsonEditor, X-SEED [57], POV-RAY 3.6 [58], VESTA
[59].
S5
S6. Description of the crystal structure of Ag2S2O7.
Ag2O7S2
γ = 85.841 (1)°
Mr = 391.88
V = 287.90 (1) Å3
Triclinic, P¯ 1
Z=2
a = 6.8199 (1) Å
CuKα radiation, λ = 1.540600, 1.544390 Å
b = 6.8462 (1) Å
µ = 24.13 mm-1
c = 6.93734 (9) Å
T = 296 K
α = 86.855 (1)°
cylinder, 18 × 0.3 mm
β = 63.055 (2)°
Ag2S2O7 crystallizes in triclinic system, (P1, Z = 2, see Table above) and is isostructural with Na2S2O7
[60]. The present structure is reported in the standard (Niggli reduced cell) setting, to which the published
Na2S2O7 structure [60] can be transformed using the (0 1 0, 1 0 0, 0 0 -1) matrix. The Ag(I)–Na(I)
isomorphism is not unexpected, and exists for many compounds of these two cations. Notably the sulfates
of Ag(I) [61],[51],[62] and Na(I) [63],[64],[65],[51],[66] are isostructural, Fddd space group.
The crystal structure of silver(I) disulfate(VI) consists two non-equivalent silver atoms in the unit cell.
There are four shorter Ag1-O bonds with distances from 2.417 (9) Å to 2.662 (14) Å, and additional four
long bonds with Ag1-O distance between 2.751 (17) Å and 2.946 (15) Å. The average Ag1-O bond length
is 2.69 (2) Å, noticeably longer than the average Ag2-O bond (see below). The second
crystallographically unique silver cation, Ag2, has quite different coordination sphere from Ag1 (see Fig.
3). Ag2 is coordinated by six oxygen atoms arranged in the form of a slightly deformed octahedron.
Figure 3. The unit cell of Ag2S2O7; view emphasizes two distinctly different coordination spheres of Ag1
and Ag2 atoms and the strongest argentophilic interaction (Ag2-Ag2). [Symmetry codes: (i) 1-x, 1-y, 1-z;
(ii) 1-x, y, z; (iii) 1-x, -y, 1-z; (iv) 2-x, -y, 1-z; (v) x, y, z-1; (vi) 1+x, y, z-1; (vii) x, y, z-1.]
The average Ag2–O distance is 2.42 (2) Å, which is smaller than Ag–O distance in silver(I) sulfate (2.509
Å) [51]. The bond-valence analysis performed with PLATON [55] with parameters for Ag–O bonds taken
from literature [67],[68],[69] yields valences of Ag atoms somewhat apart from unity, between 0.893 (12)
S6
and 1.284 (17) Å. The coordination of a larger Ag1 cation by eight O atoms in Ag2S2O7 differs from that
of a smaller Na+ cation by seven O atoms in Na2S2O7 (Fig. 4). The longest Ag1-O1 separation of 2.95 Å
is still within the bonding distance while the analogous Na1-O5 distance of 3.46 Å must be considered as
non-bonding.
Figure 4. Layer of cations connected by the dishulphate groups of (a) Ag2S2O7 and (b) Na2S2O7 [60].
Geometry of disulfate(VI) anion is very similar to that found for Na2S2O7. The S-O-S bridge is
asymmetric with the S-O bonds distance 1.671 (16) Å and 1.537 (14) Å; the asymmetry is thus more
pronounced than that for the sodium analogue (1.6524 Å vs. 1.6063 Å, respectively). The asymmetry of
the S-O-S bridge in Ag2S2O7 is also confirmed by solid-state DFT calculations (see Table 2). The
potassium analogue the S-O-S bridge is ideally symmetric with S-O distances of 1.6417 Å [60]. The S-OS angle of 125.6 (8)° in Ag2S2O7 is similar to that observed for Na2S2O7 (125.7°) and
K2S2O7 (124.25°).
S7. DFT calculations.
To support the structural refinement of Ag2S2O7 solid-state DFT calculations for the Na2S2O7-type and
K2S2O7-type model unit cells have been carried out. In calculation, both the Local Density Approximation
(LDA) and Generalized Gradient Approximation (GGA), with the energy cutoff at 600 V, electronic
convergence of 10 -7 eV/atom, ionic convergence of 10 -5 eV/atom, and the Monkhorst-Pack Grid of
2x2x2 and 2x3x4 k-points (for the Na2S2O7-type cell and the K2S2O7-type respectively) were utilized.
Interestingly, our total energy DFT full crystal structure optimisations suggest that energy difference
between the K2S2O7- and Na2S2O7-type is negligible (3.3 kJ/mol in favour of the K2S2O7-type cell at the
LDA level and 10.7 kJ/mol in favour of the Na2S2O7 at the GGA level, at a typical error of the DFT
methods of 10 kJ/mol, see Table below). It is therefore conceivable that the K2S2O7-type silver(I)
disulfate(VI) might also exists. Since the K2S2O7-type has its DFT-predicted volume per formula unit
smaller by 1.4–3.2% than the Na2S2O7-type, it is supposed that the K2S2O7-type Ag2S2O7 might be
searched for at elevated pressure conditions.
S7
Table. Comparison of the unit cell vectors and angles, of the unit cell volume and of the calculated energies per one
formula unit for Ag2S2O7 in the experimental P-1 structure as well as from the LDA and GGA calculations.
Theoretical results for a hypothetical Ag2S2O7–type C2/c polymorph were also shown. As expected, the LDA
method overestimates while the GGA one underestimates compound's density. The experimental unit cell constants
were transformed using the (0 1 0, 1 0 0, 0 0 -1) matrix to match the published crystal structure of Na2S2O7.
exp P¯ 1 Na2S2O7-type Na2S2O7-type K2S2O7-type K2S2O7-type
P¯ 1
P¯ 1
C2/c
C2/c
LDA
GGA
LDA
GGA
-6480.4
-5723.8
-6483.7
-5713.1
-3.3
+10.7
Energy per 1 FU
(kJ/mol)
∆(K2S2O7–Na2S2O7)
(kJ/mol)
a
(Å)
6.846
6.810
7.111
11.846
12.726
b
(Å)
6.820
6.754
6.997
6.706
7.024
c
(Å)
6.937
6.783
7.141
6.577
6.830
α
(°)
116.9
119.6
115.7
90.0
90.0
β
(°)
93.1
97.2
97.3
94.3
94.5
γ
(°)
85.8
85.3
83.4
90.0
90.0
V
(Å3)
287.9
269.1
308.5
260.5
304.3
4.52
4.83
4.22
4.99
4.27
d
3
(g/cm )
S8. Projections emphasizing relationship between the crystal structures of AgSO4 and Ag2S2O7.
Figure 5A. Projection 1. The unit cells are marked with solid line. Ag – grey, S – yellow and green, O –
red balls. The SO4 anions (green S) must move close to the neighbouring SO4 anions (yellow S) in order
to form pyrosulphate anions (and release oxygen), at substantial readjustment of lattice parameters. The
areas highlighted in blue guide an eye while emphasizing the structural relationship between Ag
sublattices of Ag(II)SO4 and Ag(I)2S2O7.
S8
Figure 5B. Projection 2. The unit cells are marked with solid line. Ag – grey, S – yellow and green, O –
red balls. The SO4 anions (green S) must move close to the neighbouring SO4 anions (yellow S) in order
to form pyrosulphate anions (and release oxygen), at substantial readjustment of lattice parameters. The
areas highlighted in blue guide an eye while emphasizing the structural relationship between Ag
sublattices of Ag(II)SO4 and Ag(I)2S2O7.
Figure 5C. Projection 3. The unit cells are marked with solid line. Ag – grey, S – yellow and green, O –
red balls. The SO4 anions (green S) must move close to the neighbouring SO4 anions (yellow S) in order
to form pyrosulphate anions (and release oxygen), at substantial readjustment of lattice parameters. The
areas highlighted in blue guide an eye while emphasizing the structural relationship between Ag
sublattices of Ag(II)SO4 and Ag(I)2S2O7.
S9
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