Disproportionation of Ag(II) to Ag(I) and Ag(III) in fluoride systems and syntheses and structures of (AgF+)2AgF4-MFe6 - salts (M = As, Sb, Pt, Au, Ru)

Article abstract of DOI:10.1021/ic9905603

Interaction of Ag⁺ salts in anhydrous liquid hydrogen fluoride, aHF, with AgF₄^- salts gives amorphous red-brown diamagnetic Ag^IAg^IIIF₄, which transforms exothermally to brown, paramagnetic, microcrystalline Ag^IIF₂ below 0°C. Ag^IAu^IIIF₄ prepared from Ag⁺ and AuF₄^- in aHF has a tetragonal unit cell and a KBrF₄ type lattice, with a = 5.788(1) A?, c = 10.806(2) A?, and Z = 4. Blue-green Ag^IIFAsF₆ disproportionates in aHF (in the absence of F^- acceptors) to colorless Ag^IAsF₆ and a black pseudotrifluoride, (Ag^IIF⁺)₂Ag^IIIF₄ ^-AsF₆^-. The latter and other (AgF)₂AgF₄MF₆ salts are also generated by oxidation of AgF₂ or AgF⁺ salts in aHF with F₂ or in solutions of O₂⁺MF₆^- salts (M = As, Sb, Pt, Au, Ru). Single crystals of (AgF)₂AgF₄AsF₆ were grown from an AgFAsF₆/AsF₅ solution in aHF standing over AgF₂ or AgFBF₄, with F₂ as the oxidant. They are monoclinic, P2/c, at 20°C, with a = 5.6045(6) A?, b = 5.2567(6) A?, c = 7.8061(8) A?, β = 96.594(9)°, and Z = 1. The structure consists of (AgF)_nⁿ⁺ chains (F-Ag-F = 180°, Ag-F-Ag = 153.9(11)°, Ag-F = 2.003(4) A?), parallel to c, that enclose stacks of alternating AgF₄^- and AsF₆^-, each anion making bridging contact with four Ag(II) cations of the four surrounding chains caging them. There is no registry between the ordered array in one cage and that in any neighboring cage . The F-ligand anion bridges between the anions and, with the Ag(II) of the chains, generates a trifluoride-like structure. (AgF)₂AgF₄AsF₆ [like other (AgF)_nⁿ⁺ salts] is a temperature-independent paramagnet except for a Curie tail below 50 K.

Full text of DOI:10.1021/ic9905603

4
570
Inorg. Chem. 1999, 38, 4570-4577
Disproportionation of Ag(II) to Ag(I) and Ag(III) in Fluoride Systems and Syntheses and
+
-
-
Structures of (AgF )2AgF4 MF6 Salts (M ) As, Sb, Pt, Au, Ru)
†
Ciping Shen, Boris Zˇ emva, George M. Lucier, Oliver Graudejus, John A. Allman, and
Neil Bartlett*
Chemical Sciences Division, Lawrence Berkeley National Laboratory, and Department of Chemistry,
University of California at Berkeley, Berkeley, California 94720
ReceiVed March 10, 1999
Interaction of Ag+ salts in anhydrous liquid hydrogen fluoride, aHF, with AgF4 salts gives amorphous red-
-
I
III
II
brown diamagnetic Ag Ag F4, which transforms exothermally to brown, paramagnetic, microcrystalline Ag F2
I
III
+
-
below 0 °C. Ag Au F4 prepared from Ag and AuF4 in aHF has a tetragonal unit cell and a KBrF4 type lattice,
with a ) 5.788(1) Å, c ) 10.806(2) Å, and Z ) 4. Blue-green Ag FAsF6 disproportionates in aHF (in the absence
of F acceptors) to colorless Ag AsF6 and a black pseudotrifluoride, (Ag F )2Ag F4 AsF6 . The latter and other
AgF)2AgF4MF6 salts are also generated by oxidation of AgF2 or AgF salts in aHF with F2 or in solutions of
O2 MF6 salts (M ) As, Sb, Pt, Au, Ru). Single crystals of (AgF)2AgF4AsF6 were grown from an AgFAsF6/
AsF5 solution in aHF standing over AgF2 or AgFBF4, with F2 as the oxidant. They are monoclinic, P2/c, at 20
II
-
I
II
+
III
-
-
+
(
+
-
°
C, with a ) 5.6045(6) Å, b ) 5.2567(6) Å, c ) 7.8061(8) Å, â ) 96.594(9)°, and Z ) 1. The structure consists
n+
of (AgF)n chains (F-Ag-F ) 180°, Ag-F-Ag ) 153.9(11)°, Ag-F ) 2.003(4) Å), parallel to c, that enclose
-
-
stacks of alternating AgF4 and AsF6 , each anion making bridging contact with four Ag(II) cations of the four
surrounding chains “caging” them. There is no registry between the ordered array in one “cage” and that in any
neighboring “cage”. The F-ligand anion bridges between the anions and, with the Ag(II) of the chains, generates
n+
a trifluoride-like structure. (AgF)2AgF4AsF6 [like other (AgF)n salts] is a temperature-independent paramagnet
except for a Curie “tail” below 50 K.
I
III
Introduction
fully realized (the prepared Ag Ag F4 having a particle size
too small for structural characterization), but the thermodynamic
The Ag(II) oxidation state is peculiar to fluoro-ligand systems.
Although, in its ligand-field effects, oxygen is close to fluorine,
I
III
instability of Ag Ag F4 has been confirmed by its exothermic
1
II
transition to Ag F2.
2
,3
I
Ag(II) does not occur in oxides where, typically, AgO is Ag -
Partial disproportionation of Ag(II) to Ag(I) and Ag(III) has,
however, been observed in association with the solvolysis of
III
-
Ag O2. Attempts to disproportionate AgF2, to prepare AgF4 ,
by using highly basic solutions in aHF (in which Ag(I)F and
+
-
the salt AgF AsF6 in aHF:
-
the heavier-alkali-metal AgF4 salts are all highly soluble) did
not succeed:
4
AgFAsF (c) f AgAsF (c) + (AgF) AgF AsF (c) +
6
6
2
4
6
-
+
-
2AsF (solv) (2)
5
2
AgF (c) (with F in aHF) N Ag (solv) + AgF (solv)
2
4
(1)
the colorless AgAsF6 (as a consequence of its lower density)
But the stability of AgF4- salts toward solvolysis in aHF made
it possible to attempt the synthesis of Ag Ag F4 in that solvent.
The existence of AgAuF4 and the finding here, that this salt
has the same structure as its lighter-alkali-metal AAuF4 salts
4
II
III
sedimenting more slowly than the black product (Ag F)2Ag F4-
AsF6 (concisely: Ag3AsF12).
I
III
5
This paper details these findings and provides other synthetic
routes to the mixed-valence Ag3AsF12. Syntheses are also given
for its isostructural relatives Ag3MF12 (M ) Sb, Pt, Au, Ru).
Single-crystal X-ray diffraction analysis of Ag3AsF12 has
provided a structural basis for all. High thermodynamic stability,
deriving from the rather close-packed pseudotrifluoride structure,
may be responsible for the ready formation of these Ag(II)Ag-
(III) mixed-valence compounds.
6
(
which are themselves isostructural with their AAgF4 rela-
7
I
III
tives ), gave impetus to the notion that Ag Ag F4, with such a
symmetrical lattice, could, perhaps, have sufficient kinetic
stability to be isolable in that form. This hope has not been
†
Miller Visiting Professor, UCB (1993), from the Jo zˇ ef Stefan Institute,
University of Ljubljana Jamova 39, 1000 Ljubljana, Slovenia.
(
1) Dunitz, J. D.; Orgel, L. E. AdVances in Inorganic Chemistry and
Experimental Section
Radiochemistry; Academic Press Inc.; New York, 1960; Vol. 2, pp
1
-56.
Apparatus and Techniques. Work involving aHF was carried out
in apparatus constructed entirely from fluorocarbon polymers, T-reactors
being made from FEP tubing (CHEMPLAST, Inc., Wayne, NJ 07480)
(
(
(
2) Jansen, M.; Fischer, P. J. Less-Common Met. 1988, 137, 123.
3) Standke, B.; Jansen, M. Z. Anorg. Allg. Chem. 1986, 535, 39.
4) Lutar, K.; Jesih, A.; Leban, I.; Zˇ emva, B.; Bartlett, N. Inorg. Chem.
8
with Teflon valves and Swagelok fittings, as previously described.
1989, 28, 3467.
(
(
(
5) Sharpe, A. G. J. Chem. Soc. 1949, 2901.
6) Engelmann, U.; M u¨ ller, B. G. Z. Anorg. Allg. Chem. 1991, 598, 103.
7) Hoppe, R.; Homann, R. Z. Anorg. Allg. Chem. 1970, 379, 193.
(8) Zˇ emva, B.; Hagiwara, R.; Casteel, W. J., Jr.; Lutar, K.; Jesih, A.;
Bartlett, N. J. Am. Chem. Soc. 1990, 112, 4846.
1
0.1021/ic9905603 CCC: $18.00 © 1999 American Chemical Society
Published on Web 10/04/1999

+
-
-
(
AgF )2AgF4 MF6 Salts
Inorganic Chemistry, Vol. 38, No. 20, 1999 4571
The metal vacuum and fluorine handling line was also as described
previously. All solid starting materials and products were transferred
Table 1. X-ray Powder Data (Debye-Scherrer Method, Cu KR
4
4
Radiation, Ni Filter) for AgAuF , Tetragonal Cell, with a )
5.788(I) Å, c ) 10.806(2) Å, V/Z ) 90.49(5) Å3
and weighed within the dry argon atmosphere of a Vacuum Atmo-
spheres Corp. DRILAB. X-ray powder diffraction photographs (XRDPs)
2
4
2
4
1
/d × 10
1/d × 10
8
were obtained as previously described, as were magnetic measurements
Icalca
I/I0
vvw
vw
w
obs calc hkl Icalca
I/I0
ms
mw
m
w
w
obs
calc
hkl
9
employing a SQUID.
Materials. Anhydrous HF (aHF; Matheson) was first dried in an
b
5
9
199
8
4
8
3
3
2
2
6
6
3
7
6
3
2
1
7
8
4
4
4
6
7736 7340 244
7885 7869 228
8119 8104 512
8476 8456 336
9167 9161 1110
9545 9552 440
10243 10257 408
345 343 002
596 597 110
944 940 112
1197 1194 200
1376 1370 004
1538 1537 202
1585 1578 211
1644
1955 1967 114
2242 2263 213
2386 2388 220
2567 2564 204
2741 2741 222
3692 3680 116
3770 3758 224
4357 4355 134
4789 4776 400
5365 5373 330
5480 5481 008
5723 5716 332
FEP tube containing K
and then in one containing O
of Shamir and Binenboym. BF
2
NiF
6
(Ozark-Mahoning Pennwalt, Tulsa, OK)
AsF . O AsF was prepared by the method
and AsF (Ozark-Mahoning) were
checked by IR spectroscopy to ensure absence of major impurities and
2
1
6
2
6
0
100 vvs
3
5
3
0
8
3
2
b
1
1
4
8
1
3
2
3
3
1
2
7
7
2
8
1
4
ms
m
vw
vw
then used as supplied. AgF
in aHF at ∼20 °C. AgFBF
were O PtF SbF
2
was prepared by the fluorination of AgF
vw
vvw
vvw
vww
vvw
ms
vs
vvw
ms
ms
vw
w
vvw
vw
w
mw
m
9
was prepared as previously described, as
m, brc 10511 10492 532
4
1
1
12
13
9
14
4
2
9
6
,
O
2
6
15
,
O
2
RuF
6
,
AgAsF
6
, AgPtF
6
,
XeF
5
AgF
4
,
w
w
10868 10844 156
10941 10922 444
11478 11451 248
11566 11549 1310
11959 11940 620
12134 12116 604
12343 12332 0012
13251 13232 356
13337 13310 264
13531 13526 2012
13954 13937 3310
14722 14720 2212
15043 15033 448
15280 15268 172
15280 15268 552
15529 15522 640
AgBF
Preparations. AgAuF
.5092 mmol) was placed in one arm of a T-reactor and AgF (97.2
mg, 0.7662 mmol) in the other, and aHF (1.5 mL) was condensed in
each limb. The KAuF dissolved to a yellow solution but left a small
4
, and KAuF
4
.
m, br
m, br
vw
vw
vvw
mw
m
vw
vw
vw
w
4
4 4
from KAuF and AgF. KAuF (158.9 mg,
1
2
0
4
1
1
brown residue, so this solution was decanted slowly, at 20 °C, into the
colorless solution of the AgF to give a yellow precipitate in a colorless
-
supernatant solution (indicating total precipitation of the AuF
4
). The
colorless solution was removed by decantation, and the yellow solid
was washed (by back-distilled aHF) three times and vacuum-dried. An
XRDP of the yellow diamagnetic solid (178.4 mg, 0.4685 mmol)
5974 5970 420 11 ms
6070 6068 136
4
showed only the pattern of AgAuF , which was indexed on the basis
1
5
5
ms
vww
of a tetragonal unit cell with a ) 5.788(1) Å, c ) 10.806(2) Å, V )
mw, br 6132 6146 404
3
3
62.0(2) Å , and Z ) 4 (see Table 1), and that of the solid from the
decantate (82.5 mg) showed a complex pattern containing lines of
AgAuF and AgF.
Attempts To Prepare AgAuF
Ag) and AgF. AuF or AgF , each prepared from its KAF
vvw
mw
6301 6313 422 11 vw, br 16226 16227 608
6689 6675 208 19 mw, br 16324 16325 1510
4
a
I
calc placed the atoms in the following positions of space group
4
and AgAgF
4
from AF
3
(A ) Au,
I4/mcm (140):
salt,16 was
3
3
4
x
y
z
Ag
Au
F
0
0
0
/
1/
0
4
placed in one arm of a T-reactor and a large molar excess of AgF in
the other. AgF dissolved in aHF was poured into the limb containing
1
2
the AF
20 °C. The AF
the residual weight on removal of the AgF solution. An XRDP showed
unchanged AuF ; in the case of AgF
, there was some conversion16 to
Ag
Preparation of Ag Ag F
3
(A ) Ag, Au) and the reactor agitated for more than 1 day at
0.1688
0.1688
0.8768
∼
3
(A ) Ag, Au) was unchanged in appearance, as was
Atom positions were obtained from synchrotron powder diffraction
b
data (Graudejus, O.; Bartlett, N. To be Published). Impurity line.
c
br: broad.
3
3
3 8
F .
I
III
4
. Various other attempts were made to
, all carried out in aHF: (a) AgF + KAgF ; (b)
; (c) AgBF + KAgF . Reaction (a) gave only
as did reaction (b). Although the insolubility of Ag Ag F
I
III
synthesize Ag Ag F
XeF AgF + AgBF
4
4
5
4
4
4
4
II
I
III
Ag F
the low solubility of AgBF
2
4
and
in aHF rendered reaction (c) slow, it did
4
I
III
I
III
provide Ag Ag F
4
2 4
essentially free of AgF . The red-brown Ag Ag F
was on one occasion observed to transform rapidly to light-ochre-
II
2
colored Ag F (the latter established subsequently by its characteristic
XRDP), accompanied by vigorous boiling of the aHF, indicative of
the exothermicity of that change. The details that follow are for a
I
III
4
preparation which gave Ag Ag F , the XRDP of which revealed only
II
AgBF
4 2
contamination and no Ag F . SQUID measurements did exhibit
a weak paramagnetism (shown in Figure 1) indicative of contamination
II
2
by a trace of a weakly paramagnetic impurity, but this was not Ag F ,
17
since this is revealed by its characteristic field dependence below 163
K. The very low values of ø suggest that the bulk of the material is
I
III
Figure 1. Molar susceptibility, ø
M 4
, versus T (K) for Ag Ag F admixed
g
with AgBF
4
.
(
9) Casteel, W. J., Jr.; Lucier, G.; Hagiwara, R.; Borrmann, H.; Bartlett,
diamagnetic. One arm of a T-reactor was loaded with KAgF
4
(111.3
N. J. Solid State Chem. 1992, 96, 84.
mg, 0.499 mmol) and AgBF (89.8 mg, 0.461 mmol), aHF (1.5 mL)
4
(
(
(
(
10) Shamir, J.; Binenboym, J. Inorg. Chim. Acta 1968, 23, 101.
11) Bartlett, N.; Lohmann, D. H. J. Chem. Soc. 1962, 5253.
12) McKee, D. E.; Bartlett, N. Inorg. Chem. 1973, 12, 2738.
13) Edwards, A. J.; Falconer, W. E.; Griffiths, J. E.; Sunder, W. A.; Vasile,
J. J. Chem. Soc., Dalton Trans. 1974, 1129.
was added, and the mixture was brought from -81 to +10 °C over
-
∼24 h, with constant agitation. The yellow solution color (AgF
4
) faded,
and a homogeneous red-brown insoluble solid was produced. The
supernatant solution (still pale yellow) was decanted to the other limb
and the aHF removed under vacuum. No attempt was made to wash
the red-brown residue. The composition of the products was computed
on the assumption that all Ag(I) remained with the aHF-insoluble
(
(
(
14) Graudejus, O.; Elder, S. H.; Lucier, G. M.; Shen, C.; Bartlett, N. Inorg.
Chem. 1999, 38, 2503-2509.
15) Lucier, G.; Elder, S. H.; Chac o´ n, L.; Bartlett, N. Eur. J. Solid State
Inorg. Chem. 1996, 33.
16) Zˇ emva, B.; Lutar, K.; Jesih, A.; Casteel, W. J., Jr.; Wilkinson, P.;
Cox, D. E.; Von Dreele, R. B.; Borrmann, H.; Bartlett, N. J. Am. Chem.
Soc. 1991, 113, 4192.
+
residue and that all K transferred with the decanted solution. Found,
red-brown residue (XRDP showed only a weak AgBF
4
pattern): 116.4
, 79.9 mg; for 0.188 mmol
, 36.5 mg; total, 116.4 mg. Found, as a pale yellow solid
from the decanted solution (XRDP showing KAgF and KBF ): 86.4
I
III
mg. Required: for 0.274 mmol of Ag Ag F
of AgBF
4
(
17) Gruner, E.; Klemm, W. Naturwissenschaften 1937, 25, 59. Charpin,
P.; Diamoux, A. J.; Marquet-Ellis, H.; Nguyen-Nghi. C. R. Acad. Sci.
4
1967, 264, 1108.
4
4

4
572 Inorganic Chemistry, Vol. 38, No. 20, 1999
Shen et al.
Table 2. X-ray Powder Data (Debye-Scherrer Method, Cu KR
mg. Required: for 0.274 mmol of KBF
KAgF , 50.3 mg; total, 84.8 mg.
Disproportionation of AgFAsF
one limb of a T-apparatus was treated with an aliquot (∼1 mL) of
aHF, to give a blue solution (akin to that formed when AgF and AsF
in a 1:2 molar ratio dissolve in a small amount of aHF) and a black
solid. The blue solution was decanted from the black solid, and the
aHF and AsF
added to the AgFAsF
insoluble black solid, which by successive rinsings and decantations
was added to the original solvolysis product, the blue solution again
separated from the mixture, and the remaining AgFAsF
as before. This was repeated several times until most of the AgFAsF
had been solvolyzed. Toward the end, it became apparent that the black
solid was accompanied by a colorless solid which sedimented more
slowly than the black solid in the aHF solution and so formed an upper
layer in the sediment. XRDPs of the mixed solid product revealed that
it contained AgAsF
to that of a trifluoride, such as RuF
black solid). It was found that oxidation of the AgFAsF
or with F
in aHF at ∼20 °C left the black solid uncontaminated by a
second phase. It was also noted that when the black solid was exposed
to aHF containing AsF , AgF was released. That, and the preparation
4
, 34.5 mg; for 0.225 mmol of
Radiation, Ni Filter) for Ag
3
AsF12a
4
6
in aHF. AgFAsF
6
(∼600 mg) in
1/d × 10
2
4
1/d × 10
2
4
I/I0
ms
s
ms
m
ms
ms
vvw
vw
vvw
vw, brb
vw, br
vw
m
w
vvw
mw
ms
m
m
Icalc obs calc hkl
53 671 665 002
100 692 685 110 vw
36 1252 1243 112h
18 1295 1290 200
10 1459 1448 020
I/I0
Icalc
obs
calc hkl
2
5
w
2
1
3
4
3
3
3
3
1
3
2
2
3
2
0
3
3
3
2
3
2
2
1
1
2
2
2
1
2
1
1
2
2
2
2
2
2
6160 6161 330
6245 6253 402
6358 6352 116h
6449 6453 134
6449 6455 042
6489 6507 332h
6565 314
w
w
w
5
were removed under vacuum. A fresh aliquot of aHF,
retrieved from the decantate, again produced an
6
18 1459 1456 112 vw
2
3
2
4
4
4
1646 1652 210 unobs
1748 1743 20 2h vw
1784 1770 120 vvw
1882 1859 013 vw
1882 1883 121h
1927 1925 211
6
was recovered
6604 6609 420
6632 6639 206h
6845 6849 422h
6971 6972 404h
6971 6991 116
7070 7081 240
7116 7145 332
7313 7309 043
7435 7434 026
7540 7533 242h
7674 7700 422
7954 7916 206
7954 7959 242
8077 8087 226h
8165 8183 334h
8282 8316 316h
8411 8419 424h
8411 8427 510
8411 8451 044
9346 9316 244h
9346 9363 226
9346 9370 150
9608 9625 512
9891 9872 406h
9891 9886 136
9891 9929 152h
10018 10024 514h
10156 10121 424
10156 10141 152
10156 10167 244
6
w
w
14 2117 2113 022 vw
8
2172 2168 202 vw
2247 imp? vvw
2669 2661 004 vw
1
8
6
(the colorless solid) and showed a pattern akin
1
9
3
(this was characteristic of the
with O AsF
6
7
6
2
14 2746 2738 220 vw
14 3142 3133 11 4h vw
13 3202 3190 22 2h w, br
14 3267 3265 310 w, br
2
5
3
m
-
mw, br
mw, br
mw, br
ms
3
7
8
7
6
7
6
6
9
5
6
3
4
2
1
3
1
2
3573 3526 20 4h vw
3573 3558 114 vvw
3573 3580 130 vww
3621 3611 31 2h w, br
3621 3616 222 w, br
4134 4108 024 w, br
4134 4138 13 2h wv, br
4235 4250 312 wv, br
4358 4351 132 wv, br
4358 4377 204 vw
4976 4973 22 4h wv, br
5148 5162 400 wv, br
5300 5288 31 4h wv, br
5409 5402 40 2h vww, br
5812 5790 040 wv, br
5812 5824 224 wv, br
6008 5087 006 vw, br
6008 134h
of AgF
4
salts from the black solid with alkali-metal fluorides,
-
suggested that the black solid contained AgF
4
. The pseudotrifluoride
nature of the black solid and various gravimetries for high-yield
syntheses (see below) indicated the composition Ag
Interaction of AgFAsF with Massive aHF. The disproportionation
of AgFAsF to AgAsF and Ag AsF12 just described does not hold if
a large multimolar excess of aHF is added to the AgFAsF (i.e., when
the AsF concentration in the aHF from the solvolysis is very low).
Under those circumstances, the solid product is largely AgF
Quantitative Oxidation of AgAsF to AgFAsF by O AsF
C. A T-reactor was loaded with AgAsF (128.8 mg, 0.4340 mmol) in
the main tube and with O AsF (100.1 mg, 0.4531 mmol) in the sidearm,
and aHF (dried first with K NiF and then with O AsF ) was distilled
1.5 mL) onto each solid. The O
batches, into the suspension of AgAsF
3
AsF12.
ms
6
mw, br
mw, br
w
m, br
m, br
mw
vw
mw
vw
m
6
6
3
6
5
2
.
6
6
2
6
, at ∼20
°
6
2
6
2
6
2
6
(
2
AsF
6
solution was poured, in several
m
w, br
w, br
6
at ∼20 °C. The mixture evolved
2
O and gave an intense blue solution as the mixing proceeded, and all
solid AgAsF
(
6
was consumed. Removal of volatiles in vacuo
a
2
The calculated 1/d values and intensities of reflections are based
on the parameters obtained from the structure analysis on a perfectly
disordered single crystal: a ) 5.6045(6) Å, b ) 5.2567(6) Å, c )
e10- Torr) left a blue-green solid, the XRDP of which indicated
3
9,20
6
only the pattern of AgFAsF . Product weight: 145.5 mg; 0.434 mmol
3
AgFAsF
6
requires 137 mg. (Some loss of container weight, resulting
7.8061(8) Å, â ) 96.594(9)°, V ) 228.5(8) Å , Z ) 1, space group
+
P2/c. b br: broad.
in apparent higher product mass, often occurs when O
used in the oxidations.)
2
2
and F are
Preparation of Ag
prepared in several ways: (1) by the fluorination of AgFAsF
2) by oxidation, using O AsF , of (a) AgF , (b) AgFAsF
AgFBF . The methods in (2) were used in the Ag
Pt, Ru) preparations. Route 2a provided the compound Ag
high purity and yield: AgF (69.3 mg, 0.475 mmol) and O AsF
6
3
AsF12. This black aHF-insoluble solid was
of a primitive monoclinic cell (see Table 2). The weight of black solid
was 95 mg; that expected for 0.1584 mmol of Ag AsF was 99.2 mg.
6
in aHF;
6
, or (c)
3
12
(
2
6
2
Preparation of Ag
AgFBF in aHF. The experimental arrangement was like that for Ag
AsF12, the salt AgFBF (58.3 mg, 0.2728 mmol) in the place of the
AgF and O PtF (100.3 mg, 0.2941 mmol) in the place of O AsF
The O PtF
(in ∼1.5 mL of aHF) partly in solution, and the remainder
in the slurried suspension, was added in small portions to the stirred
suspension of the AgFBF
3 2 6
PtF12 from the Interaction of O PtF with
4
3
MF12 (M ) Sb, Au,
AsF12 in
(36.8
4
3
-
3
4
2
2
2
2
6
2
6
.
mg, 0.167 mmol) were loaded respectively into the sidearm and the
main tube of a prepassivated T-shaped Teflon-FEP reactor. Some aHF
2
6
(
∼1.5 mL), dried over O
to the AgF and to the O
into the AgF suspension. Oxygen evolution was immediately observed,
2
AsF
6
in a separate FEP reactor, was transferred
4
(in ∼1.5 mL of aHF). Immediately the
2
2
AsF
6
. The O AsF solution was poured slowly
2
6
precipitation of a nearly black solid (having a dark red reflectance)
2
was observed. The mixture was agitated at ∼20 °C for 30 min, and
and a black solid was produced. This mixture was agitated for ∼30
min. Then the supernatant solution was decanted into the main tube
and the black solid was washed with back-distilled aHF (five times) to
the point where the black solid no longer settled quickly but remained
several minutes in suspension in the aHF. This was the signal that
soluble salts had been largely removed. All volatiles were removed
2 6
the yellow supernatant solution (containing the excess O PtF ) was
decanted to the other limb. The nearly black solid was washed with
back-distilled aHF until the washings were free of color and then
-
3
vacuum-dried (e10 Torr). The XRDP (see Table 3) was complex
II IV
and indicated the presence of Ag Pt F
phase. The data were indexed on a monoclinic cell akin to that of Ag
AsF12 for the dominant phase, the remaining lines then being largely
6 3
as well as an Ag AsF12-like
-
3
under a dynamic vacuum (e10 Torr). The XRDP showed only the
3
-
pseudotrifluoride pattern which was completely indexed on the basis
14
II IV
due to the rhombohedral cell of the Ag Pt F
weighed 81.7 mg. Required for conversion of all Ag(II) to equimolar
quantities of the two products: for 0.0682 mmol of AgPtF , 28.3 mg;
for 0.0682 mmol of Ag PtF12, 50.8 mg; total, 79.1 mg.
Preparation of Ag AuF12 from O AuF and AgF
aHF. With arrangements similar to those used for the synthesis of Ag
6
. The insoluble solid
(
(
(
18) Kemmitt, R. D. W.; Russell, D. R.; Sharp, D. W. A. J. Chem. Soc.
1963, 4408.
6
19) Casteel, W. J., Jr.; Wilkinson, A. P.; Borrmann, H.; Serfass, R. E.;
Bartlett, N. Inorg. Chem. 1992, 31, 3124.
20) Gantar, D.; Frlec, B.; Russell, D. R.; Holloway, J. H. Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun. 1987, C43, 618.
3
3
2
6
2
in Acidified
3
-

+
-
-
(
AgF )2AgF4 MF6 Salts
Inorganic Chemistry, Vol. 38, No. 20, 1999 4573
Table 3. X-ray Powder Data (Debye-Scherrer Method, Cu KR
Radiation, Ni Filter) for Ag
Ag
3
RuF12 and Ag
3
SbF12 Preparations. These were carried out in
PtF12, using AgFBF and
salt. The XRDP data for each product are
given in Tables S1 and S2, respectively (Supporting Information).
Ag MF12 Salts with Alkali-Metal Fluorides in aHF. The salts
interact with alkali-metal fluorides (AFs) in aHF to generate a solution
of the AAgF and AMF (A ) Li has highest solubility, and A ) Cs,
the least) and an insoluble residue of AgF . The interaction of Ag
3
PtF12, Monoclinic Cell with a ) 5.69(1)
essentially the same manner as that of Ag
3
4
+ -
2 6
the appropriate O MF
Å, b ) 5.25(1) Å, c ) 7.81(1) Å, â ) 97.7(1)°, Z ) 1, V ) 231(1)
3
Å , Possible Space Group P2/c
2
4
2
4
3
1
/d × 10
1/d × 10
I/I0
vw
Icalca obs calc hkl
I/I0
ms
vw
Icalca obs calc hkl
4
6
574
603
2267
3
-
2
vw
vs
7
2671 2673 004
AsF12 with KF is representative. A solution of KF (25.5 mg, 0.439
mmol) in aHF in the sidearm of a T-reactor was poured onto a
51
00
668 668 002 ms
668 677 110 vw, br
14 2714 2710 220
2792
b
b
1
suspension of Ag
20 °C. The black solid was immediately converted to a yellow solution
and a brown insoluble residue. The XRDP of the yellow solid from
the decantate showed the pattern of KAgF strongly, lines characteristic
of KAsF and KHF also being present. The brown residue was AgF
Single-Crystal Growth of Ag AsF12. The reaction vessels for crystal
growth were usually constructed of /
Teflon valves with Kel-F stems and Teflon tips. A restriction, ∼1 cm
away from the sealed end of the sidearm, was made by pinching the
FEP tubing under heat to less than half its diameter. The purpose of
this was to slow the diffusion of F
AgFAsF was loaded into the main arm of the FEP reactor, the other
starting material, either AgF or AgFBF (in slight molar deficit of the
AgFAsF ), was loaded into the sidearm, and aHF (1-2 mL) was
condensed onto the AgFAsF . This gave a blue solution and a small
amount of black solid. After the black solid had settled, the blue solution
was carefully decanted onto the solid in the sidearm. F was then
admitted into the reactor until the total pressure was about 1000 Torr.
The reactor was then left undisturbed for about 1 week for crystal
growth from this solution. During crystal growth, the blue solution
3
AsF12 (111 mg, 0.177 mmol) in aHF (1.5 mL) at
w
w
707
737
784
vw
ms
ms
2928
∼
14 3099 3105 114h
13 3099 3135 222h
14 3181 3194 310
3255
vw
vvw
s
3
1031 1031 012 ms
4
39 1220 1223 11 2h vw, br
19 1272 1258 200
1371
12 1452 1451 020 ms
20 1452 1468 112 vw
6
2
2
.
b
s
w
ms
7
8
7
3503 3494 312h
3577 3580 130
3577 3596 114
3805
3
vw
s
s
ms, br
ms, br
vw, br
vw, br
vw, br
ms
3
8
in. FEP tubing, Teflon tees, and
b,c
1564
ms
7
6
6
8
4131 4125 024
4131 4125 132h
4235 4231 312
4370 4371 132
4669
4
2
3
2
1680 1681 20 2h ms
1858 1865 013 vw
1858 1871 12 1h ms
1962 1911 211 vvw
2
during crystal growth. Typically,
6
2
4
16 2119 2120 022 vvw
2183 2172 202 vvw
4835
6
vw
8
4
5118 5130 314h
6
a
2 4 6
Calculated using the Parameters from (AgF) AgF AsF single-
b
2
crystal analysis. These lines, or contributions to them, are attributable
to Ag Pt F (ref 14). br: broad.
6
II IV
c
Table 4. X-ray Powder Data (Debye-Scherrer Method, Cu KR
Radiation, Ni Filter) for Ag
3
AuF12, Monoclinic Cell with a )
.66(1) Å, b ) 5.24(1) Å, c ) 7.79(1) Å, â ) 97.5(1)°, Z ) 1, V )
2 4
usually became much paler; meanwhile, the initial AgF or AgFBF
5
2
slowly diminished as highly reflective black crystallites grew, from
solution, on the reactor wall. At the end of the crystal growth, the
solution was carefully decanted back into the main tube, to leave the
crystals on the sidearm wall, from which they were retrieved (in the
3
29(1) Å , Possible Space Group P2/c
2
4
2
4
1
/d × 10
1/d × 10
a
a
I/I
0
I
calc
obs
calc hkl
I/I
0
I
calc
obs
calc hkl
-3
DRILAB) after the system had been vacuum-dried (10 Torr) for
m
vs
s
w
s
s
vvw
vvw
vvw
m
vw
w
51
100
675
686
671 002
682 110
w
w
4
7
8
7
7
7
6
6
8
4
6
3
4
3
2
3
3471 3470 204h
3533 3531 312h
3610 3595 130
3610 3608 114
several hours.
2 3 6
The multifaceted, highly reflective, jet black (AgF ) AsF crystallites
were roughly cubical. They were usually very small, tended to form
aggregates, and were usually twinned. The most satisfactory batch, from
which a suitable single crystal of (AgF
the reaction of AgFBF
present in the aHF.
b
39 1233 1232 11 2h s, br
19 1268 1270 200 s, br
12 1463 1457 020 s, br
3610 3640
22
2
)
3
AsF
6
was obtained, was from
20 1463 1474 112 m, br
4138 4141 024
4138 4145 132h
4270 4257 312
4398 4387 132
4398 4439 204
4927 4927 224h
5056 5082 400
5190 5181 314h
5873 5895 224
6126 6136 330
6330 6358 116h
4
, AgFAsF
6
, and F
2
with a small amount of KBF
4
4
2
2
1703 1699 20 2h m, br
1884 1874 013 w, br
1884 1882 12 1h s, br
3
Crystal Structure Determination of Ag AsF12. Crystals were
manipulated under a dry argon atmosphere in the DRILAB on a
prepassivated Teflon sheet. The selected crystal was mounted in a 0.5
mm diameter quartz capillary, the narrow end of which had been further
drawn down to a long taper. Preliminary Laue and precession
photographs indicated monoclinic Laue symmetry and yielded cell
dimensions close to those derived from the X-ray powder data (see
Table 2).
16 2126 2128 022 s, br
8
7
14 2720 2727 220 w, br
14 3123 3124 11 4h w, br
13 3159 3156 22 2h w, br
14 3224 3223 310 w, br
2186 2184 202 m, br
2684 2684 004 vw, br
s
s
s
m
a
The crystal used for data collection was transferred to an Enraf-
Nonius CAD-4 diffractometer. Automatic peak search and indexing
procedures yielded the same monoclinic cell as derived from the X-ray
powder diffraction data and precession photographs. Testing showed
that the cell was indeed primitive and that there was no superlattice
present. Table 5 gives the crystal data and X-ray experimental
parameters, and Table 6, the interatomic distances and angles. Positional
and thermal parameters are given in Table S3 (Supporting Information).
A total of 1463 raw intensity data were collected. Inspection of the
azimuthal scan data showed a variation of Imin/Imax ) 0.82 for the
average curve. An empirical correction based on the observed variation
was applied to the data as a first approximation. The structure was
solved by Patterson methods in space group P 1h . Refinement and
elucidation of additional atoms proceeded via standard least-squares
and Fourier techniques.21 Examination of the triclinic model demon-
strated the correct monoclinic space group, P2/c (the apparent absence
of h0l, l * 2n has been found), and refinement continued in that group
Calculated using the parameters from (AgF)
2
AgF
4
AsF
6
single-
b
crystal analysis. br: broad.
AsF12, AgF
slowly into a solution of O
aHF (∼2 mL), to which BF
the solubilization of the AgF
contact with the yellow O AuF
solid precipitated. In the washing of the AgF
with cold back-distilled aHF containing BF
2
(143.2 mg, 0.982 mmol) in aHF (∼2 mL) was shaken
AuF (145.8 mg, 0.425 mmol) dissolved in
(∼0.14 mmol) had been added to aid in
[as Ag (BF ]. As the AgF made
solution, O
2
6
3
2
+
-
4 2
2
)
2
2
6
2
was evolved and a black
residue from the sidearm
2
3
, the characteristic blue
color of dissolved Ag(II) was observed, but this rapidly dissipated on
-
pouring into the yellow AuF
2 h, and the excess O AuF
and washed over to the sidearm. The XRDP of the black solid showed
an Ag AsF12 type pattern, which was fully indexed on a monoclinic
cell of that type (see Table 4), and that of the orange solid from the
decantate proved it to be O AuF . The observed weight of Ag
was 244.7 mg; 0.327 mmol of Ag AuF12 requires 244.9 mg. The
was 39.6 mg, which in excess should have
6
solution. The mixture was agitated for
1
2
6
in the supernatant solution was decanted
3
2
6
3
AuF12
3
observed residue of O
been 33.6 mg.
2
AuF
6
(21) MolEN-1990; Delft Instruments, X-ray Diffraction D.V.: Rontgenweg
1, 2624 BD Delft, The Netherlands, 1990.

4574 Inorganic Chemistry, Vol. 38, No. 20, 1999
Shen et al.
Table 5. Crystal and Data Parameters for Ag
3
AsF12
scattering factor for the neutral atoms were used,23 and all scattering
factors were corrected for both the real and imaginary components of
anomalous dispersion.24
formula
fw
space group
a/Å
b/Å
c/Å
Ag AsF12
626.5
P2/c
5.6045(6)
5.2567(6)
7.8061(8)
96.594(9)
228.5(8)
1
3
Inspection of the residuals ordered in ranges of (sin θ)/λ, |F |, and
o
parity and values of the individual indexes showed no unusual features
or trends, other than those caused by the strong pseudotranslation of
1
2
/ c in the structure. There was no indication of secondary extinction
â (deg)
in the high-intensity low-angle data.
3
V/Å
Z
Results and Discussion
T/K
F
298
100.6
calcd/g cm-3
The favored disproportionation of silver in AgO to Ag(I) and
2
radiation, λ/Å
reflns measd
residuals
0.710 73 (Mo KR)
Ag(III) contrasts with the behavior of the mixed-oxidation-
I
III
(h, +k (l
state fluoride Ag Ag F4, prepared in these studies, which
a
b
R ) 2.44; R
) [∑w(|F | - |F
Table 6. Crystal and Data Parameters for Ag
w
) 2.89
2
II
undergoes exothermic conversion to Ag F2:
a
b
2]1/2.
o
R ) ∑||F
o
| - |F
c
||/∑|F
o
|.
R
w
o
c
|) /∑wF
I
III
II
Ag Ag F f 2Ag F
(3)
4
2
3
AsF12
As/Ag2-F2
As/Ag2-F3
As-F4
Ag2-F4
F2-F3
1.80(2)
1.81(2)
1.72(3)
2.61(3)
2.51(3)
2.36(4)
2.38(3)
3.19(2)
3.01(2)
3.14(3)
2.98(3)
3.11(3)
3.09(3)
3.02(4)
3.09(4)
Ag1-F1
Ag1-F2
Ag1-F3
2.003(4)
2.34(2)
2.32(2)
I
III
It was anticipated that Ag Ag F4, like Ag(I)Au(III)F4, would
have its square-planar anions arranged perpendicular to one
another and all parallel to the 42 axis of the KBrF4 type structure
-
-
6,7
observed in alkali-metal AgF4 and AuF4 salts and, as found
here, for AgAuF4 (see Table 1). It was hoped that this simple
symmetric structure would provide kinetic stability. With the
F2-F3
F2-F4
F3-F4
F1-F2
F1-F3
F1-F4
F2-F3
F2-F4
F3-F3
F3-F4
F3-F4
2.59(3)
2.62(3)
2.60(3)
2.96(3)
3.12(2)
3.09(3)
3.22(3)
3.26(3)
3.16(4)
3.08(3)
3.26(3)
F2-F4
F3-F4
F1-F2
I
III
synthetic approach used to obtain Ag Ag F4
F1-F3
F1-F4
aHF, e 0 °C
I
+
III
-
F2-F2
Ag BF (c) + K (solv) + Ag F (solv)
8
4
4
F2-F3
I
III
+
-
Ag Ag F (c) + K (solv) + BF (solv) (4)
F2-F4
4
4
F3-F3
F3-F4
the mixed-valence red-brown solid was always noncrystalline,
probably as a consequence of the small particle size associated
with the insolubility of the material in aHF and its rather rapid
generation at low temperatures [both deliberately employed to
reduce the possibility of making the thermodynamically more
F1-Ag1-F1
F1-Ag1-F2
F1-Ag1-F3
F2-Ag1-F3
F3-Ag1-F3
F2-Ag2-F3
F2-Ag2-F4
F3-Ag2-F3
F3-Ag2-F4
F2-As-F2
180
F1-Ag1-F2
F1-Ag1-F3
F2-Ag1-F2
F2-Ag1-F3
F2-Ag2-F2
F2-Ag2-F3
F2-Ag2-F4
F3-Ag2-F4
F4-Ag2-F4
F2-As-F3
94.4(6)
87.8(5)
180
87.6(7)
180
91.8(9)
86.8(8)
86.7(9)
180
88.2(9)
93.2(8)
180
93.3(9)
154(2)
85.6(6)
92.2(5)
92.4(7)
180
88.2(9)
93.2(8)
180
93.3(9)
180
91.8(9)
86.8(8)
86.7(9)
180
II
favorable Ag F2].
II
The thermodynamic stability of Ag F2 does contrast with the
failure to generate AuF2 from Au(SbF6)2, that product25 dis-
proportionating to Au(0) and Au(III), i.e.
F2-As-F3
F2-As-F4
aHF
2
+
-
II
III
4
Au (solv) + 8F (solv)
8 Au (Au F ) (c) + Au(c)
F2-As-F4
F3-As-F3
4 2
(5)
F3-As-F4
F3-As-F4
F4-As-F4
Ag1-F1-Ag1
Ag1-F2-As/Ag2
As-F4-Ag2
136.0(9)
127(2)
Ag1-F3-As/Ag2
137.2(9)
and in highly basic aHF (with which AgF2 does not react) Au(II)
is completely converted to Au(III) and Au(0):
-
II
III
-
with a completely disordered model for Ag2 and the As and half-
occupancy for F4 (that closest to As, along c).
8
F (solv) + 3Au (Au F ) (c) f 8AuF (solv) + Au(c)
4 2 4
(6)
After solution of the structure and assignment of the correct space
2
2
group, an empirical correction was applied to the data on the basis of
the combined differences of F and F following refinement of all atoms
This difference [represented by eq 1 contrasted with (5) and
(6)] can be ascribed to a large relativistic effect at gold,2
which enhances the binding of the Au s electrons and simul-
taneously (by the enhanced screening effect of the s electrons)
causes the d electrons to be less bound. This effect causes
metallic gold to be more strongly bonded than metallic silver
and, at the same time, makes for easier oxidation of gold to
Au(III) than of silver to Ag(III).
6-28
o
c
with isotropic thermal parameters (corr(max) ) 1.32, corr(min) ) 0.79;
no θ dependence). Removal of systematically absent data and averaging
of redundant data (R ) 4.3% for observed data) left 670 unique data
I
in the final data set.
The final residuals for 40 variables refined against the 213 data for
2
2
which F >2.5σ(F ) were R ) 2.44%, R ) 2.89%, and GOF ) 1.06.
w
The R value for all 670 data was 15.2%. (This very large value is in
part an artifact of the way that reflections with negative measured
intensities are treated in the calculation of Rall. In part it is due to the
fact that only 15 0kl and general hkl reflections with l ) 2n + 1 are
(
23) Cromer, D. T.; Waber, J. T. International Tables for X-ray Crystal-
lography; The Kynoch Press: Birmingham, England, 1974; Vol. IV,
Table 2.2.B.
24) Cromer, D. T.; Waber, J. T. International Tables for X-ray Crystal-
lography; The Kynoch Press: Birmingham, England, 1974; Vol. IV,
Table 2.3.1.
“
observed” in the data set.)
(
The quantity minimized by the least squares program was ∑w(|F
o
|
2
-
|F
c
|) . The p factor, used to reduce the weight of intense reflections,
(
25) Elder, S. H.; Lucier, G. M.; Hollander, F. J.; Bartlett, N. J. Am. Chem.
Soc. 1997, 119, 1020.
was set to 0.03 throughout the refinement. The analytical forms of the
(
26) Pitzer, K. Acc. Chem. Res. 1979, 12, 271.
(
22) Walker, N., Stuart, D. Acta Crystallogr., Sect A 1983, A39, 159 (as
(27) Pyykk o¨ , P.; Desclaux, J.-P. Acc. Chem. Res. 1979, 12, 276.
(28) Pyykk o¨ , P. Chem. ReV. 1988, 88, 563.
used by the program DIFABS in MolEN).

+
-
-
(
AgF )2AgF4 MF6 Salts
Inorganic Chemistry, Vol. 38, No. 20, 1999 4575
Table 7. Comparison of Cell Dimensions for Ag
Au, Pt, Sb, Ru)
3
MF12 (M ) As,
a
a
a
RuF12a
Ag
3
AsF12 Ag
3
AuF12 Ag
3
PtF12 Ag
3
SbF12 Ag
3
a (Å)
b (Å)
c (Å)
5.6045(6)
5.2567(6)
7.8061(8)
5.66
5.24
7.79
97.5
229
5.69
5.25
7.81
97.7
231
5.70
5.27
7.83
97.2
233
5.67
5.23
7.80
97.2(4)
230(2)
â (deg) 96.594(9)
3
V (Å ) 228.5(8)
a
The standard deviation being always 1 in the last digit unless
otherwise noted.
3
Figure 2. Ordered structural unit for the structure of Ag AsF12. The
ellipsoids are scaled to represent the 75% probability surface.
Although strongly basic aHF failed to disproportionate aHF-
insoluble Ag F2 (eq 1), it was found that dissolved Ag(II) would
Figure 3. Molar susceptibility, ø , versus T (K) for Ag AsF .
M
3
12
II
3
2
disproportionate in moderately acidic aHF. Precipitation of a
black product, insoluble in aHF, was first noted in the studies
of Zˇ emva and co-workers29 when 1 equiv of AsF5 was added
to AgF3. An insoluble black solid was also produced when
AgFAsF6 was treated with fluorine in aHF or when (in an
attempt at Berkeley to intercalate the puckered-sheet-structure
1.81(2) Å is compatible with the average of Ag-F (in KAgF4)
3
3
) 1.889(3) Å and As-F (in KAsF6) ) 1.719(3) Å, which is
1.804 Å. The As-F4 distance of 1.72(3) Å is not significantly
different from that expected for As(V)-F. It should be noted
-
-
that the F-ligand bridging (including that of AsF6 with AgF4 )
from each anion to its four closest Ag(II) ions gives each Ag(II)
or Ag(III) ion a distorted octahedral F-ligand environment, not
+
-
of) AgF2 was oxidized by O2 AsF6 . The black product of the
last reaction was recognized as having a pseudotrifluoride
XRDP, and the entire pattern was convincingly indexed on a
-
much different from that of the AsF6 . This brings the (AgF)2-
34
AgF4AsF6 structure close to that of the trifluoride structure
3
5
II
IV
3
0
3 6
of RhF or the pseudotrifluoride Pd Pd F .
monoclinic distortion of a rhombohedral trifluoride lattice.
It was found that relatives of (AgF)2AgF4AsF6 could be
This, in combination with gravimetry, eventually fixed the
composition of the black solid as Ag3AsF12. Methods were then
worked out for the slow generation of Ag3AsF12 from AgF2, to
produce single crystals. The most effective route was the slow
fluorination of a blue solution of silver(II) fluoroarsenate
-
-
prepared, with AsF6 replaced by MF6 (M ) Sb, Ru, Pt, Au),
the generally useful approach being to oxidize AgF2 (solubilized
+
-
in aHF with BF3), or AgFBF4, with the appropriate O2 MF6
salts as oxidizers:
(
obtained by decantation from its solvolysis productsssee
aHF
+
-
+
-
below) in contact with either solid AgF2 or solid AgFBF4. The
structure, illustrated in Figure 2, with interatomic distances and
angles in Table 6, is in its essence, the salt (AgF )2AgF4 AsF6 ,
the cations being chains akin to those first described by Gantar
et al. for AgFAsF6 and those subsequently observed in a
variety of AgF salts from these laboratories.
cations, running parallel to c, enclose stacks of alternating AgF4
and AsF6 . An ordered stacking sequence of the anions is
required, as adjacent AsF6 would result in F4 ligand collision
and repulsion of the anions. This would result in significant
variation in the z parameters of the As and Ag2 atom positions,
whereas the data fix the z parameters precisely. The ordered
anion stacks, however, are not in registry with one another, and
this renders all of the Ag(II) ions of the cation chains effectively
equivalent. The observed As/Ag2-F distance (Table 6) of
3AgF (solv) + 3BF + O (solv) + MF (solv)
8
4
2
6
(
AgF) AgF MF (c) + 3BF (g)(solv) + O (g) (7)
+
-
-
2 4 6 3 2
The close similarity of their XRDPs and their unit cells (see
Table 7) indicates that essentially the same pseudotrifluoride
structure occurs in all of these materials.
The magnetic behavior of (AgF)2AgF4AsF6 (see Figure 3) is
very like that of AgFAsF6 and indicates that the nearly
temperature-independent paramagnetism is a property of the
2
0
+
9,31
The chain
-
-
-
9,31
chain cation. Although this is consistent with a partially filled
36
band for the cation obedient to Fermi-Dirac statistics, neither
the anticipated Peierls distortion nor electrical conduction has
n+
ever been observed in these (AgF)n systems. Even contacts
to single crystals of (AgF)2AgF4AsF6 with massive gold rods
failed to find evidence of electrical conductance along the
(
29) Jesih, A.; Lutar, K.; Zˇ emva, B. Unpublished observations, 1988.
(32) Lutar, K.; Mili c´ ev, S.; Zˇ emva, B.; M u¨ ller, B. G.; Bachmann, B.; Hoppe,
R. Eur. J. Solid State Inorg. Chem. 1991, 28, 1335.
(33) Grafner, G.; Kruger, G. J. Acta Crystallogr., Sect. B 1974, B30, 250.
(34) Grosse, L.; Hoppe, R. Z. Anorg. Allg. Chem. 1987, 552, 123.
(35) Tressaud, A.; Winteberger, M.; Bartlett, N.; Hagenmuller, P. C. R.
Acad. Sci., Ser. C 1976, 282, 1069.
(30) The original indexing of the pattern was achieved with a pseudotriclinic
2
distortion of a trifluoride-like rhombohedral cell, with a* ) 0.0541,
2
2
b* ) c* ) 0.0529, 2a*b*cos γ* ) 0.0386 ) 2a*c*cos â*, and
2
b*c*cos R* ) 0.0390, the equalities of which indicated the true
monoclinic nature of the lattice.
(
31) Lucier, G.; Munzenberg, J.; Casteel, W. J., Jr.; Bartlett, N. Inorg. Chem.
(36) Kittel, C. Introduction to Solid State Physics; Wiley: New York, 1986;
p 413.
1995, 34, 2692.

4576 Inorganic Chemistry, Vol. 38, No. 20, 1999
Shen et al.
+
expected conducting path (c). It must be pointed out, however,
that even massive gold could be surface oxidized and fluorinated
by such a powerful oxidizer,31 and this could provide an
insulating barrier.
Perhaps the most surprising aspect of (AgF)2AgF4AsF6 is that
it is sufficiently stable thermodynamically to drive the dispro-
portionation of Ag(II) to Ag(I) and Ag(III), as AgFAsF6 is
solvolyzed by aHF:
Reaction 1 may involve interaction of Ag (solv) with the
+
solvated radical O2F(solv) rather than with O2 (solv), since the
38
weakness of the O2F base and the merely moderate strength
of AsF5 as a F acceptor in the aHF solvent may mean that
the O2AsF6 solution is not fully ionized:
-
31
aHF
+
-
O (solv) + AsF (solv) { } O F(solv) + AsF (solv) (13)
2
6
2
5
+
Attack on Ag (solv) by O2F(solv) in the presence of AsF5(solv)
aHF limited
2
+
4AgFAsF6
8 AgAsF (c) + Ag AsF (c) +
could then provide the observed Ag (solv):
6
3
12
2
AsF (solv) (8)
5
+
-
Ag (solv) + AsF (solv) + O F(solv) +
6
2
aHF
This occurs when the amount of added aHF is small and the
resultant acidity (AsF5 concentration) moderately high. A
mixture of colorless AgAsF6 and black Ag3AsF12 is formed.
These solids sediment at different rates, the latter being more
dense (4.55 versus 4.20 g cm ), resulting in the white solid
depositing above the black in the aHF. Addition of fluorine or
O2AsF6 (see below) to this mixture converts the AgAsF6 to
AgFAsF6:
2+
-
AsF (solv)
8 Ag (solv) + 2AsF (solv) + O (g) (14)
5
6 2
Removal of AsF5 and aHF from this solution gives pure, blue-
green AgFAsF6, but as soon as aHF is added to this, the
solvolytic disproportionation represented in eq 8 occurs. Neither
reaction 11 nor reaction 12, however, gives a Ag3MF12 product.
For formation of the latter, it appears to be necessary to
disproportionate the AgFMF6 salt.
-
3
In the interaction of O2PtF6 with AgFBF4, the main product
is the mixed-valence salt (AgF)2AgF4PtF6, but Ag Pt F6 is a
aHF
1
II IV
/2
F (g) + AgAsF (c)
8 AgFAsF (c)
(9)
2
6
6
sizable byproduct that is easily detected in the XRDP of the
products (see Table 3). If we assume that the generation of Ag3-
PtF12 requires the disproportionation of AgFPtF6
Thus, with these oxidizers present and the reaction of eq 8
repeated, all of the solid can be converted to Ag3AsF12. The
interaction of AgFAsF6 with a large excess of aHF (with the
consequence that the acidity in AsF5 is low) leads to simple
solvolysis and AgF2 production:
-
4
AgFPtF (c) + 2BF f AgPtF (c) + Ag PtF +
6
4
6
3
12
-
2
BF (g) + 2PtF (solv) (15)
3
6
aHF large
AgFAsF6
8 AgF (c) + AsF (solv)
2
5
(10)
analogously to eq 8, AgPtF6, which is14 Ag Pt F6, should
II IV
II IV
represent one-quarter of the initial AgFBF4. Ag Pt F6, a salt
Formation of Ag3AsF12 appears to be a consequence of the
solvolytic disproportionation of AgFAsF6, since oxidation of
of Ag(II) (probably as a result of its insolubility in aHF), does
+
not interact with the dissolved O2 . The observed yields of Ag3-
2+
the blue solutions of Ag (solv) does not generate it. Certainly
the salt O2AsF6 does not interact with the blue solution in aHF
prepared by adding two molar aliquots of AsF5 to one of AgF2.
On the other hand, O2AsF6 rapidly and quantitatively oxidizes
AgAsF6 to such a blue solution, from which clear, blue-green
AgFAsF6 solution is recovered:37
PtF12 and AgPtF6 are close to those expected on the basis of eq
1
5. This stands in contrast to the interaction of AgFBF4 with
O2AuF6, where Ag3AuF12 is produced free of AgAuF6 (see
Table 4).
-
6
The AuF6 (solv) species has a very stable dt2g electron
-
14
configuration. Unlike PtF6 (solv), which has an electron
affinity g60 kcal mol , AuF6 (solv) is not a strong one-
-
1
-
aHF
+
-
2+
AgAsF (c) + O (solv) + AsF (solv)
8 Ag (solv) +
6
2
6
electron oxidizer since its lowest lying empty orbital is of
-
-
2
AsF (solv) + O (g) (11)
antibonding σ character. In PtF6 (solv) on the other hand, the
6
2
6
addition of an electron generates the filled-subshell dt2g species,
2-
The interaction of AgAsF6 with O2PtF6 proceeds quite
differently from (11), there being no significant O2 evolution.
Evidently the Ag(I) oxidation to Ag(II) is brought about by the
PtF6 (solv). When, therefore, the disproportionation comparable
to that represented in eq 15 occurs for AgFAuF6, the AgAuF6
1
4
I
V
I
product is Ag Au F6. The latter salt, like Ag AsF6 and unlike
-
II IV
II IV
+
PtF6 , which produces the insoluble Ag Pt F6 product, O2AsF6
being the aHF-soluble product:
Ag Pt F6, is oxidized by O2 to give soluble Ag(II) species,
and so the conversion to Ag3AuF12 is completed.
-
The RuF6 species also has a favorable electron configuration
(high-spin dt2g ) with favorable exchange energy. It is not a
strong one-electron oxidizer and, with Ag , gives Ag Ru F6.
The oxidation of AgFBF4 by O2RuF6 therefore is akin to the
oxidations involving O2AsF6 and O2AuF6, and the product is
clean Ag3RuF12.
+
-
3
AgAsF (c) + O (solv) + PtF (solv) f AgPtF (c) +
6
2
6
6
-
3
1
+
I
V
+
2
O (solv) + AsF (solv) (12)
6
The different outcomes of the two reactions (eqs 11 and 12)
probably stem from the anionic nature of the PtF6- oxidizer,
2+
Since, in strongly acidified aHF, where all Ag(II) is Ag -
solv), there is no oxidation by O2 to give the Ag3MF12 salts
+
which must interact rapidly in its attractive encounter with Ag -
+
(
(
solv) (from the slightly soluble AgAsF6). Electron transfer to
and, on the other hand, basic or neutral aHF gives only AgF2,
it is clearly necessary to regulate closely the acidity of the aHF,
if the Ag3MF12 salts are to be obtained efficiently in high purity.
14
2+
2-
generate the close-packed pseudotrifluoride lattice of Ag PtF6
must occur immediately. The insolubility of this salt in aHF
contributes to the simplicity of reaction 12.
-
It appears that BF4 provides the appropriate buffering control.
This derives from the weak-acid nature of BF3, which has low
(
37) It should be noted that, at -80 °C (the solubility of O2 in aHF then
being higher and the T∆S term for eq 11 much smaller), the reverse
2
+
reaction is essentially complete; i.e., all Ag (solv) is reduced to
AgAsF6(c) by O2, which then precipitates as O2AsF6.
(38) Lucier, G. M.; Shen, C.; Elder, S. H.; Bartlett, N. Inorg. Chem. 1998,
37, 3829-3834.

+
-
-
(
AgF )2AgF4 MF6 Salts
Inorganic Chemistry, Vol. 38, No. 20, 1999 4577
solubility in the aHF solvent. So, when O2MF6 acts as an
oxidizer for AgFBF4, it is the release of BF3 that keeps the
acidity essentially constant:
the AuF2-composition sheets, as would be anticipated for the
intercalation of AuF2, if it existed and were isostructural with
AgF2. Yet the oxidation of AgF2 has given (so far), not the
related structure but, rather, (AgF)2AgF4MF6. In passing, it
3
AgFBF + O MF f Ag MF + O (g) + 3BF (g) (16)
31
4
2
6
3
12
2
3
should be noted that in AgFRuF6 the Ag(II) coordination is
roughly square (and akin to that of Ag(II) in AgF2),4 so the
failure to form the silver analogue of Au(AuF4)2Au(MF6)2
cannot be attributed to a distinct favoring of two-coordination
by cationic Ag(II).
0,41
As a consequence of the reactions expressed in eqs 8 and 9,
the action of elemental fluorine on AgFAsF6 converts one-third
of the Ag(II) to Ag(III). The latter can be recovered as an alkali-
-
metal AgF4 salt by treating the black solid with alkali fluoride
42
2+
-
25
Comparison of the isostructural salts Ag (SbF6 )2 and
in aHF:
2+
-
2+
Au (SbF6 )2 indicates that each A (A ) Ag, Au) distorts
-
2+
the SbF6 to the same extent, this despite the Ag having a
-
2
F (solv) + (AgF) AgF AsF (c) f 2AgF (c) +
43
2+
2
4
6
2
higher first electron affinity than Au (21.5 and 20.5 eV,
respectively). It therefore remains possible that the Ag(AgF4)2-
Ag(SbF6)2 relative of the gold compound may yet be made. A
similar synthetic challenge is the preparation of a gold relative
-
-
AgF (solv) + AsF (solv) (17)
4
6
-
For the heavier alkali metals (K, Rb, Cs), the AsF6 salts are
-
2 4 6
of the silver salts (AuF) AuF MF .
of low solubility in aHF, whereas the AgF4 salts are highly
soluble. Therefore, this treatment provides for ready preparation
Acknowledgment. The authors gratefully acknowledge
support from the National Science Foundation, under Grant No.
DMR-9404755, and the Director, Office of Energy Research,
Office of Basic Energy Sciences, Chemical Science and
Materials Science Divisions of the U. S. Department of Energy,
under Contract No. DE-AC-03-76SF00098. B. Zˇ . participated
in the work during his tenure of a Miller Visiting Professorship
(Spring Semester, 1993) for which professorship the Miller
Institute, U.C. Berkeley, is thanked. O.G. also gratefully
acknowledges the Alexander von Humboldt Foundation for a
Feodor-Lynen Fellowship. Refinement of the Ag3AsF12 structure
was completed with the assistance of Dr. F. Hollander of the
U.C. Berkeley College of Chemistry CHEX-RAY facility.
-
of AgF4 salts by room-temperature fluorination of AgFAsF6
in aHF and without the need of photodissociation of the F2.
The latter is required39 for the direct synthesis of AgF4 from
AgF2 and F2 in basic aHF.
-
It is surprising that the oxidation of Ag(II) in aHF (especially
+
the interaction between AgF2 and O2 salts) should generate
(
(
AgF)2AgF4MF6 and not the silver relative of Au(AuF4)2Au-
SbF6)2. The mixed-valence gold compound25 is the product of
the action of fluorine on the salt Au(SbF6)2 in solution in aHF:
2
+
-
4
Au (solv) + 8SbF (solv) + F (g) f
6 2
Au(AuF ) Au(SbF ) (c) + 6SbF (solv) (18)
4
2
6 2
5
Supporting Information Available: Listings of X-ray powder
diffraction data, positional and thermal parameters, crystal data, and
X-ray experimental details. This material is available via the Internet
at http://pubs.acs.org.
The [Au(AuF4)2Au]2 component of the structure25 is a
+
II
slightly distorted relative of a puckered sheet of the Ag F2
structure.40,41
-
The SbF6 species are packed closely between
IC9905603
(
(
(
39) Lucier, G. M.; Whalen, J. M.; Bartlett, N. J. Fluorine Chem. 1998,
9, 101-104.
40) Charpin, P.; Plurien, P.; Mereil, P. Bull. Soc. Fr. Mineral. Cristallogr.
970, 93, 7.
8
(42) Gantar, D.; Leban, I.; Frlec, B.; Holloway, J. H. J. Chem. Soc., Dalton
Trans. 1987, 2379.
(43) Moore, C. E. Ionization Potentials and Ionization Limits DeriVed from
the Analyses of Optical Spectra; NSRDS-NBS 34; National Bureau
of Standards: Washington, DC, 1970.
1
41) Jesih, A.; Lutar, K.; Zˇ emva, B.; Bachmann, B.; Becker, S.; M u¨ ller,
B. G.; Hoppe, R. Z. Anorg. Allg. Chem. 1990, 588, 77.