Room temperature syntheses of AuF6- and PtF6- salts, Ag+AuF6-, Ag2+PtF62-, and Ag2+pdF62-, and an estimate for E

Article abstract of DOI:10.1021/ic981397z

Solutions of AuF₄^- or PtF₆^2- salts, prepared from the metals at ～20 °C, in liquid anhydrous hydrogen fluoride (aHF), made basic with alkali fluorides, are further oxidized by photodissociated F₂ (visi

Full text of DOI:10.1021/ic981397z

Inorg. Chem. 1999, 38, 2503-2509
2503
-
-
-
Room Temperature Syntheses of AuF6 and PtF6 Salts, Ag+AuF6 , Ag2+PtF62-, and
Ag2+PdF62-, and an Estimate for E(MF6 ) [M ) Pt, Pd]
-
O. Graudejus, S. H. Elder, G. M. Lucier, C. Shen, and N. Bartlett*
Chemical Sciences Division, Lawrence Berkeley National Laboratory, and Chemistry Department,
University of California, Berkeley, California 94720
ReceiVed December 7, 1998
-
2-
Solutions of AuF4 or PtF6 salts, prepared from the metals at ∼20 °C, in liquid anhydrous hydrogen fluoride
(aHF), made basic with alkali fluorides, are further oxidized by photodissociated F2 (visible or near-UV light) to
-
-
-
2-
give AuF6 or PtF6 salts, including O2+AuF6 (with O2 in the F2). Similar photochemical oxidation of PdF6
salts does not occur. This new synthetic approach has provided LiAuF6 and LiPtF6 for the first time, each of
which has the LiSbF6 type (R3h) structure with (hexagonal cell): LiAuF6, a ) 4.9953(9) Å, c ) 13.704(3) Å, V/Z
) 98.71(6) Å3; LiPtF6, a ) 5.0236(7) Å, c ) 13.623(2) Å, V/Z ) 99.25(5) Å3. Interaction of AuF6 with Ag+
-
gives Ag+AuF6- (R3h, a ) 5.283(3) Å, c ) 15.053(6) Å, V/Z ) 121.3(2) Å3), whereas PtF62- or PdF62- stabilize
2-
Ag2+ as Ag2+Pt(Pd)F6 (R3h; AgPtF6: a ) 5.049(8) Å, c ) 14.46(2) Å, V/Z ) 106.4(5) Å3; and AgPdF6, a )
5.00(4) Å, c ) 14.6(2) Å, V/Z ) 105(3) Å3). New cubic modifications (probable space group Ia3) have been
found for AgMF6 (M, a value, Å): Ru, 9.653(10); Os, 9.7318(9); Ir, 9.704(2). The preference for Ag2+Pt(Pd)F6
2-
over Ag+Pt(Pd)F6 is attributed to a second electron affinity of Pt(Pd)F6, E(Pt(Pd)F6-)> 60 kcal mol-1
.
-
Introduction
The latter salts were first reported but not structurally identified
by Mu¨ller and Hoppe.7 These AgMF6 salts are compared
structurally with others of the same stoichiometry.
Recent work in these laboratories1 showed that gold or the
platinum metals, (except rhodium) are able to react at room
temperature with F2 in aHF, containing an alkali fluoride, to
The stabilization of Ag2+ by PtF62- or PdF62- indicates that
the first ionization potential of these dianions is unusually high
-
-
2-
provide salts of AuF4 or MF6 (M ) Ru, Os, Ir), or PtF6
.
2-
for MF6 transition element species and an estimate of that
This, and similar findings by Holloway and co-workers2 for the
preparation of ammonium salts of the platinum metal fluoro-
anions, gave broad and easy access to noble-metal fluorocom-
energy, expressed as E(MF6-), has been attempted.
Experimental Section
-
-
plexes, but neither AuF6 nor PtF6 were included, nor other
related high oxidation-state salts such as AgF4- and NiF62-. It
was quickly found in these laboratories that photochemical
excitation of the F2 (sunlight or near-UV), the preparative
conditions otherwise being similar, gave AuF6- or PtF6- salts.
In addition, it was shown that even the difluorides AgF2 and
Materials. Anhydrous HF and fluorine were supplied by Matheson
Gas Products (East Rutherford, NJ), Ag2O by Lancaster Synthesis Inc.
(99+%; Windham, NH) and Au by ROC/RIC (99.99%; Sun Valley,
CA). Pd, Pt and Ir were supplied by Engelhard Corp. (East Newark,
NJ), Os by Strem Chemicals (Newburyport, MA) and Ru from Johnson
Matthey & Co. (London, UK). The alkali fluorides (Allied Chemical,
B&A quality, Morristown, NJ) were dried at 150 °C under dynamic
vacuum (<10-6 Torr).
The noble metals were always used as fine powders. Ruthenium,
osmium and iridium were heated (∼700 °C) under hydrogen, to
minimize oxide coating, the metals being cooled in hydrogen and
otherwise exposed only to dry argon or nitrogen. Otherwise, the metal
powders were used as supplied.
NiF2, which are themselves insoluble in aHF, would react with
the F atoms in basic aHF to give3,4 salts of AgF4- and NiF6
.
2-
-
Attempts to similarly prepare PdF6 salts have failed.
Although AuF6- and PtF6- salts were originally prepared at
higher temperatures and fluorine pressure in nickel bombs5,6
more than twenty-six years ago, this is the first time that the
salts LiAuF6 and LiPtF6 have been prepared and structurally
characterized. This paper gives a description of the syntheses
AgF was prepared from Ag2O through reaction with aHF. The AgF
obtained in that way is orange in the solid state and dissolves in aHF
yielding a colorless solution with no residue. To avoid photodecom-
position it was stored in an FEP tube wrapped with Al foil. AgF2 was
synthesized by oxidation of AgF in aHF with F2 at room temperature.
-
-
of the AuF6 and PtF6 salts and compares the new LiAuF6
and LiPtF6 with other relatives of the third transition series. It
-
also reports the new Ag+AuF6 salt which is contrasted
Li2PtF6,1 AuF3,8 SF3MF6 (M ) Os, Ir), RuF5,10 Ag(BiF6)2,11
9
structurally and chemically with Ag2+PtF62- and Ag2+PdF6
.
2-
K2MF6 (M ) Pd, Pt), Cs2PdF6,1 O2AsF6,12 PdF4,13 AgAsF6,11 and
1
11
AgPF6 were prepared as previously described.
(1) Lucier, G.; Elder, S. H.; Chacon, L.; Bartlett, N. Eur. J. Solid State
Inorg. Chem. 1996, 33, 809.
(2) Holloway, J. H.; Hope, E. G.; Puxley, C. D. Eur. J. Solid State Inorg.
Chem. 1996, 33, 821.
(7) Mu¨ller, B.; Hoppe, R. Z. Anorg. Allg. Chem. 1972, 392, 37.
(8) Einstein, F. W. B.; Rao, P. R.; Trotter, J.; Bartlett, N. J. Chem. Soc.
1967, 478.
(3) Lucier, G. M.; Whalen, J. M.; and Bartlett, N. J. Fluor. Chem. 1998,
89, 101.
(4) Whalen, J. M.; Lucier, G. M.; Chaco´n, L.; and Bartlett, N. J. Fluor.
Chem. 1998, 88, 107.
(5) Leary, K.; Bartlett, N. J. Chem. Soc., Chem. Commun. 1972, 903.
(6) Bartlett, N.; Lohmann, D. H. J. Chem. Soc. 1962, 5253.
(9) Jha, N. K. Ph.D. Thesis, University of British Columbia, 1965; p 102.
(10) Casteel, W. J., Jr.; Wilkinson, A. P.; Borrmann, H.; Serfass, R. E.;
Bartlett, N. Inorg. Chem. 1992, 31, 3124.
(11) Lucier, G. M.; Mu¨nzenberg, J.; Casteel, W. J., Jr.; Bartlett, N. Inorg.
Chem. 1995, 34, 2692.
(12) Shamir, J.; Binenboym, J. Inorg. Chim. Acta 1968, 2, 37.
10.1021/ic981397z This article not subject to U.S. Copyright. Published 1999 by the American Chemical Society
Published on Web 04/30/1999

2504 Inorganic Chemistry, Vol. 38, No. 10, 1999
Graudejus et al.
Apparatus and Technique. A nickel vacuum line, fluorine handling
mg) by decantation, and all volatiles were removed. The XRDP of the
solid obtained from the decanted solution (847.6 mg) showed an LiSbF6-
type pattern (a ) 4.9953(9) Å; c ) 13.704(3) Å; see Table S2).
Decantation of the solution of excess CsF left a residue of CsAuF6
(825.0 mg; 1.859 mmol), the XRDP of which was entirely that of
CsAuF6.17
equipment, and Teflon valves were used as previously described.14 For
1
all preparations two /2- or 1-in. o.d. FEP tubes (CHEMPLAST Inc.,
3
Wayne, NJ), each sealed at one end and drawn down to /8-in. o.d. at
the other, were joined at right angles to a Teflon Swagelock T
compression fitting. This assembly was joined to a Teflon valve by a
small section of 3/8-in. o.d. FEP tubing drawn down to 1/4-in. o.d. Such
a reactor was connected to the vacuum line via an 1-ft. length of 1/4-in.
o.d. FEP tubing which facilitates the decantation of solutions from one
arm to the other. The T reactors were evacuated, passivated with fluorine
(2 atm) and evacuated again before use.
Anhydrous HF was condensed from the cylinder into a Teflon-valved
reservoir FEP tube containing K2NiF6 (Ozark-Mahoning Pennwalt,
Tulsa, OK) in order to destroy traces of water.
KAuF6 from Au, KF, and F2. Au (62.7 mg, 0.318 mmol) and KF
(21.6 mg, 0.372 mmol) were placed in one arm of an FEP T reactor,
and aHF (∼3 mL) was condensed at -196 °C. After being warmed to
∼20 °C, the potassium fluoride dissolved and the reactor was
pressurized with fluorine. Agitation overnight afforded a yellow solution
of KAuF4. The T apparatus was pressurized again with fluorine (1400
Torr) and agitated overnight under UV irradiation (low-pressure Hg
lamp). All volatiles were removed under dynamic vacuum. The XRDP
17
18
of the product showed the pattern of KAuF6 with slight KAuF4
All solids were manipulated in the dry Ar atmosphere of a Vacuum
Atmospheres Corp. DRILAB.
impurity.
Attempted Fluorination (with UV Irradiation) of K2PdF6 and
Cs2PdF6. Solutions of Cs2PdF6 or K2PdF6 in aHF, which were
pressurized with F2 (∼1 atm), were irradiated with UV for extended
periods (>24 h). The constant product weights and the negligible F2
consumption indicated that oxidation had not occurred.
Preparations. General Comments for AMF6 and A2MF6 Salts
(A ) Alkali). Preparations in aHF can make use of the high solubility
of each alkali fluoride in this solvent,15 the low solubility of the heavier
-
alkali MF6 salts and the moderately good solubility of the LiMF6.
The reverse relationship holds for A2MF6 salts, where Li2MF6 are
usually of low solubility and A ) K, Cs of much higher solubility.
LiPtF6 from Li2PtF6 and F2. Li2PtF6 prepared from Pt, 2LiF, and
F2 in aHF at ∼20 °C as previously described1 is of low solubility in
aHF (the statement1 that it is “very soluble” should read slightly soluble).
Li2PtF6 (427.6 mg, 1.324 mmol) was placed in one arm of the T reactor
and aHF (5 mL) condensed on it. At ∼20 °C some of the Li2PtF6
dissolved to yield a faintly yellow solution. Fluorine to 1500 Torr was
added, and the reactor was placed (with agitation) in the sunlight. The
color of the solution gradually intensified (repressurized with fluorine
after 3 days), and after 9 days the bright yellow solution was decanted
and all volatiles removed. The XRDP of the solid from the decantate
(287.2 mg; 0.909 mmol) showed only the characteristic pattern of an
LiSbF6-type compound (a ) 5.0236(7) Å, c ) 13.623(2) Å; see Table
S1); that of the residue (137.3 mg; 0.425 mmol) showed only Li2PtF6.
O2AuF6 from AuF3 and F2 (O2 Contamination). An attempt to
prepare AuF5 directly from AuF3 in aHF employing photo dissociation
of F2 did not succeed but produced O2AuF6 (via O2, probably from a
small leak). AuF3 (680.2 mg; 2.678 mmol) in aHF (∼13 mL) at ∼20
°C was agitated with F2 (6 mmol) and O2 impurity, in an FEP T reactor,
in the sunlight for 20 days. The bright yellow solution was decanted
from unreacted AuF3. The XRDP of the bright yellow solid from the
decanted solution revealed that it was O2AuF6,16,17 the residue being
unreacted AuF3.
Synthesis of AgIMVF6 Salts (Table 1 Gives Quantities; M ) Os,
Ir, Au, Ru, Bi). The silver-containing salt (AgF or AgBF4) was loaded
into one tube of a passivated FEP T reactor inside the DRILAB. The
appropriate noble metal salt (LiAuF6, SF3OsF6, SF3IrF6, RuF5) or
bismuth fluoride, BiF5, was placed in the other tube of the reactor. For
the synthesis of AgMF6 with M ) Au, Os, Ir, Bi, aHF was condensed
onto each of the reagents. Upon warming to room temperature, the
salts dissolved completely affording colorless (AgF, AgBF4, BiF5,
SF3OsF6, SF3IrF6) or yellow (LiAuF6) solutions. As the respective AgF
and AgBF4 solutions were slowly poured onto the SF3MF6 (M ) Os,
Ir) and BiF5 solution, there was vigorous gas evolution (SF4 or BF3)
and a solid precipitated (orange AgIrF6, colorless AgOsF6, and light
yellow AgBiF6). For the synthesis of AgRuF6 the AgF solution was
poured slowly onto the dry RuF5. AgRuF6 formation was immediately
evident as the green RuF5 was replaced by an orange solid (in <1 min).
For the synthesis of AgAuF6, both limbs of the reactor were cooled to
about -50 °C (methanol/dry ice), the AgF solution was poured into
the other arm to precipitate an orange-brown solid (colorless superna-
tant), and the mixture was agitated at -50 °C for ∼10 min.
All AgMF6 salts were insoluble in aHF and were washed with it
(typically three times). Volatiles were removed under dynamic vacuum.
For AgAuF6 the tube containing it was always kept at ∼-50 °C.
Because AgRuF6 was photosensitive, the FEP storage tubes were
wrapped in Al foil. The XRDP of the AgMF6 salts gave a cubic unit
cell for M ) Ru, Os, Ir {M, a value, Å: Ru, 9.653(10); Os, 9.7318(9);
Ir, 9.704(2); see Tables S3-S5}, a trigonal-rhombohedral one for
AgAuF6 {a ) 5.283(3) Å, c ) 15.053(6) Å; see Table S6} and a
tetragonal one for AgBiF6 {a ) 5.079(2) Å, c ) 9.552(3) Å; see Table
S7}.11
Preparations of AgPt(Pd)F6 (Table 1 Gives Quantities): (a)
Interaction of AgAsF6 with O2PtF6. The yellow solution over solid
O2PtF6 in aHF was agitated, at ∼20 °C, with the colorless slightly
soluble AgAsF6 until the solution color of PtF6- had almost disappeared,
there being a deep-red insoluble residue. Decantation and washing
(several times) provided yellow tinted crystalline O2AsF6 (XRDP
showing only this). The yellow color probably comes from a small
quantity (too small to give an XRDP) of O2PtF6. The XRDP of the
deep-red insoluble product gave a pattern that was wholly indexed on
the basis of a rhombohedral cell {hexagonal cell with a ) 5.049(8) Å,
c ) 14.46(2) Å; see Table S8}.
LiAuF6 (CsAuF6) from AuF3 and LiF (CsF). An FEP T reactor
was loaded with AuF3 (654.1 mg, 2.576 mmol for LiAuF6; 463.0 mg,
1.823 mmol for CsAuF6) in one arm and LiF (99.5 mg, 3.836 mmol)
or CsF (450.3 mg, 2.964 mmol), respectively, in the other, and aHF
(∼2 mL) was condensed at -196 °C in each limb of each T reactor.
The alkali fluoride was dissolved in the aHF at 20 °C, and the solution
was poured onto the AuF3 (itself insoluble in aHF) to produce a yellow
-
solution of AuF4 over some undissolved AuF3. F2 was added to a
total pressure of 1500 Torr, and each reactor was placed in the sunlight
and agitated for 8 days. Much of the remaining AuF3 dissolved within
1 day. After 4 days the reactor was repressurized with F2 (1500 Torr)
and replaced in the sunlight. In the case of the reaction to produce
LiAuF6 already after 1 day the color of the solution intensified to bright
lemon yellow while in the case of CsAuF6 the solution color faded
because of the low solubility of that product, this solubility being further
lowered by the common ion effect of the excess cesium fluoride. Four
days later the reactor was re-attached to the vacuum line, the aHF was
cooled to -196 °C, and the excess fluorine was pumped off. The
solution of LiAuF6 was separated from a small amount of residue (23.2
(b) Interaction of Ag(BiF6)2 with K2Pt(Pd)F6. Interaction of solid
Ag(BiF6)2 shaken slowly into a -50 °C solution of K2Pt(Pd)F6 produced
a brown precipitate. Complete Ag(BiF6)2 transfer was ensured by
washing over with two back-distillations of aHF. The brown precipitate
was washed with aHF at ∼20 °C (three times). An XRDP of this solid
gave a rhombohedral-like pattern as observed in (a) but less crystalline
(13) Zemva, B.; Lutar, K.; Jesih, A.; Casteel, W. J., Jr.; Bartlett, N. J. Chem.
Soc., Chem. Commun. 1989, 346.
(14) Lutar, K.; Jesih, A.; Leban, I.; Zemva, B.; Bartlett, N. Inorg. Chem.
1989, 28, 3467.
(15) Jache, A. W.; Cady, G. H. J. Phys. Chem. 1952, 56, 1106.
(16) Graudejus, O.; Mu¨ller, B. G. Z. Anorg. Allg. Chem. 1996, 622, 1076.
(17) Bartlett, N.; Leary, K. ReV. Chim. Min. 1976, 13, 82.
(18) Hoppe, R.; Homann, R. Z. Anorg. Allg. Chem. 1970, 379, 194.
(19) Heyns, A. M.; Pistorius, C. W. F. T. Spectrochim. Acta 1976, 32A,
535.

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-
Room Temperature Syntheses of AuF6 and PtF6 Salts
Inorganic Chemistry, Vol. 38, No. 10, 1999 2505
Table 1. Summary of Reaction Weights for the Syntheses of AgMF6 Saltsa
reactant 1
reactant 2
aHF (mL)
insol. product
decantate
LiAuF6
126.4
(0.398)
AgF
69.9
(0.551)
AgAuF6
166.9
(0.399)
167
AgF(HF)n/LiF(HF)n
mobs
nobs
mcalc
1
40.1
SF3IrF6
241
(0.610)
AgF
118
(0.930)
AgIrF6
248
(0.599)
252
AgF(HF)n
SF4 v
SF4 v
mobs
nobs
mcalc
0.75
0.75
1.5
1.0
2.6
2.3
1.5
1
SF3OsF6
264
(0.671)
AgF
104
(0.820)
AgOsF6
265
(0.643)
277
AgF(HF)n
mobs
nobs
mcalc
RuF5
409
(2.086)
AgF
311
(2.451)
AgRuF6
650
(2.013)
674
AgF(HF)n
mobs
nobs
mcalc
BiF5
347
(1.142)
AgBF4
206
(1.058)
AgBiF6
467
(1.084)
456
BiF5
BF3 v
mobs
nobs
mcalc
K2PtF6
292
(0.754)
Ag(BiF6)2
524
(0.695)
AgPtF6
KBiF6/K2PtF6
mobs
nobs
mcalc
333b
489
290
503
722
23
18
K2PdF6
316
(1.058)
Ag(BiF6)2
752
(0.998)
AgPdF6
KBiF6/K2PdF6
mobs
nobs
mcalc
357b
724
328
KPtF6
61
(0.175)
AgF
43
(0.339)
AgPtF6
AgF(HF)n/KF(HF)n
mobs
nobs
mcalc
79b
73
O2PtF6
90.0
(0.264)
AgAsF6
78.3
(0.264)
AgPtF6
114.1
(0.274)
110.0
O2AsF6
41.7
mobs
nobs
mcalc
58.3
a n, mmol in parentheses; m, weights, in mg calculated and observed (observed in bold type). b These solids were not taken to dryness before
they were washed with aHF, hence they were contaminated by (noncrystalline) adsorbed salts.
16,22
than it. The two patterns (AgPdF6 and AgPtF6) were nearly indistin-
guishable in line positions {a ) 5.00(4) Å, c ) 14.6(2) Å for AgPdF6;
see Table S9}.
a cubic pattern similar to the one of O2PtF6
(Ia3) and the patterns
were fully indexed on an I cubic unit cell with Z ) 8 (see Table S3-
S5). The observed line intensities match well with those calculated using
the MF6 ion positional parameters from the single-crystal structure16
-
(c) Interaction of AgF with KPtF6. A solution of AgF in aHF was
added to dry KPtF6, and the mixture was agitated at ∼20 °C (2 h). The
red-brown product was washed (2×) with aHF to remove AgF excess.
XRDP of the red-brown product showed a complex pattern akin to
that of Ag2SnF6 with AgF2 possibly also present. Fluorination of it in
aHF at ∼20 °C (1400 Torr of F2) overnight produced a red-brown (aHF
insoluble) product the XRDP of which was a combination of the pattern
of rhombohedral-like AgPtF6 (obtained in (a)) with that of AgF2
{evidently the crystalline component (Ag2PtF6) had been fluorinated
to AgF2 and AgPtF6}.
(d) Interaction of AgF2 with PdF4 in BrF3/BrF5. Interaction of
AgF2 with PdF4 in BrF3/BrF5 at 90 °C followed by fluorination with
F2 at 250 °C gave a product the powder pattern of which showed the
rhombohedral-like pattern of AgPtF6 obtained in (a) together with some
weak lines of an unidentified phase.
X-ray powder diffraction samples were prepared as previously
described,14 the X-ray diffraction pattern (XRDP) being recorded on
film using Ni-filtered Cu KR radiation (General Electric Co. precision
camera, Straumanis loading). The program ERACEL20 was used for
the refinement of the lattice parameters which incorporates the Nelson-
Riley extrapolation function.21 The AgMF6 salts (M ) Os, Ir, Ru) show
1
1
of O2PtF6 with Ag atoms in /4
/
1/4 (8a). These AgMF6 salts were
4
previously reported to adopt the KNbF6 structure type,23 however the
cubic form (reported here for the first time) is always obtained from
aHF solution. The same holds for KSbF6. AgIAuVF6 is isostructural
with LiSbF6 (R3h) and is so far the only Ag+MF6- salt of a second- or
third-row transition series element known to adopt this structure type.
The XRDP pattern (see Table S6) contained also lines of some AgAuF4
impurity.24 AgPtF6 and AgPdF6 are also isostructural with LiSbF6 (see
Table S8 and S9); however, they are to be formulated as AgIIMIVF6
and not AgIMVF6. The possible departure from rhombohedral symmetry
(that could arise from a Jahn-Teller distortion associated with Ag2+
)
could be largely masked by the breadth of the lines. If so, the departure
from rhombohedral symmetry must be subtle. There is a hint of small
line splitting in the more crystalline samples of AgPtF6 (obtained from
the rather slow interaction of AgAsF6 with O2PtF6). AgBiF6 (see Table
S7) is isostructural with KNbF6 (tetragonal, P4h2m) as previously
reported for AgMF6 (M ) Os, Ir, Ru).23
(22) Ibers, J. A.; Hamilton, W. C. J. Chem. Phys. 1966, 44, 1748.
(23) Kemmitt, R. D. W.; Russell, D. R.; Sharp, D. W. A. J. Chem. Soc.
1963, 4408.
(20) Laugier, J.; Filhol, A. Local version of program CELREF; Nantes,
France, 1978.
(21) Nelson, J. B.; Riley, D. P. Proc. Phys. Soc. (London) 1945, 57, 160.
(24) Mayorga, S. Ph.D. Thesis, University of California at Berkeley, 1988;
p 106; characterized by a tetragonal pattern with a ) 5.798(3) Å, c )
10.806 Å, V ) 363.2(5) Å3, Z ) 4.

2506 Inorganic Chemistry, Vol. 38, No. 10, 1999
Graudejus et al.
LiRhF6
Table 2. Trigonal Unit Cells for the Rhombohedral (R3h) LiMF6 Salts of the Second and Third Transition Series31
a
LiNbF6
LiMoF6
LiRuF6
a/Å
c/Å
c/a
5.304(2)
13.576(4)
2.560(2)
5.190
13.585
2.618
5.0751(4)
13.543(1)
2.6685(4)
100.70(3)
5.0161(6)
13.547(2)
2.7007(8)
98.40(4)
V/Z
110.3(2)
105.6
LiReF6(?)a,b
LiOsF6
LiIrF6
LiPtF6
LiAuF6
a
LiTaF6
LiWF6
a/Å
c/Å
c/a
5.3120(7)
13.609(2)
2.5619(8)
110.85(4)
5.234
13.606
2.600
5.057 (?)
13.735 (?)
2.716 (?)
5.1007(5)
13.608(2)
2.6679(7)
102.20(4)
5.061(1)
13.622(3)
2.692(2)
5.0236(7)
13.623(2)
2.7118(8)
99.25(5)
4.9953(9)
13.704(3)
2.743(2)
V/Z
107.6
101.4 (?)
100.67(7)
98.71(6)
a These data were taken from Kemmit et al.23; all other cell parameters were obtained in this work from XRDP taken with Cu KR radiation (Ni
filter), the indexing being carried out with the program ERACEL which refines lattice parameters applying a Nelson-Riley extrapolation function.
b Eight out of 23 lines in the powder pattern of the compound could not be indexed on the basis of a rhombohedral unit cell; the authenticity of the
compound is therefore doubtful.
Although the remaining valence electrons of PtF62- constitute
a weakly antibonding set of t2g symmetry, which has highly
Magnetic measurements were carried out using a Superconducting
Quantum Interference Device (SQUID) as previously outlined.25 The
6
favorable exchange energy,30 the F atoms in aHF solution break
temperature dependence of the magnetic susceptibility was measured
for AgPdF6 and AgAuF6. AgPdF6 was found to be a Curie-Weiss
paramagnet with Θ ) 4.4 K, µ ) 1.80 µB. This value is lower than the
one previously reported7 (µ ) 1.97 µB). This can be attributed to some
diamagnetic contamination (adsorbed KBiF6) of the sample measured
here. AgAuF6 was found to be diamagnetic. The magnetic properties
of AgOsF6 (µ ) 2.95 µB), AgIrF6 (µ ) 1.24 µB), and AgRuF6 (µ )
3.91 µB) have been reported previously,11,26 indicating that Ag+ and
M5+ (M ) Os, Ir, Ru) are present in these compounds.
-
this configuration and efficiently generate PtF6
:
PtF6 (solv) + F(solv) f PtF6 (solv) + F-
(2)
2-
-
(solv)
The analogous reaction with PdF62-, however, does not occur.
Evidently as with Ag(III) the tighter binding of the 4d electrons
relative to 5d electrons causes Pd(V) to be inaccessible, at least
by this route. The decrease in formula-unit volume with increase
in atomic number for the set of LiMF6 salts, given in Table 2,
is much more marked in the second transition series than in the
third, and clearly indicates that the effective nuclear charge
builds up more, with atomic number, across the second than
across the third transition series.
Results and Discussion
Since AuF4- and PtF62- can be made from the elements1,2 at
20 °C, in aHF made basic with good F- donors, it is evident
from the present work that similar conditions will produce
-
-
AuF6 and PtF6 if the F2 is photodissociated. In practice it is
often more convenient to make the quinquevalent salts starting
from the AuF4- and PtF62- precursors, but in some cases (e.g.
KAuF6) the synthesis can be conveniently managed in one step
with high yield since the KAuF6 is of modest solubility
compared to KF (and KAuF4) contaminant, which are therefore
readily removed, in aHF solution, by decantation from the
precipitated KAuF6 salt.
6
-
The dt2g valence electron configuration of AuF6 is so
stable toward oxidation that the powerful one-electron oxidizer
Ag(III) in acidified aHF is unable to release AuF6, although
that same reagent generates PtF6, RuF6, and RhF6 in high yields
from their MF6- salts.32 This stability of AuF6- is in agreement
with the large electron affinity, E(AuF6), calculated by Miyoshi
and Sakai33 of 9.56 eV. The higher nuclear charge of gold must
be the most important factor in the greater oxidation resistance
of AuF6- relative to PtF6- the ionization potential of which34-36
() E(PtF6)) is ∼ 8 eV, but the more favorable exchange energy
-
The easy addition of fluorine (as F atoms) to AuF4 to
-
generate AuF6
-
-
(solv)
6
5
AuF4 (solv) + 2F(solv) f AuF6
(1)
of the dt2g configuration of Au(V) relative to the dt2g
configuration of Pt(V) must also contribute. The tighter binding
-
-
stands in contrast to the failure14 to similarly prepare AgF6
even using the excellent F atom source, KrF2. This facile
oxidation of Au(III) is attributable to the weaker binding of the
d orbital electrons of the gold, because of the tighter binding
of s orbital electrons resulting from the high nuclear charge at
the gold nucleus (a relativistic effect). This relativistic effect27,28
is much less significant for silver, where the high effective
nuclear charge, at least in Ag(III), causes the 4d orbital electrons
to be tightly held. This is seen especially in the small size of
-
of all electrons in AuF6 versus PtF6 is seen in the smaller
effective volume of the former (see Table 2).
-
-
These facile syntheses of AuF6 and PtF6 in aHF provide
for the preparation of a wide variety of salts of which the LiMF6
are new. It is also of interest that even O2+AuF6- is preparable
with this approach using O2/F2 mixtures with AuF3 in aHF. It
is plausible that the photochemistry generates37 O2F, which
although a weak base in aHF is nevertheless able to generate
the 4dz electron pair of Ag(III) compared29 with Au(III), the
(30) Orgel, L. E. Introduction to Transition Element Chemistry, 2nd ed.;
J. Wiley & Sons Inc.: New York, 1966.
(31) Graudejus, O.; Bartlett, N. To be published.
2
latter formula unit volume being 5 Å3 bigger than the former.
(32) Lucier, G.; Shen, C.; Casteel, W. J., Jr.; Chacon, L.; Bartlett, N. J.
Fluor. Chem. 1995, 72, 157. Lucier, G. M. Ph.D. Thesis; LBNL Report
No. LBL-37334, University of California, Berkeley, 1995.
(33) Miyoshi, E.; Sakai, Y. J. Chem. Phys. 1988, 89, 7363.
(34) Nikitin, M. I.; Siderov, L. N.; Korobov, M. V. Int. J. Mass Spectrom.
Ion Phys. 1981, 37, 13.
(35) Bartlett, N. Angew. Chem., Int. Ed. Engl. 1968, 7, 433.
(36) Bartlett, N.; Okino, F.; Mallouk, T. E.; Hagiwara, R.; Lerner, M.;
Rosenthal, G. L.; Kourtakis, K. AdV. Chem. Ser. 1990, 391, 226.
(37) Lucier, G. M.; Shen, C.; Elder, S. H.; Bartlett, N. Inorg. Chem. 1998,
37, 3829.
(25) Casteel, W. J., Jr.; Lucier, G.; Hagiwara, R.; Borrmann, H.; Bartlett,
N. J Solid State Chem. 1992, 96, 84.
(26) Hepworth, M. A.; Robinson, P. L.; Westland, G. J. J. Chem. Soc.
1954, 4268.
(27) Pitzer, K. Acc. Chem. Res. 1979, 12, 271.
(28) Pyyko¨, P.; Desclaux, J.-P. Acc. Chem. Res. 1979, 12, 276. Pyykko¨, P.
Chem. ReV. 1988, 88, 563.
(29) Zemva, B.; Lutar, K.; Jesih, A.; Casteel, W. J., Jr.; Wilkinson, A. P.;
Cox, D. E.; Von Dreele, R. B.; Borrmann, H.; Bartlett, N. J. Am. Chem.
Soc. 1991, 113, 4192.

-
-
Room Temperature Syntheses of AuF6 and PtF6 Salts
Inorganic Chemistry, Vol. 38, No. 10, 1999 2507
Table 3. Comparison of Ag+AuF6 and Ag2+[Pt(Pd)F6]2- with
-
O2 salts. The previously observed37 rapid low-temperature
+
some Ag+EF6 Salts
-
oxidation of AuF4- by O2+ or O2F in aHF indicate that AuF6
-
would be quickly made by either of these oxidizers.
CsCl-type (8:8)
arrangement
NaCl-type (6:6)
arrangement
-
Because the AuF6 has a filled subshell, dt2g6, it has a poor
electron affinity, E(AuF6-), since an added electron must be
AgIRuVF6
orange
Ia3
AgIIPdIVF6
c
d
a
placed in an antibonding σ orbital (eg*). This is in marked
color
SG
a (Å)
c (Å)
V/Z (Å3)
brown
R3h
5.00(4)
14.6(2)
105(3)
contrast to PtF6-, where an additional electron (to give PtF6
)
2-
5
enters the t2g set, filling it, and in the process enhancing the
exchange energy for that set by ∼50%. These effects explain
the oxidation of Ag+ by PtF6- and the stabilization of Ag2+ by
PtF62- or PdF62- and the inability of AuF6- to oxidize Ag+ to
9.653(10)
112.4(4)
AgIOsVF6
white
AgIIrVF6
orange
Ia3
AgIIPtIVF6
brown
AgIAuVF6
brown
c
c
Ag2+
:
color
SG
a (Å)
c (Å)
V/Z (Å3)
Ia3
R3h
R3h
9.7318(9)
9.704(2)
5.049(8)
14.46(2)
106.4(5)
5.283(3)
15.053(6)
121.3(2)
AuF6 (solv) + Ag+(solv) f Ag+AuF6
(3)
(4)
-
-
(c)
115.21(4)
114.23(8)
Pt(Pd)F6 (solv) + Ag2+(solv) f Ag2+Pt(Pd)F6
2-
2-
AgBiF6
light yellow
P4h2m
5.079(2)
9.552(3)
123.2(2)
AgSbF6
white
AgAsF6
white
Pa3
AgPF6
white
Pa3
(c)
color
SG
a (Å)
c (Å)
V/Z (Å3)
Ia3
The reactions in eq 4 are especially remarkable since the Ag2+
ion in aHF is able to oxidize32 O2 to O2+ and Xe to Xe(II) salts.38
9.857(5)2)
7.773(7)
7.563(4)
Interaction of O2+PtF6 with AgAsF6 to give Ag2+PtF6
-
2-
119.7(2)
117.4(5)
108.2(2)
a The XRDP of AgPdF6 was broad-lined and weak, and nearly
indistinguishable from that of AgPtF6. The VFU is certainly close to
the one of AgPtF6. b The lattice parameters were recalculated from ref
40. c The cubic modification (probable SG Ia3) was obtained for the
first time. Previously a tetragonal KNbF6-type structure has been
reported for those compounds.23 d AgRhF6 has been reported to be
black; however, no structural information was given.7
AgAsF6(c) + O2 (solv) + PtF6 (solv) f Ag2+PtF6
+
+
-
2-
(c)
+
-
(solv)
O2 (solv) + AsF6
(5)
establishes that PtF6- is a potent oxidizer. The failure to oxidize
PdF62- with F atoms, in the same way as for PtF6- from PtF6
,
2-
-
∼20 Å3, this being a measure of how much larger Na+ is than
the octahedral hole in the approximately close-packed F ligand
array. Since Ag+ is similar in size to Na+, it might, therefore,
have been expected that the AgEF6 salts would also have
adopted 6:6 coordination throughout the series, but as the data
in Table 3 show, this is not the case.
implies that the unknown PdF6 should be an even more
powerful oxidizer than PtF6-. Although the magnetic properties
-
of AgPt(Pd)F6 do not discriminate between Ag+MF6 and
Ag2+MF62-, since each possesses one unpaired electron, (the
Ag+MF6- in the dt2g5 configuration of the anion, the Ag2+MF6
,
2-
in the d9 configuration of the cation) there can be no doubt that
the appropriate formulation is the latter one. The unit cell size
For the closed-shell, group 15 AgEF6 salts, there is a switch
and chemistry establish that the formulation is Ag2+Pt(Pd)F6
.
2-
in structure type,23,41 the smaller anions PF6 and AsF6
-
-
For AgAuF6, its diamagnetism and unit cell (see Table 3) show
-
adopting NaCl-type structures, and the larger (SbF6- and BiF6-),
variants of the CsCl structure type. The cubic forms reported
here for AgMF6 (M ) Ru, Os, Ir) are new, these having been
previously described as having the KNbF6 structure type.23 The
data for the second and third transition series AgEF6 salts show
that the switch from NaCl to CsCl type is even more subtly
correlated with anion size, since AgRuF6 and AgIrF6 both adopt
CsCl type lattices, whereas AgAuF6 has a LiSbF6 structure (i.e.,
NaCl relative), even though the VFU of the LiEF6 relatives (see
Table 2) differ by no more than 2 Å3. Comparing VFU(AgAuF6)
) 121 Å3 with VFU(LiAuF6) ) 99 Å3, each of which adopts
the NaCl-like LiSbF6 structure, we see that the Ag+ is ∼22 Å3
larger than the Li+ in effective volume (a value close to that
already noted earlier for Na+). A similar comparison of the
CsCl-type lattice VFU(AgRuF6) ) 112 Å3 with that of the NaCl
type VFU(LiRuF6) ) 101 Å3 shows that the AgRuF6 lattice is
∼11 Å3 more closely packed than if it had adopted the NaCl-
type lattice. This better packing provided by the AgMF6 of CsCl-
type structure holds in general for cations of the size of Ag+ or
larger. An aspect of the closer packing of the CsCl type
arrangement is that it places the nearest like-charged ions closer
together than does the NaCl arrangement. This is illustrated well
by the cubic AgRuF6 structure (smallest VFU of all salts of CsCl-
unambiguously that it is Ag+AuF6
.
Data for the LiMF6 salts of the second and third transition
series, given in Table 2, show that the AuF6 has the smallest
-
effective MF6- volume of the third transition series. Evidently
because effective nuclear charge increases more with increasing
atomic number in the second than in the third transition series,
the effective volume of LiRhF6 is smaller,31 and it is the last of
that series, PdF6- and AgF6- being unknown. All other known
LiEF6 salts adopt the rhombohedral variant of the (6:6 coordi-
nate) NaCl type arrangement (which is named from the LiSbF6
structure39). This is essentially a hexagonal close-packed array
of F ligands containing ordered arrangements of E and Li in
octahedral holes. The structure can be attributed to the small,
hard, and highly polarizing Li+ strongly attracting, octahedrally,
-
-
six F ligands of surrounding MF6-. The smallest EF6 (PF6
)
results in a formula unit volume,23 VFU, of only 88 Å3 for LiPF6,
whereas for the largest anion represented so far in this structure
type,31 TaF6-, VFU(LiTaF6) ) 111 Å3. This gives an approximate
estimate for the sizes of the anions since the Li+ can be taken
to contribute very little to the cell volume in each case. This is
not so for the Na+ ion in the NaEF6 salts, which also for the
most part adopt the same LiSbF6 structure, or cubic relatives
(Pa3 or Fm3m), all variants of 6:6 coordination. Generally, for
any given LiSbF6 lattice E, VFU(NaEF6) exceeds VFU(LiEF6) by
-
type structure) in which the nearest RuF6 are 4.83 Å apart,
(38) Zemva, B.; Hagiwara, R.; Casteel, W. J., Jr.; Lutar, K.; Jesih, A.;
Bartlett, N. J. Am. Chem. Soc. 1990, 112, 4846.
(39) Burns, J. H. Acta Crystallogr. 1962, 15, 1098.
(40) Bode, H. Z. Anorg. Allg. Chem. 1951, 267, 62.
(41) Babel, D. Struct. Bonding (Berlin) 1967, 3, 1.

2508 Inorganic Chemistry, Vol. 38, No. 10, 1999
Graudejus et al.
whereas in LiRuF6 the closest interionic distance of like ions42
is 5.075 Å. Even in the smallest NaCl-type LiEF6 (LiPF6), the
of AgPtF6 a possible line splitting could be present, in which
case the true symmetry must be lower than the rhombohedral
symmetry assumed here). The pattern is convincingly indexable
on the basis of a LiSbF6 type rhombohedral cell. It is clear that
if the material were Ag+PtF6- the formula unit volume should
be slightly larger than that of AgAuF6, just as LiPtF6 is ∼0.4
Å3 larger than LiAuF6 (see Table 2), i.e., VFU(Ag+PtF6-) ≈ 122
Å3. The simple explanation for the observed formula unit
-
closest like-ion distance23 is 4.921 Å. It is probable that EF6
ions in cubic or rhombohedral CsCl-type cells cannot be placed
much closer than they are in AgRuF6 since their repulsive
interactions would then become severe. When the symmetry is
tetragonal, as in the AgBiF6 cell, the octahedra can be stacked
more efficiently, each with a 4-fold axis parallel to the a,b plane
and a super imposed octahedron at right angles, such that the
two F- ligands, of one octahedral edge, pack tetrahedrally with
the like F ligands of the octahedron packing closely with it
(above and below z). This requires 42 axes parallel to z. For
octahedrally close-packed spheres of radius r the ideal c axis
volume, of ∼106 Å3 (which will not be significantly different
2-
if the symmetry is lower), is the formulation Ag2+Pt(Pd)F6
,
in which the Coulomb attraction is four times greater than in
Ag+AuF6-, or what might have been Ag+Pt(Pd)F6-. The
Ag2+Pt(Pd)F62- formulation is also in harmony with the failure
of these materials to combine with fluorine. The Ag+MF6- salts
(M ) As, Ru, Ir) and Ag+BF4-, all add fluorine easily to form
AgF+ salts11,25 (AgPF6 gives AgF2 and PF5, and AgOsF6 gives
x
for such an arrangement would be (4 + 2 2)r.
For unmeshed octahedral EF6- species, they are thinnest when
measured along a 3-fold axis. Such symmetry is appropriate
for the packing of the octahedra in cubic or rhombohedral
lattices. For an octahedral collection of spherical F- ligands of
radius r, the separation of one 3-fold set of F nuclei from the
AgF2 and OsF6). The salt AgF+AuF6 has also been prepared
-
previously in these laboratories25 and is isostructural with46
-
AgF+AsF6
.
-
-
It is of interest that each of PtF6 and RuF6 is able to
stabilize6,16,47 O2+. The salts have similar unit cells6,16,47 and
stability with respect to dissociation. In harmony with these
x
x
other is 2r 2/ 3. For the total effective thickness of the octa-
hedral cluster in the 3-fold axis direction, we must add 2r. There-
x
x
fore this effective thickness is 2r(1 + 2/ 3). If the thickness
is 4.83 Å, as in AgRuF6, we have r ) 1.33 Å. This is slightly
less than the commonly accepted value43 (1.36 Å) for the van
similarities the electron affinity of RuF6 should be close to that
34-36
of PtF6
which is ∼8 eV. It might have been expected,
therefore, that the second electron affinity would also have
nearly the same value for both ions. But RuF6 does not
-
der Waals radius for the F- ligand. Clearly, MF6 closest
2-
distances less than 4.83 Å, would signify strong repulsion.
Indeed, in AuF6-, where the effective nuclear charge is high
enough to raise the ionization potential33 ∼1 eV higher than in
the ruthenium ion,35 the AuF6- as a whole must be effectively
smaller than RuF6-. But at this point the repulsive interactions
of AuF6- (which would surely be placed less than 4.83 Å apart
in a CsCl-type lattice) seem to render that arrangement less
favorable than the less well packed NaCl structure. As is
indicated in Table 3, this structure has a closest AuF6- interionic
stabilize Ag2+. The close structural relationship of AgRuF6 to
AgIrF6 (each has a CsCl-type cell, such as would also be
expected for Ag+PtF6-) and its reported magnetic behavior11,26
establish that the ruthenium salt is Ag+RuF6-. This must signify
a smaller second electron affinity for RuF6 than for PtF6, since
the unit cells of the AgMF6 salts of the same charge must be
similar, as is the case for a variety1,48 of RuF6- compared with
2-
2-
PtF6-, and RuF6 compared with PtF6 salts. The lattice
energetics of the ruthenium and platinum relatives must therefore
be similar.49 Consequently, it is plausible to assign the greater
second electron affinity of PtF6 to the favorable exchange energy
-
distance of 5.283(3) Å. The larger EF6 are associated with
lower effective nuclear charge at E (e.g., Ta(v)), and this in
turn must mean that the F ligands of the larger anions are more
5
benefit when dt2g becomes dt2g6. In the conversion of the
-
electron rich and polarizable, i.e. much softer than in the AuF6
ruthenium dt2g3 to dt2g4 there is no increase in exchange energy.
ion. In any case, in the CsCl type structures with large anions,
the like ions are further apart than 4.83 Å, the separation distance
being (at least approximately) the anion diameter.
2-
The preference of the formulation Ag2+PtF6 to that of
Ag+PtF6- requires that the electron affinity of PtF6-, E(PtF6-),
and the lattice energy benefit provided by Ag2+PtF62- relative
to Ag+PtF6- must exceed the ionization enthalpy for conversion
of Ag+ to Ag2+. The last term50 is 496 kcal mol-1. The lattice
enthalpy49 for Ag+PtF6- based on the anticipated formula unit
volume is -139 kcal mol-1. On the basis of the observed
Although the XRDP of the (rapidly) precipitated AgPt-
(Pd)F6 is broad-lined and of heavy background, the pattern is
unmistakably akin to that of AgAuF6, but of cell size much
closer to that of PdPtF6. Indeed direct comparison of XRDP
patterns of AgPt(Pd)F6 (which were nearly the same in
diffraction-line placement) with those of AgAuF6 and PdPtF6
immediately indicated that the platinum and palladium salts
2-
volume for Ag2+PtF6 (of ∼106 Å3) and assuming that the
lattice energy of A2+B2- is four times that of A+B-, the lattice
energy is estimated to be 575 kcal mol-1. The change in lattice
energy is therefore ∼436 kcal mol-1. Therefore E(PtF6-) is
required to be >60 kcal mol-1 for such an oxidation to occur.
This approaches the electron affinity of a fluorine atom,51 E(F)
) 78.4 kcal mol-1. It is clear, however, that E(PdF6-) must be
even larger than E(PtF6-).
belonged to the family of M2+MF6 R3h materials.44 The
2-
formula unit volume derived from the indexing of each of the
patterns was ∼106 Å3, which is slightly larger than that45 of
PdPtF6 (104 Å3), in harmony with the greater antibonding effect
of the d9 configuration of Ag2+ compared to that of the d8 of
Pd2+. Although there could be a Jahn-Teller distortion arising
from the d9 configuration this, if it occurs, must be sufficiently
subtle to be masked by the broadening of the lines (as a
consequence of small crystallite size; in more crystalline samples
Acknowledgment. The authors gratefully acknowledge the
support of this work by the Director, Office of Energy Research,
(46) Gantar, D.; Frlec, B. Acta Crystallogr. 1987, C43, 618.
(47) Edwards, A. J.; Falconer, W. E.; Griffiths, J. E.; Sunder, W. A.; Vasile,
J. J. Chem. Soc., Dalton Trans. 1974, 1129.
(48) Casteel, W. J., Jr.; Horwitz, T. Eur. J. Solid State Inorg. Chem. 1992,
29, 649.
(42) This equals the trigonal cell a parameter. The rhombohedral a gives
the next nearest like-ion neighbor distances.
(43) Pauling, L. The Nature of the Chemical Bond, 3rd ed.; Cornell
University Press: Ithaca, NY, 1960; p 346.
(44) Babel, D.; Tressaud, A. In Inorganic Solid Fluorides; Hagenmuller,
P., Eds.; Academic Press: London, 1985; Chapter 3, pp 97-105.
(45) Rao, P. R. Ph.D. Thesis, University of British Columbia, 1965. Bartlett,
N.; Rao, P. R. Proc. Chem. Soc. 1964, 393.
(49) Shen, C.; Hagiwara, R.; Mallouk, T. E.; Bartlett, N. AdV. Chem. Ser.
1994, 26, 555.
(50) Moore, C. E. NRDS-NBS (Washington, DC) 1970, 34.
(51) Hotop, H.; Lineberger, W. C. J. Phys. Chem. Ref. Data 1975, 4, 539.

-
-
Room Temperature Syntheses of AuF6 and PtF6 Salts
Inorganic Chemistry, Vol. 38, No. 10, 1999 2509
Office of Basic Energy Sciences, Chemical Sciences Division
of the U.S. Department of Energy under Contract Number DE-
AC-03-76SF00098. O.G. also gratefully acknowledges the
Alexander von Humboldt Foundation for a Feodor-Lynen-
Fellowship, and S.H.E. acknowledges the National Science
Foundation for a fellowship under Grant CHE-9302414. We
also thank Dr. A. Tressaud for the preparation of AgPdF6 in
BrF3/BrF5 and Dr. M. Whalen for carrying out the attempts to
-
prepare PdF6
.
Supporting Information Available: Tables S1-S9, listing mea-
sured and calculated 1/d2 as well as the respective estimated and
calculated intensities and (hkl) values. This material is available free
of charge via the Internet at http://pubs.acs.org.
IC981397Z