X-ray Crystal Structures of r-KrF
2
, [KrF][MF
6
] (M ) As, Sb, Bi), [Kr
2
F
3
][SbF
6
]‚KrF
2
,
[Kr
2
F
3
]
2
[SbF
6
]
2
‚KrF
2
, and [Kr
2
F
3
][AsF
6
]‚[KrF][AsF
6
]; Synthesis and Characterization of
[Kr
2
F
3
][PF
6
]‚nKrF
2
; and Theoretical Studies of KrF
2
, KrF
+
, Kr
2
F
3
+
, and the [KrF][MF
6
]
(M ) P, As, Sb, Bi) Ion Pairs
†
John F. Lehmann,
‡
David A. Dixon,
§
and Gary J. Schrobilgen*
,‡
Department of Chemistry, McMaster University, Hamilton, Ontario L8S 4M1, Canada, and
William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National
Laboratory, 906 Batelle Boulevard, P.O. Box 999, KI-83, Richland, Washington 99352
ReceiVed October 23, 2000
The crystal structures of R-KrF
2
and salts containing the KrF
+
and Kr
2
F
3
+
cations have been investigated for the
first time using low-temperature single-crystal X-ray diffraction. The low-temperature R-phase of KrF
2
crystallizes
in the tetragonal space group I4/mmm with a ) 4.1790(6) Å, c ) 6.489(1) Å, Z ) 2, V ) 113.32(3) Å
3
,R
1
)
0.0231, and wR
2
) 0.0534 at -125 °C. The [KrF][MF
6
] (M ) As, Sb, Bi) salts are isomorphous and isostructural
and crystallize in the monoclinic space group P2
1
/c with Z ) 4. The unit cell parameters are as follows: -[KrF]-
[AsF
6
], a ) 5.1753(2) Å, b ) 10.2019(7) Å, c ) 10.5763(8) Å, ) 95.298(2)°, V ) 556.02(6) Å
3
,R
1
) 0.0265,
and wR
2
) 0.0652 at -120 °C; [KrF][SbF
6
], a ) 5.2922(6) Å, b ) 10.444(1) Å, c ) 10.796(1) Å, ) 94.693-
(4)°, V ) 594.73(1) Å
3
,R
1
) 0.0266, wR
2
) 0.0526 at -113 °C; [KrF][BiF
6
], a ) 5.336(1) Å, b ) 10.513(2)
Å, c ) 11.046(2) Å, ) 94.79(3)°, V ) 617.6(2) Å
3
,R
1
) 0.0344, and wR
2
) 0.0912 at -130 °C. The Kr
2
F
3
+
cation was investigated in [Kr
2
F
3
][SbF
6
]‚KrF
2
, [Kr
2
F
3
]
2
[SbF
6
]
2
‚KrF
2
, and [Kr
2
F
3
][AsF
6
]‚[KrF][AsF
6
]. [Kr
2
F
3
]
2
-
[SbF
6
]
2
‚KrF
2
crystallizes in the monoclinic P2
1
/c space group with Z ) 4 and a ) 8.042(2) Å, b ) 30.815(6) Å,
c ) 8.137(2) Å, ) 111.945(2)°, V ) 1870.1(7) Å
3
,R
1
) 0.0376, and wR
2
) 0.0742 at -125 °C. [Kr
2
F
3
]-
[SbF
6
]‚KrF
2
crystallizes in the triclinic P1 h space group with Z ) 2 and a ) 8.032(3) Å, b ) 8.559(4) Å, c )
8.948(4) Å, R) 69.659(9)°, ) 63.75(1)°, γ ) 82.60(1)°, V ) 517.1(4) Å
3
,R
1
) 0.0402, and wR
2
) 0.1039
at -113 °C. [Kr
2
F
3
][AsF
6
]‚[KrF][AsF
6
] crystallizes in the monoclinic space group P2
1
/c with Z ) 4 and a )
6.247(1) Å, b ) 24.705(4) Å, c ) 8.8616(6) Å, ) 90.304(6)°, V ) 1367.6(3) Å
3
,R
1
) 0.0471 and wR
2
)
0.0958 at -120 °C. The terminal Kr-F bond lengths of KrF
+
and Kr
2
F
3
+
are very similar, exhibiting no
crystallographically significant variation in the structures investigated (range, 1.765(3)-1.774(6) Å and 1.780-
(7)-1.805(5) Å, respectively). The Kr-F bridge bond lengths are significantly longer, with values ranging from
2.089(6) to 2.140(3) Å in the KrF
+
salts and from 2.027(5) to 2.065(4) Å in the Kr
2
F
3
+
salts. The Kr-F bond
lengths of KrF
2
in [Kr
2
F
3
][SbF
6
]‚KrF
2
and [Kr
2
F
3
]
2
[SbF
6
]
2
‚KrF
2
range from 1.868(4) to 1.888(4) Å and are similar
to those observed in R-KrF
2
(1.894(5) Å). The synthesis and Raman spectrum of the new salt, [Kr
2
F
3
][PF
6
]‚
nKrF
2
, are also reported. Electron structure calculations at the Hartree-Fock and local density-functional theory
levels were used to calculate the gas-phase geometries, charges, Mayer bond orders, and Mayer valencies of
KrF
+
, KrF
2
, Kr
2
F
3
+
, and the ion pairs, [KrF][MF
6
] (M ) P, As, Sb, Bi), and to assign their experimental vibrational
frequencies.
Introduction
The known compounds of krypton are limited to the +2
oxidation state and include KrF
2
,
1-9
salts of the KrF
+
,
10-18
and
Kr
2
F
3
+ 11-13,15,16,18
cations, the molecular adducts KrF
2
‚MOF
4
(M ) Cr, Mo, W),
19,20
KrF
2
‚nMoOF
4
(n ) 2, 3),
19
KrF
2
‚VF
5
,
21
and KrF
2
‚MnF
4
,
22
the RCN-KrF
+
(R ) H, CF
3
,C
2
F
5
, n-C
3
F
7
)
cations,
23,24
and Kr(OTeF
5
)
2
.
25
While the strong oxidant char-
acters of KrF
2
, KrF
+
, and Kr
2
F
3
+
provide clean, low-temperature
synthetic routes to BrF
6
+
,
13,26
ClF
6
+
,
27
OsO
2
F
4
,
28
AuF
5
,
14
and
TcOF
5
,
29
they have also served as a significant impediment to
their detailed structural characterization by single-
†
Dedicated to the memory of our colleague and friend, Karel (Drago)
Lutar (December 1, 1947-September 2, 2000) in recognition of his many
outstanding contributions to the field of inorganic fluorine chemistry.
* To whom correspondence should be addressed.
‡
McMaster University.
§
Pacific Northwest National Laboratory.
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10.1021/ic001167w CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/22/2001