Homoleptic, σ-bonded octahedral superelectrophilic metal carbonyl cations of iron(II), ruthenium(II), and osmium(II). Part 2: Syntheses and characterizations of [M(CO)6][BF4]2 (M = Fe, Ru, Os)

Article abstract of DOI:10.1021/ic0482483

As the first examples of homoleptic, σ-bonded superelectrophilic metal carbonyl cations with tetrafluoroborate [BF₄]_- as the counter anions three thermally stable salts of the composition [M(CO) ₆[BF₄]₂ (M = Fe, Ru, Os) have been synthesized and extensively characterized by thermochemical, structural, and spectroscopic methods. A common synthetic route, the oxidative carbonylation of either Fe(CO)₅ (XeF₂ as the oxidizer) or M₃(CO) ₁₂ (M = Ru, Os) (F₂ as the oxidizer) in the conjugate Bronsted-Lewis superacid HF/BF₃, was employed. The thermal behavior of the three salts, studied by differential scanning calorimetry (DSC) and gas-phase IR spectroscopy of the decomposition products, has been compared to that of the corresponding [SbF₆]^- salts. The molecular structures of [M(CO)₆]-[BF₄]₂ (M = Fe, Os) were obtained by single-crystal X-ray diffraction at 100 K. X-ray powder diffraction data for [M(CO)₆][BF₄]₂ (M = Ru, Os) were obtained between 100 and 300 K in intervals of 50 K. All three salts are isostructural and crystallized in the tetragonal space group /4/m (No. 87). As for the corresponding [M(CO)₆][SbF₆]₂ salts (M = Fe, Ru, Os), similar unit cell parameters and vibrational fundamentals were also found for the three [BF₄]^- compounds. For the structurally characterized salts [M(CO)₆][BF₄] ₂ (M = Fe, Os), very similar bond parameters for both cations and anions were found. Hence, the invariance of structural and spectroscopic properties of [M(CO)₆]²⁺ cations (M = Fe, Ru, Os) extended from the fluoroantimonates [Sb₂F₁₁]^- and [SbF₆]^- as counteranions also to [BF₄] ^-.

Full text of DOI:10.1021/ic0482483

Inorg. Chem. 2005, 44, 4206−4214
Homoleptic,
Cations of Iron(II), Ruthenium(II), and Osmium(II). Part 2: Syntheses
and Characterizations of [M(CO) ][BF ] (M Fe, Ru, Os)
σ-Bonded Octahedral Superelectrophilic Metal Carbonyl
)
6
4 2
Maik Finze,† Eduard Bernhardt,† Helge Willner,*,† Christian W. Lehmann,‡ and Friedhelm Aubke§
FB C-Anorganische Chemie, Bergische UniVersit a¨ t Wuppertal, Gaussstrasse 20, D-42097
Wuppertal, Germany, Max Planck Institut f u¨ r Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470
M u¨ lheim an der Ruhr, Germany, and Department of Chemistry, The UniVersity of British
Columbia, VancouVer, British Columbia V6T 121 Canada
Received December 13, 2004
As the first examples of homoleptic,
as the counter anions three thermally stable salts of the composition [M(CO)
synthesized and extensively characterized by thermochemical, structural, and spectroscopic methods. A common
synthetic route, the oxidative carbonylation of either Fe(CO) (XeF as the oxidizer) or M (CO)12 (M Ru, Os) (F
as the oxidizer) in the conjugate Brønsted Lewis superacid HF/BF , was employed. The thermal behavior of the
three salts, studied by differential scanning calorimetry (DSC) and gas-phase IR spectroscopy of the decomposition
products, has been compared to that of the corresponding [SbF ]-
]- salts. The molecular structures of [M(CO)
Fe, Os) were obtained by single-crystal X-ray diffraction at 100 K. X-ray powder diffraction data for
(M Ru, Os) were obtained between 100 and 300 K in intervals of 50 K. All three salts are
][SbF
Fe, Ru, Os), similar unit cell parameters and vibrational fundamentals were also found for the three
σ-bonded superelectrophilic metal carbonyl cations with tetrafluoroborate [BF
]-
4
6
][BF (M Fe, Ru, Os) have been
4
]
2
)
5
2
3
)
2
−
3
6
6
[
BF
4
]
2
(M
)
[
M(CO)
6
][BF
4
]
2
)
isostructural and crystallized in the tetragonal space group I4/m (No. 87). As for the corresponding [M(CO)
salts (M
BF
]- compounds. For the structurally characterized salts [M(CO)
6
6 2
]
)
[
4
][BF ]
6 4 2
(M
)
Fe, Os), very similar bond parameters
for both cations and anions were found. Hence, the invariance of structural and spectroscopic properties of [M(CO)
6
]2
+
2 6
) Fe, Ru, Os) extended from the fluoroantimonates [Sb F
11]- and [SbF ]- as counteranions also to
cations (M
-
[
BF
4
] .
Introduction
metals are unique on several accounts, as discussed in the
7
1
preceding paper. Both experimental and calculated data for
Among superelectrophilic, homoleptic metal carbonyl
cations with metals in oxidation states of 2+ or 3+ reported
8
9
1
square-planar and linear superelectrophilic, homoleptic
2
-4
2-4
metal carbonyl cations and various derivatives
differ in
by us in recent years,
the regular octahedral cations
2+
(M ) Fe, Ru, Os)5-7 formed by the group 8
many respects from those of their octahedral counterparts
6
[M(CO) ]
-
2-4,8,9
and are available only for [Sb
2
F11] salts so far.
*
To whom correspondence should be addressed. E-mail: willner@
The high intrinsic stability of the octahedral M(CO)
6
uni-wuppertal.de. Phone: (+49) 202-439-2517. Fax: (+49) 202-439-3053.
†
‡
§
coordination geometry is manifested in the existence of metal
Bergische Universit a¨ t Wuppertal.
Max Planck Institut f u¨ r Kohlenforschung.
The University of British Columbia.
n-
hexacarbonylate anions [M(CO)
6
]
(n ) 2, 1) in groups 4
10,11
12-14
and 5,
neutral M(CO)
6
in group 6,
cations of the
(1) Olah, G. A. Angew. Chem., Int. Ed. Engl. 1993, 32, 167.
(2) Willner, H.; Aubke, F. Angew. Chem., Int. Ed. Engl. 1997, 36, 2402.
(3) Willner, H.; Aubke, F. In Inorganic Chemistry Highlights; Meyer,
G., Wesemann, L., Naumann, D., Eds.; Wiley-VCH: Weinheim,
Germany, 2002; Vol. 2, p 195.
(7) Bernhardt, E.; Bach, C.; Bley, B.; Wartchow, R.; Westphal, U.; Sham,
I. H. T.; von Ahsen, B.; Wang, C.; Willner, H.; Thompson, R. C.;
Aubke, F. Inorg. Chem. 2005, 44, 4189-4205.
(8) Willner, H.; Bodenbinder, M.; Br o¨ chler, R.; Hwang, G.; Rettig, S. J.;
Trotter, J.; von Ahsen, B.; Westphal, U.; Jonas, V.; Thiel, W.; Aubke,
F. J. Am. Chem. Soc. 2001, 123, 588.
(9) Bodenbinder, M.; Balzer-J o¨ llenbeck, G.; Willner, H.; Batchelor, R.
J.; Einstein, F. W. B.; Wang, C.; Aubke, F. Inorg. Chem. 1996, 35,
82.
(
(
4) Willner, H.; Aubke, F. Organometallics 2003, 22, 3612.
5) Bernhardt, E.; Bley, B.; Wartchow, R.; Willner, H.; Bill, E.; Kuhn,
P.; Sham, I. H. T.; Bodenbinder, M.; Br o¨ chler, R.; Aubke, F. J. Am.
Chem. Soc. 1999, 121, 7188.
(
6) Wang, C.; Bley, B.; Balzer-J o¨ llenbeck, G.; Lewis, A. R.; Siu, S. C.;
Willner, H.; Aubke, F. J. Chem. Soc., Chem. Commun. 1995, 2071.
4206 Inorganic Chemistry, Vol. 44, No. 12, 2005
10.1021/ic0482483 CCC: $30.25
© 2005 American Chemical Society
Published on Web 05/10/2005

[M(CO)
6 4 2
][BF ] (M ) Fe, Ru, Os)
type [M(CO)
6
]+ in group 7,15,16 and recently reported [Ir-
tion reactions will be explored. Despite its lower Brønsted
3+
17
26,27
6
(CO) ]
in [Ir(CO)
6
][SbF
6
]
3
‚4HF. Because of the intrinsic
acidity,
HF/SbF
elsewhere:
the system offers two clear advantages over the
1
2+
18,19,26,27
7
stability of superelectrophilic [M(CO)
6
]
(M ) Fe, Ru,
5
superacid used in the preceding study and
Os),5 it should be possible to generate the solvated cations
-7
2-5,8,9,17
(i) oxidative side reactions as observed
1
8,19
5,7
in superacidic media, other than HF/SbF
these cations by anions other than [Sb
Alternate synthetic methods such as halide abstraction
from precursors of the form M(CO) (M ) Fe, Os, X )
Cl, Br) by the Lewis acids AlX (X ) Cl, Br) at elevated
temperatures and CO pressures, a methodology that allowed
the synthesis of the group 7 cations [M(CO)
Tc, Re) as [AlX
erroneous claims.1
5
,
and stabilize
for SbF
5
are not feasible and (ii) oligomerization of the
11]- or [SbF
] .
- 2-7
anions, observed in the HF/SbF
for the formation of two types of salts,
improbable in HF/BF
Oxidative carbonylation2
choice. Suitable precursors such as Fe(CO) or M (CO)
12
system
18,19,28
and responsible
2
F
6
5
5
-7
is highly
2
6,27
X
4 2
3
.
-4,29
3
becomes the method of
5
3
+
6
] (M ) Mn,
(M ) Ru, Os) are commercially available, and it is
-
2+
4
] salts, had failed, reportedly resulting in
anticipated that all three [M(CO)6] salts (M ) Fe, Ru, Os)
5,16
can be synthesized by a common route. Both XeF , used
2
5
,7
A promising approach is suggested by the recent synthesis
previously by us in this role, and F will be employed as
2
of [Co(CO)
5
][(CF
3
)
3
BF],20 according to eq 1
external oxidizing agents. In addition, an attempt will be
made to synthesize the related salt [Fe(CO)
6
][AsF
6
]
2
, which
aHF,CO
-
would permit a comparison to the corresponding [Sb
2
F11] ,
Co (CO) + 2(CF ) BCO + 2HF
8
2
8
3 3
25 °C
-
5,7
-
[
6 4
SbF ] , and [BF ] salts.
2
[Co(CO) ][(CF ) BF] + H (1)
5 3 3 2
]2+ salts5,7 with both
The well-characterized [M(CO)
6
-
]- provide an excellent opportunity for
[
Sb
2
F
11] and [SbF
6
which contains the first trigonal-bipyramidal metal carbonyl
a comparison, which will include (i) structural aspects of
Fe(CO) ][BF and [Os(CO) ][BF , (ii) thermal stabilities
and thermal decomposition modes, (iii) estimated lattice
4
,20
3 3
cation. In the synthesis, the elusive Lewis acid (CF ) B
[
6
]
4 2
6
4 2
]
3 3 2
) F] -
BCO,2 and the acidium ion [H
1,22
+
is replaced by (CF
solv) is found to act as an oxidizing reagent in an oxidative
(
3
0,31
energies using a recently reported approach,
and (iv)
2-4
carbonylation. However, as more fully investigated sub-
vibrational spectra supported by DFT calculations for the
23
-
sequently, slow degradation of [(CF
3 3
) BF] in aHF occurs,
-
2+
[BF
4
] anion and published data for the [M(CO)
6
]
cations
-
resulting in the formation of [C BF
2
F
5
3
] (solv) and HCF
3
,
3
2
(M ) Fe, Ru, Os).
which limits the use of this novel reaction system.
In addition to the degradation and rearrangement reactions
of the anion in the conjugate superacid HF/(CF
F] is found to be difficult. Protonation of
, observed some time ago in liquid
HCl, becomes a competing process as found in preliminary
Experimental Procedures
2
0
3
)
3
BCO,
+
oxidation by [H
2
Apparatus. Volatile materials were manipulated in stainless steel
or glass vacuum lines of known volume, equipped with capacitance
pressure gauges (type 280E, Setra Instruments, Acton, MA). The
glass lines were equipped with PTFE stem valves (Young, London),
and the stainless steel lines were fitted with bellow valves (Balzers
type BPV 25004 and Nupro type SS4BG) as well as Gyrolok and
Cajon fittings. For synthetic reactions in aHF, 100-mL reactors were
used, consisting of PFA bulbs with an NS 29 socket standard taper
substrates such as Fe(CO)
5
24
2
5
experiments, which will be discussed elsewhere.
In this study, the use of the conjugate Brønsted-Lewis
26,27
superacid HF/BF
3
as the reaction medium in carbonyla-
(
(
(
10) Ellis, J. E. AdV. Organomet. Chem. 1990, 31, 1.
11) Ellis, J. E. Organometallics 2003, 22, 3322.
12) Cotton, F. A.; Wilkinson, G. AdVanced Inorganic Chemistry, 5th ed.;
Wiley: New York, 1988.
13) Elschenbroich, C. Organometalchemie, 4th ed.; Teubner: Wiesbaden,
Germany, 2003.
(Bohlender, Lauda, Germany) in connection with a PTFE NS 29
cone standard taper top and a PFA needle valve (type 204-30
Galtek, fluoroware, Chaska, MN). The parts were held together by
(
-
5
a metal compression flange, and the reactor was leak-tight (<10
-1
(
14) Crabtree, R. H. The Organometallic Chemistry of the Transition Metals,
mbar L s ) without use of grease. Solid materials were manipulated
inside an inert atmosphere box (Braun, Munich, Germany) filled
with argon, with a residual moisture content of less than 0.1 ppm.
2nd ed.; Wiley: New York, 1994.
(
(
(
15) Abel, E. W.; Tyfield, S. P. AdV. Organomet. Chem. 1970, 8, 117.
16) Beck, W.; S u¨ nkel, K. Chem. ReV. 1988, 88, 1405.
17) von Ahsen, B.; Berkei, M.; Henkel, G.; Willner, H.; Aubke, F. J. Am.
Chem. Soc. 2002, 124, 8371.
Chemicals. Anhydrous HF (used as received) and F
from Solvay AG, Hannover, Germany), CO (standard grade, Messer
GmbH, Krefeld, Germany), Fe(CO) (purity not stated, BASF AG,
Ludwigshafen, Germany), M (CO)12 (M ) Fe, Ru, Os) (Strem
Chemicals), Fe (CO)12 (Aldrich), and all standard chemicals were
2
(both gifts
(
18) Hyman, H. M.; Quaterman, L.; Kirkpatrik, M.; Katz, J. J. J. Phys.
5
Chem. 1961, 65, 123.
(
(
19) Gillespie, R. J.; Moss, K. C. J. Chem. Soc. A 1966, 1170.
20) Bernhardt, E.; Finze, M.; Willner, H.; Lehmann, C. W.; Aubke, F.
Angew. Chem., Int. Ed. 2003, 42, 2077.
21) Terheiden, A.; Bernhardt, E.; Willner, H.; Aubke, F. Angew. Chem.,
Int. Ed. 2002, 41, 799.
22) Finze, M.; Bernhardt, E.; Terheiden, A.; Berkei, M.; Willner, H.;
Christen, D.; Oberhammer, H.; Aubke, F. J. Am. Chem. Soc. 2002,
3
3
obtained from commercial sources.
(
Vibrational Spectroscopy. Infrared spectra were recorded at
room temperature on an IFS-66v FT spectrometer (Bruker, Karlsru-
(
1
24, 15385.
23) Finze, M.; Bernhardt, E.; Z a¨ hres, M.; Willner, H. Inorg. Chem. 2004,
3, 490.
(
(28) Culmann, J. C.; Fauconet, M.; Jost, R.; Sommer, J. New J. Chem.
1999, 23, 863.
4
(
(
(
24) Iqbal, Z.; Waddington, T. C. J. Chem. Soc. A 1968, 180.
25) Finze, M.; Bernhardt, E.; Willner, H., manuscript in preparation.
26) Olah, G. A.; Prakash, G. K. S.; Sommer, J. Superacids; Wiley: New
York, 1985.
(29) Willner, H.; Aubke, F. Chem.sEur. J. 2003, 9, 1668.
(30) Jenkins, H. D. B.; Roobottom, H. K.; Passmore, J. Inorg. Chem. 2003,
42, 2886.
(31) Jenkins, H. D. B.; Roobottom, H. K.; Passmore, J.; Glasser, L. Inorg.
Chem. 1999, 38, 3609.
(27) O’Donell, T. A. Superacids and Acidic Melts as Inorganic Reaction
Media; VCH: Weinheim, Germany, 1993.
(32) Jonas, V.; Thiel, W. Organometallics 1998, 17, 353.
Inorganic Chemistry, Vol. 44, No. 12, 2005 4207

Finze et al.
Table 1. Crystallographic Data for [M(CO)6][BF4]2 (M ) Fe, Os) at
00 K
lattice constant refinements, and structure calculations were all
1
Pow
36
carried out using the STOE WinX
Synthetic Reactions. (a) [Fe(CO)
reactor, fitted with a PTFE-coated magnetic stirring bar, was
charged with 250 mg of XeF (1.2 mmol) in a drybox. At -196
C, 220 mg of Fe(CO) (1.1 mmol) was transferred in vacuo into
the reaction vessel, followed by 5 mL of anhydrous HF and 4.5
mmol of BF . After the addition of CO (4.5 mmol) at -196 °C,
suite of programs.
empirical formula
C6B2F8FeO6
C6B2F8O6Os
6
][BF . A 100-mL PFA
4 2
]
formula weight (g mol-1
)
397.53
531.88
color
colorless
tetragonal,
I4/m, (No. 87)
7.4114(3)
10.8790(3)
597.58(3)
2
2.209
3.75-33.14
0.0267
colorless
tetragonal,
I4/m, (No. 87)
7.4802(1)
10.9445(3)
612.38(2)
2
2.885
3.30-27.73
0.0379
2
crystal system,
space group
a (Å)
°
5
3
c (Å)
3
the reactor was allowed to warm to room temperature, giving a
clear colorless solution. The mixture was stirred vigorously for 1
h and then kept at room temperature without stirring. After 3 days,
a white precipitate had formed. The reaction mixture was stored
for one additional week, to ensure completion of the reaction. All
volatile compounds were removed in vacuo, leaving a white solid
material. The reactor was brought into a drybox, and 320 mg of
V (Å )
Z value
Fcalc (Mg m-3)
θ range (deg)
a
R1 [I > 2σ(I)]
wR2 (all data)
goodness-of-fit on F
b
0.0705
1.083
0.0952
0.770
2
a
R1 ) (∑||Fo| - |Fc||)/∑|Fo|. wR2 ) [∑w(Fo2 - Fc ) /∑wFo ]
b
2 2
2 1/2
.
[
Fe(CO)
of the IR spectra, the formation of Fe(CO)
Calcd. for C FeO : C, 18.13%. Found: C, 13.19%; H, ca.
.3%. The low carbon content is probably due to partial hydrolysis
6
][BF
4
]
2
(0.8 mmol, 73%) was isolated. During recording
5
was observed. Anal.
he, Germany). For each spectrum, 64 scans were co-added with an
apodized resolution of 2 cm-1. Solid samples were measured either
as powders, crushed between AgBr disks, or as Nujol mulls between
AgBr disks in the region 5000-400 cm-1. Raman spectra were
recorded at room temperature with a Bruker RFS100/S FT Raman
spectrometer using the 1064 nm exciting line of a Nd:YAG laser.
Crystalline samples contained in large melting point capillaries
6
B
2
F
8
6
0
6 4 2
of [Fe(CO) ][BF ] in agreement with problems that arose during
recording of the IR spectra. The compound was found to be
thermally stable to about 95 °C (80 °C, DSC), where decomposition
with gas evolution (BF ) began.
A light gray residue was obtained.
3
(b) [Ru(CO) ][BF . In a drybox, 300 mg of Ru (CO)12 (0.5
3
, CO, and traces of SiF
4
and CO
2
(
8
2 mm o.d.) were used for recording spectra in the region of 3500-
0 cm with a resolution of 1 cm . For each spectrum, 256 scans
-1
-1
6
]
4 2
mmol) was placed into a 100-mL PFA reactor fitted with a PTFE-
coated magnetic stirring bar. Five milliliters of anhydrous HF and
fluorine (3.6 mmol) was condensed into the reactor while being
cooled with liquid N . Subsequently, the reaction mixture was held
2
at -78 °C and slowly warmed to room temperature while being
stirred for 5 h. Then, at -196 °C, all volatile compounds were
removed in vacuo, and F (1.4 mmol) was added again. The reaction
2
mixture was slowly brought to room temperature and stirred
overnight. A light gray solution was obtained. The reactor was
were co-added, and the Raman intensities were corrected by
calibration of the spectrometer with a tungsten halogen lamp.
Differential Scanning Calorimetry. Thermoanalytical measure-
ments were made with a Netzsch DSC204 instrument. Temperature
and sensitivity calibrations in the temperature range of 20-500 °C
were carried out with naphthalene, benzoic acid, KNO
3 3
, AgNO ,
LiNO , and CsCl. Portions of about 5-10 mg of the solid samples
3
were weighed and contained in sealed aluminum crucibles. They
were studied in the temperature range of 20-500 °C with a heating
recooled, using liquid N
under reduced pressure. At -196 °C, BF
2
, and all volatile compounds were removed
(5.6 mmol) and CO (5.6
-1
rate of 10 K min ; throughout this process, the furnace was flushed
with dry nitrogen. For the evaluation of the output, the Netzsch
Proteus 4.0 software was employed.
3
mmol) were transferred into the reactor. The reaction mixture was
warmed to room temperature, and an off-white solid precipitated
immediately. After the reaction mixture had been kept at ambient
temperature for 1 day, all volatiles were pumped off, giving an
off-white solid. The reactor was transferred into a drybox, and 415
Single-Crystal X-ray Diffraction. Crystals suitable for X-ray
diffraction were obtained from HF solutions. Diffraction data were
collected at 100 K on a KappaCCD diffractometer (Bruker AXS)
using Mo KR radiation (λ ) 0.71073 Å) and a graphite mono-
6 4 2
mg of [Ru(CO) ][BF ] (0.9 mmol, 66%) was isolated. Anal. Calcd.
33
chromator. Crystal structures were determined using SHELXS-97,
for C Ru: C, 16.28%. Found: C, 16.14%. Despite the good
6 2 8 6
B F O
2
and full-matrix least-squares refinement based on F was performed
agreement between the calculated and observed carbon content, an
unknown impurity was detected by X-ray powder diffraction. A
yellow-colored sample was found to be thermally stable to ∼115
3
4
using SHELXL-97. No absorption corrections were applied.
Molecular structure diagrams were drawn using the program
Diamond.35 A summary of experimental details and crystal data is
presented in Tables 1 and S1.
°
C (most likely because of the impurity), and on further heating to
1
90 °C (195 °C, DSC), vigorous gas evolution (BF
and a black residue was produced.
c) [Os(CO) ][BF . A PFA reactor, fitted with a PTFE-coated
magnetic stirring bar, was charged with 306 mg of Os (CO)12 (0.34
mmol) inside a drybox. At -196 °C, 5 mL of anhydrous HF and
.7 mmol of fluorine were condensed into the PFA vessel. At room
3
, CO) was noted,
6 4 2
Powder X-ray Diffraction. Samples of [M(CO) ][BF ] (M )
Fe, Ru, Os) were filled into thin-walled glass capillaries of 0.5-
mm diameter inside a glovebox. Data for M ) Fe and Ru were
collected at room temperature using Cu KR radiation (λ ) 1.54056
Å) on a PANalytical X′Pert MPD using a hybrid monochromator
and, in the case of M ) Fe, an additional secondary monochromator
to suppress iron fluorescence. Data for M ) Os were collected
using an STOE STADI P powder diffractometer equipped with a
Ge primary monochromator, also using Cu KR radiation. Graphics,
(
6
4 2
]
3
2
temperature, the reaction mixture was stirred for 3 h. Subsequently,
more fluorine (1 mmol) was added at -196 °C, and the reaction
mixture was slowly warmed to room temperature. After 3 h, all
3
volatiles were removed in vacuo at -196 °C, and BF (4.1 mmol)
and CO (4.1 mmol) were added. The reaction mixture was warmed
to room temperature, and within 20 min, a clear light yellow
solution was obtained. After 1 h, colorless crystals began to form.
(
(
(
33) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure Solution;
University of G o¨ ttingen; G o¨ ttingen, Germany, 1997.
34) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure Refine-
ment; University of G o¨ ttingen; G o¨ ttingen, Germany, 1997.
35) Diamond-Visual Crystal Structure Information System, version 2.1;
Crystal Impact GbR: Bonn, Germany, 1996-1999.
(36) WinXPOW, version 1.10; STOE & CIE GmbH: Darmstadt, Germany,
2002.
4208 Inorganic Chemistry, Vol. 44, No. 12, 2005

6 4 2
[M(CO) ][BF ] (M ) Fe, Ru, Os)
Scheme 1. Two-Step Oxidative Carbonylation of M3(CO)12 (M ) Ru, Os) in HF/BF3 and aHF
Within 1 day, the solution had turned from light yellow to light
gray. After 5 days, all volatiles were removed in vacuo, and the
reaction vessel was transferred into a drybox. A total of 388 mg of
moisture sensitive within the series [M(CO) ][BF ] (M )
6
4 2
Fe, Ru, Os). During recording of the IR spectra, the formation
of Fe(CO) was observed, whereas the Ru and Os compounds
are stable under the same conditions.
The formation of [Fe(CO) ][BF
that of [Fe(CO) ][Sb
, which is obtained in ∼50% yield.
Identified byproducts include [Fe(CO) ][SbF , which is also
structurally characterized; paramagnetic Fe[SbF , which
has been reported previously, detected by magnetic sus-
5
[
Os(CO)
crystalline solid. Anal. Calcd. for C
Found: C, 13.23%. The compound was thermally stable up to ∼300
C (280 °C, DSC). The gaseous decomposition products consisted
of CO and BF , as well as some CO and SiF . The residue was
black, and a film of metallic Os had formed inside the reactor.
d) Attempted Synthesis of [Fe(CO) ][AsF . Into a 250-mL
flask, fitted with a PTFE valve and a magnetic stirring bar were
added 0.390 g (1.99 mmol) of Fe(CO) , ca. 8 mL of C SO F (in
further attempts, CH Cl or CF ClCCl F), 7.0 mmol of AsF , and
.3 mmol of CO by condensation. Upon warming of the reaction
6
][BF
4
]
2
(0.72 mmol, 72%) was obtained as a white
6
2 8 6
B F O Os: C, 13.55%.
6
4 2
] is much simpler than
5
6
2 11 2
F ]
°
6
6 2
]
3
2
4
5
6 2
]
3
8
(
6
6 2
]
5
39
ceptibility measurements; and 6SbF
3
‚5SbF
5
, which indi-
7
5
F
4 9
2
cates that SbF functions as a co-oxidizer. None of these
5
2
2
2
2
5
3
byproducts or their equivalents are formed in HF/BF .
2
]2+(solv) (M ) Ru, Os)
In contrast, the cations [M(CO)
6
mixture to room temperature, the initial green color changed to
yellow within 30 min. After 3 days, all volatiles were removed in
vacuo with the reactor kept at room temperature. The residue of
are generated in this study from the precursors M
two distinct steps: oxidation by F in aHF, followed by
carbonylation of the product in HF/BF
As illustrated in Scheme 1, the first step, the oxidation of
3
(CO)12 in
2
2
6,27
3
.
0
.687 g or 1.14 mmol would suggest a yield of ∼57%, but the
thermally unstable material was found to be inhomogeneous:
according to its Raman spectrum, it contained, in addition to [Fe-
4
0,41
40,41
42
M
3
(CO)12 (M ) Ru, Os)
by XeF
2
or F
2
in aHF, has
been studied previously by C and 19F NMR spectros-
13
6 6 2 6 2 11 2 6 2 6
(CO) ][AsF ] , some [Fe(CO) ][As F ] , Fe[AsF ] , FeF[AsF ],
FeF , and possibly FeF
2
3
.
40,41
copy,
M(CO)
observation of [M(CO)
and several products have been identified: cis-
(M ) Ru, Os)
4
0,41
4
F
2
is the main product. The
Results and Discussion
Synthetic Aspects. Oxidative carbonylation2
by us recently for the synthesis of [(Co(CO)
+
40,41
5
F] (M ) Ru, Os)
suggests some
-4,29
was used
CO redistribution. The minor constituents [M (CO) F (µ-
2
7 3
2
0
+
5
][(CF)
3
BF],
F)], [M (CO) F (µ-F)] , and [{M(CO) F(µ-F)} ] (M ) Ru,
2
8
2
3
4
40,41
- 40
starting from Co
2
(CO)
8
in the new superacid HF/(CF
3
)
3
-
Os)
and the anions mer- and fac-[Ru(CO) F ]
are not
3
3
BCO.2 As discussed in the Introduction, the acidium ion
1,22
expected to persist in HF/BF3.
To continue the generation of [M(CO)
+
[H
2
F] acts as an internal oxidant, an approach first described
]2+(solv) (M ) Ru,
6
37
by Souma et al.
An attempt to adapt this method to the generation of [Fe-
Os) as described here, all excess F
after the completed oxidation. For the carbonylation step,
CO and BF are added. The latter increases the Brønsted
2
is removed in vacuo
2
+
(CO)
6
]
3 3
by oxidation of Fe (CO)12 in HF/BF results in
3
protonation instead, according to eq 2
26,27
acidity of the reaction medium
ability.
and enhances its ionizing
HF/BF , CO
3
Fe (CO) + 3HF + 3BF + 3CO -196 to 25 °C8
As seen in Scheme 1, all four major components of the
3
12
3
40,41
mixture
are cleanly converted by solvolytic carbonylation
3
[HFe(CO) ][BF ] (2)
5 4
2
+
6
into [M(CO) ] (solv) (M ) Ru, Os) just as the initial
oxidation products of Fe(CO)
5
, the transients Fe(CO)
4
F
2
, and
The isolated product is of limited thermal stability and is
identified by its Raman spectrum.25
+
7
[Fe(CO) F] are carbonylated either in HF/SbF or in HF/
5
5
2
+
]2+ in HF/SbF
in HF/BF proceeds
,5,7
3 6
BF to [Fe(CO) ] . The substitution of fluoride by CO is
In analogy to the generation of [Fe(CO)
6
5
suggested to involve ionic dissociation in superacids2 to
6,27
the oxidation of Fe(CO)
according to
5
by XeF
2
3
(37) Xu, Q.; Inoue, S.; Souma, Y.; Nakatani, H. J. Organomet. Chem. 2000,
HF/BF ,CO
606, 147.
3
Fe(CO) + XeF + CO + 2BF 196 to 25 °C8
(38) Gantar, D.; Leban, I.; Frlec, B.; Holloway, J. H. J. Chem. Soc., Dalton
Trans. 1987, 2379.
5
2
3
-
[
Fe(CO) ][BF ] + Xe (3)
(39) Nandana, W. A. S.; Passmore, J.; White, P. S. J. Chem. Soc., Dalton
Trans. 1987, 1623.
6
4 2
(
(
(
40) Coleman, K. S.; Holloway, J. H.; Hope, E. G. J. Chem. Soc., Dalton
After removal of all volatiles in vacuo, the new salt is
obtained as a colorless, crystalline powder in an isolated yield
Trans. 1997, 1713.
41) Brewer, S. A.; Holloway, J. H.; Hope, E. G. J. Chem. Soc., Dalton
Trans. 1994, 1067.
42) Coleman, K. S.; Fawcett, J.; Holloway, J. H.; Hope, E. G.; Nassar, R.
J. Fluorine Chem. 2001, 112, 185.
6 4 2
of 73%. [Fe(CO) ][BF ] is thermally stable to 95 °C (80
°
C, DSC). It was found that the iron compound is the most
Inorganic Chemistry, Vol. 44, No. 12, 2005 4209

Finze et al.
Table 2. Selected Structural and Thermochemical Properties of [Fe(CO)6]2+ Salts
Vformula unit
(Å )
UPota
(kJ mol
F- affinityb
Tdecomposition
major volatile
decomposition products
3
-1
-1
compound
)
(kJ mol
)
(°C)
[Fe(CO)6][BF4]2
[Fe(CO)6][AsF6]2
[Fe(CO)6][SbF6]2
299c
1564
1450
1431
348
433
504
90
25
190
2BF3 + 6CO
2AsF5 + 6CO
6CO
d
403
e
425
a
Reference 30. b Of the respective Lewis acid.49 This Article. d Estimated value, see text. e Ref 5.
c
2
+
and the V values for the three [BF
4
]- salts are very similar
form short-lived transients of the type [M(CO)
n
4
]
(M ) Fe,
3
Ru, Os; n ) 4, 5), which act as soft acids or class b
(vide infra), it follows that the Upot values within each triad
agree closely. For the Upot of [Fe(CO) ][AsF , the estimate
is based on the calculated or published partial volumes of
acceptors44 toward CO to form stable d [M(CO)
6
] (solv)
2+
6
6
6 2
]
11]-, [SbF
] ,
- 7
30
(
M ) Fe, Ru, Os) and then salts with [Sb
2
F
6
-
2+
-
or [BF
4
] as counteranions.
[Fe(CO)
6
]
6
and [AsF ] .
Hence, the soft and hard acid and base concept of
Pearson43 or the metal ion classification of Ahrland et al.44
that had previously been invoked to rationalize the formation
The volume per formula unit and Upot values are listed in
Table 2. The lattice energies increase from 1431 kJ mol
-1
-
1
for [Fe(CO)
6
6
][SbF ]
2
6 4 2
to 1564 kJ mol for [Fe(CO) ][BF ] .
2-4,29
2+
of superelectrophilic metal carbonyl cations
by reductive
This is not surprising given that, in [Fe(CO)
is found to be inversely proportional to the anion radius.
An intermediate Upot value of 1450 kJ mol for [Fe(CO)
6
]
salts, Upot
29
45
solvolytic carbonylation is found useful here, to rationalize
their formation by oxidative carbonylation as well.
-
1
6
]-
In summary, the use of alternate conjugate Brønsted-
[AsF provides no indication that this salt does not exist at
ambient temperature because it loses CO at room tempera-
ture.
6 2
]
Lewis superacids2 such as HF/BF
6,27
, discussed here, or of
3
HF/(CF
3
)
3
BCO, reported elsewhere,2
0,25
results in an en-
hanced importance of oxidative carbonylation as a synthetic
method for the generation of homoleptic metal carbonyl
6 6 2
For [Fe(CO) ][SbF ] , the following thermal decomposi-
tion sequence is observed upon heating
2
-4,29
cations.
6 4 2
The synthesis of the triad [M(CO) ][BF ] (M
T > 190 °C
T > 350 °C
8 FeF2 (4)
-2SbF5
)
Fe, Ru, Os) provides the basis for a comparison to the
[Fe(CO) ][SbF ]
8 Fe[SbF6]2
6
6 2
-
6CO
-
5,7
6
corresponding triad of [SbF ] salts, in regard to their
38
thermochemical properties and thermal decomposition modes,
which are discussed next.
6 2
Decarbonylation produces paramagnetic Fe[SbF ] , which
has a layer structure and is identified by temperature-
5
Thermochemical Properties and Thermal Decomposi-
dependent magnetic susceptibility measurements. In the triad
2+
tion Modes of Various [Fe(CO)
6
]
Salts. Little attention
[M(CO) ][SbF ] (M ) Fe, Ru, Os), increasing onset tem-
6
6
has been paid in the past to thermochemical properties of
peratures for the decarbonylation process of 190, 280, and
2
-4,29
superelectrophilic homoleptic metal carbonyl cation salts,
350 °C, respectively, reflect the increasing strength of the
and only occasionally7,8 have thermal decomposition studies,
using differential scanning calorimetry (DSC), been re-
2+
M-C bonds in the [M(CO) ] cations (M ) Fe, Ru, Os)
6
4
6,47
due to relativistic effects and polar contributions to the
ported.7 The extensively characterized [M(CO)
,8
]
2+
salts (M
2+ 48
6
M-C bond due to polarization of the CtO bond by M .
-
- 4-7
-
)
Fe, Ru, Os) with [Sb
2
F11] , [SbF
6
] ,
or [BF
4
]
as
The nature of the residues from the thermolysis of [M(CO) ]-
6
7
counteranions provide the basis for an exploratory investiga-
tion of their thermochemical properties and the observed
[SbF ] (M ) Ru, Os) is unclear.
6
2
In the triad [M(CO) ][BF ] (M ) Fe, Ru, Os), the thermal
6
4 2
thermal decomposition modes.
stability, with onset temperatures of 80, 195, and 300 °C,
+
]2 salts are chosen for the
-
For this study, the [Fe(CO)
6
respectively, is lower than that of the [SbF6] salts. The
following reasons: (i) reliably determined molecular struc-
thermal decompositions, formulated for [Fe(CO) ][BF ] as
6
4 2
5,7
tures for [Fe(CO) ][SbF ]
6 6 2
6 4 2
and [Fe(CO) ][BF ] are known,
T > 80 °C
and their unit cell volumes per formula unit allow an estimate
[Fe(CO) ][BF ]
8 FeF + 2BF + 6CO (5)
2 3
6
4 2
30,31
of their lattice energies, Upot, as reported by Jenkins et al.;
ii) a detailed DSC study of [Fe(CO) ][SbF , complemented
(
6
]
6 2
indicate the simultaneous loss of CO and BF
thermal event. DSC studies for [M(CO) ][BF
3
in a single
(M ) Ru,
by gas-phase IR spectra of the decomposition products, is
6
4
]
2
7
found in part I of this study; and (iii) a reason for the lack
Os) involve as yet unidentified intermediates. In all instances,
the simultaneous evolution of CO and BF , together with
traces of CO and SiF , is observed.
Reversible phase transitions, observed for all three [M(CO)
[SbF salts (M ) Fe, Ru, Os) in the range of 150-170 °C
of thermal stability of elusive [Fe(CO)
6 6
][AsF ]
2
and our
3
failure to isolate this compound (see Experimental Proce-
dures) must be provided.
2
4
6
]-
For the estimate of lattice energies Upot,30 experimentally
6 2
]
5
,7
determined unit cell volumes V for [Fe(CO)
Fe(CO) ][BF are used. Because the unit cell volumes in
the triad [M(CO)
6 6
][SbF ]
2
and
in their DSC plots, are not detected for any of the three
[
6
4 2
]
5
,7
(45) Johnson, D. A. Some Thermodynamic Aspects of Inorganic Chemistry;
6
6 2
][SbF ] (M ) Fe, Ru, Os) are identical
Cambridge University Press: Cambridge, U.K., 1968.
(
46) Pyykk o¨ , P. Chem. ReV. 1988, 88, 563.
(
(
43) Pearson, R. J. J. Am. Chem. Soc. 1963, 85, 3533.
44) Ahrland, S.; Chatt, J.; Davies, N. R. Q. ReV. Chem. Soc. 1958, 12,
65.
(47) Pyykk o¨ , P.; Desclaux, J. P. Acc. Chem. Res. 1979, 12, 276.
(48) Goldman, A. S.; Krogh-Jespersen, K. J. Am. Chem. Soc. 1996, 118,
12159.
2
4210 Inorganic Chemistry, Vol. 44, No. 12, 2005

6 4 2
[M(CO) ][BF ] (M ) Fe, Ru, Os)
Figure 1. Formula unit of [Fe(CO)6][BF4]2 in the crystal structure (50%
probability).
[
BF
of the type Fe[BF
thermal decomposition of [Fe(CO)
4
]- salts. There is also no evidence for an intermediate
, either after the synthesis or during the
][BF
4 2
]
6
4
]
2
.
Figure 2. Measured (lower trace) and simulated (upper trace) powder
diffractogram of [Ru(CO)6][BF4]2. An unknown impurity can be seen in
the lower trace.
A measure for the thermal stability of fluoroanions is found
in the calculated fluoride ion affinities of the respective
molecular fluro Lewis acids.49 Data relevant to this study
-1
5
are listed in Table 2 and follow the order SbF (504 kJ mol )
-
1
-1
>
AsF
this Article, [M(CO)
elusive [Fe(CO) ][AsF
C than the three [SbF
instabilities of the constituent [BF
5
(433 kJ mol ) > BF
3
(348 kJ mol ). As shown in
6
][BF ]
4 2
(M ) Fe, Ru, Os) and the
] have higher lattice energies at 25
6 2
6
] salts. Upon heating, the thermal
6
-
°
-
-
4
6
] and [AsF ] anions
provide a facile dissociation pathway for the thermolyses of
-
-
the [BF
4
] and [AsF
6
] salts. Hence, it is not surprising that
1
the vast majority of all superelectrophilic metal carbonyl
2
-4,29
cations
5 5
are generated in SbF or HF/SbF and form salts
-
-
of high thermal stability, with either [Sb
2 6
F11] or [SbF ] as
counteranions.
Structural Aspects. (a) General Comments. Whereas for
5,7
5,7
6
the triads [M(CO) ][Sb
F
2 11
]
2
and [M(CO)
6
][SbF
6
]
2
(M
)
Fe, Ru, Os) reliable and accurate molecular structures are
5,7
obtained for all six salts by single-crystal X-ray diffraction,
this is not the case for the tetrafluoroborates [M(CO) ][BF
M ) Fe, Ru, Os). Single-crystal data are obtained only for
Fe(CO) ][BF and [Os(CO) ][BF as summarized in
6
4 2
]
(
[
6
4
]
2
6
4 2
]
Table 1. More detailed listings of crystal data, their acquisi-
tion, and structure solutions are found as Supporting Infor-
mation in Table S1.
A satisfactory structure solution is possible for [Fe(CO)
6
]-
]-
[
[
BF
BF
4
]
]
2
(Figure 1). The accuracy of the data for [Os(CO)
6
4
2
is reduced by twinning (Figure S1). To establish a
]-
(M ) Fe, Ru, Os) and to permit a comparison to those
structural similarity of the crystal data for the triad [M(CO)
BF
for the corresponding [SbF
are obtained from powder diffraction data for [M(CO)
BF (M ) Ru, Os); for M ) Ru, see Figure 2. A new
6
[
4
]
2
-
5,7
6
] salts, the unit cell parameters
Figure 3. Temperature dependence of the unit cell volume and of the
deviation of the cell constants from a cubic meter in [Ru(CO)6][BF4]2 and
6
]-
[
4 2
]
[Os(CO)6][BF4]2. For data, see Supporting Information.
dimension is added by determining the temperature depen-
dency of the unit cell parameters a and c and the unit cell
volume V in the temperature range of 100-300 K, with
Fe, Ru, Os) crystallize in the tetragonal system, as do the
5
,7
previously reported [M(CO)
can be derived from the CaF
all tetrahedral holes. Because the local site symmetry for
6 6 2
][SbF ] salts. The structure
measurements made in 50 K increments for [M(CO)
M ) Ru, Os). The results are presented in Figure 3 and are
discussed next.
Crystal Data and Unit Cell Dimensions for [M(CO)
BF (M ) Fe, Ru, Os). The [M(CO) ][BF salts (M )
6 4 2
][BF ]
2
prototype, with the anions in
(
-
-
the [BF
space groups for the two triads are found: I4/m (No. 87)
for [M(CO) ][BF and P4/mnc (No. 128) for the corre-
sponding [SbF
both space groups.
4
6
] ions is 4h and that of [SbF ] is 222, different
6
]-
[
4
]
2
6
4 2
]
6
4 2
]
-
7
6
] salts, with a common Z value of 2 for
(
49) Christe, K. O.; Dixon, D. A.; McLemore, D.; Wilson, W. W.; Sheehy,
J. A.; Boatz, J. A. J. Fluorine Chem. 2000, 101, 151.
Inorganic Chemistry, Vol. 44, No. 12, 2005 4211

Finze et al.
Table 3. Unit Cell Dimensions and Volumes for the Complex Salts
Table 4. Structural Data [M(CO)6][BF4]2 (M ) Fe, Os) and
[M(CO)6][SbF6]2 (M ) Fe, Ru, Os)
[M(CO)6][BF4]2 and [M(CO)6][SbF6]2 (M ) Fe, Ru, Os)
[BF
]-
[SbF
Ru
]-
6
M
4
M(CO)6]2
+
Fe
Ru
Os
[
Fe
Os
Fe
Os
BF4]-
a
a (Å)
7.4114(3)
7.4745(4)b
7.4802(1)
[
[
[
Bond Lengths (Å)
T ) 100 K c (Å)3
10.8790(3) 10.9364(10) 10.9445(3)
597.58(3)
(152.8)
M-C
M-C
1.907(2)
1.905(1)
1.118(3)
1.119(2)
1.996(19)
2.00(3)
1.162(91)
1.155(54)
1.917(7) 2.020(6) 2.013(8)
1.903(6) 2.026(6) 2.026(6)
1.096(9) 1.100(8) 1.109(11)
1.114(8) 1.101(6) 1.101(7)
ax
V (Å )
Vcalc (Å )
610.99(4)
(159.5)
7.6114(5)b
10.9733(9)
635.71(5)
(171.8)
612.38(2)
(160.0)
7.6103(10)b
10.9617(7)
634.87(19)
(171.5)
eq
3
c
C-Oax
BF4]- a
T ) 300 K c (Å)3
C-O
eq
a (Å)
Bond Angles (deg)
180 180
M-C-Oeq 180.00(11) 178.88(355) 178.9(5) 179.3(4) 179.4(5)
V (Å )
Vcalc (Å )
M-C-Oax 180
180
180
3
c
c
SbF6]-
T ) 300 K c (Å)3
d
a (Å)
8.258(1)
12.471(2)
850.5(2)
(183.3)
8.278(1)
12.449(2)
853.1(2)
(184.6)
8.274(1)
12.421(2)
850.3(2)
(183.2)
Cax-M-Cax 180
Ceq-M-Ceq 180
Cax-M-Ceq 90
Ceq-M-Ceq 90
180
180
90
180
180
90
180
180
90
180
180
90
V (Å )
Vcalc (Å )
3
90
90
90
90
a
This Article. Powder diffraction. c Vcalc denotes partial volume of the
b
2
+
d
[M(CO)
6 4 2
][BF ] (M ) Fe, Ru, Os), as discussed previously
[
M(CO)6] cation (M ) Fe, Ru, Os). References 5 and 7.
(see Table 2). (iii) As the temperature is increased from 100
A comparison of the unit cell dimensions for the two triads
to 300 K, the unit cells appear to expand, and the values (a,
V, and Vcal) increase slightly. Conversely, the partial volumes
of [BF ] and [SbF ] are also expected to decrease when
4 6
going from 300 to 100 K. Hence, the Vcal values at 100 K
are somewhat underestimated. A detailed study of the
temperature dependence of unit cell parameters for the pair
is presented in Table 3. Single-crystal data at 100 K are used
for [M(CO) ][BF (M ) Fe, Os) (also see Table 1), and
powder data at 100 K are listed for [Ru(CO) ][BF . To
facilitate a comparison to the single-crystal data for [M(CO) ]-
-
-
6
]
4 2
6
4
]
2
6
5
,7
[
SbF
unit cell parameters derived from powder diffraction data at
00 K for [M(CO) ][BF (M ) Ru, Os) are included in
Table 3.
The unit cell parameters a and c as well as the unit cell
6 2
] (M ) Fe, Ru, Os), obtained at room temperature,
[M(CO)
6 4 2
][BF ] (M ) Ru, Os) is shown in Figure 3 and
3
6
4 2
]
discussed next.
3
1
]-
When using published partial anion volumes for [BF
4
-
and [SbF
6
] , some caution is required. Because of the limited
2
+
volumes V are remarkably constant for the [M(CO)
6
]
salts
number of structures used for their determinations, error
-
]- as
30
(
M ) Fe, Ru, Os) with either [BF
4
]
or [SbF
6
limits are quoted that might affect some of the conclusions
5,7
counteranions. Because the bond parameters and vibrational
made here.
-
-
properties of the two anions [BF
4
]
and [SbF
6
]
in the
As seen in Figure 3, when the temperature is raised
gradually from 100 to 300 K, the unit cell volume V increases
steadily, and both a and c increase as well. The increase of
a is stronger than that of c. As a consequence, the deviation
respective triads are identical,7 differences in unit cell
volumes reflect differences in cation size and, implicitly,
differences in the relative strength of the M-C bonds in these
cations.
from the cubic metric given by c/a 2 decreases slowly,
x
With the partial volumes of both [BF
4
]- and [SbF
6
]-
and a phase transition from the tetragonal to the cubic system
at temperatures well above 450 K is probable (Figure 3).
3
1
known, it is possible to calculate partial volumes for the
+
]2 cations (M ) Fe, Ru, Os) from experimental V
[
M(CO)
6
Internal Bond Parameter for the [M(CO)
(M ) Fe, Os). Whereas the preceding discussion of unit
cell dimensions for the triad [M(CO) ][BF (M ) Fe, Ru,
6 4 2
][BF ] Salts
-
values and Z ) 2 in all instances. In the [SbF
6
] triad, the
2
+
partial volumes of [M(CO)
6
3
]
(M ) Fe, Ru, Os) are at ∼300
6
4 2
]
K estimated as 184(1) Å . The calculated partial volumes
Os) is based on both single-crystal and powder X-ray
diffraction data (Tables 3 and S15), a meaningful discussion
of internal bond parameters (bond lengths and angles) is
V
cal are included in Table 3 in brackets. The partial volumes
2+
calculated in this manner for all [M(CO)
6
]
salts (M ) Fe,
Ru, Os) listed in Table 3 are included in parentheses in the
listing.
The following comments are made: (i) Whereas the unit
cell dimensions (a and c) and volumes (V and Vcal) are
possible only for [Fe(CO)
for the [Os(CO) ]
6
6
][BF
salt is limited as a result of twinning.
Selected bond data for [M(CO) ][BF (M ) Fe, Os),
obtained at 100 K, are listed in Tables 4 and 5. A formula
unit of [Fe(CO) ][BF is depicted in Figure 1, and selected
interionic contacts are shown for this salt in Figure 4.
4 2
] because the quality of data
2
+
6
4 2
]
invariant of M in the group [M(CO)
6
][SbF
6
]
2
(M ) Fe, Ru,
6
4 2
]
-
Os), they increase for the [BF
4
] complexes slightly from
50
Fe to Ru and then remain constant for [Os(CO)
6
][BF
][Sb
M ) Fe, Ru, Os). This reflects increasing M-C bond
4
]
2
. A
Calculated and experimental bond lengths and angles for
-
similar pattern is observed for the triad [M(CO)
6
2
F
11
]
2
the [BF
4
] anion in the two salts are compared in Table 6.
7
(
As can be seen, any departure from T
d
symmetry for the
-
strength. Evidence for such an increase was discussed in the
[BF
(CO)
A comparison of selected bond parameters of [M(CO)
[BF (M ) Fe, Os) with those of the triad [M(CO) ][SbF
(data obtained at 300 K) is shown in Table 4. Except for
[Fe(CO) ][SbF , where very small tetragonal distortions for
4
] anion is for [Fe(CO)
][BF ]
6 4 2
insignificant and for [Os-
-
previous section. (ii) The calculated Vcal values for the [BF
4
]
6 4 2
][BF ] unclear.
salts at ∼300 K are smaller than the corresponding values
6
]-
for [M(CO)
efficient packing of the tetrahedral [BF
6
][SbF
6
]
2
(M ) Fe, Ru, Os). This suggests a more
]
4 2
6
6 2
]
-
4
] ions into tetra-
hedral holes. This is reflected in higher lattice energies for
6
6 2
]
4212 Inorganic Chemistry, Vol. 44, No. 12, 2005

6 4 2
[M(CO) ][BF ] (M ) Fe, Ru, Os)
Table 5. CO Stretching Fundamentals of [M(CO)6]2+ (M ) Fe, Ru,
Os) in Different Salts with Fluoro Anions
[BF4]-
a
[SbF6]- b [Sb2F11]- b calcc
assignment
cation
Fe(CO)6]2
+
2238
2242
2219
2205
2216
2252
2219
2198
2214
2258
2214
2189
2210
2241
2220
2204
2216
2254
2222
2199
2216
2259
2218
2190
2211
2221 A1g ν1 ν(CO)
2188 Eg ν3 ν(CO)
2173 T1u ν6 ν(CO)
[
[
[
2
2
2
211
197
209
2186
ν(CO)avg
Ru(CO)6]2
+
2250
2235 A1g ν1 ν(CO)
2192 Eg ν3 ν(CO)
2172 T1u ν6 ν(CO)
2
2
2
211
191
208
2189
ν(CO)avg
Os(CO)6]2
+
2255
2237 A1g ν1 ν(CO)
2188 Eg ν3 ν(CO)
2166 T1u ν6 ν(CO)
2
2
2
205
180
201
2185
ν(CO)avg
a
This Article. b References 5 and 7. c Reference 32.
Figure 5. IR (Nujol) and Raman spectrum of [Os(CO)6][BF4]2.
5
6
[SbF ]
2
that involve only four of the six C atoms of the
cation. These observations provide experimental confirmation
-
for the more efficient packing of [BF
4
] in tetrahedral holes
we proposed in the previous section, based on unit cell
dimensions (see Table 3).
Both sets of values are shorter than the sum of the van
5
1
3,4,7,29
der Waals radii of 3.17 Å. In recent publications,
we
have interpreted the observed C‚‚‚F contacts in σ metal
carbonyl fluoroantimonates in terms of electron transfer from
Figure 4. Selected interionic contacts in [Fe(CO)6][BF4]2.
3,4,29
F of the anions into π* MOs of the CO ligands
on the
a
Table 6. Experimental and Calculated Structural Data for the [BF4]-
cations. The slightly more extensive electron transfer sug-
gested for [Fe(CO) ][BF relative to that in [Fe(CO) ]-
6 2
[SbF ] is expected to affect the positions of ν(CO) for both
Anion in [M(CO)6][BF4]2 (M ) Fe, Os)
4
]
6
2
6
5
metal
calca
salts in their vibrational spectra, discussed next.
Fe
Os
Vibrational Spectra. The IR and Raman spectra of [Os-
B-F (Å)
1.417
109.47
109.47
1.395(1)
109.73(5)
109.34(5)
1.389(10)-1.401(11)
108.1(5)-110.1(5)
F-B-F (2x) (deg)
F-B-F (4x) (deg)
(CO)
spectra of [M(CO)
Figures S2 and S3. To identify effects attributable to the
6
][BF
4
]
2
are depicted in Figure 5, and the respective
6
][BF (M ) Fe, Ru) are shown in
4 2
]
a
B3LYP/6-311+G(d).50
counteranion, the CO stretching fundamentals, ν
1
(A1g), ν
3
5
]2+ cations
2+
both constituent ions are reported, all [M(CO)
(
6
(E
[BF
g
), and ν
6
(T1u) of [M(CO)
6
]
(M ) Fe, Ru, Os) with
as counteranions, together
-
- 5,7
- 5,7
M ) Fe, Ru, Os) are best interpreted as regular octahedral
in both groups. This is particularly evident from the bond
4
] , [SbF
6
2 11
] , and [Sb F ]
3
2
with calculated band positions, are summarized in Table
5. Also included are ν(CO)avg values. Two effects are
discernible: (i) dependency of the band position on the metal
and (ii) dependency of ν(CO) on the counteranion.
angles, which rarely depart from 180° or 90°. The Fe-C
2
+
bond lengths in the two [Fe(CO)
6
]
salts are identical within
esd values.
7
A final point of interest concerns the interionic C‚‚‚F
contacts shown in Figure 4. The contact distances in the range
of 2.710(1)-2.795(1) Å are very slightly shorter than C‚‚‚F
In the first part of this study, we observed that ν (A )
1
1g
increases in the order Fe < Ru < Os whereas ν (E ) remains
3
g
constant or decreases slightly and ν (T ) decreases more
6
1u
-
-
distances of 2.842(5)-3.061 Å reported for [Fe(CO)
6
]-
steeply for the [SbF ] and [Sb F ] salts. As can be seen
6
2 11
6 4 2
in Table 5, for [M(CO) ][BF ] (M ) Fe, Ru, Os), the band
(
50) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
positions of the three fundamentals ν
1
(A1g), ν
3
(E
g
), and ν
6
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A., Jr.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels,
A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone,
V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.;
Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R.
L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara,
A.; Gonzales, C.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen,
W.; Wong, M. W.; Andres, J. L.; Gonzales, C.; Head-Gordon, M.;
Replogle, E. S.; Pople, J. A. Gaussian 98, revision A.6; Gaussian,
Inc.: Pittsburgh, PA, 1998.
(T1u) follow the same pattern.
A comprehensive vibrational assignment including a
normal coordinate analysis and force field calculations is
5
reported for [Fe(CO)
6
][SbF
6
]
2
, and all 13 fundamentals of
2
+
-
[M(CO)
6
]
(M ) Ru, Os) with [SbF
recently been identified. The observed fundamental vibra-
6
] as the anion have
7
2+
tions for [M(CO)
6
]
(M ) Fe, Ru, Os) in their respective
(51) Bondi, A. J. Phys. Chem. 1964, 68, 441.
Inorganic Chemistry, Vol. 44, No. 12, 2005 4213

Finze et al.
lower, on account of the lower fluoride ion affinity of BF
3
[
BF
4
]- and [SbF
6
]- 5,7 salts are listed in Table S16, where
32
49
they are compared to calculated data. As can be seen, all
as compared to that of SbF
Structural studies reported here consist of the molecular
structure determinations of [M(CO) ][BF (M ) Fe, Os)
5
.
2+
[M(CO)
6
]
cations (M ) Fe, Ru, Os) are clearly identified,
and most fundamentals are assigned. There are some gaps,
in particular, in the region below 500 cm , where for the
6
4 2
]
-
1
by single-crystal X-ray diffraction and powder X-ray dif-
fraction of the corresponding Ru and Os complex salts. The
unit cells are found to expand in the temperature range of
-
[SbF
6
] salts, band positions are occasionally obtained from
overtones and combination bands rather than being directly
observed. This procedure is more difficult and ambiguous
on account of the increased number of [BF
important regions (Table S9).
1
00-300 K, and the different changes of the cell lengths a
-
4
]
bands in
and c suggest a phase transition from tetragonal to cubic
above their decomposition temperatures.
The band positions for each fundamental in the three triads
show a very slight dependency on the counteranion: for the
The structural and vibrational studies reported here allow
2+
the following conclusions: (i) the [M(CO)
6
]
cations (M
-
-
[
SbF
6
] and [Sb
2
F
11] salts, the ν(CO) values are identical
)
Fe, Ru, Os) have structural and vibrational properties that
-
1
-
within (2 cm , whereas for the three [BF
is consistently lower by about 4-9 cm . This small margin
is consistent with the more efficient packing of [BF
4
] salts, ν(CO)
-
4
are nearly independent of the anion, [BF ] studied here and
-1
-
-
7
[
6 2
SbF ] or [Sb F11] featured in part I; (ii) the anions have
-
4
] into
identical structures and vibrational properties in the three
the tetrahedral hole, expressed in shorter C‚‚‚F contacts, due
2+
groups of [M(CO)
6
]
salts (M ) Fe, Ru, Os); (iii) in each
4,29
to slightly stronger F f π*(CO) interionic electron transfer,
2+
6
triad, the structural and vibrational features of both [M(CO) ]
cations and anions ([BF ] , [SbF ] , [Sb F11] ) are nearly
4 6 2
as discussed in the preceding section.
These admittedly small but noticeable differences not
withstanding, it is apparent that, in the three triads [M(CO)]-
-
-
-
independent of M (Fe, Ru, Os); and (iv) these features,
summarized previously, and the near absence of significant
interionic contacts illustrate the intrinsic stability of the
octahedral coordination geometry.
2 6 6 2 6 4 2
[Sb F11], [M(CO) ][SbF ] , and [M(CO) ][BF ] (M ) Fe,
Ru, Os), the structural and vibrational properties of both
cations and anions are independent of M and do not vary
with counteranion. This intrinsic stability of the octahedral
coordination in superelectrophilic σ metal carbonyl cations
Acknowledgment. Financial support by the Deutsche
Forschungsgemeinschaft, DFG, is acknowledged. Further-
more, we are grateful to Merck KGaA, Darmstadt, Germany,
and Solvay Fluor und Derivate GmbH, Bad Wimpfen,
Germany, for providing financial support and chemicals used
in these studies. We are indebted to Ms. M. Litz (University
of Wuppertal) for typing the manuscript and Dr. N. Adonin
2
+
sets the group 8 [M(CO)
6
]
cations (M ) Fe, Ru, Os) clearly
2
-4,8,9,15,16,20,29
apart from other metal carbonyl cations
but also
from other homoleptic, octahedral metal carbonyl com-
plexes.1
0-14
Conclusion
2
for a sample of XeF .
The three isostructural salts of the composition [M(CO)
BF
characterized examples of homoleptic superelectrophilic
6
]-
Supporting Information Available: Tables of atomic coordi-
nates, anisotropic displacement factors, cell parameters at different
[
4
]
2
(M ) Fe, Ru, Os) reported here are the first fully
1
temperatures, and bond lengths in the crystal structures of the
2-4,29
σ-bonded metal carbonyl cations
stabilized by an anion
-
observed and calculated vibrational frequencies of [BF
4
]
and
-
]- 2-4,29 to form isolable salts
other than [Sb
2
F
11] or [SbF
6
2+
[
M(CO)
6
]
(M ) Fe, Ru, Os). Figures of the IR spectrum of [Ru-
of relatively high thermal stability.
6 4 2 6 4 2
(CO) ][BF ] , the IR and Raman spectra of [Fe(CO) ][BF ] , and
A common synthetic route, the oxidative (F
2
, XeF
2
)
6 4 2
a view of [Os(CO) ][BF ] in the crystal structure. X-ray crystal-
carbonylation of commercially available precursors [Fe(CO)
5
,
aHF
salts
lographic files in CIF format have been deposited at the Cambridge
Crystallographic Center under the deposition numbers CCDC-
26,27
3
M (CO)12 (M ) Ru, Os)] in the Brønsted superacids
232217 for [Fe(CO)
6 4 2 6
][BF ] and CCDC-232216 for [Os(CO) ]-
or HF/BF produces the isostructural [M(CO) ][BF ]
3
6
4 2
[
BF . This material is available free of charge via the Internet at
4 2
]
(
M ) Fe, Ru, Os) in high yields. Whereas their lattice
30,31
http://pubs.acs.org.
potential energies Upot
6
are higher than those of [M(CO) ]-
(M ) Fe, Ru, Os), their thermal stabilities are
5,7
[SbF
6
]
2
IC0482483
4214 Inorganic Chemistry, Vol. 44, No. 12, 2005