Preparation and crystal structures of ruthenium and osmium oxide tetrahalides

Article abstract of DOI:10.1002/zaac.200600354

RuOF₄ as the highest valence oxide fluoride exist as a molecular compound (a = 606.0(1), b = 836.1(1), c = 626.3(1) pm, β = 91.637(3), Z = 4; P2₁/n) as well as fluorine bridged polymer (a = 547.7(2), b = 928.5(3), c = 1252.4(3) pm, Z = 8, P2₁2₁2₁). A reproducible method for pure, deep blue OsOF₄ is given. Pure OsOF₄-I is isostructural to the fluorine bridged polymeric RuOF ₄ (a = 554.6(1), b = 955.4(2), c = 1278.4(2), Z = 8, P2 ₁2₁2₁). OsOF₄-II is also a fluorine bridged polymer (a = 537.8(2), b = 1274.8(4), c = 555.2(2), β = 117.716(6)°, Z = 4, P2₁/c). OsOCl₄ again is a molecular species (a = 938.9(2), b = 561.3(1), c = 1192.0(2), β = 109.944(4)°, Z = 4, P2₁/c).

Full text of DOI:10.1002/zaac.200600354

Articles
DOI: 10.1002/zaac.200600354
Preparation and Crystal Structures of Ruthenium and Osmium Oxide
Tetrahalides
Hashem Shorafa and Konrad Seppelt*
Berlin, Freie Universität, Institut für Chemie, Anorganische und Analytische Chemie
Received December 14th, 2006.
Dedicated to Professor Karl O. Christe on the Occasion of his 70th Birthday
Abstract. RuOF4 as the highest valence oxide fluoride exist as a
molecular compound (a ϭ 606.0(1), b ϭ 836.1(1), c ϭ 626.3(1) pm,
β ϭ 91.637(3), Z ϭ 4; P21/n) as well as fluorine bridged polymer
(a ϭ 547.7(2), b ϭ 928.5(3), c ϭ 1252.4(3) pm, Z ϭ 8, P212121). A
reproducible method for pure, deep blue OsOF4 is given. Pure
OsOF4-I is isostructural to the fluorine bridged polymeric RuOF4
(a ϭ 554.6(1), b ϭ 955.4(2), c ϭ 1278.4(2), Z ϭ 8, P212121). OsOF4-II
is also a fluorine bridged polymer (a ϭ 537.8(2), b ϭ 1274.8(4),
c ϭ 555.2(2), β ϭ 117.716(6)°, Z ϭ 4, P21/c). OsOCl4 again is a
molecular species (a ϭ 938.9(2), b ϭ 561.3(1), c ϭ 1192.0(2), β ϭ
109.944(4)°, Z ϭ 4, P21/c).
Keywords: Ruthenium; Osmium; Oxyde fluorides; Raman spectra;
Crystal structure
Introduction
The RuOF4 molecule can be assumed to be a tetragonal
pyramid with an apical oxygen atom. Any additional con-
tact would be assumed to occur on the site opposite to the
oxygen atom. This, however, is not the building principle
of this polymer. The speciality of this structure is the cis-
orientation of the bridging fluorine atoms with respect to
the double bonded oxygen atom. All ruthenium-oxygen
bonds within the helical chain point into one direction, thus
creating a polar crystallographic situation.
If RuO2 is treated with undiluted elemental fluorine at
300 °C, as first published in 1987, a yellow sublimate is
formed [3]. This material has been described as RuOF3. Our
crystallographic determination, however, shows that it is a
second modification of RuOF4, see Figure 2 and Table 1.
This RuOF4 comes as a monomer with only weak inter-
actions with a second molecule, thus creating a very loose
dimer. The RuOF4 molecules are tetragonal pyramidal with
the oxygen atoms in apical positions. The contact to the
second molecule occurs through a fluorine atom positioned
opposite to the oxygen atom, as expected. This weak con-
tact is 233.6 pm long, and the bond lengths Ru-F of the
participating fluorine atom is only a little enlarged
(192.0 pm).
Three oxide tetrahalides of Ru and Os are known, but their
characterization is incomplete. This is certainly due to the
high instability of RuOF4 and OsOCl4, and the difficulty of
obtaining pure samples of OsOF4.
Results and Discussion
RuOF4
This oxide fluoride is certainly the one with the highest oxi-
dation state of Ru. Attempts to generate RuO2F4 failed, the
reaction of RuO4 with KrF2 afforded only RuOF4 [1]. The
difficulty of handling KrF2 makes this synthesis incon-
venient. The reaction of RuO2 with F2 has been published
twice [2, 3]. At 450 °C and with argon diluted F2 yellow
green crystals of RuOF4 are obtained [2]. Our crystallo-
graphic determination of this material proved it to be
RuOF4. In the crystal it appears as a fluorine bridged poly-
mer, as has been recently found also for OsO2F3
(ϭOsO3F2·OsOF4) [4]. The structure is shown in Figure 1,
numerical values are collected in Table 1. Oxygen and fluor-
ine atoms are easily distinguished by the bond lengths
towards the Ru atom, as well as by the slight difference in
electron density of O and F.
OsOF4
This compound is certainly the best described of those dis-
cussed here. A number of preparative methods has been
published. But already the physical data do not agree. Most
importantly its color has been described as blue, green, or
yellow.
By looking at the published crystallographic data on
OsF5 [5], OsO2F3 (ϭOsO3F2·OsOF4) [4], Os2O3F7
(ϭ OsO3F2·OsF5) [4], and OsO3F2 [6], the suspicion arose
* Prof. Dr. K. Seppelt, Dipl. Chem. H. Shorafa
Freie Universität Berlin
Institut für Chemie, Anorganische and Analytische Chemie
Fabeckstraße 34-36
D-14195 Berlin
Fax: ϩ49 30 83853310
e-mail: seppelt@chemie.fu-berlin.de
Z. Anorg. Allg. Chem. 2007, 633, 543Ϫ547
 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
543

H. Shorafa, K. Seppelt
Figure 2 Crystal structure of monomeric RuOF4, ORTEP repre-
sentation, 50 % probability ellipsoids. OsOCl4 has a similar struc-
ture, Os···Cl ϭ 384.4 pm.
by partial hydrolysis of OsF6 [9, 10], by reaction of OsF6
with B2O3 [11], or by reaction of OsO4 and OsF6 [12, 13].
Whenever we got crystalline material by methods de-
scribed in the literature, we obtained either one of the speci-
men described above, or compounds with serious disorder
between oxygen and fluorine atoms, and also with varying
colours. Only the method of reacting OsO4 and OsF6 for a
long time at fairly high temperatures resulted in a good
yield of OsOF4, besides some OsOF5 [13]. The OsOF4 so
obtained is deep blue and melts sharply at 100 °C. Crystals
are formed by sublimation during the synthesis or by
recrystallization from anhydrous HF. This material turned
out to be real OsOF4, see Table 1. It comes in two modifi-
cations. Sublimed material or needle shaped needles recrys-
tallized from HF are isostructural to the polymeric form
(RuOF4)x, see Figure 1. This modification has been obvi-
ously observed before, when OsOF5 has been decomposed
to OsOF4 [7]. The crystal structure had not been deter-
mined, possibly due to an error in the choice of the space
group, correctly P212121 rather than P21221, while the lattice
constants agree very well.
Figure 1 a) Crystal structure of polymeric RuOF4, ORTEP
representation, 50 % probability ellipsoids; b) View of polymeric
RuOF4 down the helical chain; OsOF4ϪI has the same structure.
that there exists a continuous system of mixed crystals of
the formula OsFxO5Ϫx, and OsOF4 is just one member of it.
OsOF4 has previously been prepared by defluorination
of OsOF5 with a hot W filament [7] or with Si in HF [8],
The second modification, OsOF4ϪII, recrystallized also
from HF, is also deep blue. It comes in large needle shaped
Table 1 Bond lengths /pm and angles /[]
(RuOF4)n
RuOF4
(OsOF4)n-I
(OsOF4)n-II
164.9(10)
OsOCl4
164.5(2)
MϭO
161.9
160.1(2)
167.6,
163.7(4)
182.3-184.0(4)
200.1-205.0(4)
167.9(10)
183.2-186.1(9)
203.2-206.8(8)
MϪXtab))
MϪXb
183.9-192.0(2)
233.6(2)
183.9-184.6(7)
204.2,
224.9-226.1(1)
384.4(1)
205.5(7)
100.4(4),
164.3(4)
85.4,
OϭM-Xt
OϭM-Xb
99.3-101.6(2)
161.3, 162.8(2)
82.9-88.3(2)
102.9-106.0(1)
172.6(1)
98.6-101.0(5)
162.6, 164.5(4)
85.3-88.7(4)
107.1-108.3(1)
173.0(1)
88.2(4)
a) Xt ϭ terminal halogen atom; b) Xb ϭ bridging halogen atom
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Z. Anorg. Allg. Chem. 2007, 543Ϫ547

Ruthenium and Osmium Oxide Tetrahalides
OsOCl4. OsOCl4 is the highest valent osmium chloride.
After all an OsCl6 has never been observed, although it
might exist [14]. OsOCl4 has first been prepared from Os,
O2, and Cl2 [15], better it is made from OsO4 and BCl3 [16].
It is a very unstable material.
Crystals are obtained by crystallization from excess re-
agent BCl3 at Ϫ82 °C. The determination of its crystal
structure is straight forward, see Table 1 and also Figure 2.
It comes as a molecule. Intermolecular interactions to a se-
cond molecule, qualitatively similar to molecular RuOF4,
are very weak: (rOs···Cl ϭ 384.4 pm, see also Figure 2). The
molecule is an almost perfect tetragonal pyramid with
r OsϭO ϭ 164.5 pm in the apical position. The Raman
spectrum of OsOCl4 has already been measured, and a
normal coordinate analysis on the basis of C4v symmetry
and of a complete assignment has been calculated [17].
Figure 3 Crystal structure of OsOF4-II, sheet like fluorine bridged
polymer. ORTEP representation, 50 % probability ellipsoids.
Computations
The monomeric species RuOF4, OsOF4, and OsOCl4 can
easily be calculated by DFT methods. This has been done
before [18Ϫ20]. If all three compounds are assumed to be
singlet species, the calculations reveal a C4v symmetry for
all of them. Our results vary somewhat in the geometrical
constants from earlier computations, but they are closer to
the structures obtained by electron diffraction for OsOF4
and OsOCl4, see Table 3. If the lengthening of some metal
halogen bonds in the solid state due to the weak bridging
is taken into consideration, than the structures of RuOF4
and OsOCl4 are also nicely reproduced.
Figure 4 Raman spectrum of OsOF4. Arrows indicate Raman
lines and their intensities of the PFA (polyperfluoro-ethylene-vinyl-
elther copolymer) container tube. The asterix indicates either the
OsϭO18 stretching frequency of OsOF4, or the OsϭO stretching
frequency of a very minor impurity.
Experimental Part
General experimental procedures: All reactions are carried out un-
der a dry argon atmosphere, e.g. by handling in a dry box with
H2O and O2 contents lower than 1 ppm. Technical anhydrous HF
is purified by vacuum distillation into a steel cylinder and stored
there above BiF5. OsO4 and RuO2·H2O have been purchased from
Chempur, RuO2·H2O is dehydrated to RuO2 by heating to 600 °C
in vacuum. Elemental fluorine is passed through NaF before use.
crystals that tend to be twinned. It is, like OsOF4ϪI, also a
cisϪfluorine bridged polymer, but the polymeric chain
forms a sheet rather than a helix, see Figure 3. OsOF4ϪII
has a marginally smaller molecular volume than OsOF4ϪI
under otherwise identical conditions. Therefore it might be
considered the thermodynamically more stable condition.
The Raman spectrum of pure OsOF4 is shown in Figure 4.
It is important to know that a spectrum can only be ob-
tained by Raman excitation with a blue laser (λ ϭ 488 nm,
2 mW). All other commonly used Raman excitation wave
lengths, especially those in the near infrared lead to strong
absorption, fluorescence, and decomposition. The Raman
spectrum cannot fully be assigned due to the polymeric nat-
ure of the material. The OsϭO stretching vibration at
1012 cmϪ1 and the OsϪF stretching vibrations in the
600Ϫ700 cmϪ1 region are obvious. Comparison to the only
published Raman spectrum of OsOF4 shows many
similarities but also some differences, possibly due to the
impurity of the previous sample [13].
OsF6 is prepared from osmium powder and 1.5 l elemental F2 in a
80 ml monel autoclave at 250-300 °C for four hrs.
Single crystals were handled in a special device [22], cut to an ap-
propriate size if necessary, and mounted on a Bruker SMART
CCD 1000 TK diffractometer, using MoKͰ irradiation, a graphite
monochromator, a scan width of 0.3° in ω, and a measuring time
of 10s per frame. Usually 1800 to 2400 frames are measured. After
semi empiral absorption correction (SADABS) by equalizing sym-
metry equivalent reflections, the SHELX programs are used for
solution and refinement [23]. Further experimental details are
deposited with the Fachinformationszentrum Karlsruhe, Gesellschaft
für wissenschaftliche technische Zusammenarbeit mbH, D-76344
Eggenstein-Leopoldshafen, under the CSD number 417248
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545

H. Shorafa, K. Seppelt
Table 2 Molecular structures and energies of RuOF4, OsOF4, and OsOCl4, calculated (DFT) and according to electron diffraction (E.D.)
RuOF4 (DFT)
OsOF4 (DFT)
OsOF4 (ED)b)
OsOCl4 (DFT)
OsOCl4 (ED)c)
Energy/a.u.a)
MϭO/pm
M-X/pm
Ϫ569.674802
161.69
185.28
Ϫ565.528955
164.56
187.65
Ϫ2007.000588
165.74
229.37
162.5(25)
183.5(7)
166.3(9)
225.8(5)
108.3(4)
OϭM-X/°
110.49
110.86
108.28
a) including zero point correction; b) Ref. [20]; c) Ref. [21]
Table 3 Experimental details of the crystal structure determinations
Compound
(RuOF4)n
RuOF4
(OsOF4)nϪI
(OsOF4)nϪII
OsOCl4
M
193.07
Ϫ140
P212121
547.7(2)
928.5(3)
1252.4(3)
90.0
636.9
8
4.87
61.03
8541
1949
110
0.073
0.032
193.07
Ϫ140
P21/n
606.0(1)
836.1(1)
626.3(1)
91.638(3)
317.2
4
282.3
Ϫ100
P212121
554.6(1)
955.4(2)
1278.4(2)
90.0
677.4
8
37.60
61.05
5118
282.3
Ϫ100
P21/c
537.8(2)
1274.8(4)
555.2(2)
117.716(6)
336.9
4
37.8
61.01
3629
1013
56
348.00
Ϫ100
P21/c
938.9(2)
561.3(1)
1192.0(2)
109.924(4)
590.6
4
23.26
61.09
7398
1785
56
T/°C
space group
a/pm
b/pm
c/pm
β/°
V/106pm3
Z
µ/minϪ1
4.89
2θmax/°
84.82
18914
2081
55
0076
reflections, collected
reflections, independent
refined parameters
wR2 (alle Daten)
R1
2025
110
0.093
0.039
0.105
0.042
0.042
0.018
0.034
((RuOF4)n), 417247 (RuOF4), 417245 (OsOF4ϪI), 417246
(OsOF4ϪII), and 417247 OsOCl4. Details can be obtained on
quoting the depository numbers, names of authors, and the jour-
nal citation.
OsOF4
200 mg (0.8 mmol) OsO4 are given into a 80 ml stainless steel auto-
clave, and after evacuation and cooling to Ϫ196 °C 1 g (3.2 mmol)
OsF6 are condensed on it. The autoclave is heated to 180 °C for
six days. Both temperature and duration of the heating are
important for the purity of the OsOF4. At Ϫ30 °C the volatiles
are pumped off for 15 min, and at room temperature some OsOF5
(200 mg, 15 %) can be trapped in a PFA tube at Ϫ78 °C. The auto-
clave is opened in the dry box. Blue, microcrystalline OsOF4 has
sublimed into the upper and cooler parts of the autoclave during
the reaction. This is resublimed at 100 °C under 1 bar of Ar. Yield
2.5-3 mmol (80-90 %). mp 100 °C (sharp), only very slightly soluble
in HF with a faint blue color at room temperature. Heating in HF
in a closed PFA tube allows recrystallization. Raman spectrum:
DFT calculations are performed by the Becke procedure [24] using
the correlation functional of Lee, Young, and Parr [25], as im-
plemented in the Gaussian program [26]. Ru is treated by the
relativistic core potential for 28 electrons and a 8s7p6d [6s5p3d]
basis set for the valence electrons, Os by a relativistic core potential
for 60 electrons and a 8s7p6d [6s5p3d] basis set for the valence
electrons, both obtained from the Institut für Theoretische Chemie
der Universität Stuttgart. An augϪccϪpVTZ basis set is used for
oxygen and fluorine, as implemented in [26].
1012, 695, 670, 633, 287, 260, 223 cmϪ1
.
(RuOF4)n
The fluorination of RuO2 is carried out in a 60 cm long and 2 cm
wide monel tube that is on one side connected to the F2/Ar supply,
on the other side to an U-tube of PFA (perfluoroethenperfluorovi-
nylether copolymer), followed by a soda lime absorber for excess
F2. 500 mg RuO2 are filled into a nickel boat and placed into the
center of the monel tube. F2/Ar (1:7) is passed slowly through the
system at 150 °C for one hour, to fluorinate any impurities. Then
the U-tube is cooled to Ϫ78 °C, and the temperature is raised to
400 °C. After about 40 min the RuO2 is consumed, and a yellow
green sublimate is formed in the U-tube. The tube is sealed off at
both ends, the RuOF4 is stored at Ϫ78 °C. It decomposes at room
temperature. The yellow modification of RuOF4 is obtained when
the same procedure is carried out at 320 °C and with undiluted
fluorine, as described in [3]. The yield is much lower.
OsOCl4 [16]
OsO4 (0.4 mmol) are given into a well dried glass ampule, and 2 g
BCl3 are condensed on it, and the tube is sealed off. At room tem-
perature a brown solution is obtained. Slow cooling to Ϫ82 °C
gives a large crop of large dark brown, needle shaped crystals of
OsOCl4.
We thank Dr. Christian Hess, Fritz-Haber-Institut der Max-Planck-
Gesellschaft, Abt. Anorganische Chemie, Berlin, for the Raman
spectrum of OsOF4, the Deutsche Forschungsgemeinschaft and the
Fonds der Chemischen Industrie for support of this work.
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Ruthenium and Osmium Oxide Tetrahalides
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