Two crystalline modifications of RuO4

Article abstract of DOI:10.1016/j.jssc.2005.07.021

RuO₄ was prepared by oxidation of elemental ruthenium. Two different modifications were obtained and investigated by X-ray single crystal diffraction. RuO₄-I has cubic symmetry (P4;-3n,Z=8,a=8.509(1)A) , and two independent tetrahedral molecules are present in the unit cell. Within the standard uncertainties in both molecules the distances Ru-O are 1.695 A. The second modification, RuO₄-II, is monoclinic (C2/c,Z=4,a=9.302(4)A,b=4.3967(10)A,c=8.454(4)A,β=116. 82(3)°) and isotypic with OsO₄. There is one independent molecule in the unit cell, which shows distances Ru-O of 1.697 and 1.701 A, respectively.

Full text of DOI:10.1016/j.jssc.2005.07.021

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Journal of Solid State Chemistry 178 (2005) 3206–3209
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Two crystalline modifications of RuO4
Ã
Martin Pley, Mathias S. Wickleder
Institut fu¨r Reine und Angewandte Chemie, Universita¨t Oldenburg, P.O. Box 2503, 26111 Oldenburg, Germany
Received 24 May 2005; received in revised form 21 July 2005; accepted 23 July 2005
Available online 26 August 2005
Abstract
RuO4 was prepared by oxidation of elemental ruthenium. Two different modifications were obtained and investigated by X-ray
(
single crystal diffraction. RuO4-I has cubic symmetry ðP4;À3n; Z ¼ 8; a ¼ 8:509ð1Þ AÞ, and two independent tetrahedral molecules
are present in the unit cell. Within the standard uncertainties in both molecules the distances Ru–O are 1.695 A. The second
(
(
(
modification, RuO4-II, is monoclinic ðC2=c; Z ¼ 4; a ¼ 9:302ð4Þ A; b ¼ 4:3967ð10Þ A; c ¼ 8:454ð4Þ A; b ¼ 116:82ð3Þ1Þ and isotypic
with OsO4. There is one independent molecule in the unit cell, which shows distances Ru–O of 1.697 and 1.701 A, respectively.
r 2005 Elsevier Inc. All rights reserved.
Keywords: Solid state structures; Molecular structures; Ruthenium; Oxides
1. Introduction
various applications, we consider the structure of this
compound as a basic information of utmost importance.
In course of our investigations of compounds with
complex oxo-anions [1] we use the tetraoxides of
osmium and ruthenium as starting materials for the
synthesis of ruthenates and osmates [2]. The tetraoxides
are known to be low melting volatile molecular solids.
Despite of their toxicity both compounds are used as
oxidants for various purposes [3]. In particular RuO4
has attracted considerable attention in organic chem-
istry because it shows remarkable difference in reactivity
compared to OsO4 [4]. Furthermore, it is frequently used
as a staining agent for polymers [5]. With respect to
these important applications, it is astounding that no
structural data of RuO4 are reported up to now. There is
only one paper from the late 1960s that claims isotypism
of RuO4 with OsO4 based on powder diffraction
measurements [6]. In the present communication, we
present the molecular and crystal structures of two
modifications of RuO4. It is only the second example of
a structurally characterized octavalent binary com-
pound. With respect to the potential of RuO4 and its
2. Experimental
2.1. Synthesis
We prepared RuO4 according to the literature
procedure by oxidation of elemental ruthenium in a
KMnO4/KOH melt, and further treatment with KMnO4
and diluted H2SO4 in aqueous solution [7]. Upon
heating the reaction mixture, RuO4 was driven off and
condensed in a cooling trapas yellow-orange crystals.
Interestingly, two different crystal forms could be
distinguished: needles and cubes. Inspection of the
crystals under a polarizing microscope revealed that
their symmetry must be different. Thus, a specimen of
each form was investigated by X-ray single crystal
diffraction.
Caution: The preparation of RuO4 and all manipula-
tions must be done under special safety precautions.
RuO4 is very toxic and highly volatile. It is necessary to
work in a well ventilated hood and to wear appropriate
eye protection.
Ã
Corresponding author. Fax: +49 441 798 3352.
E-mail address: mathias.wickleder@uni-oldenburg.de
(M.S. Wickleder).
0022-4596/$ - see front matter r 2005 Elsevier Inc. All rights reserved.
doi:10.1016/j.jssc.2005.07.021

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3207
2.2. X-ray crystallography
and are available on quoting the deposition numbers
given in Table 1.
The reflection intensities of a block-shaped single crystal
(approx. 0.1 ꢀ 0.1 ꢀ 0.15 mm) of RuO4-I and a needle-
shaped single crystal of RuO4-II were measured with an IP
diffractometer (IPDS II, Stoe & Cie) at 170 K. The
structure solutions were successful assuming the space
group P4;À3n for RuO4-I and C2/c for RuO4-II using
direct methods provided by the program SHELXS-86 [8].
Least-squares refinements were carried out with SHELXL-
97 [8], and for all atoms anisotropic thermal displacement
parameters were introduced. Finally, numerical absorp-
tion corrections were carried out using the programs
X-SHAPE and X-RED [9]. Details of the data acquisition
and the crystallographic data are summarized in the
Tables 1 and 2. Additionally, the data have been deposited
with the Fachinformationszentrum Karlsruhe, D-76344
Eggenstein-Leopoldshafen (crysdata@FIZ-Karlsruhe.de)
3. Results and discussion
The X-ray single crystal investigations revealed that
RuO4 is dimorphic and has a cubic and monoclinic
crystal structure. In the unit cell of the cubic modifica-
tion, hereafter named RuO4-I, two crystallographically
independent RuO4 molecules are present. One RuO4
molecule has the symmetry 23 (T with respect to the
nomenclature of Schoenflies) according to the location of
the respective ruthenium atom on the Wyckoff position
2a of space group P4;À3n. Accordingly, the molecule
shows six ideal tetrahedral angles (Table 2). The other
molecule exhibits four symmetry (S4) with ruthenium on
the 6c position, and only minor distortions from ideal
Table 1
Crystallographic data of the two modifications of RuO4
RuO4-I
RuO4-II
165.03
Formula weight (g/mol)
Unit cell parameters
165.03
(
(
a ¼ 8:509ð1Þ A
a ¼ 9:302ð4Þ A
(
b ¼ 4:3967ð10Þ A
(
c ¼ 8:454ð4Þ A
b ¼ 116:82ð3Þ1
Cell volume
Z
616.1(1) A3
8
308.6(2) A3
4
Exp. density
Crystal shape
Crystal size
Crystal system
Space group
Measuring device
Radiation
3.559 g/cmÀ3
Block
3.553 g/cmÀ3
Needle
0.1 ꢀ 0.1 ꢀ 0.15 mm3
0.1 ꢀ 0.1 ꢀ 0.3 mm3
Cubic
P4;À3n
Monoclinic
C2/c
Stoe IPDS II
Mo-Ka (graphite monochromator; l ¼ 71.07 pm)
Temperature
Ymax
Index range
170 K
281
281
À11phX11
À11pkX11
À11plX11
01ooo1801; 21
(2 runs at j ¼ 01,901)
180
À12phX12
À5pkX5
À11plX10
o-range; o-increment
01ooo1801; 21
(2 runs at j ¼ 01,901)
Number of exposures
Irradiation/exposure
Detector distance
Absorption correction
Absorption coefficient
Tmin/Tmax
180
4 min
100 mm
5
100 mm
Numerical, after crystal shape optimisation [12]
4.887 mmÀ1
0.2990, 0.5839
4.895 mmÀ1
0.2970, 0.5638
9480
Measured reflections
Unique reflections
Observed with I42sðIÞ
Rint=Rs
Structure determination
Scattering factors
Goodness of fit
1522
371
257
189
347
0.0674/0.0141
0.0871/0.0540
SHELXS-86, SHELXL-97 [11]
Intern. Tables. Vol. C
1.18
1.11
R1; wR2 (I42s(I))
R1; wR2 (all data)
Flack-x
0.0245; 0.0540
0.0254; 0.0600
0.26
0.0431; 0.1162
0.0442; 0.1170
Deposititory no.
CSD415303
CSD415306

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3208
Table 2
Atomic coordinates, Wyckoff notation and selected distances and angles for RuO4-I and RuO4-II
Atom
Wyckoff
x/a
y/a
z/a
RuO4-I
Ru1
Ru2
O1
2a
6c
0
3/4
0
1/2
0
0
8e
24i
0.8850(9)
0.8647(6)
x
x
O2
0.3887(6)
0.8809(4)
RuO4-II
Ru1
O1
4e
8f
8f
0
0.2408(1)
0.4658(9)
0.0165(9)
3/4
0.6938(4)
0.9238(4)
0.1186(4)
0.1180(4)
O2
Distances(A) and angles(1)
RuO4-I
RuO4-II
Ru1–O1
Ru2–O2
1.695(13) (4x)
1.696(5) (4x)
Ru1–O1
Ru1–O2
1.697(3) (2x)
1.701(4) (2x)
O1–Ru1–O1
O2–Ru2–O2
109.47 (6x)
109.3(1) (4x)
109.8(3) (2x)
O1–Ru1–O1
O2–Ru1–O2
O1–Ru1–O2
O1–Ru1–O2
108.9(3)
108.9(2)
109.4(2) (2x)
110.1(2) (2x)
Fig. 1. Crystal structures of RuO4-I (left) and RuO4-II (right). Both crystals consist of tetrahedral RuO4 molecules, which are drawn in a polyhedral
style. The arrangement of the molecules is different in the two modifications leading to cubic (RuO4-I) and monoclinic (RuO4-II) symmetry,
respectively.
tetrahedral symmetry are found with respect to the
observed angles. In both molecules the Ru–O distances
are equal within the standard uncertainties, and found to
be 1.695 A (Table 2). The monoclinic modification of
ruthenium tetraoxide, RuO4-II, is isotypic with OsO4
[10]. Crystallographically, there is only one RuO4
molecule in the unit cell, which has the symmetry 2 (C2
according to Schoenflies) with respect to the location of
the Ru atom on the 4e site of space group C2/c.
However, judged from the nearly identical distances
Ru–O of 1.697(3) and 1.701(4) A (Table 2) and the
almost tetrahedral angles O–Ru–O (108.9(2)–110.1(2)1)
the molecule is essentially a perfect tetrahedron. Within
the standard deviations the distances Ru–O are almost
the same as found for RuO4-I. Moreover, the distances of
both modifications are only slightly different from those
reported for OsO4 (1.684 and 1.710 A, respectively) [10].
However, the deviation from ideal tetrahedral symmetry
is more prominent in OsO4 as can be seen from the
respective angles O–Os–O which range from 106.61 to
110.71.
The difference between the crystal structures of the
two modifications of RuO4 is the arrangement of the
RuO4 molecules with respect to each other (Fig. 1). This
can be seen best by comparing the distances between the
tetrahedra-centers in both compounds. In the crystal
structure of RuO4-II one RuO4 molecule is surrounded
by 12 other molecules, leading to distances Ru–Ru

ARTICLE IN PRESS
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3209
between 4.397 and 5.144 A. Contrastingly, in the
structure of RuO4-I one of the two crystallographically
different molecules has 12 neighbor tetrahedra with the
distances Ru–Ru being uniformly 4.757 A, and the
second RuO4 molecule has even 14 neighbors with the
respective distances ranging from 4.255 to 5.211 A.
Although the packing of the tetrahedral molecules is
different in both modifications, the molar volumes are
identical (46.4 cm3/mol).
Forschungsgemeinschaft (Graduiertenkolleg 549) is also
gratefully acknowledged.
References
[1] M.S. Wickleder, Chem. Rev. 102 (2002) 2011–2087.
[2] M.S. Wickleder, M. Pley, J. Solid State Chem. 177 (2004)
2073–2078.
Another description of the two crystal structures can
be given, when the arrangement of the oxygen atoms in
both structures is regarded as a ccpof spheres. Then, 1/8
of the tetrahedral voids must be filled by the metal
atoms. It is easy to imagine that there will be different
possibilities to distribute the metal atoms over the
tetrahedral holes, and that the structures of RuO4-I and
RuO4-II are only two of the possible filling patterns. As
another example the crystal structure of SnI4 (space
group Pa3) can be given, which follows the same motif
[11]. Finally it should be mentioned that a similar
dimorphism as reported here for RuO4 has been found
for OsF2O2 some 30 years ago [12]. However, upto now
we were not able to detect a phase transition between the
two modifications of RuO4 by means of temperature
dependent XRD.
[3] (a) I.W.C.
E Arends, T. Kodama, R.A. Sheldon, Topics
Organomet. Chem. 11 (2004) 277–320;
(b) B. Plietker, J. Org. Chem. 69 (2004) 8287–8296;
(c) L.S.M. Miranda, M.L. Vasconcellos, Synthesis 11 (2004)
1767–1770.
[4] (a) J. Frunzke, Ch. Loschen, G. Frenking, J. Am. Chem. Soc. 126
(2004) 3642–3652;
(b) S. Ranganathan, K.M. Muraleedharan, D. Bhattacharyya,
D. Kundu, J. Ind. Chem. Soc. 75 (1998) 583–589.
[5] H.G. Haubruge, A.M. Jonas, A.M.R. Legras, Polymer 44 (2003)
3229–3234.
[6] J. Trehoux, D. Thomas, D.G. Nowogrocki, G. Tridot, C. R. Seances.
Acad. Sci. C 268 (1969) 246–249.
[7] G. Brauer, Handbuch der praparativen anorganischen Chemie,
¨
F. Enke, Stuttgart, 1975, p. 1750-1.
[8] (a) G.M. Sheldrick, SHELXS-86, Program for the Solution of
¨
Crystal Structures, Gottingen, Germany 1986;
(b) G.M. Sheldrick, SHELXL-97, Program for the Refinement of
Crystal Structures, Gottingen, Germany 1997.
¨
[9] (a) X-SHAPE 1.01, Crystal Optimisation for Numerical Absorp-
tion Correction, Stoe & Cie, Darmstadt, Germany 1996;
(b) X-RED 1.07, Data Reduction for STADI4 and IPDS, Stoe &
Cie, Darmstadt, Germany 1996.
Acknowledgments
[10] B. Krebs, K. Hasse, Acta Crystallogr. B 32 (1976) 1334–1337.
[11] H. Reuter, R. Pawlak, Z. Kristallogr. 216 (2001) 34–38.
[12] R.D. Burbank, J. Appl. Crystallogr. 7 (1974) 41–44.
We thank Prof. G. Meyer, University at Cologne, for
generous support. Financial support of the Deutsche