Molybdenum difluoride dioxide, MoO2F2

Article abstract of DOI:10.1021/ic1000864

MoO₂F₂ is prepared by pyrolysis of (Na ⁺H₂O)₂ cis-MoO₂F₄ ^2-. A preliminary model of the structure is obtained from powder data: it has a triangular columnar structure with three fluorine bridges between the three molybdenum atoms and with oxygen bridges between the layers. (a = 1605, b = 384, c = 1395 pm, Pnma, Z = 12). The closest related structure is that of TiF₄, except that the orientation of the triangular columns is different.

Full text of DOI:10.1021/ic1000864

Inorg. Chem. 2010, 49, 4263–4267 4263
DOI: 10.1021/ic1000864
Molybdenum Difluoride Dioxide, MoO2F2
Hashem Shorafa,† Halil Ficicioglu,† Farhad Tamadon,† Frank Girgsdies,‡ and Konrad Seppelt*,†
†
€
Anorganische und Analytische Chemie, Institut fu€r Chemie, Freie Universitat, Fabeckstrasse 34-36, D-14195 Berlin,
Germany, and ‡Department of Inorganic Chemistry, Fritz Haber Institut, Faradayweg 4-6, D-14195 Berlin, Germany
Received January 25, 2010
MoO2F2 is prepared by pyrolysis of (NaþH2O)2 cis-MoO2F42-. A preliminary model of the structure is obtained from
powder data: it has a triangular columnar structure with three fluorine bridges between the three molybdenum atoms
and with oxygen bridges between the layers. (a = 1605, b = 384, c = 1395 pm, Pnma, Z = 12). The closest related
structure is that of TiF4, except that the orientation of the triangular columns is different.
Introduction
then a model would result in which all fluorine atoms are in
bridging positions, and the oxygen atom are terminal and in
cis position to each other.
However, there are exceptions from these simple rules:
Isoelectronic NbOF3 and also TaOF3 obviously have six
coordinated metal atoms in a SnF4 type structure, but there
seems to be an O, F disorder with some oxygen atoms also in
bridging positions.6,7
ReO3F, where a six coordination would demand at least one
bridging oxygen atom, has indeed a helical chain structure with
one fluorine and one oxygen bridge in cis position, while the
other two oxygen atoms are cis positioned in terminal posi-
tions.8 TcO3F is isoelectronic to MoO2F2. In the solid state it is a
The theoretical interest on MoO2F2 is twofold. First, its
molecular structure is expected to be different from main
group compounds with similar composition, for example,
1
SO2F2. The structures of the latter can qualitatively be
described by the valence shell electron pair repulsion model.2
This simple model fails for MoO2F2. Theoretical predictions
based on calculations predict an OdModO angle of about
106° and the F-Mo-F angle at 113°.3
Experimental values for the MoO2F2 molecular structure
seem to be unknown, but the related MoO2Cl2 has indeed
such a structure with OdModO 104.0(20)° and Cl-Mo-Cl
112.0(10)°.4 Simplified, it can be said that two double bonded
atoms to transition metal atoms will preferentially have
angles close to 90° to avoid occupation of the same metal
d-orbital by the π bonds of the ligands.
The solid state structure of MoO2F2 is also unknown.
Certainly the molecule will undergo polymerization via
ligand bridging, a coordination number of six with a close
to octahedral structure is most likely, with two bridges
between molybdenum atoms. Alternatively, a five coordinate
polymer with one bridge could also occur. Among transition
metal fluoride oxides bridging occurs usually through the F
atoms; MoOF4 is a prominent example out of very many
known compounds.5 If this behavior is applied to MoO2F2,
fluorine bridged dimer with additionally one weak O Tc
3 3 3
interaction, so the coordination could be described as 5 þ 1.9
MoO2F2 is reported to be obtained in the reactions 110, 211,
312, 413, 514,15, 614, and 716 as follows:
430°C
MoO3 þ NF3
MoO F ðmass spectrumÞ
f
2
2
þ NOþMoO2F3
ð1Þ
-
€
€
(6) Kohler, J.; Simon, A.; van Wullen, L.; Cordier, S.; Roisnel, T.;
Poulain, M.; Somer, M. Z. Anorg. Allg. Chem. 2002, 628, 2683–2690.
(7) Brink, F. J.; Withers, R. L.; Cordier, S.; Poulain, M. J. Solid State
Chem. 2006, 179, 341–348.
(8) Supez, J.; Marx, R.; Seppelt, K. Z. Anorg. Allg. Chem. 2005, 631, 2979–
2986.
(9) Supez, J.; Abram, U.; Hagenbach, A.; Seppelt, K. Inorg. Chem. 2007,
46, 5591–5595.
(10) Glemser, O.; Wegener, J.; Mews, R. R. Chem. Ber. 1967, 100, 2474–
2483.
(11) Ward, B. J.; Stafford, E. F. Inorg. Chem. 1968, 7, 2569–2573.
(12) Bartlett, N.; Robinson, P. L. J. Chem. Soc. 1961, 3549–3550.
(13) Aynsley, E. E.; Nichols, R.; Robinson, P. L. J. Chem. Soc. 1953, 623–
626.
(14) Atherton, M. J.; Holloway, J. H. J. Chem. Soc., Chem. Commun.
1978, 254–255.
(15) Ruff, O.; Eisner, F. Chem. Ber. 1907, 40, 2926–2935.
(16) Brisdon, A. K.; Holloway, J. H.; Hope, E. G. J. Fluorine Chem. 1998,
89, 35–37.
*To whom correspondence should be addressed. E-mail: seppelt@chemie.
fu-berlin.de.
(1) Hagen, K.; Cross, V. R.; Hedberg, K. J. Mol. Struct. 1978, 44, 187–
193.
(2) Gillespie, R. J.; Robinson, E. A. Angew. Chem. 1996, 108, 539–560.
Gillespie, R. J.; Robinson, E. A. Angew. Chem., Int. Ed. Engl. 1996, 35, 495–
514.
(3) Kaupp, M. Chem.;Eur. J. 1999, 5, 3631–3643.
(4) Zasorin, I. M.; Spiridonov, E. Z.; Novikov, V. P.; Kupreev, G. I.
Koord. Khim. 1975, 1, 574. Zasorin, I. M.; Spiridonov, E. Z.; Novikov, V. P.;
Kupreev, G. I. Coordination Chem. (Engl. Transl.) 1975, 1, 473.
(5) Edwards, A. J.; Stevenson, B. R. J. Chem. Soc. A 1968, 2503–2510.
Edwards, A. J.; Stevenson, B. R. J. Chem. Soc., Chem. Commun. 1967, 462–
463.
r
2010 American Chemical Society
Published on Web 04/09/2010
pubs.acs.org/IC

4264 Inorganic Chemistry, Vol. 49, No. 9, 2010
Shorafa et al.
Table 1. Crystallographic Data for Na2MoO2F4 H2O, MoO2F2 2DMF, and MoO2F2
3
3
a
Na2MoO2F H2O
3
MoO2F2 2DMF
3
MoO2F2
chemical formula
Mr
cryst. syst.
space group
temp (°C)
a/pm
F4H2MoNa2O3
265.92
orthorhombic
P212121 (No. 19)
-140
543.6(1)
575.5(1)
1914.3(4)
90
598.86
4
2.95
2.36
7349, 1822
0.0473, 0.1199, 1.262
93
C6F2H14MoN2O4
312.13
monoclinic
C2/c
F2MoO2
165.94
orthorhombic
Pnma (No. 62)
23
1605.9(8)
386.46(1)
1395.14(7)
90
864.5(2)
12
3.825
4.4
232
-140
1253.8(2)
782.4(1)
1157.1(2)
98.982(3)
1121.2
b/pm
c/pm
ss/deg
V/106 pm3
Z
4
1.849
1.195
9379, 1711
0.0205, 0.0541, 1.120
75
Dcalcd/g cm-3
μ/mm-1
measured and independent
R(F1), Rw(F2), S
parameters
0.15(RI)
35
a Powder data, Rietveld refinement, see text and Figure 3.
500°C
1000 TU diffractometer, using Mo KR irradiation, a graphite
monochromator, a scan width of 0.3° in ω, and a measuring
time of 20 s per frame. After semiempirical absorption
corrections (SADABS) by equalizing symmetry-equivalent
reflections, the SHELX programs were used for solution
and refinement18. Results are summarized in Table 1, experi-
mental details in Table 2.
Powder data were obtained first with a Stoe Stadi/P
powder diffractometer with Cu KR radiation and a sample
in a 0.3 mm silica capillary. In a second experiment the
diffraction measurements were performed in Bragg-Brentano
reflection geometry on a Bruker AXS D8 Advance diffract-
ometer equipped with a secondary graphite monochromator
(Cu KR radiation) and scintillation detector. This sample
powder was handled in a glovebox and filled into the recess
of a sealable airtight sample holder, yielding a flat surface of the
sample bed. The data acquisition was performed in five con-
secutive scans with a counting time of 3 s/step and a step width
of 0.02° 2θ. After confirming that the diffraction patterns
exhibited no significant change over the total acquisition time
of 20 h, the five data sets were summed up to yield a total
counting time of 15 s/step.
MoO3 þ LiF
MoO F ðgas ir:Þ
ð2Þ
ð3Þ
ð4Þ
ð5Þ
f
2
2
MoO3 þ SeF4 f MoO2F2 SeF4
3
MoO3 þ IF5 f 2MoO2F2 3IF5
3
MoO2Cl2 þ HF f MoO2F2
HF
MoO2Cl2 þ XeF2
MoO F ði:r:Þ
ð6Þ
f
2
2
120°C
Na2MoO4 þ IF5
MoO F ðRamanÞ
ð7Þ
f
2
2
There is so far no reliable mode of preparation for
MoO2F2. The first two reactions show the presence of
MoO2F2 molecules in the gaseous state at high temperature.
Reactions 3 and 4 produce adducts, whose structural details
are unknown. We will show below that MoO2F2 does not
tolerate anhydrous HF, so that the products of reaction 5 and
6 cannot be MoO2F2, as indicated also by the published
vibrational spectra. Reaction 7 produces a product similar to
that of reaction 6, and also adduct formation with IF5 is
expected.10
Na2MoO2F4 2H2O. Na2MoO2F4 is obtained by dissolving
3
1 g of Na2MoO4 in 3 mL of hydrofluoric acid containing 13.3%
HF by warming under stirring to approximately 50 °C. The
colorless solvent is cooled to room temperature, and a colorless
solid crystallizes out. The liquid is decanted, and the solid is
dried in vacuum, see below. Single crystals of Na2MoO2F4
2H2O are grown by slow cooling from 50 °C to room tempera-
ture.
3
19F-NMR (D2O, RT): δ = 84.21 ppm, w1/2 = 1000 Hz.
Raman (solid, RT): 971(100), 922(50), 571(10), 549(2), 427(2),
380(25), 311(25), 299(10,sh), 276(4), 229(1), 207(2), 179(2),
144(4), 144(10), 94(10) cm-1. IR (NaCl, RT): 3436 (m, vbroad),
193(w), 1889(w), 1852(w), 1632(w), 1381(w), 974(vs), 930(vs),
582(vs), 550(vs), 442(s), 407(vs) cm-1
Experimental Section
General experimental procedures:
Moisture sensitive materials were handled in the dry argon
atmosphere of a glovebox with a water content of less than
1 ppm. Volatile compounds were manipulated in a vacuum line.
Solvents were dried by standard methods. NMR spectra
were recorded using a JEOL NMR-LA 400 spectrometer
(1H at 399.65 MHz, 13C at 100.4 MHz, and 19F at 376.00
MHz). Chemical shift values are reported with respect to
tetramethylsilane (TMS) (1H, 13C) and CCl3F (19F). Raman
spectra were recorded on a Bruker RFS 100 FT-Raman
spectrometer. Mass spectra were recorded on a Varian
MAT 711 instrument.
MoO2F2. Na2MoO2F4 2H2O is dried overnight in vacuum
3
and filled into a Monel cylinder, with a water cooled top. Slow
heating to 400° in vacuum for 24 h results in the formation of a
yellow-gray sublimate at the cooled top of the cylinder. Resu-
blimation in a 30 mm long silica tube in vacuum results in a
slightly yellow, plastic material. A 200 mg portion of this is filled
into a silica tube, oxygen up to 1 bar is added, and the silica tube
is sealed. Repeated slow heating to 280° and cooling to 240 °C
produced a white, cottonlike material. Only material with direct
Single crystals were handled in a special device 17, cut to an
appropriate size, and mounted on a Bruker SMART CCD
€
(18) Sheldrick, S. Program for Crystal Structure Solution; Universitat
€ € €
Gottingen: Gottingen, Germany, 1986; Sheldrick, S. SHELXS; Universitat
(17) Schumann, H.; Genthe, W.; Hahn, E.; Hossein, M.-B.; Helm, D. v. d.
€ €
Gottingen: Gottingen, Germany, 1997.
J. Organomet. Chem. 1986, 28, 2561–2567.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4265
Table 2. Mo-O and Mo-F Bond Lengths (pm) and Angles (deg)
Na2MoO2F2 H2O
3
MoO2F2 2DMF
3
Mo-O
168.5(5), 170.6(6)
169.5(1)
223.5(1)b
189.9(1)
Mo-F
axa) 192.8(5), 196.3(5)
eqa) 206.4, 212.6(4)
102.7(3)
O-Mo-O
F-Mo-F
103.3(1)
78.38(6)b
155.19(8)
ax 158.2(2)
eq 75.6(2)
c
MoO2F2
Figure 1. Anion cis MoO2F4 in the crystal structure of (NaþH2O)2
2-
d
cis-MoO2F42-, Ortep representation, 50% probability ellipsoids.
Mo-Obr
194.2(5), 195.7(7), 194.4(4)
Mo-Fbr
212(2), 215(3), 209(2), 203(2), 205(3), 203(2)
173(2)-177(3)
169(3), 162(2), 167(2)
Mo-O,Fte
Mo-O-Mo
Mo-F-Mo
167(2), 170(2), 152(2)
a ax = axial, eq = equatorial relative to the MoO2 plane. b Mo
O
3 3 3
contacts to DMF. c powder data, Rietveld refinement, see text. d br =
bridging atom. e Terminal, disordered O and F atoms.
contact to the silica wall turned slightly blue, indicating reduc-
tion to lower molybdenum compounds.
Raman spectrum (yellow plastic material). 1085 (w, MoOF4),
1013 s, 852 s, br, 685 m, 450 w, br, 397 m, 280 m, 154 w, cm-1
.
Raman spectrum (white cryst.): 1085 (w, MoOF4), 1014 m,
830 vs, 581 w, 396 w, 374 w, 353 w, 344, 281 m, 271 w, sh, 281 m,
271 w, sh, 202 w, 189 w, 117 w, cm-1
.
Mass spectrum, (EI rel to 98Mo), m/z = 168 (MoO2F2þ
100%), 149 (MoO2Fþ, 45%), 133 (MoOFþ, 10%), 130 (MoO2
10%), 114(MoOþ, 5%), 98 (Moþ, 5%).
,
,
þ
Figure 2. Structure of MoO2F22 DMF in the crystal, Ortep representa-
3
tion, 50% probability ellipsoids.
MoO2F2 2DMF. A 300 mg portion of the yellow sublimate is
3
We assumed, as it turned out correctly, that MoO2F2 is a
very coordinatively unsaturated compound, so that presence
of any basic material has to be avoided.
loaded into a prepassivated 8 mm PFA ampule. N,N-dimethyl-
formamide (DMF, 3 mL) is added to the ampule followed by
1 mL of propionitrile. The mixture is allowed to warm to room
temperature, stirred for 15 min to homogenize, and cooled
slowly to -78 °C to give colorless crystals of the air stable
At first we isolated Na2MoO2F4 2H2O in pure form from
3
Na2MoO4 and aqueous HF by a variation of the method for
the preparation of K2MoO2F4 (cis) 19. It is important to work
with an 13% HF concentration in H2O. NaHF2 as a side
product can be separated by fractional crystallization. The
compound MoO2F2 2DMF.
3
X-ray Powder Measurement and Structure Determination.
Powder data could be indexed resulting in lattice constants
as shown in Table 1. The orthorhombic cell with V = 864.5 ꢀ
106 pm3 contains 12 molecular units, if a volume of 17-18 ꢀ
106 pm3 is assumed for O and F atoms and Mo atoms occupying
octahedral holes. At this point it became evident that the
structure may be related to that of TiF4, although the metric
of the latter is quite different (with exception of the b axis and the
cell volume). Setting the Mo atom in reasonable positions gave
the starting model. First, refinements were done by the program
LX15LS of WIF David, 1919 Science Division, Butterford
Appleton Lab, Chilton, U.K. The program Topas [Topas v3,
copyright 1999, 2000 Bruker AXS] was used to perform further
Rietveld structure refinements on this structure model. At first
displacement factors were not refined and arbitrarily set to unity
for all atoms, and a single displacement factor was refined later for
all atoms. The background was fitted using a second order
Chebychev polynomial plus two pseudo-Voigt functions describing
two broad bumps in the background. The peak shapes were
described using the fundamental parameters approach, that is,
an instrument function which was calculated from the known
instrument parameters was numerically convoluted with the sam-
ple peaks function. The latter consisted of two Lorentzian con-
tributions, one with a 1/cos(θ) and one with a tan(θ) dependence.
identity of this salt is established by its single crystal structure
2-
which shows isolated Naþ H2O and cis-MoO2F4 units,
3
see Figure 1. Bond lengths and angles, see Table 1, have the
expected values. The Raman spectrum serves as a test for the
purity (absence of the symmetric stretching mode 628 cm-1
and the lattice mode at 144 cm-1 of HF2-), and also it shows
the characteristic two strong ModO stretching vibrations
close to 1000 cm-1 characteristic of the cis-MoO2 configu-
ration, see Experimental Section.
Na2MoO2F4 H2O is then pyrolized in vacuum. Till 260 °C
3
only the crystal water is liberated, as is evidenced by the DTA
measurement and the almost complete disappearance of the
broad H2O band at 3436 cm-1 in the IR spectrum. At 300 °C
MoO2F2 sublimes out of the salt as a slightly yellow, glassy
material. This is completely amorphous according to X-ray
powder measurements.
300°C
Na2MoO2F4
2NaF þ MoO F
f
2
2
The vacuum pyrolysis has also been done in a mass
spectrometer where the parent ion MoO2F2þ as the one with
highest mass has been identified.
Results
Our approach has been to obtain MoO2F2 in a reproducible
and straightforward way. After testing the previously described
reactions, we found that often the products have been MoOF4,
H3OþMo2O2F9-, or mixtures of unclear compositions.
(19) Chaminade, J. P.; Mouton, J. M.; Villeneuve, G.; Conzi, M.;
€
Pouchard, M.; Hagenmuller, P. J. Sol. State Chem. 1986, 65, 27–39.

4266 Inorganic Chemistry, Vol. 49, No. 9, 2010
Shorafa et al.
Figure 3. X-ray powder diagram of MoO2F2: Upper trace, dots: experimental intensity, line: calculated model. middle trace: position of calculated lines.
lower trace difference experimental/calculation. Arrows: indicate strongest deviation.
MoO2F2 is a very reactive species. Organic solvents usually
cause reduction under formation of blue deposits. Only from
a dimethylformamide solution have we been able to grow
single crystals. These contain two DMF molecules attached
to the molybdenum atom via their oxygen atoms, trans
positioned to the ModO bonds, so that the coordination of
the molybdenum atom is now distorted octahedral, see
extremely thin needles like cotton wool. This material is
by far too fine for a single crystal structure determination.
X-ray data from the powder could be obtained, however,
and lattice constants and the space groups Pnma or Pna21,
can be secured. To minimize the number of parameters and
in analogy to the TiF4 structure, the centrosymmetric space
group Pnma was chosen for further refinement. As can be
seen in Figure 3, the powder data are far from perfect. There
seems to be a strong background, possibly from residual
amorphous material. Also some lines do not belong to the
bulk material. Their intensity varies, so there must be an
impurity present. Raman data indicate the presence of
MoOF4, but the known X-ray data cannot be fitted to the
impurity lines. But it is quite possible that MoOF4 exists in
other modifications than the one reported. (The structurally
related ReO2F3 comes in four different modifications8)).
Rietveld refinement in space group Pnma produced the
position of three independent molybdenum atoms in the
cell. These form triangular columns, see Figure 4. The
Figure 2. A similar compound, MoO2F2 2THF has been
3
accidentally found, possibly by hydrolysis of MoF4NCl
3
THF, and also has been characterized by a single crystal
structure determination 20. Recently MoO2F2 2(R3)PO
3
(R = CH3, C6H5) have been obtained by a chlorine-fluorine
exchange reaction from MoO2Cl2(CH3)3PO 21. MoO2F2
dissolves in anhydrous HF under partial oxygen fluorine
exchange. The resulting mixture could not be fully ana-
lyzed. A part of crystalline material seems to be H3Oþ-
Mo2O2F9- according to an imperfect single crystal struc-
ture determination. So any preparative method in presence
of HF should be useless. All in all it seems impossible to
find a suitable solvent for preparation of single crystals of
neat MoO2F2.
Mo Mo separation between the layers of the columns
3 3 3
is 386 pm, the separations within one triangle are 406, 410,
and 414 pm, and between columns the shortest separa-
tions are 499, 500, and 502 pm.
Structural Model for MoO2F2. Similar to ReO3F8
annealing of amorphous MoO2F2 resulted in crystalliza-
tion. But still there are shortcomings: At the necessary
temperature of 290 °C MoO2F2 starts to decompose,
which is indicated by the appearance of a blue color. If
the sample is kept in quartz tubes under a mild pressure (a
few bar) of oxygen, the decomposition seems to be slowed
down. Glassy yellow MoO2F2 then changes into white,
The Rietveld refinement also provides the positions of
bridging atoms between layers and within the triangles. The
bridging atoms between layers are equidistant from the Mo
atoms, with slightly bent bridge angles. The resulting bond
distances of about 195 pm are typical for a Mo-O-Mo
bridge, as in MoO3 (194.8 pm,22 198.0 pm23), or in ReO3
(20) Riehl, M.; Wocadlo, S.; Massa, W.; Dehnicke, K. Z. Anorg. Allg.
Chem. 1996, 622, 1195–1199.
(21) Davis, M. F.; Levason, W.; Ratnani, R.; Reid, G.; Rose, T.; Webster,
M. Eur. J. Inorg. Chem. 2007, 306–313.
(22) Kihlborg, L. Ark. Kemi 1963, 21, 357–364.
(23) Balerna, A.; Bernieri, E.; Burattini, E.; Kuzmin, A.; Lusis, A.;
Purans, J.; Cikmach, P. Nucl. Instrum. Methods Phys. Res. 1991, A308,
234–239.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4267
Figure 4. Structural model of MoO2F2 from X-ray powder data. Term-
inal atoms are fluorine and double bonded oxygen atoms, most likely in a
disordered manner.
(186.6 pm,24 187.825) to name but a few examples. The
Mo Mo distances within the layers of 411 and 417 pm
3 3 3
calls for a Mo-F-Mo bridge. In MoOF4 this (asymmetric
and bent) bridge results in a Mo Mo separation of
3 3 3
410.9 pm.5 In MoO2F2 the Mo-F-Mo bridges are essen-
tially symmetric and slightly bent. The total structure
resembles that of TiF4.26 As can be seen in Figure 4 and 5,
only the relative orientation of the triangular columns are
different in MoO2F2 and TiF4. This may be due to the fact
that the outer boundary of the TiF4 columns are only
fluorine atoms, but in MoO2F2 they are fluorine and oxygen
atoms. The terminal oxygen and fluorine atoms in the
MoO2F2 structure were difficult to locate in the Rietveld
refinement, but the vibrational spectra can help somewhat.
The Raman spectrum changes considerably upon anneal-
ing. The amorphous product has only one distinct ModO
stretching vibration at 1013 cm-1 and a very broad feature
between 800 and 950 cm-1. After annealing the distinct
vibration remains at 1014, but the broad feature narrows to
a vibration at 830 cm-1. If the two oxygen atoms would be
both terminal, then two sharp vibrations in the 1000 cm-1
area should be observed. A good example for this is the
Figure 5. Comparison of the MoO2F2 (above) and the known TiF4
(below) structure, view in both cases along the b axis. Note that the
orientation of the triangular columns to each other is different.
fluorine are quite similar, bond lengths (ModO ca. 170
pm, Mo-F ca. 190 pm) and bond angles are quite different.
The possible presence of both oxygen and fluorine
bridges is paralleled in the structure of NbOF3, where
oxygen atoms seem to be disordered over all possible
positions, and ReO3F, where ordered oxygen and fluor-
ine bridges occur in an ordered manner.
Conclusion
Crystalline MoO2F2 has a triangular columnar structure,
similar to the TiF4 structure. The whisker type of the crystal
shape is understandable with this structure model. More
precise information about the oxygen and fluorine positions
might be obtainable from synchrotron and neutron powder
measurements, which are planned. But even then severe
disorder of the terminal oxygen and fluorine atoms could
hamper these efforts, as is indicated by a first experiment with
synchrotron radiation.
2-
Raman spectra of the ReO3F polymer, or the MoO2F4
anion, see Experimental Section. In agreement with the
arguments from the Rietveld refinement there is obviously
only one terminal oxygen atom and then, as a consequence,
one terminal fluorine atom. The strong Raman vibration at
830 cm-1 could derive from the Mo-O-Mo bridge.
The two terminal atoms are expected to conclude the
distorted octahedral coordination of the molybdenum
atoms. The difficulty in locating is almost certainly an O/
F disorder. While the electron densities of oxygen and
Acknowledgment. We gratefully acknowledge help with
the interpretation of the powder data of MoO2F2 by
Dr. Rupert Marx, Berlin, and financial support from
the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie.
(24) Meisel, K. Z. Anorg. Allg. Chem. 1932, 207, 121–128.
(25) Jørgenson, J. E.; Jorgensen, D. J.; Batlogg, B.; Remeika, P.; Axe,
J. D. Phys. Rev. Ser 3 1986, B 33, 4793–4798.
(26) Bialowons, H.; Muller, M.; Muller, B. G. Z. Anorg. Allg. Chem. 1995,
621, 1227–1231.
Supporting Information Available: Crystallographic data in
CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
€
€