Crystal structures and phase-transition dynamics of cobaltocenium salts with bis(perfluoroalkylsulfonyl)amide anions: Remarkable odd-even effect of the fluorocarbon chains in the anion

Article abstract of DOI:10.1002/chem.201300186

Crystal structures and thermal properties of cobaltocenium salts with bis(perfluoroalkylsulfonyl)amide (C_nF_2n+1SO ₂)₂N anions [n=0 (1), 1 (1 a), 2 (1 b), 3 (1 c), and 4 (1 d)] and the 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonylamide anion (2) were investigated. In these solids, the cations are surrounded by four anions around their C₅ axis, and stacking of these local structures forms two kinds of assembled structures. In the salts with even n (1, 1 b, and 1 d), the cation and anion are arranged alternately to form mixed-stack columns in the crystal. In contrast, in the salts with odd n (1 a and 1 c), the cations and anions independently form segregated-stack columns. An odd-even effect was also observed in the sum of the phase-change entropies from crystal to melt. All of the salts exhibited phase transitions in the solid state. The phase transitions to the lowest-temperature phase in 1, 1 a, and 2 are accompanied by order-disorder of the anions and symmetry lowering of the space group, which results in the formation of an ion pair. Solid-state ¹³C NMR measurements on 1 a and 1 b revealed enhanced molecular motions of the cation in the higher-temperature phases. Copyright

Full text of DOI:10.1002/chem.201300186

FULL PAPER
DOI: 10.1002/chem.201300186
Crystal Structures and Phase-Transition Dynamics of Cobaltocenium Salts
with Bis(perfluoroalkylsulfonyl)amide Anions: Remarkable Odd–Even
Effect of the Fluorocarbon Chains in the Anion
Tomoyuki Mochida,*[a] Yusuke Funasako,[a] Takashi Inagaki,[a] Meng-Jiao Li,[a]
Kotaro Asahara,[b] and Daisuke Kuwahara[b]
Abstract: Crystal structures and ther-
mal properties of cobaltocenium salts
with bis(perfluoroalkylsulfonyl)amide
are arranged alternately to form
mixed-stack columns in the crystal. In
contrast, in the salts with odd n (1a
and 1c), the cations and anions inde-
pendently form segregated-stack col-
umns. An odd–even effect was also ob-
served in the sum of the phase-change
entropies from crystal to melt. All of
the salts exhibited phase transitions in
the solid state. The phase transitions to
the lowest-temperature phase in 1, 1a,
and 2 are accompanied by order–disor-
der of the anions and symmetry lower-
ing of the space group, which results in
the formation of an ion pair. Solid-
state 13C NMR measurements on 1a
and 1b revealed enhanced molecular
motions of the cation in the higher-
temperature phases.
(CnF2n+1SO2)2N anions [n=0 (1),
1
(1a), 2 (1b), 3 (1c), and 4 (1d)] and
the 1,1,2,2,3,3-hexafluoropropane-1,3-
disulfonylamide anion (2) were investi-
gated. In these solids, the cations are
surrounded by four anions around their
C5 axis, and stacking of these local
structures forms two kinds of assem-
bled structures. In the salts with even n
(1, 1b, and 1d), the cation and anion
Keywords: anions · ionic liquids ·
metallocenes · phase transitions ·
solid-state structures
Introduction
It is known that the melting points and melting entropies
of molecular crystals such as n-alkanes exhibit odd–even ef-
fects with respect to the number of carbon atoms in the
alkyl chain, which originate from the different packings of
odd-chain and even-chain compounds.[6] In salts relevant to
ionic liquids, such effects have been observed in the thermal
properties of imidazolium salts with long alkyl chains[7] and
in the structures of imidazolium-related salts.[8] However,
little has been reported on the anion chain dependence of
the thermal properties and structures of the ionic liquids
with bis(perfluoroalkylsulfonyl)amide anions.[3a,9,10]
Recently, we reported that alkyl metallocenium salts with
bis(perfluoroalkylsulfonyl)amide anions become ionic liq-
uids,[11] whereas the corresponding cobaltocenium salts are
solids at room temperature.[11a] We thought that these solids
are suitable for structural investigations to elucidate the
thermodynamic features of the key anions. This article dis-
cusses the thermal properties and crystal structures of cobal-
tocenium salts with the bis(perfluoroalkylsulfonyl)amide
anions (CnF2n+1SO2)2N [n=0 (1), 1 (1a), 2 (1b), 3 (1c), and
Ionic liquids are salts with melting points below 1008C, and
their physicochemical properties have been investigated ex-
tensively in recent years.[1] Most ionic liquids contain onium
cations, but ionic liquids with metal-containing cations are
also known.[2] As counteranion, bis(perfluoroalkylsulfonyl)-
ACHTUNGTRENNUNGamACHTUNGTRENNUNGide anions (CnF2n+1SO2)2N, in particular that with n=1
(abbreviated as Tf2N), are often used because they are more
effective in lowering the melting point of the salt than other
anions.[1a–c,3] The melting points are determined by the free-
energy relationship between the liquid and solid phases,
which is affected by intermolecular interactions and dynam-
ics in the solid state. Hence, to understand the origin of the
low melting points, elucidation of the thermodynamic and
structural characteristics of their salts in the solid state is im-
portant.[4,5]
[a] Prof. Dr. T. Mochida, Y. Funasako, Dr. T. Inagaki, M.-J. Li
Department of Chemistry
4 (1d)] and the 1,1,2,2,3,3-hexafluoropropane-1,3-disulfo
ACHTUNGTRENNUNGnyl-
AHCTUNGTRENNUNG
Graduate School of Science
Kobe University
Kobe, Hyogo 657-8501 (Japan)
E-mail: tmochida@platinum.kobe-u.ac.jp
tion and properties of 1a–d and 2 were reported previous-
ly,[11a] whereas 1 was newly prepared in this study. In the
present study, a remarkable odd–even effect with respect to
the anion chain length was found in the structures and ther-
mal properties of the solids. We also used solid-state
13C NMR spectroscopy to investigate molecular motions in
[b] K. Asahara, Prof. Dr. D. Kuwahara
The University of Electro-Communications
Chofu, Tokyo 182-8585 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201300186.
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Figure 1. Structural formulas of the cobaltocenium salts investigated in
this study.
these solids, because phase transitions in metallocenium
salts often accompany changes in molecular motion.[12]
Figure 3. Total phase change entropies DStotal of 1a–d and 3a–d plotted
against the carbon number n in the anion (CnF2n+1SO2)2N.
markable odd–even effect with respect to the carbon
number n in the fluorocarbon chain of the anion. Such an
odd–even effect in DStotal has been also observed in normal
alkanes,[6] fluoroalkanes,[13] and mesogenic compounds with
alkyl chains.[14] The increases observed from 1a (n=1) to 1c
(n=3) and from 1b (n=2) to 1d (n=4) are comparable
(15–20 JKÀ1 molÀ1); in each case, the change is due to the
addition of four difluoromethylene groups. Compounds 3a–
d also exhibited the same tendency. These increases are
smaller than expected, considering that DStotal in alkyl imid-
Results and Discussion
Thermal properties: Salt 1 melted at 274.38C with accompa-
nying decomposition. The melting point was remarkably
higher than those of 1a–d, which are in the range 138–
1928C. Differential scanning calorimetry (DSC) measure-
ments revealed that 1 exhibits phase transitions at À43.7,
63.9, and 155.68C, accompanied by entropy changes of 21.0,
9.6, and 8.0 JKÀ1 molÀ1, respectively. The DSC data for 1a–d
and 2 have been reported previously.[11a] The phase sequen-
ces for these salts are shown in Figure 2. All of the salts ex-
hibited phase transitions in the solid state, whereby the
lowest-temperature phases are designated as phase I. The
sums of the entropies of melting and crystal–crystal phase
transitions (DStotal) for 1a–d and relevant ionic liquids 3a–
d[12a] (Figure 1) are shown in Figure 3. The data show a re-
AHCTUNGTREGaNNNU zolium and alkyl ferrocenium ionic liquids increases by 6–
10 JKÀ1 molÀ1 per methylene group[15] and even higher en-
tropy is expected for difluoromethylene groups.[16] This is
probably because the chains are short, and a similar phe-
nomenon has been also observed in alkyl imidazolium ionic
liquids.[15b]
Among 1 and 1a–d, the salts with even n (1, 1b, and 1d)
commonly exhibited three phase transitions in the solid
state. The small melting entropies of the highest-tempera-
ture phases (phase IV) in 1b and 1d (14.4 and
13.3 JKÀ1 molÀ1, respectively) indicate that these phases are
highly disordered. Although the molecules in the highest-
temperature phase of 1b were found to undergo anisotropic
rotation (see below), they can be regarded as ionic plastic
phases[17] having melting entropies smaller than
20 JKÀ1 molÀ1.[18] It is plausible that the highest-temperature
phases in 1 and 2 are also highly disordered, considering
their molecular shape and the phase sequences. In contrast,
the salts with odd n (1a and 1c) exhibited fewer phase tran-
sitions and large melting entropies, which suggest less disor-
der in these solids.
Structural odd–even effects: In this section, the general fea-
tures of the crystal structures of 1 and 1a–d and their corre-
lation with the thermal properties are discussed. In these
salts, each cation is surrounded by four anions around its C5
axis (Figure 4a), except that 1c has three neighboring
anions. This unit is stacked to form two kinds of assembled
structures (Figure 4b) depending on the carbon number n in
the anion, with a remarkable odd–even effect. The salts with
even n (1, 1b, and 1d) adopt mixed-column structures, in
Figure 2. Phase sequences of 1, 1a–d, and 2. The transition tempera-
ACHTUNGTRENNUNG
tures [8C] and transition entropies [JKÀ1 molÀ1] are shown. Highly disor-
dered phases are indicated by an asterisk.
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Cobaltocenium Salts with Bis(perfluoroalkylsulfonyl)amide Anions
FULL PAPER
formations of the fluoroalkyl chains are mostly all-trans,
whereas the torsion angles in the chain deviate slightly from
1808 because of steric repulsion between the fluorine
atoms.[20] Because the odd–even effect in n-alkanes origi-
nates from the influence of the terminal CH3 groups on
their crystal packing,[6] the end-group effect may be also im-
portant in the present salts. For the anions with even n (Fig-
ure 5a), the terminal CF3 groups face the cyclopentadienyl
(Cp) rings of the cation to form the mixed-column structure.
This configuration is unfavorable for the anions with odd n,
because their terminal CF3 groups are directed outward
from the molecular long axes, as is indeed found in 1a and
1c (Figure 5b).
The odd–even effect observed in DStotal should be ascribed
to the odd–even effect in the structure. In n-alkanes, com-
pounds with even numbers of carbon atoms have higher
densities and exhibit larger DStotal than those with odd
ones.[6] The harder crystal lattice due to the higher density
leads to smaller entropy gain through thermal excitation of
lattice vibrations and larger entropy gain through phase
transitions. Therefore, in the present salts, the larger DStotal
in the segregated-column salts may be due to their possible
denser crystal packing, likely resulting from interlocking of
the terminal CF3 groups between the anions in the column.
This seems to hold for 1c, the density of which was large as
determined crystallographically, but the density of 1a was
comparable to those of the others and hence this point is
not clear. The comparison of DStotal, which virtually corre-
sponds to the entropy of transition from the ordered crystals
to liquids, is not strict, because 1b has some disorder in
phase I (see below), but this does not affect the overall ten-
dency. Concerning the high temperature phases, it seems
reasonable that the mixed-column structures exhibited ionic
plastic phases at high temperatures, because each ion is sym-
metrically surrounded by oppositely charged ions in the
structure. The absence of such phases in the segregated-
column salts may be consistent with their heterogeneous
local crystal environment.
Figure 4. Schematic illustration of the assembled structures of the cations
and anions in 1 and 1a–d. a) The primary structure formed by the
cation–anion interactions around the C5 axes of the cation. b) Two types
of secondary structures formed by stacking of the primary structures.
which the anions and cations are arranged alternately,
whereas the salts with odd n (1a and 1c) adopt segregated-
column structures. The X-ray structures of the anions in 1
and 1a–d and their neighboring molecules in the columns
are shown in Figure 5. All of the anions adopted the trans
(C2) conformation (Figure 5), in which the two fluoroalkyl
groups are on the opposite sides of the central S-N-S plane.
This conformation is more stable than the cis (C1) confor-
mation and more often found in the solid state.[5,19] The con-
The structure of 2 consists of the same structural unit as
seen in 1 and 1a–d, in which four anions surround the
cation. The assembled structure, however, is neither the
mixed-column structure nor the segregated-column struc-
ture, and is more isotropic due to the ring shape of the
anion.
Structural changes through phase transitions: The crystal
structures in phases I and II were determined for all salts
except for 1c, and this allowed elucidation of the structural
changes through the phase transitions. The transitions in 1,
1a, and 2 are accompanied by order–disorder of the anions
and exhibit large transition entropies (21.0, 8.5, and
14.0 JKÀ1 molÀ1 for 1, 1a, and 2, respectively). In contrast,
the order–disorder of the anions in 1b and 1d is unchanged
in phases I and II, which is consistent with their small transi-
tion entropies (3.1 and 3.7 JKÀ1 molÀ1, respectively).
Figure 5. The molecular arrangements around the anions in the columnar
structures in the a) mixed-column salts (1, 1b, and 1d) and b) segregated-
column salts (1a and 1c). The molecular structure of 1d in phase II and
those of the other compounds in phase I are shown. Dashed lines indi-
cate cation–anion contacts.
In 1, 1a, and 2, the central nitrogen atom (-S-N-S-) in the
anion is disordered over two sites in phase II, as is found in
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T. Mochida et al.
several Tf2N salts,[5b] whereas the anions are ordered in
phase I and form ion pairs with the neighboring cation.
These transitions accompany symmetry lowering of the crys-
tal lattice. The change of the local crystal environment is
shown below. In these salts, one cation is surrounded by
four anions around its C5 axis (Figure 4a). For example, the
arrangements of the anions around the cation in 1 in
tances in 1a–d are shorter than the van der Waals contact
distances by about 0.3 ꢁ, which probably results from the
cation–anion electrostatic interactions. Such weak intermo-
lecular CH···X interactions are often observed in the crystal
structures of ionic liquids with bis(perfluoroalkylsulfonyl)-
ide anions.[4,10] There are no such CH···X contacts in 2.
ACHUTNGRENaNUG mACHTUNGTRENNUGN
Conformational changes of the related anions at phase tran-
sitions have been discussed for several onium salts.[5] This
study has revealed a strong tendency for disorder of the
anions and their ordering accompanying ion-pair formation
in the low temperature phases.
ACHTUNGTRENNUNGphases I and II are shown in Figure 6. In this salt, the cation
The structural features of each salt in phases I and II are
described in the following sections. Structure determinations
on the higher-temperature phases were unsuccessful.
Crystal structures of salts with even n: Salts 1, 1b, and 1d
exhibit mixed-column structures. The packing diagrams of 1
in phases I and II are shown in Figure 7a. The space group
ꢀ
changed from monoclinic C2/m (phase II) to triclinic P1
(phase I). The unit cells were much changed at the phase
transition, whereas the cell volumes were comparable. In
phase II, the cations and anions in the unit cell are located
at the vertices and face-centered positions, respectively (Fig-
ure 7a, upper). The Cp ring of the cation contacts the SO2F
group of the anion, which forms an alternate column ex-
tending along the ac direction. The central nitrogen atom of
the anion was disordered over two sites with equal occupan-
cies and the SO2F groups exhibit rotational disorder. A
layer structure in which one cation is surrounded by four
anions and vice versa is formed in the bc plane, and, as dis-
cussed above (Figure 6), one of the four anions forms an ion
pair with the cation in phase I associated with ordering of
the anion. The cation–anion arrangement in phase I is slight-
ly altered from that in phase II and deviates from an ideal
mixed-column structure.
Figure 6. Molecular arrangements around the cation of 1 in a) phase II
and b) phase I. Dotted lines show Co···X (X=O, N) distances shorter
than 5 ꢁ. The Co···N ion-pair-like interaction in b) is indicated by a
thicker dotted line.
has the same distances to the four neighboring anions in
phase II (Co···N 4.83 ꢁ) owing to the higher crystal symme-
try and anion disorder (Figure 6a). In phase I, however, one
of the nitrogen atoms of the anions comes closer to the
cation to form a cation–anion pair (Co···N distance: 4.60 ꢁ),
associated with ordering of the nitrogen atom (Figure 6b).
In the bis(perfluoroalkylsulfonyl)amide anions, the central
nitrogen atom is the most negatively charged. Hence, it is
reasonable to regard this as ion pairing considering the
long-range nature of the Coulombic force. The other anions
are close to the Co ion at the
oxygen atoms. The molecular
arrangements around the cation
in the other salts are shown in
Figure S1 (Supporting Informa-
tion). The phase transitions in
1a and 2 closely resemble that
in 1 in terms of the order–disor-
der of the anion and the resul-
tant ion pairing. In contrast,
anion order–disorder in 1b and
1d are unchanged in phases I
and II. In both phases, 1b con-
tains two disordered anions and
one ordered anion, whereas 1d
contains only ordered anions
that form ion pairs.
The Co···X distances (X=N,
O) between the cation and
anion in these salts are longer
Figure 7. Packing diagrams of a) 1 in phase II (top) and phase I (bottom), b) 1b in phase I, and c) 1d in
phase II (left) and phase I (right). In b), only cation 2 and anions 2 and 3 are shown for simplicity. The hydro-
distances, but the CH···X dis- gen atoms have been omitted for clarity.
than the van der Waals contact
AHCTUNGTRENNUNG
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Cobaltocenium Salts with Bis(perfluoroalkylsulfonyl)amide Anions
FULL PAPER
The packing diagram of 1b in phase I is shown in Fig-
ure 7b. The unit-cell dimensions, space groups (triclinic P1),
and the molecular arrangements are almost the same in
rhombic while maintaining the unit-cell dimensions, which
suggests that the anion in this phase undergoes rotation
along the molecular long axis.
ꢀ
ACHTUNGTRENNUNGphases II and I. The crystal structure is more complicated
than those of the other salts. The asymmetric unit contains
two cations (cations 1 and 2), one ordered anion (anion 1),
and two disordered anions (anions 2 and 3), and half the
molecules are independent. In the disordered anions, both
the nitrogen and oxygen atoms are disordered over two
sites, and the pentafluoroethyl groups are rotationally disor-
dered. The columns formed by anion 1 and cation 1 are ar-
ranged orthogonal to the columns formed by anions 2 and 3
and cation 2. Both cations 1 and 2 are surrounded by four
anions (Figure S1b, Supporting Information), forming ion
pairs with anions 2 and 1, respectively. Anion 3 forms no ion
pair and exhibits larger thermal ellipsoids than the other
anions. The unit-cell dimensions in high-temperature phase
III are comparable to those of phases I and II. The crystal
system in high-temperature phase IV is orthorhombic;
hence, the cations and anions may be undergoing anisotrop-
ic rotation.
Crystal structures of the salts with odd n: Salts 1a and 1c
exhibit segregated-column structures. The packing diagrams
of 1a in phases I and II are shown in Figure 8a. The space
group changed from monoclinic C2/m (phase II) to C2/c
(phase I), accompanied by cell doubling along the column
direction. The molecular arrangements are almost the same
in both phases. The cation columns and anion columns are
extended along the c axis in phase I. In the cation column,
the cations form dimers through p–p interactions between
the Cp rings, and the dimers are separated by voids sur-
rounded by four CF3 groups of the anions. In the anion
À
À
column, the SO2CF2 groups contact with each other be-
tween the anions. The cation columns are surrounded by
four anion columns and vice versa (Figure 8a, bottom). The
anion exhibits disorder in phase II, whereby the nitrogen
atom and the oxygen atoms are both disordered over two
sites, and the trifluoromethyl groups exhibit rotational disor-
der. Two of the four anions surrounding the cation have
equal Co···N distances of 4.78 ꢁ (Figure S1a, Supporting In-
The packing diagrams of 1d are shown in Figure 7c. The
space group changed from monoclinic C2/c (phase II) to tri-
ꢀ
clinic P1 (phase I). The unit-cell volume in phase I is half of
that of phase II, and such a de-
crease in cell volume in the
lower-temperature phase is a
rare phenomenon. In both
phases, the anion is ordered
and the cation is surrounded by
four anions around its C5 axis,
similar to 1 (Supporting Infor-
mation Figure S1d), forming
ionic layers on bc planes at x=
0
and 0.5 (Figure 7c, left).
There are fluorous layers be-
tween them, in which perfluoro-
ACHTUNGTRENNUNGalkyl groups contact each other.
AHCTUNGTRENNUNG
In phase II, one of the four sur-
rounding anions forms an ion
pair with the cation (Co···N
4.62 ꢁ). The anion adopts a
symmetrical structure, and the
terminal CF3 groups face the
Cp rings of the adjacent cation
to form a mixed-column struc-
ture extending along the a axis
in a zigzag manner. In phase I,
however, the anion has an un-
symmetrical structure in which
one of the chains adopts
a
gauche conformation. This
chain contacts the Cp rings in
the cation through three fluo-
rine atoms of the bent CF2CF2
group. In phase III, the crystal
Figure 8. a) Packing diagrams of 1a in phase II (top) and phase I (middle) projected perpendicular to the
column. The bottom figure is a projection along the columns in phase I. b) Packing diagrams of 1c in phase I,
projected along [101] (top) and [101] (bottom). c) Packing diagrams of 2 in phase II (top) and phase I
ꢀ
(bottom). The hydrogen atoms have been omitted for clarity. The dashed lines connecting the centroids of the
symmetry changed to ortho- neighboring cyclopentadienyl rings in a) and b) are merely guides to the eye.
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T. Mochida et al.
formation), whereas the anion is ordered in phase I and
forms an ion pair with a neighboring cation (Co···N 4.51 ꢁ).
The packing diagram of 1c in phase I is shown in Fig-
ure 8b. The structure in phase II could not be determined.
The space group of phase I is monoclinic P21/c, and the
anions are ordered. Columnar arrangements of the cations
their highest-temperature phases. Detailed analyses of mo-
lecular motion by NMR spectroscopy will be reported in the
future.
Conclusion
ꢀ
and anions extend along [101]. The cation column is sur-
rounded by six anion columns to form a hexagonal-like ar-
rangement (Figure 8b, bottom). The number of anion col-
umns is twice that of the cation columns, which is a conse-
quence of the long anion (Figure S1c, Supporting Informa-
tion). This salt is exceptional in that the cations are sur-
rounded by three anions. Only one of the two
crystallographically independent cations forms an ion pair
(Co···N 4.49 ꢁ).
Cobaltocenium salts with bis(perfluoroalkylsulfonyl)amide
anions (CnF2n+1SO2)2N (n=0–4) exhibit an odd–even effect
in their total phase-change entropies. This phenomenon is
ascribed to difference in their assembled structures, similar
to the case of n-alkanes. These salts exhibit columnar assem-
bled structures; in the salts with even n, the anion and
cation are arranged alternately in the columns, whereas the
cations and anions form independent columns in the salts
with odd n. These salts, as well as the salt with 1,1,2,2,3,3-
hexafluoropropane-1,3-disulfonylamide anion, exhibit suc-
cessive phase transitions in the solid state. The appearance
of ionic plastic phases in the salts with even n seems to be
consistent with the mixed-column structure. The molecular
motions increase in the higher-temperature phases, as re-
vealed by solid-state 13C NMR spectroscopy.
The bis(perfluoroalkylsulfonyl)amide anions are impor-
tant anions that are frequently used as components of ionic
liquids. To understand thermodynamic aspects of their melt-
ing, it is important to investigate their behaviors from the
crystal to the melt. By focusing on solids with the simple co-
baltocenium cation, we could elucidate the effect of the
anions on the melting entropies and their structural features
in the solid state. These anions show disorder of the central
nitrogen atoms, which often induces more uniform and
weaker cation–anion interactions by breaking the ion pairs
that exist in the lower temperature phases. Modes of molec-
ular motion are further enhanced at higher temperatures.
Both factors contribute to the thermodynamic features of
salts with these anions. There results should contribute to
the understanding of the thermal properties of salts with
these and related fluorinated anions. The structural odd–
even effects and their consequences are interesting from the
viewpoint of crystal engineering.
Crystal structure of 2 having a cyclic anion: The crystal
structures of 2 in phases I and II are shown in Figure 8c.
The space group changed from orthorhombic Pbcm
ACHTUNGTRENNUNG(phase II) to Pbca (phase I), accompanied by cell doubling
along the a axis. The structures are more isotropic than
those of the other salts due the quasispherical molecular
shape of the anion. In phase II, the anion ring exhibits two-
fold conformational disorder; the nitrogen atom and the
central carbon atom in the CF2CF2CF2 group are disordered
over two sites. The ordered anion in phase I adopts the ener-
getically favorable chair conformation. Two of the four
anions surrounding the cation have equal Co···N distances
(4.37 ꢁ) in phase II, whereas one of the anions forms an ion
pair with a cation in phase I (Co···N 4.25 ꢁ; Figure S1e, sup-
porting information).
Solid-state 13C NMR spectra: The molecular motion of the
cobaltocenium cation in 1a and 1b was investigated by
solid-state 13C NMR spectroscopy. The line widths of the
powder 13C NMR spectra of 1a are 117, 89, and 69 ppm at
À408C (phase I), À148C (phase II), and 218C (phase III),
respectively (Figure S2a, Supporting Information). The line
width in phase I corresponds to that of an ordered cation,
and the value is larger than that of neutral ferrocene in a
static state (79 ppm).[21] In this phase, the cation undergoes
only rotational jump around the C5 axis. The much de-
creased line widths in the higher-temperature phases indi-
cate that the cation has additional motions other than the C5
rotational jump in the high-temperature phases. The spectra
in the high-temperature phases were tentatively analyzed on
the basis of a model assuming precession of the cation
around the C5 axis,[22] which provided precession angles of
238 and 328 in phases II and III, respectively. In 1b, the line
widths of the spectra are 111, 102, and 88 ppm at À458C
(phase I), 188C (phase III), and 308C (phase IV), respective-
ly (Figure S2b, Supporting Information). The same analysis
as above provided precession angles of 178 and 248 for
Experimental Section
General: Compounds 1a–d and 2 were prepared according to the litera-
ture report.[11a] [CoCp2]PF6 and potassium bis(fluorosulfonyl)amide (K-
AHCTUNTGREG[NNUN (FSO2)2N]) were purchased from Sigma-Aldrich and Kishida Chemical,
respectively. DSC measurements were performed by using a TA Q100
differential scanning calorimeter from À160 to 3258C at a scan rate of
10 KminÀ1. Solid-state 13C NMR spectra were recorded on a Tecmag
Apollo spectrometer (operating at 75.431 MHz for 13C) equipped with a
Doty XC MAS 4 mm probe head. The 13C NMR experiments were per-
formed with the following parameters: a 4.8 ms p/2 pulse, a 55.6 kHz 1H
decoupling field, and a 30 s recycle delay.
Preparation of 1a: An aqueous solution of [CoCp2]PF6 (100 mg,
ACHTUNGTRENNUNGphases III and IV, respectively. These results unambiguously
0.299 mmol) and
KACTHNGUETRN[UNG (FSO2)2N] (131 mg, 0.598 mmol) was stirred for
indicate that the molecular motions of the cations are gradu-
ally enhanced in the higher-temperature phases in both salts,
whereas the cations maintain anisotropic rotation even in
30 min and then extracted with dichloromethane. The organic fraction
was dried over anhydrous magnesium sulfate and evaporated to dryness.
The product was recrystallized from ethanol. Yield: 102 mg (87.9%).
6262
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Chem. Eur. J. 2013, 19, 6257 – 6264

Cobaltocenium Salts with Bis(perfluoroalkylsulfonyl)amide Anions
FULL PAPER
Table 1. Crystallographic parameters for 1, 1b,and 1d.
1
1b
1d
Phase I
Phase II
Phase I
Phase II
Phase I
Phase II
empirical formula
formula weight
T [K]
C10H10CoF2NO4S2
C14H10CoF10NO4S2
C18H10CoF18NO4S2
369.24
100
569.28
100
769.32
100
298
240
298
crystal system
space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
triclinic
P1
monoclinic
C2/m
12.405(5)
8.505(4)
6.584(3)
90
93.943(5)
90
693.0(5)
2
triclinic
P1
triclinic
P1
triclinic
P1
monoclinic
C2/c
23.100(6)
10.856(3)
10.735(3)
90
98.619(3)
90
2661.7(1)
4
ꢀ
ꢀ
ꢀ
ꢀ
7.316(4)
9.816(5)
9.982(5)
79.397(7)
71.188(6)
73.631(7)
647.6(6)
2
10.509(3)
11.936(3)
17.404(7)
104.312(5)
101.283(5)
104.134(4)
1937.6(11)
4
10.693(3)
12.104(3)
17.530(6)
104.417(5)
101.724(5)
104.743(3)
2037.1(11)
4
10.5048(2)
10.7338(2)
12.205(2)
95.765(2)
114.221(2)
92.746(2)
1242.7(4)
2
a [8]
b [8]
g [8]
V [ꢁ3]
Z
1calcd [gcmÀ3
]
1.894
1.682
372
1.770
1.572
372
1.916
1.197
1128
1.856
1.160
1128
2.056
1.024
756
1.920
0.956
1512
m [mmÀ1
(000)
]
F
A
reflns collected
2720
1646
9370
9834
5939
6074
independent reflns
2240
655
6815
7089
4280
2344
R
(int)
0.0663
0.0157
0.0814, 0.2371
0.0821, 0.2402
1.108
0.0322
0.0244
0.0133
0.0204
0.0840, 0.2552
0.0903, 0.2636
1.075
R1, wR2 [I>2s(I)]
R1, wR2 (all data)
GOF on F2
0.0479, 0.1376
0.0565, 0.1484
1.111
0.0724, 0.1924
0.0887, 0.2068
1.032
0.0684, 0.1830
0.1106, 0.2144
1.026
0.0295, 0.0909
0.0304, 0.0912
1.216
parameters
182
0.850, À0.657
55
704
3.317, À1.535
703
0.713, À0.413
397
0.312, À0.485
200
0.701, À0.593
D1max,min [eꢁÀ3
]
0.758, À0.585
M.p. 274.38C (DSC, accompanied by decomposition immediately after
melting); FTIR (cmÀ1): 500, 1012, 1218 (SO), 1419 (SO), 1457, 1472; ele-
mental analysis calcd (%) for C10H10O4NS2CoF2: C 32.53, H 2.73, N 3.79;
found: C 32.98, H 2.76, N 3.90.
pirical absorption corrections (SADABS)[24] were applied. In 1, the mole-
cules in phase II were disordered, leaving minor electron density peaks
(D1<0.85 eꢁ3) unassigned; the residual electron densities are found
around the Cp carbon atoms of the cation and around the central nitro-
gen atom and the SO2F groups of the anion. The F and O atoms in the
X-ray crystallography: X-ray diffraction data for single crystals of 1, 1a–
d, and 2 were collected on a Bruker SMART APEX II Ultra CCD dif-
fractometer with MoKa radiation (l=0.71073 ꢁ). Crystallographic param-
eters of the salts are listed in Tables 1 and 2. All calculations were per-
formed with SHELXL.[23] The nonhydrogen atoms were refined aniso-
tropically, and hydrogen atoms were inserted at calculated positions. Em-
À
SO2F groups are disordered, which results in averaged C X distances
(X=F or O). Disorder treatment was unsuccessful due to conversion
problems, and the atom assignments in the group are tentative. In 1b, the
CF2CF3 groups of the anion are highly disordered, leaving some electron
densities unassigned (D1max =3.32 eꢁ3).
Table 2. Crystallographic parameters for 1a, 1c, and 2.
1a
1c
2
Phase I
Phase II
Phase I
Phase I
Phase II
empirical formula
formula weight
T [K]
C12H10CoF6NO4S2
C16H10CoF14NO4S2
669.30
C13H10CoF6NO4S2
469.26
100
481.27
298
263
100
313
crystal system
space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
monoclinic
C2/c
16.650(5)
13.725(4)
16.484(5)
90
monoclinic
C2/m
16.632(5)
14.057(5)
8.748(5)
90
monoclinic
P21/c
17.847(3)
16.269(3)
16.256(3)
90
orthorhombic
Pbca
14.887(3)
14.479(3)
16.172(4)
90
orthorhombic
Pbcm
7.298(2)
15.602(5)
15.698(5)
90
a [8]
b [8]
117.336(3)
90
3746.4(16)
8
1.863
1.357
120.675(5)
90
1759.1(13)
4
1.772
1.291
111.743(2)
90
4384.1(13)
8
2.028
1.119
90
90
90
90
1787.5(9)
4
1.788
g [8]
V [ꢁ3]
3485.8(14)
8
1.834
1.305
1920
Z
1calcd [gcmÀ3
]
m [mmÀ1
(000)
]
1.273
960
F
A
1872
936
2640
reflns collected
7905
4219
19724
14996
7847
independent reflns
2955
1611
7340
3079
1652
R
(int)
0.0278
0.0267, 0.0587
0.0347, 0.0630
1.032
0.0297
0.0895, 0.2196
0.1057, 0.2340
1.008
0.0377
0.0261
0.0211
0.0978, 0.2860
0.1102, 0.3030
1.047
R1, wR2 [I>2s(I)]
R1, wR2 (all data)
GOF on F2
0.0349, 0.0846
0.0443, 0.0883
1.069
0.0483, 0.1234
0.0681, 0.1447
1.025
parameters
235
0.317, À0.339
173
1.014, À0.656
685
0.731, À0.438
244
0.626, À0.611
145
1.029, À0.641
D1max,min [eꢁÀ3
]
Chem. Eur. J. 2013, 19, 6257 – 6264
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6263

T. Mochida et al.
The packing diagrams were drawn with ORTEP-3[25] and Mercury.[26]
CCDC 902768 (1, 100 K), 902769 (1, 298 K), 902770 (1a, 100 K), 902771
(1a, 298 K), 902772 (1b, 100 K), 902773 (1b, 298 K), 902774 (1c, 100 K),
902775 (1d, 100 K), 902776 (1d, 298 K), 915718 (2, 298 K), and 915719
(2, 313 K) contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from The Cambridge Crystal-
lographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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We thank Dr. Y. Furuie (Kobe University) for elemental analysis and M.
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Received: January 18, 2013
Published online: April 9, 2013
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Chem. Eur. J. 2013, 19, 6257 – 6264