Phase transitions and thermal properties of decamethylferrocenium salts with perfluoroalkyl-sulfonate and -carboxylate anions exhibiting disorder

Article abstract of DOI:10.1016/j.jorganchem.2012.04.005

Decamethylferrocenium salts with perfluoroalkylsulfonate anions (C _nF_2n+1SO₃-n = 1, 4, and 8) and perfluoroalkylcarboxylate anions (C_nF_2n+1CO₂-; n = 1-4) were prepared to investigate the effects of the anion on the thermal behaviors of the salts. Differential scanning calorimetry (DSC) measurements revealed that all the salts exhibited phase transitions in the solid state. Salts with an octamethylferrocenium cation or decamethylcobaltocenium cation exhibited different phase sequences from those of the corresponding decamethylferrocenium salts. Structural changes associated with the phase transitions were investigated crystallographically for two salts. The phase transition in [Fe(C₅Me₅)₂](CF ₃SO₃) at -121.6 °C was accompanied by ordering of the cation conformations into eclipsed and staggered conformations in different ratios. The unit cell volume became six times larger and the space group changed from Pmn2₁ to P1 in the low-temperature phase. The phase transition in [Fe(C₅Me₅)₂](C₃F ₇CO₂) at -115 °C was not accompanied by any change in the unit cell or the space group (P2₁/c). The libration or displacements of the anions that existed in the high-temperature phase was suppressed in the low-temperature phase, associated with a slight rotational displacement of the molecules. Anions with longer perfluoroalkyl chains exhibited disorder in the solid state even at low temperatures.

Full text of DOI:10.1016/j.jorganchem.2012.04.005

Journal of Organometallic Chemistry 713 (2012) 35e41
Contents lists available at SciVerse ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Phase transitions and thermal properties of decamethylferrocenium salts with
perfluoroalkyl-sulfonate and -carboxylate anions exhibiting disorder
,
b
c
Shota Hamada a, Yusuke Funasako a, Tomoyuki Mochida a , Daisuke Kuwahara , Kenji Yoza
*
a Department of Chemistry, Graduate School of Science, Kobe University, Rokkodai, Nada, Kobe, Hyogo 657-8501, Japan
b The University of Electro-Communications, Chofu, Tokyo 182-8585, Japan
c Bruker AXS K.K., Moriya, Kanagawa, Yokohama, Kanagawa 221-0022, Japan
a r t i c l e i n f o
a b s t r a c t
Decamethylferrocenium salts with perfluoroalkylsulfonate anions (CnF2nþ1SO3ꢀ; n ¼ 1, 4, and 8) and
perfluoroalkylcarboxylate anions (CnF2nþ1CO2ꢀ; n ¼ 1e4) were prepared to investigate the effects of the
anion on the thermal behaviors of the salts. Differential scanning calorimetry (DSC) measurements
revealed that all the salts exhibited phase transitions in the solid state. Salts with an octamethylferro-
cenium cation or decamethylcobaltocenium cation exhibited different phase sequences from those of the
corresponding decamethylferrocenium salts. Structural changes associated with the phase transitions
were investigated crystallographically for two salts. The phase transition in [Fe(C5Me5)2](CF3SO3) at
ꢀ121.6 ꢁC was accompanied by ordering of the cation conformations into eclipsed and staggered
conformations in different ratios. The unit cell volume became six times larger and the space group
changed from Pmn21 to P1 in the low-temperature phase. The phase transition in [Fe(C5Me5)2](C3F7CO2)
at ꢀ115 ꢁC was not accompanied by any change in the unit cell or the space group (P21/c). The libration or
displacements of the anions that existed in the high-temperature phase was suppressed in the low-
temperature phase, associated with a slight rotational displacement of the molecules. Anions with
longer perfluoroalkyl chains exhibited disorder in the solid state even at low temperatures.
Ó 2012 Elsevier B.V. All rights reserved.
Article history:
Received 11 November 2011
Received in revised form
22 March 2012
Accepted 5 April 2012
Keywords:
Decamethylferrocene
Perfluoroalkylcarboxylate
Perfluoroalkylsulfonate
Crystal structure
Phase transition
Orderedisorder
1. Introduction
phase transitions in metallocenium salts with fluorinated anions. In
this paper, we report the thermal properties of the metallocenium
Metallocenium salts often exhibit phase transitions in the solid
state, and these transitions are frequently associated with changes
in molecular motion [1]. This tendency is partly ascribed to their
nearly spherical molecular shapes. The simplest example is fer-
rocenium hexafluorophosphate, which exhibits a phase transition
to an orientationally disordered phase at 74 ꢁC, as shown by
calorimetry, solid state NMR, and X-ray crystallography [2].
Mössbauer spectroscopy has also been used to investigate
molecular motion in ferrocenium salts [3]. Phase transitions in
cobaltocenium derivatives and related compounds have been
investigated extensively [4].
We have investigated phase transition phenomena in ferrocene-
based compounds, such as electronic phase transitions [5] and
orderedisorder transitions [6]. Recently, we prepared metal-
locenium salts with trifluoromethanesulfonamide [7]; these salts are
ionic liquids with melting points below 100 ꢁC [8]. In this context, we
became interested in thermal properties such as melting points and
salts shown in Chart 1; decamethylferrocenium ([FeCp*2]þ) salts
with perfluoroalkylsulfonate anions (CnF2nþ1SO3ꢀ, n ¼ 1, 4, and 8)
and perfluoroalkylcarboxylate anions (CnF2nþ1CO2ꢀ, n ¼ 1e4) have
beenprepared.CF3SO3 isabbreviatedtoOTf. Forcomparison, wehave
also prepared cobaltocenium salts and octamethylferrocenium salts
with these anions. All the salts investigated in this study were found
to exhibit phase transitions in the solid state. These salts were crys-
tallographically examined to elucidate the characteristics of the
perfluoroalkyl chains in the solid state.
2. Results and discussion
2.1. Preparation and thermal properties
ꢀ
The salts with OTfꢀ or CnF2nþ1CO2 (n ¼ 1e4) were prepared by
chemical oxidation of metallocenes with silvꢀer salts of the corre-
sponding anions. The salts with CnF2nþ1SO3 (n ¼ 4 or 8) were
prepared by anion exchange of metallocenium nitrates.
[FeCp*2](CF3CO2)$1/3H2O and [FeCp*2](C2F5CO2)$H2O were obtained
as hydrates.
* Corresponding author. Tel./fax: þ81 78 803 5679.
E-mail address: tmochida@platinum.kobe-u.ac.jp (T. Mochida).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.04.005

36
S. Hamada et al. / Journal of Organometallic Chemistry 713 (2012) 35e41
Chart 1. Chemical formulas of metallocenium salts with perfluoroalkyl-sulfonate and
-carboxylate anions.
The melting points and decomposition temperatures of these
salts are listed in Table 1. The decomposition temperatures of the
sulfonate salts were 312e348 ꢁC, determined by thermogravimetric
(TG) analysis (ꢀ3 wt%). The OTf salts decomposed without melting,
whereas [FeCp*2](C4F9SO3) and [CoCp*2](C4F9SO3) melted at
around 250 ꢁC, and [FeCp*2](C8F17SO3) melted at 287 ꢁC, before
decomposition. In contrast, the carboxylate salts were much less
thermally stable; [FeCp*2](CnF2nþ1CO2) (n ¼ 1e4) and the corre-
sponding octamethylferrocenium salts decomposed at tempera-
tures below 180 ꢁC without melting, as a result of thermal
decomposition of the anions [9].
Dehydration of the hydrate salts was observed by TG analysis. In
[FeCp*2](CF3CO2)$1/3H2O, a slight weight loss corresponding to
dehydration occurred at around 104 ꢁC (ꢀ1.3 wt%), although this
was not clear, and decomposition occurred at 125 ꢁC (ꢀ3 wt%).
[FeCp*2](C2F5CO2)$H2O exhibited a weight loss of ꢀ3.2% at 105 ꢁC,
Fig. 2. Phase sequences of (a) [FeCp*2](CnF2nþ1CO2) and (b) [Fe(C5
-
Me4H)2](CnF2nþ1CO2). The phase transition temperatures (ꢁC) and transition entropies
(J molꢀ1 Kꢀ1) are shown above and below each diagram, respectively.
Table 1
Melting points (Tm) and decomposition temperatures (Tdec) of metallocenium salts
with perfluoroalkyl-sulfonate and -carboxylate anions.
Compounds
Tm
Tdec
[FeCp*2](OTf)
[CoCp*2](OTf)
[FeCp*2](C4F9SO3)
ea
316b
ea
322b
249
250
287
ea
323b
[CoCp*2](C4F9SO3)
[FeCp*2](C8F17SO3)
[FeCp*2](CF3CO2)$1/3H2O
[FeCp*2](C2F5CO2)$H2O
[FeCp*2](C3F7CO2)
[FeCp*2](C4F9CO2)
[Fe(C5Me4H)2](CF3CO2)
[Fe(C5Me4H)2](C2F5CO2)
[Fe(C5Me4H)2](C3F7CO2)
348b
312b
104b,d, 125b
105b,d, 153b
173b
ea
ea
ea
173c
ea
170b
ea
165b
ea
168b
a
Decomposed before melting.
b
Fig. 1. Phase sequences of [MCp*2](CnF2nþ1SO3) (M ¼ Fe, Co). The phase transition
temperatures (ꢁC) and transition entropies (J molꢀ1 Kꢀ1) are shown above and below
each diagram, respectively.
Determined by TG analysis (ꢀ3 wt%).
c
Visually determined.
d
Dehydration.

S. Hamada et al. / Journal of Organometallic Chemistry 713 (2012) 35e41
37
Table 2
Thermal data for the phase transitions in [MCp*2](CnF2n+1SO3).
Table 4
Thermal data for the phase transitions in [Fe(C5Me4H)2](CnF2nþ1CO2).
Compound
Phase
transitions
T (ꢁC)
D
H
DS
Compound
Phase
transitions
T (ꢁC)
D ) D )
H (kJ molꢀ1 S (J molꢀ1 Kꢀ1
(kJ molꢀ1
)
(J molꢀ1 Kꢀ1
)
[FeCp*2](OTf)
III / II
II / I
II / I
IV / III
III / II
II / I
ꢀ120.6
146.5
112.7
ꢀ37.4
ꢀ0.6
0.7
13.2
9.7
3.3
0.1
4.9
31.4
25.2
14.0
0.5
[Fe(C5Me4H)2](CF3CO2) II / I
[Fe(C5Me4H)2](C2F5CO2) III / II
35.6 6.1
24.2 0.5
39.6 0.3
ꢀ35.4 4.5
14.7 5.7
41.5 11.9
22.0
1.5
0.8
6.2
6.5
[CoCp*2](OTf)
[FeCp*2](C4F9SO3)
II / I
[Fe(C5Me4H)2](C3F7CO2) IV / III
III / II
II / I
88.6
0.8
2.1
12.6
I / Liquid
II / I
II / I
248.8
ꢀ111.9
ꢀ30.5
17.2
0.2
0.6
33.1
1.3
2.6
[CoCp*2](C4F9SO3)
[FeCp*2](C8F17SO3)
compare these data with those for the corresponding deca-
methylferrocenium salts, because of their different compositions, it
is likely that the octamethylferrocenium salts exhibit more phase
ꢀ
transitions, as seen by comparison of the salts with C3F7CO2
.
which corresponds to dehydration (calcd ꢀ3.5 wt%), and decom-
position started at 153 ꢁC (ꢀ3 wt%).
Some of these phase transitions may be related to the
orderedisorder transitions of octamethylferrocene [7].
The results of the calorimetric analyses suggest that salts with
longer perfluoroalkyl chains in the anion tend to exhibit simpler
phase sequences and smaller entropies of solid-phase transitions.
Since the melting entropies of these salts could not be measured
because of their high melting points or decomposition, no discus-
sion of the residual entropies at low temperatures is possible.
However, it is highly plausible that disorder of the perfluoroalkyl
chains remains at low temperatures for anions with longer chains,
as is also suggested crystallographically (vide infra).
2.2. Phase transitions in the solid state
All the salts exhibited phase transitions in the solid state.
Thermal data for the phase transitions, determined by differential
scanning calorimetry (DSC) measurements, are listed in Tables 2e4.
The phase sequences of the sulfonate salts [MCp*2](CnF2nþ1SO3)
(M ¼ Fe and Co) are shown schematically in Fig. 1. The transition
temperatures and transition entropies are shown in the figure. In
these salts, differences in metal species were found to affect the
phase behaviors, as reported for [MCp2][PF6] [10]. [FeCp*2](OTf),
which
exhibited
phase
transitions
D
at
ꢀ120.6
ꢁC
2.3. Structural changes in [FeCp*2](OTf) associated with phase
transition
(D
S ¼ 4.9 J molꢀ1 Kꢀ1) and 146.5 ꢁC (
S ¼ 31.4 J molꢀ1 Kꢀ1); the latter
is probablya transition to a plastic phase. Despite being isostructural
at room-temperature (vide infra), [CoCp*2](OTf) exhibited no phase
transitions at low temperatures, whereas the salt exhibited a broad,
[FeCp*2](OTf) exhibited a phase transition at ꢀ121.6 ꢁC. We
performed X-ray analyses of this salt above and below the phase
successive transition at around 112.7 ꢁC (
D
S ¼ 25.2 J molꢀ1 Kꢀ1). In
[MCp*2](C4F9SO3) (M ¼ Fe, Co), the ferrocenium salt exhibited
complicated phase behavior, showing phase transitions
at ꢀ37.4 ꢁC, ꢀ0.6 ꢁC, and 88.6 ꢁC (sum of the transition entropies:
D
Stotal ¼ 16.6 J molꢀ1 Kꢀ1), whereas the cobaltocenium salt exhibited
only one phase transition with
a small transition entropy
(<2 J molꢀ1 Kꢀ1) at ꢀ111.9 ꢁC. [FeCp2*](C8F17SO3) exhibited only one
phase transition with a small transition entropy at ꢀ30.5 ꢁC.
The phase sequences of the carboxylate salts [FeCp*2](CnF2nþ1CO2)
(n ¼ 1e4) are shown in Fig. 2a. [FeCp*2](CF3CO2)$H2O exhibited three phase
transitions, at ꢀ5.3 ꢁC, 57.0 ꢁC, and 72.0 ꢁC(
D
D
Stotal ¼ 58.2 molꢀ1Kꢀ1). The salt
with n¼ 2 exhibited a transition at 64.4 ꢁC(
S¼ 79.1 J molꢀ1 Kꢀ1). The large
transition entropies indicate that their high-temperature phases are highly
disordered. In contrast, the salts with n ¼ 3 and 4 exhibited transitions with
small transition entropies at ꢀ114.7 ꢁC and ꢀ114.3 ꢁC, respectively.
The phase sequences of the corresponding octamethylferroce-
nium salts (n ¼ 1e3) are shown in Fig. 2b. The salt with n ¼ 1
exhibited a solid-phase transition at 35.6 ꢁC (
D
S ¼ 22.0 J molꢀ1 Kꢀ1).
The salt with n ¼ 2 exhibited two phase transitions at 24.2 ꢁC and
39.6 ꢁC with small transition entropies. The salts with n ¼ 3
exhibited three phase transitions at ꢀ35.4 ꢁC, 14.7 ꢁC, and 41.5 ꢁC
(D
Stotal ¼ 25.3 J molꢀ1
K
ꢀ1). Although it is not possible to simply
Table 3
Thermal data for the phase transitions in [MCp*2](CnF2nþ1CO2).
Compound
Phase
T (ꢁC)
D ) D )
H (kJ molꢀ1 S (J molꢀ1 Kꢀ1
transitions
[FeCp*2](CF3CO2)$1/3H2O IV / III
ꢀ5.3 8.4
57.0 1.6
72.0 7.6
31.3
4.9
22.0
79.1
7.2
Fig. 3. Packing diagrams of [FeCp*2](OTf) determined at (a) ꢀ100 ꢁC (room-temper-
ature phase) and (b) ꢀ153 ꢁC (low-temperature phase). Only half of the unit cell
contents are shown for clarity. In the low-temperature structure, the corresponding
room-temperature unit cell is shown by dashed lines, and the conformations of the
cation are indicated by E (eclipsed) and S (staggered). Hydrogen atoms have been
omitted for clarity.
III / II
II / I
[FeCp*2](C2F5CO2)$H2O
[FeCp*2](C3F7CO2)
[FeCp*2](C4F9CO2)
II / I
II / I
II / I
64.4 26.7
ꢀ114.7 1.1
ꢀ114.3 0.5
3.1

38
S. Hamada et al. / Journal of Organometallic Chemistry 713 (2012) 35e41
The structure of the low-temperature phase is shown in Fig. 3b.
The space group changed to P1, anda superstructurewas formed. The
repeating units became three times and two times longer with
respect to the a- and b-axes, respectively, compared with the room-
temperaturestructure(Fig. 3b,dashedlines). Theunitcellcontains12
cations and anions. The Cp* rings in the cation are ordered, and the
unit cell contains eight cations with the eclipsed conformation and
four cations with the staggered conformation, indicated by (E) and
(S), respectively, in Fig. 3b. The superstructure originates from the
different conformers of the cations and canting of the OTf anions.
The conformational differences among the cations as well as the
polar orientation of the anion resulted in the non-centrosymmetric
space group.
In contrast to [FeCp*2](OTf), no phase transition was observed in
[CoCp*2](OTf) at low temperatures. The crystal structure of this salt
at ꢀ183 ꢁC was found to be isomorphous (orthorhombic Pmn21)
with the room-temperature phase of [FeCp*2](OTf), with cell
parameters a ¼ 12.471(2) Å, b ¼ 8.709(1) Å, c ¼ 9.692(2) Å, and
V ¼ 1069.6(3) Å. The cell volume of the cobaltocenium salt was
slightly smaller than that of the ferrocenium salt, which is consistent
with the smaller molecular volume of the cobaltocenium cation.
Fig. 4. Packing diagram of [FeCp*2](C3F7CO2) determined at (a) ꢀ100 ꢁC (room-
temperature phase) and (b) ꢀ173 ꢁC (low-temperature phase). Hydrogen atoms have
been omitted for clarity.
transition temperature. The crystallographic parameters deter-
mined at ꢀ100 ꢁC and ꢀ153 ꢁC are listed in Table 5. The packing
diagram for the room-temperature phase at ꢀ100 ꢁC is shown in
Fig. 3a. The crystal belongs to the orthorhombic system with space
group Pmn21, which is a polar space group. In the unit cell, one
cation is surrounded by eight anions, and vice versa, showing
a cesium-chloride-like cationeanion arrangement. The C5-axis
of the cation and the C3-axis of the anion are arranged parallel
along the [011] direction. The space group imposes Cs symmetry on
both the cation and the anion. The OTf anions are ordered. In the
cation, one of the Cp* rings exhibits elongated thermal ellipsoids,
which suggests the presence of disorder [7]. This is presumably
ascribable to steric effects between the cation and anion; the Cp*
ring adjacent to the trifluoromethyl groups has more room, which
allows disorder, whereas the larger sulfonate group sterically
hinders the motion of the neighboring Cp* ring. In the bc-plane, the
orientations of the cations and anions are aligned in one direction
(Fig. 3). The molecular orientations in the neighboring planes are
almost perpendicular. However, the polarity remains along the c
direction, and this results in the polar space group.
2.4. Structural changes in [FeCp*2](C3F7CO2) associated with phase
transition
[FeCp*2](C3F7CO2) exhibited a phase transition at ꢀ115 ꢁC. The
crystallographic parameters of this salt determined at ꢀ173 ꢁC and
at ꢀ100 ꢁC are listed in Table 6. The packing diagrams in the high-
temperature phase and in the low-temperature phase are shown
in Fig. 4a and b, respectively. The space group (P21/c) was
unchanged, and the unit cell parameters as well as the molecular
arrangement were nearly the same in both phases. The thermal
ellipsoids of the anion are very large in the high-temperature
phase, suggesting molecular libration or displacements, whereas
they are suppressed in the low-temperature phase. The cations
and anions are slightly rotated, approximately around the [104]
direction associated with the phase transition. The anions may
attain larger space for librations in the high-temperature phase as
a result of rearrangement of the molecular packing. In the unit cell,
the fluoroalkyl groups of the anions are in contact with each other
along the b-axis, whereas the carboxylate groups are surrounded
by cations. One of the Cp* rings of the cation faces the fluoroalkyl
Table 5
Crystallographic parameters for [FeCp*2](OTf) at 120 K and 173 K.
Table 6
120 K
C21H30F3FeO3S
475.36
120
Triclinic
P1
0.71 ꢂ 0.59 ꢂ 0.47
9.6832(13)
17.587(2)
37.869(5)
89.964(2)
89.964(2)
89.960(2)
6449.1(15)
12
173 K
Crystallographic parameters for [FeCp*2](C3F7CO2) at 100 K and 173 K.
Empirical formula
Formula weight (g molꢀ1
Temperature (K)
Crystal system
Space group
Crystal size (mm3)
a (Å)
100 K
C24H30F7FeO2
539.33
100
Monoclinic
P21/c
0.53 ꢂ 0.14 ꢂ 0.09
9.4827(12)
9.6394(12)
26.754(3)
101.765(4)
2394.1(5)
4
173 K
)
173
Orthorhombic
Pmn21
0.20 ꢂ 0.15 ꢂ 0.10
12.693(3)
8.783(2)
9.715(2)
90
90
90
1083.1(4)
2
1.458
Empirical formula
Formula weight (g molꢀ1
Temperature (K)
Crystal system
Space group
Crystal size (mm3)
a (Å)
)
173
Monoclinic
P21/c
0.53 ꢂ 0.14 ꢂ 0.09
9.6657(15)
9.6945(15)
26.685(4)
102.793(5)
2438.4(6)
4
b (Å)
c (Å)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
b (Å)
c (Å)
b
(ꢁ)
Volume (Å3)
Z
Volume (Å3)
Z
dcalcd. (g cmꢀ3
)
1.469
dcalcd. (g cmꢀ3
)
1.496
1.469
Reflections collected
Independent reflections
Parameters
36,265
31,163
3134
0.0396, 0.1059
0.0586, 0.1174
1.075
7840
2700
146
0.0562, 0.1364
0.0888, 0.1557
1.008
Reflections collected
Independent reflections
12,457
4543
317
0.0841, 0.1971
0.0925, 0.2031
1.049
12,617
4626
317
0.0887, 0.2438
0.1033, 0.2578
1.054
Parameters
b
R1a, wR2b (I > 2
s
(I))
R1a, wR2 (I > 2
s
(I))
R1a, wR2b (all data)
R1a, wR2 (all data)
b
Goodness-of-fit on F2
Goodness-of-fit on F2
P
P
P
P
a
a
R1
¼
kFoj ꢀ jFck= jFoj.
R1
¼
kFoj ꢀ jFck= jFoj.
P
P
P
P
wR2 ¼ ½ wðFo2 ꢀ Fc2Þ2= wðFo2Þ2ꢃ1=2
.
wR2 ¼ ½ wðFo2 ꢀ Fc2Þ2= wðFo2Þ2ꢃ1=2
.
b
b

S. Hamada et al. / Journal of Organometallic Chemistry 713 (2012) 35e41
39
Table 7
Lattice constants of decamethylmetallocenium salts determined at ꢀ173 ꢁC.
Compounds
Crystal system
a (Å)
b (Å)
c (Å)
b
(ꢁ)
V (Å3)
[FeCp*2](C4F9SO3)
[CoCp*2](C4F9SO3)
[FeCp*2](C8F17SO3)
[FeCp*2](C4F9CO2)
Orthorhombic
Orthorhombic
Monoclinic
12.274(4)
12.097(5)
13.357(7)
9.960(6)
17.534(5)
17.419(5)
13.655(7)
9.462(6)
13.025(4)
13.094(5)
17.999(9)
27.435(18)
90
90
93.48(2)
97.98(7)
2803.0(5)
2754.9(17)
3213.2(3)
2704.0(2)
Monoclinic
moiety of the anion, and the other ring is close to the Cp* ring of an
adjacent cation.
ascribed to dipoleedipole interactions with the fluorine atoms. A
MAS NMR spectrum of the diamagnetic salt [CoCp*2](C4F9SO3)
(Fig. 5b) exhibited sharp peaks corresponding to the ring and
methyl carbons at 94.6 ppm and 8.3 ppm, respectively. The fluo-
roalkyl carbons were observed at 112 ppm as a broad peak because
of the dipoleedipole interactions. To detect possible changes
in molecular motion at low temperatures, the temperature
dependence of static NMR spectra were also measured for this salt,
but the spectra were unchanged in the temperature range down
to ꢀ93 ꢁC.
2.5. Crystallographic features of other salts
Theunitcellparametersfor[FeCp*2](CnF2nþ1SO3)(n¼ 4and8)and
[FeCp*2](C4F9CO2) determined at ꢀ173 ꢁC are listed inTable 7. In these
salts, thestructures could not be fully refined because of the extensive
disorder of the perfluoroalkyl chains. The structures of
[MCp*2](C4F9SO3) (M ¼ Fe and Co) are different from each other, and
this is probably associated with their different phase sequences.
A Cambridge Structural Database (CSD) search revealed that the
3. Conclusion
structures of about
a
dozen compounds involving per-
fluoroalkylsulfonate or perfluoroalkylcarboxylate anions with n > 2
are known. They are mostly disordered [11], and there are fewer
known structures of perfluoroalkylsulfonates than of per-
fluoroalkylcarboxylates. This may be partly ascribed to the difficulty
of analyzing the structures of such compounds, which are often
accompanied by extensive disorder, as seen in the present study.
Decamethylferrocenium salts with perfluoroalkylsulfonate
and perfluoroalkylcarboxylate anions were prepared and their
thermal behaviors characterized. The carboxylate salts were
thermally less stable than the sulfonates. These salts exhibited
phase transitions in the solid state, and the corresponding deca-
methylcobaltocenium salts exhibited different phase sequences.
Crystallographic investigations revealed structural changes asso-
2.6. Solid state 13C NMR
ciated with the phase transitions in two salts. In [Fe(C5
-
Me5)2](CF3SO3), the transition is associated with the ordering of
the cation conformations into eclipsed and staggered conforma-
tions in different ratios at low temperatures. The unit cell volume
became six times larger as a result of this ordering. The phase
transitions in [Fe(C5Me5)2](C3F7CO2) at low temperatures were
accompanied by suppression of libration or displacements of the
anion, associated with rotational rearrangements of molecules in
the unit cell. The phase transitions in other salts are probably
associated with orderedisorder transitions, as a result of the
nearly spherical molecular shapes of the cations and the charac-
teristics of the fluorinated anions. A general tendency of the per-
fluoroalkyl anions to give extensive disorder even at low
temperatures was found. Investigation of the thermal properties of
alkylferrocenium salts with lower melting points is underway in
our laboratories.
Solid state 13C NMR spectra of [MCp*2](C4F9SO3) (M ¼ Fe, Co)
were investigated. In the magic-angle-spinning (MAS) NMR spec-
trum of [FeCp*2](C4F9SO3) (Fig. 5a), peaks of the ring and methyl
carbons were observed at 253 ppm and ꢀ24 ppm, respectively, as
broad peaks resulting from paramagnetism of the cation. The
chemical shifts are in accordance with the literature values for
decamethylferrocenium salts [12]. The fluoroalkyl carbons of the
anion were observed at around 115 ppm, which is the usual
chemical shift for fluoroalkanes [13]. The broadness of the peak is
4. Experimental
4.1. General
[FeCp*2], [CoCp*2], LiCF3CO2, AgOTf, and AgCnF2nþ1CO2
(n ¼ 1e3) were purchased from SigmaeAldrich. C4F9CO2H, AgNO3,
and LiCnF2nþ1SO3 (n ¼ 4 and 8) were purchased from Wako.
AgC4F9CO2 was prepared according to a literature method [14].
Elemental analyses were carried out using a Yanaco MT5 analyzer.
DSC measurements were performed using a TA Instrument Q100
differential scanning calorimeter in the temperature range
90e430 K at a scan rate of 10 K minꢀ1. Thermogravimetric (TG)
analyses were performed on a Rigaku TG8120 under a nitrogen
atmosphere at a heating rate of 5 K minꢀ1. Solid state NMR spectra
were recorded on a Tecmag Apollo spectrometer (operating at
75.431 MHz for 13C and 299.9515 MHz for 1H) equipped with
a Doty XC MAS 4-mm probe head in the temperature range
180e298 K.
Fig. 5. 13C solid state MAS NMR spectra of (a) [FeCp*2][C4F9SO3] (spinning frequency
10.4 kHz) and (b) [CoCp*2][C4F9SO3] (spinning frequency 5.1 kHz) at 20 ꢁC.

40
S. Hamada et al. / Journal of Organometallic Chemistry 713 (2012) 35e41
4.2. [MCp*2](NO3) (M ¼ Fe, Co)
dichloromethane. The organic layer was dried over magnesium
sulfatetoproduce59mgof[FeCp*2](CF3CO2) (88%yield). The product
was recrystallized from a mixture of dichloromethane and diethyl
ether. [FeCp*2](CF3CO2)$1/3H2O: Calcd (%) for C22H30.66O2.33FeF3: C,
59.34; H, 6.94; N, 0. Found: C, 59.22; H, 7.19; N, 0. FTeIR (KBr, cmꢀ1):
785, 834, 987, 1050, 1309, 1497, 1679 (CO), 2350. Other salts were
prepared similarly. [FeCp*2](C2F5CO2)$H2O: 78% yield. Calcd (%) for
C23H32O3FeF5: C, 54.45; H, 6.36; N, 0. Found: C, 54.79; H, 6.35; N, 0.
FTeIR (KBr, cmꢀ1): 783, 821, 1050, 1212, 1232, 1322, 1370, 1460, 1681
(CO) 2371. [FeCp*2](C3F7CO2): 60% yield. Calcd (%) for C24H30O2FeF7:
C, 53.45; H, 5.61; N, 0. Found: C, 53.36; H, 5.68; N, 0.18. FTeIR (cmꢀ1):
763, 792, 811, 957, 982, 1108, 1220, 1324, 1697 (CO), 2360.
[FeCp*2](C4F9CO2): 71.2% yield. Calcd (%) for C25H30O2FeF9: C, 50.95;
H, 5.13;N, 0. Found:C, 51.30;H, 5.54;N, 0. FTeIR(cmꢀ1):711, 737, 793,
953, 1023, 1107, 1191, 1219, 1323, 1695 (CO), 2916.
To a stirred solution of [FeCp*2] (200 mg, 0.612 mmol) in acetone
was added an aqueous solution of a slight excess of AgNO3 (120 mg,
0.706 mmol). The mixture was stirred for 30 min, and the solution
was filtered to remove silver deposits and excess silver salt. After
evaporation of the solvent, the residue was extracted with
dichloromethane (100 mL) and washed with water. The organic
phase was dried over magnesium sulfate and evaporated to give
green crystals of [FeCp*2](NO3) in 84% yield. FTeIR (KBr, cmꢀ1):
1020, 1370 (NO), 1620, 1745, 2955. [CoCp*2](NO3) was prepared
similarly, under
a
nitrogen atmosphere, using deca-
methylcobaltocene (39.5 mg, 0.120 mmol) and silver nitrate (19 mg,
0.112 mmol), yielding 34.1 mg of yellow crystals in 80% yield. FTeIR
(KBr, cmꢀ1): 1025, 1352 (NO), 1629, 1680. These salts were used for
anioneexchange reactions without further purification.
4.6. [Fe(C5Me4H)2](CnF2nþ1CO2) (n ¼ 1e3)
4.3. [MCp*2](OTf) (M ¼ Fe, Co)
These salts were prepared as described for [FeCp*2](CnF2nþ1CO2).
The products were recrystallized from mixtures of dichloromethane
and hexane. [Fe(C5Me4H)2](CF3CO2): 86% yield. Calcd (%) for
C20H26O2FeF3: C, 58.41; H, 6.37; N, 0. Found: C, 58.72; H, 6.48; N, 0.
AgOTf (13.8 mg, 5.37 ꢂ 10ꢀ2 mmol) in acetonitrile was added
dropwise to an acetonitrile solution of [FeCp*2] (15.8 mg,
4.84 ꢂ 10ꢀ2 mmol). After stirring for 1 h at room-temperature, the
solution was filtered, evaporated, and the residue was dried under
vacuum. The powder was again dissolved in acetonitrile, filtered,
evaporated, and dried under vacuum to produce 21 mg of
[FeCp*2](OTf) (91% yield). The product was recrystallized by slow
diffusion of diethyl ether into an acetonitrile solution. Anal. Calcd
(%) for C11H10F3FeO3S: C, 53.05; H, 6.37; N, 0. Found: C, 53.26; H,
6.57; N, 0. FTeIR (cmꢀ1): 748, 1026, 1134 (SO), 1274 (SO), 1384, 1479.
[CoCp*2](OTf) was prepared by the same method, using AgOTf
(36.0 mg, 0.14 mmol), [CoCp*2] (49.4 mg, 0.15 mmol), and acetone
solvent, under a nitrogen atmosphere. Yellow plate crystals were
obtained in 89% yield. Anal. Calcd (%) for C21H30F3O3SCo: C, 52.72;
H, 6.32; N, 0. Found: C, 52.36; H, 6.32; N, 0. FTeIR (cmꢀ1): 748,1026,
1149 (SO), 1280 (SO), 1384, 1483.
FTeIR (cmꢀ1): 668, 813, 1025, 1196, 1691 (CO), 2020, 2359. [Fe(C5
-
Me4H)2](C2F5CO2): 96% yield. Calcd (%) for C21H26O2FeF5: C, 54.68;
H, 5.68; N, 0. Found: C, 54.75; H, 5.78; N, 0. FTeIR (KBr, cmꢀ1): 692,
781,1169,1201,1680 (CO), 2350. [Fe(C5Me4H)2](C3F7CO2): 98% yield.
Calcd (%) for C22H36O2FeF7: C, 50.68; H, 6.96; N, 0. Found: C, 50.48; H,
6.56; N, 0. FTeIR (cmꢀ1): 725, 765, 1011, 1148, 1200, 1309, 1692 (CO),
2360.
4.7. X-ray crystallography
X-ray diffraction data for single crystals of [FeCp*2](OTf),
[CoCp*2](OTf), and [FeCp*2](C3F7CO2) were collected on a Bruker
SMART APEX II CCD diffractometer, using Mo
Ka radiation
4.4. [MCp*2](CnF2nþ1SO3) (n ¼ 4 and 8; M ¼ Fe, Co)
(
l
¼ 0.71073 Å). Crystal data, data collection parameters, and
analysis statistics for these compounds are listed in Tables 5and 6.
The data were corrected for absorption using the SADABS program
[15]. All calculations were performed using SHELXL [16]. The
structure was solved by direct methods (SHELXS 97) and expanded
using Fourier techniques. The non-hydrogen atoms were refined
anisotropically. Empirical absorption corrections were applied. The
hydrogen atoms were inserted at the calculated positions and
allowed to ride on their respective parent atoms. ORTEP-3 [17] was
used for molecular graphics. Although the unit cell of [FeCp*2](OTf)
in the low-temperature phase was very close to orthorhombic, the
correct space group turned out to be triclinic P1. Although a check
using the PLATON program [18] suggests Pmn21, this space group is
improbable because different conformers overlap and disorder is
caused by symmetry constraints. Analyses assuming the mono-
clinic space groups P21, Pn, and Pc also resulted in improbable
disordered structures.
Water solutions of [FeCp*2](NO3) (50 mg, 0.111 mmol) and
LiC4F9SO3 (43.5 mg, 0.142 mmol) were mixed and stirred for
30 min, and then extracted with dichloromethane. The organic
phase was washed with water, dried over magnesium sulfate, and
evaporated, to produce 64.1 mg of [FeCp*2](C4F9SO3) (47% yield).
The product was recrystallized from dichloromethaneehexane.
Calcd (%) for C24H30O3SFeF9: C, 46.09; H, 4.84; N, 0. Found: C,
46.07; H, 5.01; N, 0. FTeIR (cmꢀ1): 652, 667, 1128 (SO), 1228, 1261
(SO). [CoCp*2](C4F9SO3) was prepared by the same method, using
[CoCp*2](NO3) (50 mg, 0.111 mmol) and LiC4F9SO3 (47.3 mg,
0.154 mmol), to produce 59.0 mg of the product (85% yield). The
product was recrystallized by slow diffusion of diethyl ether into
a dichloromethane solution. Calcd (%) for C24H30O3SCoF9: C, 45.87;
H, 4.81; N, 0. Found: C, 45.63; H, 4.83; N, 0. FTeIR (cmꢀ1): 653,
1052, 1129 (SO), 1207, 1264 (SO), 1482. [FeCp*2](C8F17SO3) was
obtained by the same procedure, in 54% yield. When extracting
this salt, a saturated aqueous solution of sodium chloride was
added. Calcd (%) for C28H30O3SFeF17: C, 40.74; H, 3.66; N, 0. Found:
C, 40.56; H, 3.70; N, 0. FTeIR (cmꢀ1): 618, 751, 1030, 1144 (SO),
1195, 1261 (SO).
CCDC-822999 ([FeCp*2](OTf) at ꢀ100 ꢁC), CCDC-823000
([FeCp*2](OTf) at ꢀ153 ꢁC), CCDC-823460 ([FeCp*2](C3F7CO2)
at ꢀ100 ꢁC), and CCDC-790933 ([FeCp*2](C3F7CO2) at ꢀ173 ꢁC).
Diffraction data for the other salts were collected at ꢀ173 ꢁC, but
their structures could not be fully determined because of extensive
disorder, and only cell parameters are listed in Table 7.
4.5. [FeCp*2](CnF2nþ1CO2) (n ¼ 1e4)
Acknowledgments
A water solution of AgCF3CO2 (37.1 mg, 0.168 mmol) was added
dropwise to an acetone solution of [FeCp*2] (50 mg, 0.153 mmol).
Afterstirringthe solutionfor30min, silverdepositswereremovedby
filtration, and the filtrate was evaporated, and extracted with
We thank Y. Furuie (Kobe University) for elemental analyses and
M. Nakama (Crayonsoft Inc., Tokyo) for providing a Web-DB system.
This work was financially supported by KAKENHI (No. 21350077)

S. Hamada et al. / Journal of Organometallic Chemistry 713 (2012) 35e41
41
(b) T. Mochida, K. Takazawa, H. Matsui, M. Takahashi, M. Takeda, M. Sato,
Y. Nishio, K. Kajita, H. Mori, Inorg. Chem. 44 (2005) 8628e8641.
[6] (a) T. Mochida, K. Yoza, J. Organomet. Chem. 695 (2010) 1749e1752;
(b) T. Mochida, Y. Funasako, H. Azumi, Dalton Trans. 40 (2011) 9221e9228;
(c) Y. Funasako, T. Mochida, Kenji Yoza, J. Organomet. Chem. 698 (2012)
49e52.
from the Japan Society for the Promotion of Science (JSPS). We also
thank the anonymous reviewers for their valuable comments.
Appendix A. Supplementary material
[7] (a) T. Inagaki, T. Mochida, Chem. Lett. 39 (2010) 572e573;
(b) T. Inagaki, T. Mochida, M. Takahashi, C. Kanadani, T. Saito, D.Kuwahara,
Chem. Eur. J.. doi: 10.1002/chem.201200151; (c) Y. Funasako, T. Mochida,
T. Inagaki, T. Sakurai, H. Ohta, K. Furukawa, T. Nakamura, Chem. Commun. 47
(2011) 4475e4477.
CCDC-822999, CCDC-823000, CCDC-823460 and CCDC-790933
contain the supplementary crystallographic data for this paper.
These data can be obtained free of charge from the Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif.
[8] (a) M. Armand, F. Endres, D.R. MacFarlane, H. Ohno, B. Scrosati, Nat. Mater. 8
(2009) 621e629;
(b) I. Krossing, J.M. Slattery, C. Daguenet, P.J. Dyson, A. Oleinikova,
H. Weingärtner, J. Am. Chem. Soc. 128 (2006) 13427e13434.
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[11] S. Rau, L. Böttcher, S. Schebesta, M. Stollenz, H. Görls, D. Walther, Eur. J. Inorg.
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[12] H. Heise, F.H. Köhler, M. Herker, W. Hiller, J. Am. Chem. Soc. 124 (2002)
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[13] S.K. Quek, I.M. Lyapkalo, H.V. Huynh, Tetrahedron 62 (2006) 3137e3145.
[14] M. Hausptschein, A.V. Grosse, J. Am. Chem. Soc. 73 (1951) 2461e2463.
[15] G.M. Sheldrick, SADABS: Program for Semi-empirical Absorption Correction,
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