Thermal analysis, phase transitions and molecular reorientations in [Fe(OS(CH3)2)6](ClO4)2

Article abstract of DOI:10.1007/s10973-017-6181-z

Thermogravimetric analysis connected with quadruple mass spectroscopy (TG/MS) for an identification of [Fe(OS(CH₃)₂)₆](ClO₄)₂ decomposition products, carried out to determine its thermal stability, has indicated that the title compound does not change its mass till ca. 385?K. Above this temperature, it starts slowly to lose a part of (CH₃)₂SO ligands, which begins to form a liquid phase, in which the title compound partially dissolves. Finally, at ca. 476?K, when two from six coordinated (CH₃)₂SO were detached from central atom, the [Fe(OS(CH₃)₂)₄](ClO₄)₂ is formed. At ca. 514?K this sample explodes. Differential scanning calorimetry (DSC) measurements performed in the temperature range of 100–443?K revealed existence of two anomalies on DSC curves. The first, a big one, at T_c?≈?338?K is associated with the phase transition: crystal phase Cr. 1???rotational phase Rot. 1, and the second, a small one, at T_m1?≈?414?K is associated with two parallel processes, which are: decomposition of [Fe(OS(CH₃)₂)₆](ClO₄)₂ with the DMSO release and dissolution of [Fe(OS(CH₃)₂)_6?x](ClO₄)₂ in DMSO. The large value of solid–solid phase transition entropy change (?S_c?≈?79.3?J?mol^?1?K^?1) and small value of the melting process (?S_m?≈?5.8?J?mol^?1?K^?1) indicate on such large configurational disorder in the high-temperature phase that this phase can be considered as a rotational phase (so called also as “plastic crystals”). The results of the vibrational and reorientational dynamics of (CH₃)₂SO ligands and ClO₄ ^? anions in the high- and low-temperature phases of [Fe(OS(CH₃)₂)₆](ClO₄)₂, investigated by Fourier transform infrared absorption spectroscopy, show that even in the low-temperature phase the CH₃ groups in (CH₃)₂SO ligands and also the ClO₄ ^? anions perform fast (correlation time τ_R?≈?10^?12?s) reorientational motions. These reorientational motions above T_c temperature became so fast that in the rotational phase they turn into nearly free rotational motions.

Full text of DOI:10.1007/s10973-017-6181-z

J Therm Anal Calorim
DOI 10.1007/s10973-017-6181-z
Thermal analysis, phase transitions and molecular reorientations
in [Fe(OS(CH ) ) ](ClO )
3
2 6
4 2
1
1
El z_ bieta Szostak
•
Anna Migdał-Mikuli
Received: 6 October 2016 / Accepted: 7 February 2017
Ó The Author(s) 2017. This article is published with open access at Springerlink.com
Abstract Thermogravimetric analysis connected with
quadruple mass spectroscopy (TG/MS) for an identification
of [Fe(OS(CH ) ) ](ClO ) decomposition products, car-
infrared absorption spectroscopy, show that even in the low-
temperature phase the CH groups in (CH ) SO ligands and
3
3 2
-
also the ClO anions perform fast (correlation time
3
2 6
4 2
4
-
12
ried out to determine its thermal stability, has indicated that
the title compound does not change its mass till ca. 385 K.
Above this temperature, it starts slowly to lose a part of
sR & 10
motions above T temperature became so fast that in the
s) reorientational motions. These reorientational
c
rotational phase they turn into nearly free rotational motions.
(
CH ) SO ligands, which begins to form a liquid phase, in
3 2
which the title compound partially dissolves. Finally, at ca.
76 K, when two from six coordinated (CH ) SO were
Keywords Thermal analysis (TG/QMS) Á Phase
4
transitions Á Vibrational and rotational motions Á DSC Á
Fourier transform infrared absorption spectroscopy (FT-IR)
3
2
detached from central atom, the [Fe(OS(CH ) ) ](ClO ) is
3
2 4
4 2
formed. At ca. 514 K this sample explodes. Differential
scanning calorimetry (DSC) measurements performed in the
temperature range of 100–443 K revealed existence of two
anomalies on DSC curves. The first, a big one, at
Tc & 338 K is associated with the phase transition: crystal
phase Cr. 1 $ rotational phase Rot. 1, and the second, a
small one, at Tm1 & 414 K is associated with two parallel
processes, which are: decomposition of [Fe(OS(CH ) ) ]
Introduction
The rich and diverse polymorphism of compounds of the
type: [M(DMSO) ](ClO ) (where M = Cd, Co, Mn, Zn,
4 2
6
Ni, Mg, Sr and DMSO = (CH ) SO) was the subject of our
3 2
interest since 2003 [1–7]. We have found that these sub-
stances possess both orientationally ordered and highly
disordered crystal phases. Some from those just recently
mentioned are rotational phases, so-called plastic crystals.
Certain from the all detected phases have stable and
another have metastable character.
3
2 6
(
ClO4)2 with the DMSO release and dissolution of
Fe(OS(CH ) ) ](ClO ) in DMSO. The large value of
[
3
2 6-x
4 2
solid–solid phase transition entropy change (DS &
c
-
1
-1
K ) and small value of the melting process
7
9.3 J mol
-
1
-1
K ) indicate on such large configu-
(
DS & 5.8 J mol
m
rational disorder in the high-temperature phase that this
phase can be considered as a rotational phase (so called also
as ‘‘plastic crystals’’). The results of the vibrational and
According to Selbin et al. [8] and Currier and Weber [9]
title compound precipitated as a pale yellow crystals and
explodes in the vicinity of 423 K. Its infrared absorption
spectrum suggests that DMSO ligands are bonded to a
central metal through the oxygen atom [8–10]. Berney and
Weber [10] have claimed that the study of
-
reorientational dynamics of (CH ) SO ligands and ClO
3
2
4
anions in the high- and low-temperature phases of
[
Fe(OS(CH ) ) ](ClO ) , investigated by Fourier transform
3 2 6 4 2
[Fe(OS(CH ) ) ](ClO ) is difficult because of its
3 2 6 4 2
rapid decomposition.
&
El z_ bieta Szostak
szostak@chemia.uj.edu.pl
The general aim of the present study is to discover the
polymorphism of the fresh synthesized [Fe(OS(CH ) ) ]
3
2 6
1
(ClO ) sample. The temperature ranges of DSC mea-
4 2
Faculty of Chemistry, Jagiellonian University, ul.
Ingardena 3, 30-060 Krak o´ w, Poland
surement will be selected based on the results obtained by
123

E. Szostak, A. Migdał-Mikuli
-
MIR) and 400–50 cm (FT-FIR), and with a resolution of
1
thermogravimetric method. Additional aim of conducted
research is to find connections between those detected
phase transitions and eventual changes in the speed of
stochastic reorientational motions of DMSO ligands and
-1
2 cm . The FT-FIR spectra were recorded for the sample
suspended in Apiezon grease and placed on polyethylene
window. The FT-MIR spectra were recorded for the sample
mixed with Nujol and placed between two KBr pellets. An
Advanced Research System(ARS)heliumDE-202Acryostat
and water-cooled helium ARS-2HW compressor working in
a closed cycle manner, with controlled heating and cooling
rates and temperature stabilization within ± 0.2 K, were used
to obtain the spectra at high temperatures. The temperature of
the ‘‘cold finger’’ was measured with an accuracy of ± 1 K,
but the sample temperature, in particular, in a high-temper-
ature range could have been several Kelvin higher.
-
ClO4 anions and/or with eventual a change of the crystal
structure. We would like to draw these information by
means of Fourier transform infrared absorption spec-
troscopy measurements performed in a function of tem-
perature at cooling and heating the title compound.
Experimental
Preparation procedure of a polycrystalline sample was
analogical to the synthesis of the analogous compounds
with DMSO ligands [1–7]. Chemical composition of the
synthesized sample was analysed by determination of
percentage content of carbon, hydrogen and sulphur using
an EURO EA 3000 elemental analyser with the accuracy of
Results and discussion
Thermogravimetric analysis
±
0.3%. Theoretical contents: C, 19.92%; H, 5.01%;
Figure 1 shows TG and DTG curves recorded for [Fe(OS
(CH ) ) ](ClO ) inaflow of Argon ata constantheating rateof
S, 26.59%. Found: Mg, 3.32%; C, 19.33%; S, 26.24%. The
elemental analysis of the title compound confirmed the
presence of the stoichiometric number of six DMSO
molecules in the complex cation.
3
2 6
4 2
-1
10 K min in the temperature range of 290–650 K. Obtained
results indicate that the compound does not change its mass till
ca. 385 K. Above this temperature, [Fe(OS(CH ) ) ](ClO )
3
2 6
4 2
Thermal analysis of the examined compound was made
first of all in order to check its thermal stability. The ther-
mogravimetric (TG/DTG) measurements were performed
starts to decompose. In the first stage of the thermal decom-
position, which take place within the temperature range
385–447 K, two molecules of dimethylsulfoxide are released
and [Fe(OS(CH ) ) ](ClO ) is formed. This compound is
e
using a Mettler Toledo TGA/SDTA 851 apparatus. A sample
3
2 4
4 2
weighing 3.6581 mg was placed in a 150-ll Al O crucible.
stable up to 476 K, and then, it starts to lose next DMSO
molecules. Suddenly, just above 514 K intense decomposition
of created substance connected with an explosion takes place.
Figure 2 presents TG curve and QMS curves of the
particular gaseous products of [Fe(OS(CH ) ) ](ClO )
4 2
2
3
The measurements were made in a flow of argon (Ar 6.0;
3
0 cm min ) from 293 up to 651 K with a constant heating
-1
8
-1
rate of 10 K min . The temperature was measured by a Pt–
Pt/Rh thermocouple with the accuracy of ± 0.5 K. Evolved
gaseous products from the decomposition of the compound
were identified using a ThermoStar GSD300T Balzers
quadruple mass spectrometer (QMS). The temperature cali-
bration of the TG instrument was done by using indium, zinc
and aluminium melting points temperature and compares
3
2 6
thermal decomposition. During the TG experiment, the
QMS spectra of masses were followed from m/e = 10 to
80; however, for reasons of graphic clarity, only the masses
Á
Á
of m/e = 15, 16, 28, 44, 48, and 35 representing: CH , O
3
Á
or CH , CO or C H , CO , SO and Cl are shown in Fig. 2.
4
2
4
2
-6
themwiththeliteraturevalues. Itsaccuracyisequalto10 g.
The mass spectrometer was operated in electron impact mode
The QMS spectra indicate that within the temperature
range 385–513 K title compound lose mainly DMSO
molecules, what was registered as a distinct peak at the
(
EI) using channeltron as a detector. Screening analyses were
performed in the selected ion monitoring (SIM) mode.
The DSC measurements of [Fe(OS(CH ) ) ](ClO )
m/e = 15 (CH ) line and rather small anomaly at m/e = 44
3
(CS/CO ) line. At the temperature 514 K (explosion of the
2
3
2 6
4 2
compound were made for two samples using two different
DSC instruments. A Perkin-Elmer PYRIS 1 DSC instru-
ment was used in the temperature range of 100–443 K
sample) besides the products of DMSO decomposition
(signals m/e = 28, 44, 48, 15 i 16), the chlorine and oxy-
gen molecules from decomposition of perchlorate anions
are additionally emitted (signals m/e = 35, 16).
(
sample A = 6.16 mg). A Mettler Toledo DSC 821e
instrument was used in the temperature range of
98–443 K (sample: B = 6.26 mg). The details of the
2
DSC measurements
DSC experiment were the same as described in [11].
The infrared absorption measurements were performed
using a Bruker VERTEX 70v Fourier transform infrared
spectrometer in the spectral ranges of: 4000–400 (for FT-
The DSC curves were obtained for two [Fe(OS
(CH ) ) ](ClO ) samples (A and B) with different masses.
3
2 6
4 2
The results have not shown any significant changes in the
1
23

3 2 6 4 2
Thermal analysis, phase transitions and molecular reorientations in [Fe(OS(CH ) ) ](ClO )
Fig. 1 Mass loss valuated on
TG curve of the
1.5
1.0
0.5
1
00
[
3 2 6 4 2
Fe(OS(CH ) ) ](ClO ) sample
Δm < 0.1%
measured in the temperature
range of 290–650 K
Decomposition
with explosion
8
6
4
2
0
0
0
0
0
Δm = 21.4%
Δm = 16.2%
0.0
–
–
–
15
16
17
–18
3
00
350
400
450
500
550
600
650
T/K
Fig. 2 TG and QMS curves of
thermal decomposition of
4
140
120
00
80
3
3
3
3
2
2
2
22
2
1
6
4
2
0
8
6
4
[
3 2 6 4 2
Fe(OS(CH ) ) ](ClO )
1
3
2
1
60
m/z = 28, CO, C H
2
4
40
20
0
8
m/z = 44, CS, CO2
m/z = 48, SO
0
0
0
.8
2
1
0
.6
.4
m/z = 15, CH3
m/z = 16, O, CH4
0.2
0.0
+
m/z = 35, CI, H S
3
0
3
00
350
400
450
500
550
600
650
T/K
h
c
character of the DSC curves, so we will present here only
the results obtained for sample A. The measurements were
performed with different scanning rate and also with initial
and final heating and cooling conditions, in order to check
whether synthesized compound can create such
metastable phases like did other previously studied com-
pounds of [M(OS(CH ) ) ](ClO ) type [1–7].
T
= 338.3 and T
= 338.3 K (where indexes h and
onset
onset
c denote heating and cooling of the sample, respectively).
The phase transitions temperatures determined for the
h
onset
sample
c
B
were as follows:
T
= 337.3 and
T
onset
= 337.4 K. The mean values of the phase transition
h
temperature are: T = 338.3 ± 0.3 K (at heating) and at
c
c
T = 338.3 ± 0.3 K (at cooling) with the estimated
-
3
2 6
4 2
c
1
-1
K . The large
Figure 3 presents the temperature dependences of the
heat flow (DSC curves) obtained on heating (upper curve)
and on cooling (lower curve) of the sample A in the tem-
perature range 100–385 K. One distinct anomaly was
registered on each of these two DSC curves at:
entropy change DS & 79.3 ± 6.2 J mol
c
value of transition entropy change indicates considerable
configurational disorder in the high-temperature phase (so-
called ODIC crystals [1–7, 12]). The absence of hysteresis
of the phase transition temperature at T and sharpness of
c
123

E. Szostak, A. Migdał-Mikuli
[
Fe(OS(CH ) ) ](CIO )
4 2
not transform into the metastable phase while the sample was
cooled down, opposite to other investigated by us earlier
compounds of the type: [M(OS(CH ) ) ](ClO ) [1–7].
3
2 6
100
3
2 6
4 2
8
6
4
2
0
0
0
0
0
Figure 4 presents DSC curves obtained during heating
and cooling of the sample A from 290 to 443 K with a
Rot. 1
Rot. 1
-
1
scanning rate of 40 K min . At the temperature range of
90–385 K, we can see a very big and sharp anomaly at Tc
2
connected with the phase transition: phase Cr. 1 ? phase
Rot. 1. Later, while heating hermetically closed sample A,
being in the Rot. 1 phase, up to 443 K, it experiences a
reversible phase transition at Tm1 = 414.1 ± 0.4 K into
the phase named L0. This phase transition is observed as a
small and broad anomaly on DCS curve. The entropy
change calculated for this phase transition is
Cr. 1
Endo
Exo
Cr. 1
200
100
150
250
300
350
400
-
1
-1
DS & 5.8 ± 0.5 K J mol
K . The thermodynamic
m
T/K
parameters of the detected phase transitions obtained dur-
Fig. 3 DSC curves registered in the temperature range of 100–385 K
with a
ing heating are presented in Table 1.
during heating and cooling of [Fe(OS(CH
scanning rate of 20 K min
3
)
2 6
) ](ClO
4
)
2
It is not possible to determine the nature of the observed
phases only on the basis of DSC measurements. However,
using a microscope we have observed that phases Cr. 1 and
Rot. 1 were the solid phases and L0 is partially melted
phase. Taking into account the findings from thermal
analysis, we can postulate that at Tm1 the sample became
partially dissolved in liquid DMSO, which arises out from
-1
[
Fe(OS(CH ) ) ](CIO )
6
5
4
3
2
1
0
0
0
0
0
0
0
3 2 6 4 2
L0
Rot. 1
the thermal decomposition of [Fe(OS(CH ) ) ](ClO ) to
3 2 6 4 2
L0
[Fe(OS(CH ) ) ](ClO ) (compare ‘‘Thermogravimetric
3 2 4 4 2
Cr. 1
analysis’’ section), because the sample is at this DSC
experiment hermetically closed in the calorimetric vessel.
Moreover, it was concluded from the large value of the
Rot. 1
Cr. 1
Endo
Exo
entropy change of the phase transition DS (see Table 1)
c
that phase Cr. 1 is orientationally dynamically disordered
crystal, so-called ODIC, and phase Rot. 1 is more likely
rotational phase, so-called plastic crystal.
3
00
320
340
360
380
400
420
440
T/K
Fig. 4 DSC curves registered in the temperature range of 290–443 K
during heating and cooling of [Fe(OS(CH ](ClO with a
scanning rate of 40 K min
Vibrational spectra
3
)
)
2 6
4 2
)
-1
2?
The [Fe(OS(CH ) ) ] complex cation can be described in
3
2 6
the S point group, with the normal vibrations belonging to
6
the anomaly suggest that the detected phase transition is of
the second-order type. Thus, the title compound has twosolid
phases in the temperature range of 100–385 K: high tem-
perature (phase Rot. 1) and low temperature (phase Cr. 1). It
is very interesting that in the high-temperature phase of
the symmetry species C = 29A ? 29E ? 30A ? 30-
vib
g
g
u
0
Eu (or C
the methyl groups as point masses). The ‘‘g’’ modes are
= 11A ? 12A ? 11E ? 12E considering
g u g u
vib
Raman active whereas the ‘‘u’’ modes are IR active
[
10, 13, 14].
[
Fe(OS(CH ) ) ](ClO ) , regardless of a scanning rate, does
3 2 6 4 2
h
c
c
Table 1 Thermodynamic parameters of the detected phase transitions obtained at heating (T
c 3 2 6 4 2
) and at cooling (T ) of [Fe(OS(CH ) ) ](ClO )
Phase transition
3 2 6 4 2
[Fe(OS(CH ) ) ](ClO )
h
c
c
c
-1
-1 -1
K
T
/K
T
/K
DH/kJ mol
DS/J mol
T
m1
c
Rot. 1 $ L0
Cr 1 $ Rot. 1
414.1 ± 0.4
338.3 ± 0.3
413.2 ± 0.5
338.3 ± 0.3
2.45 ± 0.17
5.8 ± 0.5
T
26.79 ± 2.09
79.3 ± 6.2
1
23

3 2 6 4 2
Thermal analysis, phase transitions and molecular reorientations in [Fe(OS(CH ) ) ](ClO )
3 2 6 4 2
Table 2 Comparison of the band positions of the infrared spectra of solid [Fe(OS(CH ) ) ](ClO ) and liquid DMSO at room temperature
IR of solid [Fe(OS(CH
3
)
2
)
6
4
](ClO )
2
and liquid DMSO at room temperature
Literature data [8–10, 15]
a
This paper in: Apiezon, Nujol
b
DMSO literature data [13, 15–17]
Tentative assignments
a
5
7
8
1
1
1
1
2
2
2
2
3
3
3
4
4
4
4
6
6
7
7
9
9
9
9
9
9
9
1
1
1
1
1
1
1
1
1
1
3
2 m
6 m
6 m
m
m
m
L
L
L
(lattice)
(lattice)
(lattice)
a
a
a
a
a
a
12 w
27 w
55 w
c (FeOS)
c (FeOS)
157 w
3
T (CH )
82 m
12 m
27 m
T (CS)
T (CS)
T (CS)
a
a
225 w
262 m
a
65 sh
d (CSC)
d (CSC)
x (CSC)
s (CSC)
d (CSC)
a
86 m
19 m
39 vs
a
320 sh
340 m
307 w
335 m
383 m
a
a
63 m
a
02 sh
a
14 s
402 sh
415 m
438 m
m
m
m
m
s
s
(FeO)
(FeO)
a,b
37 s
as (FeO)
a,b
b
77 m
20 m
s
(FeO)
623 m
670 vw
720 m
d
d
(OClO)F
2
b
b
77 w
670 m
700 m
m
m
s
(CS)
11 m
18 m
as (CS)
b
b
01 vw
900 vw
957 vs
q (CH
(ClO)A
q (CH
3
)
b
b
b
36 vs
50 sh
59 sh
931 vs
950 s
m
s
1
3
)
m
m
s
s
(SO)
(SO)
b
69 vw
b
88 sh
b
99 s
989 vs
1006 m
1012 s
1032 s
q (CH
q (CH
q (CH
3
)
3
)
3
)
b
019 sh
b
034 w
074 br
b
b
1075 br
m
m
as (ClO)F
as (ClO)F
2
2
089 sh
b
300 w
313 w
322 w
1294 sh
1311 w
d
d
s
s
(HCH)
(HCH)
b
b
b
405 m
1406 vw
1419 s
d
d
d
as (HCH)
as (HCH)
as (HCH)
b
419 w
445 sh
013 sh
b
b
1437 m
2991 m
m
as (CH)
vw very weak, w weak, sh shoulder, m medium, s strong, vs very strong, m stretching, q rocking, d scissoring, b bending-in-plane, c bending-out-
of-plane, T torsion
-
4
-1
m (ClO)A = 928 cm ,
-1
m = d (OClO)E = 459 cm ,
The unperturbed tetrahedral ClO anion has nine normal
-
s
1
2
-1
d
modes. The vibrational representation of ClO under T point
d
m = m (ClO)F = 1119 cm
and m = d (OClO)F =
4
3
as
-1
625 cm . All of them are Raman active, but only two of them:
2
4
d
2
-
4
group is: Cvib = A ? E ? 2F . Thus, an isolated ClO
1
2
anion has four vibration frequencies (in wavenumbers): m =
m and m , of F symmetry, are infrared active [10, 13–15].
1
3
4
2
123

E. Szostak, A. Migdał-Mikuli
The experimental IR fundamental frequencies for
Fe(OS(CH ) ) ](ClO ) are reported in Table 2. The
To determine whether the observed phase transitions are
correlated with changes in the reorientational dynamics of
[
3
2 6
4 2
-
assignment of the bands is based on the well-characterized
spectra of dimethyl sulfoxide [13, 15–17], perchlorate
the OS(CH ) ligands and/or of the ClO anions, we fol-
3
2
4
lowed the analysis of the full width at half maximum
(FWHM) described by Carabatos-Nedelec and Becker,
which is based on the theory used for the damping asso-
ciated with an order–disorder mechanism [18, 19]. The
reorientational correlation time sR is the mean time
between the instantaneous jumps from one potential well to
the other, and it is defined by the following formula:
anion
[15]
and
the
vibrational
spectra
of
[
Fe(OS(CH ) ) ](ClO ) obtained experimentally and pre-
3
2 6
4 2
sented in [8–10].
Molecular motions
FT-FIR investigations
The Fourier transform far-infrared (FT-FIR) spectra of title
ꢀ
ꢁ
Ea
s ¼ s exp
ð1Þ
R
1
kBT
-
1
compound within the wavenumber range of 500–50 cm
where s
energy activation E
reorientation and k
?
is the relaxation time at an infinite temperature T,
were registered during heating and cooling of the sample in
the temperature range of 280–350 and 20–350 K, respec-
tively. The selected FIR spectra recorded for title com-
pound in the temperature range of 280–350 K are
illustrated in Fig. 5. The spectrum registered at 280 K in
a
is the potential barrier height for
is the Boltzmann constant. When
B
2
2
x s
phonon mode, the temperature dependence of the FWHM
ꢀ 1, where x = 2pm is the frequency of a particular
R
is determined by following expression [19, 20]:
ꢀ
-
1
ꢁ
the range of 295–190 cm
contains four main bands
Ea
(
denoted by dotted lines in Fig. 5). Two of them: at 286
1
FWHM ¼ ða þ bTÞ þ c exp À
ð2Þ
RT
-
and at 265 cm are connected with the d(CSC) scissoring
vibrational modes, and two at 227 and at 212 cm are
-
1
where a, b, c and E are the fitting parameters. Here the E
a a
connected with the T(CS) ligand torsional modes. At
is the activation energy of the reorientation process,
3
50 K, only two bands are visible in the mentioned
R = N k is gas constant and N is Avogadro’s constant.
A B A
regions. As can be seen in Fig. 5 below the PT temperature
The linear part of Eq. (2) corresponds to the vibrational
relaxation, and the exponential term corresponds to the
reorientational relaxation. The last one is connected with
thermal molecular reorientational motions of a diffusion
nature.
-
the intensity of the band at 286 cm increases and the
1
-
1
band at 220 cm
splits into two components. These
characteristic changes of the FT-FIR spectra may suggest
2
that the symmetry of [Fe(OS(CH ) ) ] lowers below the
?
3
2 6
Tc temperature.
The temperature dependence of the FWHM of the IR
1
-
band at 339 cm , assigned to the s(CSC) mode, is pre-
sented in Fig. 6. The FWHM was obtained by fitting with
[
Fe(OS(CH ) ) ](CIO )
3 2 6 4 2
Heating
Cooling
30
2
2
2
2
8
6
4
2
3
3
3
50 K
45 K
40 K
280 300 320 340 360 380
–1
T
c
Wavenumber/cm
3
3
30 K
20 K
τ(CSC) mode at 339 cm–1
3
3
2
10 K
00 K
80 K
20
1
1
1
8
6
4
5
00 400 300 200 100
500 400 300 200 100
Tc
Wavenumber/cm–1
Wavenumber/cm–1
0
50
100
150
200
250
300
350
400
Fig. 5 Thermal evolution of the FT-FIR spectrum of
Fe(OS(CH ](ClO recorded upon heating and cooling in the
wavenumber range of 500–50 cm . Temperature of the phase
transition at T is marked by horizontal arrow, and the IR bands,
which split or disappear with increasing temperature, are denoted by
vertical dashed line
T/K
[
3 2
)
)
6
4 2
)
-
1
Fig. 6 Temperature dependence of the infrared bandwidth (FWHM)
connected with s(CSC) mode. Solid red line represents fitting of Eq. (2)
to the experimental points. Dash vertical line denotes phase transition
c
c
temperature T registered by DSC upon cooling. (Color figure online)
1
23

3 2 6 4 2
Thermal analysis, phase transitions and molecular reorientations in [Fe(OS(CH ) ) ](ClO )
Table 3 Fitted parameters a, b, c and E
dependence of the FWHM of the IR band connected with s(CSC) and
a
for the temperature
16
15
d
d
(OClO)F
2
modes
Band at 339 cm
-
1
-1
Parameters
Band at 620 cm
d
1
1
1
1
1
4
3
2
1
0
s(CSC)
d
(OClO)F
2
–
1
δ (OC1O)F mode at 620 cm
d
2
I
I
II
-
1
1
1
a (cm
b (cm
)
15.6
10.6
13.0
-
-1
)
-3
-3
K
1.5 9 10
77.1
-1.2 9 10
1.8
-
3
c (cm
)
117.8
-1.7 9 10
-
1
)
E
a
(kJ mol
6.8
10.0
2.9
Tc
0
50
100
150
200
250
300
350
400
T/K
the Lorentz function, and a typical deconvolution of the
spectrum at 350 K is illustrated in the inset. In Fig. 6 the
solid line is fitted to experimental points by Eq. (2), and the
fitting parameters are listed in Table 3. We observe a large
Fig. 8 Temperature dependence of the infrared bandwidth (FWHM)
connected with d (OClO)F mode. Solid red lines represent fitting of
Eq. (2) to the experimental points. Dash vertical line denotes phase
d
2
c
transition temperature T registered by DSC upon cooling. (Color
reduction in the FWHM value at T and with decreasing of
c
figure online)
temperature the FWHM values exponentially decrease. The
former observation indicates that the rate of reorientational
motions changes abruptly at T . The latter provides the
c
FT-MIR investigations
The FT-MIR spectra of [Fe(OS(CH ) ) ](ClO ) were
activation energy for the rotational motion of ligands
-
1
Ea = 6.8 ± 1.7 kJ mol . At the low-temperature end, the
FWHM becomes almost constant, and even starts to
increase, indicating that only the vibrational relaxation
process is involved.
3 2 6
4 2
-
1
obtained in the spectral range of 4000–500 cm during
heating and subsequently cooling the sample in the tem-
perature range of 290–370 and 12–370 K, respectively.
Figure 7 presents selected MIR spectra registered for
-
1
[
Fe(OS(CH ) ) ](CIO )
[Fe(OS(CH ) ) ](ClO ) in the range of 1600–500 cm .
3 2 6 4 2
3
2 6
4 2
*
*
No significant changes of the FT-MIR spectra at the phase
transition temperature range can be seen, which suggests
*
*
*
*
*
that the phase transition at T & 338 K is probably con-
c
3
3
3
70 K
45 K
40 K
*
nected with changes of the reorientational dynamics of
-
CH groups or ClO anions.
3
4
Tc
Figure 8 demonstrates the temperature dependence of
-1
the FWHM of the band at 620 cm , associated with
3
30 K
20 K
10 K
3
3
dd(OClO)F2 mode, and shows that during cooling the
sample FWHM decreases exponentially down to the phase
transitions region, next FWHM becomes discontinuous and
during further cooling FWHM decreases exponentially
down again till to ca. 170 K, next it becomes almost con-
stant indicating that only the vibrational relaxation process
is involved. In Fig. 8 the solid line is fitted to experimental
points by Eq. (2), and the fitting parameters are listed in
3
2
00 K
90 K
Heating
Cooling
1
600 1400 1200 1000 800 600 1600 1400 1200 1000 800 600
Wavenumber/cm–1 Wavenumber/cm–1
Fig. 7 Thermal evolution of the FT-MIR spectrum recorded for
Fe(OS(CH ](ClO upon heating and cooling in the wavenumber
range 1600–500 cm . Temperatures of the phase transitions at T are
marked by horizontal arrows, and the asterisks indicate Nujol
vibrations
Table 3. The estimated activation energy values for per-
-1
[
3 2
) )
6
4
)
2
chlorate anions are: E (I) = 10.0 ± 0.5 kJ mol
and
-
1
a
c
-
Ea(II) = 2.9 ± 0.1 kJ mol for the high- and low-tem-
1
perature phase, respectively.
123

E. Szostak, A. Migdał-Mikuli
Conclusions
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-
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Open Access This article is distributed under the terms of the
Creative Commons Attribution 4.0 International License (http://crea
tivecommons.org/licenses/by/4.0/), which permits unrestricted use,
distribution, and reproduction in any medium, provided you give
appropriate credit to the original author(s) and the source, provide a
link to the Creative Commons license, and indicate if changes were
made.
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23