994
Bull. Chem. Soc. Jpn. Vol. 86, No. 8 (2013)
New Ionic Plastic Crystals in a New Class
(R = Me, Et, and Pr) salts as pioneers of a new region of ionic
plastic crystals.
below Tmp with a two-terminal method employing an Andou
AG-4303 LCR meter equipped with an Al sheet. The powdered
sample was pressed into a disc 1 cm in diameter and ca. 1-mm
thick. As the specimens were hygroscopic, air around the probe
was replaced by dry N2 gas.
Experimental
Sample Preparation.
The crystals of NR4BEt3Me
(R = Me, Et, Pr, and Bu) and NRxR¤4¹xBEt3Me (R = Me, Et,
and Pr) were prepared by adding LiBEt3Me to NR4Br and
NRxR¤4¹xX (X = Cl, Br, or I) in aqueous solution, respectively.
Some compounds of NR4X and NRxR¤4¹xX were obtained
commercially: NMe4Br (Wako Junyaku Co.); NEt4Br and
NPr4Br (Kanto Kagaku Co.); and NBu4Br, NEtMe3I, NEt3-
MeCl, and NEtPr3I (Tokyo Kasei Industry Co.). Whole speci-
mens treated in this study were prepared by modifying a
protocol in previous reports.39,40 NEt2Me2Br was prepared by
refluxing molar equivalents of EtBr and NEtMe2 in ethanol
at 60 °C for 8 h. NEt3PrBr was obtained by the same process,
employing PrBr and NEt3 instead of EtBr and NEtMe2. NEt2Pr2I
was obtained by refluxing diethylformamide (Et2NCHO) solu-
tion containing PrI and K2CO3 at 80 °C for 48 h. After con-
centrating the solution by keeping the temperature constant at
80 °C, dichloromethane was added. By abstracting and drying
the solution, the NEt2Pr2I crystals were isolated. In order to
prepare LiBEt3Me specimens, MeLi dissolved in diethyl ether
and BEt3 in hexane diluent (Kanto Kagaku Co.) were employed.
In this direct reaction, a three-necked flask equipped with a
stirrer, silicone caps, condenser, and thermometer was used;
air in the flask was substituted by N2 gas. A 15 cm3 sample of
XRD powder patterns were obtained using a Bruker D8
ADVANCE equipped with a Cu anticathode. The measure-
ments were performed employing a rotating stage and ttk450
probe at room and other temperatures, respectively. Spectra
were recorded using a scan range of 5-40° with a step angle
of 0.02°.
Solid-state 1H NMR spectra were recorded at a Larmor
frequency of 600.13 MHz using a Bruker Avance 600 spec-
trometer (14.01 T). The samples were packed in a ZrO rotor
with an outer diameter of 2.5 mm. Spectra were obtained by
Fourier transformation (FT) of free-induction-decay (FID)
signals that were obtained after a ³/2 pulse. 1H chemical
shifts (CS) were calibrated relative to an external adamantane
(¤ = 1.91 ppm) reference. Spin-lattice relaxation time (T1) of
1
the H nucleus was obtained by using the inversion recovery
method. A sample temperature was controlled and recorded by
a Bruker VT-2000. Solid-state 13C (I = 1/2) NMR spectra were
recorded at a Larmor frequency of 150.9 MHz by using the
same spectrometer. The sample was packed in a ZrO rotor with
an outer diameter of 4.0 mm. 13C NMR spectra were recorded
without a cross-polarization method, because it has been
reported if rates of motion of the molecules in crystals are fast
enough, peak intensities of a rare spin (natural abundant 13C
nucleus) become small compared with those obtained using
a single pulse sequence.41 The CS of the 13C nuclei were
calibrated by an external adamantane (¤ = 29.47 ppm) refer-
ence; the reference signals were detected with magic-angle-
spinning (MAS) ratio of 5 kHz. Recycle times of 5 and 20 s
were employed for solid-state 1H NMR and 13C NMR measure-
ments, respectively. This spectrometer can be used to measure
solution samples by exchanging the solid probe with another
probe with a 5.0-mm-diameter coil. In order to assign the
synthesized specimens, 1H and 13C NMR measurements of
the prepared sample dissolved in deuterium-substituted solvent
¹3
dried hexane was placed in the flask and 5 cm3 of 1.0 mol dm
MeLi in diethyl ether was added at 0 °C. The same volume of
BEt3 in hexane solution (1.0 mol dm¹3) was slowly added into
the flask at 0 °C with continuous stirring. After keeping the
solution temperature at 0 °C for 0.5 h, 10 cm3 of water was
gradually poured into the flask to decompose the unreacted
specimens. After evaporating diethyl ether and hexane, Li-
BEt3Me was obtained. The NR4BEt3Me crystal was synthesized
by mixing molar equivalents of NR4X and LiBEt3Me in aque-
ous solution of 100 cm3 at 0 °C. The NRxR¤4¹xBEt3Me sample
was prepared using the same process by employing NRxR¤4¹xX
instead of NR4X. After filtering the resultant solid, the crys-
tal was dissolved in 10 cm3 of acetone and the solution was
poured into 400 cm3 of water at 0 °C with continuous stirring for
0.5 h (in the case of NEt3PrBEt3Me and NEt2Pr2BEt3Me, 100
cm3 volume of water was used because of its high solubility
compared to the other compounds). After filtering the solid, the
NR4BEt3Me and NRxR¤4¹xBEt3Me crystals (excepting NEt3-
PrBEt3Me and NEt2Pr2BEt3Me) were dried in a desiccator with
P2O5 and were kept in a freezer for 2 days. NEt3PrBEt3Me
and NEt2Pr2BEt3Me specimens were dried in vacuo for 6 h. In
1
were carried out. CS values of H and 13C nucleus were cali-
brated by employing an inner reference of tetramethylsilane
(TMS) (¤ = 0.00 ppm). The decomposition of samples in the
solids was checked by solid-state 1H MAS NMR measurements
with an MAS ratio of 30 kHz.
Results and Discussion
DSC.
DSC thermograms of NR4BEt3Me (R = Me, Et,
Pr, and Bu) and NRxR¤4¹xBEt3Me (R = Me, Et, and Pr) salts
recorded from 210 K are shown in Figure 1. The variation
appearing at around 210 K is due to instrument noise. The
largest signal is observed in the NMe4BEt3Me, NEt4BEt3Me,
NEtMe3BEt3Me, NEt2Me2BEt3Me, and NEt3MeBEt3Me crys-
tals at around 600 K. In addition, these compounds gradually
release heat above ca. 480, 390, 400, 450, and 440 K, respec-
tively. These large peaks and monotonous exothermic signals
can be assigned to decomposition, because the reduction of
specimens was determined to be at around 500 K in test tubes.
In this paper, the symbols Tmp and Ttr1, Ttr2, etc., are used to
indicate the transition temperatures at the melting point and
1
order to check all specimens synthesized in this study, H and
13C NMR measurements in DMSO-d6 solvent were carried out.
Measurements.
DSC analysis was performed using a
Shimadzu DSC-60 and Seiko Instruments Inc. SSC/5200 calo-
rimeter with a reference sample of Al2O3. The samples were
heated from 210 K at rates of 5 °C min¹1. From these results,
we determined melting points (Tmp) and transition temperatures
in the solid phase as well as entropy changes at these transition
temperatures.
Electrical conductivity measurements at 1 kHz were carried
out at temperatures ranging from room temperature to just