Differential scanning calorimetry (DSC) thermograms, X-ray diffraction (XRD) analysis, electrical conductivity (
σ), and
7Li NMR spectroscopy characterization of
n-C
m H
(2m?+?1)COOM solids (M = Li, Na, K;
m?=?13, 15, 17, 19, 21) and mixed crystals
n-C
21H
43COOLi
x K
(1???x) (0.25?≤?
x?≤?0.75) was performed as a function of temperature. DSC thermograms of
n-C
m H
(2m?+?1)COOM revealed several solid-solid phase transitions with large entropy changes. Electrical conductivity studies established that
n-C
m H
(2m?+?1)COOLi crystals are poor electrical conductors. In contrast,
n-C
m H
(2m?+?1)COOK salts were found to have
σ values of 10
???7–10
???8 S·cm
???1. Since the crystal structures and phase-transition temperatures of both
n-C
m H
(2m?+?1)COOLi and
n-C
m H
(2m?+?1)COOK crystals were similar, they were able to form mixed crystals with the structure
n-C
x H
(2m?+?1)COOLi
x K
(1???x). DSC thermograms of the mixed crystals showed a small entropy change at the melting point (Δ
S mp?<?13 J K
???1 mol
???1), in addition, large Δ
S values at the solid-solid phase transition temperature. The
σ values obtained for mixed crystals were roughly one order of magnitude greater than those determined for
n-C
21H
43COOK crystals.
7Li NMR spectra of the mixed crystals recorded at various temperatures suggested that the self-diffusion of Li
?+? ions was excited in the highest-temperature solid phase. Based on these results, we have classified these mixed crystals as rotator crystals.
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