Polymorphism of Alkali Bis(fluorosulfonyl)amides (M[N(SO2F)2], M = Na, K, and Cs)
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- 作者：Kazuhiko Matsumoto ; Takaaki Oka ; Toshiyuki Nohira ; Rika Hagiwara
- 刊名：Inorganic Chemistry
- 出版年：2013
- 出版时间：January 18, 2013
- 年：2013
- 卷：52
- 期：2
- 页码：568-576
- 全文大小：546K
- 年卷期：v.52,no.2(January 18, 2013)
- ISSN：1520-510X
文摘
The polymorphic behavior of Na, K, and Cs salts of the bis(fluorosulfonyl)amide anion N(SO2F)2鈥?/sup> has been investigated by means of differential scanning calorimetry (DSC), single-crystal and powder X-ray diffraction, and Raman spectroscopy. All of the polymorphs observed in the present work (three for Na[N(SO2F)2], two for K[N(SO2F)2], and two for Cs[N(SO2F)2]) are stable enough for analyses at room temperature. With increasing temperature, form II of Na[N(SO2F)2] undergoes a solid鈥搒olid phase transition to form I, whereas another form (form III) crystallizes from the melt upon cooling. The anions in forms I and II of Na[N(SO2F)2] have trans and cis conformations, respectively, at 113 K, while cis鈥搕rans disorder is observed for the anion in form I at 298 K. Form I of K[N(SO2F)2], with a melting point of 375 K, is the stable form at room temperature, whereas solidification from the molten state during DSC gives rise to form II with a melting point of 336 K. Both forms I and II of K[N(SO2F)2] have anions in the cis conformation. The difference between the two potassium polymorphs arises from their crystal packing modes. In the case of Cs[N(SO2F)2], form I melts at 387 K, whereas form II undergoes a solid鈥搒olid transition to form I at 330 K. The anion of form I in Cs[N(SO2F)2] has an oxygen/fluorine disorder that exhibits an oxygen/fluorine eclipsed conformation, even at 113 K. The powder X-ray diffraction pattern of form II matches that of the previously known Cs[N(SO2F)2] structure of the trans conformer. Vibrational frequencies observed with Raman spectroscopy do not necessarily show the same trend as those calculated for the energy-minimized cis or trans conformers in the gas phase due to packing effects.