Polymorphs of rubidium nitrate and their crystallographic relationships

Abstract

The crystal structure relationships between the four thermal polymorphs (IV – 437 K – III – 492 K – II – 564 K – I) of RbNO3 are discussed. Trigonal IV, a = 10.55(2), c = 7.47(2) Å at 298 K, Z = 9, and space group P31 (or its enantiomorph P32) has Rb atoms arranged on a pseudocubic sublattice defined by [Formula: see text] and related segments. The ordered NO3 groups are enclosed within respective pseudocubes and form close to ideal 8-fold anion–cation coordination with the surrounding Rb atoms. At IV → III, each of the appropriate (1/3) <10.1> and (1/3) <11.1> segments of IV (forming the Rb atom sublattice) transform to a cell edge of an ideal s.c. lattice of Rb atoms, a = 4.39(1) Å, Z = 1, and space group Pm3m. The orientationally disordered NO3 groups in III form another close to ideal 8-fold anion–cation coordination with the Rb atoms. At III → II, the s.c. lattice of III changes to form a larger b.c.c. lattice, a = 8.84(3) Å, Z = 8, in II. A parallel-axes unit cell relationship, i.e. <100>III//<100>II and 2(a)III = (a)II, exists between III and II. The NO3 group in II is postulated to form a close to ideal 8-fold anion–cation coordination with the surrounding Rb atoms. At II → I, II transforms to a f.c.c. lattice, a = 7.32 Å, Z = 4, and space group Fm3m. The NO3 group in I forms a close to ideal 6-fold anion–cation coordination with the surrounding Rb atoms. It is suggested that [Formula: see text] and related segments in II, which form a trigonal Rb atom sublattice, a = 7.65(3) Å and α = 109.47°, after II → I, transform to orthogonal cell edges of the cubic lattice of I.

Physicochemical Characterization of Ionic Liquid Binary Mixtures Containing 1-Butyl-3-methylimidazolium as the Common Cation

“…The melting points of the pure ionic liquids are shown in Table , and acceptable agreement in the transition temperatures with published data has been observed for the pure compounds ([C 4 C 1 Im]­[NO 3 ], [C 4 C 1 Im]­[CH 3 SO 3 ], and [C 4 C 1 Im]­Cl). − This table also presents the glass-transition and solid-phase transition temperatures determined in this work. For [C 4 C 1 Im]­[NO 3 ], a solid–solid transition at T = 279 K was also observed, which is in accordance with the values reported by Strechan et al The presence of polymorphs in the nitrate family of ILs has been already studied and confirmed by several authors. ,− Furthermore, the metastability of [C 4 C 1 Im]­Cl was herein noticed, with the melting temperature present in the second heating cycle at T = 342 K without further crystallization in the following cycles. For this pure compound, a glass-transition temperature was found at T = 231 K. These results are in agreement with previous works which have evidenced the presence of a liquid-crystalline phase in metastable chloride-based ILs. , Furthermore, in the study of Yamamuro et al, the authors noticed that the IL did not crystallize at the fusion temperature in the cooling cycle.…”

“…32 This presence of polymorphs in the nitrate family of ILs has been already studied and confirmed by several authors. 32,[37][38][39][40] Furthermore, the metastability of [C4C1Im]Cl was herein noticed, with the melting temperature present in the second heating cycle at T = 342 K without further crystallizations in the following cycles. For this pure compound, a glass transition temperature was found at T = 231 K. These results are in agreement with previous works which have evidenced the presence of a liquid-crystalline phase in metastable chloride based ILs.…”

Mixing enthalpies of solid solutions (Cs1−x,Rbx)NO3 at T=(298.15 and 473.15)K

“…In order to get homogeneous mixtures without decomposition, mixtures, 2 g, were previously melted several times at a temperature a few degrees over the melting point. Trigonal [3][4][5][6][7][8][9] a (296 to 427) K [10][11][12] Trigonal [10,11] b (440 to 509) K [1,3,6,10] Cubic (CsCl) [3][4][5]8] b (439 to 683) K [1,[10][11][12] Cubic (CsCl) [1,12] c (509 to 560) K [8,10,13,14] Trigonal [8,9,15]; Tetragonal [3]; Cubic [4,7,14] d (560 to 584) K [8,9,16] Cubic (NaCl) [8] k (564 to 584) K [17][18][19][20] ?…”

Sequence of Structural and Magnetic Phase Transitions in (NO)Mn6(NO3)13

“…This ferroelectric phase returns into the nonpolar one below 383 K. 11 The RbNO 3 evidence the structural phase transitions at 437, 492, and 564 K. These transitions are accompanied by the small changes in the Rb sublattice from pseudocubic to the cubic one. 12 Alkali metal nitrites ANO 2 (A = Li, Na, K, Rb, Cs) pass through order−disorder structural transformations in both metal and nitrite subsystems. 13 Room-temperature ferroelectric NaNO 2 transforms into antiferroelectric and paraelectric phases at 436 and 438 K, respectively.…”