Stable and metastable mixed crystals in the orientationally disordered state of the [(CH3)3CCl]+[(CH3)2CCl2] system

Abstract

Stable and metastable mixed crystals in the orientationally disordered (OD) state of the 2 methyl 2 chloro p rop ane ððCH 3 Þ 3 CClÞþ 2; 2 dichlorop rop ane ððCH 3 Þ 2 CCl 2 Þ binary system were characterized from crystallo graphic and thermodynamic points of view. Large concentration domains of stable rhombohedral (R) and metastable face centered cubic (FCC) mixed crystals were found despite the non isomorphism relationship between the stable FCC phase of ðCH 3 Þ 3 CCl and the stable R phase of ðCH 3 Þ 2 CCl 2. In addition, a third OD phase region was observed in the ðCH 3 Þ 2 CCl 2 rich side of the system. It is simp le cubic (SC) and metastable with resp ect to the stable R p hase region. This corresp onds to the binary extension of the R SC stable metastable relationship found for pure ðCH 3 Þ 2 CCl 2 .

Two-component System CCl4 + (CH3)3CBr: Extrema in Equilibria Involving Orientationally Disordered Phases

“…tert- Butyl compounds have stimulated a large number of theoretical studies as well as have been the object of considerable experimental efforts to elucidate the nature of the disorder and, more specifically, the hindrance to the orientational disorder. − …”

“…According to this similarity, a number of Z = 21 molecules per unit cell was assigned. Nevertheless, it should be noticed that the thermodynamic behavior of the OD phases of CCl 4 is quite different. − Upon cooling from the liquid, it crystallizes to an OD phase Ia (FCC) and upon further cooling to another OD phase Ib (R). When cooling is limited such that Ia is formed, this phase Ia melts upon heating without passing back through phase Ib.…”

Relationship between the two-component system 1-Br-adamantane + 1-Cl-adamantane and the high-pressure properties of the pure components

“…9(a), the entropy factor for both  = M and  = O. Such an inequality should be attributed to the easiness of formation of mixed crystals into an orientationally disordered phase, as it was shown previously in many other two-component systems involving such phases [1][2][3][4][5][6][7]. Fig.…”

“…Even more, the field of phase diagrams involving at least two chemical species, the temperature-composition (T-X) phase diagrams, is generally decoupled from the field of the polymorphic behavior at high pressure. Nevertheless, thermodynamics imposes an univocal relation between the controlled pressure and temperature conditions at which a polymorph should exist and the physical properties derived at normal pressure and, hence, the properties that can be extracted from a temperature-composition phase diagram [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. The other way around also holds, properties derived for stable or metastable phases emerging in the temperature-composition phase diagrams can provide information about the nature of high-pressure phases even when they do not exist as stable phases at normal pressure.…”

Modelling Phase Equilibria in Systems with Organic Solid Solutions

“…Reports on the formation of alloys, or solid solutions, of organic compounds, although still rare, have been appearing regularly in the last few years for aromatic compounds, such as substituted benzenes and naphtalenes [1][2][3], pyrene and anthracene [4][5][6], for carbohydrates [7], terpenes [8], neopentane derivatives [9][10] and fulerenes, besides solid solutions of C 60 with C 70 [11][12] solid solutions of C 60 in sulphur have been reported [13]. Nevertheless it is among the molecules with long n-alkyl chains such as n-alcohols [14], fats [15], soaps [16] and alkanes [17][18][19][20] that solid solutions appear more frequently.…”