Two-Component System Cycloheptanol (C7) + Cyclooctanol (C8):  An Extraordinary System

Abstract

The two-component system cycloheptanol (C7) + cyclooctanol (C8) has been studied by means of thermal analysis, X-ray powder diffraction, and dielectric spectroscopy. In a first step, the polymorphism of pure C7 and C8 has been revised, and new unpublished crystallographic data of the stable phases have been reported. Evidence for the isomorphism relationship between the simple cubic (SC) phases of both of the pure components has been seen through the continuous evolution of the lattice parameters, the continuous evolution of the dielectric strength, and the existence of a two-phase equilibrium [SC + L]. Despite the solid polymorphism of the pure components, the SC state has been observed to be the sole mixed solid state between 170 K and [SC + L] equilibrium. To perform a complete thermodynamic analysis, measurements of the excess enthalpy in the liquid state were undertaken. These measurements together with the experimental melting-phase diagram allow us to determine the excess thermodynamic properties of the mixed SC state via a compensation law. Dielectric data have been used to interpret the excess properties, and the existence of short-range orientatonal order for the mixed SC state has been inferred. In addition, this OD mixed state has been classified as extraordinary in light of the log T C−log T m plot.

Solid phases in cycloheptanol: Dynamic disorder and glass transitions

“…Stable polymorphism C 7 -OH is one of the cyclic alcohols which exhibits the most complicated polymorphism, due to the existence of a great amount of metastable phases. From an earlier work [27], it seems to be clear that three different solid phases (denoted on cooling from the liquid state as I, II and III) could be identified down to about 170 K. Their transition temperatures (earlier consigned in Table 1 of the Ref. [27]) seem to be consistent with those obtained from several experimental techniques, in previous published works [21][22][23]25].…”

“…From an earlier work [27], it seems to be clear that three different solid phases (denoted on cooling from the liquid state as I, II and III) could be identified down to about 170 K. Their transition temperatures (earlier consigned in Table 1 of the Ref. [27]) seem to be consistent with those obtained from several experimental techniques, in previous published works [21][22][23]25]. Preliminary X-ray diffraction experiments [27] revealed that phase I is simple cubic with a unit-cell parameter of 11.54(1) Å at 273 K (Z = 8) and phase II is tetragonal with unit-cell parameters of a = 19.487(2) Å and c = 11.7805(2) Å at 248.15 K (Z = 24).…”

“…[27]) seem to be consistent with those obtained from several experimental techniques, in previous published works [21][22][23]25]. Preliminary X-ray diffraction experiments [27] revealed that phase I is simple cubic with a unit-cell parameter of 11.54(1) Å at 273 K (Z = 8) and phase II is tetragonal with unit-cell parameters of a = 19.487(2) Å and c = 11.7805(2) Å at 248.15 K (Z = 24). As for X-ray diffraction patterns concerning phase III did not seem to have the required precision to indicate unambiguous lattice symmetry.…”

“…As for X-ray diffraction patterns concerning phase III did not seem to have the required precision to indicate unambiguous lattice symmetry. Anyway, a possible orthorhombic symmetry with similar a and c parameters as tetragonal phase II and one slightly different parameter b, was suggested [27].…”

“…As for its solid state polymorphism, a great amount of works has been published up to now, in which several experimental techniques have been used [20][21][22][23][24][25][26][27]. Surprisingly, next to nothing devoted to the structural features of the solid states has been published [27]. There exists a wide consensus in the scientific literature about three stable solid phases, although, some evidences for an additional stable solid phase have been reported [20,22].…”