Issue 20, 2022

Polymorphism and solid–solid phase transitions of hydrogen bonded 2-adamantanol and 2-methyl-2-adamantanol compounds

Abstract

The polymorphic behavior at normal pressure as a function of temperature of 2-adamantanol (C10H16O) and 2-methyl-2-adamantanol (C11H18O) has been investigated by single-crystal and powder X-ray diffraction as well as differential scanning calorimetry. Our findings demonstrate that the previously reported specific heat anomaly at around 238 K for C10H16O consists of a single-crystal to single-crystal IV–III high-order phase transition without change of space group (P[1 with combining macron], Z = 6, Z′ = 3). The combined use of single-crystal and powder X-ray diffraction demonstrates that phase IV would be fully ordered only at 0 K. As the temperature increases, the hydrogen atoms linked to the oxygen atoms are found to be disordered between two sites, reaching an occupancy factor of 50% each at the IV–III transition temperature. An order parameter related to the continuous change of the β lattice parameter can account for this IV–III high-order phase transition. Furthermore, a mechanism is proposed for the first-order transition from phase III to phase II (monoclinic, C2/m, Z = 12, Z′ = 1.5), in which O atoms are disordered between 2 sites (50% occupancy factor). Single-crystal X-ray diffraction of the low-temperature phase of C11H18O, stable below 368 K, shows unambiguously a fully ordered orthorhombic structure (Pbcn, Z = 16, Z′ = 2), contrary to the previously reported space group (Pcc2). Below melting temperature, both compounds display a high-temperature orientationally disordered (plastic) phase (Fm[3 with combining macron]m, Z = 4), like most of the adamantane derivatives.

Graphical abstract: Polymorphism and solid–solid phase transitions of hydrogen bonded 2-adamantanol and 2-methyl-2-adamantanol compounds

Associated articles

Supplementary files

Article information

Article type
Paper
Submitted
09 Mar 2022
Accepted
14 Apr 2022
First published
18 Apr 2022

CrystEngComm, 2022,24, 3692-3700

Polymorphism and solid–solid phase transitions of hydrogen bonded 2-adamantanol and 2-methyl-2-adamantanol compounds

A. Salvatori, P. Negrier, S. Massip, A. Muñoz-Duque, P. Lloveras, M. Barrio and J. Tamarit, CrystEngComm, 2022, 24, 3692 DOI: 10.1039/D2CE00324D

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