Enantio-tropic phase transition and twinning in 2,2,3,3,4,4-hexa-fluoro- pentane-1,5-diol

Jeong Myeong Ha, Victor G Young

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Abstract

Four crystal structure determinations of 2,2,3,3,4,4-hexa-fluoro-pentane-1, 5-diol (HFPD), C5H6F6O2, were conducted on a single specimen by varying the temperature. Two polymorphs of HFPD were found to be enantio-tropically related as phases (I) and (II), both in the space group P1. These structures contain closely related R 4 4(20) sheets. A structure determination was completed on form (Ia) at 283 K. Form (Ia) was then supercooled below the phase transition temperature at 279 to 173 K to give form (Ib) for a second structure determination. Metastable form (Ib) was transformed by momentary warming and recooling to give form (II) for a third structure determination at 173 K. Form (II) transformed to form (Ic) upon warming to 283 K. Enantio-tropic phase transitions between phases (I) and (II) were confirmed with X-ray powder diffraction and differential scanning calorimetry. Form (Ia) was found as a twin by nonmerohedry by a reflection in (011). This twinning persists in all phases described. Additional twinning was found after the phase (I) to phase (II) transformation. These two additional twin components are related to the first pair by a 180° rotation about the (012) plane. This latter pair of twins persisted as the specimen was warmed back to form (Ic) at 283 K.

Original languageEnglish (US)
JournalActa Crystallographica Section C: Crystal Structure Communications
Volume65
Issue number8
DOIs
StatePublished - Aug 19 2009

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