First High Pressure Crystallization and Study of Disorder Modes in Isostructural Dihaloperfluoroethanes (Preprint)
Abstract
A group of isostructural crystals has been identified for a series of 1,2-dihalotetrafluoroethanes X(CF2)2Y (X = Br, I; Y = Br, I). 1,2-Dibromotetrafluoroethane (BrCF2CF2Br), 1,2-diiodotetrafluoroethane (ICF2CF2I) and 1-bromo-2-iodotetrafluoroethane (BrCF2CF2I), have been in-situ pressure crystallized in a diamond-anvil cell and their structures determined by X-ray diffraction. All the crystals are monoclinic, space group P21/n, with the midpoint of the C-C bond located at the centre of inversion. The freezing pressures of these compounds have been determined to be 0.80(5) GPa, 0.30(5) GPa and 0.10(5) GPa for BrCF2CF2Br, BrCF2CF2I and CF2ICF2I, respectively. In the structure of ICF2CF2I, the -CF2-CF2- moiety is orientationally disordered about the intramolecular I...I axis at 0.16(5) GPa, but it becomes ordered at 0.86(5) GPa. The BrCF2CF2I crystal structure is disordered in a different way: the -CF2-CF2- is ordered but the Br and I atoms are substitutionally disordered with equal occupancies. The CF2BrCF2Br structure is completely ordered. The formation of isostructural crystals by these compounds and different types of molecular disorder can be rationalized by the intermolecular interactions at varied thermodynamical conditions. The cohesion forces in these structures are dominated by I...I. Br...Br and (Br/I)...(Br/I) contacts, but (Br/I)...F contacts are considerably shorter in BrCF2CF2I than in ICF2CF2I and BrCF2CF2Br.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 25, 2007
- Accession Number
- ADA477883
Entities
People
- Andrzej Katrusiak
- Anna Olejniczak
- Ashwani Vij
Organizations
- Air Force Research Laboratory