title: Phase transition of [2,2]-paracyclophane--an end to an apparently endless story.
abstract: In this contribution, the solid-state low-temperature phase structure of [2,2]-paracyclophane is unambiguously characterised by single-crystal X-ray analysis. Additionally, a heat capacity measurement was undertaken, which proves the existence of a λ-type phase transition at 45 K, a transition that is connected with the formation of a secondary Cp/T feature at 60 K. The low-temperature phase (<45 K) crystallises in the lower symmetry space group P4n2, whereas the high-temperature phase (>60 K) crystallises in space group P4(2)/mnm. This proves what has been postulated both by experimental and theoretical chemists but has repeatedly been dismissed as speculation many times.
authors.affiliation: Institut für Anorganische Chemie, Georg-August-Universität, Tammannstraße 4, 37077 Göttingen (Germany).
authors.forename: Hilke
authors.initials: H
authors.lastname: Wolf
authors.forename: Dirk
authors.initials: D
authors.lastname: Leusser
authors.lastname: Mads R V Jørgensen
authors.forename: Regine
authors.initials: R
authors.lastname: Herbst-Irmer
authors.forename: Yu-Sheng
authors.initials: YS
authors.lastname: Chen
authors.forename: Ernst-Wilhelm
authors.initials: EW
authors.lastname: Scheidt
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Scherer
authors.forename: Bo B
authors.initials: BB
authors.lastname: Iversen
authors.forename: Dietmar
authors.initials: D
authors.lastname: Stalke
keywords: paracyclophane; phase transitions; space group ambiguity; structure elucidation; thermal motion