title: Elucidating the ring inversion mechanism(s) for biscalixarenes.
abstract: Biscalix[4]arene can be constructed from a calix[4]arene by substitution of a methylene bridge hydrogen by another equivalent moiety. The use of biscalix[4]arenes (biscal) as precursors for the creation of new polymetallic clusters such as single-molecule magnets has potential in the fields of data storage and other applications. Polymetallic clusters involving biscal are expected to preferentially involve octadentate binding to two metal centers (one metal center per tetraphenolic pocket), requiring full inversion of one of the annular rings. In this work, we use density functional theory to establish the mechanism behind this process, considering the various energy pathways and providing insight into the preferred route to full and partial inversion. Fourteen possible pathways to full inversion are presented, including all transition states (up to seven per pathway). Subsequently, the lowest energy pathway to full inversion was found to have a barrier height of 19.31 kcal mol(-1). Solvent optimizations using PCM (with and without SMD) and CPCM solvent models suggest long-range solvent effects may be relatively unimportant in the inversion process. This study represents the first use of density functional theory to elucidate the entire potential energy surface, including barrier heights, of the ring inversion process of biscalix[4]arenes.
authors.affiliation: Institute of Chemical Sciences, Heriot Watt University , Edinburgh EH14 4AS, United Kingdom.
authors.forename: Paul
authors.initials: P
authors.lastname: Murphy
authors.forename: Scott J
authors.initials: SJ
authors.lastname: Dalgarno
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Paterson