title: Onset of three-centre, four-electron bonding in peri-substituted acenaphthenes: a structural and computational investigation.
abstract: Two series of sterically crowded peri-substituted acenaphthenes have been prepared, containing mixed halogen-chalcogen functionalities at the 5,6-positions in A1-A6 (Acenap[X][EPh] (Acenap = acenaphthene-5,6-diyl; X = Br, I; E = S, Se, Te) and chalcogen-chalcogen moieties in A7-A12 (Acenap[EPh][E'Ph] (Acenap = acenaphthene-5,6-diyl; E/E' = S, Se, Te). The related dihalide compounds A13-A16 Acenap[XX'] (XX' = BrBr, II, IBr, ClCl) have also been prepared. Distortion of the acenaphthene framework away from the ideal was studied as a function of the steric bulk of the interacting halogen and chalcogen atoms occupying the peri-positions. The acenaphthene series experiences a general increase in peri-separation for molecules accommodating heavier congeners and maps the trends observed previously for the analogous naphthalene compounds N1-N12 (Nap[X][EPh], Nap[EPh][E'Ph] (X = Br, I; E/E' = S, Se, Te). The conformation of the aromatic ring systems and subsequent location of p-type lone-pairs dominates the geometry of the peri-region. The differences in peri-separations observed for compounds adopting differing conformations of the peri-substituted phenyl group can be correlated to the ability of the frontier orbitals of the halogen or chalcogen atoms to take part in attractive or repulsive interactions. Density-functional studies have confirmed these interactions and suggested the onset of formation of three-centre, four-electron bonding under appropriate geometric conditions.
authors.affiliation: School of Chemistry, University of St Andrews, St Andrews, Fife, UK.
authors.forename: Lara K
authors.initials: LK
authors.lastname: Aschenbach
authors.forename: Fergus R
authors.initials: FR
authors.lastname: Knight
authors.forename: Rebecca A M
authors.initials: RA
authors.lastname: Randall
authors.forename: David B
authors.initials: DB
authors.lastname: Cordes
authors.forename: Alex
authors.initials: A
authors.lastname: Baggott
authors.forename: Michael
authors.initials: M
authors.lastname: Bühl
authors.forename: Alexandra M Z
authors.initials: AM
authors.lastname: Slawin
authors.forename: J Derek
authors.initials: JD
authors.lastname: Woollins