title: 1,1',3,3',6,6',8,8'-Octachloro-9,9'-bifluorenylidene and perchloro-9,9'-bifluorenylidene, two exceedingly twisted ethylenes.
abstract: The syntheses of 1,1',3,3',6,6',8,8'-octachloro-9,9'-bifluorenylidene (1), its precursors, and the byproduct 3,3',5,5'-tetrachloro-4-(trichloromethyl)biphenyl (5) are described. Accurate structural X-ray data on 1 and on perchloro-9,9'-bifluorenylidene (2) are reported and discussed. Because of chlorine overcrowding, the dihedral angles between their two identical fluorenylidene moieties are abnormally large, the central-ethylene twist angles being 55 and 66 degrees, respectively. Significant out-of-plane carbon-chlorine bond bending is likewise exhibited. Their ESR spectra and magnetic measurements prove that they are singlet species. The exceptionally large bathochromic displacements of their UV-vis absorption spectrum with respect to that of their parent hydrocarbon are mainly attributed to bond bending and molecular warping.
authors.affiliation: Institut de Ciència de Materials de Barcelona (CSIC), Campus Universitari de Bellaterra, 08193 Cerdanyola, Spain. elies.molins@icmab.es
authors.forename: Elies
authors.initials: E
authors.lastname: Molins
authors.forename: Carlos
authors.initials: C
authors.lastname: Miravitlles
authors.forename: Enrique
authors.initials: E
authors.lastname: Espinosa
authors.forename: Manuel
authors.initials: M
authors.lastname: Ballester