ARSENIC(III), ANTIMONY(III), AND BISMUTH(III) TRIHALIDE COMPLEXES OF [2.2.2]PARACYCLOPHANE - FROM WEAK VANDERWAALS COORDINATION TO STRONGLY DIRECTIONAL PI-COMPLEXATION WITH SINGLE OR DOUBLE EXTERNAL ETA-6 COORDINATION

[2.2.2]Paracyclophane forms the adducts C24H24 . AsCl3 (1), C24H24 . (SbCl3)2 . 1/2 C6H6 (2), and C24H24 . (BiCl3)3 . C6H6 (3). For solutions in polar solvents NMR spectra indicate extensive dissociation and/or fluxionality. In the crystals adduct 1 features a weak addition of the AsCl3 molecule to one open side of a paracyclophane molecule with long intermolecular contacts approaching C3v symmetry. - Crystalline 2 shows SbCl3 coordination to two of the benzene rings of the hydrocarbon in a quasi-centered eta-6 mode, while one of the benzene rings remains uncoordinated. Chlorine-bridging between antimony atoms leads to tetrameric units (SbCl3)4 in the lattice. - In the bismuth compound 3 each benzene ring of the hydrocarbon is engaged in centroid (eta-6)pi complexation, with the BiCl3 units crosslinked by chlorine bridges. The average of the Bi - ring distances (3.08, 2.98, and 2.99 angstrom) is shorter than for the Sb - ring distances in 2 (3.047 and 3.050 angstrom), indicating stronger bonding. The crystal benzene is not coordinating.