DINUCLEAR DOUBLE HELICATES INCORPORATING A 1,3-PHENYLENE SPACER - THE CRYSTAL AND MOLECULAR-STRUCTURE OF DIACETATO1-KAPPA-2O-,2-KAPPA-2O-BIS[MU-1,3-BIS(4-METHYLTHIO-2,2'-BIPYRIDIN-6-YL)BENZENE-1-KAPPA-2N,N'-2-KAPPA-2N'',N''']DINICKEL BIS(HEXAFLUOROPHOSPHATE)

Linking two bipyridine units by a 1,3-phenylene spacer has provided a novel class of ligand which promotes the spontaneous self-assembly of double helicates upon reaction with transition-metal ions. Interaction with copper(I) or silver(I) resulted in dinuclear double-helical complexes with the metal ions occupying pseudo-tetrahedral co-ordination sites. Reaction with cobalt(II) or nickel(II) acetates gave similar dinuclear double-helical structures with a didentate acetate ligand completing the co-ordination sphere of each metal to give a pseudo-octahedral geometry. The crystal structure of [Ni2L22(O2CMe)2][PF6]2 [L2=1,3-bis(4-methylthio-2,2'-bipyridin-6-yl) benzene] has been determined. The two metal centres are separated by 5.875 angstrom. In contrast to the helicates formed by the linear oligopyridines, no significant pi-stacking interactions are observed between pyridine moieties on the helical strands.