Dinuclear double helicates incorporating a 1,3-phenylene spacer; the crystal and molecular structure of diacetato-1x2O-,2x2O-bis[µ-1,3-bis(4-methylthio-2,2′-bipyridin-6-yl)benzene-1x2N,N′:2x2N″,N‴]dinickel bis(hexafluorophosphate)

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Abstract
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 [Ni2L2 2(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 Å. In contrast to the helicates formed by the linear oligopyridines, no significant π-stacking interactions are observed between pyridine moieties on the helical strands.