Metallosupramolecular assembly of dinuclear double helicates incorporating a biphenyl-3,3′-diyl spacer; molecular structure of bis{3,3′-bis[4-(methylsulfanyl)-2,2′-bipyridin-6-yl]biphenyl-x ²N,N′: x²N″,N‴]}dicopper(I) hexafluorophosphate

Linking two 2,2′-bipyridine metal-binding domains by a biphenyl-3,3′-diyl spacer provided a new type of helicand, 3,3′-bis[4-(methylsulfanyl)-2,2′-bipyridin-6-yl]biphenyl (L), which has been shown to form dinuclear double-helical complexes with a range of transition-metal ions. The copper(I) complex [Cu₂L₂] [PF₆]₂ has been structurally characterised [orthorhombic, space group Pba2, a = 23.023(5), b = 23.206(5), c = 12.224(2) Å, Z = 4, wR₂ = 0.259 for all data]. These complexes show increased intermetallic separations with respect to analogous complexes formed with ligands in which the metal-binding domains are directly linked or are connected by a 1,3-phenylene spacer. This provides an additional level of control in the deliberate design of molecules containing helical motifs. Stacking interactions do not appear to be of importance in the stabilisation of these helical structures. The biphenyl spacer does not appear to be sufficiently flexible to permit the formation of triple-helical complexes.