Self-assembly and crystal structure of a dinuclear dihelicate silver(I) complex with an ethane-bridged dimeric bipyridine ligand

An asymmetric ethane-bridged dimeric bipyridine ligand, 1-(5′-methyl-2,2′-bipyridin-5-yl)-2-(6′-methyl-2,2′-bipyridin-6-yl)ethane (L) was synthesized, and a double-stranded helical complex [Ag2L2](PF6)2 · 0.5Et2O was obtained by reaction of L with silver(I) ion. An X-ray analysis of the complex shows that the two ligands intertwine around the two silver atoms with distorted tetrahedral geometry in a head-to-tail configuration. The distance between the two silver atoms is 8.10 Å. The complex was also characterized by ESMS, 1H-n.m.r. spectroscopy and cyclic voltammetry. The formation of the head-to-tail species indicates that the ligand strands in the helicates adopt the arrangement spontaneously so as to minimize the steric repulsion between the substituents of the pyridine rings. The complex is the first example of a dinuclear silver(I) double-stranded helix with an ethane-bridged dimeric bipyridine ligand.