Bis(bipyridine)-phenanthroline double-stranded helicates of the d10 metals:: zinc(II), silver(I) and copper(I) helicates

The new ligand 2,9-bis[(6-methyl-2,2'-bipyridin-6'-yl)methyleneoxymethylen-yl]-1,10-phenanthroline (1) was prepared and was shown to self-assemble into double-stranded helicates upon reaction with Cu+, Ag+ and Zn2+, thus affording the first trinuclear double-stranded zinc helicate. The [(1)(2)M-3](3n+) [M = Cu+(n = 1), Ag+(n = 1) or Zn2+(n = 2)] helicates were characterized by is, 2D and diffusion NMR. FAB mass spectrometry corroborated the structure of the silver and the copper helicates and [(1)(2)Cu-3](3+) was characterized by X-ray crystallography. The detailed assignments of the H-1 NMR spectra of these helicates have shown that H-10 absorbs at a much higher field when compared to the other protons of these complexes. This high-field shift is a unique characteristic of the helicates of 1 and is not found in structurally related helicates. The NMR spectra of these helicates, at room temperature, are consistent with an average solution structure having a D-2 symmetry. Variable-temperature H-1 NMR (VT-NMR) reveals that the silver helicate of 1 is much more labile than its copper helicate. From the VT-NMR spectra it seems that two, nearly separate, stages are observed in the dissociation process of [(1)(2)Ag-3](3+) The activation energy of the first process for [(1)(2)Ag-3](3+) in DMSO-d(6) was found to be 16.6 +/- 0.2 kcal mol(-1). As expected, the energy barriers for the respective copper helicate are even higher, The crystal structure of [(1)(2)Cu-3](3+) shows that the total length and the pitch length are approximate to 17 and 12 Angstrom respectively.