Formation of a solubilized cobalt block oligomer from a M2L-type double helicate

Abstract

The multi-dentate ligand, 2,3,5,6-tetrakis(2,2′-bipyridyl)pyrazine (L) and divalent cobalt self-assemble to a block co-polymer-like oligomer in solution, which contains at least the L₇Co₈ fragment. The extent of oligomerization is sensitive to the water content in acetonitrile solution. In the solid state, the simple monomer [LCo₂(CH₃CN)₄][ClO₄]₄ is isolated. The X-ray structure of the crystallized material (containing four CH₃CN solvate molecules) reveals a double-helical complex with two heptadentate Co(II) sites, and a helical pitch of ∼28.1 Å. Coupled Co(I/II) redox processes are observed between the two metal centres.