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

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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 ∼28.1A˚ . Coupled Co(I/II) redox processes are observed between the two metal centres.