Self-Assembly of Tetra- and Hexanuclear Circular Helicates

The self-assembly of the tris-bipyridine ligands BI and BII with iron(II) salts yields polynuclear complexes displaying structures of cyclic double-helix type, termed circular helicates [n]cH (of order n). With BI in which the bipyridine units in the ligand are connected by ethylene bridges, penta- or hexanuclear architectures [5]cH and [6]cH are obtained, depending on the anion present during the self-assembly process. The elongated tris-bipyridine ligand BII with oxypropylene bridges forms a tetranuclear circular helicate [4]cH, whose structure has been confirmed by crystal structure determination. The possible oligomeric combinations of tris-bipy ligands and iron(II) ions may be considered to constitute the potential members of a virtual combinatorial library, generated via dynamic combinatorial chemistry, from which a specific real constituent of the virtual set of circular helicates is expressed in given conditions.