A designer ligand field for blue-green luminescence of organoeuropium(II) sandwich complexes with cyclononatetraenyl ligands

A novel eta(9)-coordinated double-decker sandwich complex of divalent europium is synthesized. The complex exhibits blue-green photo-luminescence at 516 nm, which is significantly blue-shifted from those of other organoeuropium(II) sandwich complexes (similar to 630 nm). The blue-shift was quantitatively explained by the weakened electrostatic field of the expanded 10-pi ring.