Hg···Hg···Hg Interaction Stabilizes Unusual Trinuclear Double Sandwich Structure of Mercury(II) Porphyrins.

For the first time, fully characterized and stable trinuclear "double sandwich" molecules are reported with Hg(II) ion using a highly flexible porphyrin dimer. The molecules display interesting and intense luminescence properties at room temperature. The present investigation clearly demonstrates that attractive mercurophilic interactions do play an essential role in bringing two porphyrin macrocycles exactly on top of each other with an unfavorable fully eclipsed geometry to produce short Hg···Hg distances. Interactions between Hg(II) dz2 orbitals provide the directionality with a linear Hg3 core having short Hg···Hg distances despite the fact that ligand framework is highly flexible.