Synthesis and characterization of dinuclear ruthenium complexes with tetra-2-pyridylpyrazine as a bridge

The syntheses and characterization of a series of complexes of the general formula [Cl(bpy')Ru(tppz)Ru(bpy')Cl](PF6)(2), where tppz is tetra-2-pyridyl pyrazine and bpy' is 2,2'-bipyridine or substituted 2,2'-bipyridine, are de scribed. Preparations with 2,2'-bipyridine or 4,4'-dimethyl-2,2'-bipyridine (1 and 2, respectively) give mixtures of two isomers. The isomers of 2 wer e separated chromatographically and the X-ray crystal structure of the cis isomer was solved. Significant distortion is observed in both the coordinat ion geometry around each ruthenium atom and in the tppz ligand resulting in short intramolecular Ru ... Ru and Cl ... Cl separations (6.558(1) and 5.8 80(2) Angstrom, respectively). Ligands containing two bipyridine groups lin ked through eight- and nine-atom bridges have also been synthesized. The le ngth of the bridge between bipyridine groups allows for the formation of ci s complexes 3-5 having the general formula shown above but prevents formati on of a trans isomer.