Synthesis and characterization of [Ru(1-3;5,6-.eta.-cyclooctadienyl)(.eta.6-cyclooctatriene)]PF6 and its use as a precursor into 1-3:5,6-.eta.- and 1-5-.eta.-cyclooctadienyl ruthenium(II) complexes. The X-ray crystal structure determinations of [Ru(1-3:5,6-.eta.-cyclooctadienyl)(.eta.6-cyclooctatrie