CYANO-BRIDGED COMPLEXES OF TRANS-TETRAKIS(PYRIDINE)RUTHENIUM(II)

Reaction of trans[RuCl(py)(4)(Me(2)CO)](+) with cyanide ion produces t rans-RuCl2(py)(4) and trans-[Ru(OCH3)(2)(py)(4)](+), but almost no tra ns-RuCl(CN)(py)(4). The asymmetrical bimetallic complex salt trans-[Cl (py)(4)Ru(NC)Ru(py)(4)(CN)]PF6 (1) was prepared by reaction of trans-[ RuCl(py)(4)(Me(2)CO)](+) with an excess of trans-Ru(CN)(2)(py)(4). The symmetrical trimetallic complex salt -[Cl(py)(4)Ru(NC)Ru(py)(4)(CN)Ru (py)(4)Cl](PF6)(2) (2) was prepared by reaction of trans-Ru(CN)(2)(py) (4) with two equivalents of trans-[RuCl(py)(4)(Me(2)CO)](+). Electroni c coupling between the outer Ru(II) centers in 2 is significant, as ev idenced by a Delta E(1/2) value of ca. 100 mV for the Ru-III/II couple s. The chloride ligands in 2 are substituted in the presence of AgCF3C O2 in refluxing acetonitrile/water to give the symmetrical derivative (py)(4)Ru(NC)Ru(py)(4)(CN)Ru(py)(4)(MeCN)](PF6)(4) (3). This transform ation causes a marked increase in the electronic coupling through the central Ru unit, as evidenced by a Delta E(1/2) value of 280 mV for th e outer Ru-III/II couples in 3. The single-crystal X-ray structures of trans-Ru(CN)(2)(py)(4) . 2CH(3)CN and -[Cl(py)(4)Ru(NC)Ru(py)(4)(CN)R u(py)(4)Cl](PF6)(2) . 5CH(3)CN . C5H5N (2 . 5CH(3)CN . C5H5N) have bee n determined. The complex trans-Ru(CN)(2)(py)(4) . 2CH(3)CN, chemical formula C26H26N8Ru crystallizes in the orthorhombic system, space grou p Pbcn with a = 10.4714(11) Angstrom, b = 15.0098(18) Angstrom, c = 16 .1018(15) Angstrom, and Z = 4. The salt 2 . 5CH(3)CN . C5H5N, chemical formula C77H80Cl2F12N20P2Ru3, crystallizes in the orthorhombic system , space group Pnnm with a = 14.882(7) Angstrom, b = 23.187(6) Angstrom , c = 24.034(7) Angstrom, and Z = 4. The binding of two trans-{RuCl(py )(4)}(+) groups has very little effect on the geometry of the trans-Ru (CN)(2)(py)(4) unit. The complex in 2 has an almost perfectly Linear g eometry with eclipsed trans-{Ru(py)(4)}(2+) units, and bond lengths in dicating d pi(Ru-II) --> pi(CN) back-bonding from both C- and N-bonde d Ru centers. The Ru-Cl bond length is 2.4212(24) Angstrom.