Cyanide adducts on the diruthenium core of [Ru2(L)4](+) (L = ap, CH3ap, Fap, or F3ap). Electronic properties and binding modes of the bridging ligand.
The products of the reaction between CN(-) and four different diruthenium complexes of the type Ru(2)(L)(4)Cl where L = 2-CH(3)ap (2-(2-methylanilino)pyridinate anion), ap (2-anilinopyridinate anion), 2-Fap (2-(2-fluoroanilino)pyridinate anion), or 2,4,6-F(3)ap (2-(2,4,6-trifluoroanilino)pyridinate anion) are reported. Mono- and/or dicyano adducts of the type Ru(2)(L)(4)(CN) and Ru(2)(L)(4)(CN)(2) are found exclusively as reaction products when either the 2-CH(3)ap or the ap derivative is reacted with CN(-), but diruthenium complexes with formulations of the type Ru(2)(F(x)ap)(3)[mu-(o-NC)F(x-1)ap](mu-CN) or Ru(2)(F(x)ap)(4)(mu-CN)(2) (x = 1 or 3) are also generated when Ru(2)(Fap)(4)Cl or Ru(2)(F(3)ap)(4)Cl is reacted with CN(-). More specifically, four products formulated as Ru(2)(Fap)(4)(CN), Ru(2)(Fap)(4)(CN)(2), Ru(2)(Fap)(3)[mu-(o-NC)ap](mu-CN), and Ru(2)(Fap)(4)(mu-CN)(2) can be isolated from a reaction of CN(-) with the Fap derivative, but the exact type and yield of these compounds depend on the temperature at which the experiment is carried out. In the case of the F(3)ap derivative, the only diruthenium complex isolated from the reaction mixture has the formulation Ru(2)(F(3)ap)(3)[mu-(o-NC)F(2)ap](mu-CN) and this compound has structural, electrochemical, and spectroscopic properties quite similar to that of previously characterized Ru(2)(F(5)ap)[mu-(o-NC)F(4)ap](mu-CN). Both the mono- and dicyano derivatives synthesized in this study possess the isomer type of their parent chloro complexes. The Ru-Ru bond lengths of Ru(2)(ap)(4)(CN) and Ru(2)(2-CH(3)ap)(4)(CN) are longer than those of Ru(2)(ap)(4)Cl and Ru(2)(CH(3)ap)(4)Cl, respectively, and this is accounted for by the strong sigma-donor properties of the CN(-) ligand as compared to Cl(-). The Ru-C bonds in Ru(2)(ap)(4)(CN)(2) are significantly shorter than those in Ru(2)(ap)(4)(CN), thus revealing a greatly enhanced Ru-CN interaction in the dicyano adduct, a result which is also indicated by the fact that nu(CN) in Ru(2)(ap)(4)(CN)(2) is 50 cm(-1) higher than nu(CN) in Ru(2)(ap)(4)(CN). Although both (4,0) Ru(2)(ap)(4)(CN)(2) and (3,1) Ru(2)(Fap)(4)(CN)(2) possess the same formulation, there are clear structural differences between the two complexes and this can be explained by the fact that the two cyano derivatives possess a different binding symmetry of the bridging ligands. Each mono- and dicyano adduct was electrochemically investigated in CH(2)Cl(2) containing TBAP as supporting electrolyte. Ru(2)(ap)(4)(CN), Ru(2)(CH(3)ap)(4)(CN), and Ru(2)(Fap)(4)(CN) undergo one reduction and two oxidations. The two dicyano adducts of the ap and Fap derivatives are characterized by two reductions and one oxidation. The potentials of these processes are all negatively shifted in potential by 400-720 mV with respect to half-wave potentials for the same redox couples of the monocyano derivatives, with the exact value depending upon the specific redox reaction.