The Synthesis and Characterization of Potassium 2,2‘-Bipyridinetetranitroruthenate

We report a convenient synthesis of K(2)[Ru(bpy)(NO(2))(4)] via the thermal displacement of benzene from [(Bz)Ru(bpy)Cl]Cl (Bz = eta(6)-C(6)H(6); bpy = 2,2'-bipyridine) by nitrite ion in methanol solution. K(2)[Ru(bpy)(NO(2))(4)] has been fully characterized by elemental analysis, X-ray crystallography, and (1)H NMR, IR, UV-vis, and emission spectroscopy. Reaction of K(2)[Ru(bpy)(NO(2))(4)] with pyridine under mild or forcing conditions produces fac-K[Ru(bpy)(NO(2))(3)(py)] and cis-[Ru(NO(2))(2)(bpy)(py)(2)] (py = pyridine), respectively. We report full characterization data for these compounds, including crystal structures. The d pi(Ru) --> pi*(bpy) charge-transfer band in the electronic spectra of K(2)[Ru(bpy)(NO(2))(4)] and fac-[Ru(bpy)(NO(2))(3)(py)] displays a significant solvent dependence. The energy of the absorption band correlates linearly with the Gutmann solvent acceptor number. The solvatochromic response of these nitro complexes is essentially identical to that of the analogous cyanide complexes, indicating that the mechanism previously proposed to explain the solvatochromism of the cyanide complexes may need to be reexamined.