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

We report a convenient synthesis of K2[Ru(bpy)(NO2)4] via the thermal displacement of benzene from [(Bz)Ru(bpy)Cl]Cl (Bz = η6-C6H6; bpy = 2,2‘-bipyridine) by nitrite ion in methanol solution. K2[Ru(bpy)(NO2)4] has
been fully characterized by elemental analysis, X-ray crystallography, and 1H NMR, IR, UV−vis, and emission
spectroscopy. Reaction of K2[Ru(bpy)(NO2)4] with pyridine under mild or forcing conditions produces fac-K[Ru(bpy)(NO2)3(py)] and cis-[Ru(NO2)2(bpy)(py)2] (py = pyridine), respectively. We report full characterization data
for these compounds, including crystal structures. The dπ(Ru) → π*(bpy) charge-transfer band in the electronic
spectra of K2[Ru(bpy)(NO2)4] and fac-[Ru(bpy)(NO2)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.