Amine-bridged binuclear palladium(II) complexes with inosine. Equilibrium studies and DFT calculations

Complex-formation equilibria involving trans-diamine palladium(II) (Pd-II), 4,4-bipyridine (bpy), and inosine were investigated at 25 degrees C and 0.1M (NaNO3) ionic strength. The stability constants of all possible mono-nuclear and binuclear complexes were determined. The concentration distribution diagram for the binuclear complexes of Pd-II-bpy-inosine reveals the complexes that predominate in the physiological pH range and the quite feasible interaction of the binuclear complex Pd-II-bpy-Pd-II with inosine as a DNA constituent. On the basis of DFT calculations (B3LYP/LANL2DZp), the structures of the investigated equilibrium species show typical bond lengths for Pd-O and Pd-N bonds. The C-C bond in [Pd(4,4-bpy)(NH3)(2)(OH2)](2+) is clearly shortened to 1.47 angstrom, leading to reduced aromaticity in bpy. Comparison with model compounds suggests that the uncoordinated aromatic ring can be understood as an electron donating group.