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

Abstract

Complex-formation equilibria involving trans-diamine palladium(II) (Pd^II), 4,4′-bipyridine (bpy), and inosine were investigated at 25 °C and 0.1 M (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 Å, leading to reduced aromaticity in bpy. Comparison with model compounds suggests that the uncoordinated aromatic ring can be understood as an electron donating group.

Keywords:

• Palladium
• 4,4’-bipyridine
• Kinetic
• DFT
• Aromaticity

Acknowledgement

The authors kindly thank Prof. Tim Clark for hosting this work in the CCC and the Regionales Rechenzentrum Erlangen (RRZE) for a generous allotment of computer time.