Acid–base equilibria of co-ordinated ligands. Part 1. The effect of basicity of co-ordinated nitrogen donors upon the acidity of chelating 8-aminoquinoline in some dicationic platinum(II) complexes

Abstract

Cationic complexes of the type [Pt(8NH₂-quin)L₂][ClO₄]₂, and [Pt(8NH2-quin)(L–L)][ClO₄]₂(8NH₂-quin = 8-aminoquinoline), where L and L–L are mono- and bi-dentate nitrogen donors respectively, have been prepared. In aqueous solution, they undergo reversible deprotonation of the amino group of the quinoline ligand. The corresponding ionization constants (K_a^c) have been determined by UV/VIS spectrophotometry at 25 °C and I= 0.1 mol dm^–3. The linear free-energy relationship pK_a^c=α+βpK_a^L is verified for the para-substituted phyridines, pK_a^L referring to the basicity of L in water at 25 °C.