Detailed equilibrium and kinetic studies on axial water ligand substitution reactions of the "lantern-type" platinum-(III) binuclear complex, [Pt 2(μ-HPO 4) 4(H 2O) 2] 2-, with halide and pseudo-halide ions (X - = Cl -, Br -, and SCN -) were carried out in acidic aqueous solution at 25°C with I = 1.0 M. The diaqua Pt(III) dimer complex is in acid dissociation equilibrium in aqueous solution with -log K h1 = 2.69 ± 0.04. The consecutive formation constants of the aquahalo complex (K 1 X) and the dihalo complex (K 2 X) were determined spectrophotometrically to be log K 1 Cl = 2.36 ± 0.01 and log K 2 Cl = 1.47 ± 0.01 for the reaction with Cl - and log K 1 Br = 2.90 ± 0.04 and log K 2 Br = 2.28 ± 0.01 for the reaction with Br -, respectively. In the kinetic measurements carried out under the pseudo-first-order conditions with a large excess concentration of halide ion compared to that of Pt(III) dimer (C X- ≫ C Pt), all of the reactions proceeded via a one-step first-order reaction, which is a contrast to the consecutive two-step reaction for the amidato-bridged platinum(III) binuclear complexes. The conditional first-order rate constant (k obs) depended on C X- as well as the acidity of the solution. From kinetic analyses, the rate-limiting step was determined to be the first substitution process that forms the monohalo species, which is in rapid equilibrium with the dihalo complex. The reaction with 4-penten-1-ol was also kinetically investigated to examine the reactivity of the lantern complex with olefin compounds.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry
- Inorganic Chemistry