Cobalt, Iron and Ruthenium Complexes of Picolinic and Dipicolinic Acids: Syntheses, Solution Properties and Kinetics of Electron Transfer Reactions With Cytochrome C(II) and Some Inorganic Reductants

Abstract

Tris picolinate complexes of CO¹¹¹ and RU¹¹¹ have been synthesized, and their standard potentials measured (432 ±10, 403 ±2 mV) at 25ºC and ionic strength 0.1 mol dm^-3. The self-exchange rate constant of Ru ( pic )₃^O/- was found to be (1 .4 ±0.9)×10⁸ dm³ mol^-1 s^-l, from reaction with cytochrome C(II), Co( bpy )₃²⁺ and ~Co( phen )₃²⁺. For the reaction between Fe( dipic )²- and cytochrome ~(II), at 2S260C, pH 5.5 and I 0.1 mol dm-3 (KNO₃), the second-order rate constant was (3.2 ±0.l)×10⁵ dm³ mol^-1 s^-1,with ΔH+ 19.9 ±0.9 kJ mol^-1 and ΔS+ -72.8 ±.7 J K^-1 mol^-l. The self-exchange rate constant of Fe( dipic )₂^-/2- was reevaluated as (5.8 ±0.2)×10⁶ dm³ mol^-l s^-1.