Preparation and characterisation of 2,2′-bipyridine-4,4′-disulphonic and -5-sulphonic acids and their ruthenium(II) complexes. Excited-state properties and excited-state electron-transfer reactions of ruthenium(II) complexes containing 2,2′-bipyridine-4,4′-disulphonic acid or 2,2′-bipyridine-4,4′ dicarboxylic acid

Abstract

We report the syntheses of 2,2′-bipyridine-4,4′-disulphonic acid (H₂bp-4,4′-ds) and 2,2′-bipyridine-5-sulphonic acid (Hbp-5-s), and several ruthenium(II) complexes derived therefrom, including [Ru(bp-4,4′-ds)₃]^4–,[Ru(bipy)(bp-4,4′-ds)₂]^2–(bipy = 2,2′-bipyridine), [Ru(bipy)₂(bp-4,4′-ds)], and [Ru(bp-5-s)₃]^– and their 2,2′-bipyridine-4,4′-dicarboxylic acid (H₂bpdc) analogues, viz. [Ru(bpdc)₃]^4–, [Ru(bipy)(bpdc)₂]^2–, and [Ru(bipy)₂(bpdc)]. Some novel thioalkyl derivatives of 2,2′- bipyridine, including 4,4′-di(methylthio)-2,2′-bipyridine, 4,4′-di(ethylthio)-2,2′-bipyridine, and 4,4′,6,6′-tetra(methylthio)-2,2′-bipyridine, were also prepared and characterised during the course of this investigation. The luminescent states of the complexes [Ru(bp-4,4′-ds)₃]^4–,[Ru(bipy)(bp-4,4′ds)₂]^2–, [Ru(bpdc)₃]^4–, [Ru(bipy)(bpdc)₂]^2–, and [Ru(bipy)₂(bpdc)] were studied using variabletemperature lifetime measurements. Studies of the quenching of {[Ru(bipy)₃]²⁺}*, {[Ru(bipy)₂(bpdc)]}*, {[Ru(bipy)(bp-4,4′-ds)₂]^2–}*, and {[Ru(bp-4,4′-ds)₃]^4–}* by 1,1′-dimethyl-4,4′-bipyridinium bromide (methyl viologen) in aqueous solution as a function of ionic strength have demonstrated that the effects of charge in these electron-transfer reactions can be understood in terms of conventional theories of ionic reactions whilst, at the same time, confirming the effective charges of the ruthenium(II) complex ions. The rate constants for the quenching of {[Ru(bp-4,4′-ds)₃]^4–}* and {[Ru(bipy)(bp-4,4′-ds)₂]^2–}* by copper(II) ions in neutral aqueous solution show unusual (non-Arrhenius) temperature dependences. A novel kinetic scheme involving parallel innerand outer-sphere quenching mechanisms has been proposed to account for the observed behaviour. The luminiscence decay of {[Ru(bipy)₂(bpdc)]}* in the presence of aqueous copper(II) ions at pH 3.5 is non-exponential. This is interpreted in terms of a combination of static and dynamic quenching effects.