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