EFFECT OF COORDINATION MODE ON THE PHYSICAL-PROPERTIES OF PYRAZINYLTRIAZOLE LIGANDS BOUND TO BIS(2,2'-BIPYRIDYL)-RUTHENIUM(II)

The physical properties of the two co-ordination isomers of the bis(2,2'-bipyridyl)ruthenium(II) complex of 3-(pyrazin-2-yl)-1,2,4-triazole have been studied. In particular the acid-base properties have been analysed with respect to the nature of the ligand and the co-ordination mode of the triazole ring. The ground-state pK(a) (acid) values of 3.1 and 5.3 obtained for the N2 and N4 isomers respectively indicate that the N2 site of the triazole ring is a stronger sigma-donor than is the N4 atom. The excited-state pK(a) values obtained for deprotonation of the triazole ring are unusual and support earlier suggestions that in the compounds containing the neutral pyrazinyltriazole ligands the lowest pi* level is based on the pyrazinyltriazole ligand, while for the deprotonated ligands this level is 2,2'-bipyridine based.