Influence of the 5-substituent of uracils and uridines on eta(super 2) coordination of Ru(super II)(hedta)1- at the C-5 - C-6 bonds

The mixing of 5-substituted uracils and uridines (X = F, Cl, Br, I and COOH as 5-substituents) with Ru(hedta)(H2O)1- causes complexation by the eta(super 2) and N-3 binding modes, except for the substituents X = CH3 and COOH. A significant increase in isomer distribution occurs as a function of the withdrawing character of X, with the maximum value at 85% eta(super 2) coordination for X = Cl. A small decrease in the amount of eta(super 2) isomer occurs for the Br- and I-substituted ligands because of modest steric effects. Isomers of both eta(super 2)- and N-3-coordinated complexes occur for 5-fluoroudine.