A new bidentate ligand bearing a single carboxylate functionality, 2-(2'-pyridyl)pyrimidine-4-carboxylic acid (cppH), has been prepared and applied in the synthesis of a series of ruthenium(II) complexes. Reaction of this new ligand with Ru-II(bpy)(2)Cl-2 led to the unexpected oxidation of the starting material to give [Ru-III(bpy)(2)Cl-2]Cl center dot H2O and a low yield of [Ru-II(bpy)(2)(cppH)](PF6)(2) center dot H2O (1) on addition of an aqueous KPF6 solution (bpy = 2,2'-bipyridine and cpp = 4-carboxylate-2'-pyridyl-2-pyrimidine). An X-ray crystal structure determination on crystals of la, [Ru-II(bpy)(2)(cpp)](PF6), obtained from slow evaporation of an aqueous solution of 1 revealed that the nitrogen para to the carboxylate group in the cpp(-) ligand coordinates to the ruthenium(II) center rather than that ortho to this group. The same complex was prepared via decarbonylation of [Ru-II(cppH)(CO)(2)Cl-2] center dot H2O in the presence of bpy and an excess of trimethylamine-N-oxide (Me3NO), as the decarbonylation agent. The coordination of cppH in the precursor is the same as in the final product. The related complex [Ru-II(phen)(2)(cppH)](PF6)(2) center dot 2H(2)O (2) (phen = 1,10-phenanthroline) was similarly synthesized. [Ru-II(bpy)(dppz)(cppH)](PF6)(2) center dot CH3CN (3) (dppz = dipyrido[3,2,-a;2',3-c]phenazine) was also prepared by photochemical decarbonylation of [Ru-II(bpy)(CO)(2)Cl-2] giving [Ru-II(bpy)(CO)Cl-2](2) followed by bridge splitting with dppz to generate [Ru-II(bpy)(dppz)(CO)Cl](PF6) center dot H2O. This intermediate was then reacted with cppH to produce 3, as a mixture of geometric isomers. In contrast to 1, X-ray crystallography on the major product isolated from this mixture, [Ru-II(bpy)(dppz)(cpp)](NO3) center dot 10H(2)O, 3(N3) indicated that the nitrogen adjacent to the carboxylate was coordinated to ruthenium(II). Full characterization of these complexes has been undertaken including the measurement of UV-visible and emission spectra. Electrochemical and spectroelectro-chemical studies in acetonitrile show that these complexes undergo reversible oxidation from Ru-II to Ru-III at potentials of 983 +/- 3 mV, 1004 +/- 5 mV, and 1023 +/- 3 mV versus Fc(0/+) (Fc = Ferrocene) for 1, 2, and 3(N3), respectively.