The acid-base and electrochemical properties of the MLCT excited states and the one-electron-reduced forms of the three Ru(bpy)(3)(-)()(p)()(pypm)(p)()(2+) complexes, where bpy = 2,2'-bipyridine, pypm = 2-(2'-pyridyl)pyrimidine, and p = 1-3, have been examined in aqueous solution; a determination has been made of the ground- and excited-state electrochemical potentials, the values of the pK(a) and deprotonation rate constants of the conjugate acids of the excited states and the one-electron-reduced complexes, and the kinetics of the second-order decays of the reduced species. Comparison is made with the behavior of the analogous 10 complexes of the form Ru(bpy)(3)(-)()(m)()(-)()(z)()(bpm)(m)()(bpz)(z)()(2+), where bpm = 2,2'-bipyrimidine, bpz = 2,2'-bipyrazine, m and z = 0-3, and m + z

The one-electron reduction of Ru(bpy)2(AB)2+, hereafter RuAB2+, where bpy = 2,2‘-bipyridine and AB = 2,2‘:3‘,2‘‘:6‘‘,2‘‘‘-quaterpyridine, in aqueous solution has been studied using pulse radiolysis. RuAB2+ is reduced by eaq - (k = 6.2 × 1010 M-1 s-1 at ambient ionic strength (I) and k = 4.6 × 1010 M-1 s-1 at I = 0.1 M) and by CO2 •- radical (k = 1 × 108 M-1 s-1 at I = 0.1 M), generating RuAB•+. The spectra of RuAB•+ and its conjugated acid (RuABH•2+) were obtained; the pK a of RuABH•2+ (8.0) has been determined. The rate constants for the protonation of RuAB•+ (k H = 7.9 × 109 M-1 s-1) and the deprotonation of RuABH•2+ (k - H = 79 s-1) have been evaluated as have the rate constants for proton exchange (k f = 3.4 × 107 M-1 s-1 and k r = 5.5 × 106 M-1 s-1) between the RuAB•+/RuABH•2+ and H2PO4 -/HPO4 2- couples. The results from this work are compared with those obtained previously for 13 Ru(II) complexes that contain bpy, bpm (2,2‘-bipyrimidine), bpz (2,2‘-bipyrazine), and pypm (2-(2‘-pyridyl)pyrimidine) ligands. In addition, since RuAB2+ can be viewed as a substituted Ru(bpy)3 2+ complex that contains a bpy residue, a comparison is also made of the reductions of RuAB2+ and bpy.