The synthetic intermediate cis(out),cis-[Ru(Cl)2(HL)(DMSO)2], 1 (DMSO = dimethyl sulfoxide), and four new mononuclear ruthenium complexes with general formula out/in-[Ru(HL)(trpy)(X)]m+ (trpy = 4-tert-butylpyridine; X = Cl–, m = 1, 2a+ and 2b+; X = H2O, m = 2, 3a2+ and 3b2+) based on the ligand 1H-pyrazole-3-carboxylic acid, 5-(2-pyridinil)-, ethyl ester (HL), are synthesized and characterized by analytical, spectroscopic, and electrochemical methods. A linkage isomerism is observed for a DMSO moiety of 1, and relevant thermodynamics and kinetics values are obtained through electrochemical experiments and compared to literature. Different synthetic routes are developed to obtain isomeric 2a+ and 2b+, with different relative yields. Water oxidation activity of3a2+ and 3b2+ is analyzed by means of electrochemical methods, through foot of the wave analysis, yielding kobs values of 1.00 and 2.23 s–1, respectively. Chemically driven water oxidation activity is tested using [(NH4)2Ce(NO3)6] as sacrificial electron acceptor, and turnover number (TON) and turnover frequency (TOF) values of TON = 10.8 and TOFi = 58.2 × 10–3 s–1 for 3a2+and TON = 4.2 and TOFi = 15.4 × 10–3 s–1 for 3b2+ are obtained.