The basic aqueous coordination chemistry of Ru-II has been studied using the catalytically important TPPTS phosphine (TPPTS = trisodium salt of 3,3 ',3 ''-phosphinetriylbenzenesulfonic acid) and small gas molecules (H-2, CO, N-2) as ligands. As a result, new water-soluble ruthenium mixed hydride complexes, presumably key species in many industrial catalytic processes, have been formed and identified. The Ru-II mixed hydrides were synthesized, and their formation was followed in situ by multinuclear NMR spectroscopy, pressurizing aqueous Ru-II-TPPTS systems with H-2 and CO gas in sapphire NMR tubes. The formation equilibrium of these complexes is highly dependant on the temperature and the gas pressures. Under 50 atm of N-2, the unique [RuH(CO)(N-2)(TPPTS)(2)(H2O)](+) complex has been identified, which could be the first step toward dinitrogen activation.