Platinum(II) bi- and terpyridyl chloro complexes, Pt (dcbpy)Cl-2 and [Pt(ttpy)Cl](+), where dcbpy = 4,4'-dicarboxyl-2,2'-bipyridine and ttpy = 4-tolyl-2,2':6',2"-terpyridine, are used to investigate the nature of the active catalyst for the photocatalytic production of hydrogen from water. In a Pt(II) chloro system that contains a sacrificial electron donor, either MeOH or triethanolamine (TEOA), and titanium dioxide (TiO2) as an electron relay, sizable amounts of H-2 can be observed upon UV bandgap irradiation. The quantity of H2 can be significantly reduced in the presence of mercury under the same conditions. Using a known sensitizer, [Pt(ttpy)(phenylacetylide)](+) (1), combined with a Pt (11) chloro complex in a similar system, there is a substantial induction period until the evolution of H-2, under visible light (lambda > 410 nm) irradiation. It is suggested that the Pt(II) chloro complexes are simply acting as precursors to Pt colloids that function as the H-2 generating catalyst.