By the combination of carboxylate and phosphonate ligands, we herein report a nanosized H2[Ti18(μ3-O)14(μ2-O)6(O3P-Phen)2(PA)16(OPri)14] (PTC-51) (HPA = propionic acid, O3P-Phen = phenyl phosphonate), whose structure can be observed as the linkage of independent phosphonate supporting and carboxylate bridging hexanuclear Ti(iv) clusters. We also demonstrate a concise crystalline phase diagram, which shows the important effect of phosphonate and carboxylate ligand ratio during synthetic reactions. The photocatalytic H2 evolution activities of the obtained polyoxotitanate materials have been studied, with carboxylate-Ti6 presenting the maximum H2 production rate up to 267.78 μmol g-1 h-1.