A large manganese-doped polyoxotitanate nanocluster Ti₂₈MnO₃₈(OEt)₄₀H₂, has been synthesized solvothermally. Its structure is arranged around the four-coordinate Mn²⁺ dopant atom in a Keggin-type structure. A significant reduction of the band gap relative to that of undoped polyoxotitanate clusters is observed.