Molecular solid solution of lanthanide-titanium-oxo clusters with enhanced photocatalytic hydrogen evolution

Molecular solid solutions of metal clusters containing different metal centers with well-defined structures can accurately regulate the HOMO-LUMO gap, but are rarely available. Herein, a series of colorless lanthanide-titanium-oxo clusters Ln₂Ti₄(μ₂-O)₂(μ₃-O)₄(Piv)₁₀(THF)₂ (Ln₂Ti₄, Ln = Eu, Gd, Tb, and Ce, HPiv = pivalic acid) were synthesized by the reaction of pivalic acid with Ln(Ac)₃ and titanium isopropoxide. The light yellow crystal of cluster solid solutions Eu₂Ti_4−xCd_x, containing a mixture of Eu₂Ti₄ and Eu₂Ti₃Cd, was obtained by in situ doping Cd²⁺ and S²⁻. Eu₂Ti_3.92Cd_0.08 displays efficient photocatalytic hydrogen evolution activity without a co-catalyst, which is up to 2.6 times that of Eu₂Ti₄. Femtosecond time-resolved transient absorption spectroscopy and spin-polarized density functional calculations showed that the enhanced photocatalytic performance of Eu₂Ti_4−xCd_x can be attributed to the narrower HOMO-LUMO gap and lower LUMO position than that of Eu₂Ti₄. This studyprovides an in situ doping method to realize the simple preparation of cluster solid solution.