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)3and titanium isopropoxide. The light yellow crystal of cluster solid solutions Eu2Ti4−xCdx, containing a mixture of Eu2Ti4and Eu2Ti3Cd, was obtained by in situdoping Cd2+and S2−. Eu2Ti3.92Cd0.08displays 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 Eu2Ti4−xCdxcan be attributed to the narrower HOMO-LUMO gap and lower LUMO position than that of Eu2Ti4. This studyprovides an in situdoping method to realize the simple preparation of cluster solid solution.