Two polymolybdate-based complexes and their graphene composites with visible-light photo-responses

Abstract

Two polymolybdate-based complexes formulated as (H₂L1)₂(Mo₄O₁₃) (1) and (L2)₂(HL2)₂(Mo₈O₂₅)·7H₂O (2) have been hydrothermal synthesized and structurally characterized by single-crystal X-ray diffraction. In complex 1, one-dimensional (1D) [Mo^V₄Mo^VI₄O₂₆]_∞⁸⁻ chain is constructed by vertice-sharing {MoO₆} octahedra, and the uncoordinated protonated [H₂L1]²⁺ species link different [Mo₈O₂₆]_∞⁸⁻ chains via supramolecular forces. In complex 2, the [Mo₈O₂₅]²⁻ moieties are linked by the μ₃-[HL2]⁺ and μ₂-L2 ligands into 1D chain. Complex 2 possesses more narrow band gap than complex 1, and it shows stronger photocurrent response than complex 1 under the visible light (650 nm > λ > 350 nm). The different densities of states (DOS) of the two complexes are attributed to their different compositions and frameworks, thus giving rise to their different band gaps. With the addition of graphene into the two complexes, the electroconductivity of the complex/graphene composite material is much improved, and 2/graphene composite material shows much improved electrocatalytic activity for the H₂ evolution reaction (HER) than complex 2.