A 3D all-inorganic architecture based on the [H2W12O42]10− building block with different alkaline-earth metal linkers: crystal structures, surface photovoltage and photoluminescent properties

Abstract

Three-dimensional (3D) all-inorganic polyoxometalate compounds, Ca₂Na₆[H₂W₁₂O₄₂]·30H₂O (1), Sr₄H₂[H₂W₁₂O₄₂]·26H₂O (2), Sr₄Na₂[H₂W₁₂O₄₂]·30H₂O (3) and Ba₄Na₂[H₂W₁₂O₄₂]·29.5H₂O (4) have been synthesized and their structures consist of [H₂W₁₂O₄₂]¹⁰⁻ building units and alkaline-earth metal cations (Ca²⁺, Sr²⁺ and Ba²⁺) as linkers. The most interesting feature is that compound 2 represents the first example of a 3D all-inorganic framework in which the paradodecatungstate-B anions [H₂W₁₂O₄₂]¹⁰⁻ were linked by pure alkaline-earth metal cations. Moreover, each [H₂W₁₂O₄₂]¹⁰⁻ building unit in compound 2 acts as a decadentate ligand coordinated with ten Sr²⁺ ions, which represents the highest coordination number of [H₂W₁₂O₄₂]¹⁰⁻ with alkaline-earth metal cations so far. Another interesting feature is that compounds 1–4 exhibit a clear response to surface photovoltage and electric field-induced surface photovoltage, which is indicative of the semiconductor property and suggests these compounds have potential applications as photocatalysts and light-to-electricity conversion materials.