Synthesis and Structures of a New Series of Silver-Vanadate Hybrid Solids and Their Optical and Photocatalytic Properties

Three new silver-vanadate hybrid solids, [Ag(bpy)]4V4O12·2H2O (I), [Ag(dpa)]4V4O12·4H2O (II), and Ag4(pzc)2V2O6 (III) (bpy = 4,4′-bipyridine, dpa = 1,2-bis(4-pyridyl)-ethane, pzc = pyrazinecarboxylate), were synthesized by hydrothermal methods and characterized using single crystal X-ray diffraction (I, P21/c, Z = 4, a = 11.375(2) Å, b = 14.281(4) Å, c = 13.598(3) Å, β = 91.46(1)°; II, P21/c, Z = 8, a = 13.5748(3) Å, b = 15.3372(4) Å, c = 14.1854(3) Å, β = 114.1410(9)°; III, P1̅, Z = 2, a = 3.580(1) Å, b = 11.839(4) Å, c = 19.321(7) Å, α = 89.110(7)°, β = 87.719(9)°, γ = 86.243(8)°), thermogravimetric analysis, and UV−vis diffuse reflectance. The structures of I and II are constructed from neutral {Ag4V4O12}n layers of clusters that are pillared via the coordination of organic ligands (bpy for I and dpa for II) to the Ag sites in each layer. Conversely, the structure of III is composed of a three-dimensional {Ag2(pzc)+}n coordination network with channels containing {VO3−}n chains. The lattice water molecules can be removed upon heating to ≥180 °C for I (reversibly) and to ≥120 °C for II (irreversibly). All three decompose with the removal of organic ligands at higher temperatures of >200−300 °C. Their optical bandgap sizes were measured to be 2.77 eV for I, 2.95 eV for II, and 2.45 eV for III, which decrease most notably as a result of the band widening for the more extended vanadate structure in III. All three hybrid solids are photocatalytically active for the decomposition of methylene blue under UV light (λ < 400 nm; 1.01, 0.64, and 2.65 mg L−1 h−1 for I, II, and III, respectively), while only III exhibits a high activity under visible-light irradiation (λ > 400 nm; 1.20 mg L−1 h−1). These new hybrid solids are among the first reported to exhibit high photocatalytic activities under either ultraviolet or visible-light irradiation and have also been analyzed with respect to the effect of the different organic ligands on their atomic- and electronic-structures.