Novel vanadium(V) compounds with a layer structure: Synthesis, crystal structures, and solid state NMR spectroscopy of [(VO₂)₂(4,4′-bpy)_0.5 (4,4′-Hbpy)(XO₄)]·H₂O (X = P and As)

A novel vanadium(V) phosphate and the arsenate analogue, [(VO₂)₂(4,4′-bpy)_0.5 (4,4′-Hbpy)(XO₄)]·H₂O (X = P and As; bpy = bipyridine), have been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction. They are the first structurally characterized compounds in the vanadium (V)/4,4′-bpy/phosphate (or arsenate) systems. The two compounds are isostructural and crystallize in the triclinic space group P1̄ (No. 2) with a = 7.9063(3) Å, b = 10.2201(4) Å, c = 12.1336(5) Å, α = 113.4652(7)°, β = 95.7231(7)°, γ = 94.4447-(7)°, and Z = 2 for the phosphate, and a = 7.8843(6) Å, b = 10.3686(7) Å, c = 12.2606(9) Å, α = 113.464(1)°, β = 95.560(1)°, γ = 94.585(1)°, and Z = 2 for the arsenate. The structure consists of phosphate-bridged vanadium(V) double chains linked through 4,4′-bpy ligands to form a sheet with the monoprotonated 4,4′-Hbpy⁺ ligand being coordinated to the metal atom as a pendent group. The ¹H MAS NMR spectrum exhibits four resonances at 14.2, 9.5, 7.2, and 3.7 ppm with an intensity ratio close to 1:6:6:2, corresponding to three different types of protons in 4,4′-bpy and 4,4′-Hbpy⁺ and one type of protons in H₂O. The peak at 14.2 ppm can be assigned to the proton bonded to the pyridine nitrogen atom, which confirms the presence of 4,4′-Hbpy⁺.