Hydrothermal syntheses and structural characterization of two novel arsenic-vanadium clusters: [Co(2,2′-bpy)₃]₂[As ₈V₁₄O₄₂(H₂O)]•3H₂O and [2,2′-bpy][Ni(2,2′-bpy)₃]₂[As ₈V₁₄O₄₂(H₂O)]•3H₂O

Two new arsenic-vanadium clusters, [Co(2,2′- bpy)₃] ₂[As₈V₁₄O₄₂(H₂O)] • 3H₂O (1), [2,2′-bpy][Ni(2,2′-bpy)₃] ₂[As₈V₁₄O₄₂(H₂O)] • 3H₂O (2) (2,2′-bpy=2,2′-bipyridine), have been hydrothermally synthesized and characterized by IR, elemental analysis, UV-VIS, EPR, TGA, XPS, and single crystal X-ray diffraction analysis. Crystal data: 1, triclinic, P1, a=14.368(3) Å, b=16.753(3) Å, c=24.632(5) Å, α=94.15(3)°, β=93.16(3)°, γ=113.05(3)°, Z=2; 2, monoclinic, P2₁/c, a= 30.2150(4) Å, b=14.0690(3) Å, c=26.0536(3) Å, β=106.8960(10)°, Z=4. X-ray crystallographic studies showed that crystals 1 and 2 are both composed of discrete cluster anion [As₈V₁₄O₄₂(H₂O)]^4- and transition metal coordination complexes [M(2,2′-bpy)₃] ²⁺ (M=Co or Ni). Interestingly, compound 2 contains another neutral organic space filler of 2,2′-bpy. To the best of our knowledge, compounds 1 and 2 are the first examples of structurally characterized vanadium/2,2′-bpy/arsenate polyoxometallates.