Syntheses, structures and physical characterization of two new three-dimensional mixed-valence hexadecavanadate derivatives

Two new hexadecavanadate derivatives, (bpy)[Zn(4,4′-bpy)2]2[H4ClV16O38]·6H2O 1 and (bpy)[Co(4,4′-bpy)2]2[H4ClV16O38]·6H2O 2 (bpy = 4,4′-bipyridine), were synthesized under the hydrothermal conditions and structurally characterized by IR, XPS and EPR spectroscopy, redox titration and single-crystal X-ray diffraction. The two compounds are isostructural and crystallize in the tetragonal non-centrosymmetric space group P-4n2 (No. 118) with a = 17.124(2), b = 17.124(2), c = 14.724(3) Å, V = 4317.5(12) Å3 and Z = 1 for the compound 1, and a = 17.038(2), b = 17.038(2), c = 14.754(3) Å, V = 4282.9(12) Å3 and Z = 1 for the compound 2. Compounds 1 and 2 were constructed from 4-connected {H4ClV16O38} clusters and 6-connected Zn(II) or Co(II) ions, extending in the three dimensions. Square channels with an opening of ca. 7.2 × 7.2 Å were formed through the twining double left-handed helical chains composed of MII octahedral complexes bridged by bpy molecules, which were filled by water and free bpy molecules. Magnetic property was also studied.