Syntheses and X-ray Crystal Structures of Zirconium(IV) and Hafnium(IV) Complexes Containing Monovacant Wells−Dawson and Keggin Polyoxotungstates

The syntheses and crystal structures of a series of zirconium(IV) and hafnium(IV) complexes with Dawson monovacant phosphotungstate [α₂-P₂W₁₇O₆₁]^10- and in situ-generated Keggin monovacant phosphotungstate [α-PW₁₁O₃₉]^7-, which was obtained by a reaction of [α-PW₁₂O₄₀]^3- with Na₂CO₃, are described. K₁₅H[Zr(α₂-P₂W₁₇O₆₁)₂]·25H₂O (K-1), K₁₆[Hf(α₂-P₂W₁₇O₆₁)₂]·19H₂O (K-2), (Et₂NH₂)₁₀[Zr(α-PW₁₁O₃₉)₂]·7H₂O (Et₂NH₂-3), and (Et₂NH₂)₁₀[Hf(α-PW₁₁O₃₉)₂]·2H₂O (Et₂NH₂-4), being afforded by reactions in aqueous solutions of monolacunary Dawson and Keggin polyoxotungstates with ZrCl₂O·8H₂O and HfCl₂O·8H₂O followed by exchanging countercations, were obtained as analytically pure, homogeneous colorless crystals. Single-crystal X-ray structure analyses revealed that the Zr(IV) and Hf(IV) ions are in a square antiprismatic coordination environment with eight oxygen atoms, four of them being provided from each of the two monovacant polyanion ligands. Although the total molecular shapes and the 8-coordinate zirconium and hafnium centers of complexes 1−4 are identical, the bonding modes (bond lengths and bond angles) around the zirconium(IV) and hafnium(IV) centers were dependent on the monovacant structures of the polyanion ligands. Additionally, the characterization of complexes 1−4 was accomplished by elemental analysis, TG/DTA, FTIR, and solution (³¹P and ¹⁸³W) NMR spectroscopy.