Triaquahenicosatungstodiphosphate(6–) heteropolyanion, [P2W21O71(OH2)3]6– : X-ray crystallographic and 183W nuclear magnetic resonance structural studies

Abstract

The single-crystal X-ray structure of K₄H₂[P₂W₂₁O₇₁(OH₂)₃]·28H₂O [space group P6₃/mmc, a= 16.295(2), c= 19.771(5)Å, and Z= 2; Mo radiation, R= 0.037 for 1 042 unique data] has been determined and the ¹⁸³W n.m.r. spectrum of the anion in H₂O–D₂0 has been recorded. The anion has true point symmetry C_2v but occupies a D_3h site in the crystal with orientational disorder about a crystal three-fold axis. It contains two α-A-PW₉O₃₄^9– units, each with C_3v symmetry, linked through three equatorial WO(OH₂)⁴⁺ units. Two equatorial W atoms are closer to, and the third is further from, the anion (crystal C₃) axis. The H₂O ligand on the unique W is directed towards the interior of the anion and is hydrogen-bonded to the oxo Iigand, also directed internally, on each of the other equatorial W.