Organoarsonates Enable Single-Site Condensation of Hexalacunary {P₂W₁₂} Polyoxotungstates

A systematic study of the condensation reactions of arylarsonic-functionalized [α-P₂W₁₂O₄₈]^14- units in acidic aqueous media identified that the specific presence of an amino group in the ortho position of the phenyl rings induces a dimerization process that allowed isolation of discrete dimeric polyanions [(o-H₂N-C₆H₄-AsO₃)₄P₄W₂₄O₈₅]^14- (1) with an unprecedented polyoxometalate skeleton characterized by two seminal {P₂W₁₂} groups joined via a single W-O-W bridge. At the same time, addition of divalent transition metal ions (Mn^II, Co^II, and Ni^II) in the reaction mixture directed a condensation process on a completely different pathway resulting in one-dimensional (1D) coordination polymers based on V-shaped [{M(H₂O)₄}P₄W₂₄O₉₂(C₆H₆AsNO)₂]^14- polyanions (M = Mn^II (2), Co^II (3), and Ni^II (4)). All polyanions were isolated as hydrated mixed potassium/dimethylammonium salts and thoroughly characterized in the solid state. ³¹P NMR studies showed that the discrete cluster 1 is comparatively stable in 1 M LiCl aqueous solution and thus represents a potential precursor for subsequent reactions.