Trilacunary A-β-Keggin tungstogermanates and -silicates functionalized with phenyltin(IV) electrophiles

The first organic derivative of a β-Keggin tungstogermanate, the monomeric Keggin anion [{(C₆H₅)Sn(OH)}₃(A-β-GeW₉O₃₄)]⁴⁻ (1), was the only species isolated from the reaction of (C₆H₅)SnCl₃ with Na₁₀[A-β-GeW₉O₃₄] in water, whereas the Si-analogue [{(C₆H₅)Sn(OH)}₃(A-β-SiW₉O₃₄)]⁴⁻ (2) and two dimeric tungstosilicates, the unprecedented species [{(C₆H₅)Sn(A-β-H₃SiW₉Sn₂O₃₇)}₂O₂]⁸⁻ (3) and the known sandwich-type polyanion [{(C₆H₅)Sn(OH)}₃(A-β-H₃SiW₉O₃₄)₂]⁸⁻ (4), were isolated starting from [A-β-SiW₉O₃₄]¹⁰⁻. The novel polyanion 3 can be described as the product of a double Sn–C hydrolysis followed by condensation of two subunits of 2 through double Sn–O–Sn bridge formation. Solid-state characterization has been carried out by infrared spectroscopy, thermogravimetry and single-crystal X-ray diffraction, representing the first structural analysis for 4. A full solution multinuclear NMR (¹H, ¹³C, ¹¹⁷Sn, and ¹⁸³W) and solid-state ¹¹⁷Sn CP-MAS NMR study enabled full characterization of 1. A weak 1-dimensional polyanion association through (Sn)O–HO_t hydrogen contacts involving one of the protonated bridging O atoms of the (C₆H₅)₃Sn₃O₁₂ corner-shared triad is observed for 1 by X-ray diffraction, resulting in a local C_s pseudosymmetry for the Sn centers detected by solid-state ¹¹⁷Sn NMR spectroscopy.