Three Zr(IV)-Substituted Polyoxotungstate Aggregates: Structural Transformation from Tungstoantimonate to...

Three novel Zr-substituted polyoxotungstate aggregates [H₂N(CH₃)₂]₇NaH₂[Zr₂Sb₂O₃(A-α-PW₉O₃₄)₂]·16H₂O (1), [H₂N(CH₃)₂]₆H₁₂[ZrSb₄(OH)O₂(A-α-PW₈O₃₂)(A-α-PW₉O₃₄)]₂·33H₂O (2), and [H₂N(CH₃)₂]₄Na_11.5H_4.5[Zr₄W₈Sb₄P₅O₄₉(OH)₅(B-α-SbW₉O₃₃)₂]·53H₂O (3) have been made in hydrothermal reactions of the [B-α-SbW₉O₃₃]^9- precursor with Zr⁴⁺ cations and PO₄^3- anions in the presence of dimethylamine hydrochloride and sodium acetate buffer (pH = 4.8) and structurally characterized. Different pH values induce structural transformation from tungstoantimonate (TA) to tungstophosphate (TP). 1 is a di-Zr-substituted sandwich-type TP, the tetranuclear heterometallic [Zr₂Sb₂O₃]⁸⁺ entity sandwiched by two [A-α-PW₉O₃₄]^9- moieties. 2 is a double sandwich-type structure, which can be perceived as two equivalent sandwiched [Sb₃(PW₈O₃₂)(PW₉O₃₄)]^11- further sandwiching one [Sb₂Zr₂(OH)₂O₄]⁴⁺ core to form a novel large-size sandwich-type architecture. Different from 1 and 2, 3 is a tetra-Zr-substituted sandwiched configuration, in which two [B-α-SbW₉O₃₃]^9- fragments sandwich a unique 21-core Sb-P-W-Zr oxo cluster ({Zr₄W₈Sb₄P₅}). Furthermore, the catalytic oxidation of aromatic thioethers by 3 as the heterogeneous catalyst has been investigated, showing high conversion and remarkable selectivity as well as excellent recyclability.