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

Three novel Zr-substituted polyoxotungstate aggregates [H ₂ N(CH ₃ ) ₂ ] ₇ NaH ₂ [Zr ₂ Sb ₂ O ₃ ( A -α-PW ₉ O ₃₄ ) ₂ ]·16H ₂ O ( 1 ), [H ₂ N(CH ₃ ) ₂ ] ₆ H ₁₂ [ZrSb ₄ (OH)O ₂ ( A -α-PW ₈ O ₃₂ )( A -α-PW ₉ O ₃₄ )] ₂ ·33H ₂ O ( 2 ), and [H ₂ N(CH ₃ ) ₂ ] ₄ Na _11.5 H _4.5 [Zr ₄ W ₈ Sb ₄ P ₅ O ₄₉ (OH) ₅ ( B -α-SbW ₉ O ₃₃ ) ₂ ]·53H ₂ O ( 3 ) have been made in hydrothermal reactions of the [ B -α-SbW ₉ O ₃₃ ] ^9- precursor with Zr ⁴⁺ cations and PO ₄ ^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 [Zr ₂ Sb ₂ O ₃ ] ⁸⁺ entity sandwiched by two [ A -α-PW ₉ O ₃₄ ] ^9- moieties. 2 is a double sandwich-type structure, which can be perceived as two equivalent sandwiched [Sb ₃ (PW ₈ O ₃₂ )(PW ₉ O ₃₄ )] ^11- further sandwiching one [Sb ₂ Zr ₂ (OH) ₂ O ₄ ] 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-SbW ₉ O ₃₃ ] ^9- fragments sandwich a unique 21-core Sb-P-W-Zr oxo cluster ({Zr ₄ W ₈ Sb ₄ P ₅ }). 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.