Self-assembly of Keggin-type U(vi)-containing tungstophosphates with a sandwich structure: an efficient catalyst for the synthesis of sulfonyl pyrazoles

Abstract

The reaction of UO₂(OAc)₂ and Na₉[A-PW₉O₃₄] in solution with different pH values leads to the formation of two Keggin-type sandwich polyoxometalates, namely Na₁₁H(H₂O)₃₁[Na(UO₂)(A-PW₉O₃₄)]₂·7H₂O (1) and Na₁₂(H₂O)₂₉[Na(UO₂)(A-PW₉O₃₄)]₂·7H₂O (2), which have been characterized by single-crystal X-ray diffraction, FT-IR spectroscopy, and PXRD techniques. Compounds 1 and 2 crystallize in similar conditions with different pH values and show similar sandwich crystal structures except that one extra Na(I) ion acts as a bridging linker in compound 2 than in 1. It is notable that 1 exhibits excellent catalytic activity for the synthesis of sulfonyl pyrazoles via the condensation and cyclization reaction of sulfonyl hydrazides with 1,3-diketones, and the yield of the desired product is up to 99%. This is the first report to investigate the catalytic properties of U-containing polyoxometalates.