A Wavy Multiple Tm(III)-Containing Open Wells-Dawson Silicotungstate: Synthesis, Structure, and Catalytic Application

A Tm(III)-rich silicotungstate Na{Tm₃(H₂O)₁₇[Tm₂(H₂O)₇(Si₂W₁₈O₆₆)]}·35H₂O (TmSiW) based on the open Wells-Dawson-type [Si₂W₁₈O₆₆]^16- building unit was synthesized by the reaction of Na₁₀[α-SiW₉O₃₄]·18H₂O, itaconic acid, and TmCl₃ in a HAc/NaAc buffer solution. Five kinds of Tm(III) ions were found in this compound and further linked the {Tm₂Si₂W₁₈} subunit to form an interesting wavy 1D chain structure, which achieved the introduction of more lanthanide (Ln) ions into the [Si₂W₁₈O₆₆]^16- unit for the first time. TmSiW contains multiple exposed Tm-metal active sites, making it an efficient catalyst for the acetalization of 2-aminobenzamides/2-aminobenzenesulphonamides with aldehydes. A series of 2,3-dihydroquinazolinones and 3,4-dihydro-2H-1,2,4-benzothiadiazine-1,1-dioxides could be obtained in excellent yields under green and mild conditions.