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Two unusual nanosized Nd3+-substituted selenotungstate aggregates simultaneously comprising lacunary Keggin and
Hailou Li1, Chen Lian, Lijuan Chen
1Henan Key Laboratory of Polyoxometalate Chemistry, College of Chemistry and Chemical Engineering, Henan University, Kaifeng, Henan 475004, China. ljchen@henu.edu.cn zhaojunwei@henu.edu.cn.
Abstract:
Two unique nanosized Nd3+-substituted selenotungstates Na9K8{[W3Nd2(H2O)3(NO3)O6](B-α-SeW9O33)2(α-Se2W14O52)}·35H2O (1) and [H2N(CH3)2]7H9Na4{[W2Nd2(H2O)8O6(OH)2(β-Se2W14O52)][W3Nd2(H2O)6O7(B-α-SeW9O33)2]2}·84H2O (2) were prepared by reacting NaSeO3, Na2WO4·2H2O with Nd(NO3)3·6H2O in aqueous solution by controlling different cations and pH values. 1 was synthesized at pH = 4.3 in the presence of KCl, whereas 2 was synthesized at pH = 3.0 in the presence of [H2N(CH3)2]·Cl. The most striking structural feature of 1 and 2 is the coexistence of vacant Keggin and Dawson segments in the polyoxoanion, which is extremely rare in the field of polyoxometalate chemistry. The trimeric polyoxoanion of 1 can be perceived as a fusion of one α-type tetravacant Dawson [α-Se2W14O52]14- unit and two trivacant Keggin [B-α-SeW9O33]8- segments sealing a trigonal bipyramid pentanuclear [W3Nd2(H2O)3(NO3)O6]11+ cluster, while the pentameric polyoxoanion of 2 can be described as one β-type tetravacant Dawson [β-Se2W14O52]14- fragment and four trivacant Keggin [B-α-SeW9O33]8- segments anchoring a saddle-shaped [W8Nd6(H2O)20O20(OH)2]24+ cluster. In addition, the measurements of catalytic oxidation of aromatic thioethers show that 2 as a catalyst possesses extremely outstanding catalytic performance under mild reaction conditions.
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