Two unusual nanosized Nd-substituted selenotungstate aggregates simultaneously comprising lacunary Keggin and Dawson polyoxotungstate segments.

Two unique nanosized Nd-substituted selenotungstates NaK{[WNd(HO)(NO)O](B-α-SeWO)(α-SeWO)}·35HO (1) and [HN(CH)]HNa{[WNd(HO)O(OH)(β-SeWO)][WNd(HO)O(B-α-SeWO)]}·84HO (2) were prepared by reacting NaSeO, NaWO·2HO with Nd(NO)·6HO 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 [HN(CH)]·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-SeWO] unit and two trivacant Keggin [B-α-SeWO] segments sealing a trigonal bipyramid pentanuclear [WNd(HO)(NO)O] cluster, while the pentameric polyoxoanion of 2 can be described as one β-type tetravacant Dawson [β-SeWO] fragment and four trivacant Keggin [B-α-SeWO] segments anchoring a saddle-shaped [WNd(HO)O(OH)] 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.