Rare‐Earth‐Guided Hierarchical Assembly of Teddy‐Bear‐Like Giant Nickel‐Tungstate Polyoxometalates

The controlled assembly of giant polyoxometalates (POMs) remains a significant challenge in inorganic chemistry. Herein, we demonstrate that rare‐earth ions can direct distinct structural outcomes in nickel‐substituted tungstate systems. Hydrothermal reaction of the flexible precursor [B‐ α ‐SbW 9 O 33 ] with KH 2 PO 4 , Er 2 O 3 , and NiCl 2 yielded a giant all‐inorganic cluster {W 88 Ni 39 } (1) , adopting an unprecedented “Teddy‐Bear”‐like architecture. Under identical conditions, omission of Er 2 O 3 (or replacement with Dy 2 O 3 ) afforded the smaller cluster {W 55 Ni 17 } (2) , corresponding to the “head” of the “Teddy‐Bear”. Notably, Dy 2 O 3 improves the crystallization yield of {W 55 Ni 17 } relative to the rare‐earth‐free reaction. Remarkably, replacing Er 2 O 3 with Gd 2 O 3 afforded a giant tetramer {W 140 Gd 10 Ni 48 } (3) , whose monomer is analogous to the [W 33 Ni 21 ] “Teddy‐Bear body” motif in {W 88 Ni 39 } . These clusters rank among the largest discrete tungsten‐based POM assemblies known. Importantly, the crystallization of {W 88 Ni 39 } and {W 140 Gd 10 Ni 48 } enables an efficient organic‐free separation of the rare‐earth oxides Er 2 O 3 and Gd 2 O 3 with a separation factor of 360.37, revealing a new strategy based on structure‐directed hierarchical assembly for selective crystallization in rare‐earth‐mediated POM systems.