Polyoxometalate-Based Well-Defined Rodlike Structural Multifunctional Materials: Synthesis, Structure, and Properties

The unpredictability of the polyoxometalate (POM) coordination model and the diversity of organic ligands provide more possibilities for the exploration and fabrication of various novel POM-based materials. In this work, a series of POM-based lanthanide (Ln)-Schiff base nanoclusters, [Ln(H₂O)₂(DAPSC)]₂[Ln(H₂O)₃(DAPSC)]₂[(SiW₁₂O₄₀)]₃·15H₂O (Ln = Sm, 1; Eu, 2; Tb, 3), have been successfully isolated by the reaction of classical Keggin POMs, a Ln³⁺ ion, and a Schiff-base ligand [2,6-diacetylpyridine bis(semicarbazone), abbreviated as DAPSC]. Both the hindrance effect of the organic ligand and charge balance endow the cluster with fascinating structural features of discrete and linear arrangement. The title compounds with dimensions of ca. 4 × 1 × 1 nm³ are first trimeric polyoxometalate-based nanosized compounds, constructed by saturated POM anions (SiW₁₂O₄₀^4-, denoted as SiW₁₂). Moreover, the properties (stability, electrochemistry, third-order nonlinear optics, and magnetism) of the compounds have also been studied.