Ionic strength effect on regulating the synthetic assembly of polyoxometalate clusters with slow magnetic relaxation behavior

Abstract

Three novel polyoxometalate (POM) clusters of K₁₀Na₁₀[Dy₃(H₂O)₆Ni(H₂O)(W₃O₁₁)(B-α-SbW₉O₃₃)₃]·(H₂O)₄₅ (1), (NH₄)₅K₄Na₈[Dy₃(H₂O)₆Sb^V(H₂O)(W₃O₁₁)(B-α-SbW₉O₃₃)₃]·(H₂O)₅₀ (2), and (NH₄)₉Na[Ni₂(H₂O)₆(WO₂)₂(B-β-SbW₉O₃₃)₂]·(H₂O)₂₄ (3) were successfully obtained using the same precursor under different ionic strength conditions. Structural analysis showed that compounds 1–3 possess discrepant structural characteristics in 1 M KCl, 1 M NH₄Cl, and saturated NH₄Cl, respectively. Among them, 2 is the first reported lanthanide cluster including both Sb³⁺ and Sb⁵⁺ in POM derivatives. Furthermore, the analysis of ac magnetic data proved that 1 and 2 embodied dramatic field-induced slow magnetic relaxation, and the effective barrier of 2 was estimated as U_eff/K_B = 21.10 K based on the Orbach process. It was found that the structure and magnetic properties of POM materials can be regulated using an effective and satisfactory ionic strength-controlled strategy.