Tricine-supported polyoxo(alkoxo)lanthanide cluster {Ln₁₅} (Ln = Eu, Gd, Tb) with magnetic refrigerant and fluorescent properties

A family of polyoxo(alkoxo)lanthanide cluster {Ln₁₅} (Ln = Eu (1), Gd (2), Tb (3)) was successfully isolated via a simple hydrolysis reaction of lanthanide metal ions in the presence of tricine ligands. X-ray diffraction analyses revealed that {Ln₁₅} displayed a wheel-like structure with a µ₅-chloride anion as a template. Interestingly, each analog showed distinctive functions based on the different Ln(III) ions. Complexes 1 and 3 in the solid state emitted the characteristic fluorescence of Eu(III) or Tb(III). The fluorescence lifetimes of the ⁵D₀ excited state for 1 and the ⁵D₄ excited state for 3 were tested, and the values were 890 and 250 μs, respectively. Meanwhile, gadolinium analog 2 exhibited a magneto-caloric effect at ultralow temperatures with a maximum −ΔS_m value of 29.9 J·kg⁻¹·K⁻¹ at 3 K and 7 T.