Two pairs of chiral lanthanide–oxo clusters Ln14 induced by amino acid derivatives

Abstract

Two pairs of pure enantiomers of high-nuclearity chiral lanthanide–oxo clusters with the formulas [Y₁₄(L)₁₆(μ₃-OH)₁₆(H₂O)₂₀]·(ClO₄)₁₀·xH₂O (x ≈ 55; L = L-L⁻ for L-Y₁₄; L = D-L⁻ for D-Y₁₄) and [Dy₁₄(L)₁₆(μ₃-OH)₁₆(H₂O)₂₀]·(ClO₄)₁₀·xH₂O (x ≈ 67; L = L-L⁻ for L-Dy₁₄; L = D-L⁻ for D-Dy₁₄) were prepared in the presence of chiral ligands N-acetyl-L-alanine (L-HL) and N-acetyl-D-alanine (D-HL). Structural analysis showed that four cubane-like units as building blocks sharing vertices formed the lanthanide–oxo cluster unit {(ClO₄)₂@[Y₁₂(μ₃-OH)₁₆]}¹⁸⁺ with two ClO₄⁻ as anion templates. The remaining Y³⁺ ions were connected to the opposite position of {(ClO₄)₂@[Y₁₂(μ₃-OH)₁₆]}¹⁸⁺ through four L-L⁻, respectively. High-resolution electrospray ionization mass spectrometry (HRESI-MS) captured the signals of the cluster fragment {Y₁₂(OH)_16−x(O)_x} (x = 4, 5, 6, 7, 8) and the unbroken dimer of {Y₁₂(L-L)₁₂(OH)_16−x(O)_x}₂ (x = 4, 5, 12) from L-Y₁₄ in a mixed solution of methanol and dichloromethane, suggesting that {Ln₁₂(OH)_16−x(O)_x} is a stable cluster unit that could be further assembled into higher-nuclearity lanthanide–oxo clusters in solution. The solid-state circular dichroism (CD) spectra of compounds L-Y₁₄/D-Y₁₄ and L-Dy₁₄/D-Dy₁₄ displayed mirror symmetry effects in the range of 220–250 nm. The study of magnetic properties showed that L-Dy₁₄ had a weak antiferromagnetic interaction and displayed SMM-like behavior in the absence of a dc field.