Formation of nanocluster {Dy12} containing Dy-exclusive vertex-sharing [Dy4(μ3-OH)4] cubanes via simultaneous multitemplate guided and step-by-step assembly

Abstract

The formation of high-nuclearity clusters of lanthanide usually involves many complicated self-assembly processes. Thus, tracking the formation process is extremely difficult and research on the assembly mechanism is very rare. In this study, a Dy-exclusive nanocluster containing vertex-sharing [Dy₄(μ₃-OH)₄] cubanes, denoted as [Dy₁₂(L)₈(OH)₁₆(CH₃O)₈(H₂O)₈]·(CH₃O)₄ (Dy₁₂, L = quinoline-2-carboxylate), was designed and synthesized from L and DyCl₃·6H₂O. Eight quinoline-2-carboxylate ligands were encapsulated on the periphery of the Dy₁₂ cluster, which served to stabilize the core. The high stability of the Dy₁₂ cluster core was further confirmed by high-resolution electrospray-ionization mass spectrometry (HRESI-MS). With increased ion-source energy, only CH₃O⁻ and OH⁻ bridging ligands were replaced inside the Dy₁₂ cluster. Notably, eight intermediate fragments were successfully observed from the Dy₁₂ cluster formation by time-dependent HRESI-MS. First, ligand L captured Dy³⁺ to give Dy₁, which further formed Dy₂ through μ₂-O bridging. The Dy₁₂ cluster was constructed in one step with four Dy₂ and four Dy³⁺ as templates: L → Dy₁ → Dy₂ → Dy₁₂. Moreover, a series of Dy₃–Dy₆ fragment peaks with relatively weak intensities were observed, and an alternative stepwise-assembly route was proposed: L → Dy₁ → Dy₂ → Dy₃ → Dy₄ → Dy₅ → Dy₆ → Dy₁₂. On comparing the two different assembly methods, the multitemplate guided assembly formed Dy₁₂ was found to be dominant. To the best of our knowledge, this study was the first to propose the involvement of two self-assembly mechanisms in the construction of lanthanide clusters, as further confirmed by HRESI-MS. Magnetic studies further showed that Dy₁₂ clusters exhibited field-induced single-molecule magnet behavior.