Stepwise Assembly Mechanism of Acid-Resistant Dy III –Ni II Core–Shell Single-Molecule Magnets with Elucidated Growth Pathway

The 3d transition metal ion NiII was successfully assembled around the lanthanide ion DyIII to construct a core–shell single-molecule magnets (SMMs), [Dy3Ni6(HL)6(μ3–OH)6(NO3)3]·9.5CH3CN, exhibiting remarkable resistance to acidic environments. High-resolution electrospray ionization mass spectrometry (HR-ESI-MS) revealed six intermediate fragments, enabling the elucidation of a stepwise assembly pathway: {L} → {DyL2} → {DyNiL2} → {DyNi2L2} → {Dy2Ni2L2} → {Dy3Ni6L6}. Magnetic analysis verified that the cluster operates as a single-molecule magnet with an effective energy barrier (Ueff) of 19.41 K under zero applied dc field. It is noteworthy that this cluster demonstrates remarkable stability in aqueous environments, typical organic solvents, and high-concentration acetic acid (HAc) aqueous solutions─a feat seldom achieved by zero-dimensional (0D) coordination clusters. This outstanding chemical robustness represents a significant advance in the field of paramagnetic metal clusters. Overall, this work underscores the critical role of a sequential self-assembly strategy in stabilizing heterometallic lanthanide-transition metal architectures and paves the way for the rational design of durable core–shell lanthanide-based clusters.