In Situ Reaction Forms Uniform Mixed Heterometallic LnIII2MnII4 (Ln = DyIII and GdIII) Clusters: Assembly Mechanism and Insights into Performance

The unclear assembly mechanism seriously hinders the preparation and application of 3d-4f heterometallic clusters. Two new heterometallic nanoclusters [Dy₂Mn₄(HL)₄(OAc)₆]·5EtOH·H₂O (1) and [Gd₂Mn₄(HL)₄(OAc)₆]·4EtOH·4H₂O (2) were obtained from the in situ condensation reaction of 3-amino-1,2-propanediol with 2-hydroxy-1-naphthaldehyde. The intermediate species in the cluster 1 synthesis process were tracked by time-dependent high-resolution electrospray ionization mass spectrometry (HRESI-MS), further revealing the possible formation mechanism (Dy → DyL₂ →DyMn₂L₂ → DyMn₃L₂ → DyMn₄L₃ → Dy₂Mn₄L₄). Magnetic studies indicated that the antiferromagnet Ln^III-Mn^II (Ln = Dy^III and Gd^III) interaction was operative in both titled clusters. Furthermore, the performance of the clusters was regulated by adjusting the type of rare earth ions (Dy^III and Gd^III). The research results showed that cluster 2 containing Gd^III exhibited an excellent longitudinal relaxation rate (r₁) with 1.95 mM^-1 s^-1 under 0.5 T and a relatively suitable r₂/r₁ value (3.88), which indicated that it can be used as a new and efficient T₁ MR contrast agent. Cluster 1 containing Dy^III displayed antipathogenic activities against clinical MRSA strain with an MIC of 32 μg/mL. This work not only provided a reference for revealing the assembly mechanism of 3d-4f heterometallic clusters but also confirmed its potential application in the biomedical field.