Multifunctional Dysprosium(III) Complexes with Single-Molecule Magnetic Properties for Magnetic Resonance Imaging and Broad-Spectrum Antibacterial Applications

Abstract The development of multifunctional materials capable of integrating diagnostic and therapeutic functions is of increasing interest for advanced biomedical applications. Herein, we report the synthesis and characterization of two tetranuclear dysprosium complexes, [Dy4(L1)4(OAc)4] (1) and [Dy4(L2)4(OAc)4] (2), constructed from Schiff-base ligands bearing different halogen substituents. Single-crystal X-ray diffraction analysis revealed that both complexes possess closely related planar Dy4 architectures with distorted eight-coordinate Dy(III) centers. Magnetic studies demonstrated slow magnetic relaxation behavior with effective energy barriers (Ueff) of 14.68 K and 19.36 K for 1 and 2, respectively, confirming their single-molecule magnet characteristics. Beyond their magnetic properties, both dysprosium complexes exhibited remarkable multifunctional biomedical potential. Antibacterial investigations demonstrated broad-spectrum activity against both Gram-positive and Gram-negative pathogens, including methicillin-resistant Staphylococcus aureus (MRSA), S. aureus, α-hemolytic Streptococcus, Escherichia coli, and Proteus vulgaris, with inhibition efficiencies exceeding 99% under optimized conditions. Furthermore, magnetic resonance imaging (MRI) studies revealed concentration-dependent contrast enhancement and favorable relaxivity behavior under a 0.5 T magnetic field. The measured transverse relaxation rates (r2) are 1.45 and 0.67 mM−1 s−1. Meanwhile, their r2/r1 ratios match the characteristic of transverse relaxation-dominated T1/T2 dual-mode relaxation, which indicates their potential utility as MRI probes. This work highlights the potential of dysprosium-based molecular materials as multifunctional platforms that combine magnetic properties, antibacterial performance, and MRI capability within a single molecular system. These findings provide a foundation for the future development of lanthanide-based theranostic materials for biomedical applications.