Template syntheses, molecular structures, and antimicrobial activities of two novel Schiff-base macrocyclic lanthanide complexes

Based on the template-assisted cyclocondensation procedure, two Schiff-base macrocyclic mononuclear lanthanide complexes (Pr-2_l and Nd-2_l) with the “lasso-type” architecture have been synthesized. According to X-ray structure analysis, the central ten-coordinate lanthanide ions (Pr³⁺ and Nd³⁺) in two complexes have distorted bicapped square antiprism geometry, and this geometry is completely encircled by two axial chelating nitrates on each side of the 23-membered macrocyclic plane and six donors in the macrocyclic skeleton. With the higher relatively inhibitory rates, the complex Pr-2_l can show significant antimicrobial activities against C. albicans and MRSA with lower MIC values (7.81 and 3.91 μg·mL⁻¹), while complex Nd-2_l exhibited good antimicrobial activities for S. aureus, C. albicans, and MRSA whose MIC values are 1.95, 7.81, and 3.91 μg·mL⁻¹. This current work is believed to provide another practical approach to further construct new antimicrobial materials by the use of Schiff-base and lanthanide antimicrobial fragments.