Coordination site manipulation of the annular growth mechanism to assemble chiral lanthanide clusters with different shapes and magnetic properties

Abstract

Chiral lanthanide clusters provide a platform for molecular-based materials with coordination between chirality and magnetism and exhibit great application prospects in the fields of three-dimensional displays, magneto-optical memories, and spintronic devices. To date there is no reliable self-assembly rule for the directional design of chiral lanthanide clusters with specific shapes and functions. Further, we are the first to achieve the directional construction of chiral lanthanide clusters with different shapes and magnetic properties by regulating the hydroxyl coordination sites at different positions on the ligands by manipulating the annular growth mechanism. Specifically, we carried out the reaction of R/S-mandelic acid hydrazide, 2,5-dihydroxybenzaldehyde and DyCl₃·6H₂O with methanol and water as mixed solvents under solvothermal conditions at 80 °C to obtain mutual enantiomers tetranuclear chiral lanthanide clusters R/S-1. In R/S-1, first, two HL¹ ligands captured one Dy(III) ion to form a template unit Dy(L¹)₂, and following this, four Dy(L¹)₂ template units were well-ordered and arranged at the four vertices of the square, which were induced by a bridge anion μ₄-O²⁻, to undergo the annular growth mechanism to form square-shaped clusters R/S-1. Replacing 2,5-dihydroxybenzaldehyde with 2,3,4-trihydroxybenzaldehyde in the reaction system, hexanuclear chiral clusters R/S-2 were obtained. Changing the hydroxyl coordination sites enabled one H₃L² ligand to capture two Dy(III) ions, forming a template unit Dy₂L², following which three Dy₂L² were connected by a μ₃-OH⁻ bridge anion along the annular growth to form a triangular pyramid-shaped hexanuclear chiral lanthanide cluster R/S-2. Circular dichroism spectra indicated that R/S-1 and R/S-2 were two pairs of enantiomers. Magnetic studies showed that the R-1 chiral cluster was a typical single-molecule magnet under a zero dc field, and it exhibited a distinct double relaxation behavior. To the best of our knowledge, this is one of the rare examples of chiral lanthanide clusters with double relaxation behavior. This work provides an effective method for the directional construction of chiral lanthanide clusters with different connections and shapes and opens up a new horizon for the design and synthesis of multifunctional materials with magneto-optical applications.