Rare-Earth Inverse Sandwich Compounds Supported by A Dianionic Five-Membered Aromatic Ligand

Abstract

Even for a simple bimetallic rare-earth single-molecule magnet (SMM), the parallel alignment of the local anisotropy axes with the axis connecting the two rare-earth ions is still a significant synthetic challenge and rarely achieved. Here, by utilizing the dianionic compound [Na2(C4B)Et4Me2N(THF)2]2, we present the first synthesis and comprehensive characterization of a series of rare-earth(III) inverse-sandwich compounds with the chemical formula as [(μ:η5:η5-(C4B)Et4Me2N)RE2(BH4)4(THF)2]·toluene (1-RE), where RE = Gd, Dy, Y; (C4B)Et4Me2N = 1-(N,N-dimethylamino)-2,3,4,5-tetraethylborolyl; THF = tetrahydrofuran. Magnetic investigations confirm the existence of strong antiferromagnetic exchange interactions (J = −0.56 cm−1 for 1-Gd) in compounds 1-Gd and 1-Dy, indicating that the dianionic five-membered aromatic ligand is an advantageous bridge to enhance the exchange interactions between the rare-earth centers. The dilution treatment of Dy analogue (1-Dy@Y) reveals that the magnetic interactions between Dy(III) ions are capable of effectively suppressing the quantum tunneling of magnetization. Theoretical calculations on 1-Dy demonstrate that the local anisotropy axes are almost colinear to the axis connecting the two dysprosium ions. This work provides the first rare-earth inverse sandwich compounds supported by a dianionic five-membered aromatic ligand, and further reveals the opportunities for the synthesis of high-performing polynuclear rare-earth SMMs with a similar strategy.