Taming Super-Reduced Bi23-Radicals with Rare Earth Cations

Here, we report the synthesis of two new sets of dibismuthbridged rare earth molecules. The first series contains a bridging diamagnetic Bi22- anion, (Cp*2RE)2(mu-eta 2:eta 2-Bi2), 1-RE (where Cp* = pentamethylcyclopentadienyl; RE = Gd (1-Gd), Tb (1-Tb), Dy (1-Dy), Y (1-Y)), while the second series comprises the first Bi23- radical-containing complexes for any d or f-block metal ions, [K(crypt-222)][(Cp*2RE)2(mu-eta 2:eta 2-Bi2 center dot)]center dot 2THF (2 RE, RE = Gd (2-Gd), Tb (2-Tb), Dy (2-Dy), Y (2-Y); crypt-222 = 2.2.2cryptand), which were obtained from one-electron reduction of 1-RE with KC8. The Bi23- radical-bridged terbium and dysprosium congeners, 2-Tb and 2-Dy, are single-molecule magnets with magnetic hysteresis. We investigate the nature of the unprecedented lanthanide-bismuth and bismuth-bismuth bonding and their roles in magnetic communication between paramagnetic metal centers, through single-crystal X-ray diffraction, ultraviolet-visible/ near-infrared (UV-vis/NIR) spectroscopy, SQUID magnetometry, DFT and multiconfigurational ab initio calculations. We find a pi z* ground SOMO for Bi23-, which has isotropic spin-spin exchange coupling with neighboring metal ions of ca. -20 cm-1; however, the exchange coupling is strongly augmented by orbitally dependent terms in the anisotropic cases of 2-Tb and 2-Dy. As the first examples of p-block radicals beneath the second row bridging any metal ions, these studies have important ramifications for single-molecule magnetism, main group element, rare earth metal, and coordination chemistry at large.