Structural and Magnetization Dynamics of Borohydride-Bridged Rare-Earth Metallocenium Cations.

The structure and magnetic properties of the bimetallic borohydride-bridged dysprosocenium compound [{(η-Cp)(η-Cp)Dy}(μ:κ:κ-BH)][B(CF)] ([][B(CF)]) are reported along with the solution-phase dynamics of the isostructural yttrium and lutetium analogues (Cp is 1,2,4-tri(-butyl)cyclopentadienyl, Cp is tetramethyl(-butyl)cyclopentadienyl). The synthesis of [][B(CF)] was accomplished in the 2:1 stoichiometric reactions of [(η-Cp)(η-Cp)Dy(BH)] () with [CPh][B(CF)], with the metallocenes obtained from reactions of the half-sandwich complexes [(η-Cp)M(BH)(THF)] () (M = Y, Dy, Lu) with NaCp. Crystallographic studies show significant lengthening of the M···B distance on moving through the series , , and , with essentially linear {M···B···M} bridges in .

Dominance of Cyclobutadienyl Over Cyclopentadienyl in the Crystal Field Splitting in Dysprosium Single-Molecule Magnets.

Replacing a monoanionic cyclopentadienyl (Cp) ligand in dysprosium single-molecule magnets (SMMs) with a dianionic cyclobutadienyl (Cb) ligand in the sandwich complexes [(η -Cb'''')Dy(η -C Me Bu)(BH )] (1), [(η -Cb'''')Dy(η -Pn )K(THF)] (2) and [(η -Cb'''')Dy(η -Pn )] (3) leads to larger energy barriers to magnetization reversal (Cb''''=C (SiMe ) , Pn =1,4-di(tri-isopropylsilyl)pentalenyl). Short distances to the Cb'''' ligands and longer distances to the Cp ligands in 1-3 are consistent with the crystal field splitting being dominated by the former. Theoretical analysis shows that the magnetic axes in the ground Kramers doublets of 1-3 are oriented towards the Cb'''' ligands.

Enhanced single-molecule magnetism in dysprosium complexes of a pristine cyclobutadienyl ligand.

Intact transfer of the cyclobutadienyl ligand [C(SiMe)] to yttrium and dysprosium (M) produces the half-sandwich complexes [M{η-C(SiMe)}(BH)(THF)] as coordination polymers with bridging sodium or potassium ions. The dysprosium versions are single-molecule magnets (SMMs) with energy barriers of 371(7) and 357(4) cm, respectively. The pristine cyclobutadienyl ligands provide a strong axial crystal field that enhances the SMM properties relative to related cyclopentadienyl compounds.