Half-Sandwich Complexes of DyIII: A Janus-Motif with Facile Tunability of Magnetism

Three half-sandwich organometallics [(Cp-R)Dy(DBM)(2)(THF)]center dot solvent [Cp-R = Cp* (1Dy, Cp* = C5Me5), Cp-4PrPh (2Dy, Cp-4PrPh = C5Pr4Ph), Cp' (3Dy, Cp' = C5Me4TMS, solvent = THF), DBM- = dibenzoylmethanoate anion, THF = tetrahydrofuran, TMS = trimethylsilyl] with a Janus structural motif, where the ligands of DBM- and [Cp-R](-) are widely used in Dy-III/beta-diketonate and Ln(III)/cyclopentadienyl systems, were synthesized, structurally and magnetically characterized, and theoretically investigated. Single-crystal structural analysis reveals that the three complexes crystallize in the same space group P2(1/c). All the molecules display slow magnetic relaxation in the absence of an applied magnetic field, and the magnetic hysteresis loops of 2Dy and 3Dy can be observed under a magnetic field sweep rate of 10 Oe/s, indicating all three complexes are single-ion magnets (SIMs). The modifications of the Cp-ring lead to the distinct increment of the energy barrier from 46 K (1Dy) to 76 K (2Dy) to 320 K (3Dy). Ab initio calculations show that the ground Kramers doublet is strongly axial with gz approaching the value of 20 expected for the pure M-J = +/- 15/2 state, and the magnetic anisotropy axes for three complexes share a similar orientation which is perpendicular to the molecular pseudosymmetric axis. Electrostatic analyses confirm the magnetic anisotropy orientations and reveal that proper charge distribution of the coordination sphere (including the first and second) around Dy-III ion enhances the magnetic anisotropy. Further investigation of the relaxation mechanisms suggests the energy barrier should be carefully used to evaluate single-ion magnets if Raman process is dominant in the low temperature range.