Synthesis and Magnetic Properties of Bis-Halobenzene Decamethyldysprosocenium Cations

The decamethyldysprosocenium cation, [Dy-(Cp*)2]+ (Cp* = {C5Me5}), was a target single-molecule magnet(SMM) prior to the isolation of larger dysprosocenium cations,which have recently shown magnetic memory effects up to 80 K.However, the relatively short Dy···Cp*centroid distances of [Dy-(Cp*)2]+, together with the reduced resonance of its vibrationalmodes with electronic states compared to larger dysprosoceniumcations, could lead to more favorable SMM behavior. Here, wereport the synthesis and magnetic properties of a series of solvatedadducts containing bis-halobenzene decamethyldysprosoceniumcations, namely [Dy(Cp*)2(PhX-κ-X)2][Al{OC(CF3)3}4] (X = For Cl) and [Dy(Cp*)2(C6H4F2-κ2-F,F)(C6H4F2-κ-F)][Al{OC-(CF3)3}4]. These complexes were prepared by the sequentialreaction of [Dy(Cp*)2(μ-BH4)]∞ with allylmagnesium chloride and [NEt3H][Al{OC(CF3)3}4], followed by recrystallization fromparent halobenzenes. The complexes were characterized by powder and single crystal X-ray diffraction, NMR and ATR-IRspectroscopy, elemental analysis, and SQUID magnetometry; experimental data were rationalized by a combination of densityfunctional theory and ab initio calculations. We find that bis-halobenzene adducts of the [Dy(Cp*)2]+ cation exhibit highly bentCp*···Dy···Cp* angles; these cations are also susceptible to decomposition by C−X (X = F, Cl, Br) activation and displacement ofhalobenzenes by O-donor ligands. The effective energy barrier to reversal of magnetization measured for [Dy(Cp*)2(PhF-κ-F)2][Al{OC(CF3)3}4] (930(6) cm−1) sets a new record for SMMs containing {Dy(Cp*)2} fragments, though all SMM parametersare lower than would be predicted for an isolated [Dy(Cp*)2]+ cation, as expected due to transverse ligand fields introduced byhalobenzenes and the large deviation of the Cp*···Dy···Cp* angle from linearity promoting magnetic relaxation.