Influence of weakly coordinating anions binding to the hexa-tert-butyl dysprosocenium cation

Abstract

Complexes containing isolated dysprosocenium cations, [Dy(Cp^R)₂][WCA] (Cp^R = substituted cyclopentadienyl, WCA = weakly coordinating anion), have recently emerged as leading examples of high-temperature single-molecule magnets (SMMs) due to a combination of the axial orientation and rigidity of the Cp^R rings. However, our understanding of the effects of transverse fields on the magnetic properties of [Dy(Cp^R)₂]⁺ cations is underdeveloped. Here we investigate the impact of equatorially-bound WCAs via the synthesis of the Dy(III) bis-Cp^R complexes [Dy(Cp^ttt)₂{AlCl[OC(CF₃)₃]₃-κ-Cl}] (1) and [Dy(Cp^ttt)₂{AlCl(C₂H₅)[OC(C₆F₅)₃]₂-κ-Cl}] (2), and their characterisation by single crystal XRD, elemental analysis, ATR-IR and NMR spectroscopy, and ab initio calculations. Despite the similarity of the Dy coordination spheres in 1 and 2 we find that their effective energy barriers to reversal of magnetisation are vastly different (U_eff = 886(17) cm⁻¹ and 559(18) cm⁻¹, respectively) and they both show waist-restricted magnetic hysteresis at 2 K. Together, these data provide fresh insights into the sensitivity of the magnetic properties of [Dy(Cp^R)₂]⁺ cations to relatively weak equatorial interactions.