Influence of weakly coordinating anions binding to the hexa-<i>tert</i>-butyl dysprosocenium cation

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 <i>via</i> the synthesis of the Dy(III) bis-Cp^R complexes [Dy(Cp^ttt)₂{AlCl[OC(CF₃)₃]₃-κ-<i>Cl</i>}] (1) and [Dy(Cp^ttt)₂{AlCl(C₂H₅)[OC(C₆F₅)₃]₂-κ-<i>Cl</i>}] (2), and their characterisation by single crystal XRD, elemental analysis, ATR-IR and NMR spectroscopy, and <i>ab initio</i> 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 (<i>U</i>_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.