Single-molecule magnets (SMMs) exhibit retention of magnetization under certain conditions, and therefore have potential applications in high density binary data storage. However, the viability of even the best-performing SMMs in such applications is currently limited as the desired magnetic properties have not yet been observed at temperatures that are suitable for practical usage. Some of the most promising high-temperature SMMs that have been studied so far are those involving dysprosocenium cations and related derivatives; the remarkable magnetic properties of this family of complexes has been attributed to the incorporation of substituted cyclopentadienyl (Cp R ) ligands, which: i) provide the steric bulk required to achieve axial ligand fields, enhancing the magnetic anisotropy of the Dy 3+ cation and hindering Orbach relaxation; and, ii) are rigid and thus impede molecular vibrations, suppressing Raman relaxation. Further stabilization of the ground mJ state of Dy 3+ in dysprosocenium cations, and concurrent destabilization of the least magnetic mJ state, could be achieved by increasing the strength of the axial ligand field through the reduction of Dy … Cp R distances by using smaller Cp R ligands. The isolation of the decamethyldysprosocenium cation, [Dy(Cp*)2] + (Cp* = {C5Me5}), has therefore long been a desirable target for the SMM community. The effective energy barrier to relaxation of magnetization (Ueff) value of the hypothetical [Dy(Cp*)2] + cation was calculated to be above 1000 cm -1 by Gao and co-workers in 2016. Recent work by Reta et al. concluded that although the linearity of the [Dy(Cp*)2] + cation and therefore its Ueff value would be reduced compared to the [Dy(C5 i Pr5)(Cp*)] + cation, the vibrational modes may be shifted off-resonance with electronic states that could lead to comparatively slower relaxation rates. However, it has been shown that the relatively small steric bulk of the Cp* ligand (cf. C5 i Pr5 and Cp ttt , C5H2 t Bu3-1,2,4) is not sufficient to block equatorial ligand interactions and allow the isolation of the [Dy(Cp*)2] + cation, even with weak donor ligands and weakly coordinating anions (WCAs). All SMMs containing {Dy(Cp*)2} fragments that have been reported to date have shown suppressed SMM properties compared to isolated dysprosocenium cations. Following our recent reports of the heteroleptic dysprosocenium complex [Dy(Cp ttt )(Cp*)][Al{OC(CF3)3}4] and its mono-halobenzene-solvated adducts, we resolved to apply these methods to {Dy(Cp*)2} analogues. Here we report the synthesis of the putative WCA-bound complexes "[{Ln(Cp*)2}{Al[OC(CF3)3]4}]" (Ln = Y, Dy), together with a family of halobenzene-bound {Dy(Cp*)2} + cations with the same WCA derived from this starting material. We found that the reduced steric bulk of the {Dy(Cp*)2} fragment permits a greater number of transverse ligand interactions, and increases the propensity of the cation to promote C-X activation and form decomposition products. The halobenzene adducts of {Dy(Cp*)2} + are characterized by single crystal (SCXRD) and powder X-ray Diffraction (PXRD), elemental analysis, ATR-IR spectroscopy, elemental analysis and SQUID magnetometry. The magnetic data are rationalized by complete active space self-consistent field spin-orbit (CASSCF-SO) calculations. We find that coordination of haloarenes promotes magnetic relaxation via structural distortions and an increased transverse field, but we observe a Ueff value of 930 (6) cm -1 for [Dy(Cp*)2(PhF-κ-F)2][Al{OC(CF3)3}4] that sets a new benchmark for {Dy(Cp*)2}containing SMMs.