indicating that one molecule of hexane in the lattice per unit cell is lost upon preparation of samples of 1-Dy for analysis; this could further account for the comparatively low carbon and hydrogen values obtained, but due to experimental uncertainties we do not adjust formula weights for the analysis of magnetic data (see below). and). The molar magnetic susceptibility-temperature product χT is 14.0 cm 3 K mol -1 at room temperature, similar to that predicted for a free Dy(III) ion ( 6 H15/2, χT = 14.2 cm 3 K mol -1 ) and the CASSCF-SO-calculated value (see Supporting Information Fig. ). There is minimal variation in χT with temperature until 13 K, at which point a sharp decline is observed that is typical of magnetic blocking. Open magnetic hysteresis loops are present at 2 K and remain open up to TH = 14 K at a sweep rate of 22 Oe s -1 in the zero-field region (Fig. ), with a large drop at Peaks were observed in zero-field AC susceptibility data for 1-Dy at temperatures between 18-52.5 K, and these data fitted well to generalized Debye models (fit with CC-FIT2, see Supporting Information Fig. and S27 and Table ). To determine the low temperature relaxation dynamics, magnetisation decay measurements of 1-Dy were performed in zero field between 2-12 K (see Supporting Information Figs. and). The decays at T ≤ 10 K clearly indicate two different relaxation timescales in 1-Dy, necessitating a double stretched exponential model (Equation ), while data at T = 12 K exhibits only single stretched exponential decay (Equation ). The relaxation profile of 1-Dy (Fig. ) shows clear exponential Orbach relaxation at high-temperatures, switching to a power-law Raman process below 𝜏 switch = 39 K. At low temperatures, there are two clear relaxation processes: one with faster rates showing temperatureindependent relaxation dynamics indicative of QTM, and one with slower rates that follows the higher-temperature Raman profile. The fraction of the two processes is approximately 50 : 50 at the lowest temperatures, with the faster component becoming more dominant as the temperature increases (Supporting Information Table ). The relaxation profile was globally fitted to a model with Orbach (10 = Cl, Br), but in those cases Orbach magnetic relaxation proceeds via only the second excited state, versus the 5 th excited state here. properties compared to other leading Dy(III) bis-Cp R SMMs. To summarise, we have synthesised and characterised a new class of Ln SMM, where the magnetic anisotropy and resultant magnetic properties are dominated by only one anionic ligand. purity. As a result, 1-Dy shows open magnetic hysteresis up to 14 K, which is comparable to the best-performing Dy(III) bis-Cp* complexes reported to date. We have also demonstrated the facile displacement of fluorobenzene from 1-Y in a salt metathesis reaction to give a Ln metallocenium cation, [Y(Cpʹʹʹ)(Cp*)(FPh)2] + , that could not be isolated by standard abstraction methodologies. We envisage that extending the synthetic methods herein to a wider range of [Ln(L)(XPh)n] 2+ dications (L = anionic ligand, X = halogen) will provide complexes with interesting properties, which can be exploited as useful starting materials to hitherto unknown heteroleptic Ln complexes, including high temperature Ln SMMs.