A series of dysprosium(iii) metallocenium salts, Dy(Cp ) B(C F ) (R = H ( ), Me ( ), Et ( ), iPr ( )), was synthesized by reaction of DyI with the corresponding known NaCp (R = H, iPr) and novel NaCp (R = Me, Et) salts at high temperature, followed by iodide abstraction with H(SiEt ) B(C F ) . Variation of the substituents in this series results in substantial changes in molecular structure, with more sterically-encumbering cyclopentadienyl ligands promoting longer Dy-C distances and larger Cp-Dy-Cp angles. Dc and ac magnetic susceptibility data reveal that these structural changes have a considerable impact on the magnetic relaxation behavior and operating temperature of each compound. In particular, the magnetic relaxation barrier increases as the Dy-C distance decreases and the Cp-Dy-Cp angle increases. An overall 45 K increase in the magnetic blocking temperature is observed across the series, with compounds exhibiting the highest 100 s blocking temperatures yet reported for a single-molecule magnet. Compound possesses the highest operating temperature of the series with a 100 s blocking temperature of 62 K. Concomitant increases in the effective relaxation barrier and the maximum magnetic hysteresis temperature are observed, with displaying a barrier of 1468 cm and open magnetic hysteresis as high as 72 K at a sweep rate of 3.1 mT s . Magneto-structural correlations are discussed with the goal of guiding the synthesis of future high operating temperature Dy metallocenium single-molecule magnets.