The observation of both separated ion-pair and contact ion-pair forms of [Dy(Cp ttt )(Cp*)] + has confirmed the prediction made by AtomAccess that this cation is at the borderline of forming interactions with additional ligands. Whilst the smaller [Dy(Cp*)2] + cation is to be a high performance SMM, AtomAccess has confirmed that its coordination site is significantly larger than [Dy(Cp ttt )(Cp*)] + . The isolation of [Dy(Cp*)2] + will therefore be challenging and may require an alternative synthetic approach, such as using a more weakly coordinating anion than [Al{OC(CF3)3}4] -. This work has demonstrated that AtomAccess is both a powerful analytical and predictive tool, as it accurately projects the size and topology of potential atomic binding sites; we therefore envisage that this program can be applied in future to a wealth of challenges in exploratory synthetic chemistry.