Using Diffusely Charged Bridging Ligands to Maximize Single-Ion Anisotropy and Dipolar Coupling in Dinuclear ErCOT...

The building-block approach toward higher-dimensional molecular magnets is predicated on the tension between the goals of installing strong magnetic anisotropy while enhancing long-range magnetic cooperativity. We describe the dinuclear complex [Bu₄N][(Er^TMSCOT)₂(μ-I)₃] (1-I₃), wherein the design philosophy for optimizing single-ion anisotropy and intramolecular dipolar coupling merge. Static and dynamic magnetometry reveal longer time scale magnetic relaxation at low temperatures and a higher barrier to spin reversal at high temperatures relative to other [(ErCOT)₂(μ-X)₃]^- examples. Ab initio computational analysis ascribes the low temperature behavior to dipolar coupling and high temperature behavior to well-separated pure Kramers doublets in the single-ion limit. Furthermore, we analyze how 1-I₃ compares to geometrically similar single-molecule magnets, uncovering their dependence on not only the bistable ground state but also the entire low-energy manifold. The static and dynamic properties are compared to several [(ErCOT)₂(μ-X)₃]^- derivatives to develop a consistent framework of magneto-structural correlation within this extended family of molecular magnets. Bridging ligands with higher electron density increase the dipolar coupling bias via shorter Er-Er distances and raise the energy of the first excited state through destabilization of the m_J = $\pm |\frac{13}{2}⟩$ doublet with consequent lowered energy of the second excited state through stabilization of the m_J = $\pm |\frac{1}{2}⟩$ doublet.