In Silico Investigation to Rationalize the Effect of Weak Donor versus Strong Donor Halides as Bridges in Dinuclear...

Among the lanthanides, the Dy(III) ions are found to be superior candidates for obtaining the best single-molecule magnets, resulting in a high energy barrier for the reversal of magnetization and blocking temperatures. When two identical Dy(III) ions are connected solely by one or two bridging ions in dinuclear systems, they result in an enhanced energy barrier compared to the energy barrier of individual Dy(III) ions, thanks to the Dy···Dy magnetic exchange interaction. Especially, bridging ions such as halides, hydroxides, and hydrides are better mediators for exchange and help achieve the strong anisotropic nature of the Dy(III) ions. However, among halides, determining which one provides a better ligand environment, by comparing different halide-bridged {Dy₂} complexes so that it can lift the degeneracy of Dy(III) ions to a substantial barrier, has not yet been explored. To understand this strategy, we performed detailed ab initio CASSCF (SINGLE_ANISO and POLY_ANISO) calculations on eight {Dy₂} SMMs with different di-μ-halide bridges that possess large energy barriers proven experimentally, as well as on 12 modeled structures. Our detailed computational analysis predicts that the weak-field halides, such as bromide- and iodide-bridged complexes, yield the largest energy barrier compared to fluoride- and chloride-bridged complexes.