Investigating How the Charge and Distance of Equatorial Ligands Impact the Structural, Magnetic, and Electronic Properties within the [Dy(Tp ^2-py )F] ⁺ Moiety

Due to the recent success of [Dy(Tp^2-py)F(THF)₂](PF₆) (Tp^2-py = hydrotris(3-(2'-pyridyl)-pyrazol-1-yl)borate) as a single-ion magnet (SIM), which increased the effective anisotropic energy of the [Dy(Tp^2-py)F(X)₂]⁺ moiety to <i>U</i>_eff = 661(6) cm^-1, we report the systematic study of replacing the equatorial solvent ligands within this moiety with 4,4'-bipyridine, MeOH, TMSO, DMSO, DMF, and H₂O, along with the heteroleptic solvent ligand complex of MeOH/THF. The minute changes in the structural properties, <i>i</i>.<i>e</i>., the Dy-F and Dy-solvent coordination bond distances, and the use of solvent molecules capable of hydrogen bonding result in a striking difference in the magnetic and electronic properties. Through a combination of magnetometry and <i>ab initio</i> calculations we have found that the [Dy(Tp^2-py)F(X)₂]⁺ moiety produces pure (<i>m</i>_J ≈ 0.99| ± 15/2⟩) and highly axially anisotropic (<i>g</i>_<i>z</i> ≈ 19.8) ground states due to the presence of the hard terminally coordinated fluoride ion, however the solvent molecules coordinated equatorially along with the isolation of the [Dy(Tp^2-py)F(X)₂]⁺ cation play important roles in the slow magnetic relaxation behavior. While the THF adduct still reigns supreme, the use of these alternative solvent ligands results in zero-field SIM behavior for all analogues, presenting Orbach-type magnetic relaxation with energy barriers between 342(11) ≤ <i>U</i>_eff ≤ 661(6) cm^-1.