Following a novel synthetic strategy where the strong uniaxial ligand field generated by the Ph3SiO− (Ph3SiO−=anion of triphenylsilanol) and the 2,4‐di‐tBu‐PhO− (2,4‐di‐tBu‐PhO−=anion of 2,4‐di‐tertbutylphenol) ligands combined with the weak equatorial field of the ligand LN6, leads to [DyIII(LN6)(2,4‐di‐tBu‐PhO)2](PF6) (1), [DyIII(LN6)(Ph3SiO)2](PF6) (2) and [DyIII(LN6)(Ph3SiO)2](BPh4) (3) hexagonal bipyramidal dysprosium(III) single‐molecule magnets (SMMs) with high anisotropy barriers of Ueff=973 K for 1, Ueff=1080 K for 2 and Ueff=1124 K for 3 under zero applied dc field. Ab initio calculations predict that the dominant magnetization reversal barrier of these complexes expands up to the 3rd Kramers doublet, thus revealing for the first time the exceptional uniaxial magnetic anisotropy that even the six equatorial donor atoms fail to negate, opening up the possibility to other higher‐order symmetry SMMs.

Three dysprosium(III) single-molecule magnets (SMMs) with the rare hexagonal bipyramidal geometry have been isolated for the first time. Following a novel synthetic strategy where the strong uniaxial ligand field generated by the Ph₃SiO^- (Ph₃SiO^- = anion of triphenylsilanol) and the 2,4-di-^tBu-PhO^- (2,4-di-^tBu-PhO^- = anion of 2,4-di-tertbutylphenol) ligands combined with the weak equatorial field of the ligand L^N6, leads to [Dy^III(L^N6)(2,4-di-^tBu-PhO)₂](PF₆) (<b>1</b>), [Dy^III(L^N6)(Ph₃SiO)₂](PF₆) (<b>2</b>) and [Dy^III(L^N6)(Ph₃SiO)₂](BPh₄) (<b>3</b>) hexagonal bipyramidal complexes with high anisotropy barriers of U_eff = 973 K for <b>1</b>, U_eff = 1080 K for <b>2</b> and U_eff = 1124 K for <b>3 </b>under zero applied dc field. <i>Ab initio</i> calculations predict that the dominant magnetization reversal barrier of these complexes expands up to the 3rd Kramers doublet, thus revealing for the first time the exceptional uniaxial magnetic anisotropy that even the six equatorial donor atoms fail to negate, opening up the possibility to other higher-order symmetry SMMs. <br>

Two new air-stable axial Dy(iii) single-ion magnets, [Dy(H2O)5(HMPA)2]Cl3·HMPA·H2O (1) and [Dy(H2O)5(HMPA)2]I3·2HMPA (2) (HMPA = hexamethylphosphoramide), exhibit magnetic hysteresis which remains open up to 9 K for 1@Y and 10 K for 2@Y, respectively. Ab initio calculations, using step-by-step elimination of fragments to generate a series of model complexes, reveal that the secondary coordination sphere plays a key role in controlling the magnetisation reversal barrier and predict that the removal of outer-sphere molecules and anions will enhance the barrier further.

A combined synthetic, structural, magnetic and computational study gives insight into improving the single-molecule magnet behaviour of stable high-coordinate Dy(iii) complexes.

We generate a new air-stable pseudo-D5h Dy(III) Single-Molecule Magnet (Ueff = 1108 K, TB = 14 K) by combining a weak equatorial ligand field from a macrocyclic LN5 ligand with...