Chemical and in silico tuning of the magnetisation reversal barrier in pentagonal bipyramidal Dy(iii) single-ion magnets

Two new air-stable axial Dy(iii) single-ion magnets, [Dy(H2O)(5)(HMPA)(2)]Cl(3)HMPAH(2)O (1) and [Dy(H2O)(5)(HMPA)(2)]I(3)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.