A highly anisotropic family of hexagonal bipyramidal Dy(III) unsaturated 18-crown-6 complexes exceeding the blockade barrier over 2700 K: a computational exploration.

In the present work, we have explored a series of unsaturated hexa-18-crown-6 (U18C6) ligands towards designing highly anisotropic Dy(III) based single-ion magnets (SIMs) with the general formula [Dy(U18C6)X 2 ] + (where U18C6 = [C 12 H 12 O 6 ] (1), [C 12 H 12 S 6 ] (2), [C 12 H 12 Se 6 ] (3), [C 12 H 12 O 4 S 2 ] (4), [C 12 H 12 O 4 Se 2 ] (5) and X = F, Cl, Br, I, O t Bu and OSiPh 3 ). By analysing the electronic structure, bonding and magnetic properties, we find that the U18C6 ligands prefer stabilising the highly symmetric eight-coordinated hexagonal bipyramidal geometry (HBPY-8), which is the source of the near-Ising type anisotropy in all the [Dy(U18C6)X 2 ] + complexes. Moreover, the ability of sulfur/selenium substituted U18C6 ligands to stabilize the highly anisotropic HBPY-8 geometry makes them more promising towards engineering the equatorial ligand field compared to substituted saturated 18C6 ligands where the exodentate arrangement of the S lone pairs results in low symmetry. Magnetic relaxation analysis predicts a record barrier height over 2700 K for [Dy(C 12 H 12 O 6 )F 2 ] + and [Dy(C 12 H 12 S 6 )X 2 ] + (where X = F, O t Bu and OSiPh 3 ) complexes, nearly 23% higher than those of the top performing Dy(III) based SIMs in the literature.