Comparison of two field-induced Er^III single ion magnets

We present the synthesis, magnetic and photophysical properties of four mononuclear Ln^III complexes in two isostructural lattices containing Gd^III and Er^III. A heptadentate Schiff base ligand and acetate versus trifluoroacetate were used to synthesise complexes 1-4, among which the two Er^III complexes 2 and 4 exhibit field-induced SIM behaviour with almost similar U_eff values (31.6 K for 2 and 32.7 K for 4). Ab initio calculations show the structure of the low-lying energy states and highlight that there is already significant tunnelling in the ground doublet state, but the application of a weak magnetic field of 0.05 T is sufficient for ac magnetic measurements to suppress tunnelling in the ground state. The calculated main magnetic axes (g_Z) of the ground Kramers doublets show small differences between the two Er^III compounds 2 and 4 due to their different ligand fields.