Effect of the capping ligand on luminescent erbium(III) β-diketonate single-ion magnets

Erbium complexes featuring beta-diketonate ligand 2,4-hexanedione (Hh) and N, N-donor-ligands 2,2-bipyridine (bipy), 5-nitro-1,10-phenanthroline (5NO(2)phen) and bathophenanthroline (bath) have been synthesized. The structures of the ternary complexes [ Er(h) 3(bipy)], [ Er(h) 3(5NO2phen)] and [ Er(h) 3(bath)] have been determined by single crystal X-ray diffraction. Excitation of the complexes in the ultraviolet region (337 nm) led to near infrared (NIR) luminescence at 1532 nm characteristic of the trivalent erbium ion in the three compounds, with an improved antenna effect in the 5-nitro-1,10-phenanthroline complex. The AC susceptibility studies conducted at frequencies ranging from 33 to 9995 Hz and at temperatures in the 1.7 to 10 K range revealed that the application of a static magnetic field induces a slow magnetic relaxation in all three compounds. The complex with the bulkier capping ligand (bathophenanthroline) exhibits the highest energy barrier U/k(B) = 23 K.