Energy Barrier Enhacement by Ligand Substitution in Tetrairon(III) Single-Molecule Magnets

A dramatic increase of the energy barrier (Ueff) in tetrairon(III) single-molecule magnets can be achieved by simple chemical modification. Site-specific replacement of the six methoxide bridges in [Fe4(OMe)6(dpm)6] (Hdpm=dipivaloylmethane; Ueff/kB=3.5 K) with two tripodal 1,1,1-tris(hydroxymethyl)ethane (H3thme) ligands affords the compound [Fe4(thme)2(dpm)6] (see figure) with Ueff/kB=15.6(2) K and a magnetic relaxation time exceeding 1000 s below 0.2 K.