A novel class of tetrairon(III) single-molecule magnets with graphene-binding groups

Abstract

Tripods of general formula R’–O–CH 2C(CH 2OH) 3 are excellent site-specific ligands for the preparation of functionalized Fe 4 single-molecule magnets. Herein, we describe the synthesis and characterization of two novel complexes designed to bind graphene surfaces, in which the R group consists of an alkyl spacer –(CH 2) n – ( n = 6 and 10) and a terminal pyrenyl moiety. The site-specific ligand substitution on [Fe 4(OMe) 6(dpm) 6] (Hdpm = dipivaloylmethane) with the new tripods has been studied with 2H NMR on isotopically-enriched samples, revealing that, once formed, these clusters are stable in solution over long timescales. It was not possible to isolate the new compounds as crystalline solids, nevertheless they were chemically characterized by elemental analysis and 1H NMR. The presence of the pyrenyl ending groups prompted us to investigate the effect of metal complexation on fluorescence, and a full pyrene-to-iron cluster excitation energy transfer was observed. The analysis of the magnetic behaviour revealed an S = 5 ground spin state with a negative zero-field splitting parameter D = −0.42 cm −1.