Structure, magnetic properties and thermal sublimation of fluorinated Fe4 Single-Molecule Magnets

Fluorinated tetrairon(III) Single-Molecule Magnets (SMMs) [Fe4(L1)2(dpmF6)6] (1dpmF6), [Fe4(L2)2(dpmF6)6] (2dpmF6), and [Fe4(L2)2(pta)6] (2pta) were assembled combining the tripodal ligands H3L1 = 2-hydroxymethyl-2-phenylpropane-1,3-diol and H3L2 = S-5-hydroxy-4,4-bis(hydroxymethyl)pentyl ethanethioate with fluorinated β-diketones analogues of dipivaloylmethane (Hdpm), namely 1,1,1-trifluoro-2,6,6-trimethyl-2-(trifluoromethyl)heptane-3,5-dione (HdpmF6) and pivaloyltrifluoroacetone (Hpta). The new compounds, along with [Fe4(L1)2(dpm)6] (1dpm) and [Fe4(L1)2(pta)6] (1pta), were designed in order to investigate the effect of fluorination degree on processability by thermal sublimation. The two different functional groups on the tripodal ligands, i.e. C6H5 in H3L1 and (CH2)3SAc in H3L2, are suitable for promoting physisorption and chemisorption on surfaces, respectively. Direct current magnetic data are typical for the metal-centred triangular topology of Fe4 complexes, with antiferromagnetic nearest-neighbour coupling constants in the range 16–18 cm−1 and an S = 5 ground spin state. Alternating current susceptibility measurements showed that slow magnetic relaxation persists in fluorinated compounds. When heated in high vacuum (10−7 mbar), 2dpmF6 and 2pta undergo thermal decomposition before subliming, while 1dpmF6 was found to sublimate at 497 ± 5 K in the same conditions, being the third sublimable SMM of this family after 1pta (440 ± 5 K) and 1dpm (500 ± 10 K).