Introduction of ester and amido functions in tetrairon(iii) single-molecule magnets: synthesis and physical characterization?

Dalton Transactions Pub Date: 2010-05-29 DOI: 10.1039/C0DT00111B

Abstract

Tetrairon(III) complexes with a propeller-like structure derived from [Fe4(OMe)6(dpm)6] (1) (Hdpm = 2,2,6,6-tetramethylheptane-3,5-dione) are providing a growing class of Single Molecule Magnets (SMMs) displaying unprecedented synthetic flexibility and ease of functionalization. Herein we report the synthesis, crystal structures and magnetic properties of two novel tetrairon(III) SMMs, [Fe4(esterC5)2(dpm)6] (2) and [Fe4(amideC5)2(dpm)6]·Et2O·4MeOH (3·Et2O·4MeOH), in which functionalization of the cluster core is achieved using ester and amido linkages, respectively. To this aim, two new tripodal ligands were prepared by acylation of pentaerythritol (2,2-bis(hydroxymethyl)propane-1,3-diol) and TRIS (2-amino-2-(hydroxymethyl)propane-1,3-diol), namely H3esterC5 = RC(O)OCH2C(CH2OH)3 and H3amideC5 = RC(O)NHC(CH2OH)3 with R = n-butyl. The compounds were structurally investigated by single-crystal XRD, which demonstrated coordination of the tripodal ligands to the cluster core. The products display SMM behavior with anisotropy barriers Ueff/kB? 11 K due to a high-spin (S = 5) ground state and an easy axis anisotropy, described by D = ?0.421 cm?1 in 2 and ?0.414 cm?1 in 3·Et2O·4MeOH. The departure of Ueff from the total splitting of the S = 5 ground multiplet, U/kB? 15 K, has to be ascribed to the sizeable rhombic anisotropy that characterizes the two compounds (E = 0.021 cm?1 in 2 and 0.019 cm?1 in 3·Et2O·4MeOH), as confirmed by master matrix calculations of the temperature-dependent relaxation time.

Graphical abstract: Introduction of ester and amido functions in tetrairon(iii) single-molecule magnets: synthesis and physical characterization
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