New Single‐Molecule Magnets by Site‐Specific Substitution: Incorporation of “Alligator Clips” into Fe₄ Complexes

Abstract

Abstract“Alligator clips” suitable for grafting on H‐terminated silicon or gold surfaces have been incorporated into single‐molecule magnets (SMMs) of the Fe4 family. Tripodal ligands 2,2‐bis(hydroxymethyl)‐10‐undecen‐1‐ol (H3L1) and 11‐(acetylthio)‐2,2‐bis(hydroxymethyl)undecan‐1‐ol (H3L2) have been used to replace the six methoxide bridges in [Fe4(OMe)6(dpm)6], affording new Fe4 derivatives [Fe4(L1)2(dpm)6] (1) and [Fe4(L2)2(dpm)6] (2) in high yield (Hdpm = dipivaloylmethane). The molecular structures have been unambiguously established by XRD combined with ESI‐MS and magnetic characterization techniques, including DC and AC magnetometry and high‐frequency EPR spectroscopy. The two SMMs have an S = 5 ground state and an easy‐axis magnetic anisotropy leading to slow relaxation of the magnetization at low temperature, with effective anisotropy barriers of 15.9(2) K in 1 and 15.1(2) K in 2. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

X‐Ray Magnetic Circular Dichroism Picks out Single‐Molecule Magnets Suitable for Nanodevices

“…A very good agreement is observed for Fe 4 , as shown in Figure 4, assuming the same Spin-Hamiltonian parameters determined on bulk samples, i.e., S ¼ 5, D/k B ¼ À0.629 K, and g ¼ 2.00. [17] If the same procedure is repeated for Mn 12 with S ¼ 10, D/k B ¼ À0.66 K and g ¼ 2.00, [1] the calculated field dependence is found to deviate significantly from the corresponding dichroic signal (Fig. 2b).…”

“…The 12 , [1,15] and [Fe 4 (L) 2 (dpm) 6 ], Fe 4 , [16,17] where Hdpm is dipivaloylmethane and H 3 L is a tripodal ligand derived from 2-hydroxymethyl-1,3-propanediol. Both types of clusters are characterized by a large spin value of the ground state, S ¼ 10 and S ¼ 5, respectively, and an easy-axis magnetic anisotropy which generates an energy barrier for magnetization reversal of approximately 70 and 20 K, respectively.…”

“…The sub-Kelvin XMCD setup used in this work, combined with the high beam stability of SLS, are expected to provide the required sensitivity. 6 ] (H 3 L ¼ 11-(acetylthio)-2,2-bis(hydroxymethyl) undecan-1-ol; Hdpm ¼ dipivaloylmethane) were synthesized following reported preparation methods [15,17]. Pure, crystalline samples were dissolved in dicloromethane (99.8% purity, purchased from Fluka) to give $10 À3 M solutions.…”

“…[10,11] The derivatives employed in this study, whose structures are shown in Figure 1a and b, have RCO 2 H ¼ 4-(methylthio)benzoic acid [15] and H 3 L ¼ 11-(acetylthio)-2,2-bis(hydroxymethyl)undecan-1-ol, respectively. [17] Samples were prepared by drop-casting millimolar solutions of each SMM in dichloromethane on a clean and flat polycrystalline Au(111) support and allowing for complete solvent evaporation. All operations were carried out in a portable glove box directly connected to the preparation chamber of the XMCD setup (see Experimental Section).…”

Understanding Single‐Molecule Magnets on Surface

“…The improvement in the behavior of this molecule was carried out through the replacement of the methoxo bridges with two tripodal ligands, forcing the molecular core into a more rigid and axially elongated structure that enhances the magnetic anisotropy [22]. The additional advantage of these ligands is their potentiality in introducing further functional groups that are well-suited for direct surface grafting [23].…”