Tetrairon(III) Single-Mol. Magnets (SMMs) with a propeller-like structure exhibit tuneable magnetic anisotropy barriers in both height and shape. The clusters [Fe4(L1)2(dpm)6] (1), [Fe4(L2)2(dpm)6] (2), [Fe4(L3)2(dpm)6]·Et2O (3·Et2O), and [Fe4(OEt)3(L4)(dpm)6] (4) were prepd. by reaction of [Fe4(OMe)6(dpm)6] (5) with tripodal ligands R-C(CH2OH)3 (H3L1, R = Me; H3L2, R = CH2Br; H3L3, R = Ph; H3L4, R = tBu; Hdpm = dipivaloylmethane). The iron(III) ions exhibit a centered-triangular topol. and are linked by six alkoxo bridges, which propagate antiferromagnetic interactions resulting in an S = 5 ground spin state. Single crystals of 4 reproducibly contain at least two geometric isomers. From high-frequency EPR studies, the axial zero-field splitting parameter (D) is invariably neg., as found in 5 (D = -0.21 cm-1) and amts. to -0.445 cm-1 in 1, -0.432 cm-1 in 2, -0.42 cm-1 in 3·Et2O, and -0.27 cm-1 in 4 (dominant isomer). The anisotropy barrier Ueff detd. by a.c. magnetic susceptibility measurements is Ueff/kB = 17.0 K in 1, 16.6 K in 2, 15.6 K in 3·Et2O, 5.95 K in 4, and 3.5 K in 5. Both |D| and Ueff increase with increasing helical pitch of the Fe(O2Fe)3 core. The 4th-order longitudinal anisotropy parameter B40, which affects the shape of the anisotropy barrier, concomitantly changes from pos. in 1 (compressed parabola) to neg. in 5 (stretched parabola). With the aid of spin Hamiltonian calcns. the obsd. trends were attributed to fine modulation of single-ion anisotropies induced by a change of helical pitch.

Tuning Anisotropy Barriers in a Family of Tetrairon(III) Single-molecule Magnets with an S=5 Ground State / S., ACCORSI; A. L., BARRA; A., CANESCHI; G., CHASTANET; CORNIA, Andrea; FABRETTI COSTANTINO, Antonio; D., GATTESCHI; MORTALO', Cecilia; E., OLIVIERI; PARENTI, Francesca; P., ROSA; R., SESSOLI; L., SORACE; W., WERNSDORFER; ZOBBI, Laura. - In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. - ISSN 0002-7863. - STAMPA. - 128:(2006), pp. 4742-4755. [10.1021/ja0576381]

Tuning Anisotropy Barriers in a Family of Tetrairon(III) Single-molecule Magnets with an S=5 Ground State

CORNIA, Andrea;FABRETTI COSTANTINO, Antonio;MORTALO', Cecilia;PARENTI, Francesca;ZOBBI, Laura
2006

Abstract

Tetrairon(III) Single-Mol. Magnets (SMMs) with a propeller-like structure exhibit tuneable magnetic anisotropy barriers in both height and shape. The clusters [Fe4(L1)2(dpm)6] (1), [Fe4(L2)2(dpm)6] (2), [Fe4(L3)2(dpm)6]·Et2O (3·Et2O), and [Fe4(OEt)3(L4)(dpm)6] (4) were prepd. by reaction of [Fe4(OMe)6(dpm)6] (5) with tripodal ligands R-C(CH2OH)3 (H3L1, R = Me; H3L2, R = CH2Br; H3L3, R = Ph; H3L4, R = tBu; Hdpm = dipivaloylmethane). The iron(III) ions exhibit a centered-triangular topol. and are linked by six alkoxo bridges, which propagate antiferromagnetic interactions resulting in an S = 5 ground spin state. Single crystals of 4 reproducibly contain at least two geometric isomers. From high-frequency EPR studies, the axial zero-field splitting parameter (D) is invariably neg., as found in 5 (D = -0.21 cm-1) and amts. to -0.445 cm-1 in 1, -0.432 cm-1 in 2, -0.42 cm-1 in 3·Et2O, and -0.27 cm-1 in 4 (dominant isomer). The anisotropy barrier Ueff detd. by a.c. magnetic susceptibility measurements is Ueff/kB = 17.0 K in 1, 16.6 K in 2, 15.6 K in 3·Et2O, 5.95 K in 4, and 3.5 K in 5. Both |D| and Ueff increase with increasing helical pitch of the Fe(O2Fe)3 core. The 4th-order longitudinal anisotropy parameter B40, which affects the shape of the anisotropy barrier, concomitantly changes from pos. in 1 (compressed parabola) to neg. in 5 (stretched parabola). With the aid of spin Hamiltonian calcns. the obsd. trends were attributed to fine modulation of single-ion anisotropies induced by a change of helical pitch.
128
4742
4755
Tuning Anisotropy Barriers in a Family of Tetrairon(III) Single-molecule Magnets with an S=5 Ground State / S., ACCORSI; A. L., BARRA; A., CANESCHI; G., CHASTANET; CORNIA, Andrea; FABRETTI COSTANTINO, Antonio; D., GATTESCHI; MORTALO', Cecilia; E., OLIVIERI; PARENTI, Francesca; P., ROSA; R., SESSOLI; L., SORACE; W., WERNSDORFER; ZOBBI, Laura. - In: JOURNAL OF THE AMERICAN CHEMICAL SOCIETY. - ISSN 0002-7863. - STAMPA. - 128:(2006), pp. 4742-4755. [10.1021/ja0576381]
S., ACCORSI; A. L., BARRA; A., CANESCHI; G., CHASTANET; CORNIA, Andrea; FABRETTI COSTANTINO, Antonio; D., GATTESCHI; MORTALO', Cecilia; E., OLIVIERI; PARENTI, Francesca; P., ROSA; R., SESSOLI; L., SORACE; W., WERNSDORFER; ZOBBI, Laura
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11380/309300
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