title: A family of enneanuclear iron(II) single-molecule magnets.
abstract: Complexes [Fe9(X)2-(O2CMe)8{(2-py)2CO2}4] (X(-)=OH(-) (1), N3(-) (2), and NCO(-) (3)) have been prepared by a route previously employed for the synthesis of analogous Co(9) and Ni(9) complexes, involving hydroxide substitution by pseudohalides (N3(-), NCO(-)). As indicated by DC magnetic susceptibility measurements, this substitution induced higher ferromagnetic couplings in complexes 2 and 3, leading to higher ground spin states compared to that of 1. Variable-field experiments have shown that the ground state is not well isolated from excited states, as a result of which it cannot be unambiguously determined. AC susceptometry has revealed out-of-phase signals, which suggests that these complexes exhibit a slow relaxation of magnetization that follows Arrhenius behavior, as observed in single-molecule magnets, with energy barriers of 41 K for 2 (tau 0=3.4 x 10(-12) s) and 44 K for 3 (tau 0=2.0 x 10(-11) s). Slow magnetic relaxation has also been observed by zero-field 57Fe Mössbauer spectroscopy. Characteristic integer-spin electron paramagnetic resonance (EPR) signals have been observed at X-band for 1, whereas 2 and 3 were found to be EPR-silent at this frequency. 1H NMR spectrometry in CD3CN has shown that complexes 1-3 are stable in solution.
authors.affiliation: Institute of Materials Science, NCSR Demokritos, 15310 Aghia Paraskevi Attikis, Greece. tbou@ims.demokritos.gr
authors.forename: Athanassios K
authors.initials: AK
authors.lastname: Boudalis
authors.forename: Yiannis
authors.initials: Y
authors.lastname: Sanakis
authors.forename: Juan Modesto
authors.initials: JM
authors.lastname: Clemente-Juan
authors.forename: Bruno
authors.initials: B
authors.lastname: Donnadieu
authors.forename: Vassilios
authors.initials: V
authors.lastname: Nastopoulos
authors.forename: Alain
authors.initials: A
authors.lastname: Mari
authors.forename: Yanick
authors.initials: Y
authors.lastname: Coppel
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Tuchagues
authors.forename: Spyros P
authors.initials: SP
authors.lastname: Perlepes