Details

Autor(en) / Beteiligte

• Boudalis, Athanassios K.
• Sanakis, Yiannis
• Clemente-Juan, Juan Modesto
• Donnadieu, Bruno
• Nastopoulos, Vassilios
• Mari, Alain
• Coppel, Yanick
• Tuchagues, Jean-Pierre
• Perlepes, Spyros P.

Titel

A Family of Enneanuclear Iron(II) Single-Molecule Magnets

Ist Teil von

• Chemistry : a European journal, 2008-03, Vol.14 (8), p.2514-2526

Ort / Verlag

Weinheim: WILEY-VCH Verlag

Erscheinungsjahr

2008

Quelle

Wiley-Blackwell Full Collection

Beschreibungen/Notizen

• 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 Co9 and Ni9 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 (τ0=3.4×10−12 s) and 44 K for 3 (τ0=2.0×10−11 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. Single‐molecule magnets: Pseudohalide substitution in the ferrous enneanuclear complex [Fe9(OH)2(O2CMe)8{(2‐py)2CO2}4] does not disrupt its structure, but leads to the analogous N3− and NCO− complexes (see graphic). These exhibit stronger ferromagnetic interactions and higher ground‐state spins. They are also found to behave as single‐molecule magnets at low temperatures.