Alain Mari

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

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.

Investigation of the iron–carbon bonding for alkyl, alkynyl, carbene, vinylidene, and allenylidene complexes using 57Fe Mössbauer spectroscopy

Abstract The synthesis of the iron allenylidene [Cp*(dppe)Fe(CCC(OCH3)CH3)][BPh4] (7) was achieved in one step, from the reaction of the Cp*(dppe)FeCl (8) with 1 equiv. of Me3–Si–CC–CCH. By working in methanol and in the presence of NaBPh4, the complex 7 was isolated in 85% yield as a dark green powder. Comparison of the Mossbauer parameters of a series of 16 compounds having the same Cp*(dppe)Fe backbone and a end-bound hydrocarbon ligand shows that it is possible to identify both the oxidation state of the metal (FeII vs. FeIII) and the metal–carbon bonding (single vs. double bond) of the terminal hydrocarbon ligands using Mossbauer spectroscopy.

Synthesis and characterization of copper, manganese and zinc complexes of the bidentate diisocyano ligands 2,5-dimethyl 2,5-diisocyanohexane (TMB) and 1,2-diisocyanoethane(DHB)

Abstract By reaction of 2,5-dimethyl 2,5-diisocyanohexane (TMB) and 1,2-diisocyanoethane (DHB) with CuX2 (X = CF3SO−3, ClO−4, BF−4), three types of complexes were isolated and characterized by magnetic susceptibility and EPR spectroscopy. In the violet CuL2X2 compounds, CuII atoms are in a square-planar environment and not magnetically interacting. For the mixed-valence green complexes Cu2L3X3, the CuII and CuI metal centres both have a tetrahedral coordination, and the presence of independent CuII and CuI atoms in a 1:1 ratio was deduced from a magnetization experiment. Diamagnetic CuI complexes CuL2X were also isolated. TMB complexes were prepared with MnII and ZnII. In the former case, high-spin Mn(TMB)(CF3SO3)2·2H2O and low-spin Mn(TMB)3(PF6)2 complexes were obtained, whereas ZnII gave Zn2(TMB)3(CF3SO3)2·2H2O. The v(CN) frequency in the infrared spectra increases with the charge on the complex, and for complexes of the same charge, decreases when the diisocyanide-to-metal ratio increases. Although solubility was improved by using CF3SO−3 as counter ion, it remained low and the complexes are likely to be polymeric, with the diisocyanide ligands in extended conformations playing a bridging role.