Jean-Pierre Tuchagues

A single molecule magnet (SMM) with a helicate structure

The X-ray structure determination of [L2Cu2Gd2(NO3)6(H2O)2](0.5H2O) (L = bis-[(2-hydroxy-3-ethoxyphenyl)methylene]-4,4′-methylenedianiline) confirms the existence of a tetranuclear double-stranded homotopic and unsaturated helicate. In each Cu–Gd pair, the reduced Cu⋯Gd distance allows ferromagnetic Cu–Gd superexchange interactions through two phenoxo oxygen atoms. Replacement of gadolinium ions by terbium ions yields the first example of a helicate behaving as a single molecule magnet (SMM).

Iron(II) complexes of ortho-functionalized para-naphthoquinones 1. Synthesis, characterization, electronic structure and magnetic properties

Abstract A series of six high-spin ferrous complexes of ortho-functionalized paraquinone ligands of the type M(L)2(H2O)2, L = anion of the lawsone derivative, are synthesized where the bound quinone ligands are found to be in their fully oxidized form and the coordinating centers are the C-2 phenolate and the C-1 carbonyl. Thermal studies indicate that the two water molecules are coordinated and their loss leads to the decomposition of the chelates. Variable temperature magnetic susceptibility studies establish the high-spin state of the iron and confirm the quinone formulation of the ligands while Mossbauer data clearly establish the +2 oxidation state for the iron centers. Finally, the electronic absorption data indicate that the six high-spin ferrous complexes described herein are isostructural species including the O6 chromophore and the cyclic voltammetry confirms that the lawsone ligands are coordinated in their quinone form while the iron centre is at the +2 oxidation state.

Iron(II) complexes with polydentate Schiff base ligands as models of the photosynthetic mononuclear non-heme ferrous sites. Synthesis, characterization, molecular crystal structure, EXAFS and XANES studies, Mössbauer spectroscopy and magnetic properties

Abstract A series of four high-spin ferrous complexes of polydentate Schiff base ligands has been prepared and studied with IR, X-ray absorption and Mossbauer spectroscopy and variable-temperature magnetic susceptibility. The ligands include potentially tridentate and hexadentate Schiff bases with N2O and N4O2 donor sets, respectively, and result from the condensation of 5-nitrosalicylaldehyde with 2- (aminoethyl)pyridine or tetramines. The results obtained provide evidence that the four complexes described herein are mononuclear high-spin iron(II) species at room temperature. The crystal and molecular structure of [Fe(5NO2-salaep)2] (1) has been determined. 1 crystallizes in the orthorhombic system, space group Pbcn with Z=4 and a=14.756(3), b=9.682(3), c=18.632(4) A. The structure was solved by the heavy-atom method and refined to conventional agreement indices R=0.042 and Rw=0.043 with 2845 unique reflections for which I>3σ. The structure of 1 consists of [Fe(5NO2-salaep)2] complex molecules stacked through π interactions involving the salicylaldimine rings of adjacent molecules to afford ribbons along the [001] direction. The central iron atom of each molecule is triply coordinated to two 5NO2-salaep ligands, affording a distorted coordination octahedron. The Mossbauer spectroscopy is consistent with an increase of the distortion of the iron(II) ligand environment in the series from Fe11(5NO2,-salaep)2] (1) to Fe11[5NO2-sal-N(1,5,9,13)] (4). The variable temperature magnetic susceptibility evidences appreciable zero-field splitting of the iron(II) ground state in [Fe11(5NO2-salaep)2] (1) and Fe11[5NO2-sal-N(1,5,8,12)] (3). 1 exhibits several properties required to afford a modelling of the iron center of the ‘ferroquinone complex’ of photosystem 2. Fe11[5NO2-sal-N(1,4,7,10)] (2) exhibits a thermally induced 5T2g ↔ 1A1g spin conversion with unprecedented features: iron(II) center in a N4O2 ligand environment, spin conversion of discontinuous nature occurring in two steps separated by a 30 K broad spin equilibrium domain in which c. 50% of high-spin and low-spin molecules coexist.

Coordination of gadolinium(III) ions with a preformed μ-oxo diiron(III) complex: structural and magnetic data

A hexadentate ligand LH2 n(LH2 n= 1,2-bis((3-methoxysalicylidene)amino)ethane) reacts with iron(III) ions to yield a μ-oxo complex (LFe)2O, 1, which may function as a ligand towards gadolinium(III). The resulting product is a tetranuclear complex [LFeGd(NO3)3]2O, 2. Its structure has been determined by single crystal X-ray crystallography: 2, monoclinic P21/n n(No. 14), a n= 15.346(2), b n= 17.372(2), c n= 19.625(2) nA, β n= 100.59(1)°, Z n= 4. The thermal dependence of the χMT product (χM n= molar magnetic susceptibility) and the field dependence of the magnetization (M) have been measured and analyzed according to the spin cluster model. In both complexes the Fe–Fe interaction is antiferromagnetic with a magnitude of −115.3 cm−1 n(1) and −101.4 cm−1 n(2). In the latter compound an exchange coupling is operative within each (FeIII, GdIII) pair. Modelling of the experimental data (χMT and M) leads to the conclusion that this interaction is small and, unexpectedly, antiferromagnetic.